Independent of alkalinity addition: Ammonia recovery via gas permeable membranes driven by self-sustained alkalinity in anaerobic digestate with low-rate aeration

This research evaluated the efficacy of self-sustaining alkalinity driven gas permeable membrane (SSAD-GPM) in ammonia recovery under low-rate aeration. This research initially confirmed the role of HCO 3 − and CO 3 2− in enhancing alkalinity release and ammonia conversion. It was determined that providing alkalinity through HCO 3 − necessitates the consumption of inorganic carbon (IC), and highlighting the criticality of maintaining a HCO 3 − /NH 4 + ratio exceeding 1.0 to optimize ammonia removal efficiency (>90.5 %). Alkalinity via CO 3 2− involves a two-stage hydrolysis process, consuming IC only in the second phase. Then, comparing SSAD-GPM with alkalinity addition driven GPM (AAD-GPM) for real anaerobic digestate treatment, SSAD-GPM demonstrated an initial ammonia removal efficiency of 99.1 %, which reduced to 82.8 % after 40 days of operation. In contrast, the efficiency of AAD-GPM decreased to 62.6 %. Superior anti-fouling performance of SSAD-GPM, due to aeration-induced turbulence, mitigated concentration polarization and fouling. Efficiency was restored to 98.1 % post-cleaning with tap water. Lastly, this research assessed the alkalinity consumption and cost of various ammonia removal/recovery strategies, demonstrating that SSAD-GPM can substantially lower operating costs, yielding a net profit of $0.081/kg N. These findings underscore the potential of SSAD-GPM as a cost-effective approach for treating high ammonia‑nitrogen wastewater with sufficient self-sustaining alkalinity (HCO 3 − /NH 4 +  > 1.0).