Probiotic effects of anaerobic co-digestion substrates

Manure is often added to stabilise anaerobic digesters especially when co-digesting high-energy substrates such as whey. While different researchers have attributed its beneficial effect to various components including alkalinity, nutrients or trace elements this research instead aimed to determine whether microorganisms, such as lactic acid bacteria which are naturally present in the feedstocks, were having a notable beneficial effect on biogas production. Casein whey and cow manure were co-digested with primary sludge and produced 151.1% biogas compared to the control reactor digesting primary sludge alone. It was found that targeting the microorganisms in the manure via autoclaving decreased reactor performance to only 112.8% compared to the control potentially indicating that the manure is providing a probiotic effect. It was also found that storing casein whey (which is needed to balance out its seasonal production peaks) produces microorganisms that play a similarly important role as evidenced by the decrease in performance from 151.1% to 112.9% when they were removed via filtration.