Optimizing anaerobic digestion of waste-activated sludge and dairy manure by pre- and post-hydrolysis with Caldicellulosiruptor species
Lignocellulose and peptidoglycans are recalcitrant to anaerobic digestion. The extremophilic bacterial process (EBP) uses anaerobic, hyperthermophiles in the Caldicellulosiruptor genus to enhance anaerobic digestion (AD) by increasing bioavailability of lignocellulose and peptidoglycans. Treatment with Caldicellulosiruptor species is a patented two-stage system in which hydrolysis can occur either before (pre) or after (post) AD. The potential impact of EBP on AD was evaluated by: 1) The increase in volatile fatty acids (VFA) from treatment with Caldicellulosiruptor bescii and four Caldicellulosiruptor species before and after AD of dairy manure and waste activated sludge (WAS). 2) The survival and activity of functionally essential AD microorganisms through EBP of dairy manure. 3) The decrease in volatile solids and shifts in microbial communities induced by EBP pre- and post-AD of WAS. EBP increased acetate ion concentrations by at least a factor of 2 in all configurations except post-AD WAS. EBP pre-AD with WAS demonstrated the most pronounced effect with acetate levels increasing 36-fold with the Caldicellulosiruptor consortium and 31-fold increase with C. bescii relative to controls. EBP pre-AD favored the activity of hydrogenotrophic archaea over acetoclastic archaea. Bacterial rather than archaeal species generally survived and remained more active. WAS volatile solids were halved without altering the AD microbial community in the EBP post-AD system. Overall, EBP proved to be an effective method to enhance AD efficiency of WAS and dairy manure with both pre-AD and post-AD.