Regular articleBiocathode denitrification of coke wastewater effluent from an industrial aeration tank: Effect of long-term adaptation

- Biocathode denitrification of coke wastewater effluent (CWE) was achieved.
- Direct exposure to CWE in the initial stage led to dramatic inhibitory effects.
- Long-term adaptation promoted recovery of active cells and electron transfer.
- The dominant cathodic denitrifiers were represented by genus Thiobacillus.

Despite recent advances in the development of autotrophic denitrification, wherein the electrode is used directly as the electron donor (known as biocathode denitrification), very little attention has been given to this approach for removal of nitrate in real industrial wastewater. This study shows that a bioelectrochemical reactor poised at −0.50 V (vs. a saturated calomel electrode (SCE)) achieved successful nitrate removal from coke wastewater effluent (CWE) sampled from an industrial aeration tank. The results show that direct exposure to CWE initially led to dramatic inhibitory effects, as evidenced by the observed lack of apparent cathodic current and small variations in the concentration of NO3−-N. However, long-term adaptation of the biocathode to the CWE remarkably increased the rate of dinitrification, from 2.35 (Cycle 1) to 4.93 (Cycle 3), 14.4 (Cycle 7) and 16.5 mg NO3−-N L−1 d−1 (Cycle 10). Both confocal laser scanning microscopy (CLSM) and electrochemical impedance spectrometry (EIS) characterizations provided evidence that long-term adaptation can induce recovery of active cells and promote electron transfer between the bacteria and the cathode. Analysis of bacterial structures suggests that cathode-driven autotrophic denitrifiers represented by Thiobacillus play an important role in nitrate reduction.

103