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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.

Ionic liquids have received lots of attention due to their physical and chemical characteristics. They are honoured the sustainable "Green Solvent". In this paper, the QSPR/QSAR (quantitative structure-property/activity relationships) method was used to study the quantitative relationship between the toxicity and structure of 43 kinds of imidazolium ionic liquids, 10 kinds of substances were used to carry out the external test. The model contains six structural descriptors selected from heuristic method, and R2, R2(CV), F and S2 of the model were 0.921, 0.894, 70.35, 0.098 respectively. Test set was used to conduct external validation, and the R2 was 0.952. The result showed that this model had good reliability, and can be used to predict the toxicity of imidazolium ionic liquids.

Experiments were conducted to investigate reductive attenuation of nitrobenzene (NB) by Fe2+ in subsurface environment and influences of hydrochemical constituents such as water hardness, SO4(21), NO3- and Cl-. Experimental results indicated that concentration of Fe2+ and NB both had influences on NB reduction. The highest reducing efficiency obtained while n(Fe2):n(NB) was 5.88:1 under the condition of pH 6.8 and 10 degrees C. The deoxidization efficiency of NB was up to 57.63% over 48 h. Mg2+ and CO3(2-) could inhibit the reduction of NB, and the reduction efficiency reached 51.05% and 49.96% in 48 h while Mg2+ was 150 mg/L and CO3(2-) was 50 mg/L, respectively; the inhibition was enhanced with increasing of Mg2+ and CO3(2-) concentration, and the deoxidization efficiency of NB was 6.98% only while Mg2+ was 800 mg/L. SO4(21), NO3- and Cl- have small influence on NB reduction, the deoxidization efficiency was less than 50% in 48 h. HCO3- can accelerate the reaction, and the reduction efficiency was up to 60% in 8h. These baseline relationships provide a way to quantitatively evaluate the extent of natural attenuation in contaminated site.

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 sandmedium sandcoarse sand. Volatilization and biodegradation are important factors in affecting natural attenuation of diesel in vadose zone.

Columns filled with fine sand were constructed to investigate influences of subsurface environment and main constituent variations caused by landfill leachate pollution on pH buffer capacity and redox buffer capacity of sediments. Experimental results indicated that the subsurface environment had significant impacts on pH and redox buffer capacity. The pH buffer capacity increased 12.4%, 10.8%, 19.8% and 11.1% in MGZ/SRZ, IRZ, NRZ and ORZ compared with background value, respectively. pH buffer and redox buffer were interaction and inter-promotion, which influenced natural attenuation processes of pollutants in subsurface directly. Content of iron oxides, organic substrate, SOC2(2-) and NH4+ -N in sediments had different impacts on pH buffer and redox buffer capacity, and the overall pollution buffer capacity of system was comprehensive results of constituents.

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.

A simulated column filled with fine sand was constructed to investigate pH buffering capacity of aquifer sediments and its variation in different redox zones. Experimental results indicated that background pH buffering capacity of sediments was 324.93 pH(-1) mmol/kg, and the buffering capacities of cation exchange, calcium carbonate, silicate and secondary were 41.77 x pH(-1), 86.53 pH(-1), 47.33 pH(-1) and 149.31 x pH(-1) mmol/kg, respectively. pH buffering capacity increased 12.4%, 10.8%, 19.8% and 11.1% in MGZ/SRZ, IRZ, NRZ and ORZ, respectively. Cation exchange capacity (CEC) and base exchangeable cation (BEC) content of sediments in redox zones were lower than background content which was 11.59 x pH(-1) and 8.52 x pH(-1) mmol/kg, respectively. Base cation saturation was increasing first and then then decreasing, and it was higher than background of 63.47%. Therefore, the aquifer sediments have high pH buffering capacity. Research on the pH buffering capacity of landfill leachate polluted aquifer sediments in redox zones could provide theoretical evidences for remediation of polluted sites.

It was found that the naturally attenuation of BTEX occurred. In this process, volatilization and biodegradation are the important mechanisms. Taking benzene for example, at the concentration of 11.40 mg/L, the relative proportions of volatilization and biodegradation accounting for natural degradation were 16.36% and 4.91%. Comparatively, at the concentration of 3.30 mg/L for toluene, the relative proportions of volatilization and biodegradation accounting for natural degradation were 11.04% and 41.50%. It demonstrated that different components of BTEX had different attenuation trends. Furthermore, the higher the concentration of BTEX was, the faster the BTEX volatilized, and more important volatilization was. The effect of biodegradation on toluene was more efficiency, whose proportion accounting for natural degradation was 41.50%, and xylene only occupied 8.49%, while, benzene and ethylbenzene were hardly degraded.

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.

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.

A column filled with fine sand was constructed to investigate pH buffering capacity and redox buffering capacity of aquifer media. Experimental results indicated that calcium carbonate played a significant role in pH buffering; with the aggravating of landfill leachate pollution, the pH buffering capacity of calcium carbonate was increased; it increased from background value, which was 1.62 x pH(-1) mmol/kg, to 41.3 x pH(-1) mmol/kg. With the aggravating of landfill leachate pollution, the oxidation capacity (OXC) of aquifer media was decreased, and the reduction capacity (RDC) was increased. In unpolluted aquifer media, Fe3+ was the main component of OXC, and accounted for about 70.5% of OXC; TOC was the main component of RDC, and accounted for about 98.7% of RDC. Species of the minerals was related to the degree of pollution; large fraction of amorphous Fe3+ and part of crystalline Fe3+ were reduced near the pollution source, and the reduced product was mainly precipitated as FeCO3 and FeS. Deposit of produced Fe2+ led to ion-exchangeable Fe2+ content increased from 0.5% of uncontaminated aquifer media to 3%. Therefore, Fe3+ may act as a very significant redox buffer in aquifer.

