Efficient dechlorination of chlorinated solvent pollutants under UV irradiation by using the synthesized TiO_2 nano-sheets in aqueous phase

Titanium dioxide （TiO2）, which is the widely used photo-catalyst, has been synthesized by simple hydrothermal solution containing tetrabntyl titanate and hydrofluoric acid. The synthesized product has been applied to photo-degradation in aqueous phase of chlorinated solvents, namely tetra- chloroethene （PCE）, tdchloroethene （TCE） and 1,1,l-trichloroethane （TCA）. The photo-degradation results revealed that the degradation of these harmful chemicals was better in UV/synthesized TiO2 system compared to UV/commerciai P25 system and UV only system. The photo-catalytic efficiency of the synthesized TiO2 was 1.4, 1.8 and 3.0 folds higher compared to the commercial P25 for TCA, TCE and PCE degradation, respectively. Moreover, using nitrobenzene （NB） as a probe of hydroxyl radical （.OH）, the degradation rate was better over UV/synthesized TiO2, suggesting the high concentration of .OH generated in UV/synthesized TiO2 system. In addition, .OH concentration was confirmed by the strong peak displayed in EPR analysis over U~/synthesized TiO2 system. The characterization result using XRD and TEM showed that the synthesized TiO2 was in anatase form and consisted of well-defined sheet-shaped structures having a rectangular outline with a thickness of 4 rim, side length of 50 nm and width of 33 nra and a surface 90.3 m^2/g. XPS analysis revealed that ≡Ti-F bond was formed on the surface of the synthesized TiO2. The above results on both photocatalytic activity and the surface analysis demonstrated the good applicability of the synthesized TiO2 nano-sheets for the remediation of chlorinated solvent contaminated groundwater.

Electrolytic groundwater circulation well for trichloroethylene degradation in a simulated aquifer

An in situ groundwater remediation process, termed EGCW, was developed in this study by integrating in-well groundwater electrolysis into groundwater circulation well. Groundwater circulation carries electrolytically generated O2 and H2 into the impacted aquifer for in situ biodegradation of contaminants. In a two-dimensional tank filled with field sandy sediments,simulated trichloroethylene(TCE)-contaminated groundwater was circulated between an injection well with electrodes inside and a pumping well. Results from a 50-day EGCW experiment show that in-well electrolysis oxygenated most region near the injection well, and 10 mg/L TCE was mainly biodegraded aerobically to about 2.7 mg/L(73% removal) by the indigenous microbes. Aerobic TCE degradation was enhanced by the pulsed addition of acetate. Together with the proofs of stable carbon isotope fractionation(enrichment factor:-0.57‰–-1.53‰) and microbial community variation after EGCW treatment, aerobic cometabolism was proposed to be the most likely mechanism for TCE degradation. It is interesting to find that the intrinsic organic carbon in aquifer matrix could fuel the aerobic TCE degradation, particularly at low TCE concentrations. EGCW treatment is advantageous in terms of supplying appropriate dosages of electron acceptor(O_(2)) and donor(H_(2)) for in situ bioremediation because groundwater electrolysis and circulation are expedient and controllable.

Microbial responses to combined oxidation and catalysis treatment of 1,4-dioxane and co-contaminants in groundwater and soil

Post-treatment impacts of a novel combined hydrogen peroxide(H2O_(2))oxidation and WOx/ZrO_(2) catalysis used for the removal of 1,4-dioxane and chlorinated volatile organic compound(CVOC)contaminants were investigated in soil and groundwater microbial community.This treatment train removed~90%1,4-dioxane regardless of initial concentrations of 1,4-dioxane and CVOCs.The Illumina Miseq platform and bioinformatics were used to study the changes to microbial community structure.This approach determined that dynamic shifts of microbiomes were associated with conditions specific to treatments as well as 1,4-dioxane and CVOCs mixtures.The biodiversity was observed to decrease only after oxidation under conditions that included high levels of 1,4-dioxane and CVOCs,but increased when 1,4-dioxane was present without CVOCs.WO_(x)/ZrO_(2) catalysis reduced biodiversity across all conditions.Taxonomic classification demonstrated oxidative tolerance for members of the genera Massilia and Rhodococcus,while catalyst tolerance was observed for members of the genera Sphingomonas and Devosia.Linear discriminant analysis effect size was a useful statistical tool to highlight representative microbes,while the multidimensional analysis elucidated the separation of microbiomes under the low 1,4-dioxane-only condition from all other conditions containing CVOCs,as well as the differences of microbial population among original,post-oxidation,and post-catalysis states.The results of this study enhance our understanding of microbial community responses to a promising chemical treatment train,and the metagenomic analysis will help practitioners predict the microbial community status during the post-treatment period,which may have consequences for long-term management strategies that include additional biodegradation treatment or natural attenuation.

Laboratory-scale column study for remediation of TCE-contaminated aquifers using three-section controlled-release potassium permanganate barriers

A laboratory-scale study with a sand column was designed to simulate trichloroethylene（TCE） pollution in the aquifer environment with three-section controlled-release potassium permanganate（CRP） barriers.The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner.CRP particles with a 1：3 molar ratio of KMnO 4 to stearic acid showed the best controlled-release properties in pure water,and the theoretical release time was 138.5 days.The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days.The molar ratio of KMnO 4 to TCE in the three-section CRP barriers was 16：1,which was much lower than 82：1 as required when KMnO 4 solution is used directly to achieve complete destruction of TCE.This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation.

Selection of Dispersivity in Groundwater Risk Assessment

The Domenico model is used in combination with ASTM E 1739 in a Tier 2 risk assessment of chlorinated organic solvents contaminated groundwater sites to predict potential contaminant concentration in groundwater down-gradient from the point of exposure (POE). A knowledge of the dispersivity parameters is necessary for carrying out this calculation. A constant longitudinal dispersivity of 10 m is often used in analytical and numerical calculation. However, because of the scale effect of dispersion, two other main approaches are currently often used. From the viewpoint of conservative principle in risk assessment, it is necessary to determine which dispersivity data will give a higher predicted concentration, corresponding to a more conservative risk calculation. Generally, it is considered that a smaller dispersivity leads to a higher predicted concentration. This assumption is correct when dispersion is the only natural attenuation factor. However, degradation of commonly encountered chlorinated organic solvents in environment under natural condition has been widely reported. Calculations given in this paper of several representative cases show that a general consideration of the influence of dispersivity on concentration prediction is not always correct when a degradation term is included in the calculation. To give a conservative risk calculation, the scale effect of dispersion is considered. Calculations also show that the dispersivity parameters need to be determined by considering the POE distance from the source, the groundwater velocity, and the degradation rate of the contaminant.