Biodegradable Microplastics in Municipal Wastewater and Sludge Treatment Processes: A Review on Occurrence, Fate, and Effects

Abstract

Biodegradable plastics have emerged as reliable alternatives to conventional plastics for alleviating global plastic pollution. However, biodegradable plastics could also rupture into microplastics and inevitably accumulate in wastewater treatment plants (WWTPs). The fate and effects of biodegradable microplastics (BMPs) in wastewater treatment and sludge disposal processes are of great concern but have not yet been reviewed. This review comprehensively expounded the occurrence, fate, and consequential effects of BMPs in WWTPs. Specifically, the environmental contents of BMPs and the corresponding detection techniques were analyzed and compared with conventional microplastics. Furthermore, the mechanical aging, additive release, extracellular hydrolysis, and microbial biotransformation of BMPs were documented meticulously. Also, the effects of BMPs on microbial community structure and function, as well as pollutant adsorption, were underscored. The obtained knowledge would update our understanding of the risk and control of BMPs in WWTPs. Recommendations for future investigations are made.

Biodegradable Microplastics Increase N2O Emission from Denitrifying Sludge More Than Conventional Microplastics

“…The popularity of biodegradable plastics might reduce plastic waste due to the advantage of biodegradability. However, evidence suggests that biodegradable plastics would result in more microplastics under natural conditions than conventional nonbiodegradable polymers. , For the first time, this work demonstrated that the BMPs that enter wastewater not only significantly weaken the denitrification performance regardless of whether there is sufficient carbon but also lead to more N 2 O emission than conventional NBMPs at a COD:N ratio of <4:1, because of intensified electron competition and regulated electron distribution, which has important implications for fully understanding the potential impacts of microplastics on wastewater treatment and greenhouse gas emission. Despite the lower resistance to decomposition, BMPs had more severe impacts on denitrifying sludge and N 2 O emission than did NBMPs.…”

“…As for BMPs, there are different mechanisms responsible for the negative impacts, because, by contrast, the biocidal effect, ROS overproduction, and membrane damage were hardly detected. It is generally believed that NBMPs are extremely resistant to degradation in a biological wastewater treatment system because of the short solid retention time. , However, BMPs are more likely decomposed because these biodegradable polymers can be used as slow-release carbon sources during solid-phase denitrification . There might be some organic degradation intermediates of BMPs, providing a reasonable explanation for the significantly higher relative content of the fluorescent component [excitation and emission wavelengths of 251 nm (331 nm) and 415 nm, respectively] in the effluent (Figure S17).…”

“…Plastic pollution has been a significant subject in terms of the global environment and human health in recent decades, especially raising public concern since the discovery of emerging microplastics (<5 mm plastic particles). , This modern contaminant with high persistence is ubiquitous in aquatic, terrestrial, and atmospheric systems, originating from the fragmentation of plastic products or from direct emissions of manufactured microbeads. − Biodegradable plastics have been proposed as promising substitutes for conventional synthetic polymers to alleviate plastic pollution. However, complete degradation of biodegradable plastics is rarely achieved under natural conditions. , Even worse is the fact that more biodegradable microplastics (BMPs) are generated during the environmental aging of polymers. , In addition, BMPs can be fragmented faster into nanoplastics (<100 nm plastic particles) when exposed to environmental stressors such as physical wear, chemical oxidation, biofouling heat, and sunlight irradiation. , Although both microplastics and nanoplastics can be transformed into dissolved organic carbon in aquatic systems, the latter in most cases has more adverse impacts on organisms than the former . In addition, compared to conventional nonbiodegradable microplastics (NBMPs), BMPs have more oxygen-containing functional groups and relatively higher polarity, being more likely to interact with polar organic pollutants and activated sludge. , Thus, environmental risk assessment and eco-impact investigation of BMPs are urgent and challenging.…”