Electroactive microorganisms enriched from activated sludge remove nitrogen in bioelectrochemical reactor

Abstract

The bioelectrochemical anaerobic nitrogen removal was demonstrated in an anaerobic batch reactor equipped with a pair of polarized bioelectrodes. The bioelectrochemical reactor was operated in sequential batch mode after inoculating activated sludge and polarizing the electrode to 0.6 V. The medium contains ammonium, nitrite, alkalinity and trace minerals, but no organic carbon source. By the repetitive sequential operation, simultaneous removals of ammonium, nitrite and alkalinity were improved, and the electrochemical activity of the bulk sludge was confirmed from the redox peaks of the cyclic voltammogram. This indicates that ammonia oxidizing exoelectrogens (AOE) and denitritating electrotrophs (DNE) were enriched more in the bulk solution. Biogas production that mainly consisted of nitrogen was observed from the bioelectrochemical reactor, and the minor components in the biogas were methane and carbon dioxide. This demonstrates that AOE use nitrite as an electron acceptor to oxidize ammonia. The requirements of nitrite and alkalinity for the removal of ammonia nitrogen are around 0.72 mg NO2-N/mg NH4-N and 1.73 mg as CaCO3/mg NH4-N, respectively, and nitrate was not produced as a by-product. The bacterial groups involved in the bioelectrochemical nitrogen removal are electroactive autotrophs and can be enriched from activated sludge by polarized electrode. This bioelectrochemical ammonia oxidation is a novel approach recommended for treatment of nitrogen-rich wastewater.