Highlights
• A bioelectrochemical system is developed for nitrate removal from groundwater.
• Nitrate is moved from groundwater into an anode driven by an electric potential.
• Nitrate is reduced to nitrogen gas via heterotrophic denitrification.
• The present system remove nitrate from both synthetic and actual groundwater
. Abstract
This research aims to develop a new approach for in situ nitrate removal from groundwater by using a bioelectrochemical system (BES). The BES employs bioelectricity generated from organic compounds to drive nitrate moving from groundwater into the anode and reduces nitrate to nitrogen gas by heterotrophic denitrification. This laboratory study of a bench-scale BES demonstrated effective nitrate removal from both synthetic and actual groundwater. It was found that applying an electrical potential improved the nitrate removal and the highest nitrate removal rate of 208.2 ± 13.3 g NO3−-N m−3 d−1 was achieved at 0.8 V. Although the open circuit condition (no electricity generation) still resulted in a nitrate removal rate of 158.5 ± 4.2 g m−3 d−1 due to ion exchange, electricity production could inhibit ion exchange and prevent introducing other undesired ions into groundwater. The nitrate removal rate exhibited a linear relationship with the initial nitrate concentration in groundwater. The BES produced a higher current density of 33.4 A m−3 and a higher total coulomb of 244.7 ± 9.1 C from the actual groundwater than the synthetic groundwater, likely because other ions in the actual groundwater promoted ion movement to assist electricity generation. Further development of this BES will need to address several key challenges in anode feeding solution, ion competition, and long-term stability.
4. Conclusions
This study has demonstrated the feasibility of using a bench-scale bioelectrochemical system to remove nitrate from groundwater. The BES effectively attracted nitrate out of groundwater driven by electricity generation and reduced it to nitrogen gas in the anode compartment via heterotrophic denitrification. Applying an external electric force improved the nitrate removal, and it was found that 0.8V resulted in the highest nitrate removal rate. In addition to electricity generation, ion exchange was another majormechanismofnitratemigrationinto theBES anode, andthere was competition between electricity-driven and ion exchangedriven nitrate movement, in which an electricity-driven process could inhibit the ion exchange process. The ion exchange process was also affected by the ionic concentration in the anolyte. The nitrate removal rate linearly increased with the increasing nitrate concentration in groundwater. The BES also achieved successful nitrate removal from actual groundwater sampled from a well in the state of Wisconsin. Further development of the BES for in situ nitrate removal from groundwater must consider the challenges such as the selection of anode substrates, the competition between nitrate and other anions, the long-term system performance, the reactor scaling up, and the economic evaluation of this approach.
