[Formation and utilization of lactate during methane fermentation of cellulose]

The role of lactate was studied in the course of methane formation from cellulose by a mixed bacterial association. Lactate was accumulated in the medium during intensive degradation of cellulose and was assimilated in the period of active gas production. Glucose added to the medium was converted into lactate within 30 min. If lactate served as a substrate for a methane forming association which was previously cultivated in a medium containing cellulose, it was almost completely converted into methane; the lag phase was shorter than in the case of cellulose, while the rate of methane formation was higher. In the presence of sulfate in the medium, sulfate reduction preceded methane production from lactate. The combined culture Desulfovibrio vulgaris+Methanosarcina grew in the medium containing lactate, and completely converted it into methane. The formation of methane from lactate by the mixed microbial association can be attributed to the interaction between sulfate reducing and methane producing bacteria.