Evaluation of Daqahla wastewater treatment plant, aerated lagoon and ponds system

In Egypt Daqahla wastewater treatment plant (WTP) includes two anaerobic ponds, one aerated lagoon followed by three maturation ponds. It started operation in 1989. This plant is chosen as an example for evaluation as a cost-effective method for wastewater treatment in rural areas. A sanitary survey, laboratory analysis and cost survey were carried out during the period between December 1991 to September 1992. It was found that Daqahla community has high strength wastewater characterised by an average BOD5 of 454 mg/l and average SS of 508 mg/l. Furthermore, it was noticed that Daqahla WTP was loaded with an actual flow (833 m(3)/d) higher than the design flow (520 m(3)/d). In addition there was a wide fluctuation in the loads applied to the system. The system was evaluated and the average removal efficiencies of suspended solids, BOD5 and COD were 92%, 95% and 93% respectively. While there was no removal of ammonia and phosphate, with respect to the efficiency of the anaerobic ponds, it was noticed that about 50% of the organic loading was removed and this is consistent with the literature. In order to upgrade the efficiency of the aerated lagoon and the first maturation pond the design load and detention time must be taken into consideration. Sludge removal processes must be considered since the first maturation ponds was working as a settling pond. It was noticed that the second and the third maturation ponds were working as facultative ponds. To upgrade their efficiencies, the actual organic loading must not exceed the design load with a minimum retention time of 3 days per pond. The cost survey indicates that the construction cost is 63 LE/cap. Land costs in delta and desert areas are 19 and 2 LE/cap., respectively (acre prices in delta and desert are 40000 and 4000 LE respectively). Total construction cost in the delta is 82 LE/cap., while in the desert, the total construction cost is 65 LE/cap. Furthermore, the operation and maintenance cost is 12 LE/cap.year. (C) 1996 IAWQ. Published by Elsevier Science Ltd.