【作者】 管益东；

【导师】 罗安程；

【作者基本信息】 浙江大学 ， 植物营养， 2011， 博士

【摘要】 中国作为一个发展中国家,超过半数人口居住在农村地区,农村地区的生态环境质量对农民生活具有重要意义。在过去的几十年间,中国农村环境保护建设远落后于城市,农村基本上没有建立固体废物收集和处置体系。目前,中国农村固体废物与农村生活污水一起,已经成为影响农村环境卫生的主要污染源之一。此外,中国农村快速的城市化进程也是农村固体废物污染物的产量逐渐升高的原因之一,农村生态环境恶化趋势日趋严重。中国农村受到技术、投资与运行成本等因素限制,简易填埋成为农村固废的主要处置方式之一。随着我国经济的快速发展,2000年后农村地区逐渐采用规范化方式处置农村固废,原有的简易填埋场逐渐处于废弃状态。但是由于缺乏环境保护措施,废弃农村固废简易填埋场对周围环境的污染并没有得到根本防治,但目前对于此类简易填埋场的环境污染现状与相应污染控制措施等缺乏相关的系统研究。本研究以宁波市为例,对废弃农村固废简易填埋场进行了环境污染调查,在此基础上,探索采用多介质层系统(MML)处理简易填埋场垃圾渗滤液。主要研究结果如下：1.废弃农村固废填埋场环境污染调查通过现场实地调查与走访就近农村居民,表明：宁波地区有100多个废弃农村固废简易填埋场。由于填埋期较久,简易填埋场的固废物理组成与市政填埋场固废有较大差别,其中前者固废残余物含量高达85.0%,且混有较多工业固废。填埋场内固废有机质与Cd含量较高,分别达到69.8 g/kg(以干重计,下同)与17.6 mg/kg。氮和COD是垃圾渗滤液中主要污染物,但其浓度远远小于卫生填埋场的垃圾渗滤液浓度,极度地降雨稀释很可能是造成这一现象的重要原因。COD、氮与磷是简易填埋场周围地表水中主要污染物,营养盐污染远大于重金属污染,根据水质综合污染指数值,填埋场周围120 m范围内约78.0%地表水样归类为中度—严重污染。填埋场周围土壤中TN、TP与Cr、Cu、Zn和Cd有积累趋势,Cr、Cu与Cd其污染程度均为未污染—中度污染,土壤Cd污染最重。与土壤Ⅱ级标准的Cd规定值相比,场内土壤Cd平均值是其10.3倍以上,因此填埋场周围100m范围内土壤只适合作为林地,而不适合作为农业用地。2.废弃农村简易填埋场周围土壤—水稻生态系统污染以高桥简易填埋场为研究对象,研究了该填埋场周围土壤重金属与水稻重金属含量受填埋场的影响,结果表明：农村废弃填埋场周围120 m范围内,土壤—水稻生态系统已经受到污染。土壤Cd含量高于农业土壤最大允许值。重金属Igeo值表明：土壤已经受到了Cd中度污染,而土壤中Cr、Cu与Pb污染状况为未污染-中度污染。水稻根部、茎叶和籽粒均呈现显著地重金属积累趋势。水稻籽粒中Cr和Pb含量高于阈值,它们的平均含量分别是阈值的2.9-6.7倍与1.0-1.5倍。线性相关分析结果表明：填埋场渗滤液呈弱碱性是造成土壤pH升高,并进而影响水稻对Cd吸收的一个重要原因。3.MML对简易填埋场渗滤液的处理效果针对现有常规渗滤液处理工艺投资与运行成本高,操作维护较复杂等缺点,论文探索了采用MML工艺处理废弃农村固废简易填埋场渗滤液的可行性研究。MML具有管理方便与无动力处理的特点,适合处理此类填埋场渗滤液。本实验设置了4个水力负荷,并改进了土壤块(SMB)组成,在低曝气与不曝气条件下,研究了MML对渗滤液的处理效果。结果表明,MML可以有效地去除垃圾渗滤液中的COD、NH3-N与P。MML在HLR 200L/(m2·d)和400 L/(m2·d)与无曝气条件下,NH3-N去除效率与COD去除效率分别为97.4%和82.4%与72.0%和62.0%；在HLR 800和1600 L/(m2·d)与间歇曝气时,NH3-N与COD去除效率分别为62.3%和53.4%与45.3%和35.3%。由于强烈的硝化作用,TN去除效率不高,在试验结束时,MML实际上基本丧失了对TN的去除能力。在HLR 200 L/(m2-d)时,MML对P去除效率在75.6-91.9%,而其它3个水力负荷下P去除效率在26.1-54.9%之间。实验结果表明,MML用于处理该类填埋场渗滤液具有较好的前景。4.MML流态分析由于目前自然处理系统设计主要采用经验公式,而实际应用中由于受到所处地理位置、地质条件与气候等多种外界因素影响,其水流流态常常偏离设计,影响了其设计的有效性。本章实验通过投加示踪剂,求出MML停留时间分布曲线,进而明确其内部流体流动状态,明确其有效体积,为对MML反应器优化和高效利用提供依据。在水力负荷分别为200、400、800与1600 L/(m2·d)条件下,MML反应器示踪实验结果表明：(1)MML在HLR 200-1600 L/(m2·d)返混程度中等偏下(d<0.3),流动状态以平推流为主,但是随着HLR提高到实验最高负荷(1600 L/(m2·d)),反应器流态有由平推流向全混流转变的趋向。(2)水力停留时间是决定MML反应器死区比例的一个关键因素之一,二者存在良好的负相关性。更多还原

