Microplastics into vermi-wetland lower the treatment performance of organic substances and antibiotic resistance genes in excess sludge

Abstract

This study aimed to investigate the effects of MPs on the decomposition of excess sludge and reduction of antibiotic resistance genes (ARGs) in a vermi-wetland. For this, the polymethyl methacrylate (PMMA) MPs added into excess sludge were treated by a vermi-wetland inoculated by earthworms Eisenia fetida and wetland plant Acorus calamus. The results showed that the growth rates of plants and earthworms were significantly inhibited in the vermi-wetland added with MPs. The average removal rates of chemical oxygen demand and total solids for excess sludge in vermi-wetland added MPs decreased by 15.36% and 38.00%, respectively, compared to the control without adding MPs. Moreover, the abundance of 16 S rDNA and 18 S rDNA inside vermi-wetland with MPs enriched by 53.61% and 75%, respectively. In addition, the median removal rate of selected ARGs in sludge declined by 15.75%−34.27% in the MPs added vermi-wetland. Compared to the control, the MPs enhanced the mobile genetic elements of intI 1 and tnpa-04 abundance inside the vermi-wetland by 44.79% and 53.33%, respectively, which were separately attached on the MPs surface at 25.62 ng/g and 7.26 ng/g. This study suggests that the addition of MPs into vermi-wetland reduced the removal efficiency of organic substances and ARGs in the excess sludge.