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Iranian Journal of Environmental Health, Science and Engineering
Iranian Association of Environmental Health (IAEH)
ISSN: 1735-1979
Vol. 6, Num. 1, 2009, pp. 41-46

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
2Water and Wastewater Engineering Company, Tehran, Iran
*Corresponding author: k_naddafee@yahoo.com Tel: +9821 88954914/Fax: +9821 8895018841

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
entering the systems were 5500 and 17600 m3/d
for the AWSP system of M1 and M2, respectively,
which were equivalent to the expected design.
The measured average of BOD5 and COD
concentrations of raw wastewater, as around
242 and 525 mg/L, were also near the expected
design concentrations of 250 and 550 mg/L,
respectively, for BOD5 and COD. However, the average SS concentration for raw wastewater,
around 128 mg/L was well below the expected
design concentration of 220 mg/L. Thus, the raw
wastewater in Arak could be classified as medium
to strong, in terms of BOD5 and COD, and weak
to medium for SS (Metcalf and Eddy, 2003).
Analysis of pond performance parameters

AWSP system M1

As Table 3 indicates, the removal efficiencies of
BOD5, COD, and SS for the APs with HRT=2.9
days and the PFPs with HRT=11.3 days, were
42%, 13% and 20%, respectively. The SFPs with
the HRT=11.3 days, had the removal efficiencies
of 24%, 11%, and – 8% for BOD5, COD, and SS,
respectively.

AWSP system M2

As shown in Table 4, for the ASPs with the
HRT=2.7 days, the calculated removal efficiencies
of BOD5, COD, and SS were 46%, 44%, and
-39% , respectively.

With respect to the HRT=12.2, 6.4, and 6.5
days, respectively for the PFP, SFP and TFP,
the percentage removal of BOD5, COD, and SS
were 18, 48, 53; 36, 33, 8; and -10, -26, and -10,
respectively.

DISCUSSION

M1 AWSP system

With respect to the effluent quality of the PFPs
and SFPs and in comparison with the Iranian
treated wastewater standards for agricultural
irrigation that has indicated BOD5, COD, and
SS concentrations should be less than 100, 200,
and 100 mg/L, respectively, the results indicated
that the average effluent concentrations of
BOD5, COD, and SS were 91.5, 169, 114 mg/L,
respectively, for PFPs, and 70, 160, 123 mg/L,
respectively, for SFP. The effluent of the studied
PFPs complied with the considered standards in
terms of BOD5 and COD concentrations.
As shown in Figs. 3-5, although the average
effluent concentrations of BOD5 and COD of the
SFPs were lower, the average concentration of
effluent SS was higher than the concentration of
the effluent SS of the PFPs. The main constraint
in the WSPs is the high SS in the effluents, which

is primarily due to high concentrations of algal
cells in the effluent (Esen et al., 1991). Thus in
practice, the SFPs would not be required and
could be replaced with other PFPs, in parallel
with the existing PFPs, to enhance the quantity of
treated wastewater in future years and to optimize
the treated wastewater quality.

M2 AWSP system
According to Figs. 6-8, the average effluent
concentrations of BOD5, COD, and SS of the SFP and the TFP were obtained as 69, 101, 77; 76, 127,
78 mg/L, respectively. These results indicated
that not only the average effluent concentrations
of studied parameters of SFP were complied
the considered standards, but also the average
effluent concentrations of studied parameters
for the TFP were higher than those for the SFP.
Consequently, the TFP would not be required and
could be used to receive the raw wastewater, in
parallel with the SFP, to increase the treatment
capacity of the M2 AWSP.

The range of BOD5 concentrations of SPFs for
M1 and M2 were less than the results obtained
in a study conducted for stabilization ponds
in Egypt (Hamdy et al., 2006). The removal
efficiency of Arak facility for BOD5 was higher
than the removal efficiency of another study that
was conducted in Spain, as 54% (Travieso et al.,
2006). However, the removal efficiency of COD
of that study was about the same as in Arak (about
70%). In a study that was carried out in Tanzania,
the rate of COD removal was 66% for PFP, 68%
for SFP1, 71% for maturation pond (MP), and
the overall COD removal rate was about 94%,
(Kayombo et al., 2002), much higher than in
Arak which were 71% for M1 and 76% for M2.
For conclusion, the TFP of M2 can be used as a
serial SFP in order to increase Arak wastewater
plant capacity and effluent quality enhancing by
population growth. In another way for enhancing
effluent quality of Arak facility, it could be
practical to put some baffles in SPFs of both M1
and M2 to optimize HRT and plug flow condition
of wastewater, and consequently, enhancing
removal efficiencies of BOD5, COD and SS.

ACKNOWLEDGEMENTS

The authors highly appreciate the sponsorship
of Iranian Water and Wastewater Engineering
Company and Tehran University of Medical
Sciences.

 


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