FEASIBILITY OF USING TERTIARY TREATED EFFLUENTS IN IRRIGATION SYSTEMS

Transcription

1 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt 1429 FEASIBILITY OF USING TERTIARY TREATED EFFLUENTS IN IRRIGATION SYSTEMS F. M. Malallah* and A. A. M. Daifullah Water Pollution Monitoring Department, Environment Public Authority, Kuwait * Corresponding Author: f_malallah@hotmail.com ABSTRACT A careful analysis of the source water is prudent as a preliminary step to designing an irrigation system. Therefore, the ability to understand a water quality analysis is important to the irrigation system manager. Currently, a huge amount of municipal wastewater in Kuwait receives conventional treatment up to tertiary levels. A significant portion ( 67%) of generated effluent is, however, discharged and wasted into the Gulf. Tertiary treatment is a safe-guard against the chronic effects of prolonged reuse of effluents in irrigation. In this concern, the data of water quality of effluents in two sewage treatment plants in Kuwait State namely, Al-Regga and Al- Jahra are evaluated during the periods ( ) taking into account seasonal variations. It was clear that, the content of chloride, Boron and salinity are responsible for restricted irrigation use of these effluents. Severe toxicity is expected in some plants due to irrigation using water of Al-Regga sewage treatment plant due to nitrates and ammonium nitrogen levels exceed 30 ppm. According to Sodium Adsorption Ratio (SAR) values and to avoid the harmful effects of sodium, care with irrigation methods are required. Keywords: wastewater, reuse, tertiary treatment plants, restricted irrigation. INTRODUCTION Given the limited available water-resources and increasing demand, municipal wastewater can have a special role in maintaining and augmenting the water resources of Kuwait especially since wastewater effluent is estimated to be 70-80% of the freshwater consumption per capita ( Al-Awadi et al. [1]). Wastewater produced in Kuwait varies with season and the amount is expected to increase as more residential areas are connected to the sewage collection system (Al-Awadi & Rashid, [2]). Therefore, reclaimed water can be considered as a primary option for developing new water resources through water reuse in irrigation and landscaping. Presently, three sewage treatment plants at Sulaibiya (350,000 m 3 /d), Regga (102,000 m 3 /d) and Jahra (54,000 m 3 /d), are used to treat municipal wastewater (Gulf Consult [3], MPW [4]).The collected wastewater recieves primary, secondary and tertiary treatment in all treatment plants. The newly built Sulaibiya plant provides advanced treatment of

2 1430 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt ultrafiltration and reverse osmosis to refine tertiary effluent of conventional systems. In primary level treatment, physical separation processes such as screening, sedimentation and grit removal are used to remove large objects and settable solids. In secondary treatment, biological treatment processes are utilized in which microorganisms convert non-settable and dissolved organic pollutants to settable solids. Sedimentation typically follows allowing these settable solids to settle out. In the tertiary treatment, the secondary effluent is usually disinfected using chlorine and filtered to eliminate residual suspended solids. Therefore, the potential of reusing conventionally treated wastewater effluent can be increased by reducing or eliminating hazardous substances, if exist. If someone will use the water to irrigate field crops or garden purposes, a basic knowledge of water quality is very useful for irrigation system management and is an important consideration in the design and operation of the system. Levels and specific makeup of dissolved substances in irrigation water affect crop productivity and soil structure. They also determine if water is suitable for irrigation. This paper considers several areas of concern including specific items that make up water. The purpose of this work is to get better insight on quality of effluents resultant from sewage treatment plants in State of Kuwait namely, Al-Regga and Al-Jahra and the feasibility of using that water for irrigation system management. EXPERIMENTS Water Samples Four samples per month were taken near the center and below the water surface from each sewage treatment plant. These samples were analyzed at various times throughout the irrigation season. Glass or plastic containers are used for sample collection. The containers were thoroughly cleaned and rinsed before use to avoid contamination of the water sample. Sample bottles were filled completely to the top (with all air removed), carefully labeled, and tightly sealed. Samples were sent immediately to a water testing laboratory. To get better insight on the water quality, the following tests were done in the laboratory: 1. Physical and Chemical Properties: Quantities that do not identify particular chemical species but are used as indicators of how water quality may affect water uses. These are hydrogen ion (measured ph), specific conductance (conductivity), alkalinity, hardness and total dissolved solids (TDS). 2. Major Chemical Constituents: Those most often present in natural waters in concentrations greater than 1.0 mg/l. these are the cations calcium, magnesium, potassium, and sodium, and the anions bicarbonate/carbonate, chloride, fluoride, nitrate, and sulfate. Several additional chemical parameters are sometimes included

