INDUSTRIAL POLLUTION CONTROL GUIDELINES. No. 2 Concentrated Latex Industry CENTRAL ENVIRONMENTAL AUTHORITY

Transcription

1 GOVERNMENT OF THE DEMOCRATIC SOCIALIST REPUBLIC OF SRI LANKA INDUSTRIAL POLLUTION CONTROL GUIDELINES No. 2 Concentrated Latex Industry ISBN CENTRAL Environmental Authority PARISARA MAW AT HA Maligawatta NEW TOWN Colombo to SKI 1ANKA. Telephone NO: /6, 4374H7/8/9 FAX Mo: CENTRAL ENVIRONMENTAL AUTHORITY Ministry of Environment and Parliamentary Affairs PFILNTEDBY UNITED MERCHANT S LTD COLOMBO-IS

2 INDUSTRIAL POLLUTION CONTROL GUIDELINES., /9c \ - / V No 2 - Concentrated Latex Industry CEA Library Prepared by the Central Environmental Authority With Technical Assistance from The Government of the Netherlands 1992/93

3 First edition 1992 Published by the Central Environmental Authority Parisara Mawatha Maligawatta New Town Colombo 10 SRI LANKA Telephone No:449455/6, /8/9, /4/5/6 Fax No: This document may be reproduced in full or in part with due acknowledgement to the Central Environmental Authority ISBN Front Cover Design & concept by W A D D Wijesooriya Artwork by Somasiri Herath 024/waddw/guida2

4 PREFACE The Government of Sri Lanka is promoting rapid industrialization in order to create better employment opportunities for the growing work force of the country, and to increase the income level of the people. At the same time the Government is conscious of the fact that some of the existing industries significantly contribute to the deterioration of the quality of the environment in the country, especially in the urbanised and industrialized areas. Ill-planned industrialization will no doubt accelerate the process of environmental degradation. The Government has, therefore, introduced environmental legislation to enhance environmental protection and pollution control. The Central Environmental Authority (CEA) is the lead agency in the implementation and enforcement of the environmental legislation. It has initiated various programmes for the protection of the environment, with special attention on industrial pollution control. The CEA has requested technical and financial assistance from the Government of The Netherlands for a number of projects in this field. As a result technical assistance for a programme which consist of the following projects was provided by the Government of The Netherlands:? 1. Development of environmental quality standards on the basis of designated uses. 2. Development and updating of emission/discharge standards and pollution control guidelines for selected priority industries 3. Feasibility studies on pollution control for priority industries or industrial sectors 4. Study tour to The Netherlands for Sri Lankan officers involved in compliance procedures in the Environmental Protection Licensing Scheme (enforcement) Under project No 2 above, industrial pollution control guidelines, were prepared for the following eight(8) industrial sectors, considered as major polluters in Sri Lanka:- 1. Natural Rubber Industry 2. Concentrated Latex Industry 3. Desiccated Coconut Industry 4. Leather Industry 5. Dairy Industry 6. Textile Processing Industry 7. Pesticide Formulating Industry 8. Metal Finishing Industry

5 The main objective of the preparation of these guidelines was to assist the Central Environmental Authority in industrial pollution control with special reference to the introduction of the Environmental Protection Licensing Scheme. In the preparation of these guidelines attention was focused on the generation of liquid, gaseous and solid wastes and their impacts on the environment. In the process aspects of industrial counselling, including in-plant measures to prevent and reduce waste generation and measures to improve occupational safety and health were also considered. Alternative methods were discussed for end-of-pipe treatment of liquid. gaseous and solid wastes. Existing wastewater discharge quality standards were considered and intermediate standards ( with respect to the phased installation of treatment systems) were proposed in these guidelines. The guidelines were mainly prepared on the basis of data available on industrial pollution and its abatement in sri Lanka, from studies and reviews carried out in the past and from missions to Sri Lanka specifically carried out for preparation of these guidelines. The project was directed by Mr K G D Bandaratilake. Director of the Environmental Protection Division of the CEA, and coordinated by Mr W A D D Wijesooriya, Senior Environmental Scientist of the CEA. The CEA project team consisted of Mr C K Amaratunga and Mr S Seneviratne, Environmental Officers. Technical assistance was given by a team of BKH Consulting Engineers, Comprises Dr I van der Putte (team leader), Mr J G Bruins and Mr H J F Creemers. This document contains pollution control guidelines for Concentrated Industry. Latex G K Amaratunga Chairman Central Environmental Authority

