Effects of cobalt-histidine absorbent on aerobic denitrification by Paracoccus versutus LYM

To overcome the problem that ferrous complexes are easily oxidized by O₂ and then lose NO binding ability in the chemical absorption-biological reduction (CABR) process, cobalt(II)-histidine [Co(II)His] was proposed as an alternative. To evaluate the applicability of Co(II)His, the effects of CoHis absorbent on the aerobic denitrification by Paracoccus versutus LYM were investigated. Results indicated that His significantly promoted nitrite reduction. The inhibition effects of CoHis absorbent could be substantially alleviated by increasing the initial His/Co²⁺ to 4 or higher. CoHis with concentrations of 4, 8, 12, 16 and 20 mM presented no distinct effect on nitrite reduction, but slightly inhibited the reduction of nitrate, resulting in longer lag of nitrate reduction, and obviously promoted the growth of strain LYM. In the presence of 5, 10, 15 and 20 mM CoHis absorbent, the main denitrification product was N₂ (not less than 95.0%). This study is of significance in verifying the applicability of Co(II)His in the CABR process, and provides a referable CoHis absorbent concentration as 20 mM with an initial His/Co²⁺ of 4 for the future experiments.