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作为全球最大的染料生产国,我国众多染料生产及相关化工企业产生的染料废水已经成为公认的主要工业污染源之一。据2019年中国环境统计年报报道,42个行业全年处理工业废水总计274.9亿吨,其中纺织业和造纸业产生的染料废水总量占比为12.9%,约为35.46亿t[1-2]。工业生产过程中的含氮染料具有抗氧化降解、裂解后易产生致癌芳香胺等特点[3],传统的化学氧化技术对染料废水中有机污染物的降解能力已难以满足工业处理需求,因此开发高效、经济、节能的工业染料废水处理技术势在必行。
20世纪80年代逐渐发展起来的高级氧化技术(AOPs),它以产生具有强氧化性的活性氧化物种为特点,其中以羟基自由基(•OH)为代表[4]。这些活性氧化物种通过电子转移、亲电加成或取代等化学反应裂解有机官能团内部的化学键,将难降解的有机物转化为低毒或无毒的物质,实现对有机污染物的无害化处。因此,高级氧化技术被认为是处理工业染料废水中难降解污染物的有效途径,在染料废水处理方面的高效性逐渐成为研究热点。
本文以罗丹明B、罗丹明6G、橙黄G、直接红81、酸性黄23和活性蓝13等含氮染料为例,讨论高级氧化技术臭氧(O3)、芬顿(Fenton)、光催化(UV)、超声(US)、水力空化(HC)、过硫酸盐(PS)和超重力(RPB)等对上述目标污染物的降解效果,为可能应用于工业染料废水治理的环保技术提供参考价值。
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学者们一致认为羟基自由基与大多数染料发生化学反应时速率常数非常高[5]。WANG et al[6]提出臭氧和过氧化氢产生了氧自由基和羟基自由基,并且能将偶氮染料中的-N=N-裂解成更小或非发色基团。
pH值在臭氧降解印染废水的过程中至关重要。酸性环境不利于臭氧降解有机物的过程;当pH值>8.5时,染料对pH值高度敏感且不易降解。早期的报道认为臭氧能使染料分子的芳香环开环[7],受pH值变化的影响,氧化机制从臭氧的直接攻击转变为多个活性氧化物种的间接攻击,形成了复杂的链式反应机制[5]。臭氧技术的缺陷在于染料化合物极大地缩短了臭氧的半衰期,水体中pH值的波动和其他无机盐也很大程度地影响了臭氧技术的稳定性[8]。芬顿工艺降解印染废水的技术缺陷在于催化剂的絮凝产生了铁污泥[9],相比之下,光催化和过氧化氢氧化过程中因“零污泥”而更有技术优势[10]。
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单一使用超声工艺的优点是去除有机物时既不需要添加氧化剂,也不要求调整pH值。最早的时候,GOGATE et al[11]采用18个50W不同频率的换能器降解染料罗丹明B,但是染料降解率仅有7%;WANG et al[12]发现在pH值为中性时,活性艳红降解率已经达到24%、甲基紫降解率为80%[13]。
超声工艺过程中添加氧化剂可形成协同效应、提升氧化性能。据HARICHANDRAN和PRASAD[14]报道在pH值为3时,超声与臭氧和芬顿耦合后将直接红色染料的降解率上升到100%。类似地,ZHANG et al[15]在pH值为3时,采用超声联合芬顿降解了>99%的酸性橙7。在超声工艺过程中添加无机盐有助于降解染料,MEROUANI et al [16]添加了少量的碳酸盐、碳酸氢盐和硫酸钠氧化罗丹明B,在25~30 min内降解了大约100%的染料。
降解染料的氧化过程中pH值至关重要。大多数报道表明酸性pH值对降解罗丹明B有利,SIDDIQUE et al [17]也表明酸性pH值有利于降解活性蓝;BOKHALE et al [18]在碱性pH值为12.5时,罗丹明6G的降解率仅为50%~70%;这是因为酸性环境通过质子化作用提高了反应速率,强化了分子的疏水性质,加大了在气液界面处污染物与活性氧化物种有最高浓度接触的可能性,有益于降解染料。INCE et al [19]认为在碱性pH值下,碳酸根等阴离子消耗了羟基自由基,与染料分子发生了竞争,从而抑制了染料降解。
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与超声工艺类似,单一水力空化技术对染料降解率大约在25%~60%之间;水力空化与其他高级氧化技术耦合后对各种染料的降解性能均有显著提高。添加一定浓度的过氧化氢或芬顿试剂后,MISHRA et al [20]证实罗丹明B染料降解率达到99.9%;添加过氧化氢后,WANG et al[21]发现橙黄G的降解率从26%提高至99.5%,SAHARAN et al[22]报道72%的酸性红88染料发生了降解;添加臭氧后,RAJORIYA et al[23]表明活性蓝染料的降解率为72%。
