【作者】 姚俊；

【导师】 沈东升；

【作者基本信息】 浙江大学 ， 环境工程， 2011， 博士

【摘要】 随着城市土地资源的日益稀缺,焚烧技术在垃圾处理系统中的应用日益广泛,由此也产生了大量的生活垃圾焚烧炉渣。生活垃圾焚烧炉渣含有高浓度的重金属,使其在回用或填埋处置的过程中都存在一定的环境风险。为评估炉渣中的重金属污染,本研究在我国生活垃圾焚烧厂分布最多的浙江省选取了6个不同城市的典型生活垃圾焚烧厂进行炉渣取样,并分析了炉渣样品中重金属浓度和形态分布。根据重金属浓度和形态分析结果,选取Cu、Zn、Pb作为研究对象,结合炉渣的酸缓冲能力、重金属形态分布、pH-重金属溶出试验和Visual MINTEQ模型综合分析炉渣中Cu、Zn、Pb的溶出行为和溶出机理。根据溶出试验结果,进一步选择Cu和Zn作为研究对象,研究了风化预处理对炉渣中重金属形态分布和溶出行为的影响。基于以上结果,构建了三套模拟填埋场,动态探讨了不同比例炉渣与生活垃圾混合填埋对填埋场重金属释放行为及其生态风险的影响；并同时构建了两套模拟填埋场,探讨了渗滤液回灌对炉渣和生活垃圾混合填埋场的稳定化进程、重金属释放行为和生态风险的影响。主要结论为：(1)生活垃圾焚烧炉渣中含有高浓度的重金属,各重金属元素按照平均浓度从高到低依次为Zn>Mn>Cu>Pb>Cr>As>Ni>Co>Mo>Cd。其中,Zn、Mn、Cu、Pb和Cr是主要的金属元素,其平均含量均超过300mg/kg。形态分析的结果表明,炉渣中有一定比例的重金属以不稳定的可交换态和碳酸盐结合态的形式存在。据计算,1kg炉渣样品中平均有95.2mg的Cu、19.4mg的Pb和363.8mg的Zn以可交换态和碳酸盐结合态的形式存在,这些不稳定的重金属若完全溶出将对环境造成较大的影响。(2)在碱性环境下,炉渣中Cu、Zn、Pb的溶出水平较低；但当环境pH分别低于6.0、6.7和7.0时,炉渣中的Cu、Zn和Pb会大量溶出。而且,在酸性环境下,溶出的Cu、Zn和Pb具有更强的生物可利用性。炉渣中Cu和Zn的溶出受其形态的限制,而Pb的溶出则可能受到特殊矿物溶解平衡的控制,使其溶出率低于Cu和Zn。试验中,Cu和Zn的最高溶出率分别达到72.4%和45.0%,而Pb的最高溶出率仅为1.9%。由于炉渣具有较强的酸缓冲能力,单纯依靠酸性降雨很难使炉渣pH降至酸性从而使重金属大量溶出,因而一般在回用的过程中,炉渣对环境的影响不大。然而,当炉渣被置于含有大量有机酸的生活垃圾填埋场时,炉渣可能面临着较大的重金属溶出风险。(3)风化预处理改变了炉渣中Cu和Zn的形态分布。经过风化处理,炉渣中以可交换态、碳酸盐结合态和Fe-Mn氧化物结合态形式存在的Zn的比例分别由0.3%、17.1%、19.6%上升至0.7%、22.7%、36.7%；以有机物结合态形式存在的Zn的比例基本不变,而以残渣态形式存在的Zn的比例从55.1%下降至30.9%。同时,风化处理使炉渣中以有机物结合态形式存在的Cu的比例从68.7%下降至36.8%,以可交换态、碳酸盐结合态、Fe-Mn氧化物结合态和残渣态形式存在的Cu的比例分别从1.8%、2.5%、2.8%、24.1%上升至2.7%、3.7%、3.8%、53.7%。以可交换态、碳酸盐结合态和Fe-Mn氧化物结合态存在的Cu和Zn的比例升高表明,风化处理一定程度上提高了炉渣中Cu和Zn的迁移性。SPLP浸出试验结果表明,炉渣中Cu、Zn的溶出量随着风化处理的进行而有所降低。但在TCLP浸出试验中,炉渣中Cu、Zn的溶出量随着风化处理的进行有所升高。炉渣中Cu、Zn在SPLP浸出试验中溶出量的降低与风化处理使炉渣中无定形氢氧化铝含量的增加有关。但是在酸性的TCLP浸提液中,无定形氢氧化铝对金属的吸附能力受到抑制。由于风化处理提高了炉渣中Cu、Zn以可交换态、碳酸盐结合态、Fe-Mn氧化物结合态存在的比例,风化处理后,炉渣中的Cu和Zn在TCLP浸出试验中的溶出量有所升高。(4)炉渣与生活垃圾混合填埋对填埋场渗滤液中Cu浓度的影响不大,但对Zn浓度具有一定影响,其影响程度与填入炉渣的比例有关。填埋场中填入10%的炉渣会提高渗滤液中Zn的浓度,使填埋场Zn的环境释放量提高30%；填埋场填入20%的炉渣则由于填埋场的pH环境升高、反而使渗滤液中Zn的浓度有所降低。渗滤液中的Cu基本以有机物结合态的形式存在,炉渣填入填埋场不会对其形态产生较大影响。但是,炉渣的填入可以促使渗滤液中的Zn由小分子形态向大分子形态转化,降低其生物可利用性。填埋场运行初期,填入10%和20%的炉渣分别使渗滤液的EC50。值由530mmL/L下降至254mL/L和264mL/L,表明炉渣的填入增加了填埋场运行初期渗滤液的生态毒性。但是随着填埋的进行,10%和20%的炉渣填入使渗滤液的EC50值由258mL/L分别升高至294mL/L和314mL/L。这表明,炉渣的填入降低了填埋场运行后期渗滤液的生态毒性。另外,炉渣填入垃圾填埋场提高了填埋场下层垃圾的Cu、Zn含量,增加了填埋场重金属的潜在污染威胁。因而,必须加强相应的污染防范措施,防止由于内部或外部环境变化而引起填埋场重金属的非正常释放。(5)渗滤液回灌使炉渣与生活垃圾混合填埋场渗滤液pH、DOC和氨氮等理化性质快速稳定,加快了炉渣和生活垃圾混合填埋场的稳定化进程。渗滤液的回灌不会对渗滤液中Cu的浓度造成较大影响,但可以显著降低渗滤液中Zn的浓度。回灌使炉渣与生活垃圾混合填埋场CL,和Zn的累积释放量分别从11.47mg、144.01mg降低至4.71mg和14.69mg。同时,回灌促使渗滤液中的CLl和Zn从小分子形态向大分子形态转化,降低了其生物可利用性。渗滤液生态毒性试验结果表明,渗滤液的回灌使渗滤液的生态毒性有所降低。渗滤液回灌型炉渣与生活垃圾混合填埋场不但加速了填埋场的稳定化进程,而且降低了填埋场重金属的环境释放及渗滤液的生态毒性,这为新型填埋场的设计提供了新的思路。然而,渗滤液回灌会提高填埋场下层垃圾的重金属含量,增加了填埋场潜在污染威胁。因此必须加强相应的污染防范措施,防止由于内部或外部环境变化而引起回灌型炉渣和生活垃圾混合填埋场重金属的非正常释放。更多还原

【Abstract】 Due to the scarity of the land resource, incineration became a popular way for the treatment of the municipal solid waste (MSW), which resulted in the large production of municipal solid waste incinerator (MSWI) bottom ash. However, MSWI bottom ash contains high level of heavy metals. The leaching of heavy metals may inhibit its potential beneficial reuse as a secondary construction material and cause serious environmental pollution after landfill disposal. In this study, bottom ash from six typical MSW incinerators located in different cities of Zhejiang province was sampled. The content and speciation distribution of the heavy metal were analysed. Based on the results, Cu, Zn and Pb were chosen to study the long-term leaching behavior and the leaching mechanism of the heavy metals, by the combination analysis with acid neutralizing capacity (ANC), heavy metal speciation