3 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt 1431 with the major constituents because of their importance in determining water quality. These are boron, iron, manganese, nitrogen in forms other than nitrate (such as ammonia, nitrite), phosphate, and hydrogen sulfide. 3. Minor Chemical Constituents: Those most often present in natural waters in concentrations less than 1.0 mg/l. These include the so-called trace elements: cadmium, lead, chromium, cupper, zinc, nickel, vanadium and mercury. All parameters of water samples were determined according to the standard methods (APHA, [5]). The heavy metals in water were determined after digestion using atomic absorption (model: AA 680 Shmidzu). RESULTS AND DISCUSSION Sample effluent quality of the Jahra and Reqqa plants during the period ( ) appears in Table 1. Generally, the concentrations of all parameters in the effluents of both treatment plants under investigations were within the allowable limits according to appendix No.15 (Kuwait EPA, [6]). This proves that the efficiency of both plants were in good working conditions. 1. Physical and Chemical Properties These are hydrogen ion (measured ph), specific conductance (conductivity), alkalinity, hardness and total dissolved solids (TDS). ph The term ph is used to indicate the alkalinity or acidity of a substance. The ph of water affects many chemical and biological processes in water. The largest variety of aquatic animals prefer a range of When the ph is outside this range, diversity within the water body may decrease due to physiological stresses and reduced reproduction. Low ph can also allow toxic elements and compounds to become more mobile and available for uptake by aquatic plants and animals. As shown in Table 1, All ph values were around 7.0, i.e, within the KEPA levels ( ). However, it was clear that the effluents at Al-Jahra compared with that of Al-Regga are characterized by higher alkalinity, hardness, TDS, EC during the period. The TDS was greater than 1000 mg/l in Al-Jahra treatment plant in two years 2002 and Thus, the content of chloride ions was important to be evaluated. As shown in Table 1, the chloride content is always higher in Jahra plant and it appears that the concentration of chloride in Al-Regga plant is under control except in Electrical Conductivity Electrical conductivity (EC) is a measure of the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions or sodium, magnesium, calcium, iron, and aluminum cations. Organic compounds like oil, phenol, alcohol, and sugar do not conduct electrical current very well and therefore

4 1432 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt have a low conductivity when in water. Conductivity is also affected by temperature: the warmer the water, the higher the conductivity. Conductivity is also reported in units 1,000 times smaller: micromhos per centimeter (µmhos/cm) or microsiemens per centimeter (µs/cm). The conversion from electrical conductance to total dissolved solids (TDS) depends on the particular salts present in the solution. The conversion factor of 640 x EC (in mhos/cm) is applicable for converting EC values to TDS for Kuwait irrigation waters. Alkalinity Alkalinity is a measure of the capacity of water to neutralize acids. At the ph of most irrigation water, alkalinity is primarily a measure of bicarbonate in the water. As shown in Table 1, All ph values were around 7.0, i.e, more than 90% is the bicarbonate alkalinity (Eugene, [ 7]). Hardness Hardness in water is caused primarily by calcium and magnesium, although iron and manganese also contribute to the actual hardness. Hardness may be divided into two types: carbonate and noncarbonate. As shown in Table 1, total hardness is always greater than total alkalinity due to non-carbonate hardness (Barbara, [8]) Total Dissolved Solids Total solids are dissolved solids plus suspended and settleable solids in water. In stream water, dissolved solids consist of calcium, chloride, nitrate, phosphorus, iron, sulfur, other ions, and particles that will pass through a filter with pores of approximately 2 microns (0.002 mm) in size. Suspended solids include silt and clay particles, plankton, algae, fine organic debris, and other particulate matter. These are particles that will not pass through a 2-micron filter. The TDS in both treatment plants under investigations were less than 1500 ppm i.e., within the allowable values of KEPA (KEPA, [6]). 2. Major Chemical Constituents These are the cations and the anions. Several additional chemical parameters are included with the major constituents because of their importance in determining water quality (Kretschmer, et al. [9]). Calcium and Magnesium -- These elements are the main ones causing water hardness and the scale-forming properties of waters. Calcium usually is higher than magnesium as shown in Table 1. As these elements increase, the tendency for sodium to be toxic decreases. Sodium -- Sodium arises from rock and soil weathering, seawater intrusion, and sewage and irrigation waters. Large amounts of sodium, combined with chloride, give water a salty taste. If the water is for a sprinkler system, and calcium and magnesium are low, medium to high levels of sodium can defoliate sensitive plants. When the sodium in water is high relative to calcium and magnesium levels, and precipitation of Ca and Mg bicarbonates and carbonates is high, a sodium problem could develop on some soils. The sodium adsorption ratio (SAR) is useful for evaluating sodium hazard in water applied directly to the soil, (cf. Table 1).

