Bio-Aging of polyethylene during anaerobic and aerobic digestion

Presence of microplastics (MPs) in wastewater treatment plants (WWTPs) require scrutiny from two perspectives: impact of MPs on treatment and on MPs themselves. Accordingly, this study investigates the impact of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) on mesophilic aerobic and anaerobic digestion, with their concurrent characterization to discern MP biodegradation following digestion. HDPE having UV-stabilizer remains unchanged, whereas additive-free LDPE bio-ages, in both cases. On the flip side, HDPE negatively impacts anaerobic (i.e., 26 % reduction in methane) but not aerobic digestion, while LDPE affects neither. The very high LDPE doses used in our study (300 mg PE/g TS) yielding no negative impact on either aerobic or anaerobic digestion is notable. Lastly, bio-aging potential of PE is closely linked with amorphous/crystalline structure and presence/absence of additives. Such factors may affect microbial colonization, resulting in physical/chemical changes on the surface of PE and on digester operation.