【作者】 李文兵；

【导师】 沈东升；

【作者基本信息】 浙江大学 ， 环境工程， 2012， 博士

【摘要】 由于填埋场能够适应不同的垃圾类型和数量的波动并且经济有效,因此成为了大多数国家生活垃圾处理的主要方式。然而,如何解决填埋场处理垃圾过程中氮的二次污染问题一直是人们关注的热点。为了保护填埋场周边的土壤、地下水及地表水环境,亟待解决填埋场中原位脱氮的理论和技术难题,实现源头消减填埋场氮排放的目的,从而降低渗滤液的处理费用和难度。鉴于此,本文以生活垃圾填埋场和渗滤液中含量最高的变价金属元素铁作为研究对象,展开了以下几个方面的研究。首先,针对总量无法准确评价铁的环境行为的问题,借鉴土壤、海底沉积物、污水处理厂活性污泥的研究方法,研究了盐酸和草酸-草酸铵对垃圾中不同价态铁的提取效果及影响因素,并对提取条件进行了初步优化。在此基础上,研究了不同填埋龄垃圾中不同价态铁的含量。其次,以生物反应器填埋场为模型系统,构建了两种不同运行模式的模拟填埋场反应器,深入系统的研究了两种运行模式下填埋场中铁的总量释放及氧化还原变化规律,揭示了铁的不同价态与不同形态之间的关系。最后,通过研究氮素的去除效果和铁的价态变化规律,初步揭示了铁的氧化还原循环与氮素去除的潜在关系。论文获得如下主要研究成果：(1)正交试验结果表明,当盐酸浓度为1 mo1·L-1、液固比为100：1、提取时间为60min、转速为200 rpm和提取温度为35℃,盐酸对垃圾中的亚铁、三价铁和总铁的提取效果较好。当液固比为100：1、提取时间为12 h、转速为175 rpm和提取温度为30℃, Tamm’s试剂对垃圾中的亚铁、三价铁和总铁的提取效果较好。在正交试验所确定的最佳提取条件,盐酸和Tamm’s试剂二种方法对填埋龄为0-8年的垃圾中亚铁和三价铁均具有较好的提取效果。(2)不同填埋龄垃圾的基本理化性质存在较大差异,垃圾的含水率、有机质和BDM的含量随着填埋时间的增加而呈现逐渐下降的趋势。垃圾经过8年的填埋后,垃圾中的有机质和BDM由最初的72.40±1.28%和54.90±0.17%分别下降至15.20±2.93%和3.34±0.74%。盐酸和Tamm’s试剂提取态亚铁和总铁均呈现出随着垃圾填埋龄的增加而逐渐增加的趋势,除新鲜垃圾外,四个陈垃圾样品中盐酸提取态和Tamm’s试剂提取态亚铁含量之间却存在着明显的差异。(3)不同垃圾组分中的含铁量存在显著性差异,灰土和砖瓦类的含铁量最高(>30000mg kg-1),厨余类、纸类垃圾次之(10000-30000 mg kg-1),纺织物、木制品和塑料最低(<10000mg kg-1)。厨余类垃圾占填埋总质量的比例较高,是模拟填埋场反应器中铁的主要来源,对总铁的贡献率达到了45.5%。(4)不同运行模式的模拟填埋场反应器渗滤液中总铁浓度变化趋势及累积释放量存在巨大的差异,传统卫生填埋场反应器(CL)渗滤液中总铁的浓度呈现先降低后升高的趋势,而渗滤液回灌型填埋场反应器(RL)渗滤液中总铁的浓度则呈现逐渐下降的趋势。CL中总铁的释放率为1.00%,而RL中总铁的释放率则仅为0.14%。(5)两个模拟填埋场反应器渗滤液中总铁与常见的理化指标之间并无显著相关性。两个模拟填埋场反应器渗滤液中亚铁占总铁的百分比均随着反应器的运行而呈现逐渐升高的趋势,反应器RL渗滤液样品中亚铁的比例在63.0%-92.7%内变化(平均值为81.0%),反应器CL渗滤液样品中亚铁的比例在76.0%-98.8%内变化(平均值为90.0%)。两个模拟填埋场反应器渗滤液中溶解态与颗粒态铁占总铁的变化趋势与平均值基本相同,渗滤液中的三价铁与颗粒态铁均呈显著正相关(R2=0.748,RL；R2=0.833,CL)。(6)陈垃圾接种并同时加入有机碳源和硝态氮的反应体系中,加入亚铁之后发生了铁的氧化还原循环,并同时伴随着硝态氮的还原过程,还原产物为氮气和铵态氮。未加入任何有机碳源的陈垃圾接种的反应体系中,发生了无机自养型的亚铁厌氧氧化-反硝化过程。然而,由于该体系中缺少有机碳源,因此三价铁无法通过异化铁还原过程再次转化为亚铁,未发现铁的氧化还原循环过程。更多还原

