EU EV 9625

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1 EU EV9625

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3 Tampereen teknillinen korkeakoulu Vesi Ja ympâristöteknhikan laltos Tampere University of Technology Institute of Water and Environmental Engineering No. B 49 LIBRARY, INTERNATIONAL REFEREF~ CE CENTRE FOR COMMkJF.ITY WAl ER SUPPLY AND SAN~ÎATION(IRC) RO. Box 93190, 2509 AD The Hagus Tel. (070) ext RN: LO: 3(~1/. 1 Ramadhani, M. Evaluation of Vingunguti waste stabilization ponds treating municipal and industrial wastewaters Tampere, Finland 1992 UDK ISBN X ISSN X

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5 1 EVALUATION OF VINGUNGUTI WASTE STABILIZATION PONDS TREATING MLJNICIPAL AND INDUSTRIAL WASTEWATERS by Ramadhani Mussa Page TABLE OF CONTENTS 1 ABSTRACT 3 INTRODUCTION General Objectives of study Methodology and scope 6 2 WASTE STABILI2ATION PONDS Features and processes of waste stabilization ponds Anaerobic ponds Facultative ponds Maturation ponds Pond combinations Design principles Design of anaerobic ponds Design of facultative ponds Design of maturation ponds Factors affecting operation of waste stabilization ponds Climatic factors Physical factors Chemical factors Wastewater flow and composition Characteristics of receiving waters Operational problems of waste stabilization ponds 22 3 COMBINED MUNICIPAL AND INDUSTRIAL WASTEWATER TREATMENT IN WASTE STABILIZATION PONDS Characteristics of wastewater Dc)mestic wastewater characteristics Industrial wastewater characteristics Characteristics of combined wastewater Advantages of combined wastewater treatment Limiting substances in combined wastewater treatment Need of pretreatment 32 4 VINGUNGUTI WASTE STABILIZATION PONDS Background and location Physical layout Design criteria used General observations 37 5 SAMPLING, ANALYSIS AND DISCUSSION OF RESULTS Sampling and analysis Results and discussion Report on truck emptiers and guestionnaires 44

6 Biochemical oxygen demand Fecal coliforms and fecal streptococci Total dissolved solids Anunonia, nitrate and nitrite Heavy metals Dissolved oxygen, temperature and ph Flow measurement Applicability of design equations 59 6 CONCLUSIONS AND RECOMMENDATIONS Conciusions Reconunendations 62 7 REFERENCES 64 APPENDICES 68

7 3 Ramadhani, M Evaluation of Vingunguti waste stabilization ponds treating municipal and industrial wastewaters. Tampere University of Technology, Institute of Water and Environmental Engineering. Publication B p. ABSTRACT This work is mainly based on field and laboratory investigations done at Vingunguti waste stabilization ponds in Dar es Salaain, Tanzania. The ponds are treating domestic and industrial wastewater jointly. They consist of two anaerobic ponds in parallel, one facultative pond and three maturation ponds in series. Details of concerned industries were collected through questionnaires. Samples were collected twice per week from inlets and outlets of each pond unit during The laboratory analyses inciuded tests for biochemical oxygen demand (BOD 5), total dissolved solids (TDS), fecal coliforms (FC), fecal streptococci (FS), anunonia (NH3N), nitrate (N03N), nitrite (N02N), ph, copper (Cu) and chromium (Cr). These analyses were carried out at water section laboratory of Faculty of Engineering at University of Dar es Salaam. More than 20 indlustries discharge ir wastewaters into Vingunguti wast.e stabilization ponds. They inciude textile, printing paints, metal and chemical industries producing heavy metals and or toxicants that inhibit microbiological growth in ponds. The total performance of Vingunguti waste stabilization ponds was poor. Total removal efficiencies on BOD5, TDS, I~rH3N, N03N and N02N were 48 %, 44 %, 19 %, 20 % and 51 % respectively. The total efficiencies in FC and FS reduction were % and % respectively. The performance of anaerobic ponds was lowest, with BOD5 reduction of only 7 %. NH~Nwas increasing 3 % in ponds and N03N and N02N removal was only by 7 % and 17 % respectively. The poor performance of anaerobic ponds may be due to sludge accumulation, shortcircuiting or presence of illegally discharged industrial toxicants. The facultative pond showed a slightly better performance. BOD5 removal was 39 % and removals of NH3N, N03N and N02N were 4 %, 17 % and 47 % respectively. As facultative pond is directly receiving industria]. effluents, low performance may be attributed to adverse effect of industrial toxicants. Highest reduction in FC and FS was observed in facultative pond: 93 % removal of FC and 85 % removal of FS.

8 4 The maturation pond~were efficient in pathogenic only. Individual removal efficiencies in removal three maturation ponds ranged % for FC and % for FS. The treatment efficiency of Vingunguti waste stabilization ponds may be revived by rearranging order of flow in ponds: all wastewater (domestic and industrial) to flow first into anaerobic ponds, n into facultative pond and finally into maturation ponds. Pretreating industrial effluents at ir source may also improve situation.

9 5 1 INTRODUCTION 1.1 General Treatment of wastewater is necessary to prepare it for safe, hygienic, nuisance free and environmentally sound discharge onto :irrigated land surfaces or into receiving waters such as r:lvers, lakes and oceans. Waste stabilization pond system is frequently preferred wastewater treatment method particularly in tropical areas where climate is favourable for biological trealbment. High temperatures, intense solar radiation, long daylight hours and availability of lowcost land are major factors that have made waste stabilization ponds to be used successfully in tropics (Egbuniwe 1982). However, due to complexity of interactions of treatment mechanisms in ponds, existing design methods have not been able to take into account all factors influencing ir operation. Joint waste treatmerit of municipal and industrial wastewaters in stabilization ponds is increasingly regarded as environinentally and economically best way of handling wastewater probiem. Industries discharge an enormous variety of waste materials. Many industries produce toxic or nonbiodegradable wastewaters while ors produce readily biodegradable effluents that do not cause problems during treatment. Therefore, investigations on behaviour of waste stabilization ponds treating combined municipal and industrial wastewaters are important for furr improvement of design methods and operational procedures. 1.2 Objectives of study The main objectives of this study were: 1) to assess efficiency of Vingunguti waste stabilization pond system as a whole and efficiency of individual pond units 2) to study effects of various industrial effluents di.scharged into ponds and recommend appropriate measures to be taken 3) to study applicability of design equations with actual conditions 4) to give recommendations for future improvement of waste stabilization ponds treating combined domestic and industrial wastewaters.

10 6 1.3 Methodology and scope The following approach was adopted during sis study: 1) Reviewing of available literature in journals, magazines, periodicals, research reports, text books and or relevant publications. 2) Collecting data and information from Ministry of Water, Energy and Minerals, Dar es Salaam Sewerage and Sanitation Department, Howard Humphreys (Tanzania) Limited and management of various industries concerned. This included consultations and interviews with author~lties involved. 3) Field research study at Vingunguti waste stabilization pond site. The study involved wastewater sampling from established sampling points at inlets and outlets of every pond unit. The samples were n analyzed in laboratory. Some onsite analyzes were also done. Flow measurement was done by installing weirs at inlets and outlets of ponds. Record of number of trips made daily by truck emptiers was kept to enable estimation of loading into anaerobic ponds. Questionnaires were sent to various industries discharging effluents into Vingunguti ponds, asking for details on different processes involved in production, quantity and quality of wastewater discharged and or relevant details.

11 7 2 WASTE STABILIZATION PONDS Waste stabilization ponds are biological treatment units in which purification of wastewater is done with help of microorganisms. The types of microorganisms achive in purification process are determined by composition of wastewater and conditions present in treatment units. 2.1 Features and processes of waste stabilization ponds Ponds are classified according to nature of biological activity taking place within m. In se terms, stabilization ponds are classified as anaerobic, facultative and maturation Anaerobic ponds These ponds are generally used for preclarification and are usually first stage in a series of pond systems where heavily loaded wastewaters have to be treated (Karpe and Baumann 1980). Anaerobic ponds lack dissolved oxygen and active microbial population comprises strictly anaerobic microorganisms with a few traces of facultative microorganisms. The organic material present in influent is degraded by ferinentative process (Horan 1990). Anperobic process The anaerobic fe:rmentation process converts waste organic materials to methane and carbon dioxide in absence of molecular oxyg en. Figure 1 shows a diagram of metabolic steps involved in anaerobic digestion and interaction between microorganisms. COMPLEX O~GANICCOMPOUNOS (Coibe~ydrat.i.Proleki. Up~ds) 1 1 HYD~OLYS1S Legend: 1 1 fermentative bacteria 2 H 2producing acetogenic bacteria 3 H2consuming acetogenic or homoacetogenic bacteria 4 C02reducing methanogenic [~bo. bacteria 5 acetoclastic methanogenic bacteria. SIMPLE ~GANIC COMPOUNDS (Si~çar..Aminoac~du PeptId~) 1 ACIDOGEN~ LONG O4AJN FATTY ACIDS (PrcpIonot.. euiy~oi.~ste) 2 $ ACETOGEP&ESJS ACETOGEPES5 METHANO~~?~...1.J1CH4.COz Figure 1. Metabolic steps involved in anaerobic digestion (Novaes 1986).

12 8 In first stage organic substrates are hydrolyzed, resulting in simpler compounds, through enzymes produced by fermentative bacteria. In second stage, acidogenesis occurs with formation of hydrogen, carbon dioxide, acetate and higher organic acids than acetate due to activities of fernientative bacteria. The endproducts such as butyric acid are extremely malodorous (Novaes 1986). The following reactions take place (Vigneswaran et al 1986): C 6H H20 > 2CH3COOH (acetic) + 2CO2 + 4H2 (1) C6H1206 > CH3CH2CH2COOH (butyric) + 2C02 + 2H2 (2) C6H12O6 + 2H2 > 2CH3CH2COOH (propionic) + 2H20 (3) During third stage, acetogenesis occurs and organic acids produc:ed are converted into hydrogen, carbon dioxide and acetat:e by acetogenic bacteria. In addition, a part of available hydrogen and carbon dioxide is converted into acetate by homoacetogenic bacteria (Novaes 1986). The following reaction takes place (Vigneswaran et al 1986): CH3CH2COOH (propionic) + 2H20 > CH3COOH + CO2 + 3H2 (4) CH3CH2CH2COOH (butyric) + 2H2O > 2CH3COOH 2H2 (5) During last stage, a group of methano ;enic bacteria both reduces c:arbon dioxide and dec~ ~rboxylates acetate to form methane (Novaes 1986). The reduction of carbon dioxide to niethane by hydrogenuti. Lizing methane bacteria takes place through follo qing reaction (Vigneswaran et al 1986): C02 + 4H2 > CH4 + 2H2O (6) The reaction during conversion of aceti ~ acid into a mixture of carbon dioxide and methane b ~ acetoclastic methane bacteria is (Vigneswaran et al 1986 CH3COOH > CH4 + C02 (7) The resulting gaseou.s endproducts are odou~ less and when y escape to atmosphere y cont: ibute to process of BOD removal. About 70 % of 1 ~ODremoved in an anaerobic pond will be in form of methane gas. Anaerobic ponds can refore operate f )r many years without desludging (Horan 1990).

13 9 Methanogens are very sensitive to changes in ph value and y will only tolerate a ph of f rate at which volatile acids are produced exceeds rate at which y are degraded by methanogens, ph will fail and methanogens will be inhibited and ultimately killed. The growth rate of methanogens is thus limiting step and determines maximum organic loading to an anaerobic pond (Horan 1990). Temperature can also af fect methanogens. Their activity is very low below 10 C, but increases rapidly as temperature inc:reases. Temperature is, refore, an important facto:r for calculation of organic loading rate. The or process involved in anaerobic ponds is sedimentation. mechanism for This process provides an removal of BOD in form of additional suspended solids. The sedimented solids will undergo rapid anaerobic decomposition at bottom of pond. A well designed anaerobic depending pond can achieve up to a 60 % upon temperature and retention BODreduction time (Horan 1990). Figure 2 shows generalized curve for removal of BOD and pathogens in relation to retention time. BOD REMOVAL IN o o ~( MARA GLOYNA(22 C) DETENTION TIME ~DA1 Figure 2. BOD removal in relation to temperature and detention time (Karpe and Baumann 1980). When sedimented organic material is degraded, a large amount of amnionia is released as ammonium. Due to lack of oxygen, nitrification can not occur and this anunonium

14 10 leaves pond in effluent. The effluent from an anaerobic pond often contains up to 20 % more ammoniuni than is present in influent. Of particular importance in anaerobic ponds is biological interconversions undergone by suiphur containing compounds. The evolution of H 2S, which resuits from anaerobic reduction of sulphate, is responsible for odours associated with anaerobic ponds. The reaction proceeds according to following equation: CH3COOH + S H~ > 2C0 2 + H2S + 2H20 (8) This reaction is carried out by suiphate reducing bacteria and H2S is major end product (Horan 1990) Facultative ponds The major role of facultative ponds is removal of BOD. The ponds are characterized by three zones. In upper regions, near water surface, aerobic conditions prevail. At bottom of pond reduction occurs under anaerobic conditions. Between se two layers re is a facultative region, where a mixture of both reactions take place (Karpe and Baumann 1980). Aerobic zone The aerobic condit.ions at surf ace of pond are mainly due to photosyntic activity of algae growing where nutrients and light are available. Like all plants, algae produce oxygen which is absorbed by aerobic bacteria living in wastewater (Karpe and Baumann 1980). The bacteria consume oxygen in respiration and multiplication and, at same time, y break down organic matter present in wastewater. As a byproduct of ir metabolism, y release carbon dioxide, nitrogen and phosphate compounds which serve algae as nutrients and as raw material for photosynsis. Sonie of oxygen is again used by aerobic bacteria thus continuing cycle (WHO 1987). The symbiosis between algae and bacteria is summarized in Figure 3.

