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氯苯类化合物(chlorobenzenes, CBs)是一类人工合成的有机氯化合物,包括一氯苯(monochlorobenzene, MoCB)、二氯苯(dichlorobenzene, DiCB)、三氯苯(trichlorobenzene, TrCB)、四氯苯(tetrachlorobenzene, TeCB)、五氯苯(pentachlorobenzene, PeCB)和六氯苯(hexachlorobenzene, HCB). 这类化合物具有高毒性、难降解性和生物蓄积性,其中PeCB和HCB早已作为持久性有机污染物被列入《关于持久性有机污染物的斯德哥尔摩公约》受控污染物名单中,被禁止商业化生产和使用[1-2]. 而一些CBs仍在被广泛地应用于制药、农药、印刷、染色、皮革和电子制造等工业生产以及相关产品在农业生产、日常生活中的使用[3-6]. 含CBs的工业废水、城市污水和农业排水等排入自然水体,可能造成CBs水污染,直接或间接地危害生态环境和人体健康.
污水处理厂作为收集、集中处理和排放城镇污水的关键设施,也成为了污染物的潜在“二次源”. 目前,关于污水处理厂中CBs的研究主要集中在污泥介质[7-9],而污水中CBs的基础数据仍十分有限. 通过污水处理厂进出水以及各处理单元污水中CBs的含量和组成分布分析,能够了解当地工业废水或生活污水中CBs的赋存情况以及污水处理工艺对CBs的去除效率,并有助于判断排放的CBs是否会对受纳水环境造成生态危害等. 以往若干有关我国污水处理厂污水中CBs的研究[5, 10]仅分析了一部分氯苯物质,对所有同族体的赋存和去除情况缺乏全面性了解,不利于相关污染与风险的精准防控.
纺织印染行业常使用CBs作为染料及助剂的溶剂,导致纺织印染废水中往往含有CBs污染. 我国中山市、东莞市、佛山市和广州市的纺织印染废水处理厂出水中能检测到几百到几千纳克每升的CBs(Cl4-Cl6) [5]. 浙江省地处中国东南沿海、长江三角洲南翼,工业化和城市化程度高,其中纺织印染产业规模更是位列全国第一,然而省内纺织印染发达地区污水处理厂污水中CBs的赋存特征及排放风险尚无报道,亟待展开研究.
本文分析了浙江省纺织印染较发达城市两家污水处理厂污水中CBs(Cl1-Cl6)的浓度水平和组成分布特征,探讨了CBs在不同工艺处理过程中的变化规律与去除效率. 此外,还基于环境影响度和风险熵值计算模型,评估了污水处理厂排放水体中CBs可能产生的生态环境风险,为CBs水污染及风险防治提供了科学依据.
浙江省典型污水处理厂中氯苯类化合物的赋存特征及风险评估
Occurrence characteristics and risk assessment of chlorobenzenes in typically wastewater treatment plants from Zhejiang Province
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摘要: 氯苯类化合物(chlorobenzene,CBs)是一类具有高毒性、难降解和易富集性的有机氯化合物,持续受到广泛关注. 污水处理厂在城市水污染控制中发挥着重要作用,然而,目前关于污水处理厂中的CBs研究十分有限,其消减规律与排放特征仍不清楚. 本研究系统分析了浙江省两家典型污水处理厂中CBs的赋存特征、去除效率及排放潜在风险. 发现CBs在各污水处理厂污水中普遍存在,但污染水平较低,出水中CBs的总浓度范围为17.4—75.1 ng·L−1,远低于我国相关排放标准. 二氯苯是进出水中CBs的主要组成成分,占比49.3%—64.1%. 厌氧处理及污泥吸附沉淀对CBs的去除效果相对较好,但现有污水处理工艺对CBs的总体去除效果不佳,部分处理单元还存在CBs含量上升情况. 基于环境影响度(ambient severity,AS)和风险熵值(risk quotients,RQs)评估结果表明,所研究污水处理厂排放水中CBs对人体健康以及生态风险较小(AS <1,RQs <0.1). 研究结果有助于深入了解CBs在污水处理系统中的环境行为和排放风险,也为优化污水处理工艺、进一步控制和减少CBs水污染提供了基础数据。Abstract: Chlorobenzenes (CBs), a group of chlorinated organic compounds, have been concerned for their high toxicity, poor degradability, and strong ability of accumulation by the public. Wastewater treatment plants (WWTPs) play an important role in controlling the urban water pollution; whereas the research on CBs in WWTPs is extremely limited, reduction trends and emission characteristics of which are still not well-known. This study systematically analyzed the occurrence characteristics, removal efficiency, and potential risks of emission of CBs in different treatment processes of two typical WWTPs in Zhejiang Province. The results showed that CBs presented frequently in the wastewater samples from the WWTPs, but in low pollution levels. Concentrations of CBs in the effluents were in the range 17.4—75.1 ng·L−1, far below the related emission standard of China. Dichlorobenzene was the main component of CBs in the influents and effluents, accounting for 49.3%—64.1% of the total CBs. Anaerobic treatment and sludge adsorption precipitation had relatively good removal efficiency for CBs. However, the existing wastewater treatment processes generally had poor capacities for removing CBs, and some treatment processes were even found an increased effect on CB contents. Based on the evaluation results of ambient severity (AS) and risk quotient (RQ), it was indicated that the human health and ecological environmental impact of CBs in the effluent from the studied WWTPs was relatively low (AS < 1, RQ < 0.1). These findings contribute to a deeper understanding of the environmental behaviors and emission risks of CBs in WWTPs, also provide essential data for optimizing wastewater treatment processes and further controlling and reducing the CBs in wastewater.
