Investigation of the influence of Ni(ii) exposure on the simultaneous nitrification and denitrification of aerobic granules from an internal oxygen penetration perspective

Abstract

Lab-scale Sequencing Batch Reactors (SBR) were adopted to study the effects of Ni(ii) exposure on the simultaneous nitrification and denitrification (SND) of the aerobic granular sludge under different concentrations of Ni(ii) (1.0, 5.0 and 10.0 mg L−1). The degradation processes of chemical oxygen demand (COD) and nitrogen were investigated, as well as the SND efficiencies under various Ni(ii) exposure. The results showed that the low concentration of Ni(ii) (1.0 mg L−1) would stimulate degradation of COD and nitrification, while the high concentration of Ni(ii) (10.0 mg L−1) caused inhibition. Meanwhile, the denitrification process was inhibited throughout the whole period of adding Ni(ii). The highest SND efficiency was found under a 5.0 mg L−1 Ni(ii) exposure, suggesting the very close rates of the nitrification and denitrification. Additionally, the dissolved oxygen (DO) penetration depths of aerobic granules were calculated through the specific DO uptake rate test. The ratio of aerobic zones to anoxic zone in aerobic granules was also used to explain the SND efficiency variation under different concentrations of Ni(ii) exposure. It is apparent that the addition of Ni(ii) could effectively change the internal aerobic/anoxic zone in aerobic granules, thereby contributing to the variation of the SND process.