15 11 NEW CELLS 4 ALGAE LIGHT c0 2 ORGANIC MATTER GACTER IA 4 NEW CELLS Figure 3. Symbiosis of algae and bacteria in stabilization ponds (Karpe and Baumann 1980). The photosynsis process depends on light intensity. The algae population decreases with depth of pond and proportion of oxygen diminishes correspondingly. In facultative zone of pond, water contains littie oxygen and deeper in anaerobic zone, it contains no oxygen. Wind and heat are also determinants which control function of facultative ponds. Especially in tropical zones, upper water layer will heat up rapidly. Without circulation of water caused by activity of wind, a discontinuity in temperature at a depth of only 50 cm can occur. Some of algae may sink down from warm water region (above 35 C), forming a light barrier. This phenomenon will immediately cut down rate of photosynsis and production of oxygen. The pond will refore tip over and become an anaerobic one (Karpe and Baumann 1980). Anperobic zone During retention period of wastewater in facultative ponds, all solid substances form sediment at bottom. Their anaerobic reduction takes place at temperatures above 15 C, developing methane, carbon dioxide, and or anaerobic gases. Anaerobic metabolism in pond sediment serves to degrade sedimented sludge and thus increases times between desludging. Typically, desludging period for facultative ponds is 5 10 years (Karpe and Baumann 1980).

16 12 Facultative zone This zone is characterized by all processes taking place in aerobic and anaerobic zones. In addition, facultative bacteria consume combined oxygen from nitrates and sulphates when free oxygen is exhausted. The stabilization process that takes place in a facultative pond is sununarized in Figure 4. The effluent of a facultative pond taken from surf ace layer is strongly green coloured due to presence of algae. It also contains or living organisms such as microcrustaceans, bacteria and rotifers, and has a high content of dissolved oxygen. However, re are practically no suspended solids that will settle (WHO 1987). WIND SUNLIGHT CH 4 Figure 4. The stabilization process in a facultative pond (WHO 1987) Maturation ponds Maturation ponds are used mainly for reduction of pathogenic microorganisms such as viruses, bacteria and helminths. This is achieved by providing a retention time long enough (5 10 days) to reduce nuniber to required level (Horan 1990). The bacterial effect of maturation ponds is due to several natural factors including sedimentation, lack of food and nutrients, solar ultraviolet radiation, high temperatures, high ph value, predators, toxins and antibiotics excreted by some organisms, and natura]. dieof f (WHO 1987). Suitably dimensioned maturation ponds reach a reduction of coliform bacteria of % and a BODreduction of from about 60 mg/l to less than 25 mg/l. The ponds work under completely aerobic conditions and in general have a depth of m (Karpe and Baumann 1980). 8

17 Pond combinations The distribution of functions among different pond types in a stabilization pond system means that two or more types of ponds should be connected in series to achieve better effluent quality. Figure 5 shows possible pond arrangements in parallel and series. Ii) (iii) al F1 8 ~)L~IH ~~I~IH (v) 1 ~EIJ~ (v i) L~J LIJ 8L~II (ix) Legend: A = anaerobic pond F = facultative pond M = maturation pond. Figure 5. Different arrangements of ponds (WHO 1987). 2.2 Design principles Design of anaerobic ponds To attain anaerobic conditions i.n pond, of oxygen by algal photosynsis must be production inhibited and rate of oxygen utilization must exceed reaeration at surface. This is achieved by rate of designing pond as deep as practically feasible (up to 5 m or more) and ensuring a high organic loading rate (Horan 1990). There are various procedures used for design of anaerobic ponds, but all of m adopt one of following criteria: surface loading rate (kg BOD 5/had) volumetric loading rate (g BOD5/m 3d) hydraulic retention time (d).

18 14 Surface lppding rate For tropical regions, a pond is expected to be anaerobic all time i.f surface loading is more than kg BOD 5/had. Surface loading is clefined as = L~Q/10A (9) where L5 = surface i.oading (kg BOD5/had) = average i,nfluent BOD (mg O2/l~ Q = average influent flow rate (m~/d) A = surface area of pond (m 2). However, according to Gloyna (1971) cited by WHO (1987), surface loading is inadequate for sizing an anaerobic pond despite that it is still adopted by many designers. Volumetric loading rate The volumetric organic loading rate is defined as (Mara and Monte 1990): = L~Q/V (10) where Lv = volumetric organic loading rate (g/m3d) L~ = average influent BOD (mg O2/l~ Q = average influent flow rate jm~/d) V = required pond volume (mi). The required value of Lv is selected on basis of mean temperature of coldest month. Table 1 gives volumetric design loadings for anaerobic ponds and corresponding BOD 5 removals. Table 1. Design loadings for BOD5 removals in anaerobic ponds (Mara and Monte 1990). Design temperature c ric BOD Volumet 5 loading g/m 3~d BOD5 remova1 % < T 100 2T + 20 > T = design temperature Retention time Retention time is most conunonly used design parameter in anaerobic ponds. Gloyna (1971) cited by WHO (1987) has reconunended a maximum retention time of 5 days in tropical areas. The relationship between retention time and BOD reduction is given in Table 2.

19 15 Table 2. BOD reduction in anaerobic ponds as a function of retention time (Mara 1976 cited by WHO 1987). Retention time d BOD 5 reduction % Retention time is calculated as (Karpe and Baumann 1980): (11) AD/Q t = where t retent:ion time (d) A D surface area of pond (m 2) = depth of pond (m) Q = quantil:y of wastewater (m3/d) Design of facultative ponds A series of possible procedures for calculation of pond dimensions have been presented. The common empirical and kinetic approaches are McGarry and Pescod equation, Gloyna equation and Marais and Shaw first order reaction equation. McGarry and Pescod eguation Surface loading is given by following empirical formula (Mara and Pearson 1987): L 50 = 60.3(1.099)T (12) where L50 = permissible surface loading (BOD5/had) T = meari air temperature ( C). The equation has later been subjected refinements as follows: Lso = 20T 120 Ls,o = 20T 60 Ls,o = lot = 50(1.072)T to var±ous (13) (14) (15) (16) All se equations give different loads for any given temperature. Thi.s has led many designers to prefer a kinetic approach (Mara and Pearson 1987). Application of McGarry and Pescod equatiori will result in an effluent BOD5 of mg/l (WHO 1987).

20 16 Glpyna eguation Gloyna s empirical equation presumes a BOD removal of % and has following form (Gloyna 1976 cited by Banerji and Ruess 1987): V = 3.5 X lo_ 5QLu(1.O8535_T)ff~ (17) where V = Q = pond volume (m3) wastewater flow (l/d) Lu = ultimate influent BOD (mg/l) T = f = pond water temperature ( C) algal inhibition factor = sulphide or or immediate COD factor. Marpis and Shaw first order reaction eguation This kinetic approach involves following basic equation (WHO 1987): Le 1 L~ l+ktt (18) where Le = effluent: BOD 5 (mg/l) = influent: BOD5 (mg/l) kt breakdown rate at temperature T C (d~) t = retention time (d). The breakdown rate dlepends on pond temperature: kt = 0.3(i 05)T20 (19) where T = pond operating temperature ( C). From equation 19, th.e formula for calculation of pond area can be deduced as (Karpe and Baumann 1980): Q(Li Le) A= (20) 18D(1 05T20) where A Q = wastewater pond surfaceflow area(m~/d) jm 2) D = pond depth (m). The retention time (d) is given as (Karpe and Baumann 1980): t = AD/Q (21) The depth depends on prevailing climatic conditions and varies m (Table 3).

21 17 Table 3. Depth of facultative ponds in relation to envirorimental conditions and kind of sewage (modified from Karpe and Baumann 1980). Recommended depth m Environmental conditions Type of wastewater 1,0 Uniform warm temperature 1,0 1,5 Uniform warm temperature 1,5 2,0 Moderate seasonal temperature fluctuations 2,0 3,0 Wide seasonal temperature variations Presettled wastewater Untreated wastewater Raw wastewater containing settleable solids Large aniounts of settleable grit or settleable solids Design of maturation ponds The removal of fecal coliform bacteria from any pond follows a first order removal kinetics as follows (Horan 1990): Ne 1 1+kbt where Ne = number of fecal coliforms in effluent = number of fecal coliforms in influent kb = bacterial dieof f constant (d~~) t = retention time in pond (d). (22) Yanez (1982) cited by WHO (1987) has compiled data for values of dieof f constant for fecal coliform bacteria and salmonella (Table 4). Table 4. Values of dieof f constant for different bacterial species (modified from Yanez 1982 cited by WHO 1987). Organism kb d~ Temperature C Fecal coliforms Fecal coliforms Fecal coliforms 2.0 Not recorded Fecal coliforms Salmonella 0.8 Not recorded

22 18 For a nuinber of ponds in series, corresponding equation is (Horan 1990): Me 1 Ni (1 + kbta)(l + kbtf)....(1 + kbtm)n (23) where tal tf t:m = retention times of anaerobic, facultative and maturation ponds in series n = nuinber of maturation ponds required. kb is sensitive to temperature and can be expressed as: kb(t) = 2.6(l.07)(T_20) (24) Solution of design equation for maturation ponds is a trial and error procedure as equation (23) contains two unknowns: number of ponds and size that each should be. It is recommended to have many small ponds than fewer large ones with same total retention time. However, careful decision on minimum size of pond is required to prevent significant short circuiting (Mara and Pearson 1987). 2.3 Factors af fect.ing operation of waste stabilization ponds There are several factors which may, advantageously or adversely, af fect hydraulic and biological conditions of wastewater stabilization ponds. Some of se factors can be taken into account at design stage whereas ors are beyond designer s and operator s influence. Care in site selection and design can reduce impacts of some factors Climatic factors Once a pond system bas been designed and constructed, its subsequent performance relies largely on climatic factors such as wind action, temperature, rainfall, sunlight and evaporation (Lumbers and Andoh 1985). Wind Wind action is useful as it influences mixing within ponds, thus minimizing short circuiting and ensuring a reasonable uniform distribution of BOD, algae and oxygen. The depth of wind induced mixing in a pond depends largely on distance wind is in contact with water. Mara (1972) cited by Munene (1984), has indicated that this distance (unobstructed) should be about 100 m for maximum mixing.

23 19 To facilitate windinduced mixing, longest dimension of pond should lie in direction of prevailing wind. However, whenever possible, ponds must be sited downwind of community, in case odour problems arise (Horan 1990). Temperature Temperature is an important factor influencing performance of a waste stabilization pond. At higher temperatures, d:lssolved oxygen present in pond is partly liberated to atmosphere. At lower temperatures it remains in pond longer. Temperature affects photosyntic oxygen production as well as or biological reactions. Optimum oxygen production for some species of algae is obtained at 20 C, and limiting lower and upper values appear to be about 4 C and 37 Crespectively (Gloyna 1971 cited by Mayo 1988). The function of anaerobic ponds depends also on temperature. The right equilibriuni between methane and acidproducing bacteria will only be achieved if water temperature is more than 1 5 C (Karpe and Baumann 1980). Rainf all Rainfall will have some influence on pond performance and reliability. Ret:ention time in ponds is reduced during periods of rainfali. Heavy showers may dilute contents of shal].ow ponds, affecting food available to biomass. On a very hot day, ram may cool surface layer. The anaerobic sludge will n appear floating on surface and hence spoil effluent. Simultaneously, algal mats ori surface of pond will be driven to bottom. Rainfall may also add oxygen to a pond through its own clissolved oxygen and by increasing surface turbulence (WHO 1987). Solar radiation The intensity of solar radiation is an important factor for generation of oxygen through algal photosynsis. Facultative ponds rely on solar radiation and paraxneter varies mainly with latitude. Clouds also reduce available light to some extent but direct sunlight is not absolutely essential. The complex of 21 ponds at Lima, Peru, surveyed in 1979, is a dear evidence that s abilization ponds can function without direct sunlight. A blue sky is rar uncommon re, yet ponds have shown to be operating under completely normal photosyntic conditions (WHO 1987). The bacterial mortality rate in ponds is also largely influenced by th.e inactivation power of solar radiation (Mayo and Gondwe 1989).

