Electrochemical recovery of H2 and nutrients (N, P) from synthetic source separate urine water.

Abstract This study examined an electrochemical method of H2 production and nutrient recovery from synthetic source separated urine (SSU). The efficacy of H2 production was examined through hydrogen recovery experiments (HRE) using Ni foam electrodes. Similarly, nutrient (N and P) recovery was also examined in post-nutrient recovery experiments (NRE) with sacrificial Mg electrodes. To achieve higher nutrient recovery in the post-nutrient recovery process, the most important operating parameters (initial solution pH (pHi) and current density) were optimized. Optimization of NRE revealed that > 90% NH3-N and PO43--P could be recovered at 8 mA cm-2 with a pHi of 6 to 8. Notable NH3-N and PO43--P reduction were observed at an equimolar Mg2+ dissolution ratio (1:1) of Mg2+:NH4+ and a 1.1:1 ratio of Mg2+:PO43- respectively. However, poor total Kjeldahl nitrogen (TKN) reduction was observed. Thus, we anticipate that direct electrochemical conversion of urea to N2 at the anode followed by H2 generation at the cathode is a more sustainable way to reduce TKN. Batch HRE showed that the initial TKN, 1094 mg L-1 (934 mg L-1 from urea-N and 160 mg L-1 from NH4Cl), was significantly reduced to 360 mg L-1 by Ni-Ni electrolysis, whereas around 53.8 g H2 gas was received from this Ni-Ni electrolysis system with a flow rate of 5 – 5.8 g mol-1 day-1. Overall, this work produced a 68% reduction in TKN due to electrochemical conversion of urea into H2.