distribution, pH depending leaching test and Visual MINTEQ model. According to the leaching test. Cu and Zn were chosen to study the effect of weathering pre-treatment on the speciation distribution and leaching behavior of heavy metals in MSWI bottom ash. Based on above results, three sets of simulated landfills were designed to study the effect of different mass proportion of MSWI bottom ash co-disposal with MSW on the leaching behavior of Cu and Zn as well as the biological risk. Furthermore, two sets of simulated landfills were designed to study the effect of leachate recalculation on the stabilization process, heavy metal leaching behavior and biological risk of the MSWI and MSW co-disposal landfill. The main conclusions of this study were listed below.(1) MSWI bottom ash contains high level of heavy metals, and the average heavy metal content in the bottom ash followed the sequence of Zn> Mn> Cu> Pb> Cr> As> Ni> Co> Mo> Cd> Hg. Zn, Cu, Cr, Mn and Pb were the major heavy metals whose contents were above 300 mg/kg. Considerable amounts of heavy metals were presented as the exchangeable fraction and carbonate bound fraction. According to the calculation, there were 95.3 mg of Cu,19.4 mg of Pb and 363.8 mg of Zn presented as exchangeable fraction and carbonate bound fraction in 1 kg MSWI bottom ash. which had the potential to leach out and cause serious pollution to the surrounding environment.(2) The leaching of Cu, Zn, Pb was relatively low in alkine condition. However. they would be greatly leached when the pH was below 6.0,6.7 and 7.0, respectively. Moreover, the leached heavy metals had higher bioavailability in the acidic environment. The leaching of Cu and Zn was limited by their speciation distribution in MSWI bottom ash, while Pb leaching might be controlled by the precipitation and dissolution equilibrium of specific minerals, which resulted in the relatively low level of Pb leaching compared with Cu and Zn. In this study, the leaching ratio could be up to 72.4% and 45.0 for Cu and Zn. while the leaching ratio of Pb was only 1.9%. Generally. decreasing the bottom ash pH to the acid condition by acid precipitation would be a long process because of the high ANC of MSWI bottom ash. suggesting the environmental impact was negative when MSWI bottom ash was reused. However, if the MSWI bottom ash was disposed in the MSW landfill. the heavy metal might be greatly leached due to the high level of organic acid in the MSW landfill.(3) Weathering treatment could change the fractionation of Cu and Zn in MSWI bottom ash. After weathering treatment, the exchangeable fraction, carbonate bound fraction and Fe-Mn oxides bound fraction of Zn increased from 0.3%,17.1%,19.6% to 0.7%,22.7% and 36.7%, respectively. The organic matter bound fraction kept relatively steady, while the residual fraction of Zn reduced from 55.1% to 30.9%. The organic matter bound fraction of Cu decreased from 68.7% to 36.8% while the exchangeable fraction, carbonate bound fraction and Fe-Mn oxides bound fraction of Cu increased from 1.8%.2.5%,2.8%,24.1% to 2.7%,3.7%,3.8%,53.7%, respectively. It indicated the weathering treatment could increase the potential leaching ability of the heavy metals. The leaching of Cu and Zn decreased in SPLP procedure, which was probably caused by the increase of the aluminum (hydr)-oxides during the weathering treatment. However, their leaching increased in TCLP procedure, in which the leachate pH was acidic. It might be attributed to the fact that the adsorption capacity of the aluminum (hydr)-oxides was restricted in the acidic condition, and the increasing of leaching ability of Cu and Zn after the weathering treatment was therefore expressed.