24 20 Evaporptjon Intense evaporation may upset ecological balance in stabilization ponds through increase in concentration of solids. The salinity and concentration of organic matter may be increased to a point at which osmotic balance of cells of aquatic microorganisms is disturbed. It may also cause undesirable reductilon in depth of water and af fect retention regarded time. Evaporation rates as negliqible. However, up to 5 in hot mm/d and may be regions evaporation may exceed 15 mm/d (WHO 1987) Physical factors These factors are generally related to design and refore can be controlled. Water depth Stabilization ponds are normally operated at constant depth. Intense seepage and evaporation or some emergency withdrawal of pond contents may cause water level to drop on occasions, c:ausing problems. 1f depth drops to less than 0.6 m, aquatic plants are likely to grow very quickly. A large part of surface may become covered with weeds extending above water level. As penetration of sunlight will be impaired, pond efficiency may drop to an unacceptable level. In such a case, mosquito breeding ma.y also occur (WHO 1987). Water depth requirements are different for every pond type since biological processes that take place in ponds are different. Shortcircuiting Short circuiting in ponds is a cominon problem especially in deeper anaerobic ponds. It results in stagnant zones within a pond which can cause odours. It also reduces effective pond volume for wastewater treatment. These effects can be minimized by proper choice of pond geometry and proper placement of inlet and outlet structures. For anaerobic ponds, a rectangular surf ace area is reconunended with a length to breadth ratio of less than 3:1. Facultative and maturation ponds are designed to approximate plug flow mixing, refore higher length to breadth ratios (up to 15:1) are employed. The inlet and outlet structures should be placed at diagonally opposite corners (Horan 1990). Seepage A survey on ground permeability at a proposed pond site is of great importance at planning stage. This will provide information regarding need for bottom lining. Ponds built in permeable soils should be lined to

25 21 attain maximum d:lscharge, especially if effluent is to be used for agricultural purposes. Lining is also important in cases where groundwater needs to be protected from pollution (WHO 1987) Chemical ieactors The main chemical factors af fecting pond performance ph, toxic materials and oxygen. are 211 Both anaerobic and facultative ponds operate most efficiently under slightly alkaline conditions. Most organisms in ponds have a ph tolerance of and optimum range of (Abid 1983 cited by Mayo 1988). Methane fermental:ion in anaerobic ponds is af fected by ph changes. Methanogens will only tolerate a ph range of (Horan 1990). Industrial wastewaters are normally causes for extremes of ph value in ponds. It is refore recommended that y should be controlled at source rar than introducing complexity of ph adjustment at influent to ponds. ph in facultative ponds depends upon carbon dioxide concentration in medium. Due to presence of excess C02 produced by aerobic bacterial respiration during night, ph value will be low in morning hours. In evening, ph value increases as a result of algae absorbing major part of C02 in solution (WHO 1987). Toxic materipis The presence of t:oxic materials in industrial wastewaters af fects performance of waste stabilization ponds. Heavy metals, pesticides, detergents, wastes from antibioticproducing industries and many or industrial wastewaters that: inhibit biological treatment should be controlled at source (Alabaster et al 1991). Oxygen Dissolved oxygen is best indicator of satisfactory operation of a facultative or maturation pond. In a normally functioriing facultative pond, super saturation of free dissolved oxygen at surface and in subsurface layers occur during afternoon. The oxygen concentration may drop to less than 1.0 mg/l at dawn due to presence of algae. The aerobic surface layer prevents gases with odour problems, released from anaerobic layer, from coming out of pond. However, odour problems still occur from time to time in facultative ponds due to development of blue green algae when water temperatures are high.

26 22 Odour problems may also occur as a result of anaerobic patches appearing on surface of a pond when bottom temperatures rise rapidly above 22 C (WHO 1987) Wastewater fiow and coinposition Wastewater flow Stabilization ponds are sometimes designed on basis of hydraulic retention time, a parameter directly related to wastewater flow. In practice, average flow rate is quite an adequate basis for design due to relatively large volume of pond systems. Wastewater compositi~ The design of stabilization ponds is directly related to wastewater characteristics which are influenced by type of sewerage system and contributing industries. Combined sewers convey a more dilute wastewater on rainy days whereas separate sewers are less sensitive to rainfall. Infiltra.tion contributions, industrial and institutional discharges, dumping of septic tank sludge into sewers and or circumstances often af fect wastewater composition. Organic loading, in terms of BOD5 or COD, is most fundamental parameter used in design. Some parameters or than organic loading may be important where industrial wastewaters are present in sewage. These will help designer know if re is a need of providing pretreatment to protect biomass in pond system Characteristics of receiving waters The pond effluent will eir have to be disposed of somewhere (into a stream, lake, etc.) or is reclaimed for furr use. The selfcleaning and dilution capacity of a receiving water under critical flow conditions should be known to determine degree of treatment to be provided. Sometimes a heavily loaded primary pond may be sufficient, while in or cases several ponds in series are necessary as a better effluent quality is essential. 2.4 Operational problems of waste stabilization ponds Inspite of ir relative operational simplicity, problems can develop with stabilization pond systems which can cause a reduction in ir efficiency, nuisance or damage. Many of problems can be avoided or minimized by good design and rest can be preventec1 by maintaining good operational control and providing routine maintenance. Following are common problems that occur in stabilization ponds:

27 23 1) Development of algal scuni ori facultative and maturation ponds: Algal mats may sometimes accumulate on pond s surface as a result of rapid growth of blue green algae. The algal mats reduce light penetration into pond and y also produce odour problems as y decay. The scum layer may be broken up by means of water jets and It will sink to bottom of pond (Arthur 1983 and Munene 1984). Wang 1991 noted that high concentration of algae in effluents :Ls a typical problem in symbiotic algae/bacter:la systems of wastewater treatment. They often cause secondary pollution to receiving water bodies. 2) High vegetal:ion growth on embankinents: Normally pond embankments have a protective grass cover to prevent m from being eroded by wind and wave actions. However, when grass is left to grow uncontrolled, burrowing animals like moles and rats may invade area and affect safety of embankments. Therefore grass cover should always be cut short (Munene 1984). 3) Mosquito nu~lsance: Mosquitoes create problems around waste stabijlization ponds. A poorly maintained pond with a lot of growing weeds or scum provides a breeding sit:e for mosquitoes. Regular cleaning of vegetation and removal of scum is necessary to control insects (Munene 1984). 4) Odour problems: Odour problems may arise from a number of situations. Odours can be caused by nature of wastewat:er itself and also by anaerobic conditions in pond. Hydrogen sulphide, which is major compound produced by sulphur reducing bacteria, is responsible for odour problems in ponds. The best way to prevent problem is to control industrial effluents. Anor major source of odour is aminonia whic:h originates from conversion of urea to carbon dioxide and ammonia (Henry and Gehr 1980). 5) Overloaded ponds causing poor effluent quality and odour nuisance. AlSalem and Lumbers (1987) have reported a significant reduction in efficiency of Alsumra waste stabilization ponds in Jordan due to overloading. The reduction of BOD through facultative ponds was found to be about 18 % only. The poor performance was attributed to predominantly anaerobic conditions observed in most of facultative ponds. The loading to ponds was greater than that likely to lead to facultative behaviour.

28 24 3 COMBINED MUNICIPAL AND INDUSTRIAL WASTEWATER IN WASTE STABILI~ATION PONDS 3.1 Characteristics of wastewater The most frequently used characteristic wastewater are (Pujol and Lienard 1990): TREATMENT parameters Suspended solids (SS) and its organic fraction, volatile suspended sollds (VSS) whlch characterlze particular type of pollution. The chemical oxygen demand (COD) and biochemica]. oxygen demand in 5 days (BOD5) whlch guantify organic content of wastewater. COD Indicates total organic content while BOD5 indicates biodegradable orgranic content. Forms of nitrogen (N) and phosphorus (P). fertilizing elements whose dlscharges are accelerate eu.trophlc processes. These are llkely to The ph and condu,ctivity, which give a good of water ionicity. indication Fecal coliforms, which indicate risk of by pathogenic microorganisms. Heavy metals and inorganic industrial pollution salts, which infection indicate Domestic wastewater characteristics The characteristics of domestic wastewaters are linked ir origin. There are: of sewage water from toilets which organic matter contains to essentially domestic wastewater from kitchens, bathrooms, etc. The daily discharge can vary considerably depending on extent of equipment and hygienic habits such as showers or baths. These wastewaters contain, principally, organic matter as well as household products such as detergents and phosphates (Pujol and Lienard 1990). The characteristics of municipal wastewater depends on orlginal concentration in water supply, water usage and per capita consumption. Thus characteristics vary from one locality to an Dr and even from season to season within same locality (Yayehyirad 1984). The typical characteristics of domestic wastewaters in small cominunities are given in Table 5.

29 25 Table 5. Characteristics of domestic wastewater In commun:lties (Pujol and Lienard 1990). Parameter Concentratlon g/capita d COD BOD SS NNH4~ PPO4 small BOD5 and COD concentratlons confirm organic nature of domestic wastewater. The COD/BOD ratio, which Is slightly greater than 2, indlcates biodegradable nature of such water (Pujol and Lienard 1990). Treatment of municipal wastewater can, refore, be easily performed in biological treatment units like stabilizatlon ponds IndustriaiL wastewater characteristics Depending upon processes involved in an industry, re is a wide variation in wastewater composition from one type of industry to anor. In this chapter, discussion is made on seven types of industries commonly found in Tanzania: textlle industry, tanning industry, food processing industry (fruit and vegetable canning), metal industry (pickling, plating and sheet milling), chemical industry, breweries and dairies. Selection of se Industries has taken into consideration relevance of discussion to forthcoming chapters. Textile industry wastewaters Many substances present in textile effluents influence COD, some increasing it and ors depressing it. Some substances will af fect BOD, suspended solids content and ph. Some organic compounds will be difficult to destroy by biological oxidat:ion since y generally have a low BOD. These are said to be biologically hard. Those that are readily oxidized are termed soft and usually have a high BOD. However, most of organic compounds used in or extracted during textile processing are biodegradable to some degree. In absence of toxic materials, refore, blological process can be successfully used for purification of t:extile effluents (Yayehyirad 1984). A typical example is from effluents of selected textile industries in Tanzania. Textile mill operations in Tanzania, generaily, consist of weaving, dyeing, printing and finishing. The wastewaters from textile mills contain a variet:y of chemicals such as inorganic salts, organic acids, starch, hydrogen peroxide, detergent alkalis, urea and also waste products from a big number of

30 26 different dyestuffs. Textile wastewaters are usually coloured, highly alkaline, contain high BOD and suspended solids and have high temperatures (Mashauri et al 1990). Table 6 shows typical characteristics of textile effluents. Table 6. CharacterLstics of textile effluents from Germirli et al 1990). Parameter tinit BOD mg/l TSS mg/l COD Colour ph mg/l mg Pt/.1 (modified Concentration Tannery wastewaters The major sources of pollutants in tannery (Gathuo 1984): industry are constituents of raw hide which are necessarily removed or adapted during lear making process including hair substances, various proteins and natural fats of hides toger with any curing agents which may be utilized chemicals employed in lear production, eir present as surplus in ir original form or converted into or products miscellaneous pollutants arising from housekeeping in tannery, for example machine washing and or sanitary activities. The cominon pollutants and ir minimal amounts resulted in during proctuction of chrome tanned lears are given in Table 7. Table 7. Tannery effluents characteristics (modified from UNIDO/UNEP 1975 cited by Gathuo 1984). Content Concentration mg / 1 BOD 800 SS 650 Chrome Suiphide N

31 27 As raw material of tanning industry is a natural product, its soluble impurities are generally readily biodegradable and represent a large part of BOD bad in effluent. The process chemicals employed are a variety of inorganic and organic materials, affecting total solids, ph and COD. Of particular importance are appreciable quan.tities of sulphide and chromium that are present. These substances have proved to have significant effects on performance of stabilization ponds (Yayehyirad 1984). Fruit and vegetable canning industry wpstewater Wastewater is normally generated during washing and rinsing, peeling, blanching and processing. Washing and rinsing is done to remove soil, microbial contamination, leaves or stems and to remove solubles and insolubles after cutting, coring, peeling or blanching. Washing and rinsing operations constitute a major source of wastewater. The volume of water used in se operations may be up to 50 % of total usage (Gilde and Aly 1976). Peeling operations produce wastewater containing large quantiies of suspended matter primarily organic in nature. Blanching is done to expel gases from vegetables, to whiten beans and rice and precook m, to inactivate enzymes that cause undesirable flavour or colour changes in food and to prepare products for easy filling into cans. Little fresh water is added to blanching operation, refore concentration of organic materials is high due to leaching out of sugars, starches and or soluble materials from product that is blanched. Although small in volume, wastewater from blanching operation is usually highly concentrated with dissolved and colloidal organic matter (Gilde and Aly 1976). The final major sources of wastewater are from washing equipment, utencils and cookers. Also from washing of floors and general food preparation areas. Metal industry w~stewater The metal industries dealt with in this chapter are secondary mills involved with finishing operations, such as pickling, plating and sheet milling. Pickling is a process of chemically removing oxides and scales from surface of steel. This is done using water solutions of inorganic acids such as sulphuric, hydrochloric, nitric and phosphoric acids. After pickling, steel passes through rinse tanks. The sources of wastewater from pickling operations are strong spent acid solutions and rinse water (Bramer 1976). Metal plating consists of coating finished metal product with a thin sheet of anor metal for protective or decorative purposes. Processes in this operation include cleaning in alkaline solutions, rinsing, pickling,

