Bioaugmentation of anaerobic wastewater treatment sludge digestion: A perspective on microplastics removal

Abstract

Wastewater treatment sludge as a sink of microplastics is also a source of microplastics in the environment through agricultural biosolids application. Sludge treatment includes an anaerobic digestion step where bioaugmentation can be performed to concurrently boost biogas/methane production while degrading microplastics. This article aims to provide a perspective on the bioaugmentation of anaerobic sludge digestion to enhance microplastics removal based on the current available studies on microplastics-degrading anaerobes and bioaugmentation of anaerobic sludge digesters for improved methane and biogas production. It also examines the very limited existing work on bioaugmentation of anaerobic sludge digestion to remove microplastics. Numerous anaerobes such as Holomonas and Cloacamonales have been identified to have microplastics-degrading ability. In view of the complexity of sludge anaerobic digestion, this perspective article highlights the potential of Clostridium sp. which is involved in acetogenesis and has been successfully genetically engineered for microplastics biodegradation as a feasible candidate for bioaugmentation. It is of the opinion that microbial consortia derived from sludge or wastewater treatment plants offer the benefits of improving anaerobic digestion and degradation of a wider range of microplastics, especially after genetic engineering and acclimatization with volatile fatty acids and microplastics degradation. It also deems that bioaugmentation is cost-effective and could be integrated with the existing sludge treatment process though bioaugmentation of anaerobic sludge digestion is limited by the lack of pilot- and full-scale studies to enable better evaluation of its feasibility. A certain reliance on recombinant anaerobes may pose unknown risks upon their entry into the environment.