摘要
有机磷阻燃剂(OPFRs)是一类对人类健康和生态环境极具危害的新兴污染物。以两种典型OPFRs——磷酸三(2-氯)丙酯(TCPP)和磷酸三(2-氯)乙酯(TCEP)为目标污染物,通过试验研究其在间歇进水复合垂直流人工湿地(IVCW)中的去除效果、沿程去除情况及在基质和植物内的累积量,通过物料平衡分析其在人工湿地生态系统中的输入、输出、累积和转化量,探讨其可能的转化途径。结果表明:复合垂直流人工湿地对水中TCPP和TCEP有良好的去除效果,种植植物稳定运行对其去除率平均分别达74.1%±5.3%和49.3%±5.5%。人工湿地生态系统是输入OPFRs有机质的转化器,从湿地内转化去除的TCPP和TCEP分别占其总输入量的59.72%和44.6%,远大于其在基质和植物内的累积总量(2.37%和1.67%)。基质内生物降解是OPFRs转化的重要途径,TCPP和TCEP的沿程去除与基质内的溶解氧(DO)沿程消耗速率、水中易降解有机物浓度有关。植物种植对TCPP和TCEP去除的促进作用明显,但由于植物体内的浓度限制,难以通过植物收割或加大种植密度来大幅提高湿地对OPFRs的去除率。
作为溴代阻燃剂的替代品,近年来有机磷阻燃剂(Organophosphorus Flame Retardants,OPFRs)被广泛应用于建筑、化工、电子、纺织等行
人工湿地(CWs)作为一种废水生态处理及水体修复技术,因其造价低、运行管理方便、具有景观效应等优点而受到关注。目前对人工湿地处理废水的研究也由COD、N、P等常规污染物拓展到环境中的ECs领域。例如,Kang
笔者选取2种最常用的典型OPFRs——磷酸三(2-氯)丙酯(TCPP)和磷酸三(2-氯)乙酯(TCEP),探究间歇进水方式下复合垂直流人工湿地对二者的整体去除效果、沿程去除情况、在植物和基质中的累积量及可能的转化去除途径,以期为含OPFRs的废水处理及水体修复提供借鉴。
试验用复合垂直流人工湿地构造如

图1 复合垂直流人工湿地装置示意图
Fig. 1 Schematic diagram of the experimental IVCW
试验原水为模拟城市污水处理厂一级B标水质(GB 18918—2002
指标 | 药剂名称 | 浓度/(mg· |
---|---|---|
CODcr | 葡萄糖 | 60 |
SRP | 磷酸二氢钾 | 1 |
NO | 硝酸钾 | 5 |
NH | 氯化氨 | 15 |
微量元素 | Ca、Fe、Zn等 | 0.01 |
TCPP | TCPP标准试剂 | 1 |
TCEP | TCEP标准试剂 | 1 |
中文名称 | 英文缩写 | 化学结构式 | 化学分子式 | lg Kow | lg Koc | 饱和蒸汽压/mmHg |
---|---|---|---|---|---|---|
磷酸三(2-氯)丙酯 | TCPP |
![]() | C9H18Cl3PO4 | 2.59 | 2.71 |
2.02×1 |
磷酸三(2-氯)乙酯 | TCEP |
![]() | C6H12C3PO4 | 1.44 | 2.48 |
6.13×1 |
试验装置搭建完成后开始引入未添加OPFRs的原水启动人工湿地。运行约3个月,待CODcr、NH
试验中人工湿地采用周期性间歇进水的方式运行,以6 d为一周期,即连续进水运行5 d后,经放空管将湿地水完全放空,闲置复氧1 d。进水时,原水由配水箱经蠕动泵注入湿地(见
采样安排:每6 d用黑色聚乙烯瓶从Y1和Y8取样点取样,作为人工湿地的进、出水水样,同时,用仪器对湿地内DO、pH值及水温等理化指标进行现场测定。在试验运行的第75、145、245天从Y2~Y7取样点取样。测定样品中TCPP、TCEP及CODCr、NH
1)样品前处理。水样:用0.45 μm的玻璃纤维滤膜过滤去除水样中有机悬浮颗粒,取约1 mL的水样装进1 mL棕色进样小瓶中,待测。基质样品:将基质样品(火山岩/沸石混合填料、种植土)冷冻干燥5 d后粉碎、研磨,用80目比目筛进行筛分,筛分后的粉末装于棕色玻璃瓶中,于4 ℃冰箱保存直至提取。植物样品:用超纯水冲洗植物根区的土壤,自然风干表面的水汽,将植物样品按照根、茎、叶分开,分别测定其鲜重,其他处理同基质样品。
2)基质、植物样品粉末中OPFRs的提取。提取:取2 g植物样品粉末(基质样品取5 g)于离心管中,加入甲醇+二氯甲烷对TCPP和TCEP进行提取;离心管经恒温振荡(160 r/min、5 min)、超声(25 ℃、15 min)、离心(3 000 r/min、5 min)后取出上清液,继续加入甲醇并重复此过程3次。过滤:将提取液旋转蒸发至近干后用超纯水稀释至250 mL,稀释液经0.45 μm的醋酸纤维滤膜进行过滤。固相萃取:活化HLB、SAX固相萃取小柱后对滤液进行固相萃取。洗脱:用8 mL乙酸乙酯将固相萃取小柱洗脱2次至洗脱管中。氮吹:于30 ℃的水浴锅中氮吹洗脱液,氮吹至溶液近干时,加入0.5 mL正己烷。吸出氮吹管中的溶液并过0.22 μm有机滤膜,将富集好的含有机样品的溶液装进1 mL棕色进样小瓶中,待测。
3)测定。采用高效液相色谱—三重四极杆串联质谱仪(LC-MS/MS8040,岛津公司)进行分析,所用柱子型号为InertSuatain C18(150 mm×4.6 mm,5 μm,Tokyo,Japan),所用流动相A为甲醇,流动相B为超纯水,流动相A:流动相B=80%:20%,固定相为InertSuatain C18柱子—十八烷基。采用等度洗脱的方式,速度为1 mL/min,柱温为40 ℃,进样体积为10 μL,并用正离子电喷雾的多反应监测模式。
两种OPFRs在复合垂直流人工湿地试验装置中的进、出水浓度及去除率随时间变化情况如

