Nitrate removal rate in a continuous column denitrification reactor using hydrogen generated by electrolysis with carbon anodes and stainless cathodes

Abstract

An autotrophic continuous denitrification process, using hydrogen generated by electrolysis with activated carbon anodes, was experimentally demonstrated to be an effective nitrate removal process. Several fixed bed columns with polypropylene packing and honeycomb shaped activated carbon anodes and stainless rod cathodes were set in a thermostat chamber at 30°C, and potassium nitrate enriched tap water as influent was supplied at various flow rates and electric currents. Although the anode is in the same column where microbial biomass grows, sufficient nitrate removal was observed. For example, almost complete removal of nitrate and nitrite was observed at a hydraulic retention time (HRT) as short as 1.8 h. A model assuming successive denitrification reactions and plug-flow process, nitrate reduction rate = k1[NO3−] [H2], and nitrite reduction rate = k2 [NO2−]H2]1.5 was proposed. Calculated results with k1 = 1.3 mmol−1 h−1 and k2 = 3.3 mmol−1.5•h−1 agreed well with all the experimental results.