5 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt 1433 Chloride (Cl) is found in most natural waters. In high concentrations it is toxic to some plants. All common chlorides are soluble and contribute to the total salt content (salinity) of soils. The presence of sodium carbonates is suspected if the ratio of sodium to chloride is greater than (cf. Table 1). This constituent is most harmful in overhead sprinkler systems. The chloride content should be determined to properly evaluate irrigation waters if TDS is greater than 1000 mg/l. Chlorides should be below 300 mg/l to avoid damage to some plants (James, [11]). Chlorine Residual (Cl 2 ) As shown in Table 1, Chlorine residual is always higher than the KEPA levels (0.5 1 ppm), chlorine can also affect BOD measurement by inhibiting or killing the microorganisms that decompose the organic matter in a sample. Bicarbonates and Carbonates, ppm: These constituents most often are associated with calcium, magnesium, and sodium. White residues on plant foliage usually are because of high bicarbonate content of water. When calcium and magnesium bicarbonates precipitate out of irrigation water before use, sodium hazard may be increased. As shown in Table 1, All ph values were around 7.0, and Carbonate is found in some waters at high ph (>8.0). The predominant is the form of bicarbonate in alkalinity (Eugene, [ 7]). Nitrates and Ammonium Nitrogen, ppm: Nitrates have no effect on the physical properties of soil except to contribute slightly to its salinity, and nitrate is not harmful to irrigation systems. Nitrites or ammonia are considerably more toxic to aquatic life than nitrate. Generally, levels of these constituents should not be a problem if kept at 5 ppm or lower. In case of Al-Jahra, it was within ppm; and greater than 30 ppm in case of Al-Reqqa. Consequently, severe toxicity is seen in some plants (Kretschmer, et al. [9]). Phosphorus (P) is one of the key elements necessary for growth of plants and animals. Inorganic phosphorus is the form required by plants. Organic phosphate consists of a phosphate molecule associated with carbon molecules, as in plant or animal tissue. Their occurrence may also result from the breakdown of organic pesticides which contain phosphates. They may exist in solution, as particles, loose fragments, or in the bodies of aquatic organisms. Both organic and inorganic phosphorus can either be dissolved in the water or suspended (attached to particles in the water column). Rainfall can wash phosphates from grove soils into drainage ditches and canals. The levels of phosphate concentration in water arise from both treatment plants, was suitable for irrigation. (cf. Table 1). Sulfate/Sulfide (SO 2-4/ S 2- ) is abundant in nature. Sodium, magnesium, and potassium sulfates are readily soluble in water. Sulfate has no characteristic action on the soil except to contribute to the total salt content. The presence of soluble calcium will limit sulfate solubility. As can be seen from Table 1, sulfide levels were around 0.1 ppm, within the KEPA and is safe. This is due to if the irrigation water contains more than

6 1434 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt 0.1 ppm of total sulfides, sulfur bacteria may grow within the irrigation system, forming masses of slime which may clog filters and emitters. Boron (B) is essential for the normal growth of all plants, but the quantity required is very small. Plants sensitive to boron, such as dry beans, require much smaller amounts than plants that are tolerant of boron, such as corn, potatoes and alfalfa. In fact, the concentration of boron that will injure the sensitive plants is often close to that required for normal growth of tolerant plants. Some plants are more sensitive to a boron excess than others. Boron concentration greater than 2 ppm may be a problem for certain sensitive crops, especially in years that require large quantities of irrigation water. Consequently, no troubleshooting is expected from B in both treatment plants (cf. Table 1). Iron, ppm: Iron may arise from plumbing, pumps, and tanks. Iron in a soluble (ferrous) form may create emitter clogging problems at concentrations as low as 0.3 mg/l. Dissolved iron may precipitate out of the water due to changes in temperature or pressure, in response to a rise in ph, exposure to air, or through the action of bacteria. The presence of iron bacteria often results in the formation of an ochre sludge or slime mass capable of plugging the entire microirrigation system. As can be seen in Table 1, iron levels are always in Al-Jahra more than in Al-Reqqa and sometimes exceed 0.3 mg/l (James, [11]). In general, as can be seen in Table 1, The concentration of the major cations (e.g. Ca 2+ and Na 2+ ) always higher in the effluents of Al-Jahra compared with that of Al-Regga treatment plant. As shown in Table 1, the effluents at Al-Regga compared with that of Al-Jahra are characterized by higher concentrations in nutrients (PO 4 and NO 3 -N) and sulfide (S 2- ) during the period under investigations. Boron concentration is slightly above 1 ppm in Al-Riqqa in 2006 and due to some plants are more sensitive to a boron excess than others. So, it may be toxic. 3. Minor Chemical Constituents These include the so-called trace elements: cadmium, lead, chromium, cupper, zinc, nickel, vanadium and mercury. The concentration of Ni is more at Al- Jahra effluents whereas that of Zn is more at Al- Regga effluents. Also, during the period ( ), the concentrations of elements Cd; Pb; Cu; V and Fe are varied between the effluents arise from the two treatment plants. However, the concentration levels of sulfide is nearly equal in the effluents of both plants during the period ( ). Similar is the case of mercury.

