Non-carbon Dioxide Greenhouse Gas Emission From Different Municipal Wastewater Treatment Process

The dominating source of greenhouse gas （GHG）, the important factor to globalclimate anomalies, is the industrial and living activity of human. Methane（CH₄） andnitrous oxide（N₂O） are two regular non-CO₂GHGs, which Global WarmingPotential（GWP） is25and298times of that of CO₂, respectively. There is possibilitythat methane and nitrous oxide could generate and emit during the biologicalwastewater treatment process. The surface emission flux isolation chamber（SEFIC）was employed to collect the gas sample from the Xi’an No.3WWTP（the Orbal oxidation ditch process） and Xi’an NO.4WWTP（reversed A/A/O process） to determinethe generation and emission of methane and nitrous oxide from biological wastewatertreatment units and to compare the effect of operational parameters on generation andemission of non-CO₂GHG. The results and conclusions are listed below:（1） Non-CO₂GHG, methane and nitrous oxide, will emit from the biologicalwastewater treatment process. The investigation indicates that non-CO₂GHG emissionis closely related to temperature. The generation and emission are higher in summerthan in winter.（2） The generation （emission） factor of methane from two WWTPs is1181mg（CH₄）/（m³INF） and209mg（CH₄）/（m³INF）, respectively, which means there is lessmethane from Xi’an NO.4WWTP（reversed A/A/O process）.（3） The Specific methanogenic activity（SMA） and coenzyme F₄₂₀revealed thatthe quantity and activity in the influent of No.4WWTP is lower than those in No.3WWTP as the results of primary settling tank, which led to the less methane generation and emission in latter.（4） The oxidation reduction potential （ORP） is the critical factor for methanegeneration（emission） and the lower the ORP is, such as anaerobic or anoxic zone, themore methane produces（releases）.（5） Nitrous oxide generation factor and emission factor from No.3WWTP is47.26g（N₂O）/（m³INF） and36.20g（N₂O）/（m³INF）, respectively while those from theNo.4WWTP is57.22g（N₂O）/（m³INF） and54.64g（N₂O）/（m³INF）, which means thatthere were2.13times generation and1.72times of emission from No.4WWTP thanfrom No.3WWTP（6） The nitrification rate and nitrous oxide generation rate proved thatmicroorganism in Xi’an No.3WWTP is more active of nitrous oxide generation thanthose in Xi’an No.4WWTP. And nitrous oxide generation is related to nitriteconcentration and nitrite oxidation rate. The higher the concentration is, the morenitrous oxide produces and the higher the rate is, less nitrous oxide produces.（7） Microorganisms’ structure and aeration strategy are the important factor ofnitrous oxide generation and emission as well as the nitrite concentration. Themicroorganisms’ structure determines the amount of nitrous oxide produced, while theaeration strategy will affect the liquid-to-gas transfer process of aqueous N₂O, which isdirectly related to the N₂O emission.（8） From the respect of non-CO₂GHG emission, the reversed A/A/O processtakes more advantages than the Orbal oxidation ditch.The study is financially supported from “State water pollution control andtreatment technology major projects”...