Search

A two-dimension simulated sand box was set up to investigate the influencing factors, such as the initial groundwater level, aeration rate and the initial groundwater rate, that affect groundwater circulation well (GCW) by determining the intensity of groundwater circulation which was characterized by the variation of groundwater level before and after aeration. The optimal operating parameters were used to remediate nitrobenzene contaminated aquifer. The results demonstrated that: GCW could be well operated under the conditions of 45 cm groundwater level, 0.7 m3 · h(-1) aeration rate. The effects of groundwater velocity less than 1.0 m · d(-1) could be ignored. The lateral mobility rate of nitrobenzene was faster than that of longitudinal. The average concentration of nitrobenzene was 246.97 mg · L(-1) on day 50 of leakage. During the remediation of circulation well, an efficient organics remediation region was gradually formed around the circulation well. The organics in this region was removed preferentially, and the concentration decreased continuously. Besides the efficient remediation region, there was a transient region, where the concentration of organics was influenced by the combined effects of adsorption/desorption and migration potential of organics. During the whole remediation process, the concentration of nitrobenzene went through three stages described as rapid removal, slow removal. After 14h aeration, the nitrobenzene average concentration was reduced to 71.19 mg L(-1). The residual nitrobenzene was distributed in regions far away from GCW. Therefore, nitrobenzene contaminated aquifer could be well remediated by GCW, and there were optimal operation conditions and appropriate remediation time which guaranteed the best remediation effect.

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).

Simulated columns filled with fine sand were conducted to investigate influences of leachate properties on pollutants attenuation and bacterial activity in aquifer. Experimental results indicated that bacterial activity of young landfill leachate, aged landfill leachate and rain water through columns was up to maximum 0.154, 0.121 and 0.044 in 12 d, 17 d and 3 d, respectively; the maximum BOD5/COD was up to 0.683, 0.396 and 0.319 in 12 d, 8 d and 6 d, respectively, and the averaged increasing rate of pH was up to 0.074/d, 0.15/d and 0.055/d, respectively. COD removal efficiencies of young and aged landfill leachate which passed columns were 50% and 10%, respectively; NH4+ -N adsorption capacity of aquifer media was proximately 0.85 g/kg. In addition, there was correlation between organic substrate content of aquifer media and bacterial activity. Therefore, the leachate properties had profound effects on pollutants attenuation in aquifer.

Static and dynamic simulated experiments were conducted to investigate the characteristics of bacterial variation in landfill leachate polluted site, and relations between attenuation, species-distribution, bioavailability of pollutants and bacterial activity. Results indicated that bacterial activity in soil and fine sand showed a trend of increase first and then decreased with time; the increase rate was up to 0.081 d(-1) and 0.022 d(-1) at the increasing stage,and the decrease rate reached 0.0095 d(-1) and 0.005 1 d(-1) at the decreasing stage, respectively. A clear correlation between attenuation of COD and variation of bacterial activity with time was shown; the removal efficiency of COD in soil was about 30% higher than that in fine sand, and the attenuation rate of COD was 500 mg/d in fine sand approximately. There was no clear correlation between ammonium-nitrogen attenuation and bacterial activity in short-term with time. Variation of heavy metals species and bioavailability was related to their properties, redox environment, and other factors.

A box filled with sandy soil was constructed to investigate the redox zones of landfill leachate pollution plume and the distribution and varying characteristics of contaminants and redox sensitive substrates. Results indicated that the distribution and variation of pollutants and redox sensitive substrates were influenced by redox environment; Eh of water in methanogenic/sulfate reduction zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone is -148.2, -95.4, 30.6 and 223.2 mV; conductivity is 211.4, 55.2, 29.4 and 17.8 mS/m, and pH is 7.13, 6.49, 6.38 and 6.21, respectively. Methanogenic/sulfate reduction zone play significant roles for attenuation of the most organic pollutants such as ethylbenzene, dimethylbenzene, benzene, and TCE etc. Most heavy metals could deposit in methanogenic/sulfate reduction zone sediments, except As and Cd, and the highest content of Cr, Ni, Pb and Zn is 28.21, 11.58, 9.05 and 23.5 mg/kg, respectively. Concentration of CO2, sulfide, HCO3, NH4+, TOC, Fe2, NO2- and SO4(2-) are decrease with the distance away from the pollution source.

