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Seven anaerobic sludges were screened in order to obtain the most suitable methanogenic inoculum for the anaerobic treatment of wastewaters containing long-chain fatty acids (LCFA). The selection was made on the basis of the toxicity of a model compound, oleate, to acetoclastic methanogens in different sludges. The effects of three biological factors, sludge origin, specific acetoclastic methanogenic activity and sludge 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°C batch toxicity tests ranged from 0.26 to 3.34 mM for the various sludges examined. It was found that the toxicity of oleate to anaerobic sludges was not dependent upon the three biological factors. Instead, it was closely correlated to the specific surface area of sludge. Suspended and flocculent sludges, which have higher specific surface area, suffered much greater inhibition than did granular sludges. This paper suggests the use of granular sludges as appropriate inocula for reactors treating lipids (fats, oils and greases) wastewaters, to decrease the toxic impact from their hydrolysis products-LCFA.

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Influences of hydraulic retention time (HRT) on dechlorination of tetrachloroethene (PCE) were investigated in an upflow anaerobic sludge blanket (UASB) reactor inoculated with anaerobic granular sludge non-pre-exposed to chlorinated compounds. PCE was introduced into the reactor at a loading rate of 3 mg/l d. PCE removal increased from 51+/-5% to 87+/-3% when HRT increased from 1 to 4 d, corresponding to an increase in the PCE biotransformation rate from 10.5+/-2.3 to 21.3+/-3.7 micromol/d. A higher ethene production rate, 0.9+/-0.2 micromol/d, was attained without accumulation of dichloroethenes at the HRT of 4 d. Dehalococcoides-like species were detected in sludge granules by fluorescence in situ hybridization, with signal strength in proportion to the extent of PCE dechlorination.