Bioelectrochemical extraction of ammonium from low-strength wastewater with concomitant generation of high-purity hydrogen

Bioelectrochemical systems (BES) are emerging environmental biotechnology for recovering ammonia from waste streams. It has been tested extensively for treating ammonium-rich wastewater. This study examined the suitability of BES to facilitate carbon removal and ammonium extraction from a low ammonium liquor (3.7 mM) that mimics municipal wastewater, and concomitant production of high-purity hydrogen gas, which could potentially be harnessed as a fuel or internally recycled for ammonia stripping. Results showed that a two-chamber cation exchange membrane-equipped BES enabled a high hydrogen yield (22.8 m3 H2 m−3 d−1; > 98% cathodic efficiency) and chemical oxygen demand (COD) removal (80%; 2.43 kg COD m−3 d−1 at a hydraulic retention time of 4.4 h). However, for the treatment of wastewater, the system demanded high energy (2.3 kWh kg COD−1; 152 kWh kg−1 N removed) and base for pH adjustment. The technology may be more suitable for recovering ammonium from wastewaters with molar ammonium to BOD ratio closer to the desired stoichiometric ratio of four, and for waste streams containing sufficient alkalinity or pH-buffering capacity, eliminating the need for dosing cation-bearing alkali.