Anaerobic toxicity and degradability of oleic acid under mesophilic and thermophilic conditions
1997
Hwu, C.S. | Lier, J.B. van | Lettinga, G. (Wageningen Agricultural Univ. (Netherlands). Dept. of Environmental Technology)
Oleic acid, one of the major products of lipid hydrolysis, causes serious problems in anaerobic reactors treating fats-, oils- and greases-containing wastewaters. To secure useful information for optimizing treatment processes, toxicity and biodegradability tests with oleic acid were conducted at three different temperatures (30, 40 and 55 degrees) by using temperature-acclimated anaerobic granular sludges as inocula. Methanogenesis from acetate under thermophilic conditions (55 degrees) was found to be more susceptible to oleate toxicity than under mesophilic conditions (40 and 30 degrees). Fifty percent inhibition concentrations (IC50) of oleate were 0.70, 2.01 and 2.75 mM, respectively, at 55, 40 and 30 degrees. In contrast, increasing degradability was achieved with increasing temperatures. Complete mineralization of oleate to methane was attained with the specific degradation rates of 124, 41 and 33 mg oleate-COD/g VS.d at 55, 40 and 30 degrees, respectively. Moreover, inhibited methanogenic activity of the granular sludge recovered more rapidly under the thermophilic conditions at concentrations exceeding 1.97 mM. Considering an appropriate selection between thermophilic and mesophilic treatment, the contradictory effect of temperature on oleic toxicity and degradability is discussed.
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