PCBs在城镇污水处理过程中的分布规律及去除特性研究
发布时间：2018-08-30 07:47
【摘要】：持久性有机污染物(POPs)被UNEP视为 世界面临的最大环境挑战之一‖,因其具有持久性、生物累积性、高毒性和半挥发性,对人体和生态系统具有不可估量的危害。多氯联苯(PCBs)作为最具代表性的POPs之一,由于曾经大量生产和应用于多种工业领域,其在各种环境介质中广泛存在,包括城镇污水。由城镇污水传播到水环境中或回用水中的PCBs是人类健康和安全的巨大隐患。本文以EPA推荐的7种多氯联苯(PCB28、PCB52、PCB101、PCB118、PCB138、PCB153、PCB180)为目标物,采用固相萃取(SPE)、索氏提取(SOX)前处理技术和气相色谱-质谱连用法(GC-MS),考察北京市城镇污水、污泥中PCBs的存在现状及污染水平,分析污水处理过程中PCBs在污水、污泥中的分布,比较三种活性污泥法污水处理工艺(AO、A/A/O、SBR)对PCBs的去除规律和效果,研究粉末活性炭(PAC)和4种碳纳米管(SWCNT、MWCNT-8、MWCNT-30、MWCNT-50)对水中PCBs的吸附动力学和吸附等温线,采用拟一级、拟二级动力学吸附模型以及Langgmuir、Freundlich吸附等温线模型对实验数据进行拟合,分析粉末活性炭和碳纳米管对水中PCBs的吸附特性。研究结果表明:(1)本市城镇污水中ΣPCBs浓度为18.67 ng?L~(-1)~56.28 ng?L~(-1)之间,活性污泥中ΣPCBs含量在43.13~176.41 ng?g~(-1)之间,与国内外其他地区相比均处于中等水平。(2)PCBs在污水处理过程中的去除主要依靠固体悬浮颗粒和活性污泥的吸附作用,初沉池对PCBs有较好的去除效果,二级处理中的好氧阶段是去除主体,厌氧阶段高氯联苯可能发生降解生成氯代程度较低的中间产物。相比于A/O和A/A/O的普通二沉池,SBR的沉淀阶段对PCBs有较高的去除作用。相对于进水,二沉池出水中低氯联苯的比例增加、高氯联苯的比例下降;初沉池污泥中高氯联苯的比例较高,二沉池污泥中PCBs的分布与进水中相似。(3)粉末活性炭和碳纳米管都能实现对PCBs的快速吸附,对不同PCBs单体的吸附效果有所差异。粉末活性炭对PCBs的吸附在100 min以后趋于平衡,碳纳米管对PCBs的吸附在80 min以后达到平衡。相比之下,CNTs更早达到吸附平衡,且平衡吸附量更大。(4)拟一级和拟二级动力学吸附模型均能较好地拟合PAC和CNTs对PCBs的吸附过程,拟一级模型的Adj-R~2均大于0.95,拟二级模型的Adj-R~2均大于0.98。拟二级吸附模型的拟合效果更好,说明PAC和CNTs对PCBs的吸附是较为复杂的多步过程。(5)Freundlich和Langmuir吸附等温线模型都能较好的描述PAC和四种CNTs对PCBs的吸附等温过程,Langmuir模型的Adj-R~2都在0.98以上,Freundlich的模型的的Adj-R~2都在0.99以上,拟合结果较好。SWCNT对水中PCBs的最大吸附容量最大,MWCNTs次之,PAC最小,与吸附动力学结论一致。
[Abstract]:Persistent organic pollutant (POPs) is regarded as one of the biggest environmental challenges facing the world by UNEP because of its persistence bioaccumulation high toxicity and semi-volatility which has incalculable harm to human body and ecosystem. Polychlorinated biphenyls (PCBs) (PCBs), as one of the most representative POPs, is widely used in various environmental media, including municipal sewage, because of its mass production and application in a variety of industrial fields. PCBs, which is transmitted from urban sewage to water environment or recycled water, is a great hidden danger to human health and safety. In this paper, seven kinds of polychlorinated biphenyls (PCB28,PCB52,PCB101,PCB118,PCB138,PCB153,PCB180) recommended by EPA were used as the target materials, the pretreatment of (SOX) extracted by solid phase extraction of (SPE), Soxhlet and the continuous use of gas chromatography-mass spectrometry (GC-MS) were used to investigate the existing situation and pollution level of PCBs in municipal sewage and sludge in Beijing. The distribution of PCBs in sewage and sludge during sewage treatment was analyzed, and the removal law and effect of PCBs by three activated sludge wastewater treatment processes (AO,A/A/O,SBR) were compared. The adsorption kinetics and isotherm of PCBs in water by powdered activated carbon (PAC) and four kinds of carbon nanotubes (SWCNT,MWCNT-8,MWCNT-30,MWCNT-50) were studied. The experimental data were fitted by pseudo-first-order, pseudo-second-order