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Mehmet Emin Aydın, Kemal Gür Selcuk University, Environmental Engineering Department, Konya-Turkey Abstract In this work, nonpotable reuse of reclaimed municipal wastewater was evaluated. Reclaimed wastewater quality criteria and treatment requirements acording to different nonpotable reuse were investigated. Non potable reuse alternatives and applications in other countries were also considered. Caracteristics of municipal wastewater of Konya were determined by analysing the samples in terms of sum parameters such as BOD, COD, TOC, TDS, nutrients N, P and heavy metals. Potential reuse alternatives of Konya municipal wastewater and treatment requirements acording to various reuse purposes were evaluated. Introduction The number of large cities is increasing. Although small communities can find the necessary water locally. Water demand of large cities are drawn from extensive drainage areas or aquifers. A lot of large cities have to draw waters from lower quality sources or from long distances. Furthermore, wastewater is discharged usually into a surface water source or to sea. Therefore, in order to prevent water quality degradation wastewaters should be treated properly prior to disposal. Water supplied for cities are treated to comply with the requirements of potable use. However, potable use is only a fraction of the total daily water demand. The remaining fraction may be of lower quality. Usually water used for nonpotable purposes like irrigation are drawn from the same source of potable water. If reclaimed wastewater could be employed for nonpotable use, then the existing source could serve bigger population. Various water use activities that reclaimed wastewater can be substituted for potable waters could be listed as urban, industrial, agricultural, recreational, habitat restoration, ground water recharge. Urban use of reclaimed wastewater includes irrigation of parks, recreation areas, highway medians and shoulders, toilet flushing in commercial and public buildings. Reclaimed water is ideal for a lot of industries especially as cooling water, boiler-feed water and process water which always need not be in potable quality. Habitat restoration and recreational use of reclaimed water range from maintenance of landscape ponds, ornamental fountains to creation of marshland to serve as wildlife habitat. Groundwater recharge using reclaimed water is carried out in order to establish saltwater intrusion barriers in coastal aquifers, to treat reclaimed water further for future use, to augment aquifers and to provide storage. Agricultural irrigation is the biggest fraction of the total fresh water demand. Mostly reuse systems supply reclaimed wastewater for agricultural irrigation. It is estimated that irrigation water demands exceed any other use by a factor of 10 (Pair et al., 1983). Reclaimed water quality is very important for any reuse in order to assure health protection, preventing environmental degradation and avoiding public nuisance. Protection of public health may be assured by reducing pathogenic bacteria, parasites and viruses, controlling chemicals and limiting public exposure. When human exposure is not limited in a reuse application reclaimed wastewater should be treated to higher degree before use. If public access is limited to the reuse site, lower level of treatment, without compromising worker safety, may be accepted. Toxic chemicals and pathogenic microorganisms in untreated wastewater have a potential for deleterious health effect and disease transmission. However, for most reuse applications, conventional wastewater treatment processes are able to reduce these constituents to acceptable levels. Epidemiological investigations on reuse of raw or minimally-treated wastewater for food crop irrigation provided evidence of infections disease transmission (Lund, 1980; Feachem et al, 1983; Shuval et al, 1986). Chemicals usually present in wastewater are also an important concern for reuse application especially for irrigation of food crops. The mechanisms of food crop contamination, by irrigation of reclaimed water may be either physical contamination, where evaporation and repeated irrigation may cause build up of contaminants on crops or uptake of the chemical constituents through roots from irrigation water or soil. Chemical constituents may also contaminate groundwater by percolation into the ground after the reuse applications such as irrigation and groundwater recharge. Chemicals are usually considered in two categories such as inorganics and organics. Concentrations of inorganic matters in reclaimed water depend on the source of wastewater and the degree of treatment. Residential use of water approximately