沉积物活化氧气和过氧化氢产生羟自由基降解三氯乙烯的比较研究

Comparison of Sediment Activated Oxygen and Hydrogen Peroxide for Hydroxyl Radical Production and Trichloroethylene Degradation

沉积物中Fe(Ⅱ)可以活化氧气(O_(2))产生羟自由基(∙OH),从而降解有机污染物.为评估O_(2)应用于原位化学氧化(ISCO)等修复工程的潜力,通过室内静态试验体系,定量对比了不同条件下,沉积物活化O_(2)与过氧化氢(H_(2)O_(2))产生∙OH的产量、氧化剂转化效率的差异,并采用三氯乙烯(TCE)作为代表性污染物来评估两种氧化剂体系降解污染物的能力.结果表明:在pH为7的条件下,河岸带地下1 m和8 m以及化工场地下1 m和5 m沉积物悬浊液(均为50 g/L)在180 min内活化4.6 mmol/L O_(2)(假定体系中O_(2)完全溶解于水相的浓度,下同)时分别产生0.5、7.1、1.0、13.8μmol/L∙OH,活化5 mmol/L H_(2)O_(2)时分别产生1.7、39.1、72.1、102.8μmol/L∙OH.O_(2)转化为∙OH的效率为0.1%~3.0%,与H_(2)O_(2)(0.03%~2.40%)处于相近水平.在50 g/L河岸带地下8 m沉积物悬浊液中,随着O_(2)投加量由2.3 mmol/L增至7.0 mmol/L,180 min内∙OH的产量由6.7μmol/L增至7.5μmol/L,但是∙OH的产率由1.5%降至0.8%;随着H_(2)O_(2)的投加量由0.5 mmol/L增至10.0 mmol/L,180 min内∙OH的产量由12.2μmol/L增至70.4μmol/L,但∙OH的产率由2.4%降至0.7%.当向上述体系中加入三聚磷酸盐(TPP)和乙二胺四乙酸钠盐(EDTA)后,∙OH的产量和产率显著增加.在河岸带地下8 m沉积物-O_(2)(4.6 mmol/L)体系中,反应180 min内TCE(初始浓度为12μmol/L)的去除率为15.5%,高于沉积物-H_(2)O_(2)(5.0 mmol/L)体系对TCE的去除率(7.7%),然而加入1.0 mmol/L TPP后,两种体系均可以实现TCE的完全去除.研究显示,O_(2)不仅稳定性好、廉价易得,而且与沉积物反应速率适中,氧化剂有效利用率与H_(2)O_(2)处于相当水平,因此有望作为一种温和的氧化剂应用于特定需求的ISCO修复.

Fe(Ⅱ)in sediments can activate oxygen(O_(2)) to produce hydroxyl radicals(∙OH)to degrade organic pollutants.In order to evaluate the potential of O_(2) in in-situ chemical oxidation(ISCO)remediation projects,we conducted a series of batch experiments to quantitatively compare the differences between O_(2)-sediment and hydrogen peroxide(H_(2)O_(2))-sediment systems in∙OH production and oxidant conversion efficiency.Trichloroethylene(TCE)was used as a representative pollutant to evaluate the degradation capability of the two oxidant systems.The results show that the cumulative∙OH concentrations reached 0.5,7.1,1.0 and 13.8μmol/L within 180 min for oxygenation(O_(2) concentration at 4.6 mmol/L,this is the concentration at which all O_(2) is assumed to be dissolved in solution)of 50 g/L riparian sediments that were sampled at 1 m and 8 m underground and chemical factory sediments that were sampled at 1 m and 5 m underground,respectively.When O_(2)was replaced by 5 mmol/L H_(2)O_(2),the accumulation of∙OH reached 1.7,39.1,72.1 and 102.8μmol/L,respectively.The conversion efficiency of O_(2)to∙OH was 0.1%-3.0%,which was similar to H_(2)O_(2)(0.03%-2.40%).In the 50 g/L riparian sediment that was sampled at 8 m underground system,as the O_(2)concentration increased from 2.3 to 7 mmol/L,the cumulative∙OH concentrations increased from 6.7 to 7.5μmol/L within 180 min,but conversion efficiency of O_(2)to∙OH decreased from 1.5%to 0.8%.When H_(2)O_(2)concentration increased from 0.5 to 10 mmol/L,the cumulative∙OH concentration increased from 12.2 to 70.4μmol/L within 180 min,and the conversion efficiency of H_(2)O_(2)to∙OH decreased from 2.4%to 0.7%.The addition of tripolysphosphate(TPP)and ethylenediaminotetraacetate(EDTA)significantly improved∙OH production and the conversion efficiency of O_(2)/H_(2)O_(2)to∙OH.In the riparian sediment(8 m underground)-O_(2)(4.6 mmol/L)system,the removal of 12μmol/L TCE was 15.5%within 180 min,which was higher than that in riparian sediment-H_(2)O_(2)(5.0 mmol/L)system(7.7%).However,the removal of TCE reached 100%in both systems when 1 mmol/L TPP was added.Because O_(2)is not only stable,cheap and easily available,but also has a moderate reaction rate with sediment,and the utilization efficiency of oxidant is at the same level as H_(2)O_(2),O_(2)is expected to be used as a mild oxidant in some ISCO remediation projects with specific purposes.