Hydrochar alleviated the inhibitory effects of polyvinyl chloride microplastics and nanoplastics on anaerobic granular sludge for wastewater treatment

Abstract

The exposure to microplastics (MPs) and nanoplastics (NPs) has been confirmed to exhibit significant inhibitory effects on anaerobic granular sludge (AGS) for wastewater treatment, with effective mitigation strategies being accordingly imperative. Herein, this study innovatively proposed a strategy for mitigating inhibitory effects of MPs/NPs on AGS system based on coconut shell-derived hydrochar through efficiently capturing the existing polyvinyl chloride microplastics and nanoplastics (PVC-MPs and PVC-NPs) from AGS. The hydrochar increased methane production of AGS from 69.4% to 76.2% and from 65.6% to 91.4% of control when the AGSs were exposed to PVC-MPs and PVC-NPs, respectively. More extracellular polymeric substance (EPS) was secreted with the existence of hydrochar, which enhanced the protective capabilities AGS held to against the negative effects from the external toxicity of PVC-MPs and PVC-NPs, thus maintaining better AGS integrity regarding granule size and cell viability (especially for the PVC-NPs affected AGS). The hydrochar showed stronger adsorption capability to PVC-MPs and PVC-NPs than AGS, confirmed by their characteristics and adsorption kinetic tests. As a result, less plastic particles would attach AGS, inducing less oxidative stress to the microbes. Specially, it would also be less likely for PVC-NPs to penetrate through AGS surface and enter the internal core, retaining better richness of bacteria such as Bacteroidales and Syntrophobacterales in AGS. This work demonstrated hydrochar effectively alleviated the suppression on AGS caused by PVC-MPs and PVC-NPs, providing a novel strategy for improving the wastewater treatment performance under the stress of MPs and NPs.