(4) MSWI bottom ash co-disposal with MSW had little impact on the Cu concentration in leachate. However, it had some influence on the Zn concentration in the leachate, which was depended on the mass proportion of MSWI bottom ash disposed in the landfill. If 10% mass proportion of MSWI bottom ash was disposed in MSW landfill, Zn concentration in the leachate could be notably increased and the total leaching amount of Zn could be increased by 30%. However, if 20% mass proportion of MSWI bottom ash was disposed in MSW landfill, Zn concentration could be decreased, constrastly. It might be ascribed to the fact that 20% mass proportion of MSWI bottom ash would significantly increase the pH of landfill, which restricted the mobility of Zn. Cu was mainly presented as organic matter bound fraction in the leachate. The co-disposal of MSWI bottom ash with MSW in landfill had little impact on the fractionation of Cu in the leachate. However, it could facilitate the transformation of Zn fractionation from the small molecular to big molecular, which decreased the bio-availability of the leached Zn.10% and 20% mass proportion of MSWI bottom ash co-disposed with MSW would decrease EC50 of the leachate from 530 mL/L to 294 mL/L and 314 mL/L at the beginning of landfilling, respectively, indicating the co-disposal could increase the biotoxicity of the leachate. However, the EC50 of the leachate was increased from 258 mL/L to 294 mL/L and 314 mL/L at the late phase of the landfilling, indicating the co-disposal of MSWI bottom ash and MSW could decrease the biotoxicity of the leachate with the process of landfilling.Besides, Cu and Zn content of MSW from the bottom layer was higher in MSWI bottom ash and MSW co-disposed landfill than that of MSW landfill, which increased the potential threat of the landfill. Corresponding pollution prevention measures should be enhanced to prevent the potential pollution by the abnormal heavy metals releasing from the MSWI bottom ash and MSW co-disposed landfill.(5) The recirculation of leachate could accelerate the stabilization process of MSWI bottom ash and MSW co-disposed landfill. It had little impact on the Cu concentration in leachate. However, it could notably reduce the Zn concentration in the leachate. The recirculation of leachate significantly reduced the accumulated leaching amounts of Cu and Zn from 11.47mg,144.01mg to 4.71mg and 14.69mg. respectively. Due to the recirculation, the bioavailability of the leached Cu and Zn was also reduced, which meant the environmental risk by the discharge of heavy metal from landfill was greatly migrated. The bioreactor operation with leachate recirculation of MSWI bottom ash and MSW co-disposed landfill not only accerated the stabilization process of landfill, but also reduced the release of pollutant and the bio-toxicity of the leachate. providing a new idea for the designing of the landfill. However, leachate recirculation treatment would increase the heavy metal contents of MSW in the bottom layer of MSWI bottom ash and MSW co-disposed landfill, which may probably lead to the increasing of the potential environmental risk. To prevent the potential pollution by the abnormal heavy metals releasing from the landfill, relevant pollution prevention measures should be enhanced.更多还原