COMPARATIVE TOXICITY OF LONG-CHAIN FATTY-ACID TO ANAEROBIC SLUDGES FROM VARIOUS ORIGINS

Seven anaerobic sludges were screened in order to obtain the most suit able methanogenic inoculum for the anaerobic treatment of wastewaters containing long-chain fatty acids (LCFA). The selection was made on th e basis of the toxicity of a model compound, oleate, to acetoclastic m ethanogens in different sludges. The effects of three biological facto rs, sludge origin, specific acetoclastic methanogenic activity and slu dge adaptation to lipids, and a physical factor, specific surface area of sludge, on the degree of toxicity were investigated and compared. Values of the fifty percent inhibition concentration (IC50) of oleate obtained from 40 degrees C batch toxicity tests ranged from 0.26 to 3. 34 mM far the various sludges examined. It was found that the toxicity of oleate to anaerobic sludges was not dependent upon the three biolo gical factors. Instead, it was closely correlated to the specific surf ace area of sludge. Suspended and flocculent sludges, which have highe r specific surface area, suffered much greater inhibition than did gra nular sludges. This paper suggests the use of granular sludges as appr opriate inocula for reactors treating lipids (fats, oils and greases) wastewaters, to decrease the toxic impact from their hydrolysis produc ts-LCFA. Copyright (C) 1996 IAWQ.