The formation factor relates bulk resistivity to pore fluid resistivity in porous materials. Understanding the formation factor is essential in using electrical and electromagnetic methods to monitor ieachate accumulations and movements both within and around landfills. Specifically, the formation factor allows leachate resistivity, the degree of saturation, and, possibly, even the hydraulic conductivity of the waste to be estimated from non-invasive surface measurements. In this study, apparent formation factors are computed for three landfills with different types of waste as well as sediments contaminated by landfill leachate. Resistivity soundings at the closed Mallard North landfill in suburban Chicago （Illinois, USA） mapped leachate surfaces that were confirmed by monitoring wells. The resistivity of leachate-saturated waste from resistivity sounding inversions was then divided by the leachate resistivity values measured in-situ to compute apparent formation factors （Fa） ranging from 1.6 to 4.9. A global Fa of 3.0±1.9 was computed for the entire monitored portion of this landfill. At a nearby mixed laboratory waste landfill, a 2D inverted resistivity section was used to compute an Fa of 2.9. Finally, a distinctly different Fa value of 10.6±2.8 was computed for leachate-saturated retorted oil shale wastes north of Maoming （茂名）, Guangdong （广东） Province, China. Shallow aquifers in the Laohuling （老虎岭） Formation near this landfill are polluted by acidic leachate containing heavy metals and organic compounds. The Fa for aquifers containing contaminated groundwater fall in the same range as aquifers with normal groundwater, 1.7-3.9. However, models from inverted sounding curves over these contaminated areas exhibit unusually low resistivity layers, which may be diagnostic of contamination.
A pure culture using benzene as sole carbon and energy sources was isolated by screening procedure from gasoline contaminated soil.The analysis of the 16S rDNA gene sequence,morphological and physiological characteristics showed that the isolated strain was a member of genus Bacillus cereus.The biodegradation performance of benzene by B.cereus was evaluated,and the results showed that benzene could be efficiently biodegraded when the initial benzene concentration was below 150 mg/L.The metabolites of anaerobic nitrate-dependent benzene oxidation by strain B.cereus were identified as phenol and benzoate.The results of substrate interaction between binary combinations for benzene,phenol and benzoate showed that the simultaneous presence of benzene stimulated the degradation of benzoate,whereas the addition of benzene inhibited the degradation of phenol.Benzene degradation by B.cereus was enhanced by the addition of phenol and benzoate,the enhanced effects were more pronounced at higher concentration.To our knowledge,this is the first report that the isolated bacterial culture of B.cereus can efficiently degraded benzene under nitrate reducing conditions.
Junfeng DouAizhong DingXiang LiuYongchao DuDong DengJinsheng Wang
An amperometric biosensor based on screen-printed electrodes （SPEs） was developed for the determination of organophosphorus pesticides in water samples. The extent of acetylcholinesterase （AChE） deactivation was determined and quantified for pesticide concentrations in water samples. An enzyme immobilization adsorption procedure and polyacrylamide gel matrix polymerization were used for fabrication of the biosensor, with minimal losses in enzyme activity. The optimal conditions for enzyme catalytic reaction on the SPEs surfaces were acetylthiocholine chloride （ATChCl） concentration of 5 mmol/L, pH 7 and reaction time of 4 min. The detection limits for three organophosphorus pesticides （dichlorvos, monocrotophs and parathion） were in the range of 4 to 7 μg/L when an AChE amount of 0.1 U was used for immobilization.
