Study On Novel Technology Of In-situ Gaseous Bioremediation Of VOCs Stripping From Groundwater

VOCs (Volatile Organic Compounds) is a group of contaminants in the groundwater pollution. The remediation of VOCs in the groundwater includes ex-situ and in-situ remediation, as in the ex-situ remdediation the contaminanted soil or groundwater should be transferred to the surface, in-situ remediation turned to more popular. SVE (Soil Vapor Extraction) and DPE (Dual-Phase Extraction) became the latest research directions. The main principle is to extract the gaseous VOCs to the surface prior to degrade them. The techniques for gaseous VOCs removal from groundwater include biofiltration, adsorption by activated carbon, thermal incineration and catalyzed oxidation. Because of low cost and no secondary contaminants, biofiltration is a good choice, but the big reactor volume, lower elimination capacity compared to other methods and very hard to degrade refractory VOCs limit the application and development of biofiltration.This research focused on the development of novel bioreactors for soluble VOCs and insoluble VOCs, and development of novel technology for degradation of refractory VOCs. Acetone, toluene, n-hexane and TCE(trichloroethylene) were selected as the targeted contaminants, the research of technical parameters of novel bioreactor and TCE dechlorination in the anaerobic biotrickling filter was conducted as well.Compared to other research, this research contains four creative ideas:(1) In this research, the study of immobilized activated sludge reactor to treat gaseous acetone was conducted. Acetone is a typical soluble VOC. The reactor model based on the diffusion and degradation in one bead was developed, beads adjusting coefficient was applied in the model. The diffusion and kinetics characteristics of acetone in the bead were discussed. The maximum elimination capacity is 476.8 g/m3/h, which is 2 fold of the elimination capacity of conventional biotrickling filter.(2) In this research, the removal performance and impact relationship of toluene and n-hexane in the binary gas system was studied and discussed. Toluene and n-hexane are typical insoluble VOCs, and these compounds are sometimes coexisting in the groundwater. Firstly when the inlet concentration of toluene was low, the removal performance of toluene was not impacted by n-hexane, but when the inlet concentration was high, toluene degradation was inhibited by n-hexane. Secondly, no obvious inhibition on n-hexane caused by toluene was observed. The maximum elimination capacity of toluene is above 700 g/m3/h based on the lumen volume of the hollow fiber, which is several fold of elimination capacity of conventional biotrickling filter.(3) TCE dechlorination in anaerobic biotrickling filter was conducted, dechlorination performance, number and activity of genes under ORP(Oxidation Reduction Potential) variation, oxygen content variation, different electron donor and methane inhibitor were investigated as well. The elimination capacity of this reactor is above 12.0 g/m3/h. Results of ORP variation showed that after the addition of oxidants, the dechlorination performance turned to be bad but the activity of tce A gene was not inhibted too much, so the vcrA gene played the more important role in the dechlorination. Also vcrA gene was more sensitive with vitamin B12 than tceA gene.(4) In this research, kinetic parameters of TCE dechlorination were determined, the activated coefficients of ORP and oxygen variation were obtained as well. The maximum degradation rate of TCE is the biggest one among TCE, cis-DCE(cis-dichloroethylene) and VC(Vinyl Chloride). The half-saturation constant of cis-DCE is the biggest one among TCE, cis-DCE and VC which shows the affinity of enzyme of cis-DCE is the worst.