Simultaneous nitrification/denitrification in a single-chamber stainless steel bioelectrochemical reactor

The removal of nitrogen from wastewater with a low C/N ratio often requires additional carbon sources to address the shortage of electron donors, which increases the cost. We explored a simple and energy effecient means for treating wastewater with a high concentration of ammonia nitrogen under anoxic conditions without the addition of carbon sources. We constructed a stainless steel tube as an anaerobic single -chamber microbial electrolysis cell (MEC) for investigating autotrophic simultaneous nitrification/denitrification (SND). Two different structures (carbon brush vs. stainless -steel) were used to construct biocathodes and compared their performances under different voltages (1.8 V, 1.5 V, 1.2 V) applied by DC power. When voltage was applied at 1.5 V, the removal rates of TN and NH4+-N reached 19.68 +/- 0.02 mg L-1 d-1 and 21.04 +/- 0.17 mg L-1 d-1, respectively. Simultaneously, it achieved maximum TN and NH4+-N removal over 14 days (44.97 +/- 0.28 %, 48.16 +/- 0.32 %). These rates were 1.8 and 5 times of that obtained with the conventional carbon brush electrode and open -circuit control. Furthermore, microbial community and SEM analysis indicate that species of Thermomonas, Thibacillus and Thauera were the predominant autotrophic electroactive denitrifying bacteria in the reactors. Overall, we achieved a high rate of nitrogen removal, electron utilization and energy recovery in a singlechamber stainless steel MEC.