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

沉积物中Fe(Ⅱ)可以活化氧气(O₂)产生羟自由基(?OH)，从而降解有机污染物. 为评估O₂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O₂与过氧化氢(H₂O₂)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 O₂(假定体系中O₂完全溶解于水相的浓度，下同)时分别产生0.5、7.1、1.0、13.8 μmol/L ?OH，活化5 mmol/L H₂O₂时分别产生1.7、39.1、72.1、102.8 μmol/L ?OH. O₂转化为?OH的效率为0.1%~3.0%，与H₂O₂ (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O₂投加量由2.3 mmol/L增至7.0 mmol/L，180 min内?OH的产量由6.7 μmol/L增至7.5 μmol/L，但是?OH的产率由1.5%降至0.8%；随着H₂O₂的投加量由0.5 mmol/L增至10.0 mmol/L，180 min内?OH的产量由12.2 μmol/L增至70.4 μmol/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-O₂ (4.6 mmol/L)体系中，反应180 min内TCE(初始浓度为12 μmol/L)的去除率为15.5%，高于沉积物-H₂O₂ (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，O₂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H₂O₂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. 

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

Fe(Ⅱ) in sediments can activate oxygen (O₂) to produce hydroxyl radicals (?OH) to degrade organic pollutants. In order to evaluate the potential of O₂ in in-situ chemical oxidation (ISCO) remediation projects, we conducted a series of batch experiments to quantitatively compare the differences between O₂-sediment and hydrogen peroxide (H₂O₂)-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 13.8 μmol/L within 180 min for oxygenation (O₂ concentration at 4.6 mmol/L, this is the concentration at which all O₂ 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 O₂ was replaced by 5 mmol/L H₂O₂, the accumulation of ?OH reached 1.7, 39.1, 72.1 and 102.8 μmol/L, respectively. The conversion efficiency of O₂ to ?OH was 0.1%-3.0%, which was similar to H₂O₂ (0.03%-2.40%). In the 50 g/L riparian sediment that was sampled at 8 m underground system, as the O₂ concentration increased from 2.3 to 7 mmol/L, the cumulative ?OH concentrations increased from 6.7 to 7.5 μmol/L within 180 min, but conversion efficiency of O₂ to ?OH decreased from 1.5% to 0.8%. When H₂O₂ concentration increased from 0.5 to 10 mmol/L, the cumulative ?OH concentration increased from 12.2 to 70.4 μmol/L within 180 min, and the conversion efficiency of H₂O₂ 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 O₂/H₂O₂ to ?OH. In the riparian sediment (8 m underground)-O₂ (4.6 mmol/L) system, the removal of 12 μmol/L TCE was 15.5% within 180 min, which was higher than that in riparian sediment-H₂O₂ (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 O₂ 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 H₂O₂, O₂ is expected to be used as a mild oxidant in some ISCO remediation projects with specific purposes.