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城市地表径流是城市地表水体的主要水量补给[1],其中含有人类活动和自然过程产生的许多污染物,包括氮磷等营养物质、有毒有机物、重金属、悬浮固体、油、有机碳和致病菌[2]。植物滞留系统作为一种低影响开发 (low impact development,LID) 雨水管理措施,最初提出并应用于美国马里兰州乔治王子县,后来这项技术被称为雨水花园和生物渗透,并以最多样化的形式迅速成为最常用的最佳管理措施[3]。尽管该技术在控制水质方面具有重要意义,但在以前的研究中仍不能完全控制住磷的排放[4-5]。
关于生物滞留系对P去除影响的研究主要集中在不同过滤材料上[6],如 LI等[7]研究了医疗石、蛭石、泥炭土等6种填料介质对磷的去除效果发现,添加水处理残渣对总磷 (TP) 和可溶性活性磷 (SRP) 具有最佳去除率。但进一步深入研究发现一些效果不好的材料中仍会有磷浸出。由于雨水的冲刷或有机材料如堆肥、泥炭或地膜等的腐烂亦会造成磷浸出[8][9]。与纯砂子介质的植物滞留系统相比,在介质中加入少量有机质可提高磷的去除率[10]。在介质中直接加入铝和氧化铁,可显著促进磷沉淀[11]。雨水中大多数磷为颗粒态,且TP流出浓度通常与总悬浮固体 (TSS) 流出浓度相关[12],介质中的不同形态磷对富营养化的作用有所差异,生物对不同形态磷的吸收利用也不同。植物滞留系统的主要除磷机制是沉积物吸附[13-14],其中正磷酸盐PO4−3-P与金属离子 (Fe、Al、Ca) 发生化学反应,形成不溶性化合物沉淀并在水中去除[15]。关于介质中磷形态的研究越来越多,大多数磷以无机磷形态存在于介质中。钙磷是其中的主要成分,有机磷所占比例较少。至今为止,无机磷分为水溶性磷、铁磷、铝磷、钙磷、闭蓄态磷等。其中正磷酸盐是溶解磷的主要形式,可直接被植物捕获[16],也可通过过滤介质吸附以降低溶解态磷的浸出。土壤中溶解态磷去除的过程包括吸附、沉淀和离子交换[17]。但对有机磷的研究进展则较慢,形态分级较为粗略。
已有不少学者提出使用各种添加剂,如粉煤灰、膨胀页岩、生物炭、浮石、铁屑或铁丝,以提高对磷的吸附能力,从而提高其去除率[17]。然而,目前关于土壤介质添加剂的添加量对介质去除磷污染物效果的影响及各形态磷含量变化情况鲜有报道。本研究以盆栽与柱实验为主要手段,对填料层增添不同添加剂改良介质和改变pH条件后对磷的去除效果及介质中各形态磷转化进行研究,探讨了影响各形态磷含量的主要因素。使植物滞留系统能在降低雨水浓度及去除雨水径流中的污染物方面发挥更好的作用,以期为植物滞留系统的设计提供参考。
植物滞留系统中磷污染物的迁移转化
Transport and transformation of phosphorus contaminants in plant retention systems
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摘要: 植物滞留系统作为一种低影响开发 (LID) 雨水管理措施,能有效去除雨水径流中的各种污染物。为探究磷污染物在介质中的运移机理尤其是介质中磷形态的运移,通过对填料层土壤介质施加不同添加剂对磷的去除效果,以及介质中各形态磷转化机理进行研究。结果表明:土壤介质添加剂为葡萄糖、淀粉时,加入淀粉的混合介质对磷的去除率比土壤介质高,对介质中稳定有机磷及中等稳定有机磷含量变化情况没有明显影响,但介质中铁磷有一定增加。与土壤介质相比,土壤与粉煤灰混合介质对磷的去除率明显提高,且混合介质中的水溶性磷、钙磷、铝磷增加量明显增大。改变人工模拟雨水pH的实验结果显示,在含氧量高的土壤介质表层,当模拟雨水pH为7~12,介质中的无机磷中水溶性磷的增加量明显;然而,当pH小于7时,介质中的无机磷中水溶性磷 (Ads-P) 的增加量微弱。柱实验表明,在植物滞留系统深度为40 cm处开始,随着深度的增加,雨水径流的出水中各类磷的质量分数降低趋势变得缓慢。其中,每组实验柱对磷去除率的平均值由大到小的顺序为:粉煤 灰+砂土>砂土>淀粉+砂土。随着深度的增加,这3组实验柱介质中的铝磷和中等活性有机磷均减少。该研究成果可为植物滞留系统磷污染物的迁移转化提供参考。Abstract: Plant detention systems as a low impact development (LID) stormwater management measure can effectively remove various pollutants from stormwater runoff. In order to investigate the transport mechanism of phosphorus pollutants in the media especially the transport of phosphorus forms in the media. The effect of phosphorus removal by applying different additives to the fill layer soil media and the mechanism of phosphorus transformation in each form in the media were investigated. The results showed that when the soil media additives were glucose and starch, the mixed media with the addition of starch had a higher removal rate of phosphorus than the soil media, and there was no significant effect on the change of stable organic phosphorus as well as medium stable organic