Bingzhi Li

Removal of 1,1,1-trichloroethane from aqueous solution by a sono-activated persulfate process.

1,1,1-Trichloroethane (TCA), labeled as a priority pollutant by the Environmental Protection Agency (EPA) of China, can be removed from groundwater by sonochemical oxidation. The sonochemical oxidation of TCA in the presence of persulfate (PS) showed a significant synergistic effect. The operational parameters, ultrasonic frequency, PS/TCA molar ratio, radical scavenger, inorganic anions (Cl(-), CO(3)(2-), HCO(3)(-) and NO(3)(-)) and humic acid (HA), were evaluated during the investigation of the sonochemical reaction. The results showed that the degradation of TCA followed pseudo-first-order kinetics, and the rate constant was found to increase with increasing ultrasonic frequency but to decrease with both an increasing PS/TCA molar ratio and an increasing concentration of inorganic anions. With a concentration of 4.46mg/L of HA in solution, an enhanced effect was observed. Further addition of HA retarded the degradation rate of TCA. TCA could be eliminated almost completely by sono-activated persulfate oxidation, with sulfate and hydroxyl radicals serving as the principal oxidants as confirmed by the addition of radical scavengers. Eleven chlorinated degradation intermediates were detected and quantified by purge and trap gas chromatography coupled with mass spectrometry (P&T-GC-MS) in the absence of pH buffer. Three TCA degradation pathways were therefore proposed. In conclusion, the sono-activated persulfate oxidation process appears to be a highly promising technique for the remediation of TCA-contaminated groundwater.

Effects of electrokinetic treatment of contaminated sludge on migration and transformation of Cd, Ni and Zn in various bonding states.

This study assesses the effect of electrokinetic processes on the migration and bonding states of various heavy metals in municipal sludge. The transformation and migration are discussed through the examination of sludge characteristics and distribution of Cd, Zn and Ni after electrokinetic treatments. The migration and distribution of the contaminants after the electrokinetic treatments were determined for each sludge sample by sequential extraction. The noticeable changes on the average speciation fractions of Cd, Zn and Ni were observed that oxidizable heavy metals increased and reducible fraction decreased due to the application of voltage. Bivariate correlation analysis indicated that the amounts of different bonding states of Zn and Ni were significantly correlated (P<0.05) with durations and resistance. The oxidizable Zn was negatively correlated with exchangeable and reducible Zn. Moreover, reducible Zn had a close negative relationship with residual Zn. The bonding state of Ni was significantly related to the durations of electrokinetic processes, indicating the existing of mutual transformation between different speciation fractions over time. The analysis also indicated that the exchangeable Cd showed a close negative relationship with reducible Cd (P<0.01), whereas the reducible Cd was negatively related to residual Cd (P<0.05).

Synergetic degradation of Fe/Cu/C for groundwater polluted by trichloroethylene

This study investigated the enhancement of synergetic degradation of Fe/Cu/C (Fe: commercial iron, Cu: solid product of Fe reacted with CuSO(4), C: carbon powder) for simulated groundwater contaminated by trichloroethylene (TCE). Zero valent iron (ZVI) as a reducing agent was proved to be effective for TCE removal. The Fe/Cu/C system resulted in higher reduction efficiency as a result of the synergetic role of Fe/Cu and Fe/C microelectrode than the Fe (ZVI) or Fe/Cu system, and the half-life was only about 0.4 h. When m(Fe) achieved 12.5 g L(-1), the residual concentration of TCE almost leveled off. Fe:Cu = 10:1 or m(C) = 0.0086 g can induce the optimum function for TCE degradation. A neutral condition was appropriate for TCE degradation, and an acidic system slightly favored TCE dechlorination compared with an alkaline system. GC/MS analysis indicated that TCE was dechlorinated to 1,1-dichloroethene (1,1-DCE), cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC), and 1,1-DCE might be the precursor. Fe/Cu/C reduction is a highly promising technique for TCE removal, and it is an excellent alternative to enhance TCE reductive dechlorination.