Degradation Of PCBs By Activation Of Persulfate With Vanadium In Soil

Polychlorinated biphenyls (PCBs) are a class of 209 congeners that were extensively used in industry during 1929 to early 1970s due to their low flammability and electrical insulation characteristics.PCBs congeners have been widely detected in the environment because of their widespread presence and persistence.Owing to their low aqueous solubility and lipophilicity, PCBs tend to be bioaccumulatedin aquatic organisms and can be a source of various toxicities, such as hepatotoxicity, immunosuppression, reproductive and developmental toxicity, endocrine disruption, neurotoxicity and carcinogenicityMany conventional treatment technologies have been successfully applied for efficient removal of PCBs fromsoils, sediments and waste water such as incineration, physical adsorption, and chemical dehalogenation. However, these methods have some drawbacks. For example, incineration requires a large amount of fuel and can lead to the formation of highly toxic by-products, including polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-furans. The use of physical adsorption simply results in the transport of PCBs from one media to another, and therefore does not completely eliminate PCBs from the environment; moreover, the costrequired for these methods is expensive. Over past 20 years, a new promising technique that has been studied is the use of zero-valent metal (including magnesium, iron and zinc) for the chemical dechlorination of PCBs. However, this chemical dechlorination method cannot completely mineralize PCBs. Therefore, developing an efficient method for PCBs treatment is imperative.This study investiaged the degradation of PCBs by persulfate activation with vanadium species,and the degradation prodcuts of PCBs were identifiedby GC-MS. Based on the products identified by GC-MS, a transformation pathway of 2,4,4'-CB (PCB28)by persulfate activatiom with vanadium is proposed. In addition, the effects of vanadium valences and concentration, sodium persulfate concentration, as well as pH on PCBs were also examined. The degradation of PCBs in soil elute with V/SPS system was examined, and the effects of soil properties on the decomposition of was also studied. The main findings of this study are shown as follows:(1) Vanadium activated SPS was used to degrade 2,4,4'-CB(PCB28) in aqueous solution. It was found that PCB28 was efficiently degraded in the V/SPS solutions. The effects of pH, vanadium species and concentration on the degradation of PCB28 were also examined. The results showed that V(IV) was more efficient than V(V) toward SPS activation and PCB28 degradation, and lowering pH favored SPS activation and PCB28 degradation. Electron paramagnetic resonance (EPR) technique coupled with free radical quenching studies was applied to identify the dominant reactive for PCB28 degradation. The results indicated that sulfate radicals (SO4·-) and hydroxyl radicals ('OH) were the main reactive species accounted for PCB28 degradation. GC-MS was used to further identify the main intermediates for PCB28 degradation.(2) Actvation of persulfate by V for the degradation PCBs in elute was examined, which is beneficial for developing an efficient method for the remedaiton of contaminated soil. Bolyoxyethylene lauryl ether (Brij35) was used to extract PCBs forms contaminated soil. PCBs degradation in the soil extracts was then conducted by V/SPS system. The results indicated that the extracted efficiency of PCBs form contaminated sites were 40%. And a small amount of vanadium and high concentration of SPS can accelerated the degradation efficiency of PCBs in the Brij 35 solutions.It was also found that the decomposition of SPS in the soil was different due to the different soil properties, and the decomposition of SPS could be promoted by a certain amount of biochar.