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垃圾渗滤液渗漏严重污染地下水水质,其中含有大量难降解的有机污染物、重金属、无机盐等,可生化性差[1-3]。因垃圾渗滤液COD值高、自身降解以及发酵过程缓慢,一旦发生渗漏,会长期威胁地下水质量。作为重要原位修复技术的渗透性反应格栅(PRB)被应用于修复受垃圾渗滤液污染的地下水[4-6],PRB可通过填充反应介质来去除地下水中的有机污染物,由于运行成本低、处理污染物种类多、长时间处理能力强等特点,具有广阔的应用价值和市场发展前景[7-9]。因此,在PRB工程中,选取兼具经济性、缓释性以及高效性的填充材料尤为重要。
高级氧化技术(AOPs)通过金属、光和电等方式来催化氧化剂以生成具有强氧化性的自由基,从而降解垃圾渗滤液中的有机物[10]。Fenton法因其具有操作简单、无二次污染等优势,近年来被越来越多的学者用于垃圾渗滤液处理的研究和实际工程中[11-13]。Fenton法通过Fe2+催化H2O2,产生羟基自由基(HO·),将难氧化的大分子有机物降解为小分子物质甚至完全矿化,同时生成的Fe(OH)3以絮凝沉淀的方式实现污染物的去除[14-17]。然而H2O2是液体,受运输、储存等条件的限制,在处理过程中,需要调节体系pH至2~4并定时投加H2O2,故H2O2不适宜作为地下水的原位修复材料。过碳酸钠(sodium percarbonate,SPC)分子式为Na2CO3·1.5H2O2,溶于水后分解为Na2CO3和H2O2[18],pH的适用范围广,具有很好的稳定性,易于储存和运输,且无毒无害,是工业中常用的固体氧化剂和消毒剂[19-21]。目前已有将SPC用于去除有机污染物的研究。ZANG等[22]发现,SPC/Fe2+体系降解三氯乙烯(TCE)效率可达99.5%以上。白青青等[23]的研究也表明,SPC/Fe2+体系可以在pH为 2~10时可有效降解亚甲基蓝。KWARCIAK[24]等探究了SPC/Fe2+体系降解垃圾渗滤液中溶解性有机污染物(DOM)的最佳反应条件。然而SPC/Fe2+体系对有机污染物的降解机理尚不清楚,目前SPC/Fe2+体系用于修复垃圾渗滤液污染地下水的研究鲜见报道。
本研究通过构建SPC/Fe2+体系处理被垃圾渗滤液污染的地下水,探讨了体系内重要反应参数n(SPC):n(FeSO4·7H2O)、SPC的投加量和反应时间对受垃圾渗滤液污染的地下水中COD去除效果的影响,通过自由基淬灭实验、紫外-可见光谱与三维荧光光谱分析来探究SPC/Fe2+体系去除COD的机理,以期为受垃圾渗滤液污染地下水的原位修复提供理论依据。
亚铁活化过碳酸钠对垃圾渗滤液污染地下水中COD的去除
Removal of COD in groundwater contaminated by landfill leachate by ferrous-activated sodium percarbonate
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摘要: 针对垃圾渗滤液渗漏严重威胁地下水水质的问题,以过碳酸钠(sodium percarbonate,SPC)为固体氧化剂来构建地下水的原位修复技术,采用单因素法,以受污染的高COD地下水为处理对象,通过实验研究了n(SPC):n(FeSO4·7H2O)、药剂投加量、反应时间对SPC/Fe2+体系去除COD的影响和SPC/Fe2+体系的反应机理。结果表明:n(SPC):n(FeSO4·7H2O)和SPC的投加量显著影响COD的去除效能;在初始pH值为7.22、n(SPC):n(FeSO4·7H2O)=1:2.75、SPC投加量为48 mmol·L-1以及反应30 min的最佳实验条件下,COD的去除率可达82.09%;SPC/Fe2+体系通过降解类蛋白有机物和腐殖酸实现高COD地下水的有效处理,主要活性物种HO·能够有效减小腐殖质分子量及其分子间聚合度,同时降低芳香性构化程度。由此可知,SPC作为固体氧化剂有应用于实际渗透性反应格栅(PRB)工程的潜力。本研究结果可为PRB在修复受垃圾渗滤液污染地下水的实际工程提供参考。Abstract: Landfill leachate leakage is a serious threat to groundwater quality. Sodium percarbonate (SPC) was used as a type of solid oxidant to build the in-situ remediation technology of groundwater. The single factor method was used to study the remediation test on the treatment object: the polluted groundwater with high COD. The effects of n(SPC):n(FeSO4·7H2O), chemical dosage and reaction time on COD removal and the corresponding reaction mechanism of SPC/Fe2+ system were studied. The results showed that n(SPC):n(FeSO4·7H2O) and SPC dosages significantly affected the removal efficiency of COD; under the optimal experimental conditions of initial pH 7.22, n(SPC):n(FeSO4·7H2O) of 1:2.75, SPC dosage of 48 mmol·L−1 and reaction time of 30 min, the removal rate of COD could reach 82.09%; the SPC/Fe2+ system achieved the effective treatment of high-COD groundwater by degrading proteinoid organics and humic acid. The main active species HO· could effectively decrease the molecular weight of humus and its intermolecular polymerization degree, as well as the degree of aromatization. SPC as solid oxidant had a potential for its application in permeable reactive barrier(PRB) engineering. The results of this study can provide a reference for the practical engineering of PRB in the remediation of groundwater contaminated by landfill leachate.
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Key words:
- groundwater /
- landfill leachate /
- sodium percarbonate /
- chemical oxygen consumption
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表 1 原水三维荧光光谱特征峰
Table 1. Characteristic peaks of 3D-fluorescence spectrum of raw water
荧光峰编号 (Em/Ex)/nm 相对荧光强度 区域 F1 337/230 4 149 Ⅱ F2 337/278 6 976 Ⅳ F3 487/383 4 258 Ⅴ 表 2 原水处理前后特征吸光度的变化
Table 2. Changes of characteristic absorbance of raw water before and after treatment
样品 E240/E420 E250/E365 E300/E400 E253/E203 原水 25.400 4.900 7.300 0.691 处理后原水 46.425 7.955 13.148 0.198 -
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