Enzymatic remediation of polyester microfibers in sewage sludge and green compost samples

Abstract Microplastics are accumulating in all ecosystems worldwide, posing risks to biodiversity, environmental and personal health. In agricultural soils, an important source of microplastics is the application of contaminated biofertilizers such as sewage sludge and compost. Preventing micro and macro plastics from entering wastewater treatment plants (WWTPs) and compost heaps in the first place, and developing treatments for the removal of microplastics in these biofertilizers, would be a major step against microplastic pollution. In this article, a novel method for studying the potential of hydrolase enzymes as a bioremediation technique is described. Specifically, we investigated the LCC ICCG cutinase against poly(ethylene terephthalate) (PET) microfibers in buffered water, sewage sludge, and green compost, at their usual operating temperatures (55-70ºC). The assessment of biodegradation was carried out through monomer detection. Different enzyme loadings (0 – 300 µg); substrate concentrations (0 –200 mg/cm 3 ) and mixing methods (shaking – rotating) were tested. Up to 16.6 mg of PET per cm 3 of matrix were degraded in 24 h both in buffered water and sewage sludge, with slightly worse results in compost of maximum 13.9 mg/cm 3 . This difference might be attributed to the total water content of the samples, which is lower for compost. Additionally, in compost, rotational mixing slowed down degradation by 35% in comparison with shaking. The results are discussed in the context of existing limitations, cumulating in a series of recommendations for possible intervention points along the microplastic pollution chain.