NNitrate treatment is regulated throughout water treatment plants, however, groundwater sources, the primary domestic water supply for over 90% of the rural population and 50% of the total population of North America, are not as controlled. With groundwater sources being the only viable drinking source for many of these locations, sustainable treatment technology needs to be in place to mitigate the contamination. The BIO-NIX system is comprised of (i) a citric acid-loaded anion exchanger that slowly releases citric acid as the carbon source; (ii) a fixed-film bed that attaches denitrifiers to a media for biological denitrification; and (iii) a nitrate-selective anion exchanger that removes any additional nitrate passing through the fixed-film column. The purpose of BIO-NIX is to combine the kinetics of ion exchange with the sustainable removal of nitrate to nitrogen gas without use of brine as the nitrate-selective resin regenerates itself safely using self-elution. With synthetic groundwater contaminated with nitrate, BIO-NIX was tested for efficient removal of nitrate to below the MCL of 45 mg/L NO3-. Throughout 500 BV of synthetic groundwater passing through BIO-NIX, the nitrate effluent concentration did not exceed the MCL. The fixed-film column performed majority of the nitrate removal and the ion exchange column polished the removal efficiency. Comparatively, using the same synthetic groundwater, the ion exchanger alone shows the nitrate effluent concentrations remain below the MCL for approximately 350 BV. Overall, BIO-NIX outlasts the ion exchange column and provides the same removal efficiency (~90% removal) without regeneration required. BIO-NIX was tested for various interruptions including an interruption in carbon source dosing, influent nitrate concentration fluctuations, and increase in flow rate. As a result, BIO-NIX continuously ran during each interruption, and the biological degradation column performed most of the nitrate removal while the ion exchange column served as a polishing step and as a dampener during interruption periods. The effluent nitrate concentrations following the ion exchange column did not mirror the effluent nitrate concentrations following the biological column, showing that ion exchange capacity can change based on the influent concentration leading into the ion exchange column. Note that the ion exchange bed was not regenerated at all during the entire 3000 BV run.

Enhanced nitrate removal in groundwater using a biological ion exchange process without regeneration (BIO-NIX)

ACS Spring 2022

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