High rate settler in biological system for oil and soap wastewater treatment

Wastewater from an oil and soap company provided the material of this study. The company discharges 31,000 m3/d of untreated wastewater into the Nile River. The wastewater was highly contaminated with organic and inorganic pollutants. An end-of-pipe treatment scheme was devised of dissolved air flotation with/without alum followed by biological degradation. The biological unit was compact and comprised an aeration tank based on a completely mixed activated sludge process followed by a high rate settler. The unit was operated at two organic loads, namely 1.44 and 2.88 kg BOD5/m3/d. The results obtained showed that this scheme of treatment produced a high quality effluent suitable for disposal into surface water or reuse. Also, the high rate settler acted as a biological reactor as well as a settler for finely divided organic matter.