The Response of Activated Sludge Process to Hazardous Organic Wastes

Abstract

The response of a laboratory-scale activated sludge unit to diethyl phthalate, dimethyl phthalate, 2,4-dinitrophenol, 2,4-dimethylphenol and 4-nitrophenol was examined. The system tolerated phthalate esters well and the acclimation was quick. The response of the system to stepwise increasing concentrations of other hazardous compounds was observed as increasing effluent COD and solids losses from the system due to changing settling characteristics of the sludge. It was concluded that: (1) Diethyl phthalate and dimethyl phthalate do not affect activated sludge process performance, and their removal rates (measured in terms of COD) are high (95 percent or better). (2) High concentrations (in excess of 900 mg/L) of phthalate esters are tolerated well by activated sludge, and acclimation to each step increase requires just a few days. (3) Acclimation to 2,4-dinitrophenol is slower, and approximately 8 mg/L of this compound is enough to upset system performance temporarily. (4) Activated sludge is also a viable process (in terms of COD removal) for wastes containing 2,4-dimethylphenol in addition to phthalate esters and 2,4-dinitrophenol. (5) Activated sludge may not tolerate hazardous organic wastes well if the wastewater composition is complex. (6) Acclimation of activated sludge process to a particular organic compound (4-nitrophenol in this study) will improve the response of the system to a shock load by the same compound.