6 Contents Page 1. INTRODUCTION 1 2. PRODUCTION OF CONCENTRATED LATEX Production data Production process 2 3. WASTE PRODUCTION AND ENVIRONMENTAL IMPACTS Wastewater production Solid wastes and air pollution Environmental impacts 5 4. INDUSTRIAL COUNSELLING Introduction In-plant pollution control Improvement of occupational safety and health 7 5. POLLUTION ABATEMENT METHODS Introduction Separate wastewater treatment Combined wastewater treatment Ammonia stripping and anaerobic treatment DISCHARGE AND EMISSION STANDARDS REFERENCES 18 Annex I An existing concentrated latex industry wastewater treatment system

7 INTRODUCTION The production of concentrated latex in Sri Lanka is increasing rapidly due to the increased worldwide demand for goods manufactured from this substance. Concentrated latex is used for the manufacture of the so-called dipped products which are produced by dipping the mould of a specific product into the centrifuged latex. Examples of dipped products are household and surgical gloves, balloons and condoms. Concentrated latex is also used for manufacture of hose and rubber thread. The production of dipped products in Sri Lanka is growing. Most of these products are exported. Concentrated latex production generates wastewater with high concentrations of organics and ammonia. Most factories discharge their wastewater to nearby streams which are often used for various domestic purposes and irrigation. Discharge of wastewater from concentrated latex manufacture may cause serious water pollution and result in contamination of existing surface water resources. The discharge of untreated centrifuged latex factory wastewater into streams of paddy fields may also result in the emission of obnoxious odours caused by the putrefaction of organic compounds and emission of ammonia. The Government of Sri Lanka has introduced quality standards for discharge of wastewater from concentrated latex manufacture into inland surface waters (see Chapter 6). The limit values for the concentrations of specific pollutants, according to these standards, can only be fulfilled by treatment of the wastewater. This document provides guidelines for industrial pollution control, including industrial counselling and treatment of wastewater from concentrated latex manufacture. The section on wastewater treatment is based on the most generally applied methods for treatment of concentrated latex wastewater.

8 2. PRODUCTION OF CONCENTRATED LATEX 2.1 Production data The manufacture of concentrated latex is a rapidly growing industrial sector; the production of other types of rubber is decreasing. Around 110,000 tons of natural rubber are produced annually from tapped field latex. 6% of this field latex is centrifuged into concentrated latex, which is mainly used for the local manufacture of so-called dipped products (household gloves, thread, condoms, surgical gloves). Approximately 20% of the concentrated latex is exported (1990 data). Presently 9 latex centrifuging plants are in operation, of which 2 are state-owned and 7 are private. Their joint annual production of concentrated latex amounts to 6,700 tons (1990 data). In the near future 2 or 3 new factories will be constructed. A target capacity of 20,000 metric tons per annum is aimed for the concentrated latex sector as a whole, representing nearly 20% of the total rubber production. 2.2 Production process Concentrated latex is manufactured by centrifugation of field latex. Field latex has an average dry rubber content (DRC) of 30%. After tapping the latex from the rubber trees the latex is conveyed into drums or bowsers and chemicals are added for preservation and prevention of premature coagulation. These chemicals are Ammonia, Zinc-Oxide and Tetra-Methyl-Thiuram-Disulphide (TMTD). The latex is subsequently transported to the concentrated latex factories. After arrival at the factory the latex is centrifuged, producing cream latex (rubber content 60-70%) and skim latex (rubber content 5-10%). The cream latex is used directly for manufacture of dipped products, sold to other factories or exported. The skim latex is collected in coagulation tanks where concentrated sulphuric acid is added. Skim rubber coagulates, while the remaining liquid, the skim serum, is discharged. The skim rubber is milled in roller mills into sheet. For milling some water is used which is discharged. Skim rubber is a low grade crepe rubber. The plant equipment, drums and bowsers are washed with water containing formalin. The washing water is also discharged. The diagram of the process for concentrated latex production is shown in Figure

9 Field latex collection. Preserving (NH 3, ZnO, chemicals TMTD) Storage Centrifuges washing water discharge Concentrated latex Skim latex skim serum Sulphuric acid Coagulation discharge Milling milling water discharge Skim rubber Figure 2.1 Concentrated latex production process

