Upgrading an existing wastewater treatment plant based on an upflow anaerobic packed-bed reactor
Upgrading a wastewater treatment plant (WWTP) may be necessary to meet the existing effluent quality and/or to meet the stricter future effluent quality requirements and/or to increase its capacity because of population growth or sewerage expansion to serve more areas. Inability to meet the existing effluent quality may result from lack of proper plant operation and maintenance, inadequate plant design capacity and increased hydraulic or organic loading rate caused by a change in wastewater flow or characteristics (Bub et al., 1994; Qasim, 1999; WEF, 2005; Mahvi et al., 2006). As the space available at a WWTP is limited, processes are required which can accommodate the need for increased treatment capacity and/or improvement of effluent quality without requiring much more space (Brinch et al., 1994). Parkandabad WWTP is located in the city of Mashhad, Iran. The WWTP has been operating since 2000. The biological process used in the WWTP is a completely mixed aerated lagoon. The municipal WWTP was designed for a population of 100,000 person and an average influent flow of 15,200m3/d, but presently the WWTP serves a population of 152,000 person and the average flow of influent municipal wastewater is about 30,400m3/d. In addition, neighboring industries including food processing, power plant etc. discharge a combined wastewater flow of 4,600m3/d to the WWTP. At present, the effluent quality of the WWTP is undesirable and does not satisfy the Iranian effluent discharge standards, because of hydraulic and organic over-loadings, high concentration of organic matter in the influent wastewater, presence of toxic compounds in the influent and acidic or basic pH of input wastewater.