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表 1 污水处理厂排放水体CBs的环境影响度及相关数据
Table 1. The ambient severity (AS) of CBs in the effluent from WWTPs and relevant data
污染物
Pollutants a半数致死量/
(mg·kg−1)
LD50[5-6]环境介质阈值/
(μg·L−1)
DMEGWHA系统
A systemB系统
B systemC系统
C system浓度/(ng·L−1)
Concentration环境影响度/
(×10−9)
AS浓度/(ng·L−1)
Concentration环境影响度/
(×10−9)
AS浓度/(ng·L−1)
Concentration环境影响度/
(×10−9)
ASMoCB 2290 1545750 4.72 3.05 10.2 6.60 6.34 4.10 1,4-DiCB 500 337500 1.76 5.21 1.18 3.50 0.71 2.10 1,3-DiCB 1062 716850 33.7 47.0 22.2 31.0 4.00 5.58 1,2-DiCB 500 337500 12.6 37.3 6.48 19.2 3.79 11.2 1,3,5-TrCB 800 540000 0.38 0.70 < 0.61 b < 1.13 0.35 0.65 1,2,4-TrCB 756 510300 10.1 19.8 6.52 12.8 0.84 1.65 1,2,3-TrCB 1830 1235250 8.20 6.64 3.92 3.17 0.60 0.49 1,2,3(4),5-TeCB c 1500 1012500 1.33 1.31 < 0.26 b < 0.26 < 0.26 b < 0.26 1,2,3,4-TeCB 1727 1165725 0.70 0.06 < 0.38 b < 0.33 < 0.38 b < 0.33 PeCB 1167 787725 1.01 1.28 0.80 1.02 0.39 0.50 HCB 1080 729000 0.48 0.66 1.60 2.19 0.22 0.30 TAS — — — < 124 — < 81.1 — < 27.2 a MoCB、DiCB、TrCB、TeCB、PeCB和HCB分别代表一氯苯、二氯苯、三氯苯、四氯苯、五氯苯和六氯苯,TAS为总环境影响度;b该物质未检出,用检出限代替浓度进行计算;c 1,2,3,5-TeCB和1,2,4,5-TeCB无法分峰,合并定量,记为1,2,3(4),5-TeCB.
a MoCB, DiCB, TrCB, TeCB, PeCB and HCB represent monochlorobenzene, dichlorobenzene, trichlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene, respectively, and TAS is total ambient severity; b This substance was not detected and the concentration was substituted with the limit of detection for the calculation; c 1,2,3,5-TeCB and 1,2,4,5-TeCB could not be separated into single peaks and were combined for quantification, which was recorded as 1,2,3(4),5-TeCB.表 2 不同污水处理系统进出水中CBs的风险熵值及相关数据
Table 2. The Risk quotients (RQs) values and related data of CBs in the influent and effluent of different wastewater treatment systems
污染物
Pollutants a预测无效应浓度/
(μg·L−1) [5, 14, 15]
PNEC风险熵值 RQs A系统
A systemB系统
B systemC系统
C system进水 Influent 出水 Effluent 进水 Influent 出水 Effluent 出水 Effluent MoCB 2.60 0.003 0.002 0.002 0.004 0.002 1,4-DiCB 0.70 0.001 0.003 0.001 0.002 0.001 1,3-DiCB 0.96 0.020 0.035 0.014 0.023 0.004 1,2-DiCB 0.74 0.008 0.017 0.003 0.009 0.005 1,3,5-TrCB —b — — — — — 1,2,4-TrCB 1.32 0.004 0.008 0.001 0.005 0.001 1,2,3-TrCB 2.20 0.002 0.004 0.001 0.002 0.000 1,2,3(4),5-TeCB c 1.55 0.000 0.001 0.000 0.000 0.000 1,2,3,4-TeCB 1.10 0.001 0.001 0.001 0.000 0.000 PeCB 0.25 0.005 0.004 0.005 0.003 0.002 HCB 7.60 0.000 0.000 0.000 0.000 0.000 Total — 0.044 0.074 0.027 0.048 0.015 a MoCB、DiCB、TrCB、TeCB、PeCB和HCB分别代表一氯苯、二氯苯、三氯苯、四氯苯、五氯苯和六氯苯;b数据无法获取;c 1,2,3,5-TeCB和1,2,4,5-TeCB无法分峰,合并定量,记为1,2,3(4),5-TeCB.
a MoCB, DiCB, TrCB, TeCB, PeCB and HCB represent monochlorobenzene, dichlorobenzene, trichlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene, respectively; b Data not available; c 1,2,3,5-TeCB and 1,2,4,5-TeCB could not be separated into single peaks and were combined for quantification, which was recorded as 1,2,3(4),5-TeCB. -
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