Impact of soluble organic matter and particulate organic matter on anammox system: Performance, microbial community and N_(2)O production

In this study,the effects of soluble readily biodegradable COD(sCOD)and particulate slowly biodegradable COD(pCOD)on anammox process were investigated.The results of the longterm experiment indicated that a low sCOD/N ratio of 0.5 could accelerate the anammox and denitrification activity,to reach as high as 84.9%±2.8%TN removal efficiency.Partial denitrification-anammox(PDN/anammox)and denitrification were proposed as the major pathways for nitrogen removal,accounting for 91.3% and 8.7% of the TN removal,respectively.Anammox bacteria could remain active with high abundance of anammox genes to maintain its dominance.Candidatus Kuenenia and Thauera were the predominant genera in the presence of organic matter.Compared with sCOD,batch experiments showed that the introduction of pCOD had a negative effect on nitrogen removal.The contribution of denitrification to nitrogen removal decreased from approximately 14%to 3% with increasing percentage of pCOD.In addition,the analysis result of the process data using an optimized ASM1 model indicated that high percentage of pCOD resulted in serious N_(2)O emission(the peak value up to 0.25mg N/L),whichwas likely due to limited mass diffusion and insufficient available carbon sources for denitrification.However,a high sCOD/N ratio was beneficial for alleviating N_(2)O accumulation.

Effects of different external carbon sources and electron acceptors on interactions between denitrification and phosphorus removal in biological nutrient removal processes

The effects of two different external carbon sources （acetate and ethanol） and electron acceptors （dissolved oxygen, nitrate, and nitrite） were investigated under aerobic and anoxic conditions with non-acclimated process bi- omass from a full-scale biological nutrient removal-activated sludge system. When acetate was added as an external carbon source, phosphate release was observed even in the presence of electron acceptors. The release rates were 1.7, 7.8, and 3.5 mg P/（g MLVSS.h） （MLVSS： mixed liquor volatile suspended solids）, respectively, for dissolved oxygen, nitrate, and nitrite. In the case of ethanol, no phosphate release was observed in the presence of electron acceptors. Results of the experiments with nitrite showed that approximately 25 mg NO2-N/L of nitrite inhibited anoxic phosphorus uptake regardless of the concentration of the tested external carbon sources. Furthermore, higher deni- trification rates were obtained with acetate （1.4 and 0.8 mg N/（g MLVSS.h）） compared to ethanol （1.1 and 0.7 mg N/ （g MLVSS.h）） for both anoxic electron acceptors （nitrate and nitrite）.