The effect of C/N ratio on nitrogen removal in a bioelectrochemical system

The effect of C/N ratios of 2, 2.7, and 3.5 on nitrogen removal in a bioelectrochemical system (BES) was investigated. Starch was used as a carbon source for the electrogenesis phenomenon we observed in a previous study. The results showed that an increased C/N ratio helped the BES to remove nitrate and depress nitrite accumulation but did not increase autotrophic denitrification. Nitrate and total nitrogen removal were increased from 0.69 ± 0.02 g m−3 h−1 to 1.09 ± 0.16 g m−3 h−1, and from 0.52 ± 0.08 g m−3 h−1 to 0.97 ± 0.06 g m−3 h−1, respectively, when the C/N ratio was increased from 2.0 to 3.5. However, the autotrophic denitrification ratio decreased from 72.74% to 50.23% with the same increase in the C/N ratio. High C/N ratios postponed the excretion of soluble microbial products and increased electrogenesis, but did not improve the anode transformation efficiency.