zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA The effect of shock loads of long chain fatty acids (LCFA) on the activity of granular methanogenic sludge was studied with capric acid as model substrate. The results show that inhibition is primarily related to the LCFA concentration; the LCFArbiomass ratio is less im portant. A lethal threshold LCFA concentration can be distinguished in reactors with identical physical and chemical conditions and inoculum properties: the acetogenic and methanogenic population is killed virtually completely when the concentration exceeds 6.7 to 9.0 mol/m 3 capric acid. The observed variation in the threshold level may be attributable to differences in mass transfer rate from liquid to granules in different experiments. At most, 0.2% of the acetotrophic methanogens survives, when the LCFA concentration in a methanogenic digester exceeds the lethal threshold level. Mass balance analysis shows that obligate hydrogen producing acetogenic bacteria and hydrogenotrophic methanogens re cover first, followed by acetotrophic methanogens. Recovery of aceto trophic methanogenesis can be described by exponential growth of a small number of survivors. Acetotrophic methanogens do not adapt to LCFA, neither after repeated exposure to toxic concentrations, nor after prolonged exposure to nontoxic concentrations. A low LCFA (lipid) concentration in the influent promotes faster growth of acetogenic bacteria capable of degrading LCFA.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res., 66, 40 (1994).

An organism, identified as an Alcaligenes sp., was isolated from an enrichment culture in which 1,4-dichlorobenzene served as the sole carbon and energy source. During growth with 1,4-dichlorobenzene in pure culture, stoichiometric amounts of chloride were released. Growth experiments and oxygen uptake rates with other chlorinated aromatic compounds revealed a high degree of specificity of the initial dioxygenase. cis-1,2-Dihydroxycyclohexa-3,5-diene oxidoreductase and 1,2-pyrocatechase, but not 2,3-pyrocatechase, were found in cell extracts, while 3,6-dichlorocatechol and (2,5-dichloro)muconic acid could be detected as intermediates during degradation of 1,4-dichlorobenzene. It is proposed that dioxygenases are involved in the initial steps of 1,4-dichlorobenzene degradation, while ring opening proceeds via ortho cleavage.