| Abstract: | A pilot plant stabilization pond (SP) using Jerusalem wastewater primary effluent, was constructed to study the effect of hydraulic characteristics on treatment system performance. The system consists of six ponds: the first, 3 m3, and the remainder 1 m3 each. Two longitudinal baffles were installed in ponds 1 and 5, and two cross-sectional baffles in ponds 2 to 4. Pond 6 was without baffles. Two runs were made, using two theoretical detention times (TDT): 11 and 33 days. In each run, rhodamine water tracer (RWT) studies were conducted, biological oxygen demand (BOD) was determined, and physico-chemical and microbiological tests were carried out. According to the tracer study, the first pond had a flow pattern similar to an idealized completely mixed pattern. In the remaining series of ponds, the flow was similar to that of an idealized plug flow pattern, and with more efficient usage of pond volume as compared with that of a single SP. Thermal stratification occurred during the day in ponds with or without longitudinal baffles, causing hydraulic failures. However, ponds with cross-sectional baffles showed no thermal stratification, had higher microbial decay rates, and displayed improved treatment efficiency. The tested microorganisms at the exit of pond 6 were reduced by up to 1.8 logs after 11 days of TDT, and by 3.3 to 5.2 logs after 33 days of TDT. BOD was reduced by 79 and 93% respectively. In the baffled SP pilot plant, 27 days of TDT were required to achieve the WHO guidelines of 1000 F. coliforms/100 ml wastewater effluent for unrestricted irrigation. |