10 WASTE PRODUCTION AND ENVIRONMENTAL IMPACTS Wastewater production Concentrated latex production generates three different wastewater flows: wastewater from skim latex coagulation (skim serum); wastewater from washing buildings equipment, bowsers and drums; wastewater from milling the coagulum into skim rubber sheets. The major characteristics of the three types of wastewater have been given in Table 3.1. Table 3.1 Characteristics of wastewaters from concentrated latex manufacture (ref.2) Wastewater type Characteristics Volume (m 3 /t DRC) Skim serum High BOD and COD concentration 1.8 Low ph High ammonia and sulphate concentration Rubber particles Whitish colour Washing water Low concentration of pollutants Milling water (organics, rubber particles, 1.2 ammonia, preservatives) Combined plant wastewater 3.0 The wastewaters are usually combined into one flow and subsequently discharged. Data on the average composition of the combined wastewater are given in Table 3.2. Data on waste loads, expressed in kg waste per tonne Dry Rubber Content of the latex processed, are also given in Table 3.2. Solid wastes and air pollution Production of concentrated latex does not directly generate any solid wastes nor does it cause air pollution.

11 Table 3.2 Concentrated latex production Average composition of combined wastewaters and waste loads (ref.1) Parameter Concentration Waste load (kg/t DRC) COD N-total P-total Total solids Suspended solids ph 25, ,000 1, mg/l mg/l mg/l mg/l mg/l ' Environmental impacts Adverse effects of concentrated latex production on the quality of the environment are mainly caused by discharge of untreated wastewater into streams or paddy fields. The adverse effects consist of water pollution, making the water unsuitable for the purposes it is used for and damage to soils and crops. Wastewater discharge and malfunctioning wastewater treatment or disposal facilities may also cause emission of obnoxious odours, due to putrefaction of organic compounds and emission of ammonia (NHJ. 5

12 4. INDUSTRIAL COUNSELLING 4.1 Introduction The industrial counselling procedures are directed towards the introduction of environmentally sound technology ("clean technology"). Clean technologies contribute to more efficient production methods by saving energy and raw materials and reducing emissions to air, water and soil. They include good housekeeping measures, modification of production processes and raw materials use, as well as recycling of waste and process waters. Industrial counselling aims at environmentally sustainable industrial development by promoting a combination of in-plant pollution control and end-of-pipe treatment in order to protect the environment and to optimize the conservation of energy and raw materials. Additional advantages of the application of cleaner production processes are the reduction of safety hazards and the improvement of occupational health. Therefore, initial investments aimed at pollution control become more cost effective. In this chapter in-plant pollution control measures and methods to improve occupational safety and health are proposed. 4.2 In-plant pollution control Major pollutants from concentrated latex production process are organics and ammonia. There is, however, no possibility to reduce the organic waste load from the production process since the quantity of organics in the wastewater is directly related to the quantity of latex processed. Instead of using ammonia, alternative methods for preservation of the latex could be used (formalin instead of ammonia, and latex cooling). The technical and economic feasibility of alternative latex preservation methods should be studied. Preservation with formalin allows the use of weaker acids such as formic acid for the coagulation of the rubber in skim latex, instead of sulphuric acid. The waste load of the wastewater would be reduced by the use of formalin for preservation and formic acid for coagulation, because of the lower concentration of nitrogen and sulphate. The treatability of the wastewater would also improve. The addition of the correct quantity of the coagulant (sulphuric acid) is important because insufficient acid will result in incomplete coagulation and therefore waste of uncoagulated rubber while in the case of coagulant is overdosed, the excess acid persists in the effluent. Separation of wastewater flows, and re-use of washing and milling waters after treatment, could be carried out, especially in the larger factories. The technical and economic feasibility of separate treatment and re-use should also be studied.

13 4.3 Improvement of occupational safety and health Good housekeeping is imperative for the safety of the workers and for efficient production. The factory floors should be constructed in such a way that rapid removal of spills, wash water etc. is ensured. Furthermore cautious handling of corrosive chemicals such as ammonia and sulphuric acid is required. Physical contact of the workers with these chemicals should be avoided, if necessary by using protective clothes (boots, aprons, gloves, etc.). 7