kinetic adsorption model and Langgmuir,Freundlich adsorption isotherm model. The adsorption characteristics of powdered activated carbon (AC) and carbon nanotubes (CNTs) for PCBs in water were analyzed. The results showed that: (1) 危 PCBs concentration in municipal sewage was between 18.67 ng?L~ (-1) and 56.28 ng?L~ (-1), and 危 PCBs content in activated sludge was between 43.13 and 176.41 ng?g~ (-1). Compared with other regions at home and abroad, the removal of PCBs mainly depends on the adsorption of solid suspended particles and activated sludge, and the primary settling tank has better removal effect on PCBs. The aerobic stage of secondary treatment is the removal of the main body, and the degradation of high chlorinated biphenyls in anaerobic stage may produce intermediate products with lower chlorination degree. Compared with the precipitation stage of ordinary secondary settling tank SBR of A- O and A/A/O, it has higher removal effect on PCBs. Compared with the influent, the proportion of low and low chlorinated biphenyls in the effluent of secondary sedimentation tank increased, while the proportion of high chlorinated biphenyl in sludge of primary sedimentation tank decreased, and the proportion of high chlorinated biphenyl in sludge of primary settling tank was higher. The distribution of PCBs in the sludge of secondary settling tank is similar to that in influent. (3) both powdered activated carbon and carbon nanotubes can realize the rapid adsorption of PCBs, and the adsorption effects of different PCBs monomers are different. The adsorption of PCBs on powdered activated carbon tends to balance after 100 min, and the adsorption of PCBs on carbon nanotubes reaches equilibrium after 80 min. By comparison, the adsorption equilibrium was achieved earlier and the adsorption capacity was larger. (4) the pseudo-first-order and pseudo-second-order kinetic adsorption models could better fit the adsorption process of PCBs by PAC and CNTs. The Adj-R~2 of pseudo-first-order model was greater than 0.95.The Adj-R~2 of pseudo-second-order model was all greater than 0.98. The fitting effect of pseudo-two-order adsorption model is better. (5) the isotherm model of Freundlich and Langmuir can describe the isotherm process of PAC and four CNTs adsorption isotherms for PCBs. The Adj-R~2 of PAC model is more than 0.98 and the Adj-R~2 of Freundlich model is more than 0.99, which shows that the adsorption of PCBs by PAC and CNTs is more complicated. (5) the isotherm model of Freundlich and Langmuir can well describe the isotherm process of PAC and four CNTs adsorption isotherms of PCBs and the Adj-R~2 of Freundlich model is more than 0.99. The fitting results showed that the maximum adsorption capacity of PCBs in water was the largest and the second was the lowest, which was consistent with the adsorption kinetics.
