Stabilizing effect of acetate salts and in digestors receiving high levels of glucose

Abstract

Anaerobic digestors were fed daily with dairy cattle manure (5% total solids) augmented with 0-20 mM glucose and were monitored daily for gas volume and composition and volatile acid content. Propionate accumulated in digestors that were fed glucose at initial digestor concentrations of 10 mM or more. Digestors that received 14-20 mM glucose failed, but identical digestors that received 20 mM glucose plus 10 mM acetate or HCO3- did not fail. The sparing effect of HCO3- was primarily buffering and the similar behavior of digestors that received acetate suggests that acetate metabolism perhaps provided additional HCO3- for buffering. Analyses of H2 and volatile acid concentrations during a 6-8 h period following feeding in digestors fed glucose or glucose plus acetate showed that propionate and H2 accumulated simultaneously and that H2 concentrations were 3 .mu.M or less. Monitoring 13C-labeled glucose metabolism via 13C NMR indicated that glucose was primarily converted to lactate and that the major product from lactate was propionate in glucose and glucose plus acetate fermentations.