Development of Novel Bioelectrochemical Systems for in Situ Nitrate Removal from Groundwater

Abstract

This study aims to develop new approaches for in situ nitrate removal from groundwater by using bioelectrochemical systems (BES). BESs employ bioelectricity generated from organic compounds to drive nitrate moving from groundwater into the electrode chamber and reduce nitrate to nitrogen gas by heterotrophic denitrification. In first phase experiments, nitrate ions were driven into the anode chamber of a de-coupled reactor, whose electrode chambers were separated, where heterotrophic denitrification took place with organic reduction. It was proved that by applying additional electrical potential at 0.8V, the reactor could achieve highest removal rate of 208.2±13.3 g NO3--N/m3/d, when initial nitrate concentration in synthetic groundwater well is around 20 mg/L. Removal rate appeared a linear relationship with the initial nitrate concentration in groundwater. Electricity not only enhanced nitrate removal rate but also could inhibit ion exchange and prevent introducing other undesired ions into groundwater. In second phase experiments, the BES reactor was modified to single tubular. Nitrate ions transport across anion exchange membrane (AEM) into a mid-chamber between anode chamber and cathode, where they were concentrated and finally lead into anode chamber to be biological denitrificated. The slower mid-chamber water flowing, the less cost would be for operation and the flow rate affect slightly to nitrate transport. It was found that nitrate concentration could reach equilibrium after about 17 hrs. Protons produced from cathode reaction were more likely travel across AEM into mid-chamber, which restricted nitrate ions' movement. The BES was also proved feasible when applying in real groundwater and tended to produce more coulomb of charge. Further development of this BES will need to address several key challenges