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由于全球气候变化严峻,实现低碳发展对技术升级提出了新的目标和要求。有研究表明,在污水生物处理过程中产生二氧化碳(CO2)、氧化亚氮(N2O)和甲烷(CH4)等温室气体[1]。污水生物脱氮过程是N2O的直接排放源,N2O大气升温效应是CO2的298倍[2],其同时与臭氧层的破坏、全球变暖、酸雨等密切相关[1]。在污水处理过程中N2O的排放量可占到污水厂碳排放量的83%[3],因此,N2O减排是降低污水厂碳排放的重要环节[4]。N2O主要产生于硝化、反硝化反应过程,不同生物处理工艺N2O排放量不同,大型污水厂中N2O排放变化幅度大,排放因子为0~14.6%[5]。韩海成认为A2O工艺中好氧曝气池是主要N2O排放源,排放因子为6.34%~8.83%[6]。同时N2O排放受进水水质、曝气量、溶解氧浓度、进水策略等因素影响[3]。较高的进水负荷会增加硝化反应N2O排放,当污水碳氮比较低时,反硝化反应碳源不足,N2O排放量升高[3]。一氧化氮(NO)作为反硝化反应N2O转化的前体物,有助于N2O排放规律的解析[6]。
在高品质出水与碳减排双向约束下,需要寻求更为高效、低碳的污水处理技术。厌氧氨氧化工艺(anaerobic ammonia oxidation, anammox)由于其运行能耗低、无需外加碳源等优点,在生物脱氮方面已成为研究热点[7-9]。厌氧氨氧化反应中由肼(N2H4)脱氢产生N2,因此,理论上厌氧氨氧化反应不产生N2O。膜曝气生物膜反应器(membrane aerated biofilm reactor, MABR)属于膜载体生物膜反应器(membrane-supported biofilm reactor, MSBR)的一种。DUAN等[3]指出MABR是一种低N2O排放技术,空气或氧气通过透气膜渗透,有机物和氨氮在混合液侧向生物膜内部扩散,形成“逆向传质”的生物膜结构[10],该结构利于控制亚硝化反应[11]。MABR具备实现亚硝化-厌氧氨氧化反应的有利条件。通过本课题组前期研究表明,MABR耦合厌氧氨氧化工艺可实现低碳氮比生活污水中的高效脱氮[12]。MABR和厌氧氨氧化技术具备较低温室气体排放潜力,然而其温室气体排放特性尚缺乏相关参数报道。
针对生活污水处理过程中碳减排需求,本研究构建了一体式MABR,采用厌氧氨氧化工艺处理低碳氮比生活污水,在实现高效脱氮的基础上分析了N2O、NO、CH4等气体的排放规律,以期为污水处理碳减排提供参考。
膜曝气生物膜反应器处理生活污水N2O等温室气体的排放特性
Emission characteristics of N2O and other greenhouse gases from membrane aerated biofilm reactor treating domestic wastewater
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摘要: 针对生活污水处理减污降碳的需求,本研究采用膜曝气生物膜反应器(membrane aerated biofilm reactor, MABR)耦合厌氧氨氧化工艺处理低碳氮比生活污水,考察了水质污染物去除的同时,分析了甲烷(CH4)、氧化亚氮(N2O)和一氧化氮(NO)的排放特性。结果表明,MABR实现了较好的碳氮污染物去除效果,当处理进水C/N为3.00±0.14的模拟污水时,COD、NH4+-N和TN去除率分别为85.24%、90.10%和64.35%;当处理进水C/N为1.67±0.07的实际污水时,COD、NH4+-N和TN去除率分别为75.39%、96.39%和81.88%。MABR具有较低的CH4和N2O排放因子,厌氧阶段分别为(0.010 3±0.010 5)%、(0.005 0±0.005 5)%,好氧阶段分别为(0.001 5±0.001 7)%、(0.002 1±0.001 5)%,厌氧阶段是CH4和N2O排放的主要阶段。气态NO和气态N2O存在正相关关系,反硝化反应可能是N2O产生的主要路径。NO是反硝化过程N2O产生的前体物,对反硝化过程N2O的释放具有指示作用。Abstract: In this study, a membrane aerated biofilm reactor (MABR) coupled with anaerobic ammonia oxidation process was used to treat domestic wastewater with low carbon to nitrogen ratio in order to meet the demand for reduction of pollutant and carbon emission. This study investigated the removal of pollutants in wastewater and the emission characteristics of methane (CH4), nitrous oxide (N2O) and nitric oxide (NO). The results showed that the MABR achieved a good performance on carbon and nitrogen pollutant removal. When treating synthetic wastewater with C/N of 3.00±0.14, the COD, NH4+-N and TN removal efficiencies were 85.24%, 90.10% and 64.35%, respectively; when treating real domestic wastewater with C/N of 1.67±0.07, the COD, NH4+-N and TN removal efficiencies were 75.39%, 96.39% and 81.88%, respectively. The MABR had low CH4 and N2O emission factors of (0.010 3±0.010 5)% and (0.0050±0.0055)% in anaerobic stage and (0.001 5±0.001 7)% and (0.002 1±0.001 5)% in the aerobic stage, respectively, indicating anaerobic stage was the main source for CH4 and N2O emissions. Gaseous NO was positively corelated with gaseous N2O. Denitrification could be the main pathway of N2O production. Gaseous NO was the precursor of N2O production during denitrification process, which could indicate N2O emission accordingly.
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表 1 MABR不同阶段进水水质和处理效果
Table 1. The influent concentration and treatment efficiency of MABR at different stages
阶段 进水(mg·L−1) 出水(mg·L−1) 去除率/% COD NH4+-N TN COD NH4+-N TN COD NH4+-N TN 阶段1 115±1.41 39.1±0.92 39.1±0.92 17±4.24 3.89±2.22 15.72±4.96 85.24±3.51 90.1±5.61 64.35±16.49 阶段2 64±12.73 38.44±4.27 49.39±3.34 16±5.66 1.39±1.15 8.86±2.71 75.39±3.95 96.39±2.89 81.88±7.55 -
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