降解染料过程中pH值是影响效率的一个关键因素。多数研究认为在酸性pH值条件下才能取得> 90%的降解率,pH值为2~3比5~8更有利于染料降解[12];RAJORIYA et al[24]发现在碱性条件下水力空化与氧化剂耦合后仅降解了40%~70%的罗丹明B。
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超重力技术是一项发轫于上个世纪末的化工过程强化技术。超重力与臭氧耦合后显著提升氧化性能,最好的降解效果罗丹明B达到94%[25],活性红120和酸性红299均为93%[26],酸性黄23降解了84%[27],靛蓝胭脂红氧化了72.8%[28],酸性红B最低为72%[29]。在超重力与臭氧耦合的基础上分别加入以下试剂,加入Fe(II)后,甲基橙的脱色率达到73.3%[30],酸性红B脱色率上升到80%[29];加入过氧化氢降解染料时,酸性红B的脱色率仅77%[27];加入芬顿试剂后,酸性红B的脱色率增大到92%[29],酸性黄23达到94%[27];加入过硫酸盐+Fe(II)后,甲基橙的脱色率提高到83.4%[30];加入光催化和纳米TiO2颗粒后,酸性黄23达到100%[27]。在超重力中加入过硫酸盐和Fe(II)后,甲基橙的脱色率提升到90%[30];继续加入过氧化氢,酸性黄23的脱色率增大到95%。大多数研究认为超重力强化了液-液或液-固之间传质促进生成了更多的活性氧化物种。
实际废水中存在的其他物质的竞争作用对染料降解有显著影响。采用超重力-臭氧工艺处理活性红120和酸性红299 溶液,这两种染料的模拟溶液降解率在2 min之内均可达到100%,而主要由这两种染料组成的实际印染废水在处理30 min后降解率为93%[26]。文献中报道的超重力降解效果基本上在20 min内完成,这就极大地降低了染料废水的处理成本。
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采用不同外场与反应介质耦合的高级氧化技术降解部分染料废水的技术参数,见表1。
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(1) 各种高级氧化技术耦合用于降解含氮染料是今后发展趋势,通过外场(超声、光催化、水力空化和超重力)与各种氧化剂(臭氧、芬顿、过硫酸盐和过氧化氢)耦合技术连用,均能显著提高对染料分子的降解能力。
(2) pH值是影响含氮化合物降解效率的重要因素,酸性环境pH(2~3)有利于提高含氮染料的反应速率,也有少数研究报告认为在碱性条件下降解效果较好。
(3) 现有实验室工艺处理的染料废水浓度在1 000 mg/L 以内,但工业实际废水含有污染物的复合基质,需要对整体处理过程的工艺条件进一步优化与研究。
高级氧化技术治理含氮染料废水的研究进展
Review on degradation of nitrogen-containing dyeing wastewater using advanced oxidation processes
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摘要: 染料废水是目前难治理的工业废水之一,高级氧化技术被认为是处理工业染料废水中难降解污染物的有效途径。本文归纳了高级氧化技术的类型,阐述了高级氧化技术降解染料废水的影响因素,列举了高级氧化技术对几种含氮化合物的降解效果;为可能应用于染料废水治理过程中的环保技术提供参考价值。Abstract: At present, dyeing wastewater was one of industrial wastewater to be treated difficultly. The advanced oxidation processes could effectively process the high content of refractory pollutants of industrial dyeing wastewater. This paper summarized the types of advanced oxidation processes and expounded the factors affecting the degradation of the wastewater. The degradation effect of several important N-containing compounds from dyeing wastewater by advanced oxidation processes was proposed. The paper could provide a reference for the environmental technologies on dyeing wastewater treatment.
