基于实测的城市生活垃圾露天焚烧有害重金属大气排放特征及环境效应研究

Open burning of municipal solid waste (MSW) is an important contributor to the emission of fine particles and toxic heavy metals, which can directly affect urban air quality and human health, and has become a prominent environmental pollution problem in developing countries. In China, the content of toxic heavy metals in MSW is much higher and the percentage of MSW open burning has reached up to nearly 30%. Nowadays, the prevention of toxic heavy metals pollution has aroused much more concern. Thus, study on atmospheric emission characteristics and environmental effect of toxic heavy metals from MSW open burning is really imminent. In this study, the database of atmospheric emission factors of five precedent-controlled toxic heavy metals (Hg, As, Pb, Cd, and Cr) from MSW open burning will be established based on experimental measurements under two different ways of burning at individual residences and dumps. By using Taguchi experimental design method, the emission contribution of single component and the interaction between different components during MSW open burning processes will be investigated. A computation model for the calculation of toxic heavy metals emission factors from open burning of MSW with universal and representative components will be proposed. By sample collecting and analyzing of different combustion products, the transformation and migration mechanism of heavy metals during open burning will be revealed. Numerical simulation, in combination of field tests, will be applied to evaluate the environmental effect of toxic heavy metals emissions from MSW open burning. The main propose of this study is to provide fundamental data and evidence for the improvement of urban air quality, and the protection of human health.

城市生活垃圾（MSW）露天焚烧是细粒子和有害重金属排放的重要贡献者，在以中国为代表的发展中国家，已演变为突出的环境污染问题，直接影响城市环境空气质量及居民身体健康。我国MSW中重金属含量水平偏高，且露天焚烧部分的比例高达近30%，在重金属污染防治备受关注的今天，MSW露天焚烧源有害重金属大气排放特征及环境效应研究迫在眉睫。本项目基于现场实测建立露天堆烧和垃圾箱内焚烧两种方式下5种优控有害重金属（Hg、As、Pb、Cd和Cr）的大气排放因子库；依据Taguchi方法开展实验设计，解析复杂成分MSW露天焚烧过程单一垃圾组分的排放贡献及不同组分间的交互作用，提出具有普适性和代表性的排放因子计算方法体系；通过对不同焚烧产物开展样品采集与分析，揭示有害重金属的迁移转化机制；结合数值模拟和现场实测，评估MSW露天焚烧有害重金属大气排放的环境效应，从而为改善城市空气质量、保障民众健康提供基础数据和依据。

城市生活垃圾（MSW）露天焚烧现象频发，低燃烧温度和缺氧条件的焚烧过程可排放大量大气污染物进而对环境及人体健康造成危害。本项目立足于此研究背景，针对城市生活垃圾露天焚烧这一重要污染排放源，基于实际源排放测试，系统开展了源排放特征研究，并初步构建了部分典型有害重金属排放清单。本项目利用稀释采样测试系统，分别选择不同物理组分和不同城市功能区MSW样品进行露天焚烧测试，考虑自然堆积和桶内焚烧两种常见燃烧方式，并利用Modified combustion efficiency（MCE）区分明火和闷烧等燃烧状态。采集污染物包括CO2、CO、SO2和NOX等气态污染物和PM2.5，并对PM2.5中碳质组分（OC和EC）、13种水溶性离子和8种重金属元素等组分构成进行分析，进而计算MSW露天焚烧过程不同MSW组分、不同燃烧方式条件下气态和颗粒态污染物排放因子。结果显示，MSW露天焚烧过程SO2、NOX、CO、CO2和PM2.5平均排放因子分别为0.36 g/kg，1.82 g/kg，40.49 g/kg，1136.66 g/kg和 8.29 g/kg。两种燃烧方式对比显示，barrel burning显著高于natural pile-up burning，主要由于barrel burning条件下的缺氧燃烧,造成更多不完全燃烧产物排放。MSW排放PM2.5中OC为主要组分，平均占比为43.9%，其次为水溶性例子，占比为31.4%，重金属元素平均占比为0.37%。利用模糊数据方法和S形曲线法获取分组份和时间变化的MSW露天焚烧排放因子，并收集全国361个地级市人口、收入水平和垃圾产生系数等活动水平数据，基于“自下而上”排放因子法，构建了2000-2013年我国MSW露天焚烧过程9种典型有害重金属元素高时空分辨率排放清单，根据估算结果，2013年我国城市生活垃圾露天焚烧过程9种重金属排放量分别为Hg 21.25吨、As 131.52吨、Pb 97.12吨、Cd 10.12吨、Cr 50.58吨、Se 81.95吨、Cu 382.42吨、Zn 1790.70吨和Ni 43.50吨。此外，基于不同控制措施，通过设计Base、Stage I和Stage II等三种不同排放情景，对2015-2030年MSW露天焚烧典型有害重金属排放变化趋势进行了预测。