adds about 300 mg/L of dissolved inorganic solids, although the added amount may change between 150 mg/L and 500 mg/L. Wastewater treatment can generally reduce many trace elements to acceptable levels for irrigation. The organic constituents in raw wastewater includes humic substances, fecal matter, kitchen wastes, detergents, oils, grease and other substances. Industrial and residential wastes can add considerable amount of synthetic organic compounds. Organic matters are usually measured by biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC). The determination of low levels organic constituents in water is possible only with sophisticated analytical instrumentation such as gas chromatography. Some other parameters in reclaimed water are important especially for agricultural irrigation. These parameters of concern are salinity, sodium, trace elements, excessive chlorine residual and nutrients. Salinity is the most important parameter for determining irrigation water suitability (Pettygrove and Asano, 1985). The soil should be drained and leached properly to prevent salt build up. Leaching is over-application of irrigation water in excess of plant needs for removing water and salt downward away from the root zone. Salinity is usually measured by electrical conductivity (EC), or total dissolved solids (TDS). Salinity is concerned because of its influence on the soil osmotic potential, specific ion toxicity and degradation of soil physical conditions. Salinity reduces the water uptake of plants because of lowering the osmotic potential of the soil. The most important ions are sodium, chloride and boron in reclaimed irrigation water. Detergents are usually the source of boron while the water softeners add sodium and chloride. Sodium salts effect the exchangeable caution composition of the soil causing lowered permeability. Sodium does not impair the plant uptake of water but reduces the infiltration of water into the soil. Plants are thus affected by deficiency soil water (Tanji, 1990). Trace elements are usually exist less than 100 mg/L in reclaimed water (Pettygrove and Asano, 1985). Some of them are necessary for plants but all of them can be toxic at higher concentrations (Tanji, 1990). The most important elements of concern at higher concentrations are cadmium, copper, molybdenum, nickel and zinc. Nickel and zinc are of less important than cadmium, copper and molybdenum since they have obvious deleterious effect in plants at lower concentrations than the levels harmful animals and humans. However, cadmium, copper and molybdenum are harmful to animals at much lower concentrations than the levels that plants may be effected. Cadmium is particularly important because it can accumulate in the food chain. Free chlorine residual less than 1 mg/L concentration has no harmful effect to plants. However, chlorine concentration more than 5 mg/L causes severe damage to most plants. United States Environmental Protection Agency (EPA) has recommended limits for constituents in reclaimed water for irrigation reuse (Table 1)  Microbiological quality requirements for agricultural irrigation with reclaimed water are applied according to plant type in USA. California has developed the first reuse regulation in 1918 and modified this regulations throughout the years. The current criteria in California were given in table 2 adopted in 1978. These criteria were taken as base for reuse standarts by other states and countries (Crook, 1991).  According to the irrigation water quality criteria in Turkish water pollution control regulations. Reuse quality conditions and treatment requirements of wastewater for irrigation changes according to the crop type (Table 3). In Turkish regulations, heavy metals concentration limits were accepted as the same values given in Table 1.  Agricultural Reuse Potential in Konya Municipal wastewater of Konya is currently discharged to Konya main drainage channel which is constructed by government water works (DSI) in 1974 in order to drain excess water from rainfall and from irrigation. Konya main drainage channel collects excess waters and wastewater of Konya and discharges them to Tuz lake which is about 150 km away. Pollution problems in Tuz lake because of this discharges are also widespread public concern. Wastewater treatment plant of Konya is planned as classical plug flow activated sludge process in two stages consisting for the years 2015 and 2030 populations and design data are given in Table 4.  