Solids retention time : its effects on carbon adsorption of organics in secondary effluents from treatment of petroleum refinery wastewaters

Abstract

A bench-scale, fill-and-draw activated sludge system was used to investigate the effects of solids retention time on the carbon adsorption of organics in effluents from activated sludge reactors. Six units were fed a simulated petroleum refinery wastewater, and operated at solids retention times of 3, 5, 10, 15, 30 and 60 days. The effluents from the activated sludge units were subjected to carbon adsorption test. Results indicate that the solids retention time exerts marked effects on the absorbability of organics remaining in the secondary effluents. The activated sludge units operated at higher solids retention times produced effluents containing lower concentration of non-absorbable compounds. Moreover, the absorbability of the absorbable compounds increased in the activated sludge units operated at higher solids retention times. A fractionation procedure indicated that the majority of the adsorption-resistant compounds was associated with low molecular weight materials.