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Iranian Journal of Environmental Health, Science and Engineering, 2009, Vol. 6, No. 1, pp. 41-46 Performance Evaluation Of Wastewater Stabilization Ponds In Arak-iran *1K. Naddafi, 1M.S. Hassanvand, 1E. Dehghanifard, 2D. Faezi Razi, 2S. Mostofi, 2N. Kasaee, 1R.Nabizadeh, 1M. Heidari
1Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Code Number: se09008 Received 4 August 2008; revised 19 October 2008; accepted 15 December 2008 ABSTRACT Arak waste stabilization pond facilities consist of two stabilization pond systems, module 1 and module 2. The existing facilities have had several problems in their operation. The objectives of this research were to evaluate the performance of stabilization ponds in wastewater treatment of the city of Arak, because of several problems in their operation, and to prepare a scheme of its upgrading, if necessary. Within the period of May to September 2007, analyses were carried out for both raw and treated wastewaters. Results of these investigations showed that the average effluent concentrations of BOD5, COD and SS taken from primary and secondary facultative ponds of module 1 were 91.5, 169, 114; and 70, 160, 123 mg/L, respectively. These results indicated that the effluent of the primary facultative ponds of module 1 were complied with the Iranian treated wastewater standards for agricultural reuse in terms of BOD5 and COD concentrations; hence the secondary facultative ponds could be changed to other primary facultative ponds in order to increase the capacity of wastewater treatment plant. For module 2, BOD5, COD, and SS average concentrations of treated wastewater for the secondary and tertiary facultative ponds were obtained as 69, 101, 77; and 76, 127, 78 mg/L, respectively. Thus the effluent of the secondary facultative pond was complied with the considered standards in terms of all studied parameters. Consequently, the tertiary facultative pond could be changed to other secondary facultative pond to upgrade both the quality and the quantity of treated wastewater. Keywords: Biological wastewater treatment, stabilization pond, upgrading INTRODUCTION Wastewater Stabilization Pond (WSP) is considered as the most appropriate system to treat the increasing flows of urban wastewater in tropical and subtropical regions of the world (Jeroen et al., 2007). WSPs are commonly used as efficient means of wastewater treatment relying on little technology and minimal, albeit regular maintenance. Their low capital and hydraulic loads have been valued for years in rural regions and in many countries wherever suitable land is available at reasonable cost (Nameche et al., 1998; Agunwamba J.C., 2001; Nelson et al., 2004; Handy et al., 2006; Kaya et al., 2007).They generally consist of a series of ponds where the wastewater has around twenty days retention time and usually a depth from one to three meters depending on the type of pond (Toumi et al., 2000). The city of Arak is located in the central part of Iran, with a population of around 490,000 inhabitants and many small and large industries. Municipal and industrial wastewaters of this city are conducted to a wastewater treatment plant through sewer. The basic wastewater treatment process in Arak is stabilization pond. However, due to inappropriate design and consideration of both biological process and physical aspects of the ponds, the existing facilities suffer serious malfunctioning problems. Hence, a program was developed within the period of May to September 2007 with case study on the existing facilities. The main objectives of the program were to train the of personnel to monitor, to and evaluate the pond performance and effluent quality of the stabilization ponds and, depending on the results obtained, to propose a scheme for upgrading and expanding WSPs, if necessary. Similar programs have been developed in many parts of the world (Escalante et al., 2000; Oakey et al., 2000; Yaghubi et al., 2000; Nelson et al., 2004). MATERIAL AND METHODS Site specifications The wastewater treatment plant of Arak is located in the north of the city, close to the main road of Arak airport. The latitudinal location of the Arak WSPs is about 34.08o N, the longitude is around 49.70 E and the pond’s altitude is 1710 m above sea level. Arak treatment plant consists of M1 and M2 facilities are in parallel to eachother and have started their operation in 1993 and 2006, for the equivalent population 25000 and 80000, respectively. As can be seen in Fig.1, the studied WSP systems are the same as classical pond configurations with anaerobic and facultative ponds. The studied wastewater treatment plants in Arak have a pretreatment unit that includes screens followed by the WSP systems. Tables 1 and 2 present the physical and operational characteristics of the AWSP systems. The M1 AWSP comprises three anaerobic ponds (APs) in parallel followed by a distribution tank that distribute the APs effluent into two parallel primary facultative ponds (PFPs), followed by two secondary facultative ponds (SFPs) in parallel (Fig. 1). The The M2 AWSP comprises also two APs in parallel followed by one PFP, SFP and TFP (Fig. 2). The treated wastewater of both M1 and M2 facilities are used for agricultural reuse. As pointed out by Mara et al (1992), the current reuse of wastewater for agriculture purposes is attractive to many local authorities, especially to those in water-scarce regions. It is known that agriculture is responsible for more than 80% of total world water consumption (Valencia E., 1998). Sampling Wastewater samples were taken weekly at the inlet and outlet of each pond. The collected samples were composite samples taken over a period of 48 hours. The samples were taken directly by means of 2 L beaker glass. Each sample of 2 L taken at a wastewater depth of 1 m was directly transferred to a 30 L sample container and fixed for physicochemical analysis (Yaghoubi et al., 2000). Sampling was conducted from May to September 2007. Climate Arak city has a relatively cold and dry climate. The maximum temperature may rise up to +35 0C in summer and may fall to -25 0C in winter. The average temperature in the coldest month is -10.480C. The average precipitation is around 300 mm and the annual relative humidity is 50 %. Analyzed parameters Total BOD5, COD and SS were determined for both influent and effluent of the modules. The measurement of flow was carried out by means of a Partial flume located at the inlet channel. Analytical approaches were based on the Standard Methods (APHA, 2005). RESULTS Total system performance evaluation The results obtained for each stage and for the total systems of M1 AWSP and M2 AWSP, are presented in Tables 3 and 4, respectively. The averages of raw wastewater flow rates AWSP system M1 As Table 3 indicates, the removal efficiencies of AWSP system M2 As shown in Table 4, for the ASPs with the With respect to the HRT=12.2, 6.4, and 6.5 DISCUSSION M1 AWSP system With respect to the effluent quality of the PFPs is primarily due to high concentrations of algal M2 AWSP system The range of BOD5 concentrations of SPFs for ACKNOWLEDGEMENTS The authors highly appreciate the sponsorship
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