The Fate of Microplastic in Wastewater Solids Treatment: Degradation of PE and PHB Microbeads in Aerobic and Anaerobic Digestion

Synthetic plastic microbeads, often found in personal care products such as face scrubbers and hand sanitizers, jeopardize aquatic life and the environment. The size and physical composition of microbeads makes challenging their removal by wastewater treatment plants, which thus discharge some microbeads with effluent into the environment. US legislation recently banned the use of synthetic and biodegradable microbeads, though the fate of biodegradable microbeads has not been proven to be the same as synthetic microbeads.Microcosm experiments were performed to investigate the degradation of PE and PHB microbeads in municipal biological wastewater treatment sludge. PE or PHB microbeads were incubated in 80 mL of activated sludge (MLSS), return activated sludge (RAS), aerobic digester sludge (AerD) and anaerobic digester sludge (AnD) for 2-23 days. Results showed partial degradation of PHB microbeads in all sludges after 16-day incubation in MLSS, RAS, AerD, and AnD with weight percent recoveries of 72%, 48%, 27%, and 13%, respectively. PE microbeads did not degrade in biological wastewater treatment microcosms. These results affirm that the fate of biodegradable polymers differs from synthetic plastic in wastewater treatment.