Chaohai Wei

Chlorinated volatile organic compounds (Cl-VOCs) in environment - sources, potential human health impacts, and current remediation technologies.

Chlorinated volatile organic compounds (Cl-VOCs), including polychloromethanes, polychloroethanes and polychloroethylenes, are widely used as solvents, degreasing agents and a variety of commercial products. These compounds belong to a group of ubiquitous contaminants that can be found in contaminated soil, air and any kind of fluvial mediums such as groundwater, rivers and lakes. This review presents a summary of the research concerning the production levels and sources of Cl-VOCs, their potential impacts on human health as well as state-of-the-art remediation technologies. Important sources of Cl-VOCs principally include the emissions from industrial processes, the consumption of Cl-VOC-containing products, the disinfection process, as well as improper storage and disposal methods. Human exposure to Cl-VOCs can occur through different routes, including ingestion, inhalation and dermal contact. The toxicological impacts of these compounds have been carefully assessed, and the results demonstrate the potential associations of cancer incidence with exposure to Cl-VOCs. Most Cl-VOCs thus have been listed as priority pollutants by the Ministry of Environmental Protection (MEP) of China, Environmental Protection Agency of the U.S. (U.S. EPA) and European Commission (EC), and are under close monitor and strict control. Yet, more efforts will be put into the epidemiological studies for the risk of human exposure to Cl-VOCs and the exposure level measurements in contaminated sites in the future. State-of-the-art remediation technologies for Cl-VOCs employ non-destructive methods and destructive methods (e.g. thermal incineration, phytoremediation, biodegradation, advanced oxidation processes (AOPs) and reductive dechlorination), whose advantages, drawbacks and future developments are thoroughly discussed in the later sections.

The behaviors and fate of polycyclic aromatic hydrocarbons (PAHs) in a coking wastewater treatment plant

The occurrence, behaviors and fate of 18 PAHs were investigated in a coking wastewater treatment plant in Songshan coking plant, located in Shaoguan, Guangdong Province of China. It was found that the target compounds occurred widely in raw coking wastewater, treated effluent, sludge and gas samples. In raw coking wastewater, high molecular weight (MW) PAHs were the dominant compounds, while 3-6 ring PAHs predominated in the final effluent. The dominant compounds in gas samples were phenathrene, fluoranthene and pyrene, while they were fluoranthene, pyrene, chrysene and benzo[k]fluoranthene for sludge. The process achieved over 97% removal for all the PAHs, 47-92% of eliminations of these target compounds in liquid phase were achieved in biological stage. Different behaviors of PAHs were observed in the primary tank, anaerobic tank, aerobic tank, hydrolytic tank and coagulation tank units, while heavier and lower ones were mainly removed in anaerobic tank and aerobic tanks, respectively. Regarding the fate of PAHs, calculated fractions of mass losses for low MW PAHs due to transformation and adsorption to sludge accounted for 15-50% and 24-49%, respectively, while the rest was less than 1%. For high MW PAHs, the mass losses were mainly due to adsorption to sludge and separation with tar (contributing 56-76% and 22-39%, respectively), and the removal through transformation was less.

Development of organovermiculite-based adsorbent for removing anionic dye from aqueous solution

This paper reports on the development of organovermiculite-based adsorbent for removing Congo Red (CR), a model anionic dye, from aqueous solution. The organovermiculite was prepared using hexadecyl trimethylammonium bromide (HDTMAB) with variations in cation exchange capacity (CEC) and was then characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results from the adsorption experiments showed that with the organic modification of 50, 100, and 200% CEC, the adsorption capacity of vermiculite towards CR was greatly improved from 2.6 to 74.07, 175.44 and 192.31 mg/g, respectively, at 298 K. The adsorption isotherm experiment was conducted at different temperatures (298, 308 and 318 K), and it was found that the uptake of CR increased with increasing temperature. Langmuir and Freundlich isotherm models were applied and the Langmuir model was found to fit the equilibrium data better. The adsorption kinetics was found to follow the pseudo-second-order model. In addition, various thermodynamic parameters such as changes in enthalpy, entropy, and the Gibbs free energy were calculated, showing adsorption to be an endothermic yet spontaneous process. The results indicated that the organovermiculite may be an effective adsorbent for the removal of anionic dyes from wastewater.

