Short-term effects of excessive anaerobic reaction time on anaerobic metabolism of denitrifying polyphosphate- accumulating organisms linked to phosphorus removal and N20 production

The short-term effect of anaerobic reaction time （AnRT） （i.e., 90, 120 and 150 min） on the denitrifying phosphorus （P） removal performance and N20 production was examined using a denitrifying enhanced biologic phosphorus removal （EBPR） sludge acclimatized with mixed acetate （HAc） and propionate （Pro） （in the molar ratio 3 ： 1） as carbon sources. The results showed that when the AnRT was prolonged from 90 to 150 rain, the anaerobic polyhydroxyalkanoate （PHA） synthesis was decreased by 15.3%. Moreover, the ineffective PHA consumption occurred in anaerobic phases and contributed to an increased NO2-N accumulation and higher flee nitrous acid （FNA） concentrations （〉t0.001-0.0011 mg HNO2-N/L） in the subsequent anoxic phases, causing a severe inhibition on anoxic P-uptake and denitrification. Accordingly, the total nitrogen （TN） and total phosphorus （TP） removal efficiencies dropped by approximately 6.3% and 85.5%, respectively; and the ratio of anoxic NzO-N production to TN removal increased by approximately 3.8%. The fluorescence in situ hybridization （FISH） analysis revealed that the sludge was mainly dominated by Accumulibacter （62.0% （SEmean = 1.5%））. In conclu- sion, the short-term excessive anaerobic reaction time negatively impacted denitrifying P removal performance and stimulated more NzQ production, and its effect on P removal was more obvious than that on nitrogen removal.

Characterization of CANON reactor performance and microbial community shifts with elevated COD/N ratios under a continuous aeration mode

The effects of increasing COD/N on nitrogen removal performance and microbial structure were investigated in a SBR adopting a completely autotrophic nitrogen removal over nitrite process with a continuous aeration mode (DO at approximately 0.15-0.2 mg/L). As the COD/N increased from 0.1 to W0.59, the nitrogen removal efficiency QMRE) increased from 88.7% to 95.5%;while at COD/N ratios of 0.59-0.82, the NRE remained at 90.7%-95.5%. As the COD/N increased from 0.82 to 1.07, the NRE decreased continuously until reaching 60.1%. Nitrosomonas sp.(AOB) and Candidatus Jet tenia (anammox bacteria) were the main functional genera in the SBR. As the COD/N increased from 0.10 to 1.07, the relative abundance of Nitrosomonas decreased from 13.4% to 2.0%, while that of Candidatus Jettenia decreased from 35% to 9.9% with COD/N < 0.82 then increased to 45.4% at a COD/N of 1.07. Aerobic heterotrophic bacteria outcompeted AOB at high COD loadings (650 mg/L) because of oxygen competition, which ultimately led to deteriorated nitrogen removal pertormance.

Experimental study of nitrite accumulation in pre-denitrification biological nitrogen removal process

The effect of dissolved oxygen(DO)concentration on nitrite accumulation was investigated in a pilot-scale pre-denitrification process at room temperature for 100 days.In the first 10 days,due to the instability of the system,the DO concentration fluctuated between 1.0 and 2.0 mg/L.In the next 14 days,the DO concentration was kept at 0.5 mg/L and nitrite accumulation occurred,with the average nitrite accumulation rate at 91%.From the 25th day,the DO concentration was increased to 2.0 mg/L to destroy the nitrite accumulation,but nitrite accumulation rate was still as high as 90%.From the 38th day the nitrite accumulation rate decreased to 15%–30%linearly.From the 50th day,DO concentration was decreased to 0.5 mg/L to resume nitrite accumulation.Until the 83rd day the nitrite accumulation rate began to increase to 80%.Dissolved oxygen was the main cause of nitrite accumulation,taking into account other factors such as pH,free ammonia concentration,temperature,and sludge retention time.Because of the different affinity for oxygen between nitrite oxidizing bacteria and ammonia oxidizing bacteria when DO concentration was kept at 0.5 mg/L,nitrite accumulation occurred.

Enzymatic nitrous oxide emissions from wastewater treatment

Nitrous oxide （N20）, a potent greenhouse gas, is emitted during nitrogen rernoval in wastewater treatment, significantly contributing to greenhouse effect. Nitrogen removal generally involves nitrification and denitrification catalyzed by specific enzymes. N20 production and consumption vary considerably in response to specific enzyme-catalyzed nitrogen imbalances, but the mechanisms are not yet completely understood. Studying the regulation of related enzymes＂ activity is essential to minimize N20 emissions during wastewater treatment. This paper aims to review the poorly understood related enzymes that most commonly involved in producing and consuming N20 in terms of their nature, structure and catalytic mechanisms. The pathways of N20 emission during wastewater treatment are briefly introduced. The key environmental factors influencing N20 emission through regulatory enzymes are summarized and the enzyme-based mechanisms are revealed. Several enzyme- based techniques for mitigating N20 emissions directly or indirectly are proposed. Finally, areas for further research on N20 release during wastewater treatment are discussed.