[Impact of depth and moisture to diesel degradation in sand layer of vadose zone].

Through the experiment simulated sand columns, the biodegradation characteristics of diesel in sand layers (including fine sand, medium sand and coarse sand) with different depths and moisture contents were studied. The results show that the depth and moisture content of medium are important factors in affecting the efficiency of diesel degradation. In the same medium conditions, the higher moisture content of the medium, the higher biological activity, and biological degradation efficiency of diesel are observed. The nature of medium affects the efficiency of diesel degradation in vadose zone. The finer particles of the medium, the higher ability of diesel degradation is. It is expressed as: fine sand > medium sand > coarse sand. Volatilization and biodegradation are important factors in affecting natural attenuation of diesel in vadose zone.

Study on mechanisms and effect of surfactant-enhanced air sparging.

In an attempt to enhance the effectiveness of air sparging, two sets of experiments were designed to investigate the mechanisms and effect of surfactant-enhanced air sparging (SEAS). The first set was performed at different surface tensions and with different kinds of surfactants (sodium dodecyl benzene sulfonate and Tween-80 [Uniqema Americas LLC, Wilmington, Delaware]), which were added into the contaminated aquifer of different media (particle distribution size = 0.25 to 0.5 mm and 5 to 10 mm). The results indicated that the air saturation in the aquifer increased rapidly at an early stage, then the increase of air saturation slowed down with the increase of airflow rate. The air saturation of medium sand increased with the decrease in water surface tension, and maximum air saturation was achieved at a surface tension of approximately 5 x 10(-2) N/m (50 dyn/cm), which was considered to be the optimum surface tension for air sparging enhancement in the medium sand aquifer. The increase of air saturation in gravel was the result of the increase of foamability and foam stability. The second group of experiments is about the removal of chlorobenzene from the medium sand aquifer. The experiments indicated that chlorobenzene removal by SEAS was more complete and efficient than that of conventional air sparging technology. However, the increase of removal rate and the decrease of lingering concentration by SEAS was not significant, with a further decrease in the surface tension when the surface tension dropped to 5.04 X 10(-2) N/m (50.4 dyn/cm).

[Study on performance of double mineral base liner using modified bentonite as active material].

The absorbing capacity of clay,roasting bentonites by 450 degrees C and dual-cation organobentonites of the pollutions in landfill leachate was compared through static experiment, and investigations were conducted into availability of controlling the permeating of landfill leachate and feasibility of removing the main pollutants in leachate on the double mineral base liners of clay/roasting bentonites by 450 degrees C and clay/dual-cation organobentonites by using nice landfill leachate as the filter fluid. Experiment indicated that the adsorption equilibrium time of landfill leachate in clay, roasting bentonites by 450 degrees C and dual-cation organobentonites was 24 h; the absorbing capacity of roasting bentonites by 450 degrees C and dual-cation organobentonites was larger than that of clay. Simultaneous the penetration coefficients of the two liners were respective 1.31 x 10(-8) cm x s(-1) and 2.80 x 10(-8) cm x s(-1); Double mineral base liners of clay/roasting bentonites by 450 degrees C owned larger absorbing capacity of NH4+, however, double mineral base liners of clay/dual-cation organobentonites had strong absorbing capacity of organic pollutants and the attenuation rate of COD was 33.82% higher than the other. Conclusion was drawn that different types of modified bentonite should be chosen as "the active layer" according to different styles of landfill pollutants.

[Contamination removal in landfill leachate by biological effect in sand layer of vadose zone].

Through the test of two sand columns for comparing, the effect on removal of pollutants in landfill leachate by biological effect in sand layer of vadose zone was studied. First, HgCl2 was confirmed as inhibitor of biological effect, and its most suitable concentration was 10 mg/L. Then, sand column 1 was leached by landfill leachate, and sand column 2 was leached by landfill leachate added 10 mg/L HgCl2. The results indicated: with the time prolonged, the biological effect was more and more obvious. When the test was finished, the concentrations of COD and BOD, respectively reduced by 2724 mg/L and 2332.5 mg/L, and the concentration of NH4+ ascended from 1282.82 mg/L to 1745.48 mg/L, but the effect of TN removal was not obvious. Because the biological effect was inhibited by inhibitor of HgCl2 , the concentrations of pollutants kept calm when landfill leachate penetrated the sand column. Based on the results of experiment, the first-order attenuation kinetics model of biodegradation in sand column was founded.