Jingchun Yan

Biochar supported nanoscale zerovalent iron composite used as persulfate activator for removing trichloroethylene

Biochar (BC) supported nanoscale zerovalent iron (nZVI) composite was synthesized and used as an activator for persulfate to enhance the trichloroethylene (TCE) removal in aqueous solutions. The degradation efficiency of TCE (0.15mmolL(-1)) was 99.4% in the presence of nZVI/BC (4.5mmolL(-1), nZVI to BC mass ratio was 1:5) and persulfate (4.5mmolL(-1)) within 5min, which was significantly higher than that (56.6%) in nZVI-persulfate system under the same conditions. Owing to large specific surface area and oxygen-containing functional groups of BC, nZVI/BC enhanced the SO4(-) generation and accelerated TCE degradation. On the basis of the characterization and analysis data, possible activation mechanisms of the Fe(2+)/Fe(3+) (Fe(II)/Fe(III)) redox action and the electron-transfer mediator of the BC oxygen functional groups promoting the generation of SO4(-) in nZVI/BC-persulfate system were clarified.

Biochar Supported Nanoscale Iron Particles for the Efficient Removal of Methyl Orange Dye in Aqueous Solutions

The presence of organic contaminants in industrial effluents is an environmental concern of increasing global importance. One innovative technology for treating contaminated industrial effluents is nanoscale zero-valent iron supported on biochar (nZVI/BC). Based on Transmission Electron Microscopy, X-Ray Diffraction, and Brunauer-Emmett-Teller characterizations, the nZVI was well dispersed on the biochar and aggregation was dramatically reduced. Methyl orange (MO) served as the representative organic contaminant for verifying the effectiveness of the composite. Using decolorization efficiency as an indicator of treatment effectiveness, increasing doses of nZVI/BC yielded progressively better results with 98.51% of MO decolorized by 0.6 g/L of composite at an nZVI/BC mass ratio of 1:5. The superior decolorization efficiency of the nZVI/BC was attributed to the increase in the dispersion and reactivity of nZVI while biochar increasing the contact area with contaminant and the adsorption of composites. Additionally, the buffering function of acid-washed biochar could be in favor of maintaining the reactivity of nZVI. Furthermore, the aging nZVI/BC for 30 day was able to maintain the removal efficiency indicating that the oxidation of nZVI may be delayed in the presence of biochar. Therefore, the composite of nZVI/BC could represent an effective functional material for treating wastewater containing organic dyes in the future.

Heterogeneously catalyzed persulfate with a CuMgFe layered double hydroxide for the degradation of ethylbenzene

CuMgFe layered double hydroxide (CuMgFe-LDH) was successfully synthesized and characterized as an efficient catalyst of persulfate (PS) for the degradation of ethylbenzene. Under the conditions of 0.2gL-1 CuMgFe-LDH and 4.0mmolL-1 persulfate at pH 7.6, the degradation efficiency of 0.08mmolL-1 ethylbenzene was 93.7% with TOC removal efficiency of 65.2% in 24h, and the concentration of Cu leached into the solution was as low as 0.095mgL-1 after the reaction. The reuse of CuMgFe-LDH showed that the catalyst was highly stable after 5 recycles. Electron Spin Resonance (ESR) test and free radical quenching experiment indicated that SO4- and OH radicals were the dominant species accounted for the degradation of ethylbenzene in the CuMgFe-LDH/persulfate system. Catalytic mechanism of the formation of a complex of Cu(II)O3SOOSO32- and the subsequent redox cycle of Cu(II)/Cu(III) accounted for the generation of radicals was proposed.

Lead adsorption by biochar under the elevated competition of cadmium and aluminum

Competitive adsorption studies are important to accurately estimate the lead adsorption capacity on biochar in soil. The structure of biochars was evaluated by Fourier-Transform Infrared Spectroscopy and X-ray Diffraction, and the competitive of Cadmium (Cd) and Aluminum (Al) with Lead (Pb) adsorption were determined by kinetic experiments and pH effects. Adsorption kinetics indicated that the adsorption amount (mg g−1) of Pb by biochar was in the decreasing order of CM400 (90.9) > BB600 (56.5) > CM100 (29.2), the presence of the oxygen-containing functional groups, Si-containing mineral, PO43− and CO32− significantly contributed to Pb adsorption by biochars. With the presence of Cd, Pb adsorption amount was reduced by 42.6%, 23.7% and 19.3% for CM100, CM400 and BB600, respectively. The Si-containing mineral, PO43− and CO32− that were rich in CM400 and BB600 has led to less competition by Cd. In addition, Al showed a strong competition with Pb leading to the adsorption being reduced by 95.8%, 82.3% and 80.6%, respectively for CM100, CM400 and BB600. This was mainly attributed to the additional acidification effect by Al resulting in a counteractive of biochar’s liming effect. Results from this study are important for accurately estimating the heavy metal adsorption by biochar in soil.

Enhanced Fenton-like Degradation of Trichloroethylene by Hydrogen Peroxide Activated with Nanoscale Zero Valent Iron Loaded on Biochar

Composite of nanoscale Zero Valent Iron (nZVI) loaded on Biochar (BC) was prepared and characterized as hydrogen peroxide (H2O2) activator for the degradation of trichloroethylene (TCE). nZVI is homogeneously loaded on lamellarly structured BC surfaces to form nZVI/BC with specific surface area (SBET) of 184.91 m2 g−1, which can efficiently activate H2O2 to achieve TCE degradation efficiency of 98.9% with TOC removal of 78.2% within 30 min under the conditions of 0.10 mmol L−1 TCE, 1.13 g L−1 nZVI/BC and 1.50 mmol L−1 H2O2. Test results from the Electron Spin Resonance (ESR) measurement and coumarin based fluorescent probe technology indicated that ∙OH radicals were the dominant species responsible for the degradation of TCE within the nZVI/BC-H2O2 system. Activation mechanism of the redox action of Fe2+/Fe3+ generated under both aerobic and anaerobic conditions from nZVI and single electron transfer process from BC surface bound C–OH to H2O2 promoted decomposition of H2O2 into ∙OH radicals was proposed.

