Hydrogen-dependent denitrification: preliminary assessment of two bio-electrochemical systems

An autotrophic biological process for the treatment of nitrate-contaminated drinking water was studied in the laboratory, with the objective of develo ping a continuous system which would be simple, stable and amenable to upsc aling. Hydrogen generated by electrolysis of the water to be treated was th e source of energy for denitrifying microorganisms. Two main process config urations were compared: (1) a single reactor where both the generation of h ydrogen and denitrification took place. and (2) a two-reactor system where water was first enriched with hydrogen in an electrolysis cell prior to ent ering a packed-bed bioreactor. The reactors were operated in a continuous m ode and granulated activated carbon served as physical support for the biom ass. Although the highest rates of denitrification (0.45 kgN m(-3) d(-1)) a nd the shortest residence times (removal of 18 mg N l(-1) in 17 min) were o btained in the single-reactor system, the two-reactor system was more stabl e and more suitable for upscaling.