Enhancing anaerobic digestion of nitrogen-rich substrates through in situ ammonia recovery using tubular gas-permeable membranes.

This study evaluated ePTFE gas-permeable membranes (GPM) to mitigate ammonia inhibition during anaerobic digestion (AD). Two semi-continuous laboratory-scale reactors were operated with swine manure and urea as nitrogen sources. One reactor was equipped with GPM for in situ ammonia recovery, while the other served as a control. Initially, methane yield (MY) remained stable at ∼ 200 L_CH4 kg_VS^-1. When free ammonia (FA) exceeded 500 mgN L^-1, MY declined by 50 %, and microbial inhibition intensified. At 700 mgN L^-1, inhibition reached 70 %, with increases in Clostridium_sensu_stricto_1, HN-HF0106, and Fastidiosipila. Methanosarcina remained dominant among archaea, showing greater tolerance to ammonium. After GPM activation, FA levels decreased and methane production recovered. The GPM system proved effective as both a preventive and corrective strategy, improving process stability and enabling ammonia recovery. These findings highlight the potential of GPM technology as a promising solution to enhance the robustness of AD treating nitrogen-rich substrates.