Biodegradation of polyethylene terephthalate microplastics by bacterial communities from activated sludge

The emerging accumulation of microplastics (MPs) in global waters is of increasing concern and it is posing great health risks to both humans and aquatic species, yet suitable technologies to remove MPs are lacking. The objective of this study was to investigate activated sludge as a source of promising biocatalysts for the removal of MPs in water. Bacterial communities in activated sludge were first screened for their potential to degrade hydrolyzable plastics from polyethylene terephthalate (PET) pre-treated at 100 degrees C for 1 hour. The consortium grew on a mineral medium with PET MPs as the sole carbon and energy source. To further assess its degrading potential, the consortium was put through a standardized CO2 evolution test at a temperature of 30 degrees C, pH 7-7.5, reactor residence time 168 days, and PET concentration of 2.63 g/L. The biodegradation extent was further validated through assessment of morphological/structural changes on the PET by means of SEM, DSC, FTIR, and viscometry analyses. Upon incubation, the consortium degraded 17% of PET. The molecular weight remained unchanged, reflecting a degradation via surface erosion. Furthermore, the biodegradation was significantly enhanced at high oxygen flow rates. Two bacterial strains within the consortium were isolated and identified as Bacillus cereus SEHD031MH and Agromyces mediolanus PNP3. Both strains thrived when individually cultured with PET while only B. cereus showed enzymatic activity during a clear-zone test. The examined bacterial strains possess a promising PET-degrading activity that can be further investigated and applied to the elimination of MPs water/wastewater through innovative and effective technologies.

Automated summary

This study explores the potential of activated sludge as a source of biocatalysts for the removal of microplastics in water. The bacterial consortium in the activated sludge was found to degrade 17% of PET microplastics, with two isolated bacterial strains showing promising PET-degrading activity, particularly Bacillus cereus which exhibited enzymatic activity.