14 5. POLLUTION ABATEMENT METHODS 5.1 Introduction Since the production of concentrated latex does neither directly generate any solid wastes nor causes air pollution, no methods for solid waste disposal and air pollution control are described in these guidelines. A number of wastewater treatment alternatives for the concentrated latex industry are described below. The wastewaters from concentrated latex production are generally combined into one flow and subsequently directly discharged or treated in a wastewater treatment plant in the factory premises. However, separation of the wastewaters into two flows could have advantages for treatment plant efficiency. Separation would result in a diluted flow (milling and washing waters) which requires little treatment and a concentrated flow (skim serum), requiring extensive treatment. The most commonly applied treatment methods for concentrated latex wastewater are biological methods, such as pond systems and low load activated sludge systems, and physical/chemical methods such as ammonia stripping. Anaerobic treatment might also be an effective method, but has not yet been applied at full scale. 5.2 Separate wastewater treatment The wastewaters from washing and milling are disposed of separately from the skim serum. a) Disposal ol washing and milling waters Washing and milling waters are relatively little polluted. No data on the composition is available, however. In many cases it may be possible to discharge this wastewater directly into streams or paddy fields if sufficient dilution or area is available. If no direct discharge is allowed due to adverse effects on the environment, the wastewater could be treated in a facultative pond. in a facultative pond the organic matter is biodegraded aerobically in the upper layers. Oxygen for aerobic biodegradation is mainly supplied by algae. Anaerobic biodegradation takes place at the bottom of the pond where suspended solids settle into a sludge. The organic surface loading rate and the pond depth are the most important design parameters for facultative ponds. The organic surface loading rate, under Sri Lanka conditions, should not exceed 440 kg BOD/ha/d and the pond depth should be not more than 1.2 m. b) Treatment of skim serum Skim serum has high concentrations of organics, ammonia and sulphate. The most applied method for treatment of skim serum is the low-load activated sludge system. The skim serum is pretreated in a rubber trap to remove rubber particles. 8

15 The low load activated sludge system consists of an aeration tank, in which the wastewater is mixed with floes of aerobic micro-organisms (activated sludge). The mixture of activated sludge and wastewater is aerated vigorously. Organic substances in the wastewater are absorbed by the active microorganisms, which biodegrade the organic matter, utilizing the breakdown products for growth and formation of new cells. As a result the sludge quantity in the aeration tank is increased. Micro-organisms die off in the aeration tank, the dead cells being oxidised (mineralization) into simpler components. Suspended solids in the wastewater are also absorbed by the activated sludge floes. The mixture is led from the aeration tank into a sedimentation tank where the floes settle into a sludge. Part of this sludge is returned to the aeration tank in order to maintain a constant concentration of activated sludge. Usually a concentration of dry solids of 4 kg/m 3 is maintained in the aeration tank. The surplus sludge has to be removed This is often treated in a sludge drying bed, which decreases its volume. Controlled disposal of wet sludge on coconut or rubber plantations is also possible. Design parameters of the low load activated sludge system are given in Table 5.1. Table 5.1 Design parameters of the low load activated sludge system Aeration tank Organic sludge loading rate 0.4 kg COD/kg sludge dry solids per day or 0.15 kg BOD/kg sludge dry solids per day Sludge dry solids 4 kg/m 3 concentration in aeration tank Oxygen requirement: - BOD degradation 0.5 kg 0 2 /kg BOD removed COD degradation 0.25 kg 0 2 /kg COD removed - Endogenous respiration 0.15 kg 0 2 /kg sludge dry solids in aeration tank - Nitrogen oxidation 4.57 kg 0 2 /kg N Aerator performance Depth 1.3 kg 0 2 /kw.h m Sludge production (dry solids) 0.5 kg/kg COD removed minus 0.04 kg/kg sludge Sedimentation tank in aeration tank per day - Hydraulic surface loading rate 0.5 m 3 /m 2.h - Retention time 2 h Sludge drying beds - Drying time 20 d - Sludge depth 0.2 m 9

16 A design example of a low load activated sludge wastewater treatment plant is described in Section 5.3. The schematical lay-out of the separate wastewater treatment system is shown in Figure Combined wastewater treatment The oxidation ditch system is the most applied low load activated sludge system for treatment of the combined wastewater. An oxidation ditch is an oval shaped aeration circuit in which the mixture of wastewater and activated sludge circulates. Circulation and aeration of the mixture is provided by brush aerators. The design of an oxidation ditch system for treatment of the combined wastewaters from a concentrated latex factory is described below. Example of design of an oxidation ditch wastewater treatment plant Design criteria Latex processing in factory = 10 t rubber/d Wastewater generation Total skim serum milling/washing 18 m 3 /d 12 m 3 /d 30 m 3 /d Wastewater composition BOD 9,500 mg/l. COD 25,000 mg/l Nitrogen 900 mg/l. ph 4.5 Dimensions 1. Rubber trap/neutralization/ equalization tank. volume 18 m 3 2. Oxidation ditch. organic waste load 750 kg COD/d. aeration tank volume 475 m 3. sludge quantity (solids) 1,900 kg. depth 1.5 m. COD removal (98%) 735 kg/d. sludge growth (solids) 290 kg/d. oxygen requirement 650 kg 0 2 /d. aeration capacity 25 kw.h 10

