[Effect of Cu2+ on Denitrification Using NO2- as an Electron Acceptor].

The short-cut biological nitrogen removal process has been widely used in industrial wastewater treatment, and denitrification is a crucial step for removing nitrogen on which the effect of Cu2+, a common heavy metal ion in wastewater, has not been studied. In this study, sludge with good short-range biological nitrogen removal characteristics in an A/O reactor was selected to investigate the short-term and long-term effects of Cu2+ on denitrification using NO2- as an electron acceptor. The results showed that Cu2+ had a significant inhibitory effect on denitrification process using NO2- as an electron acceptor, and the semi-inhibitory concentration EC50 of sludge activity was 4.79 mg·L-1. In the long-term experiment, the concentration of Cu2+ was gradually increased. When the concentration of Cu2+ was 0.5 mg·L-1and 1 mg·L-1, the denitrification activity of the sludge could be restored to the original level after acclimation. When the concentration of Cu2+ was increased to 3 mg·L-1, the denitrification performance was destroyed and difficult to recover, at which point the NO2--N removal rate was reduced to less than 10% and the denitrification system was severely inhibited. However, there was some recovery of sludge denitrification capacity after the addition of Cu2+ had been stopped for 14 days. At the same time, during the long-term effect of Cu2+, the EPS content increased, which played an important role in protecting the microorganism against Cu2+ toxicity, and increased the sludge particle size and, as a result, sludge sedimentation.

Achieving advanced nitrogen removal from low C/N wastewater by combining endogenous partial denitrification with anammox in mainstream treatment.

Successful application of mainstream anammox would be favorable for energy- and resource-efficient sewage treatment. This study presents a new strategy to achieve mainstream anammox, which combined with endogenous partial denitrification (EPD) for treating sewage wastewater. In this EPD-Anammox system, nitrite was stably produced by EPD with a nitrate-to-nitrite transformation ratio of 80%. Through adjusting the volume exchange ratio of EPD-reactor after anaerobic reaction, a suitable NO2--N/NH4+-N ratio of ∼1.20 for anammox reaction was achieved. Further, results showed a stable, high nitrogen removal efficiency (90%) with an effluent total nitrogen of 5.8 mg N/L under low C/N (∼2.9). Anammox contributed 49.8% of the overall nitrogen removal owing to the steady nitrite supply from EPD. Denitrifying glycogen-accumulating organisms (GAOs, 36.6%) having potential for endogenous denitrification and Candidatus Brocadia (34.6%) were respectively dominated in the EPD-SBR and anammox-UASB and responsible for the high nitrite accumulation and anammox reaction.

Effects of salinity build-up on the performance and microbial community of partial-denitrification granular sludge with high nitrite accumulation.

High inorganic salts inevitably impose a toxic impact on biological treatment processes. In this study, the effect of salinity on the performance and microbial community structures of partial-denitrification (PD) was firstly investigated. Results showed the denitrifying activities of non-domesticated PD sludge were completely inhibited under a temporary high salinity (≥1.5 wt%). However, after domestication, denitrifying activities maintained above 50% of the maximum with salinity build-up step-by-step from 0.0 wt% to 3.0 wt%. High nitrite production was stably achieved during 120 days with nitrate-to-nitrite transformation ratio around 90%. Further investigation showed extracellular polymeric substances content of PD sludge increased from 184.59 mg gVSS-1 to 560.64 mg gVSS-1, accompanied by the elevation of average particle size. This occurred against high salinity as a protective response of PD bacteria. Moreover, Thauera, the functional bacteria of PD system, was still dominant with the relative abundance increasing to 83.36% (3.0 wt%) from 51.33% (0.0 wt%).