Highly ordered metal ion imprinted mesoporous silica particles exhibiting specific recognition and fast adsorption kinetics

We prepared highly ordered metal ion imprinted mesoporous silica (IIMS) through co-condensation using a combination of molecular imprinting technology and traditional mesoporous materials. Copper ion is used as the template. Besides the periodic hexagonal structure, nano-sized wall thickness, and large surface area, it is found that the IIMS has highly specific recognition ability for the template. The imprinting factor of IIMS exhibits a maximum value of 3.7 at pH 2.5. The material shows fast binding kinetics for Cu2+ (complete equilibrium reach only within 5 min) and the saturation adsorption capacity reaches up to 0.39 mmol g−1. Homogeneous binding sites are confirmed by the Langmuir isothermal model and the Langmuir–Freundlich isothermal model. The heterogeneity index is 0.992 with a value similar to those found for molecularly imprinted polymers prepared using covalent imprinting. The recovery of the silica stays above 90% after six extraction–stripping cycles. Furthermore, the silica has significant potential for water treatment applications.

Distribution and migration of heavy metals in soil and crops affected by acid mine drainage: Public health implications in Guangdong Province, China.

Acid mine drainages (AMD) contain high concentrations of heavy metals, and their discharges into streams and rivers constitute serious environmental problems. This article examines the effects of AMD on soil, plant and human health at Dabaoshan mine in Guangdong Province, China. Although the large scale mining was stopped in 2011, the heavy metal pollution in soil continues to endanger crops and human health in that region. The objectives of this study were to elucidate distribution and migration of Cd, Cu, Zn, As and Pb and associated health implications to local inhabitants. We collected and analyzed 74 crop samples including 28 sugarcane, 30 vegetables, 16 paddy rice and the corresponding soil samples, used correlation and linear relationship for transformation process analysis, and applied carcinogenic and non-carcinogenic risk for hazard evaluation. Results showed that the local soils were heavily polluted with Cd, Cu and As (especially for Cd) and the mean Igeo value was as high as 3.77. Cadmium, Cu, and Zn in rice and vegetables were comparable with those found four years ago, while As and Pb in edible parts were 2 to 5 times lower than before. The root uptake of Cd and Zn contributed mainly to their high concentrations in crops due to high exchangeable fraction of soil, while leafy vegetables accumulated elevated As and Pb contents mainly due to the atmospheric deposition. Metal concentrations in sugarcane roots were higher than those in rice and vegetable roots. The risk assessment for crops consumption showed that the hazard quotients values were of 21 to 25 times higher than the threshold level for vegetables and rice, indicating a potential non-carcinogenic risk to the consumers. The estimated mean total cancer risk value of 0.0516 more than 100 times exceeded the USEPA accepted risk level of 1×10(-4), indicating unsuitability of the soil for cultivating the food crops. Therefore, the local agricultural and the land-use policies need to be reevaluated.

Efficient removal of lead from highly acidic wastewater by periodic ion imprinted mesoporous SBA-15 organosilica combining metal coordination and co-condensation

In order to develop a highly efficient method for direct removal of lead from acidic wastewater (pH 2.0), we introduce a novel highly ordered Pb2+ imprinted mesoporous silica (PbIMS) SBA-15 combining co-condensation and functionalized iminodiacetic acid (IDA). Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray (EDX) analysis provided the components of PbIMS. The solid-state 13C NMR spectra demonstrated the successful embedment of IDA in the mesoporous silica. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis confirmed that Pb2+ was coordinated by the N atom and carboxyl O atom of IDA. The results of transmission electron microscopy (TEM), small angle X-ray diffraction (XRD) and N2 adsorption–desorption measurement confirmed that the PbIMS preserved a highly ordered hexagonal P6mm mesostructure. The Brunauer–Emmett–Teller (BET) surface area was 762 m2 g−1. The saturated adsorption capacity of PbIMS toward lead reached up to 103 mg g−1 at pH 2.0, which was greater even than that of the simply modified SBA-15 by IDA at pH 4.5. The values of selectivity coefficients of PbIMS for six competing metal ions ranged from 67.3 to 12.7. The adsorption of Pb2+ reached equilibrium within 7 min. The adsorption efficiency of PbIMS was above 93% after six extraction–stripping cycles. The investigation conducted with real samples of strongly acidic wastewater demonstrated the ability of PbIMS to efficiently remove lead below the current China regulatory standard.

Methyl parathion imprinted polymer nanoshell coated on the magnetic nanocore for selective recognition and fast adsorption and separation in soils.

Core-shell magnetic methyl parathion (MP) imprinted polymers (Fe3O4@MPIPs) were fabricated by a layer-by-layer self-assembly process. In order to take full advantage of the synergistic effect of hydrogen-binding interactions and π-π accumulation between host and guest for molecular recognition, methacrylic acid and 4-vinyl pyridine were chosen as co-functional monomers and their optimal proportion were investigated. The core-shell and crystalline structure, morphology and magnetic properties of Fe3O4@MPIPs were characterized. The MP-imprinted nanoshell was almost uniform and about 100nm thick. Binding experiments demonstrated that Fe3O4@MPIPs possessed excellent binding properties, including high adsorption capacity and specific recognition, as well as fast adsorption kinetics and a fast phase separation rate. The equilibration adsorption capacity reached up to 9.1mg/g, which was 12 times higher than that of magnetic non-imprinted polymers, while adsorption reached equilibrium within 5min at a concentration of 0.2mmol/L. Furthermore, Fe3O4@MPIPs successfully provided selective separation and removal of MP in soils with a recovery and detection limit of 81.1-87.0% and 5.2ng/g, respectively.

