Fouling behavior of anion-exchange membrane during electrodialysis of biogas slurry: Correlation to applied current

Abstract

Electrodialysis draws recent attention toward valorization of biogas slurry, especially in terms of inorganic nutrient selectivity. Nevertheless, wide application of this process is impeded by organic fouling of anion-exchange membrane (AEM) dealing with such a complex stream, which lacks of a systematic investigation so far. Herein, AEM fouling by real biogas slurry under varying current density was delicately evaluated in terms of transmembrane electrical potential and membrane bulk resistance, beyond the conventional monitoring on dilute conductivity and solution pH for this desalination process. Our results showed that TMEP of the target AEM was very sensitive to the applied current, but a negligible variation of desalination rate and solution pH indicated a limited occurrence of water splitting. Then, the existence of apolar and large sized foulant in biogas slurry (probably the detected humic-like substances) and few salt crystals from the membranes together suggested that organic fouling was mainly responsible for the fouling issue. Finally, EIS data revealed Rm as the main component of membrane resistance for the fouled membrane, indicating a non-negligible internal fouling, which was also positively related to the applied current. Our result implied operating electrodialysis at a lower current density for biogas slurry is recommended from the perspective of membrane fouling mitigation and operation cost optimization in pursuit of long-term efficacy for nutrient recovery and valorization.