ACUTE TOXICITY OF OLEATE TO ACETATE-UTILIZING METHANOGENS IN MESOPHILIC AND THERMOPHILIC ANAEROBIC SLUDGES

Oleic acid, a major derivative of lipid hydrolysis, causes serious pro blems in biologically anaerobic systems treating fat/oil/grease wastew aters. Acute toxicity tests on acetate-utilizing methanogenesis were c onducted batchwise at three temperatures (30, 40, and 55 degrees C) wi th four different anaerobic sludges. Oleate inhibited flocculent sludg e more than granular sludge. Its toxicity was irrelevant to the specif ic acetate-utilizing methanogenic activity but significantly dependent on temperature. Acetate-utilizing methanogenesis under thermophilic ( 55 degrees C) conditions was found to be more susceptible to oleate to xicity than under mesophilic conditions (40 and 30 degrees C). Fifty p ercent inhibition concentrations of oleate ranged between 0.35-0.79 mM at 55 degrees C, 0.53-2.27 mM at 40 degrees C, and 2.35-4.30 mM at 30 degrees C. Oleate was over 12-fold more toxic to thermophilic floccul ent sludge than to mesophilic granular sludge. Physicochemical surface association between oleate and acetate-utilizing methanogens played a n important role in acute intoxication. With respect to temperature su sceptibility, this study suggests the application of mesophilic treatm ent to fat/oil/grease wastewaters. (C) 1997 Elsevier Science Inc.