Isomerization of n- and i-butyrate in anaerobic methanogenic systems.

Studies of the degradation of the two isomeric forms of butyrate in different anaerobic environments showed isomerization between n- and i-butyrate. Degradation rates were similar for the different examined systems and degradation rates for n-butyrate degradation were generally higher than for i-butyrate. Degradation rates for n-butyrate ranged from 0.52 to 1.39 day-1, while the rates for i-butyrate were from 0.46 to 1.15 day-1. Production of isomers was not observed when the volatile fatty acid degradation was inhibited by addition of bromoethane sulfonic acid, indicating that isomerization was coupled to the methanogenic degradation of the acid. The degree of isomerization observed during n-butyrate degradation was similar to the degree during i-butyrate degradation. Experiments indicated that the isomerization degree was higher for the thermophilic than for the mesophilic inocula.