Coking wastewater treatment plant as a source of polycyclic aromatic hydrocarbons (PAHs) to the atmosphere and health-risk assessment for workers

PAHs were identified and some of them were determined in the air around a coking wastewater treatment plant (WWTP) using passive air samplers. Seventy seven PAHs were found in the emissions from the degreasing tanks, the aeration tanks and the secondary clarifiers. ∑PAH concentrations within the plant (373.3±27.3-12959.5±685.9 ng/m(3)) were 3-41 times higher compared to the reference sites (315.7±50.2-363.4±77.5 ng/m(3)). The identification of numerous PAHs and high concentrations of these selected ones in the air of the studied sites indicated that the coking WWTP was a new source of atmospheric PAHs. Variations in the PAH pattern were observed in air within the coking WWTP. For example, Flu and Pyr accounted for 35-46% of the total contents at the degreasing tanks, but less than 10% at the hydrolytic tanks. The calculation of the diagnostic ratios suggested that PAHs in the emissions had the source characters of coal combustion. Furthermore, highly elevated PAH concentrations were determined at the degreasing tanks compared to the other tanks (i.e., aeration tanks and secondary clarifiers) and likely associated with their high concentrations in the coking wastewater and increased volatilization at high water temperature. Health risk assessments were carried out by evaluating the inhalation PAH exposure data. The resultant inhalation exposure levels due to TEQ(BaP) for workers ranged from 1.6±0.6 to 71.2±8.2 ng/m(3), and the estimated lung cancer risks were between 0.1×10(-3)±0.1×10(-4) and 5.2×10(-3)±0.5×10(-3), indicating PAHs in the air around the degreasing tanks and the aerobic tanks would have potential lung cancer risk for the operating workers.

Novel insights into anoxic/aerobic1/aerobic2 biological fluidized-bed system for coke wastewater treatment by fluorescence excitation–emission matrix spectra coupled with parallel factor analysis

Fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) was applied to investigate the contaminant removal efficiency and fluorescent characteristic variations in a full scale coke wastewater (CWW) treatment plant with a novel anoxic/aerobic(1)/aerobic(2) (A/O(1)/O(2)) process, which combined with internal-loop fluidized-bed reactor. Routine monitoring results indicated that primary contaminants in CWW, such as phenols and free cyanide, were removed efficiently in A/O(1)/O(2) process (removal efficiency reached 99% and 95%, respectively). Three-dimensional excitation-emission matrix fluorescence spectroscopy and PARAFAC identified three fluorescent components, including two humic-like fluorescence components (C1 and C3) and one protein-like component (C2). Principal component analysis revealed that C1 and C2 correlated with COD (correlation coefficient (r)=0.782, p<0.01 and r=0.921, p<0.01), respectively) and phenols (r=0.796, p<0.01 and r=0.914, p<0.01, respectively), suggesting that C1 and C2 might be associated with the predominating aromatic contaminants in CWW. C3 correlated with mixed liquor suspended solids (r=0.863, p<0.01) in fluidized-bed reactors, suggesting that it might represent the biological dissolved organic matter. In A/O(1)/O(2) process, the fluorescence intensities of C1 and C2 consecutively decreased, indicating the degradation of aromatic contaminants. Correspondingly, the fluorescence intensity of C3 increased in aerobic(1) stage, suggesting an increase of biological dissolved organic matter.

Adsorption dynamics of trichlorofluoromethane in activated carbon fiber beds.

Adsorption on carbon fixed-beds is considered as an inexpensive and highly effective way for controlling chlorofluorocarbons (CFCs) emissions. In the present work, a dynamic model under constant-pattern wave conditions has been developed to predict the breakthrough behavior of trichlorofluoromethane (CFC-11) adsorption in a fixed bed packed with activated carbon fibers (ACFs). The adsorption of CFC-11 vapor onto viscose-based ACFs was performed in a fixed bed at different test conditions. The results showed that, in a deep bed (>120 mm), the analytical model based on the external mass transfer with the Langmuir isotherm could describe the adsorption dynamics well. The model parameters, the characteristic breakthrough time and the film mass-transfer coefficients are related to such operating parameters as the superficial gas velocity, feed concentration and bed height. It was found from the breakthrough dynamics that the mass transfer from the fluid phase to the fiber surface dominated the CFC-11 adsorption onto ACFs in fixed beds.