17 washing 1 =- direct discharge (alt. 1) factory facultative pond discharge (alt. 2) skim latex coagulation skim serum equalization neutralization rubber trap oxidation ditch sludge holding tank excess sludge sedimentation Wet disposal to plantations (Alt. 2) Sludge drying beds (Alt. 1) discharge Figure 5.1 Schematical lay-out of a separate wastewater treatment system 0044:04

18 3. Sedimentation tank. surface area 2.5 m 2. length/width 1.6 m. depth 1.8 m. volume 2.6 m 3. effluent COD 500 mg/l. sludge recirculation to aeration tank. excess sludge to sludge holding tank 4. Sludge holding tank. volume 50 m 3. supernatans to aeration tank. sludge to drying beds. sludge quantity to drying beds (5% solids) 6 m 3 /d 5. Sludge drying beds. area 120 m 2 The dried sludge can be disposed of in rubber or coconut lands. It is also possible to dump the wet sludge directly from the sludge holding tank onto rubber or coconut lands. The schematic lay-out of this wastewater treatment system is shown in Figure 5.2. An existing wastewater treatment plant of the oxidation ditch system has been described in Annex I. 5.4 Ammonia stripping and anaerobic treatment a) Ammonia stripping An alternative pretreatment system consists of ammonia removal from the skim latex by ammonia stripping. An ammonia stripper consists of a packed column, through which the wastewater flows downwards. Air flows upwards through the column. Ammonia is removed from the wastewater by intense contact between the water droplets and air. Ammonia removal efficiency is improved by a high ph and a high temperature. Some parameters for the design of an ammonia stripping installation are given in Table 5.2. Table 5.2 Ammonia stripping installation. Design parameters. Optimum ph Hydraulic loading rate m 3 /m 3.h Air flow rate m 3 air per I water Column packing height 6-8 m Air pressure drop in packing mm water/m height 12

19 skim coagulation milling/washing water skim serum equalization neutralization rubber trap oxidation ditch sludge holding tank sludge sedimentation tank wet in disposal drying beds discharge plantations (Alt. 1) (Alt. 2) Figure 5.2 Schematjcai lay-out of a combined wastewater treatment plant

20 The ammonia at the top outlet of the stripper can be emitted directly into the air, or discharged through an acid solution producing an ammonium salt. The liquid effluent at the bottom of the stripper can be treated further in combination with the milling and washing wastewater in an oxidation ditch. The stripper effluent in combination with the milling and washing wastewaters could also be treated in an anaerobic reactor. Anaerobic treatment, however, can only be applied if an organic acid instead of H 2 S0 4 is used for coagulation of the stripper effluent, since a high sulphur concentration is toxic for the anaerobic treatment process. b) Anaerobic treatment After removal of the remaining rubber from the effluent of the ammonia stripper by coagulation with an organic acid, it can be combined with the other wastewaters and treated in an anaerobic reactor, of the Upflow Anaerobic Sludge Blanket type (UASB). In the UASB reactor the wastewater flows upwards through a blanket of anaerobic bacteria, which biodegrade part of the organic material into gases such as methane (CH 4 ), carbon dioxide (C0 2 ), ammonia (NHJ and hydrogen sulphide (H 2 S). The gases are collected in the upper section of the tank by a gas collector. The optimum temperature for the anaerobic process is 35 C. The major advantage of this system is that no energy input is needed, at least under tropical conditions where no heating is required. Other advantages are that the anaerobic system requires little space and that production of excess sludge is minimal because of the slow growth of anaerobic bacteria. Maximum removal efficiency of organic matter by the anaerobic system is, however, only about 90% which is generally not sufficient to meet the required discharge standards. For this reason anaerobic treatment is often considered only as a first stage or pretreatment system. An activated sludge system or rotating biological contactors can be used for further treatment. At present anaerobic treatment of rubber factory wastewater is still in an experimental stage. The most important parameters for design of an UASB reactor are given in Table 5.3. Table 5.3 UASB reactor. Design parameters ph (optimum) Temperature (optimum) 35 C (mesophilic digestion) Retention time > 8 h Organics to nutrients ratio COD : N : P = 850 : 5 : 1 Organic loading rate < 15 kg COD/m 3 /d