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Key words:
- advanced oxidation /
- nitrogen-containing organics /
- dyeing wastewater /
- degradation /
- oxidization
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表 1 高级氧化技术(臭氧、芬顿、超声、水力空化、光催化、过硫酸盐和超重力等)降解部分染料
染料 高级氧化
技术降解率
/%时间
/min初始浓度
/mg·L−1橙黄G[31] HC 25.6 120 20 HC+H2O2 99.5 120 20 HC+Fenton 99.8 120 20 活性大红[12] US 24 240 10 US+Fenton - 240 10 活性红120[32] HC 28 180 45.5 HC+H2O2 60 180 45.5 甲基紫[13] US 80 120 5 ZnO PC 70.4 210 20 酸性红14[33,34] ZnO PC+H2O2 90 210 20 UV/TiO2 90 150 20 酸性黄23[35] 光Fenton 99 60 40 Fenton 73 60 40 O3+US 100 6 100 US+Fenton 99 75 50 酸性橙7[15] US+Fenton 99 30 80 活性蓝13 HC 19 120 150 HC+O3 72 120 150 HC+H2O2 25 120 150 活性蓝19[17] US+Fenton 75 30 25 HX 35 120 40 酸性红88 HC+H2O2 72 120 40 HC+Fe-TiO2 35 120 40 HC 60 120 10 HC+H2O2 99.9 120 10 HC+Fenton 99.9 45 10 HC+CCl4 82 120 10 HC 32 120 10 HC+H2O2 53 120 10 罗丹明
B[11,16,36-41]O3 41 120 10 HC+O3 73 120 10 US 7 30 4.5×10−3 US+碳酸氢盐 99.9 50 0.5 US+碳酸盐 99.9 30 0.5 US+碳酸氢盐+硫酸钠 100 25 0.5 US 99 140 5 US+Fe - 140 5 US+Fe(II) - 140 5 US+Fe(III) - 140 5 US+CCl4 100 5 5 US+H2O2 - 140 5 US+叔丁醇 - 140 5 US+硫酸钠 - 140 5 US(涡流分散) 98 60 10 O3 92.15 15 100 UV+O3 97.8 15 100 US+O3 94 15 100 TiO2 PC(TiO2包覆SiO2) 98 240 4.79 Fenton 100 30 47.9 光-Co-TiO2-O3 100 120 50 光-Fenton 98-100 180 80 罗丹明6G[18] US+CuO 53 180 10 US+TiO2 52 180 10 US+UV+CuO 61 180 10 US+UV+TiO2 63 180 10 US+CuO+n-丁醇 70 180 10 甲基橙[30] RPB+Na2S2O8+
Fe(II)90.18【1】 - 50 RPB+O3+
Fe(II)73.3 - 200 RPB+Na2S2O8+
Fe(II)+O383.4 - 200 RPB+Na2S2O8+
Fe(II)+H2O295 - 100 酸性黄23[27] RPB+O3 84.0 - 200 RPB+O3+Fenton 94.0 - 200 酸性红B[29] RPB+O3 72 20 1000 RPB+O3+
Fe(II)80 20 1000 RPB+O3+H2O2 77 20 1000 RPB+O3+Fenton 92 20 1000 罗丹明B[25] RPB+O3 94 20 200 RPB+O3+UV 100 20 200 靛蓝胭脂红[26] RSR+O3+SBR 72.8 - 200 RSR+ PS+ Fe(II)+
SBR【2】71.6 - 200 注:1.文献中超重力环境下研究数据为脱色率;2.RSR代表超重力定-转子反应器,SBR代表序批式活性污泥工艺。 -
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