Comparative evaluation of activated sludge and electrocoagulation for microplastics removal from sewage

Abstract

Microplastics (MPs) are persistent emerging contaminants of global concern due to their potential ecological and human health risks. Sewage Treatment Plants (STPs) represent major pathways for MP discharge into aquatic environments, while conventional treatment processes are often insufficient for their complete removal, especially at small size ranges. In this study, influent and effluent samples were collected from an STP in Kafr Saad City, Damietta Governorate, Egypt, to evaluate the occurrence, characteristics, and removal efficiency of MPs. Identification was performed using visual inspection, stereomicroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and SEM–energy dispersive X-ray spectroscopy (SEM-EDX). Electrocoagulation (EC) was applied as a post-treatment using aluminum anodes and stainless-steel cathodes. The influent of STP contained 136 MPs/L, dominated by fibers (55.1%) and fragments (16.9%), while the effluent of STP after activated sludge treatment contained 23 MPs/L, corresponding to 83.1% removal. After EC treatment, MP concentrations decreased to 12 MPs/L in the influent and 2 MPs/L in the effluent, achieving over 91% removal. FTIR and SEM-EDX confirmed polyethylene and polypropylene as predominant polymers. The results highlight the limitations of conventional STPs and demonstrate EC as an effective post-treatment strategy for MP mitigation.