21 An example design of a wastewater treatment plant, consisting of ammonia stripping and anaerobic treatment, is described hereafter. Example design of a wastewater treatment plant, consisting of ammonia stripping and anaerobic treatment Design criteria Latex processing in factory = 10 t rubber/d Wastewater generation:. skim serum 18 m 3 /d. milling/washing J2 m 3 /d 30 m 3 /d Dimensions Ammonia stripper (treatment of skim serum). operational period 8 h/d. height (packing material) 6 m. wastewater flow 2.2 m 3 /h. airflow 6,000 Nm 3 /m 3. column area 0.6 m 2. N removal efficiency 80 %. effluent discharge to rubber coagulation tank water 2. Equalization/neutralization tank and rubber trap Composition of combined wastewater flow \ flow 30 m 3 /d. COD 25,000 mg/l. N 180 mg/l. tank volume 18 m 3 UASB reactor volume 50 m 3 COD removal 90 % effluent COD 2,500 mg/l biogas production 340 Nm 3 /d The effluent from the UASB reactor still has a high COD. Anaerobic treatment should therefore be considered as a pretreatment method. In order to fulfil the effluent standards the wastewater should be further treated by an aerobic treatment method, e.g. low load activated sludge treatment. A lay-out of this wastewater treatment system is shown in Figure

22 skim latex ammonia stripper coagulation skim serum acid milling washing equalization neutralization rubber trap UASB reactor biogas discharge or further aerobic treatment Figure 5.3 Schematical lay-out of a wastewater treatment plant consisting of ammonia stripping and anaerobic treatment 16

23 DISCHARGE AND EMISSION STANDARDS Since the concentrated latex industry causes no atmospheric pollution specific emission standards are not relevant for this type of industry. The Government of Sri Lanka has developed standards for the discharge of wastewater from concentrated latex production into inland waters. These standards are given in Table 6.1. Table 6.1 Sri Lanka standards for the discharge of wastewater from concentrated latex production into inland waters Parameter maximum allowable concentration or range ph suspended solids 100 mg/l total solids 1,500 mg/l BOD 60 mg/l COD 400 mg/l N-total (as N) 300 mg/l N-ammonia (as N) 300 mg/l sulphide 2 mg/l These standards can only be fulfilled by extensive biological treatment, e.g. in an oxidation ditch treatment plant. An alternative for oxidation ditch treatment is a system consisting of ammonia stripping, organic acid coagulation and anaerobic treatment. This system results in an effluent with a low N-concentration but with a too high COD-concentration. Further aerobic treatment would be required to achieve the maximum allowable CODconcentration according to the standards. Anaerobic treatment of concentrated latex factory wastewater is still not used at full scale. If anaerobic treatment experiments are successful, this method might be selected in the future as a pretreatment method, because of the relatively low operational cost of this system. In that case intermediate standards should be introduced, which have to be complied with in the first stage of a staged wastewater treatment implementation programme. The tolerance limit value for the COD-concentration of such intermediate standards should be about 2,500 mg/l. 17

24 REFERENCES 1. Wastewater Treatment for the Rubber Plantation Industry of Sri Lanka BKH Consulting Engineers Government of the Netherlands/Sri Lanka State Plantations Corporation, Evaluation of a Concentrated Latex Industry Wastewater Treatment Plant BKH Consulting Engineers, 1986

25 ANNEX I - Description of an existing wastewater treatment plant at a concentrated latex factory One concentrated latex factory in Sri Lanka is presently operating a wastewater treatment plant. The plant consists of a rubber trap, an oxidation ditch and a sedimentation tank. The skim serum, the milling water and the washing water are combined into one flow before treatment. Influent characteristics are: - flow - 8.2m 3 /d - COD - 20,000-30,000 mg/l - ph After passing through the rubber trap the wastewater is led into the oxidation ditch. The oxidation ditch has a volume of 135 m 3 and a depth of 1.2 m. Oxygen is supplied by 2 locally manufactured brush aerators (2x15 HP). The treated effluent has a COD-concentration generally below 400 mg/l. No sludge is recirculated from the sedimentation tank to the oxidation ditch. The sludge from the sedimentation tank is disposed of in coconut lands. The treated effluent is discharged into nearby paddy fields. 19