32 28 melting, chemical treatment and oiling. Wastewaters generated in plating industries include rinse water and concentrated process solutions. The metal content of effluent commonly includes tin, chromium, zinc, copper and nickel, cadmium, aluminium and iron (Longhurst and Turner 1987). In sheet and strip mills, slabs are robled with a continuous hotstrip mibl. The slabs are brought to rolling temperature in continuous reheating furnaces. The conditioned slabs are n passed through scabe breakers and highpressure water sprays dislodge boosened scales. Cooling water is n sprayed and finished strip is coiled. The sources of wastewater in sheet and strip mill operation is cooling water and sprayed high pressure water (Bramer 1976). Chemical industry wa.stewater Most of highby pollutional wastewaters from chemical industries originate from process areas. This includes water formed or ebiminated during reactions, washwaters from cleaning opera.tions, stem condensate from stripping operations and accidental bosses due to spills and carebess operation. Process wastewaters may contain a variety of constituents including a portion of feedstock chemicals, products, byproducts, side products and spent catalysts. Acidic and alkaline discharges are characteristics of most chemical industries (Parsons 1976). Brewery was tewater The production of beer has two stages, mabting of barley and brewing to beer from mabt. Brewery wastes are composed mainly of liquor pressed from wet gram, liquor from yeast recovery and washed water from various departments (Arellano 1987). The major componerits of brewery wastewater are BOD and suspended solids which are produced in brewhouse, during fermentation stage and during bottling stage. The variations in brewing tradition and household practice are refbected in effluent BOD values which are normally in range of kg/m3 (Henze 1983). The typical breweries wastewater production and composition are given in Table 8.

33 29 Table 8. Charact.eristics of effluents (modified from Henze 1983). Content Concentration SS VSS Total BOD Soluble BOD Total COD Soluble COD Total N Total P from breweries mgr / 1 ppjry products wastewater Processing and manufacturing of dairy products are water intensive operations both during product preparation and manufacturing. Maintenance of sanitation within process area also uses a bot of water. This resuits in a problem in treatment and disposal of large volume of wastewater generated. Dairy wastewaters contain phenolic substances which are supposed to be free from toxic substances. Phenols come from flavouring and from phenol sanitizing rubber boots used by workers in processing area. Or contents include BOD, SS, nitrogen sulphur, grease and oil (Table 9) (Diaz 1987). Table 9. Dairy products 1987). wastewater characteristics Parameter Unit Average concentration BOD5 Suspended solids Grease and oil ph Total solids Nitrogen Phosphates mg/l mg/l mg/l mg/l mg/l mg/l Character]Lstics (Diaz of combined wastewater Industrial wastewaters contain materials having a wide range of different characteristics. In most cases industriab effluents are composed of toxic or nonbiodegradable materials. However, it is not uncommon to find industrial effluents that cbosely resemble domestic

34 30 sewage and are refore suitable for biobogical treatment. Some inciustrial effbuents can be effectiveby treated by mixing with domestic sewage to improve nutrient balance of waste and to dibute toxic compounds present (Alabaster et al 1991). Generally, industrial wastewaters may be: nonharniful at a].b to treatment harmful to treatment processes harmful to sludge utilization useful to treatment processes or a combination wastewaters. 3.2 of above when combined with municipal Advantages of combined wastewater treatinent The easiest and most effective way of dealing with trade effluents is to admix it with domestic sewage. However, re are limits to type of effbuent which should be accepted. For exainple, discharge must not contain substances which alcne or in combination will inhibit biological processes of biobogical treatment (Holding 1990). The performance of stabilization ponds which are treating a mixture of domestic and industrial wastewaters can be put at risk by presence of hazardous chemicals in industrial wastewater fraction. Effluents from food processing indust,ries, which comprise readily biodegradable organic matter are relativeby easy to treat. In contrast, heavy metabs from metal industries, such as copper, zinc, nickel, lead, cadmium and chromium can react with microbial enzymes to retard or completely inhibit metabolism (Yayehyirad 1984). Because of ir comparatively long retention time, stabilization ponds albow a greater buffering capacity against shock loads of toxic inaterial and a longer period for biobogically hard compounds discharged from industries. Or biological treatment systems such as activated sludge and trickling filters have shorter retention times and hence back this advantage (Arthur 1983). High strength industrial wastewaters with BOD boading in range of mg BOD/l can be treated by empboying anaerobic ponds as pretreatment units. However, anaerobic processes are susceptible to inhibition by excess of subphide as hydrogen subphide. The sulphate loading rate should be kept below 500 mg SO42/m3 d (Mara and Pearson 1987). Oib and grease from industries can be well trapped in anaerobic ponds that have subsurface effluent of f take. The oil and grease are thus prevented from reaching facultative ponds and are gradually degraded in anaerobic ponds.

35 31 In case of textile effluents, joint treatment with municipal sewage can be considered to be best alternative. By combined treatment, especiably if textile wastewaters form one quarter or less of total volume, many difficulti.es are solved. Fbow, alkabinity and temperature extremes and fbuctuations can always be corrected. Also decoboration is done more efficiently (Grau 1991). Textibe effluents are normally deficient in nitrogen and phosphorus and refore it becomes necessary to add nutrient materials, like ammonium subphate, to restore balance before any biologicab treatment is given. This is why It is preferabbe to treat se effbuents in admixture with municipal sewage which will suppby required nitrogen and phosphorus (Yayehyirad 1984 and Grau 1991). The soluble impurities from tanning industry are generalby readily biodegradable and refore y can be effectiveby and cheapby treated in waste stabilization ponds toger with domestic sewage. The problem of high concentration of chromium can be taken care of in anaerobic ponds and facultative ponds arranged in series. This has been proved by performance of Nakuru waste stabilization pond system in Kenya. The average concentration of chromium in raw sewage was found to be 1.58 mg/b. Approximately, 20 % of this was removed in anaerobic ponds with a furr % removed in first facult:ative pond. The second facultative pond removed a furr % and bevels were undetectable in effluent:s from third pond (Ababaster et al 1991). 3.3 Limiting substances in combined wastewater treatment Following is a JList of common substances which could create difficubties in biological treatment units. The list serves to illustrate kind of probbems associated with treating industrial discharges toger with domestic sewages (Holding 1990). Acids and alkabi~: The optimum ph range for biobogical treatment of sewage is around Any acid or alkaline discharge which causes ph of mixed sewage to fall beyond range will require neutrabization before discharge Nonferrous metabs: Nonferrous metals such as cadmium, chromiuin, copper lead, mercury, nickel and zinc, have an inhibiting effect on biological processes. When ir sludges are reused for agricuiturab purposes, y may inhibit crop growth, be assimibated by plant and enter food chain. Oils and fats: These substances are a common occurrence in industrial wastewaters. They can inhibit atmospheric oxygen which is vital for biologicab wastewater treatment.

36 32 Pesticides and detergents: These are nonbiodegradable compounds that can kill bacteria present in ponds. 5ulphate~ and sulphides: Excess of subphides as hydrogen sulphide inhibit anaerobic processes in ponds. Additional problems occur 1f industriab effbuents contain substances with unknown environmenta]. consequences. The damage may be done before potential is even realized. For example local farmers used dried sewage sludge for soil conditioning until severe damage was noticed on a crop of pyrethruin. When sbudge was analyzed, trichlorobenzoic acid was discovered at a concentration of jiust one part in 100 M, but stil]. a sufficient amount to damage crop (Holding 1990). 3.4 Need of pretreatinent The most effbuents and with 1990). important objective of pretreating industriab is to prevent problems in sewerage system any of treatment processes empboyed (Upstone Each industry is to some extent an individual case, refore thorough study should be done to be able to characterize effluents from a particular industry and propose pretreatment possibilities. Thorough investigations are important on water balance, processes involved, chemicals used, level of housekeeping and management of water and wastewater for each industry (Rantala 1987). Pretreating textile effluents The presence of colour in textile wastewaters is a common problem. The dyes are, in general, biologically nondegradable or slowly degradable. These would consequentby lead to a very high turbidity in facultative ponds, limiting light penetration, and thus limiting algae growth. Inspite of positive features of combined treatment, in many cases effluent is still coloured. It is practically impossible to estimate beforehand decoboration effici.ency of joint treatment. Even pilot experiments do not guarantee perfect prediction of decoloration. Permanent changes of palette, types of dyes and fibres introduce unpredictable stochasticity. Fbexible pretreatment for textile effluents is thus a necessity (Grau 1991). Pretreating tannery effluents Tannery discharges have high sulphide content (up to 40 mg/l). When se discharges pass through to facultative ponds y resubt in inhibition of photosyntic algae. The pond water frequently turns bright pink due to profuse growth of purple photosyntic bacteria which utilize sulphide. They convert sulphide

37 33 to ebementab sulphur and deposit it within cel].. The profuse growth of sulphur bacteria resubts in a high turbidity in ponds. Light penetration and hence photosyntic oxygen production is thus limited. Ababaster et al (1991) have reported on poor performance of stabibization pond system in Nakuru, Kenya due to high sulphide levels in raw sewage. It is probable that 1f tanneries were to instalb a pretreatment facility for sulphide recovery, n a sufficient improvement in performance of ponds would be seen. Pretreatment is also required to reduce high amount of chromiuzn present in tannery wastewater. The common pretreatment activities inciude: Lowering concentration of SS: This is a mechanical pretreatment for capturing suspended solids such as short fibres from a textibe industry. Grease and oil removab: Grease and cii are usually lighter than water and may be separated by passing wastewater through an interceptor or grease trap. The interceptor consists of a tank divided into compartments in which grease and oh fboat to surface of wastewater and is retained by baffles. Cooling: Large volumes of hot industrial wastewaters may be coobed using cooling towers or spray ponds. Neutralization: Wastes with bow ph value may be corrected by addition of an abkabi. Usually, re is a choice of alkalis, some of which may produce a precipitate and hence require a subsequent settling stage. The most common alkalis used are sodium hydroxide and sodium carbonate. Highly alkaline wastewaters are neutrabized by inorganic acids such as hydrochboric (D~ sulphuric acid. Screening: This is designed to remove large fboating and suspended sobids by passing wastewater through racks or screens before it enters into a tretment plant. Screens may take form of bars, wires or perforated plates. Collecting solids from screens can be done by mechanicalby operated rakes. Screening reduces sobids boading on subsequent treatment system. Sreening is particularby important for food processing and textibe industries (Gilde and Aly 1976 and Diaz 1987). Grit removal: This is employed to remove smaller and more dense solids like sand and cinders. Metal industries and building construction firms normally produce this type of wastes. Grit removal may be done through channels and washing collections eir by hand or mechanically. Removed grit is typical].y land filled (Diaz 1987).

38 VINGUNG(JTI WASTE STABILIZATION PONDS Background and bocation Vingunguti waste stabilization ponds are bocated in Ilaba district in Dar es Salaam region. They can be approached by using Pugu road or Uhuru street from Dar es Salaam city centre. The ponds are about 12 km from city centre and about 200 m northwest of TAZARA (Tanzania Zambia Railway Authority) railway station (Figure 6). Figure 6. Location map of Vingunguti waste ponds (Howard Humphreys 1988). stabilization The ponds started operation in 1976, a time during which only industriab wastewaters from Pugu Road industrial area were treated. At beginning re were only four ponds; first being facultative and remaining three maturation. In 1986 rehabilitation work began due to poor performance of ponds wh±chresulted from poor maintenance. The rehabilitation work consisted of constructing a dumping station (three chanibers) to receive domestic wastewater from pit latrines and septic tanks carried by truck emptiers. Two anaerobic ponds were also added to treat domestic wastewater. These additional units started to operate in February 1990.

39 Physical bayout Vingunguti waste stabilization ponds consist of six ponds: two anaerobic ponds (A1 and A2) in parallel, one facultative pond (F) and three maturation ponds (M1, M2 and M3) connected in series (Figure 7). 0 2 ~8m A1, A2 F M1, ~ = anaerobic ponds facultative pond = maturation ponds. =!13 Figure 7. Layout plan of Vingunguti waste ponds (Howard Humphreys 1988). stabilization Combined treatment of domestic and industrial wastewater in ponds begins at first maturation pond. This pond receives wastewater from facultative and anaerobic ponds that receive industrial effluens and doxnestic sewage respectively. The firial effluent from ponds is discharged into Msimbazi River which fiows to Indian Ocean.

