A novel approach for enhancing nitrogen and hydrogen recovery from urine in microbial electrochemical gas-permeable membrane system.

Source-separated urine is a readily accessible nutrients dense waste stream that can be used to recover nitrogen and hydrogen. In the research, the microbial electrochemical gas-permeable membrane system (MEGS) is creatively introduced for urine treatment in removing organics, recovering the total ammonia nitrogen and high-value product of hydrogen (H2) as well as ammonium sulfate ((NH4)2SO4). MEGS can simultaneously realize the functions of H2 recovery, in-situ efficient alkali production at the cathode, and the efficient absorption capacity of the gas-permeable membrane (GPM). Under the action of the urease enzyme, urea is hydrolyzed into large amounts of carbonic acid and ammonium, causing the pH (7.87 ± 0.13) and conductivity (5.44 ± 0.21 mS cm-1) of the anode to increase extremely rapidly. A large amount of NH4+ was transported to the cathode chamber under the strengthening effect of the electric field, enriched, and then absorbed to produce the high-quality (NH4)2SO4 to be recovered. The findings reveal that MEGS can achieve 100 % of urea removal, 88.52 ± 0.40 % of COD removal, 94.22 ± 2.57 % of nitrogen recovery, 0.58 ± 0.03 m3 m-3 d-1 of hydrogen yield, and 3.78 kg m-3 of (NH4)2SO4 production with 78.03 ± 3.51 % of coulombic efficiency during a 30-h cycle. A benefit of $18.29 can be achieved with the recovery of (NH4)2SO4 and H2 from 1 m3 of urine. The study presents a promising idea for the efficient nutrient-energy recovery and utilization of urine.