In this work, characteristics of Konya wastewater as well as its suitability for irrigation of agricultural land in Konya were investigated in addition to the evaluation of different nonpotable reuse applications and treatment and quality requirements for different reuses. Material and Methods Wastewater samples were collected from Konya sewerage outlet once a weak for three months period. Chemical analyses of wastewater samples were carried out as described in standard methods (APHA, 1989) in order to determine electrical conductivity (EC), pH, total dissolved solids (TDS), suspended solids (SS), turbidity, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), ammonia (NH3-N), total nitrogen (total-N), phosphate (PO4-P), sodium (Na), potassium (K), calcium (Ca), magnesium (Mg) contents. In addition heavy metals such as cadmium (Cd), zinc (Zn), copper (Cu), lead (Pb), mercury (Hg) and total cromium (T-Cr) contents of wastewater samples were determined using CADAS-200 UV-Vis spectrophotometer and its ready kits. Water demands of mostly cultivated crops such as grains were calculated according to Blaney-Cridle method which is a popular method calculating irrigation water demand. The Blaney-Cridle method relies on percent of daylight hours Per month and average monthly temperature. The field area that could be irrigated was also calculated considering the amount of reclaimed wastewater, and irrigation water demand of common crops. Results Characteristics of wastewater of Konya were determined by analysing water samples taken from sewerage outlet. Analyses results are summarised in Table 5. From Table 5, it can be seen that the wastewater of Konya within the range of heavy metals limits given in Table 1 even without treatment. However, activated sludge process will remove approximately 28% of cadmium, 30% of mercury, 55% of chromium, 70% of copper and 75% of zinc (WPCF, 1989). Microbiological quality requirements given in Table 2 for grains crops would easily be satisfied provided disinfection process employed after conventional activated sludge process and surface irrigation is applied. Grain crops are grown in about 50% of cultivated land of Konya and making up about 1 357 557 hectare. Irrigation water demands of grain crops are calculated approximately as total 2155 m3/hectar, consisting of 535 m3/ha in April, 1470 m3/ha in May and 150 m3/ha in June. Effluent of wastewater treatment plant would meet irrigation water demand of 8352 hectare of grain crops if stored only three months of irrigation period. In case effluent is stored for a year, 33410 hectare of cultivated land would be irrigated until 2015. In the second stage of the treatment plant, 12529 hectare of crops would be irrigated if water is stored only three months, however, 50116 hectare can be irrigated if effluent water is stored for a year. Furthermore, N and P removal steps could be omitted from wastewater treatment plant since these constituents are beneficial as fertilizers when reclaimed wastewater is used as irrigation water. Thus, construction and operation costs of wastewater treatment plant are reduced. For a year storage of effluent of Konya wastewater treatment plant would require about 110x106 m3 storage volume would be required. A natural dry lake called Hotamış Lake, with a storage capacity of nearly 300x106 m3, is located only about 40 km away the city. Therefore, should the effluent of wastewater treatment plant would be stored in Hotamış Lake this could help restoring recreational value of the lake as well as improving effluent quality by natural oxidation and provide irrigation water to about 5% of the grains field of Konya.  References . APHA, (American Public Health Association), WPCF, AWWA, 1989, "Standart Methods for Examination of Water and Wastewater", 17th Edition, USA. . Crook, Y., 1991, "Quality Criteria For Reclaimed Water", Water Science and Technology, V24, n9, pp:109-121 . Feachem, R. G., Bradley D. J., Garelick H. & Mara D. D., 1983, "Sanitation and Disease-Health Aspects of Excreta and Wastewater Management", John Wiley & Sons, Chicester, England. . Lund, E., 1980, "Health Problems Associated with the Reuse of Sewage", WHO Seminar on Health Aspects of Treated Sewage Reuse, Algiers, Algeria. . Pair, C. H., Hinz W. H., Frost K. R., Sneed R. E. & Schiltz T. J. (ed.)., 1983, "Irrigation", fifth edition, The Irrigation Association, Virginia, USA. . Pettygrove, G. S. & Asano T. (ed.)., 1985, "Irrigation with Reclaimed Municipal Wastewater-A Guidance Manual", Lewis Publishers, Michigan, USA. . Shuval, H. I., Adin A., Fattal B., Rawitz E. & Yekutiel P., 1986, "Wastewater Irrigation in Developing Countries-Health Effects and Technical Solutions", The World Bank, Washington, USA. . Tanji, K. K. (ed.), 1990, "Agricultural Salinity Assessment and Management", American Society of Civil Engineers, New York, USA. . WPCF, (Water Pollution Control Federation), 1989, "Water Reuse-Manual of Practice", Water Pollution Control Federation, Virginia, USA. |