40 36 According to Howard Humphreys (1988), anaerobic ponds have been designed to treat domestic wastewater from Temeke area which serves about pit latrines and 600 septic tanks. However, physical observations showed that truck emptiers (Figure 8) collect wastewater (domestic) from or areas of Dar es Salaam city too. They also collect industrial wastewater from some nearby industries which have not been connected to any sewerage system. ~ Figure A truck emptier discharging wastewater into a chamber at Vingunguti waste stabilization ponds. Design criteria used This chapter gives a~ short description of formubas and design criteria used for Vingunguti waste stabilization ponds. The design parameters used are given in Table 10. Table 10. Design parameters used in design of Vingunguti waste stabibization ponds (Howard and Humphreys 1988). Parameter Unit Influent flow to ponds A1 and A2 Influent fbow to pond F Influent flow to ponds M1, M2 and M3 bad in ponds A1 and BOD5 reduction in ponds A A2 1 and A2 Temperature Effluent BOD5 Effluent FC 3/d m m3/d m3/d g/ha.d % OC mg/l no./100 ml Value < 5 < 437

41 37 For design of two anaerobic ponds, equation (11) was used: t= 5d D= 3m BOD reduction = 70 % Q = 120 m3/d for each pond. For design of facultative pond, equation (20) used: A = Q = = Le D T = = = was pond area required (m2) 1762 m3/d 400 mg/l 60 mg/l 1.3 m 20 C For design of maturation ponds, equation (22) was used to check bacteriological quality of pond contents: Ni Me kb t = = = 4 x 1O~FC counts/100 ml 5 X i0~fc 3.1 d~ 7 d/pond Using above design formulas and criteria, geometrical dimensions and hydraulic characteristics of ponds were determined (Table 11). Table 11. Pond Dimensions of Vingunguti waste stabilization ponds (Howard and Humphreys 1988). Retention time d Depth Vol unie m m3 1 A F M1 M M A 4.4 General observations Observation during study period showed that generally ponds were well taken care of by attendants. Grass was cut short regularly on embankments and paving slabs on banks of ponds were all in place (Figure 9). A few species of duck and or birds thrive in last two maturation ponds indicating that water in those pond units was cleaner than in preceding ponds.

42 38 Figure 9. A view showing facultative and maturation ponds. The paving slabs on embankments are well in place and grass has been cut short. However, folbowing negative aspects were noticed: Scum accumulated at corners of ponds especially anaerobic ponds which also possessed strong smells. Layers of thick mats were found in anaerobic ponds which, however, were removed after some days (Figure 10). Figure 10. A view of Vingunguti anaerobic ponds showing inlet pipe and scum accumulation.

43 39 The usual wastewater seen. blue/green cobour of facultative pond d:isappeared in some days and no algae was This may be brought about by toxicants from industries which were boaded in ponds periodically. However, normal condition of facultative pond water was restored after three to four days. Some of concrete channels making outlets of ponds have deteriorated thus water was leaking through embankmenlbs (Figure 11). Figure 11. One of cracked concrete channels at Vingunguti waste stabilization ponds causing wastewater to bypass installed Vnotch weir~. A considerably large portion of fence that marks boundary of pond site has been damaged and nearby residents were always trespassing through. People have built houses adjacent to pond This has made m victims of nuisance from and mosquito breeding (Figure 12). site. odour

44 40 S t t ~ Figure 12. A view showing inlet pipe into Vingunguti facultative pond conveying industrial wastewater. Neighbouring residentiab houses are adjacent to ponds. There were no fbow measurement facilities at inlets and outlets of ponds. For regular monitoring of ponds, f 10w measurement is essentiab. The final effluent from ponds was used for watering nearby gardens before rest was let to f 10w to Msimbazi River. 1f crops grown are consumed uncooked, a health hazard may occur. The raw industrial sewage was screened at inlet to facultative pond but re was no oil separation facility to remove grease and oil coming with industrial wastewater (Figure 13).

45 41 n,s.= ~ ~ ~. ~..r t.~....._~_. t r ~ t T 4 v. ~Çr ~ als. t Figure 13. Screening facility at inlet facultative pond at Vingunguti. to The inlet pi]pes into anaerobic and facultative ponds were above pond water level. This may be causing shortcircuiting.

46 42 5 SAMPLING, ANALYSIS AND DISCUSSION OF RESULTS 5.1 Sampling and analysis Sainples were collected during eight weeks (November 1991 January 1992) between 9.00 am and noon. Seven samples were collected twice per week. Samples were taken from inlets and outlets of each pond unit to enable evaluation of performance of each pond (Figure 14). k~_m~ _~~ lc._ _N_. x u n_ ~$x~~m Legend Al = AO 1 = FM 1 = M1M2 = M2M3 = 0 = = inlet for anaerobic ponds (domestic wastewater inlet) outlet for anaerobic ponds inlet for facultative pond (industrial wastewater inlet) outlet for facultative pond outlet for first maturation pond outlet for second maturation pond outlet for last maturation pond Figure 14. Sampling points at stabilization ponds. Vingunguti waste t

47 43 Composite sampling is recommended sanipling technique whereby samples are collected at regular intervals and n mixed in one large sample over a period of 24 hours. Throughout this study, however, grab sampbing has been used due to time limitation and inadequacy of sampling bottles and or necessary facilities. Pearson et al (1987) reported that for determination of ph and fecab coliforms, grab samples are required. Pearson et al (1987) also recommended two sampling periods for better evaluation of waste stabilization ponds; during hottest and coldest seasons of year. This was not possible since field study period was limited to six months. Sampling for this study was done during hottest period of year (November January). Therefore, performance of Vingunguti waste stabilization ponds can only be evaluated in this particular period and not in extreme climate periods. The parameters analysed in laboratory were biobogical oxygen demant (BOD5), total dissolved solids (TDS), fecal coliforms (FC), fecal streptococci (FS), ph, ammonia, nitrite, nitrate, copper and chromium. Samples were not collected from industries for laboratory analysis. This was due to big number of industries that were involved, Limitaion of time avaibabbe and inost important, difficulty in testing heavy metals in laboratory. Only a few sainples from Vingunguti waste stabilization ponds were tested for heavy metals during this study. Heavy metals and toxicants would have been parameters of f:lrst priority if wastewater samples from individual industries were tested. The analyses were carried out at water section laboratory of Faculty of Engineering at University of Dar es Salaam. The paraineters analysed were selected after considering importance in waste stabilization ponds, capacity of laboratory and time availabbe for study. All parameters were analyzed according to standard methods for examination of water and was tewater. Unfiltered samp:les were tested for BOD5. Analyzes were done under standard conditions: sample was stored for f ive days in dark at 20 C. In case analysis was not possible immediately after sampling, samples were stored for not more than 24 hours. Dissolved oxygen was measured, using dissolved oxygen meter, before and five days after storing sample in dark. All samples for bacteriological tests were collected in steribized sampling bottles and tested immediately on arrival at laboratory. The fecai coliform and fecal streptococci bacteria were measured using standard membrane filter procedure according to standard methods., nitrate were measured water test kit and TDS was measured by ph was determineci by Orion phmeter and tested using DR 200 Spectrophotometer. Ammonia, nitrite using Lovibond raw a HACH TDSmeter. heavy metals were The onsite tests

48 44 included determination of dissolved oxygen and temperature in ponds using temperature/dissolved oxygen meter type YS1 model 54A. 5.2 Results and discussion In this chapter, presentation and discussion is made on records obtained of truck emptiers visiting site daily and information collected from quesionnaires sent to various industries. The results of laboratory ana].yses and resubts of onsite analyses, including flow measurements, are also presented and discussed. Appendix 1 shows detailed resuits of laboratory analyses and Appendix 2 Tanzanian temporary standards for effluents Report on truck emptiers and guestionnaires Truck emptiers Table 12 shows t:rips made weekly by truck emptiers to Vingunguti waste stabilization ponds. Some difficulties were faced during interviews with truck operators: in some cases it was not possibie to obtain true information on which area of city or what industry wastewater has been collected from. Table 12. Week Truck emptiers discharging wastewater Vingungut.i waste stabilization ( ). Total no. of trips per week No. of trips residential areas No. of trips from industrial areas Name of industry KIUTA and into ponds Rajani KIUTA and Raj ani ALAF, KIUTA and Leyland Paints Average no. of trips per day = Maximum = ~ Rajani Chandaria Chandaria Minimum no. of trips per day Percentage of domestic wastewater brought by emptiers = %.

49 45 The industrial wastewater carried by truck emptiers is brought to ponds periodically, that is once after a couple of days. This implies that industries concerned drain ir wastewater into pits or underground tanks where It is stored for some days before it is taken to pond site. The average number of trips per day is 26. More than 90 % of wastewater brought to pond site in truck emptiers is domestic. According to interviewed truck operators, domestic wastewater brought to ponds was collected from different parts of Dar es Salaam city including areas beyond Temeke district. Howard Humphreys (1988) reported that anaerobic ponds at Vingunguti were designed to treat domestic wastewater from Temeke district alone. This practice, which was a result of cbosure of some or pond systems in city, may lead to suspect hydraulic overboading of ponds. puestionnaires According to questionnaires distributed to various industries (Appendix 3) along Pugu Road, information collected from operators of truck emptiers and discussion with authorities of Dar es Salaam Sewerage and Sanitation Department (DSSD), 20 industries are reported to discharge ir effluents into Vingunguti waste stabilizat:ion ponds (Table 13). However, figure may be slightly lower than actual because re are stil]. some unknown industries that use truck emptiers to deliver illegally ir wastewaters to Vingunguti pond site.

50 46 Table 13. Industrial wastewater sources and discharged into Vingunguti ponds. pollutants Industry Type of production/ activity Major pollutants Wastewater disposal TASIA production of vehicle springs oil, domestic wastewater sewer Tropical Foods fruit canning and high organic wastes, sewer bottling sugar and oil Steelwool production of steelwool domestic wastewater sewer Paper Products printing colour, suspended solids sewer Diamond Motors maintenance of vehicles grease, oil and domestic sewer and sales of spare parts sewage production of textile colour, suspended solids sewer colour, suspended solids sewer Pattex Knitwear material CALICO Textile Industry production of textile SADOLINS production of paints oils, colour sewer TAZARA workshop maintenance of automobiles oil, grease and domestic wastewater sewer TANITA cashewnut processing oil, suspended solids sewer YUASA battery manufacturing batteries acids, lead, zinc sewer ALAF manufacturing corrugated iron sheets, asbestos sheets and galvanized pipes toxic metals, heavy truck material metals Galaxy Paints production of paints oils, colour sewer Leyland Paints production of paints alkalis, colour, oil truck Rajani Oil production of cooking oi 1 oils truck KIUTA paper binding/printing colour, suspended solids truck Incar (T) maintenance of vehicles and sales of spare parts grease, oil truck Chandaria manufacturing plastic botties and toilet paper suspended solids, domestic waste truck Tanzania Autoparts pickling of steel sheets truck and sales acids, oil, domestic wastewater National Distilleries laboratory works acids, suspended solids truck

51 47 There are two categories of effiuents into Vingunguti ponds: industries through 1 those disposing wastewater directly to Vingunguti ponds 2 those draining wastewater into pits located within industrial premises. The wastewater is n collected by truck emptiers from pits and transported to Vingunguti ponds. The effluents from industries have into three groups: a discharging been sewer system categorized 1 Effluents consisting of biodegradabie organic material. Effluents from food processing industries and industries producing seed er vegetable oils fall under this category. These industries inciude Tropical Foods, TANITA and Rajani 0±1. Or industries like Steel Wool ( r) Limited and Chandaria do not use water in ir processes. The wastewater generated by such industries is almost domestic, coming from canteens and toilets. This type of wastewater can easily be treated in waste stabilization ponds. 2 Effluents containing grease and oil. Industries dealing with maintenance of automobiles such as TAZARA workshop, Incar (T) Limited, Diamond Motors and TASIA produce this type of effiuents. Grease and oil af fect performance of ponds, especially facultative and maturation ponds. 3 Toxic effiuents containing substances (lead, zinc, copper, etc), acids and producing this type of effluents industries such as CALICO Textile Knitwear; like heavy metals dyes. Industries include textiie Mili and Pattex pr:lnting industries like Paper Products and KIUTA; paints industries such as SADOLINS, Galaxy Paints and Leyland Paints; metal industries like Alaf and Tanzania Autoparts; and industries dealing with chemicals such as YUASA Battery and National Distilleries. Toxic substances inhibit biobogical growth in ponds and hence ir presence is a problem that cannot be overcome in operation of pond systems Biochemical oxygen demand Biochemical oxygen demand (BOD5) measures total amount of oxygen required to sustain biological activity in a pond. The BOD5 reduction is generally factor used for designing anaerobic and facultative ponds. The values of BOD5 at Vingunguti waste stabilization ponds during November 1991 January 1992 are given In Table 14 and Appendix 4.