A comparison of risk modeling tools and a case study for human health risk assessment of volatile organic compounds in contaminated groundwater

In order to promote the risk-based strategy in the investigation, assessment, and remediation of Chinese brownfield sites, the Health and Environmental Risk Assessment (HERA) software was developed. It is vital to validate the HERA model and compare the inter-model differences of HERA model against other available risk assessment tools. This paper discusses the similarities and differences between the Risk-Based Corrective Action (RBCA) Tool Kit and the HERA model by evaluating the health risk of organic contaminated groundwater sources for a chemical works in China for the first time. Consequently, the HERA and RBCA models yielded the identical results for Site-Specific Assessment Criteria (SSAC) under the commercial redevelopment. However, the HERA estimated more conservative and stringent SSACs under the residential scenario based on the different exposure calculations. The inhalation of indoor vapors was the most predominated exposure pathway for all the volatile organic compounds (VOCs) determined using the RBCA and HERA models. According to the HERA model, inhalation of chloroform may cause the highest unacceptable carcinogenic risk at 2.31 × 10−3 under the residential scenario. Therefore, it is recommended that a risk-based remedial strategy be developed to ensure the safe and sustainable redevelopment of the site.

Remediation of nitrobenzene contaminated soil by combining surfactant enhanced soil washing and effluent oxidation with persulfate.

The combination of surfactant enhanced soil washing and degradation of nitrobenzene (NB) in effluent with persulfate was investigated to remediate NB contaminated soil. Aqueous solution of sodium dodecylbenzenesulfonate (SDBS, 24.0 mmol L-1) was used at a given mass ratio of solution to soil (20:1) to extract NB contaminated soil (47.3 mg kg-1), resulting in NB desorption removal efficient of 76.8%. The washing effluent was treated in Fe2+/persulfate and Fe2+/H2O2 systems successively. The degradation removal of NB was 97.9%, being much higher than that of SDBS (51.6%) with addition of 40.0 mmol L-1 Fe2+ and 40.0 mmol L-1 persulfate after 15 min reaction. The preferential degradation was related to the lone pair electron of generated SO4•−, which preferably removes electrons from aromatic parts of NB over long alkyl chains of SDBS through hydrogen abstraction reactions. No preferential degradation was observed in •OH based oxidation because of its hydrogen abstraction or addition mechanism. The sustained SDBS could be reused for washing the contaminated soil. The combination of the effective surfactant-enhanced washing and the preferential degradation of NB with Fe2+/persulfate provide a useful option to remediate NB contaminated soil.

Enhanced reduction and adsorption of hexavalent chromium by palladium and silicon rich biochar supported nanoscale zero-valent iron

The potential of silicon-rich biochar and Pd were evaluated for the enhanced removal of Cr(VI) in solution by nanoscale zero-valent iron (nZVI) composites. The composition and structures of the nZVI, RS700-supported nZVI, and Pd-doped samples were analyzed by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy before and after reaction with Cr(VI). The amount of Cr(VI) removed by nZVI-RS700-Pd was considerably greater than the removal by nZVI, nZVI-Pd, or nZVI-RS700. This was mainly due to the enhanced reduction and adsorption of Cr(VI) by silicon-rich biochar and Pd. Silicon and Pd promoted the reduction of Cr(VI) due to the Fe0 crystallinity in the nZVI structures. The significantly decreased removal of Cr(VI) by the silicon-removed sample (nZVI-RS700 (-Si)) further confirmed that silicon played a significant role in the removal of Cr(VI). Cr(VI) adsorption was enhanced by the dispersion and adsorption of RS700. Following the reaction of RS700-supported nZVI with Cr(VI), ferrous chromite (FeCr2O4) was observed on the nZVI-RS700 composite surface. The formation of FeCr2O4 can be attributed to the reduction of Cr(VI) by the nZVI and coprecipitation of chromium oxide with iron on the RS700 surface. Therefore, nZVI-RS700-Pd is a potential remediation reagent that can be used to effectively treat Cr(VI)-contaminated groundwater.

Enhanced removal of Cr(VI) by silicon rich biochar-supported nanoscale zero-valent iron

Silicon-rich biochar-supported nanoscale zero-valent iron (nZVI) was studied to evaluate enhanced removal of hexavalent chromium (Cr(VI)) in solution. The compositional structures of the nZVI and biochar-supported nZVI were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectra before and after Cr(VI) reaction. The removal amount of Cr(VI) by nZVI-RS700 (rice straw pyrolyzed at 700 °C) was considerably greater than that by nZVI and other biochar-supported nZVI samples. Upon the silicon was removed from RS700 (nZVI-RS700(-Si)), a significant decreased removal of Cr(VI) was observed. It was revealed that nZVI supported by silicate particles of biochar and the promotion of iron oxidation by SiO2 both contribute to the enhanced Cr(VI) removal. We found that the reduction and adsorption both contributed to the removal of Cr(VI), ferrous chromite (FeCr2O4) was observed on the surface of the nZVI-RS700 composite. The formation of FeCr2O4 is attributed to the reduction of Cr(VI) by nZVI and the adsorption of chromium oxide with iron on the surface of RS700. Therefore, RS700-supported nZVI can be used as a potential remediation reagent to treat Cr(VI)-contaminated groundwater.