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含氯挥发性有机物 (Cl-VOCs) 是我国京津冀、长三角和珠三角地区土壤最常检测到的挥发性有机污染物 (VOCs) 之一[1-3]。Cl-VOCs挥发性强,具有环境持久性和抗生物降解性等特点,人体长期接触含氯有机物,可使机体抵抗力下降,引起神经衰弱综合征等疾病[4-6]。
Cl-VOCs污染土壤目前常用修复方法有生物降解[7]、土壤淋洗[8]、化学催化氧化[9]以及热脱附[10]。近年来,热脱附技术由于处理周期短、安全性高、二次污染小等优点[11]被广泛应用于有机污染场地的处置。热脱附是一个加热分离的过程,加热温度[12]和脱附时间[13]是影响热脱附效率的关键因素。Cl-VOCs在热脱附过程中进行脱氯和降解[14]。有研究发现在热脱附过程中添加碱性物质能促进Cl-VOCs的降解和脱氯。KAWAHARA等[15]利用加热和碱基促进有机氯组分的活化,发现碱基能促进氯原子的脱除;刘洁等[16]发现,NaOH的加入会促进污染土壤中多氯联苯的脱附和降解;黄海等[17]研究发现,碱性物质投加能有效提高硫丹的脱氯效率。这些研究均表明,碱性物质具有强化热脱附修复Cl-VOCs的潜力,但对添加碱性物质协同热脱附修复三氯苯污染土壤的工程案例鲜有报道。加热能有效去除污染土壤中的有机污染物质,但加热对土壤理化性质的改变也存在不容忽视的影响[18]。目前,国内对热脱附前后土壤理化性质变化的研究较少,土壤有机碳、有效磷、阳离子交换量和电导率是土壤性质中比较典型的指标,可以通过研究以上指标来综合评估土壤性质的变化。
以1,2,4-三氯苯(TCB)污染土壤为研究对象,选取廉价易得的NaOH、Ca(OH)2 、NaHCO3和CaCO3为添加剂进行强化热脱附实验。探究脱附时间、加热温度以及碱基添加剂对污染土壤中TCB去除效率的影响,并选取有机碳含量、有效磷浓度、土壤阳离子交换量和电导率作为热脱附前后土壤的理化性质指标进行分析验证中低温(150~350 ℃)热脱附对土壤理化性质的影响,以为TCB污染土壤热脱附的实际应用提供参考。
4种碱基添加剂对1,2,4-三氯苯污染土壤热脱附效果的影响
Effects of four base additives on thermal desorption of 1,2,4-trichlorobenzene contaminated soil
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摘要: 含氯有机物是土壤中常见的污染物质,对人体危害大,采用热脱附修复技术去除。通过改变加热温度、加热时间及添加4种碱性物质 (NaHCO3、NaOH、Ca(OH)2、CaCO3) 等条件获取TCB的去除效率及污染土壤理化性质变化情况。实验结果表明,热脱附能有效去除土壤中TCB,当温度为350 ℃加热30 min时,污染土壤中TCB去除率为83.27%;碱性物质的添加能有效强化热脱附过程,添加1%的NaHCO3、NaOH、Ca(OH)2和CaCO3后,TCB去除率分别提高了28.28、26.13、20.28、18.19%。碱性物质的添加促进了TCB的脱氯和降解,相比于无碱性物质热脱附,添加1%NaHCO3和NaOH后尾气中DCBz增加了5.4 ug·L−1和3.65 ug·L−1。热脱附后土壤有机碳、有效磷质量分数和阳离子交换量减少,电导率增大;碱基协同热脱附前后土壤的总有机碳质量分数变化不大,土壤中有效磷质量分数和阳离子交换量明显增大,脱附条件为250 ℃、30 min以及1%的Ca(OH)2时,脱附前后有效磷由57.5 mg·kg−1增大至80.2 mg·kg−1,阳离子交换量由19.72 cmol+·kg−1增大至24.4 cmol+·kg−1。本研究结果可为热脱附技术修复三氯苯污染土壤提供技术参考。Abstract: Chlorinated organic matter is a common pollutant in soil, which is harmful to human body. It is removed by thermal desorption remediation technology. The removal efficiency of TCB and the change of physical and chemical properties of contaminated soil were obtained by changing the heating temperature, heating time and adding four kinds of alkaline substances (NaHCO3, NaOH, Ca(OH)2 and CaCO3). The experimental results showed that thermal desorption colud effectively remove TCB from soil. When the temperature was 350 ℃ for 30 min, the TCB removal rate was 83.27%. The addition of alkaline substances colud effectively enhance the thermal desorption process. After adding 1% NaHCO3, NaOH, Ca(OH)2 and CaCO3, the TCB removal rates are increased by 28.28, 26.13, 20.28 and 18.19%, respectively. The addition of alkaline substances promoted the dechlorination and degradation of TCB. Compared with the thermal desorption of non-alkaline substances, the DCBz in the tail gas increased by 5.4 ug·L−1 and 3.65ug·L−1 after the addition of 1%NaHCO3 and NaOH. After thermal desorption, the mass fraction of organic carbon, available phosphorus and cation exchange capacity of soil decreased, while the electrical conductivity increased. The mass fraction of total organic carbon (TOC) in soil did not change much, but the mass fraction of available phosphorus and cation exchange capacity in soil increased significantly When the desorption conditions were 250 ℃, 30min and 1% Ca(OH)2, The available phosphorus concentration increased from 57.5 mg·kg−1 to 80.2 mg·kg−1, and the cation exchange capacity increased from 19.72 cmol+·kg−1 to 24.4 cmol+·kg−1. The results can provide technical reference for the remediation of trichlorobenzene contaminated soil by thermal desorption.
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表 1 供试土壤理化性质
Table 1. Physical and chemical properties of experimental soil
含水率/% pH 有机碳/% 有效磷/(mg·kg−1) 阳离子交换量/(cmol+·kg−1) 电导率/(mS·m−1) 12.5 7.52 1.93 48.1 19.73 13.32 -
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