52 48 Table 14. BOD5 values at Vingunguti waste stabilization ponds (November 1991 January 1992). Sample point BOD5 mean mg/l min mg/l max mg/l Al A FM M1M2 M2M According to Arthur (1983), raw domestic wastewater in African countries usualby contains 350 mg BOD5/l. This figure is different. from mean value of 186 mg BOD5/l for raw wastewater samples collected from truck emptiers believed to carry more than 90 % domestic wastewater. Mogensen and Lunddal (1991), however, obtained a mean value of 109 mg BOD5/b for raw wastewater treated in Lugalo waste stabilization ponds. This value is even bower especially when it is considered that Lugalo ponds are receiving onby domestic wastewater. Data from various waste stabilization ponds in Dar es Salaam show values of BOD5 of raw domestic wastewaters ranging Suki et al (1988) have reported average value of 137 mg/l and maximum value of 188 mg/l for BOD5 of raw domestic wastewater from residential areas in Kuala Lumpur, Malaysia. The BOD5 effluent value of 107 mg/l was higher than that recommended by Tanzania Temporary Standards (TTS) for effluents that are directly discharged into receiving water bodies (30 mg/l). There are different opinions en subject of algae and ir effect en BOD values. Varma et al (1963) cited by Mogensen and Lunddal (1991) noted that when algae die, being organic material, begin to decay and hence inc:rease BOD of sampie. The high concentration of aigae observed in maturation ponds might have similarly af fected effluent BOD5 resuits obtained. From Table 15, BOD5 removal percentages in ponds A, F, M2 and M3 were 7 %, 39 %, 20 %, 2 % and 13 % respectively. Total BOD5 removal was 48 %. Anaerobic ponds are not expected to have BOD5 removal efficiency below 60 % for design temperatures >20 C (Mara and Monte 1990). According to Howard Humphreys (1988), Vingunguti anaerobic ponds were designed for BOD5 removal of 70 %. The strong smell coming out from anaerobic ponds may also lead to suspect that ponds are not performing well. Objectionabie smeil is normally caused by overloading of ponds and hence reducing retention time or by presence of toxic substances in influent (WHO 1987). The retention time can as well be reduced when re is excessive accumulation of sludge causing reduction of pond volume. The peer performance of M1,

53 49 anaerobic ponds may also be due to shortcircuiting since inlet pipes to ponds were well above surf ace water levels of ponds. The raw wastewater may not be passing through all expected purification processes in ponds. Table 15. Efficiency of each pond unit and total effic:lency of Vingunguti waste stabilization ponds in removal of various parameters during November 1991 January Parameter Unit BOD5 NH3N FC FS TDS NO3N NO2N Cu Cr % % % % % % % % % Note: A F Ml M2 M3 Total Mean concentrations were used in calculating thé percentage removals. All values that deviated abnormally from or values were omitted (marked in brackets in Appendix 1). The influent concentrations entering pond M1 were calculated as sum of flowweighted average concentrations coming from anaerobic and facultative ponds through points AO and FM1 respectively. Mest of samples taken directly from truck emptiers contained some pesticides. Residents were said to be putting pesticides (such as DDT) in ir pit latrines or septic tanks to eradicate streng odour of sewage in ir premises and also to inhibit mosquito breeding. Pesticides are highly toxic already in very small concentrations. Values for removal of BOD5 for typical domestic sewage in facultative ponds is % (Arceivala 1989). The efficiency of facultative pond at Vingunguti in removal of BOD5 was 39 %. This bow removal may be attributed to fact that facultative pond was receiving wastewater directly from industries. The presence of toxic substances accompanying industrial wastewater causes dieof f of microorganisms hence reducing BOD removal efficiency of facultative pond. Maturation ponds are mainly designed for reducing pathogenic organisms, refore ir peer performance in removal of BOD5 can be accepted.

54 Fecal coliforms and fecal streptococci Fecal coliform (FC) and fecal streptococci (FS) tests are both applied to indi.cate fecal contamination of water and wastewater (Feachem et al 1983). In this study, tests were done to indicatte pathogenic bacteria removal in pond system. Table 16 shows calculated mean values of FC and FS counts which are also presented graphically in Figure 15. Mean, minimum and maximum values of FC and F5 counts at. Vingunguti waste stabilization ponds during November 1991 January Table 16. FC (counts/100 ml x i0~) Sample point FS (counts/100 ml x 10~) mean min max mean min max Al AO FM1 M1M M2M FC and ES 2000 (counts/100 ml x 1000),~ 1500 t, / t. t t t t. t. t. t t t 500 t F8 FC 0 Al AD 1 FM1 M1M2 M2M3 0 Sampling points Figure 15. Mean values of FC and FS counts at Vingunguti waste stabilization ponds during November 1991 January 1992.

55 51 The identical pattern of FC and FS reduction rate shown in Figure 15 by two different curves indicates that results can be relied en. Mara (1977) cited by Mogensen and Lunddal (1991) suggested that for purpose of designing stabilization ponds, a value of 1 x 108 counts/100 ml FC be used for raw domestic sewage. A value of 0.4 x 108 FC counts/100 ml was used for design of Vingunguti ponds. Both se values are above value of x 108 counts/100 ml observed en raw domestic wastewater discharged into Vingunguti ponds. The limit recommended by TTS for effluents from ponds (5 x 10~counts/i00 ml FC) has been surpassed. The final effluent contains 11.5 x i0~counts/100 ml FC. No mention has been made of effluent standards for FS. From table 15, percentage removal of FC for ponds A, F, M1, M2, and M~) were calculated as 4 %, 93 %, 62 %, 57 % and 77 % respectively. The ability of anaerobic ponds to remove FC is usually insignificant. Very high removal of FC and FS found in facultative pond which have also been indicated by sharp decline of two curves in Figure 15, may not be due to normal operation of pond itself. It may be attributed to presence of toxic substances from industries which kill mest microorganisms bacteria. :Ln pond including of pathogenic Fecal coliform reduction in each maturation pond (ranging %) averaged less than 90 % oretical reduction calculated by Marais (1974). The bower rates of dieof f of pathogens in individual maturation ponds at Vingunguti may be due to high concentration of BOD5 in ponds. Gameson and Saxon (1967) cited by Moeller and Calkins (1980) have reported that algae, as suspended solids, hinder penetration of solar radiation, thus reduce efficiency of ponds in destroying fecal coliforms. They noted that a filtered sample exposed to sunlight resulted in coliform destruction up to seven times that of unfiltered sample. The individual performance of maturation Vingunguti with fecal coliform reduction of 57 however, similar to that of West ponds at 77 % was, Hickman Creek wastewater lagoons in Kentucky, USA which showed mean reduction of fecal coliform ranging % (Moeller and Calkins 1980J~. During examining bacteriological quality of West Hickman Creek wastewater lagoons in Kentucky, USA., Moeller and Calkins (1980) noted that coliform densities in final three maturation ponds exhibited a distinct parallelism throughout sample period. That is an increase in coliform density from one sample date to next in first pond was usually accompanied by a rise in second and third ponds. Similarly, a decrease in coliform concentration in first pond was usually indicative of a decrease in final ponds. A similar

56 52 trend was observed en facultative pond (F) and two maturation ponds (M1 and M2) at Vingunguti (Figure 16). The concentrations of fecal coliforms in effluents from last maturation pond M3 were toe small to be plotted en graph. 120 FC (counts/100 ml x 1000) GO 40 M2M3 20 M1M2 FM Sampling days Figure 16. Fecal pond c:oliform densities in (F) during November and maturation ponds facultative (M1 and M2) January Total dissolved solids Table 17 shows TDS values measured at Vingunguti waste stabilization ponds during study. The graphical presentation of values is given in Appendix 4. Table 17. Mean, minimum and maximum values of Vingungut:i ponds during November Sample points TDS mean mg/l min mg/l max mg/l FM1 M1M2 M2M Al AO 1 TDS at January

57 53 The effluent standard for TDS is mg/l. The measured effluent TDS value of 400 mg/l indicates that performance of Vingunguti ponds has met effluent requirements recommended by TTS. Table 15 shows that anaerobic ponds have removed TDS contents by 47 %. According to this study, anaerobic ponds were only pond units where TDS were removed significantly. This may be due to sedimentation process that takes place in anaerobic ponds. In facultative and last maturation ponds, TDS contents have shown te increase slightly (1 7 % increase). This might be a result of suspended algae that grow in facultative and maturation ponds. The shallow depth of maturation ponds may also cause detection of high TDS values due to easy mixing of settled particles by wind action Animonia, iiitrate and nitrite Anunonia (NH3~jfl.. The amnionia concentrations are given in Table 18 and Appendix 4. The effluent requirement for ammonia reconunended by TTS is 10 mg/l N. The Vingunguti pond system has shown to meet this requirement as effluent ammonia content was 7.0 mg/l N. Table 18. Mean, minimum and maximum concentrations of aiumonia at Vingunguti. waste stabilization ponds during November 1991 January Sample point NH3N mean Al AO 1 FM1 M1M2 M2M3 0 mg/l min mg/l max mg/l The quality of effluents from Vingunguti ponds with respect to nitrate and nitrite concentrations was relatively better than of many operating ponds. Batchebor et al (1991) reported typical effluent concentrations of nitrate and nil:rite from waste stabilization ponds as 15.7 mg NO3N/l and 0.3 mg NO2N/l respectively. The effluent concentrations of nitrate and nitrite from Vingunguti waste stabilization ponds were 7.3 mg N03N/l and 0.4 mg N02N/l respectively. This may be due to bow influent concentrations of nitrogen compounds experienced by ponds.

58 54 Table 15 shows that percentage removal of ammonia in ponds A, F, M1, M2 and M3 were 3 %, 4 7 %, 11 % and 3 % respectively. The total reduction of ammenia through Vingunguti pond system was 19 %. This total removal efficiency is lower than anticipated. Removal efficiencies of anunonia in waste stabilizatien ponds have been reported up to 99 % during sunimer with a minimum value of 90 % during winter in CaLifornia (USEPA 1983). %, The removal of ammonia in ponds is carried out through nitrification precesses. These precesses, like all or biological precesses, are sensitive to presence of toxic compounds including some heavy metals found in industrial wastewaters. The ammonia removal efficiency of Vingunguti ponds may have been af fected by presence of chromium in wastewater. Beg et al (1980) found out that under shock bad condition, chromium has a significant degree of Inhibition to nitrification process (even higher than arsenic er fluoride), thus af fecting removal efficiency of ammonia in a biological treatment plant. However, effect of same toxicant over a long period of time may not be same as under shock bad conditions Heavy metals The heavy metals tested were nickel, lead, cadmium, copper and chromium. Tests for cadmium, nickel and lead were stopped after performing for two days and find no traces of metals. Copper and chromium were tested for nine days during study. The reliability of resuits of heavy metal tests (Appendix 1) is, refore, bow. Heavy metals like nickel, lead and cadmium are usually produced by such industries like metal industry and battery industry. Their concentrations at Vingunguti waste stabilization ponds may have been toe low to be detected by ava:llable equipments Dissolved oxygen, temperature and ph Due to lack of proper equipment for measuring dissolved oxygen (DO) levels and water temperatures (T) abong pond depth, as recornniended by Pearsen et al (1987), se parameters were measured en upper water levels only. The measurements were, however, taken after sampling period was over as dissolved oxygen meter for field measurements was not available at beginning. The results (Table 19), refore, cannot be directly correlated with laboratory analyzes results obtained earlier.

59 55 Table 19. Date Disse:Lved oxygen (DO) and temperature (T) measurements at Vingunguti waste stabilization pends ( ). Dissolved oxygen and temperature A0 1 FM1 M1M2 M2M3 DO mg/l T C DO mg/l T C DO mg/l T C DO ing/1 T C DO mg/l T C Average The raw industzial wastewater that enters into facultative pond had bowest average DO content (4.6 mg/b). The most interesting observation was that facultative pond effluents, however, possessed highest average DO content in pond system (12.0 mg/l). This may be mainly due to algal photosyntic processes taking place in facultative pond which caused DO content of industrial wastewater to raise tremendously. Effluents from first maturation pond had lower average DO content (7.6 ing!].) than that of effluents from facultative pond (12.0 mg/l). This was because, in addition to facultative pond effluents, first maturation pond receives also anaerobic pond effluents which had bower average DO content (5.6 mg/l). With exception of values at outlet of facultative pond, remaining values of DO content generally indicate anticipated trend of increasing DO content as purificatien process proceeds. The higher values of DO dewnstream are due to oxygen added through algal photosyntic activity. This is also signified by increase in ph dcwnstream (Oswald 1991). It was not possible to measure DO content of final effluents from pond system for whole week. Due to some rains that were falling during this period, re was a mixture of pond water and stream water at outlet of last maturation pond and readings obtained were not bogical. The average pond water temperature (at surface) was 21.9 C. The raw industrial wastewater showed to have slightly higher average temperature (22.3 C).

