Energetic valorization of ammonium resulting from nitrate electrochemical reduction-Feasibility of biohydrogen production

The main objective of this work was to examine the feasibility of coupling electrochemical and biological processes to destroy nitrate ions (NO3-) while producing biohydrogen. In this integrated process NO3- was firstly converted to ammonium using an electrochemical flow cell. After only one pass of concentrated nitrate solutions (3 gNO(3)(-) L-1) through the flow cell, ammonium ions selectivity of 98.8%, corresponding to 0.86 g NH4+ L-1 was recorded. The obtained ammonium solution was then tested as a nitrogen source to produce H-2 in a batch system involving heat-treated aerobic activated sludge. In the optimal conditions corresponding to pH 5.5 and initial glucose concentration of 15 g L-1, consumption yields were 97% and 82% for ammonium and glucose, leading to H-2 yield of 0.35 mol H-2 mol(-1) glucose consumed. The H-2 production was associated with acetic/butyric acids type fermentation. Obtained biogas contains only H-2 and CO2 and was free of methane, hydrogen sulphide, and nitrous oxide. Therefore, the targeted objectives were achieved since on the one hand selective and quantitative conversion of NO3- to NH4+ was shown and on the other hand the obtained NH4+ was completely assimilated by activated sludge with the production of biohydrogen, a clean energy carrier. (C) 2014 Elsevier By. All rights reserved.