【Abstract】 As a developing country, more than half populations in China live in rural areas. The ecological environment quality in rural areas is very important to the quality of rural residents. In the past few decades, the sanitation facilities in rural areas lag far behind the cities. Nowadays, the solid waste and the wastewater in rural regions have been one of the main barriers of affecting the sanitation and residential living in rural areas. Additionally, the rapid urbanization in rural areas in China was also one of the reasons which contribute the increasing production of solid wastes, and the environmental degradation trends in rural areas worsened gradually.Limited by the factors including the available technology, investment and operation costs, etc., the unsanitary landfills became one of the main disposal pathways of rural waste. After 2000s, they were replaced by the newly established sanitary landfills, and then they were abandoned gradually. However, there are few systematic researches on the environmental contamination of the abandoned rural unsanitary landfills and the corresponding decontamination process.We choose the Ningbo city as the representative region of east China, and investigate the current environment contamination of these unsanitary landfills. Then, the decentralized wastewater technology-the improved Multi-soil-layering system (MML) was applied to treat the leachate from these landfills. The experiment results are listed below:1. Pollution investigation of the abandoned rural unsanitary landfillsBased on the field survey and visit to the adjacent villagers, it is found that there are at least 100 unsanitary landfills in Ningbo. The was an evident difference between the physical components of solid wastes from the abandoned unsanitary landfill with the sanitary landfills, high portion of residues,85 percent, and a part of industrial waste was commingled with the rural waste. Chemical analyzation of the the adjacent surface water and soil show that the organic components and Cd content of the rural waste were high,69.8 g/kg (dry weight, DW) and 17.6 mg/kg (DW), respectively. Nitrogen and chemical oxygen demand (COD) were the primary products in the leachate in the unsanitary landfills, and their concentrations were much lower than that from the sanitary landfill. It was assumed that the great dilution effect caused the result.COD, N and P were the prevalent contaminants in the surface water around the unsanitary landfills, and the nutrient contamination was much higher than the pollution of trace elemments in surface water. According to the integrated pollution index (IPI), more than 78.0% water samples were classified as the moderate to serious pollution degree within 120 m around the unsanitary landfills.Higer average contents of soil TN, TP, Cu, Zn and Cd indicate that they have accumulation trend. Geoaccumulation index values of soil Cd and Cu show the soil moderate pollution with Cd and unpolluted to moderately polluted with Cu, respectively. Compared with the cadmium threshold level, the average soil Cd content was 10.3-fold higher. To protect the human health, the soils within 100 m around the unsanitary landfills were suitable for forest land only, not for agricultural usage.2. Heavy metal contamination in a soil-rice system in the vicinity of abandoned rural unsanitary landfillGaoqiao unsanitary landfill was chosen as the research object, and the soil and rice adjacent to the unsanitary landfill were sampled to evaluate the metal contamination of the soil-rice ecosystem. The experiment results showed that the ecosystem adjacent to the abandoned rural unsanitary landfill has been contaminated. The soil Cd was higher than the maximum allowable content of agricultural soil. Geoaccumulation index values of soil Cd suggests that the soil was moderately polluted with Cd, while the soils were unpolluted-moderately overall by Cr, Cu as well as Pb. There was a remarkable bioaccumulation trend of heavy metals in the rice organs (rice root, stem & leaf and grain). The Cr and Pb contents in rice grain were much higher than the threshold levels,2.9-6.7 folds and 1.0-1.5 folds of the legislation limits, respectively.Linear correlation analysis showed that the slightly alkaline leachate from the unsanitary landfill was one of the main factors causing the higher soil pH and then affecting the absorption of rice on the Cd.3. Treatment of leachate from rural unsanitary landfill using Multi-media layering system (MML)The existing processing technologies demand the expensive investment, high cost operation and skillful professionals to operate and maintain. Thus, it is assumed that they are not suitable for the utilization for the abandoned unsanitary landfills in the rural areas. MML has the characteristics of administrative convenience and non-power handling. Four MMLs with altered SMB and different hydraulic load rate (HLR) were applied in the experiment to investigate the treatment of the landfill leachate under without or low aeration supply. The experiment results showed that the MML could effectively treat the COD, NH3-N and P. COD and NH3-N removal efficiencies of MML were 97.4%,82.4% and 72.0%,62.0%, respectively under HLRs of 200 and 400 L/(m2-d) without aeration; COD and NH3-N removal efficiencies of M800 and M1600 were 62.3%,53.4% and 45.3%,35.3% respectively under intermittent aeration. N removal efficiency was low due to the strong nitrification effect, and MML almost lost the nitrogen removal capacity. P removal efficiency of MML was 75.6 to 91.9% under HLR 200 400 L/(m2·d), and the P removal of other three reactors was 26.1 to 54.9%. The experiment result indicated that MML presents an appealing prospect to be utilized to treat the leachate from the rural unsanitary landfill.4. Flow pattern of MMLSince the current design of natural treatment process (NTP) mainly depends on the emperial equation; however, the flow pattern of NTP often deviates the design and the designing effectiveness is impaired due to the geography location, geological condition and weather, etc. The objective of the experiment was to detect the residence time distribution (RTD) of MML, clarify its flow condition and effective volume under hydraulic load rate 200 to 1600 L/(m2·d) utilizing tracer experiment. The experiment results were listed below.The flow pattern of MML was close to plug-flow with middle backmixing (d<0.3) under hydraulic load rate (HLR) 200 to 1600 L/(m2·d). However, the flow pattern had the tendency to shift to completely stirred flow.Hydraulic retention time was one main factor determining the volume proportion of dead zone (Vd), and there was excellent linear correlation betweenθwith the latter (R2=0.999).更多还原