7 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt Irrigation Water Classification The two most important factors to look for in an irrigation water quality analysis are the Total Dissolved Solids (TDS) and the Sodium Adsorption Ratio (SAR) (Thomas, et al. [10]). The SAR indicates the amount of sodium present in soils, relative to calcium and magnesium. If the sodium fraction is too large, soil permeability may be low, and the movement of water through the soil may be restricted. SAR is important to plant growth because its magnitude is an indication of the availability of soil pore water to plant roots. The SAR can be calculated using equation 2, and the risk of low soil permeability evaluated (Eugene, [7]): [Na + ] SAR = ([Ca 2+ ] + [Mg 2+ ]) / 2 Where [Na + ] = concentration of sodium in meq/l (water) [Ca 2+ ] = concentration of calcium in meq/l (water) [Mg 2+ ] = concentration of magnesium in meq/l (water) As shown in Table 1, water having SAR values between 5 and 8 (except Al-Jahra treatment plant in 2003) and specific conductivity higher than 900 and less than 2000 mho/cm will require slight to moderate limitations on water use for irrigation due to low to medium reduction in soil permeability may occur. Consequently, Soil permeability may be diminished. Calcium added to irrigation water can lower the SAR and reduce the harmful effects of sodium. The effectiveness of added calcium depends on its solubility in the irrigation water. Calcium solubility is controlled by both the source of the calcium (e.g. calcium carbonate, gypsum, calcium chloride) and also the concentration of other ions in the irrigation water. Compared to calcium carbonate and gypsum, calcium chloride additions will result in higher concentrations of soluble calcium and be the most effective at lowering irrigation water SAR. However, calcium chloride is considerably more expensive than calcium carbonate and calcium sulfate (Thomas, et al. [10]). 5. Effects of Poor Water Quality on Soils If levels of calcium, magnesium, and sodium, as well as chlorides, sulfates, and bicarbonates, as a group or alone, are too high, crop growth can be hurt. High levels can even cause crop failure. Often it is associated with poor soil structure. Crop growth reductions because of dissolved substances in the soil are similar to drought-stressed effects. An osmotic gradient on salty soils is formed. Water uptake by plant roots is increasingly restricted as the concentration of soil salts increases.

8 1436 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt Because of this, as soil salts build up in the soil, more frequent irrigation is necessary to help flush out salts and reduce water stress. Crop species differ in their abilities to withstand salt stress. Fortunately, some of the major field crops grown are moderately to highly tolerant of elevated soil salts (James, [11]). A breakdown of soil structure is a major effect of elevated sodium. Soil aggregates are bonded by calcium and magnesium. High levels of dissolved sodium tend to displace these bonding elements and disperse the aggregates. As sodium increases, dispersion increases and soil tilth declines. Soil dispersion caused by sodium can make soils run together, crust easier, and can limit water infiltration. CONCLUSIONS Sample effluent quality of the Jahra and Reqqa plants during the period ( ) are within the allowable limits according to appendix No. 15, this proves that the efficiency of both treatment plans are in good working conditions. Average effluent quality from conventional systems (Jahra and Riqqa plants) appears to be adequate only for restricted irrigation use. i.e., use of low quality effluents in limited areas and for specific crops only. Chloride (Cl) is found in high concentrations, it is toxic to some plants and contribute to the salinity of soils. Chlorides should be below 300 mg/l to avoid damage to citrus if TDS is greater than 1000 mg/l. According to SAR values and to avoid the harmful effects of sodium, the effectiveness of added calcium depends on its solubility in the irrigation water. Consequently, care with irrigation is required. The added costs for rendering effluent for reuse through tertiary treatment (beyond secondary), advanced treatment (beyond tertiary) and transfer of treated effluent to a central storage place are important elements in the State s program of augmenting national water resources through reuse of treated effluent. The advanced treatment is directed to improve the effluent further so that the treated effluent can be reused unrestrictedly for irrigation and other purposes.