A box filled with sandy soil was constructed to investigate dynamitic development and evolution of redox zones in landfill leachate-polluted plume. The results indicated that with time elapsing and pollution aggravating, redox zones moved ahead slowly; Methanogenic zone/ sulfate reduction zone extended gradually, and then inert zone appeared with further pollution. During the whole course of the dynamitic development and evolvement of redox zones, concentrations of TOC, sulfide, NH4(+) -N, HCO3-, CO2 and Fe2+ increased with time and decreased with distance; concentrations of NO3- and DO decreased with time and increased with distance; SO4(2-) concentration decreased first and then increased over time; but decreased with distance. Moreover, with time elapsing and pollution aggravating, the Fe3+ content of sediments was decrease and TOC was increase. Within oxygen reduction zone, nitrate reduction zone, iron reduction zone and methanogenic zone/sulfate reduction zone, Fe3+ content of sediments accounted for 70.5% of OXC decreased to 56.3%, 41%, 28.3% and 15%, and the TOC accounted for 98.7% of RDC increased to 102.0%, 107.0%, 142.9% and 162.1%, respectively; Fe2+ mainly precipitated as FeS and FeCO3, and accounted for 80.6%, 175.6%, 377.7% and 555.1% of total Fe2+, respectively.

The one-dimensional breakthrough soil column experiment and static experiment were constructed to investigate the spacial and temporal pH buffering capacity of the four natural geological media. Experimental results indicate that the background pH buffering capacity of fine sand, silt sand and clay is 79.9 x pH(-1) mmol/kg, 207.5 x pH(-1) mmol/kg, 456.4 x pH(-1) mmol/kg respectively. With the time going on and the distance closer to the leaching source, for each medium which is contaminated by the landfill leachate, the total pH buffering capacity decreases, the buffering capacity of calcium carbonate buffering system decreases, the buffering capacity of the silicate and cation exchange buffering system have no obvious changes, and the buffering capacity of the aluminium and ferric oxide buffering system also decrease, but the soil's buffering capacity of aluminium buffering system increases at first and then decreases. The temporal and spacial buffering capacity for each buffering system of the fine sand all increase appreciably. The order of the pH buffering capacity of the geological media on landfill leachate is fine sand < silt sand < clay < soil. The soil and clay have a good pH buffering capacity on landfill leachate as well as the controlling effect of the pollutants' transferring and diffusion.

A soil column filled with sandy soil was constructed to investigate changes of terminal electron acceptors (TEA) and TOC in redox zones of landfill leachate pollution plume, and their models were established, respectively. Results indicated that the time of peak-concentration appearance of different reducing products was related to the ability of terminal electron acceptors to compete for terminal electrons. The most competitive ones showed sharp concentration increased earlier. For example, the peak concentration of NO2(-) appeared earlier than that of Fe2+. The concentration of TOC increased in methanogenic zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone, and its rate was 8.27, 8.56, 8.85, 9.06 and 9.11 mg/(L h), respectively. Degradation rate of contaminants by different microbes mainly depended on the amount and availability of terminal electron acceptors. The reaction rate was related to ability of terminal electron acceptors to compete for terminal electron, that is the stronger the ability of terminal electron acceptors to compete for terminal electrons, the easier could be used and consumed by microorganisms and the more sensitive to reflect on environmental pollution.

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.

Endemic fluorosis was investigated and studied in the west region of the Songnen plain, Northeast China in 2001-2002. The results showed that the fluorine distribution in aquatic environment was that the fluorine concentrations in the lake water and unconfined ground water were higher than that in the river water and confined ground water. The lake water (Alkali lake) is connected with unconfined ground water. In unconfined ground water, from the east and southeast areas to the west and the northwest areas of the plain, fluorine concentration fluctuated with high and low alternatively. The fluorine in the water comes from the weathering of rocks and minerals in the mountains and hills around the Songnen Plain. The main influence factors of the fluorine distribution in aquatic environment are discussed. Unconfined ground water containing high fluorine is used as drinking water. In this region, the fluorine concentration in drinking water is evidently correlated to the morbidity of dental and skeletal fluorosis. High fluorine concentration in drinking water has endangered human health.

A soil column filled with sandy soil was constructed to investigate redox buffering capacity of aquifer sediments and its variation in different redox zones. Results indicated that with the aggravating of landfill leachate pollution, the oxidation capacity (OXC) of sediments was decrease, and the reduction capacity (RDC) of sediments was increase. In uncontaminated aquifer sediments, Fe3 + was a main component of OXC, and account for about 70.5 % of OXC; TOC was a main component of RDC, and account for about 98.7% of RDC. In anaerobic environment, large fraction of amorphous Fe3+ and part of crystalline Fe3+ were reduced, and the reduced product was mainly precipitated as FeCO3 and FeS. In methanogenic zone/sulfate reduction zone and iron reduction zone, deposit of Fe2 + led to ion-exchangeable Fe2+ content increased from 0.5 % of uncontaminated aquifer sediments to 3% and 1.84% respectively. Therefore, sediment-bound iron may act as a very significant redox buffer in polluted aquifer, the reduction of Fe3 + and fowling precipitation and ion exchange onto the sediment of Fe2+ substantially reduces the size of the anaerobic leachate pollution plume, which may contribute substantially to the buffering of entering reduced species.