The volume of wastewater produced by intensive pig farming in such areas as Okinawa (Japan) surpasses the capacity available land for treatment and recycling. Nitrate contamination of wastewater is concern because of its negative effects on human and environmental health. A cathodic bioelectrochemical denitrification system is a modified form of a conventional microbial fuel cell operated with an anode as a power source for microbial nitrate reduction. We sought to optimize the performance of electrotrophic biocathodic denitrification using aerated swine wastewater (nitrified) and activated sludge as inoculum. The two-chambered bioelectrochemical reactors were evaluated in a batch mode at cathode potentials in the range of -0.397 to 0.797 V vs. SHE. The average nitrate removal rate was increased from 20 mg NO_3~-N m~(-3) d~(-1) (open circuit potential mode) to 38 mg NO_3~--N m~(-3)d~(-1) (applied potential to -0.597 V vs. SHE) using cation exchange membranes. Switching to anion exchange membranes accelerated the removal rate to 77.5 mg NO_3~--N m~(-3)d~(-1). Known bacterial genera capable of denitrification, such as Leptothrix, Mycobacterium, Bordetella, and Mesorhizobium, occurred in relatively higher abundance on the cathodes. Moreover, the system simultaneously eliminated organic compounds from the raw wastewater in the anode chamber to a suitable discharge level.
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