9 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt 1437 Table 1. Sample effluent quality of the Jahra and Reqqa plants during the period ( ) Year Parameter J* R** J R J R J R J R J R J R Temp. ( o C) ph T. Alkalinity, mg/l T. Hardness, mg/l Residual Cl 2, mg/l Cl, mg/l SO 4, mg/l NO 3 -N, mg/l TDS, mg/l EC, mhos PO 4, mg/l NH 3 -N, mg/l SO 3 mg/l B, mg/l Ca, mg/l Na, mg/l K, mg/l F, mg/l Cd, g/l Pb, g/l Cr, g/l Cu, g/l Zn, g/l Fe, g/l Ni, g/l V, g/l Hg, g/l J* = Al-Jahra and R**=Al-Regga

10 1438 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt REFERENCES 1- Al-Awadi, N., K. Puskas and H. Malek, Option for treated wastewater reuse in post-war Kuwait, pp , Proceedings of the First Gulf Water Conference, Al-Awadi, E., and T. Rashid, Change in Treated Wastewater Quality through Soil Aquifer Treatment. Final Report, (KISR 5724 WW002C), Gulf Consult, Final Design Report, Sulaibiya Wastewater Treatment Plant, submitted to MPW, MPW (The Ministry of Electricity and Water, Kuwait), Statistical Year Book: Water, APHP, American Public Health Association, Standard methods for examination of water and wastewater, 13 th Ed., NY, USA, KEPA, Kuwait Environmental Public Authority, Decision No. 210/2001 pertaining to the exactive by-law of the low of Environmental Public Authority, Kuwait El-Youm, # 533, p.47, Eugene R. W., Applications of Environmental Chemistry, Lewis Publications, CRC press, NY, pp , Barbara, A.H., Drinking water chemistry, Lewis Publishers, CRC press, NY, USA, p.55, Kretschmer, N., Ribbe, L. and Gaese, H., Wastewater reuse for Agriculture, Technology Resource Management & development, vol.2, Thomas, F. S., Bruce S., David F., Soil, Water and Plant characteristics Important to Irrigation, Environment- Natural Resources, James G. Thomas, Irrigation Water Quality Guidelines for Mississippi, Publication 1502, U.S. Department of Agriculture, Mississippi State University.

11 Twelfth International Water Technology Conference, IWTC , Alexandria, Egypt 1439 Appendix No. 1 (KEPA, [6]) Maximum limits of pollutants concentration in drainage treated sewage water used in irrigation Serial # Pollutant Units Max. limit 1 Hydrogen concentration, ph Biological Oxygen Demand (BOD) 5 (5 days, 20 o C) mg/l 20 3 Chemical Oxygen Demand, COD mg/l Oil and Grease mg/l 5 5 Total Suspended Solids, TSS mg/l 15 6 Total Dissolved Solids, TDS mg/l Phosphate, PO4 mg/l 30 8 Ammonia, NH3-N mg/l 15 9 Total Kjeldahl nitrogen mg/l Total removable phenol mg/l 1 11 Fluoride, F mg/l Sulfide, S mg/l Residual chlorine mg/l Dissolved Oxygen, DO mg/l > 2 15 Hydrocarbons mg/l 5 16 Flotables mg/l NIL 17 Aluminium, Al mg/l 5 18 Arsenic, As mg/l Barium, Ba mg/l 2 20 Boron, B mg/l 2 21 Cadmium, Cd mg/l Chromium, Cr mg/l Nickel, Ni mg/l Mercury, Hg mg/l Cobalt, Co mg/l Iron, Fe mg/l 5 27 Antimony, Sb mg/l Copper, Cu mg/l Manganese, Mn mg/l Zinc, Zn mg/l Lead, Pb mg/l Most probable number of total coliform MPN/100 ml Most probable number of faecal coliform MPN/100 ml Egg parasites -- < 1 35 Worm parasites -- Free