Roles of acid-producing bacteria in anaerobic digestion of waste activated sludge

Three acid-producing strains were isolated and identified. The isolated bacteria accelerated the anaerobic digestion processes. Bacillus coagulans improved TCOD removal, VS removal and biogas production. The optimal inoculum concentration of Bacillus coagulans AFB-1 was 30%. Three acid-producing strains, AFB-1, AFB-2 and AFB-3, were isolated during this study, and their roles in anaerobic digestion of waste activated sludge (WAS) were evaluated. Data of 16S rRNA method showed that AFB-1 and AFB-2 were Bacillus coagulans, and AFB-3 was Escherichia coli. The removal in terms of volatile solids (VS) and total chemical oxygen demand (TCOD) was maximized at 42.7% and 44.7% by inoculating Bacillus coagulans AFB-1. Besides, the optimal inoculum concentration of Bacillus coagulans AFB-1 was 30% (v/v). Solubilization degree experiments indicated that solubilization ratios (SR) of WAS reached 20.8%±2.2%, 17.7%±1.48%, and 11.1%±1.53%. Volatile fatty acids (VFAs) concentrations and compositions were also explored with a gas chromatograph. The results showed that VFAs improved by 98.5%, 53.0% and 11.6% than those of the control, respectively. Biochemical methane potential (BMP) experiments revealed that biogas production increased by 90.7% and 75.3% when inoculating with Bacillus coagulans AFB-1 and AFB-2. These results confirmed that the isolated acid-producing bacteria, especially Bacillus coagulans, was a good candidate for anaerobic digestion of WAS.