Fatty Acid Degradation as a Tool to Monitor Anaerobic Sludge Activity and Toxicity
In anaerobic digester systems propionate and butyrate are thought to be the major intermediates of the hydrolysis-fermentation stage." Butyrate degraders can utilize butyrate, valerate, and other higher molecular weight fatty acids as substrates. Some of these acetogens can also utilize branched volatile fatty acids (VFA) such as isobutyrate and 2-methylbutyrate. Known butyrate degraders such as Syntrophomonas sp. and Clostridium sp.8, I2-l5 do not utilize propionate. Syntrophic propionate degraders including Syntrophobacter wolini and other unspeciated s t r a i n ~ ~ , ' ~ use propionate as substrate but not butyrate or other VFAs. Other specific syntrophic acetogens such as isovalerate degraders,I6 benzoate-degraders17 also exist in anaerobic ecosystems, but are much less important than propionate and butyrate degraders in number and substrate turnover. It is reasonable, therefore, to describe the syntrophic bacteria as two sub-trophic groups, propionate degraders and butyrate degraders. The growth rates of these syntrophic acetogens is quite slow. Approximate doubling times
Organic Matter U 1 1
of 2-3 days and 5-7 days, have been reported for the butyrate and propionate degraders, respectively.