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Direct emissions of N2O, CO2, and CH4 from A/A/O bioreactor systems: impact of influent C/N ratio

Ren, Yangang, Wang, Jinhe, Xu, Li, Liu, Cui, Zong, Ruiqiang, Yu, Jianlin, Liang, Shuang
Environmental science and pollution research international 2015 v.22 no.11 pp. 8163-8173
aeration, bioreactors, carbon, carbon dioxide, chemical oxygen demand, climate change, greenhouse gas emissions, greenhouse gases, methane, nitrogen, nitrous oxide, pollutants, sewage, sewage treatment
Direct emissions of N₂O, CO₂, and CH₄, three important greenhouse gases (GHGs), from biological sewage treatment process have attracted increasing attention worldwide, due to the increasing concern about climate change. Despite the tremendous efforts devoted to understanding GHG emission from biological sewage treatment process, the impact of influent C/N ratios, in terms of chemical oxygen demand (COD)/total nitrogen (TN), on an anaerobic/anoxic/oxic (A/A/O) bioreactor system has not been investigated. In this work, the direct GHG emission from A/A/O bioreactor systems fed with actual sewage was analyzed under different influent C/N ratios over a 6-month period. The results showed that the variation in influent carbon (160 to 500 mg/L) and nitrogen load (35 to 95 mg/L) dramatically influenced pollutant removal efficiency and GHG production from this process. In the A/A/O bioreactor systems, the GHG production increased from 26–39 to 112–173 g CO₂-equivalent as influent C/N ratios decreased from 10.3/10.7 to 3.5/3.8. Taking consideration of pollutant removal efficiency and direct biogenic GHG (N₂O, CO₂, and CH₄) production, the optimum influent C/N ratio was determined to be 7.1/7.5, at which a relatively high pollutant removal efficiency and meanwhile a low level of GHG production (30.4 g CO₂-equivalent) can be achieved. Besides, mechanical aeration turned out to be the most significant factor influencing GHG emission from the A/A/O bioreactor systems.