(a) TCPP的进、出水浓度和去除率

(b) TCEP的进、出水浓度和去除率
图2 TCPP和TCEP的进、出水浓度和去除率
Fig. 2 Concentrations of influent and effluent and removal rate of TCPP and TCEP
不同OPFRs在湿地内总体去除情况差异明显。TCPP和TCEP的出水浓度和去除率分别在170、140 d后达到相对稳定(
TCPP和TCEP在人工湿地内沿流程的变化如

(a) TCPP的沿程变化及DO分布

(b) TCEP的沿程变化及DO分布
图3 人工湿地内TCPP和TCEP的沿程变化及DO分布
Fig. 3 Variations of TCPP and TCEP concentrations along the flow path and the distribution of dissolvedoxygen(DO)
对湿地内溶解氧的监测发现,这一规律与湿地床内DO的浓度梯度呈明显相关性(见
人工湿地装置运行245 d时TCPP和TCEP的去除率明显高于85、140 d,一方面说明人工湿地能逐步构建出一个稳定去除TCPP和TCEP的物理、化学、生物协同作用系统;另一方面说明植物的种植能在一定程度上促进OPFRs的去除。
湿地生态系统中有部分OPFRs有机质从水相迁移并逐步累积到基质与植物内。
试验人工湿地基质包括火山岩/沸石混合填料与上层种植土两种。试验分别测定了引入模拟废水之前和试验结束时湿地基质内TCPP和TCEP浓度,其差值作为试验期间水相向固相迁移而累积到基质内的TCPP和TCEP量,如

(a) TCPP和TCEP在基质中的累积

(b) TCPP和TCEP在植物中的累积
图4 基质、植物中TCPP和TCEP的累积情况
Fig. 4 Cumulative situation of TCPP and TCEP in substrate and plant
由
由
由
整个试验期间,根据人工湿地流量、TCPP和TCEP进、出水浓度进行物料平衡,计算两种OPFRs的总输入量和输出量,通过扣除累积于基质及植物体内未发生转化的量来分析TCPP和TCEP在湿地生态系统中发生转化所去除的量和占比,如

图5 人工湿地中TCPP和TCEP的物料平衡和转化途径
Fig. 5 Mass balance of TCPP and TCEP in IVCW and their possible transformation mechanisms
基质和植物内的累积总量对整个试验期间TCEP和TCPP去除的贡献率都非常有限,仅占TCEP和TCPP进水总输入量的2.37%和1.67%。但随着废水的输入,湿地基质内沉积物(有机物或无机物)累积量的增加可能会促进基质内TCEP和TCPP累积量的进一步增长。另外,研究表
整个试验期间,在湿地生态系统中发生转化去除的TCPP和TCEP分别为9 021.8、7 096.4 mg,占这两种OPFRs总输入量的59.72%和44.46%,远大于基质和植物内未发生转化的累积量,因此,对于输入的OPFRs有机质,人工湿地更多地扮演了转化器的角色。其转化去除可能的途径包括微生物降解、水解、光解、蒸发以及进入植物体内转化降解和随植物呼吸作用蒸腾进入大气(见
氯代OPFRs主要通过磷酸酯的水解以及脱氯和氧化的方式被生物降
种植植物前后人工湿地试验装置对OPFRs去除的对比情况如

图6 种植植物前后人工湿地TCPP和TCEP出水浓度和去除率
Fig. 6 The effluent concentrations and removal rates of TCPP and TCEP in IVCW before and after planting
1)在HRT为5.6 d、间歇运行模式下,复合垂直流人工湿地对水中TCPP和TCEP有良好的去除效果,在种植植物并稳定运行后,平均去除率分别达到74.1%±5.3%和49.3%±5.5%。
2)人工湿地系统是OPFRs有机质的转化器,从湿地内转化去除部分分别占这两种OPFRs总输入量的59.72%和44.6%,远大于其在基质和植物内的累积总量(分别占TCPP和TCEP输入总量的2.37%和1.67%)。
3)湿地基质内发生的生物降解是OPFRs转化的重要途径,TCPP和TCEP在湿地内的沿程去除与基质内的DO沿程消耗速率、水中易降解有机物浓度都明显相关。
4)植物种植对TCPP和TCEP去除的促进作用明显,但由于植物体内OPFRs浓度有限,通过植物收割或增大种植密度来大幅提高湿地对OPFRs去除率的途径并不现实。
5)湿地生态系统对OPFRs汇的作用有限,但仍可通过基质内有机和无机沉积物的累积实现OPFRs有机质在基质内累积量的持续增加。
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