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This study demonstrates a 2-stage bioelectrochemical system (BES) for autotrophic denitrification of nitrate-contaminated groundwater. Operating at 75.6 mgNO₃⁻-N L⁻¹NCC d⁻¹, the sequential system achieved >93% nitrate and total nitrogen removal, producing effluent compliant with EU/USA drinking water standards. The first stage removed bulk nitrate but accumulated nitrite and nitrous oxide intermediates; the second stage polished these intermediates. Specific energy consumption was 18.80 kWh kgNO₃⁻-N⁻¹, competitive with reverse osmosis and electrodialysis technologies.

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Abstract

Nitrate groundwater contamination is an issue of global concern that has not been satisfactorily and efficiently addressed, yet. In this study, a 2-stage, sequential bioelectrochemical system (BES) was run to perform autotrophic denitrification of synthetic groundwater. The system was run at a 75.6 mgNO3−-N L−1NCC d−1 nitrate loading rate, achieving almost complete removal of nitrate (>93%) and Total Nitrogen (TN) (>93%). After treatment in the first stage reactor values of effluent nitrate compatible with the EU and USA limits for drinking water (<11.3 and 10 mgNO3−-N L−1, respectively) were achieved. Nitrite and nitrous oxide were observed in the first stage’s effluent, and were then successfully removed in the second stage. The observed nitrate removal rate was 73.4 ± 1.3 gNO3−-N m−3NCC d−1, while the total nitrogen removal rate was 73.1 ± 1.2 gN m−3NCC d−1. Specific energy consumptions of the system were 0.80 ± 0.00 kWh m⁻³, 18.80 ± 0.94 kWh kgNO3−-N−1 and 18.88 ± 0.95 kWh kgN−1. Combination of two denitrifying BES in series herein described proved to be effective.

Keywords

NitrateDenitrificationEffluentNitriteDenitrifying bacteriaNitrous oxide

Identifiers

DOI
10.3390/w11050959
Journal
Water
Year
2019