phosphorus content in the media, but there was a certain increase of iron phosphorus in the media. Compared with the soil media, the mixed media of soil and fly ash showed significantly higher removal of phosphorus, and the increase of water-soluble phosphorus, calcium phosphorus, and aluminum phosphorus in the mixed media was significantly greater. The experimental results of changing the pH of artificial simulated rainwater showed that the increase of water-soluble phosphorus in inorganic phosphorus in the media was significant when the pH of simulated rainwater was in the range of 7-12 in the surface layer of soil media with high oxygen content, however, the increase of water-soluble phosphorus in inorganic phosphorus in the media was weak when the pH was less than 7. The column experiments showed that starting at a depth of 40 cm in the plant retention system, the tendency to reduce the effluent concentration of stormwater runoff became slower with increasing depth. The mean values of phosphorus removal rates for each of these experiment tal column groups in descending order were fly ash+sandy soil > sandy soil > starch+sandy soil. The aluminum phosphorus and moderately reactive organic phosphorus in the media of all three groups of experimental columns decreased with increasing depth. The modification research results can provide some reliable data for the migration transformation of phosphorus pollutants in plant retention system.
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Key words:
- plant retention system /
- pH /
- soil media additives /
- organic phosphorus /
- inorganic phosphorus
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表 1 “砂土+粉煤灰”混合介质中的有机磷及无机磷本底值
Table 1. Background value content of organic and inorganic phosphorus for mixed media of sandy soil+fly ash
样品名称 LOP/
(mg·kg−1)MLOP/
(mg·kg−1)MROP/
(mg·kg−1)HROP/
(mg·kg−1)Ads-P/
(mg·kg−1)Al-P/
(mg·kg−1)Fe-P/
(mg·kg−1)Obs-P/
(mg·kg−1)Ca-P/
(mg·kg−1)砂土 0.001 200 0.083 200 0.007 800 0.013 800 0.003 050 0.003 540 0.002 560 0.000 912 0.013 110 砂土+2%粉煤灰 0.002 800 0.090 600 0.008 000 0.015 200 0.003 130 0.005 890 0.003 900 0.000 958 0.013 280 砂土+4%粉煤灰 0.004 600 0.097 800 0.008 000 0.016 800 0.003 210 0.008 230 0.005 240 0.001 000 0.013 450 砂土+6%粉煤灰 0.006 400 0.105 200 0.008 000 0.018 400 0.003 280 0.010 580 0.006 580 0.001 050 0.013 620 砂土+8%粉煤灰 0.008 200 0.112 400 0.008 200 0.019 800 0.003 360 0.012 920 0.007 920 0.001 100 0.013 800 砂土+10%粉煤灰 0.010 000 0.119 800 0.008 200 0.021 400 0.003 440 0.015 270 0.009 260 0.001 140 0.013 970 注:粉煤灰百分数为体积分数。 -
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