【作者】 潘涛；

【导师】 朱晓东；

【作者基本信息】 南京大学 ， 环境科学， 2011， 博士

【摘要】 如何共同应对全球气候变化已经成为国际社会的主要议题和挑战之一。自下而上和自上而下的研究均表明,未来几十年,减缓全球温室气体的排放有着相当大的经济潜力,这一潜力能够抵销预估的全球排放的增长或将排放降至当前水平以下。2005年全球污水处理领域直接排放约6.4亿吨二氧化碳当量的温室气体。由于人口基数大,以及快速城市化地区和农村地区的污水处理设施不完善,中国污水处理领域甲烷温室气体排放量居全世界第一,占排放总量的21%。在城乡未普及管网的地区,大力发展低能耗、分散式人工湿地处理污水方法,可以避免集中污水治理模式“大管网高耗能”的弊端。人工湿地在消减环境污染物的同时,是否也减少污水处理过程的温室气体排放?本文针对这一主要问题展开研究。本文总结当前的研究进展,梳理人工湿地温室气体排放相关的机理研究。基于污水生化处理和湿地生态复合系统特征,构建碳质量平衡模型和碳排放估算公式。根据人工湿地设计、构造和运行模式,进行边界条件和参数的设定,估算甲烷排放占总碳负荷比例(潜在排放系数K)在0到0.36之间。结合湿地内部的氧化还原电位(Eh)区间及其长期水处理效果,可以快速估算人工湿地温室气体排放量。采用2006IPCC温室气体清单指南为方法学,结合案例城市常州特征,估算城乡污水处理过程的温室气体排放基准线。采用生命周期分析法(LCA),对比常州市集中污水处理和通江小区垂直流人工湿地全过程排放。比较结果表明,两者在污水收集、处理过程、以及污泥处置等全过程排放都有很大不同。集中污水处理厂处理模式的人均碳足迹为116.1 kg二氧化碳当量,其中污泥处理不当造成排放占37%,A20厌氧段甲烷排放占33%,能耗间接排放占28%,N20排放仅占2%。垂直流人工湿地处理系统的全过程人均温室气体排放为15.1 kg二氧化碳当量,仅分别相当于城市集中污水处理系统的13%,以及乡村现状排放的14.4%。温室气体减排效应明显。研究发现城市污泥填埋处置不当和乡村生活污水处理设施的缺失,不仅带来严重环境污染,而且造成大量温室气体排放。即使提高城市集中污水处理率,如果没有污泥消化处置系统,甲烷气得不到收集利用,污水排放甲烷量仍然得不到减少。本文对人工湿地工程建设和运行成本进行统计分析。以常州市为例的三种不同情景分析结果表明,大力建设以垂直流人工湿地为代表的低能耗好氧型污水处理设施,到2030年前,乡村污水处理率达到70%的目标是环境和经济可持续的。实施城市污泥深度处置和乡村生活污水处理这两项措施,2030年我国年减排潜力5560万吨二氧化碳当量,约占当前(2005基准年)全球污水处理领域温室气体总排放的8.7%,将是中国对全球气候变化减缓做出的巨大贡献。更多还原

【Abstract】 Combating climate change has become one of major issues and challenges for international communities. Both bottom-up and top-down studies indicate that there is high agreement and much evidence of substantial economic potential for the mitigation of global GHG emissions over the coming decades that could offset the projected growth of global emissions or reduce emissions below current levels. Global GHG emission in wastewater sector is approximately 640 million ton CO2 equivalent at year 2005 level. China takes the first place and emits 21 percent of global total emission in this sector.In the peri-urban and rural area where no sewers exist, it is a cost effective strategy to develop decentralized systems instead of centralized one which demands expensive sewer network and intensive energy consumption. Constructed wetland is one of the appropriate technologies in such area. The question is:whether Constructed wetlands mitigate not only water pollutions but also GHG emissions?The emission mechanism in the constructed wetlands is studied. Based on the integration of wastewater treatment plant and wetland ecosystem, a Carbon Mass Balance Model (CMBM) and a method for emission estimation are thus developed. A potential emission factor (K) is used to illustrate the CH4 emision potential in ratio to the total carbon load from both wastewater and plant photosynthesis sources. The K value is estimated from 0 to 0.36 varied upon treatment efficiency and Redox potential indicated by Eh. An emission curve is thus developed to enable rapid estimation.Using methodology of 2006 IPCC GHG inventory guidelines, our study estimates the baseline from wastewater treatment and disposal emissions in Changzhou municipality. A comparison between wastewater treatment plant (WWTP) and a subsurface vertical flow (SSVF) constructed wetland has been made, using LCA technique. The result shows the emissions are different throughout the whole life cycle process, i.e. collection, treatment and disposal. The studied WWTP model emits 116 kg CO2 equvalent a-1 pe-1 in which 37% from anaerobic sludge landfill,33% from anaerobic section in A2O process,28% from indirect emission by energy consumption and 2% from N2O emission, respectively. The studied constructed wetland model emits only 13% and 14.4%, respectively, comparing to WWTP model and rural emission baseline. Thus, SSVF constructed wetland is proved to be an effective measure for GHG emission reduction. Our study also estimates the significance of sludge and rural wastewater emissions. Even all the wastewater are collected and treated in WWTP, the CH4 emission will not be reduced unless the sludge is properly handled and CH4 is sequestrated.A cost benefit analysis has been made for construction and operation of the constructed wetlands. The comparison of three scenarios in Changzhou shows it is both economically and environmentally sustainable to reach the target of 70% rural wastewater being treated by 2030. Scaling up to nation wide, by improved sludge handling and rural wastewater treatment, GHG reduction potential by year 2030 is estimated as 55.6 million ton CO2 equavelent which is approximately 8.7% of global baseline level at year 2005. This will be a significant contribution for China to the mitigation of climate change.更多还原