Methane yield and lag correlate with bacterial community shift following bioplastic anaerobic co-digestion

Past plastic management practices have resulted in pollution. An improved management scenario may involve adding used bioplastic to anaerobic digesters to increase methane for renewable energy. In this work, effects of polyhydroxybutyrate (PHB) bioplastic anaerobic co-digestion with synthetic primary sludge on operation and microbial communities were investigated. Co-digesters treating sludge were co-fed 20% untreated or pretreated (55 °C, pH 12) PHB. Pretreament resulted in shorter lag (5 d shorter) before methane production increased after co-digestion. At steady-state, co-digesters converted 86% and 91% of untreated and pretreated PHB to methane, respectively. Bacterial communities were different before and after bioplastic co-digestion, whereas no archaeal community change was observed. Relative abundance of 30 significant bacteria correlated with methane production and lag following PHB addition. No previously known PHB degraders were detected following PHB co-digestion. Microbial communities in anaerobic digesters treating synthetic primary sludge are sufficiently capable of co-digesting PHB to produce additional methane.