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Bio-Aging of polyethylene during anaerobic and aerobic digestion
Summary
Researchers investigated how HDPE and LDPE microplastics affect aerobic and anaerobic digestion in wastewater treatment, while also characterizing whether the plastics themselves degrade. HDPE reduced methane production in anaerobic digestion by 26% but LDPE had no negative impact on either process, and only additive-free LDPE showed signs of bio-aging.
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.