60 56 ph measurement was done in laboratory. Average ph values at Vingunguti waste stabilization ponds ranged (Appendices 1 and 4), higher values being at downstream of pond system. Zimba (1986) has reported ph values ranging between 6 9 for selected pond systems in Zambia, effluent ph values being similarly higher than influent values. The higher average value of ph recorded at Vingunguti ponds (8.3) was bebow required for eptimum destruction of pathogens. Oswald (1991) reported that a ph of 9.2 for 24 hours will provide a 100 % kil]. of E. Coli and presumably most pathogenic bacteria Flow measurement Measurement of fbow were done using of steel (Figure 17). Figure Vnotch weirs made A 90 Vnotch weir installed waste stabilization pends. at Vingunguti Calibratiori of weirs was done at site: a bucket of was filbed with pond effluent at downstream side of each weir. The time to fili bucket at every weir was recorded five times. Correspending water head measurements (h) at Vnotches were also recorded. Actual discharges 1:hrough weirs were calculated from volume of bucket and time durations recorded. 4

61 57 Theoretical discharges were determined from water head measurements (h) using formula (Lindford 1981): Q 8 = (2.g)~tan (v/2)~h5/2 (25) 15 where Q h g v = = = oretical (m3/s) (m) water depth discharge over Vnotch gravitational acceleration (9.81 m/s2) Vnotch angle (90 ). The coefficient of discharge (Cd) was determined as: actual discharge Cd oreticati. discharge The resulting average coefficient of discharge for all weirs was 0.5. Discharges through Vnotches were, refore, calculated from observed water heads (h) using equation (25) muitiplied by this factor (0.5). The weirs were installed at points A0, FM 1, M12, M2M3 and 0. Influent flow into anaerobic ponds was estimated from average number of truck emptiers that reported at pond site daily. The capacity of one truck emptier was Industrial wastewater inflow into facultative pond was estimated using a currentmeter for one day. Leakage around edges of Vnotches was well prevented using streng cement mortar but it was not possible to seal cracks in some channel walls which let wastewater bypass Vnotches especially at point M1M2. Water head readings at Vnotch weirs were taken between 9.00 am and 4.30 pm, three times daily (Table 20).

62 58 Table 20. Discharge measurements stabilization ponds (10. Date Average Minimum Maximum Time at Vingunguti ). waste Discharge AO 1/s FM1 1/s M1M2 1/s M2M3 1/s 9.30 ani pm pm am 1.40 pm 3.30 pm am am 2.30 pm am pm 3.44 pm am 2.10 pm 4.20 pm It was not possible to take readings at outlet of last maturation pond (point 0). The weir installed at this point was damaged by a collapsing wall of outlet channel. As wall was leaning against weir, weir got deformed and it was unsafe to werk near place. Table 20 shows that inlet flow was always greater than eutlet fbew for each pond unit. This loss was due to leakage through cracks en channel walls, seepage through bottoni of ponds and evaporation. The percentage difference between inflow and outfiow for ponds A, M1 and M2 were 13 %, 24 % and 12 % respectively. A relatively larger fraction of effluent from pond M1 (24 %) was not passing through installed Vnotch weir. This was due to large cracks found at outlet channel of this pond causing pond effluent to bypass weir. The average loss of wastewater in each pond due to evaporation and seepage can be estimated frem anaerobic ponds and second maturation pond te be 12.5 %. t It is most likely that evaporation and seepage have taken a significant volume of pond waters causing infbow be greater than outflow. This is because study to period

63 59 coincided with hottest and dryest season of year (November January) and also because pond bottom was unlined. Table 21 shows montly temperature and rainfall recorded at University of Dar es Salaam meteorobogical station during sampling period. Table 21. Month.Ly temperature and rainf all during NovemJber 1991, December 1991 and January 1992 (University of Dar es Salaani meteorological station 1992). Month Air temperature Average rainf all max C min C mean C mm November 1991 December January The measured fbows (Table 20) were smaller than design flows. This may be because design flows were projected 20 years ahead (from 1988). Therefore ponds are new working under capacity (hydraulically) Applicability of design equations Anaerobic pond design eguatipns The actual surface boading into Vingunguti anaerobic ponds based en actual values of influent BOD5 and average infbow rate, was 850 kg/ha~d. Anaerobic ponds are required to have surface loadings more than kg/had. This shows that previded surface area of ponds was slightly (about 1.2 times) larger than required. However, surface boading is not recommended for use in sizing anaerobic ponds (Gboyna 1971 cited by WHO 1987). The volumetric loading into Vingunguti anaerobic ponds calculated with equation (10) based on actual 3 d.values The of influent BOD5 and infiow rates was 28 g/m design voluinetr:lc boading for temperatures >20 C is 300 g/m3.d (Mara and Monte 1990). This indicates that volume of anaerobic pends is about 10 times greater than required using volumetric boading rate design method. The Vingunguti anaerobic ponds were designed with retention time ined (equation 11). The design flow was 240 in3/d and retention time was selected as 5 days resulting in a total volume of 1200 m3. With actual average flow of 182 m3/d, corresponding retention time during study was 6.6 days indicating that ponds were operating fairly bebow ir capacity. However,

64 60 according to Mara (1976 cited by WHO 1987), BOD5 reduction should have been >70 % for retention times >5 days. The BOD5 reduction at Vingunguti anaerobic ponds was only 7 %. Facultative ~end design eguations Applying Marais and Shaw first order reaction equation (18) with actual values of influent and effluent BOD5 and retention time, 1. The resulting rate constant value breakdown of kt calculated with (kt) was d equation (19) and taking average temperature as 21.9 C was 0.33 d~. The lower kt value reflecs lower rate of removal of organic material in facultative pond. The bacterial dieoff constant (k~,j.. Table 22 gives actual values of kb calculated from kinetic equation (22) based on actual retention times of pond units and actual average influent and effluent fecal celiform counts at Vingunguti ponds. Table 22. Actual values of kb at Vingunguti waste ). stabilization ponds ( Pond unit Retention kb time d d~ A F M 1 M2 M3 The kb values for three maturation ponds were not exactly equal, but were closer to be constant than se for facultative and anaerobic ponds. The rate of fecal coliform dieof f in maturation ponds, refore, closely obeyed kinetic ory. The highest rate of fecal coliferm die off in facultative pond has been reflected by highest value of kb in pond system. In normal checking of pathogenic bacteria removal in waste stabilization ponds using eguation (23), kb is taken as constant for all types of ponds (anaerobic, facultative and maturation). This may not be correct as demonstrated by variation of kb values en Tabbe 22. The reduction mechanisms in three types of ponds are different. Applying equation (24) and taking pond water temperature as 21.9 C, value of kb is 2.96 d ~. This value is far different from values calculated in Table 22.

65 61 6 CONCLUSIONS AND RECOMMENDATIONS 6.1 Conciusions The quality of effluents from Vingunguti waste stabilization ponds do not comply with requirements of Tanzania temporary standards. This is concluded from higher concentrations (than standards) of most important parameters BOD5 and FC observed in final effluents from ponds. Effluent BOD5 and FC were 107 mg/l and counts/100 ml respectively whereas standard requires 30 mg/1 BOD5 and FC counts/100 ml. The concentrat:lons of NH3N, N03N, NO2N and TDS (7.1 mg/l, 7.3 mg/l, 0.4 mg/1 and 300 mg/1 respectively) have met effluent standard requirements, but this may be mainly because concentrations of parameters in raw wastewater received by ponds were already low. With exception of pathogenic bacteria removal, efficiency of Vinguriguti waste stabilization pond system was poor. Overall efficiencies in removal of BOD5, TDS and nitrogen compounds ranged %. FC and FS removal was above 98 %. overall treatment The individual performance of anaerobic ponds was worst The with a BOD5 removal efficiency of 7 % only. anticipated BOD5 removal efficiency of an anaerobic pond is above 60 %. Ammonia was increasing by 3 % in pond and nitrate and nitrite were removed by only 7 % and 17 % respectively. The anaerobic ponds have only been slightly effective in TDS removal (44 %) which, however, may be attributed to sedimentation process in pond and not biobegical activities of microorganisms. The cause of total failure of anaerobic ponds at Vingunguti was not investigated in this study. It may be due to sludge accumulation, shortcircuiting, presence of pesticides from pit latrines and septic tanks er toxicants from industries that discharge wastewater illegally using truck emptiers. The performance of facultative pond was better than anaerobic pends especially considering that facultative pond was treating purely industrial effluents. BOD5 was removed by 39 % and FC and FS by 93 % and 85 % respect~lvely. The high dieof f rate of pathogenic bacteria in facultative pond is likely to be boosted by toxicants from industrial wastewaters. The industrial toxicants may, in contrast, be adversely affecting reineval of BOD5 and nitrogen compounds. The three maturation ponds showed almost equal individual performances in pathogenic bacteria removal with last pond (M3) being slightly best. Their removal efficiencies ranging % are common in mest well operatirig maturation ponds.

66 62 Investigations en effluents from individual industries could not be covered in this study. The few laboratory tests for copper and chromium done en samples collected from facultative pond inlet at Vingunguti showed that se metals were present. Cepper and chromium may be produced by metal processing er battery manufacturing industries. More heavy metals and er toxic substances from textile, printing, paints and chemical industries abong Pugu road are likely to be present in Vingunguti ponds. In this study, it has also been observed that BOD5 of raw domestic wastewaters from pit latrines, septic tanks and even conventional sewerage systems in Dar es Salaam may be on range mg/1. The value of 350 mg/l BOD5 for raw demestic wastewater recemmended by many authors for design of waste stabilization ponds in tropical areas may be teo high for Dar es Salaam region. Hewever, for designing pends to treat combined wastewater, this value (350 mg/l) may be toe low, since effluents of some irtdustries contain high BOD5. The DO contents and ph values at Vingunguti waste stabilization ponds were rising downstream indicating that ponds were operating normally. The average ph values in maturation ponds (ranging ), which were bebow 9.0, preveci that optimum pathogenic bacteria was not achieved. 6.2 destruction of Recoinmendations Based en findings of study en Vingunguti waste stabibizatien ponds following is recommended: 1) Thoreugh investi.gatien en complete failure of Vingunguti anaerobic ponds, in particular, sheuld be carried out. Investigation en poor performance of Vingunguti pond system overall is also important. This should begin by focusing on quabity and quarltity of wastewater discharged by each concerned indust:ry. 2) A possibility Vingunguti to rearrange wastewater flow at wast:e fellow nermal order should be studied. That is, all wastewater (domestic and industrial) should enter stabilizatien ponds to raw pond system through anaerobic ponds. From anaerobic ponds, wastewater should flow into facultative pond and finally into maturation pends. Anaerobic pends are important in pretreating various types of industrial wastewaters. 3) The concerned industries should be encouraged to pretreat ir wastewaters te minimize effects of compounds irlhibitory to microbielogical activities in ponds. 4) The crown levels of raw wastewater inlet pipes entering anaerobic and facultative ponds at Vingunguti are required te be at a suf ficient depth

67 63 below pond water levels. This will enable easy mixing of raw wastewater with pond contents and hence avoid shortcircuiting. 5) Simple and eifficient means of remeving algae from final pond effluents is required to avoid secondary pollution to Msimbazi river. 6) Maintenance and repair of pond embankments and channel walls should be done whenever required to prevent furr damage. 7) Flow, ph Vingunguti analysis and temperature measurements at ponds should be recerded daily. Regular of important parameters, with emphasis en those found :Ln industrial wastewaters, should be done for better monitoring of ponds performance. This will help to make appropriate modifications to optimize performance of pond system. 8) Almost all existing formulas for design of waste stabilization ponds are principally based on removal of BOD and FC which are cemmon pollutants found in domestic wastewaters. This is because, originally, waste stabilization ponds were meant for domestic wastewater treatment. More studies should, refore, be done en effects of varieus parameters found in different industrial wastewaters en eperation of waste stabilizatien pends. This will facilitate establishment of more proper methods and formulas for designing waste stabilization pends receiving combined industrial and municipal was tewaters.