【学位授予单位】：北京建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703
本文编号：2212421
[Abstract]:Persistent organic pollutant (POPs) is regarded as one of the biggest environmental challenges facing the world by UNEP because of its persistence bioaccumulation high toxicity and semi-volatility which has incalculable harm to human body and ecosystem. Polychlorinated biphenyls (PCBs) (PCBs), as one of the most representative POPs, is widely used in various environmental media, including municipal sewage, because of its mass production and application in a variety of industrial fields. PCBs, which is transmitted from urban sewage to water environment or recycled water, is a great hidden danger to human health and safety. In this paper, seven kinds of polychlorinated biphenyls (PCB28,PCB52,PCB101,PCB118,PCB138,PCB153,PCB180) recommended by EPA were used as the target materials, the pretreatment of (SOX) extracted by solid phase extraction of (SPE), Soxhlet and the continuous use of gas chromatography-mass spectrometry (GC-MS) were used to investigate the existing situation and pollution level of PCBs in municipal sewage and sludge in Beijing. The distribution of PCBs in sewage and sludge during sewage treatment was analyzed, and the removal law and effect of PCBs by three activated sludge wastewater treatment processes (AO,A/A/O,SBR) were compared. The adsorption kinetics and isotherm of PCBs in water by powdered activated carbon (PAC) and four kinds of carbon nanotubes (SWCNT,MWCNT-8,MWCNT-30,MWCNT-50) were studied. The experimental data were fitted by pseudo-first-order, pseudo-second-order kinetic adsorption model and Langgmuir,Freundlich adsorption isotherm model. The adsorption characteristics of powdered activated carbon (AC) and carbon nanotubes (CNTs) for PCBs in water were analyzed. The results showed that: (1) 危 PCBs concentration in municipal sewage was between 18.67 ng?L~ (-1) and 56.28 ng?L~ (-1), and 危 PCBs content in activated sludge was between 43.13 and 176.41 ng?g~ (-1). Compared with other regions at home and abroad, the removal of PCBs mainly depends on the adsorption of solid suspended particles and activated sludge, and the primary settling tank has better removal effect on PCBs. The aerobic stage of secondary treatment is the removal of the main body, and the degradation of high chlorinated biphenyls in anaerobic stage may produce intermediate products with lower chlorination degree. Compared with the precipitation stage of ordinary secondary settling tank SBR of A- O and A/A/O, it has higher removal effect on PCBs. Compared with the influent, the proportion of low and low chlorinated biphenyls in the effluent of secondary sedimentation tank increased, while the proportion of high chlorinated biphenyl in sludge of primary sedimentation tank decreased, and the proportion of high chlorinated biphenyl in sludge of primary settling tank was higher. The distribution of PCBs in the sludge of secondary settling tank is similar to that in influent. (3) both powdered activated carbon and carbon nanotubes can realize the rapid adsorption of PCBs, and the adsorption effects of different PCBs monomers are different. The adsorption of PCBs on powdered activated carbon tends to balance after 100 min, and the adsorption of PCBs on carbon nanotubes reaches equilibrium after 80 min. By comparison, the adsorption equilibrium was achieved earlier and the adsorption capacity was larger. (4) the pseudo-first-order and pseudo-second-order kinetic adsorption models could better fit the adsorption process of PCBs by PAC and CNTs. The Adj-R~2 of pseudo-first-order model was greater than 0.95.The Adj-R~2 of pseudo-second-order model was all greater than 0.98. The fitting effect of pseudo-two-order adsorption model is better. (5) the isotherm model of Freundlich and Langmuir can describe the isotherm process of PAC and four CNTs adsorption isotherms for PCBs. The Adj-R~2 of PAC model is more than 0.98 and the Adj-R~2 of Freundlich model is more than 0.99, which shows that the adsorption of PCBs by PAC and CNTs is more complicated. (5) the isotherm model of Freundlich and Langmuir can well describe the isotherm process of PAC and four CNTs adsorption isotherms of PCBs and the Adj-R~2 of Freundlich model is more than 0.99. The fitting results showed that the maximum adsorption capacity of PCBs in water was the largest and the second was the lowest, which was consistent with the adsorption kinetics.
【学位授予单位】：北京建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703
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