Biohydrogen production by coupling an electrochemical system with a biological treatment

The main objective of this work was to examine the feasibility of biohydrogen production using ammonium solution resulting from nitrate electrochemical reduction. In this coupled process a concentrated nitrate solution of 3g NO₃^-L^-1 was firstly converted to ammonium using a home-made electrochemical flow cell, leading to 97% ammonium selectivity. This solution was then used as a nitrogen source to produce H₂ in a batch system involving heat-treated aerobic activated sludge. Under proved optimal conditions, pH 5.5 and 15g L^-1 initial glucose concentration a hydrogen yield of 0.35 mol H₂/mol glucose was obtained, with total consumption of the produced ammonium. The obtained biogas contains only H₂ and CO₂ and was free of methane, hydrogen sulphide (H₂S) and nitrous oxide (N₂O).