68 64 7 REFERENCES G.P., Mills, S.W., Osebe, S.A., Thitai, W.N., Pearson, H.W., Mara, D.D. and Muiruri, P Combined treatment of domestic and industrial wastewater in waste stabilization pond systems in Kenya. Water Science and Alabaster, Technebogy. Vol. 24, no. 1, p AlSalem, S.S. and Lumbers, J.P An initial evaluation of Alsumra waste stabilization ponds (Jordan). Water Science and Technelogy. Vol. 19, no. 12, p Arceivala, S.J Wastewater treatment for pollution control. McGrawHil]. Publishing Company Ltd. p Arellano, F Pellution problems and control measures for metal plating, alcohol, industrial chemicals paint manufacturing national industries. Proceedings of training course on industrial pollution for small and medium scale industries, 1987, Tagaytay, Phi].ippines. p and control November 2227, Arthur, J.P Notes en design and eperation of stabilization ponds in warm climates of developing countries. World Bank Technical Paper no. 7. The World waste Bank, Washington DC, USA. p Banerji, S.K. and Ruess, B Evabuation of waste stabilization pond performance in Missouri and Kansas, USA. Water p Science and Technobogy. Vol. 19, no. 12, Batchelor, A., Bocarre, R. and Pylous, P.J Lowcost and lowenergy wastewater treatment systems: A South African perspective. Water Vol. 24, no. 5, p Science and Technobogy. Beg, S.A., Siddiqi, R.H. and Ilias, S Inhibition of nitrification by arsenic, chromium and flouride. Journal Water Pollution Control Federation. Vol. 54, no. 5, p Bramer, H.C Water pollution control in industry. Industrial wastewater management metal handbook. McGrawHill Boek Company, New York. p. (91)(955). Diaz, A Pollution problems and control measures for food industry. Proceedings of natienal training course medium en industrial pollution control scale industries, Philippines. p November for small 2227, and Tagaytay, Egbuniwe, N Performance of a waste stabilization pond treatment plant en a University campus. African Journal of Science and Technology. Vol. 1, no. 1, p Feachem, R.G., Bradley, D.J., Garelick, H. and Mara, and Sanitation and disease: health aspects wastewater of management. World Bank Studies Supply and Sanitation. John Wiley & Sons. 501 p. D.D. excreta in Water

69 65 Gathuo, B Industrial wastewater discharges with special reference to lear industry in Kenya. M.Sc. Thesis. Tampere University of Technology, Finland. p Germirli, F., Tünay, 0. and Orhon, D An everview of textile industry in Turkey pollution profiles and treatability characteristics. Water Science and Technobogy. Vol. 22, no. 9, p Gilde, handbo p. (5 L.C. and Aly, O.M Water pellution control in ood industry. Industrial wastewater management k. McGrawHill Boek Company, New York. )(551). Grau, Water P Textile industry wastewater treatment. cience and Technology. Vol. 24, no. 1, p Greenb rg, A.E., Trussell, R.R., Clesceri, L.S. and Franse M.A Standard methods for examination of water and wastewater. 16. edition. American Public Health Asseciation (APHA), Washington, USA. p , Henry, J.G. and Gehr, R Odor control: an operator s guide. Journal Water Pollution Control Federation. Vol. 52, no. 10. p Henze, M Industrial wastewater treatment in deveboping countries. The Danish Açademy of Technical Sciences, Lyngby,, Denmark. p Holding, J Effluent treatment: options. World Water. Vol. 13, no.6, p Horan, N.J Biological wastewater treatment systems. Theory and operation. John Wiley and Sons, Chichester, England. p Howard Humphreys (Tanzania) Ltd Dar es Salaam sewerage and sanitation study preliminary engineering design and feasibility study. Final report. 508 p. Karpe, H.J. and Baumann, W Wastéwater treatment and excreta disposa]. in developing ceuntries. Report en a research project by Institute of Environniental Protection (INFU), University of Dortmund, Federal Republic of Germany. 121 p. Linford, A Flow measurement & meters. 5. edition. Lenghurst, S. and Turner, E Combined treatment of industrial no. 2, p. effluents. Industry and Environment, Vol. 10, Lumbers, J. and Andoh, B Waste stabilization pond design: Some myths behind science. Waterlines. Vol. 3, no. 4, p

70 66 Mara, D.D. and Monte, M.H.F The design and operation of waste stabilization ponds in tourist areas of Mediterranean Europe. Water Science and Technology. Vol. 22, no. 3/4, p Mara, D. and Pearson, H horrors. p Designing Marais, G.V.R Fecal bacterial stabilization ponds. Journal of engineering Division, no. 2, p against pond kinetics in Environmental Mashauri, D.A. Mkuula, S.S., Mpendazoe, F.M. and Gumbo, F Pregranune en Iurification of industrial wastewater. Country paper: Un:Lted Republic of Tanzania. In: UNIDO regional meeting on management of industrial wastewater, December 1014, 1990, Paris, France. p Mayo, A BacI:erial dieoff in waste stabilization ponds receiving domestic wastewater in Dar es Salaam, Tanzania. M.Sc. Thesis. Tampere University of Technelogy, Finland. 60 p. Mayo, A.W. and Gondwe, E.S Quality changes in ponds with different pond depth and hydraulic detention times. Water Quality Bulletin. Vol. 14, no. 3, p Moeller, J.R. and Calkins, J Bactericidal agents in wastewater lagoons and lageon design. Journal Water Pollutien Control Federation. Vol. 52, no. 10, p Mogensen, U. and Lunddal, M Evaluation waste stabilization pends, Dar es Salaam, of Lugale Tanzania. Diploma Project. Engineering Academy of Denmark. 91 p. Munene, R.F.K Performance of selected waste stabilization ponds in Kenya. M.Sc. Thesis. Tampere University of Technobogy, Finland. 111 p. Nevaes, R.F.V Microbiology of anaerobic digestion. Water Science and Technology. Vel. 18, no. 12, p Oswald, W.J Introduction to advanced integrated wastewater ponding systems. Water Science and Technology. Vol. 24, no. 5, p. 17. Parsons, W.A Water pollution control in chemical industry Industrial wastewater management handbook. McGrawHill Boek Company, New York. p. (51)(71). Pearson, H.W., Mara, D.D. and Bartone, G.R Guidelines for minimum evaluation of performance of full scale waste stabilization pond systems. Water Research, vel. 21, no. 9, p Pujol, R. quantitative and Lienard, A. characterization of Qualitative wastewater communities. Water Science and Technology. Vol. 3/4, p for 22, and small no.

71 67 Rantala, P Problems with textile wastewater discharge. Seminar en wastewater treatment in urban areas, September 79, V:Lsby, Sweden. p. 17. Suki, A., Jenny, H. and Rashid, H Efficiency of oxidation ponds~. The proceedings of l4th WEDC (Water Engineering and Development Centre) conference on water and urban services in Asia and Pacific, April 1115, 1988, Kuala Lumpur, Malaysia. p University of Dar es Sabaam meteorological station. Records en daily meteorobogical measurements Upstone, M.P Water pollution control and trade effluent policies in urban areas. In: 4th African Water Technobogy Conference, February, 2022, 1990, Nairobi, Kenya. p USEPA (United States Environmental Protection Agency) Design manual municipal wastewater stabilization ponds, Cincinnati, USA. 327 p. Vigneswaran, S., Balasuriya, B.L.N. and Viraraghavan, T Anaerobic wastewater treatment attached growth and sludge blanket process. Environmental Sanitation Reviews, no. 19/20. Envirenmental Sanitation Information Centre, Bangkok, Thailand. p. 15. Wang, B Ec:ological waste treatment and utilization systems en lowcost, energy saving/generating and reseurce recoverable technology for water pollution control in China. Water Science and Technelogy. Vol. 24, no. 5, p WHO (World Health Organization) Wastewater stabilization ponds. Principals of planning and practice. WHO EMRO Technical publicatien no. 10. WHO, Regional 0ffice For The Eastern Mediterranean, Alexandria, Egypt. 138 p. Yayehyirad, G Combined treatment of demestic and industrial wastewaters. M.Sc. Thesis. Tampere University of Technology, Finland. p Zimba, R Performance evaluation of selected stabilization pends in Zambia. MSc sis. University of Technebogy, Finland. 113 p. waste Tampere

72 68 Appendix 1 (1/5) Biochemical oxygen stabilization ponds Date (BOD5) ( at Vingunguti waste ). Sampling points Al Average *) demand (100) (80) (70) Values A (230)*)(140) (10) 140 (150) FM1 M1M2 M2M (60) (20) (160) (190) (20) (180) (40) in brackets omitted when calculating 0 average values. Total disselved solids (TDS) stabibization ponds ( Date at Vingunguti waste ). Sampling points Al AO 1 FM1 M1M2 M2M (1020)*) 230 (1200) (1210) (1200) (700) Average *) 642 Values in brackets emitted when values calculating average 1

73 69 Appendix 1 (2/5) (FC) counts Fecal coliform stabilization ponds (11. Date at Vingunguti waste ). Fecal coliform (counts/100 ml) at point Al AO 1 FM1 M1M2 M2M Average Fecal streptococci (FS) at Vingunguti waste ponds ( ). 23 stabilization 3 ml) at Date Fecal Streptecocci Al Average AO (counts/100 x i0 FM M1M2 M2M

74 70 Appendix 1 (3/5) Ammonia (NH3N) concentration at Vingunguti stabilization ponds ( ). waste Date Ammonia concentration at point Average *) Al AO 1 Fl41 M1M2 M2M3 0 mg/1 N mg/1 N mg/1 N mg/1 N mg/1 N mg/1 N mg/1 N LO (20.0)*) (20.0) (20.0) (25.0) Values in brackets omitted when values. Nitrite (N02N) concentration Stabilization ponds ( calculating at Vingunguti ). 7.1 average Waste Nitrite concentration at point Date AO mg/1 N Al mg/1 N 1 mg/1 N FM1 ing!]. N M1M2 mg/1 N M2M3 mg/]. N Average *) Values values in brackets emitted when calculating 0 mg/1 N (3.28)*) (1.13) average

75 71 Appendix 1 (4/5) Nitrate (N03N) cencentration at Vingunguti stabilization ponds ( ). Date Nitrate concentration at point Al A0 1 FM1 M1M2 mg/1 N mg/]. N mg/1 N mg/1 N mg/1 N Average *) (20.0) (20.0) M2M3 Ing!]. N Values in brackets omitted when values. 5.4 (6.8) calculating of Date Concentratien of Copper at point Average (4.00) (Cu) AO mg/l (23.00)*) (6.00) at Vingunguti ). 1 mg/l 0 mg/l Values in brackets omitted when values ponds Al mg/l copper stabilization ( ing!]. N (11.3)*) Concentration *) waste calculating average waste average

76 72 Appendix 1 (5/5) Concentration of chremium (Cr) stabilizationponds ( Date at Vingunguti Concentration of chromium at peint Al mg/l AO mg/l 1 mg/1 0 mg/l Average ph was te ). values at Vingunguti ). ( Date ph values at points waste s tab iiizat i on ponds Al A0 1 Fl41 M1M2 M2M Average

77 73 Appendix 2 Tanzania temporary standards for effluents meant for direct discharge into receiving waters (Tanzania Bureau of Standards 1988 cited by Howard Humphreys 1988). Substance Unit Maximum permissible value BOD5 mg/]. 30 TDS mg/] FC no./100 ml 5000 NH3N N03N NO2N DO mg/]. mg/]. mg/]. mg/] ph Pb Zn Cd mg/l mg/l mg/]. Cr mg/ Cu Ni mg/]. mg/i

78 74 Appendix 3 An example of a questionnaire sent to industries contributing wastewater to Vingunguti waste stabilizatien ponds. SURVEY OF INDUSTRIAI.I EFFLLJENTS OUESTIONNAIRE Name of coinpany: Tropical Foods Limited Address or location:: Plot no. 12, Vingunguti, Pugu Road Nuniber of shifts per day: 1 Work force per shift: 65 Canteen facilities: Yes Water sources: National Urban Water Authority Duration of shift: 8 h Average water consull]ption: 20 m3/d Peak rate of consumption: 1/s Goods ma.nufactured 0E processed: Canned and bottled food products Processes employed in manufacture: Raw material (fruits) sorting washing sorting juice extraction blending/mixing filling processing (applying temperature pressure) > > > > > and > Volume of process water discharged to waste: l/d Peak rate of wastewater discharge: 1/s Future development plans including introduction processes: Extensions Present treatment facilities: of new Nil Present method of disposal of liquid waste: Sewerage system that stabilization ponds goes to Vingunguti General observations: Nil Name and position ole persen interviewed: Mr Robert Mkangila Date: / Factory Engineer waste

79 75 Appendix 4 (1/3) BODS (my/1) 150:. BOD5 100 at Vingunguti waste AD Al 1 FM1 M1M2 M2M3 0 Sampling point stabilization pends FM1 M2M3 during TD5 (mg/1) Al A(J 1 M1M2 0 Sampling point TDS at Vingunquti waste stabilization ponds during

80 76 Appendix 4 (2/3) Rmmonia (mg/1 N) : H H ~ H H: 1 Al AD t t t t 1 FM1 M1M2 M2M3 0 Sampling point Concentratien of ammenia at Vingunguti waste stabilization ponds ( ). 100Nitrate conc~ntration (mg l N) AD Al 1 FM1 M1M2 M2M3 0 Sampling points Concentration of nitrate at Vingunguti waste stabilization ponds ( ).

81 77 Appendix 4 (3/3) Nitrite concentratioh (mg/1 N) 0.50 AD Al 1 FM1 M1N12 M2M3 0 Sampling points Concentration of nitrite at Vingunguti waste stabibization ponds ( ).