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近年来随着我国城镇化水平的深入推进,城市下垫面不透水层比率迅速提高,加速了径流形成过程,缩短了径流汇集时间;与此同时,人类活动增加了蓄积在城市下垫面污染物的种类和数量。二者共同作用,使得由地表径流引发的城市水体污染问题日益突出[1]。生物滞留池是用于城市雨洪管理的一种低影响开发(low impact development, LID)技术,其可通过地表径流原位滞留调节峰值流量,并通过吸附、生物吸收和降解以去除地表径流中的污染物[2]。有研究表明,生物滞留池对传统目标污染物,如重金属[3]、多环芳烃[4]、总氮、总磷等均具有较好的去除效果[5-6]。
全氟化合物(perfluorinated compounds, PFCs)是一种典型的新污染物,作为表面活性剂和保护剂被广泛应用于日常用品及工业生产中。PFCs具有生物毒性和生物累积性,可在人体内蓄积造成健康危害[7]。城市下垫面累积的全氟和多氟烷基化合物(per/polyfluoroalkyl substances, PFASs)主要来源于大气PFASs及其前体物的传输和沉降[8-9],并在雨水冲刷下进入受纳水体。有研究表明,雨季河水中的PFASs浓度水平明显高于旱季[10]。因此,地表径流中的PFCs含量不可忽视,明确生物滞留池对PFCs的削减效能对城市面源污染防治和可持续发展具有十分重要的现实意义和科学价值。
传统生物滞留系统的填料层(bioretention soil media,BSM)常由土壤与细砂混合而成,具有良好的渗透性能[11]。近年来,以煤质活性炭、沸石等为主要改良剂的生物滞留池得到了广泛运用。活性炭层可明显提高脱氮效率,使氨氮(NH3-N)和总氮(TN)的平均去除率达到80.27%和59.45%[12],沸石层对多环芳烃的去除率达40%以上[13]。然而,改良填料层对PFCs的去除能力及各污染物在系统中的空间分布特征尚不清楚。为此,本研究通过构建不同填料的生物滞留系统,利用为期1 a的模拟实验考察了改良填料下生物滞留池的水量削减效能,分析了其对常规污染物和PFCs的去除效果,探讨了PFCs是否影响常规污染物去除及其长期运行能力,以期为城市雨洪综合管理提供参考。
生物滞留池对地表径流中常规污染物及全氟化合物的去除效果
Removal of conventional pollutants and perfluorinated compounds from urban storm water by bioretention system
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摘要: 生物滞留系统是实现城市地表径流水量调控和水质净化的新型绿色生态系统,但其对全氟化合物的去除效能尚不清楚。本文构建了将传统填料与2~4 mm沸石(体积占比10%)或2~4 mm的改良煤质颗粒活性炭(体积占比10%)混合的2种柱形生物滞留系统,通过动态实验探究了此系统对地表径流中常规污染物和全氟化合物去除效果,分析了系统近1 a的运行效果。结果表明,生物滞留系统的水量削减率随运行时间的增长呈现下降的趋势,平均削减率为(29.8±8.2)%。改良煤质颗粒活性炭生物滞留池对COD、TN、TP、TOC、
$ {\mathrm{N}\mathrm{H}}_{4}^{+} $ -N的平均去除率分别为67.49%、84.78%、76.43%、80.28%、65.43%,优于以沸石为填料的滞留池。6种目标全氟化合物PFPeA、PFHxA、PFHpA、PFOA、PFOS、PFNA的去除率保持在80%以上。滞留池内污染物空间分布特征表明,PFBA主要集中于种植层,而PFPeA、PFHxA、PFHpA、PFOA、PFOS、PFNA则更集中于填料层。Abstract: Bioretention system is a new and green ecosystem to regulate the urban surface runoff and water quality purification, but its removal efficiency for perfluorinated compounds is unknown. Based on the reported concentrations of perfluorinated compounds in surface runoff, two cylindrical bioretention systems were constructed with traditional fillers mixed with 2~4 mm zeolite (volume ratio of 10%) or 2~4 mm improved coal granular activated carbon (volume ratio of 10%) as the main fillers. The removal efficiencies of conventional contaminants and perfluorinated compounds by both systems were investigated, as well as the one-year operation efficiency. The results showed that the water reduction rate decreased with the extension of operation time, and the average reduction rate was (29.8±8.2)%. After one-year operation, the average removal rates of COD, TN, TP, TOC and$ {NH}_{4}^{+} $ -N by the bioretention column with the improved coal granular activated carbon were 67.49%, 84.78%, 76.43%, 80.28% and 65.43%, respectively, which were better than bioretention column with zeolite. The removal efficiencies of PFPeA, PFHxA, PFHpA, PFOA, PFOS and PFNA maintained above 80%. The spatial distribution of pollutants showed that PFBA was mainly concentrated in the plant layer, while PFPeA, PFHxA, PFHpA, PFOA, PFOS and PFNA were concentrated in the filler layer.-
Key words:
- bioretention /
- perfluorinated compounds /
- surface runoff /
- reduction efficiency
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表 1 生物滞留装置实验条件设计
Table 1. Experimental condition design (for a single bioretention column)
实验条件 进水浓度 重现期/a 降雨历时/min 实验水量/L 降雨间隔/d 1 c 0.5 180 58 3 2 c 0.5 180 58 10 3 2c 0.5 180 58 20 -
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