Treatment System for Soil Polluted by VCOCs Utilizing Photocatalysis

三氯乙烯（TCE）和四氯乙烯（PCE）等挥发性氯化有机化合物（VCOC）已广泛用作衣服干洗、半导体清洗等的溶剂。它们的处置失控，造成土壤和地下水污染。这些污染是严重的环境问题，因为这些化学物质具有致癌性和毒性。我们设计并提出了一种利用“TiO_2光触媒片”来处理被VCOC污染的土壤的系统。该片材由TiO_2粉末和吸附剂（活性炭）组成。该吸附剂捕获了从土壤中蒸发的VCOC，还捕获了TiO_2介导的TCE气相光催化降解过程中观察到的不需要的中间体，如光气和二氯乙酰氯(DCAC)。在实际污染场地中对利用光催化剂片和太阳光的系统进行了研究。一处是旧工厂旧址，另一处是活跃的清洁车间。将旧厂区受污染的土壤与“热土（CaO）”混合以挥发化学物质（PCE），并将光触媒片覆盖在土壤上。由于该状态已保持三周，光触媒片在此期间受到太阳光照射。土壤气相中的四氯乙烯浓度在最初两天急剧下降，并在 7 天后低于可检测限。土壤中四氯乙烯浓度也低于0.01毫克/升，其浓度为日本四氯乙烯环境限值。主动清洁车间处理地下污染土壤的另一个系统是通过真空泵从污染土壤中抽吸处理 VCOC 气体。将吸入的气体引导至具有光催化片材的吸附装置。当片材被 VCOC 气体饱和时，我们将片材挂在太阳光下并在设备中重复使用。实际现场结果表明，利用光触媒片和太阳光的系统对VCOCs污染土壤的处理是有效的。较少的

Volatile chlorinated organic compounds (VCOCs) such as trichloroethylene (TCE) and tetrachloroethylene (PCE) have been widely used as solvent for dry cleaning of clothes, washing of semiconductors, and so on. They have been disposed out of control, causing the soil and groundwater pollutions. These pollutions are serious environmental problems because these chemicals are carcinogenic and toxic. We have designed and proposed a treatment system for soil polluted by VCOCs utilizing "TiO_2 photocatalyst sheets". The sheet consists of TiO_2 powder and adsorbent (activated carbon). The adsorbent traps VCOCs evaporated from the soil and also traps undesirable intermediates such as phosgene and dichloroacetyl chloride (DCAC) observed by TiO_2-mediated photocatalytic degradation of TCE in gas phase.The system utilizing the photocatalyst sheets and solar light was investigated in the actual polluted field. One field was an old factory site, and the other was an active cleaning shop. The polluted … More soil in the old factory site was mixed with "Hotsoil (CaO)" to volatilize the chemicals (PCE), and the photocatalyst sheets were covered over the soil. As the status has been kept for three weeks, the photocatalyst sheets have illuminated by solar light for the period. PCE concentrations in gas phase of the soil decreased drastically for initial two days, and they were below detectable limit after seven days. The PCE concentrations in the soil were also below 0.01 mg/L whose concentration is Japan's environmental limit of PCE. The other system to treat the polluted soil under the ground in the active cleaning shop was an aspiration treatment of VCOCs gases from the polluted soil through the well by vacuum pomp. The aspirated gases were led to an adsorption device having the photocatalytic sheets. When the sheets saturated by VCOCs gas, we hanged out the sheets under solar light and reused them in the device. The results in the actual fields show that the system using photocatalyst sheets and solar light is effective on the treatment of the soil polluted by VCOCs. Less