【Abstract】 Landfills are the predominant form of treatment of municipal solid waste (MSW) in the vast majority of the available case studies, because it is cost-effective and can accommodate different types as well as large fluctuations in the amount of waste. However, it is still a hot topic that how to find a feasible way to solve the secondary pollution of nitrogen during the process of municipal solid waste treatment by landfill. In order to protect the soil, ground water and suface water environment around landfill, achieve the purpose of in situ nitrogen removal and reduce the cost and degree of difficulty for landfill leachate treatment, theoretical and technical problems on in situ nitrogen removal must be resolved as soon as possible. Hereupon, iron, the most abundant element with variable valence in the landfill and leachate, was chosen to carry out the following research. First of all, in view of environmental behavior of iron can not be assessed accurately only by the total content of iron, the extraction conditions for extractable iron speciation (ferric and ferrous) in MSW by hydrochloric acid and acid ammonium oxalate solution (Tamm’s reagent) were investigated and optimized. Subsequently, the redox state of iron in municipal solid waste (MSW) with different deposit ages was evaluated. Secondly, two simulated MSW landfill with different operational modes were constructed based on the model of bioreactor landfill, the leaching behavior for the total content of iron and variation of iron in different oxidation state was investigated, and the correlation between particulate bound iron and Fe(Ⅲ) in the leachates of the simulated landfills was obtained. Finally, according to the nitrogen removal efficiency and the variation of iron in different oxidation state in batch experiment, the potential effect and mechanism of iron redox on nitrogen removal in the landfill was presented. The main experiments and conclusions are as follows:(1) According to the orthogonal experiments results, the optimal extraction conditions for HC1 were determined as follows:the liquid-to-solid ratio was set at 100, and then the samples were extracted at the shaking speed of 200 rpm at 35℃for 60 min by 1mol.L-1 HC1. For Tamm’s reagent, the optimal extraction conditions were extracted at the shaking speed of 175 rpm at 30℃for 12 h with the same liquid-to-solid ratio. Under the optimal extraction conditions, both extraction reagents perform very well to evaluate the redox state of iron in MSW with different deposit ages.(2) MSW samples with different deposit ages exhibited decidedly different basic physicochemical characteristics, and moisture content, organic matter content determined as LOI and BDM decreased with the increasing of deposit age. After the burial of 2 years, the organic matter content and BDM decreased from 72.40±1.28% and 54.90±0.17% to 15.20±2.93% and 3.34±0.74%, respectively. The results also showed that the yield of extractable iron increased with deposited age. In the fresh refuse, no significant difference of extractable ferrous iron was found extracted with both HC1 and Tamm’s reagent, while statistically significant differences were found for the yield extractable ferrous iron extracted by the two extractants in the other four aged refuse samples (SI to S8).(3) The results depicted that there was large amount of variability for the iron contents in different MSW. Both the contents of iron in the brick and dust were higer than 30000 mg kg-1, which was significantly higher than that in the fractions of food and fruit waste, papers and residue (10000-30000 mg kg-1) and cellulose textile, wood and plastics (<10000 mg kg-1). The food and fruit waste contributed a large amount of iron (45.5%) due to their high proportion in the MSW on dry weight basis.(4) The leaching behavior and accumulated amounts of iron leached out of the refuse by leachate from CL and RL exhibited decidedly different trends except for the initial stage. After 200 days operation, the accumulated amounts of iron leached out from CL increased with the passage of time (from 3710 to 7270 mg), while the iron leached out from RL decresed sharply from 3320 mg to 991 mg. The percentage of iron leached from CL and RL accounted 1.00% and 0.14% for the total amount in landfills, respectively. (5) No significant correlations were found between iron leaching and basic physicochemical characteristics of leachate, such as chemical oxygen demand (CODCr), dissolved organic carbon (DOC), volatile fatty acid (VFA), pH, SO42- and S2- concentrations in the leachate of the simulated landfills. Variation of ferrous and ferric iron percentage in the leachate of RL and CL exhibited similar trends during the whole operating period, ferrous iron percentages in the leachate of RL and CL increased with the passage of time. During the succeeding 200 days, the ferrous iron percentages in the leachate of RL and CL kept within the range of 63.0-92.7% with an average of 79.7% and 71.3-98.8% with an average of 89.4%, respectively. Significant positive correlations between particulate bound iron and ferric iron were found in the leachates from RL (R2=0.748) and CL (R2=0.833).(6) With the addition of organic carbon, nitrate nitrogen, ferrous iron and aged refuse, repeated anaerobic of microbial redox cycling of iron concomitant with nitrate reduction was found. During this process, nitrate was reduced to nitrogen gas and ammonium nitrogen. Without addition of organic carbon, only anaerobic ferrous iron oxidation nitrate reduction was found, redox cycling of iron did not happen and iron was always presented as ferric iron in the system.更多还原