Evaluation of separators for potential use in microbial electrolysis cells under anaerobic digester conditions

Abstract

This study presents the successful preparation of a novel chemically modified Cellophane separator with polydimethylsiloxane (PDMS) for potential use in microbial electrolysis cells (MECs) with real anaerobic digester effluent (ADE). The modified separator was assessed against commercial materials, including anion exchange membrane (AEM), cation exchange membrane (CEM), and unmodified Cellophane. They were evaluated in a conventional two-chamber electrolysis cell, serving as a surrogate for a MEC, and in a bioreactor to assess biofouling. The modified Cellophane demonstrated potential for reducing costs and enhancing separator performance. Cellophane, Cellophane + PDMS and AEM effectively prevented pH imbalances, maintaining stable anode pH levels above 7 without cathode alkalinization. However, the CEM was unsuitable due to excessive pH splitting (Δ6 pH) and elevated resistance. The study highlighted the pronounced impact of using real ADE on overpotentials and resistances of all separators. Organic acid crossover occurred across all materials, with Cellophane exhibiting higher rates (0.16–0.2 mg m⁻² s⁻¹) than CEM and AEM (0.04–0.1 mg m⁻² s⁻¹). An extensive investigation into biofouling and degradation under anaerobic digestion conditions revealed that unmodified Cellophane degraded completely within a month, whereas PDMS modification extended its durability to two months before complete disintegration occurred.