pH control for enhanced reductive bioremediation of chlorinated solvent source zones

Enhanced reductive dehalogenation is an attractive treatment technology for in situ remediation of chlorinated solvent DNAPL source areas. Reductive dehalogenation is an acid-forming process with hydrochloric acid and also organic acids from fermentation of the electron donors typically building up in the source zone during remediation. This can lead to groundwater acidification thereby inhibiting the activity of dehalogenating microorganisms. Where the soils' natural buffering capacity is likely to be exceeded, the addition of an external source of alkalinity is needed to ensure sustained dehalogenation. To assist in the design of bioremediation systems, an abiotic geochemical model was developed to provide insight into the processes influencing the groundwater acidity as dehalogenation proceeds, and to predict the amount of bicarbonate required to maintain the pH at a suitable level for dehalogenating bacteria (i.e., > 6.5). The model accounts for the amount of chlorinated solvent degraded, site water chemistry, electron donor, alternative terminal electron-accepting processes, gas release and soil mineralogy. While calcite and iron oxides were shown to be the key minerals influencing the soil's buffering capacity, for the extensive dehalogenation likely to occur in a DNAPL source zone, significant bicarbonate addition may be necessary even in soils that are naturally well buffered. Results indicated that the bicarbonate requirement strongly depends on the electron donor used and availability of competing electron acceptors (e.g., sulfate, iron (III)). Based on understanding gained from this model, a simplified model was developed for calculating a preliminary design estimate of the bicarbonate addition required to control the pH for user-specified operating conditions.     

铁粉还原应用于α-卤代羰基化合物的卤素消除研究

对铁粉还原应用于α-卤代羰基化合物的卤素消除进行了研究,实验证明,铁粉不仅可用于4-溴-2-氯-2-甲基-卜茚酮的脱氯反应,也可用于2,4-二溴-5-甲氧基-6-叔丁基-2-甲基-l-茚酮的脱溴反应,并且经过了工业化验证,给出了工业化放大时的建议.     

Feasibility study for reductive destruction of carbon tetrachloride using bare and polymer coated nickel electrodes

This research investigated the feasibility of an electrochemical reductive dechlorination method for removing carbon tetrachloride (CT) from contaminated waters. Reaction rates and Faradaic current efficiencies were measured for CT dechlorination in small flow-through reactors utilizing bare and silicone polymer coated nickel cathodes. CT dechlorination resulted in near stoichiometric production of methane. Rates of CT reduction were found to follow a first-order kinetic model for all CT concentrations investigated. CT disappearance was limited by its reaction rate, and the performance of the reactor could be approximated with an ideal plug-flow reactor model. Destruction half-life values for CT with the bare nickel electrode ranged from 3.5 to 5.8min for electrode potentials ranging from –652 to –852mV with respect to the standard hydrogen electrode (SHE). The apparent electron transfer coefficient for CT reduction was only 0.06. The low transfer coefficient can be attributed to oxides coating the electrode surface that contributed to mass transfer resistance for CT reduction. Faradaic current efficiencies for CT reduction were found to decline with decreasing electrode potential. This can be attributed to an electron transfer coefficient for water reduction of 0.33 that was significantly greater than that for CT reduction. Faradaic current efficiencies could be increased by 100–360% by coating the electrode with a silicone polymer. In addition to decreasing the rate of water reduction by acting as hydrophobic mass transfer barrier, the polymer coating resulted in small increases in CT reaction rates. The energy cost per volume of water treated was strongly dependent on the electrode potential, but only weakly dependent on the influent CT concentration over the range of practical interest. The energy costs for reductive dechlorination appear to be lower than the carbon costs for adsorptive treatment of CT. This indicates that low current efficiencies at low CT concentrations are not a significant obstacle for developing a practical treatment process. The main impediment to electrochemical treatment for removing CT from water is the slow reaction rate that requires large reactors for obtaining sufficient hydraulic detention time to meet effluent water standards.     

一种新型脱卤催化剂水相催化芳香卤化物脱卤

把起相转移作用的聚乙二醇键合到蒙脱土上(MontK10-PEG400),再将聚乙烯吡咯烷酮(PVP)配合双金属Pd-Sn(PVP-PdCl2-SnCl4)后负载其上,制成一种新型双负载双金属水相脱卤催化剂PVP-PdCl2-SnCl4/MontK10-PEG400,以甲酸钠为氢转移试剂,在水相中催化芳香卤化物脱卤,结果表明:反应温度为80°C,Pd∶Sn=4∶1(摩尔比)时,该催化剂对芳香氯化物呈现出高的脱氯活性和选择性。芳香氯化物转化率达100%。此催化剂易于制备并具有良好的重复使用性。     

Mechanism and kinetics of reductive dehalogenation of PBB (polybrominated biphenyl) in the sonolytic and ketyl radical system

The kinetics and mechanism of reductive destruction of aqueous polybrominated biphenyl (PBB) were studied. Complete degradation was achieved within 30 min of ultrasound-assisted chemical process (UACP), which involved sonication, ketyl radical and its anion, and metal catalyst (ferrous ion). Reductive dehalogenation of PBB is a first-order reaction between PBB concentration and UACP reaction time. The kinetic condition of PBB degradation was optimized in terms of temperature, dosage of radical initiator, and metal catalyst. Mechanism of reductive debromination was also proposed to explain the function of ketyl and aryl radicals on the debromination of bromobiphenyl. Two kinetic models were studied to elucidate the debromination mechanism pathway. Laboratory observed data were found to fit model predicted values obtained from equilibrium and differential equations.     

持久性有机污染物机械化学无害化处理的研究进展

机械化学处理方法是目前最有商业化应用前景的持久性有机污染物(POPs)无害化处理技术之一, 尤其适宜于发展中国家的偏远地区使用。详细介绍了POPs机械化学处理研究起源与现状, 分析了工艺原理及优点, 提出下一步研究工作的重点是强化POPs机械化学反应机理及产物结构的研究, 明确中间及最终产物的结构形态, 确认工艺安全性与有效性, 消除疑虑, 推动工艺的商业化应用。     

Simple and Highly Convenient Two‐Step Practical Procedure for the Synthesis of Optically Pure Methyl D‐erythro‐2,3‐Dihydroxybutanoate

A synthesis of enantiopure methyl D ‐erythro‐2,3‐dihydroxybutanoate has been realized using two simple and consecutive reactions on D ‐erythronolactone as the starting material. The two reactions are lactone ring opening with hydrobromic acid in methanol and subsequent reductive debromination.     

Oxidative polymerization and partial dechlorination of 2,4,6‐trichlorophenol by a mixture of peroxidase isozymes from Vaccinium myrtillus

Plant peroxidases (EC 1.11.1.7) catalyze the oxidation of phenolic pollutants in the presence of hydrogen peroxide. In the present study, extracellular peroxidases from Vaccinium myrtillus cell suspension cultures (VMP) were evaluated for their ability to polymerize 2,4,6‐trichlorophenol (TCP), a ubiquitous environmental contaminant. The effect of pH, temperature, reaction time, enzyme amount and initial pollutant concentration on the treatment efficiency was investigated in order to optimize the reaction conditions for TCP removal. An appreciable removal efficiency and a partial dehalogenation of TCP was observed over a wide range of initial pollutant concentrations (0.1–20 mmol dm^?3) and reaction conditions suggesting that VMP could be useful for potential decontamination applications. The use of polyethylene glycol in the reaction mixture allowed a reduction of the catalyst requirements needed to obtain well defined extents of TCP removal. © 2001 Society of Chemical Industry