Redox zones and the natural attenuation of pollutants in landfill leachate polluted site through analyzing data monitored around the Beitiantang Landfills of Beijing City. The results indicated that redox zones existed in Beitiantang Landfill leachate polluted sites, and 5redox zones were classified depended on distribution rules and characteristics of indicative substrates, namely methanogenic zone, sulfate reduction zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone. Attenuation efficiencies of different organic contaminants in redox zones were different. Content of volatile hydroxybenzene and cyanide in sulfate reduction zone were relative high, and they were 0.005 and 0.019 microg/L, respectively. Heavy metal content, such as Cr, Pb, Ni, As, Cu, Cd, Zn and Mn were relative high in methanogenic zone, and they were 25.11, 33.82, 29.93, 3.18, 2.3, 0.1, 283.1, 1220 microg/L, respectively. Therefore, redox zones played an important role on the attenuation of pollutants.

A column filled with sandy soil was constructed to investigate biogeochemical process of leachate polluted zones. Experimental results demonstrated that four sequent redox zones appeared in pollution plume. The zones can be named sulfate reduction zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone, ranges of them were 0-27 cm, 27-62 cm, 47-74 cm, 74-91 cm. In the redox zones bacterial community structure changed, and the preponderant bacteria were sulfate reduction bacteria (SRB), iron reduction bacteria (IRB), nitrate reduction bacteria (NRB) correspondingly, however there were other bacteria in the redox zones. Distribution of redox zones and functional bacteria means that there is not a significant boundary between redox zones, moreover one redox zone overlaps others. Evolvement of functional bacterial community brings the redox zones substitute.

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.

Adsorption of Tween 80 on sand was investigated, and the effect of inorganic salts (CaCl2), anionic surfactant (SDS) and lignosulphonates (sodium lignosulphonate or ammonium lignosulphonate) on the adsorption of Tween 80 on sand were evaluated at 25 degrees C. The results show that saturated adsorption amount of Tween 80 on sand enhance when CaCl2 or SDS is added into flushing solution of Tween 80. And the adsorption of Tween 80 on sand increase with the increase of molar fraction of CaCl2 or SDS in mixed flushing solution. And adsorption amount of Tween 80 on sand also enhance when SDS is added into sand firstly. The effects of mixing ratios and addition order of lignosulphonates on adsorption of Tween 80 were considered. The results show that with the increase of molar fraction of lignosulphonates in mixing flushing solution, adsorption amount of Tween 80 on sand decrease. The adsorption amount of Tween 80 reduce 20%-75% due to the exist of ammonium lignosulphonate is superior to sodium lignosulphonate (10%-60%) when mix the lignosulphonates-Tween 80 at the total mass ratios of 1:10, while the adsorption amount of Tween 80 reduce 70%-90% at the total mass ratios of 1:2. Lignosulphonates added into sand firstly is more efficient than that together. Therefore,use of lignosulphonates as a preflush can reduce the adsorption of surfactants on sand and is a better method to applied in in situ flushing.

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 sandsilt sandclaysoil. 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.

The solubilization of nitrobenzene by a nonionic surfactant Tween 80 was investigated at 10 degrees C. Experimental results indicated that the solubility of nitrobenzene in water was greatly enhanced by Tween 80 at surfactant concentration above CMC(critical micelle concentration) and a linear relationship was obtained between surfactant concentration and nitrobenzene concentration from the solubility curve. The molar solubilization ratio (MSR) value was 5.093 and IgKm was 3.499. The solubilization was attributed to the ethoxylation group in Tween 80 micellar. Effect of four inorganic salts such as NaCl, KCl, CaCl2 , MgCl2 on water solubilities of nitrobenzene in Tween 80 micellar solutions was also investigated by a matrix of batch experiments. Mix the Tween 80-inorganic salts at the total mass ratios of 2:1, 5:1 and 10:1. The results show that the inorganic salts at a high concentration(or = 500 mg x L(-1)) can enhance the solubilization capacities of Tween 80 micellar solution and increase the value of MSR and IgKm . Because of the salting-out effect between the micellar of Tween 80 and inorganic salts, the volume of micelle turns bigger, which may provide larger solubility volume for nitrobenzene. The mixture of nonionic surfactant and inorganic salts can be used in subsurface remediation as a flushing solution.

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.

A soil column filled with sandy soil was constructed to investigate degradation mechanism and efficiency of organic landfill leachate pollutants in subsurface environment. Experimental results indicated that iron reduction zone may be play an important role on degradation of organics, and its efficiency was up to 86.24% averagely, reduction zone for nitrate, sulfate and methanogenic followed, and that was 75.93%, 79.81%, 74.02% and 65.09% averaged, respectively. Anaerobic reducing environment could have played an important role on degradation of benzoxazole, antipyrine, indene, etc. naphthalene, cyclohexanone and part of cyclo-alkyl hydrocarbon, etc. Which were difficult to biodegrade. Maximum degradation efficiency of pollutants was different in different redox zones. For instance, in sulfate reduction zone, the highest degradation efficiency of 1, 1, 1-trichloroethane and 1, 2-dimethylbenzene was 80% and 71.43%, respectively. The highest degradation efficiencies of TCE and MTBE were in nitrate reduction zone, and reached 81.25% and 92.58%. respectively; Benzene was degraded completely in sulfate reduction zone and iron reduction zone.

A soil column filled with sandy soil was constructed to investigate biogeochemical process of leachate pollutants degradation and redox zones in subsurface environment, and variation of Fe3+, Fe2+, oxidation capacity (OXC) and reduction capacity (RDC) of fresh and contaminated soil were analyzed. Experimental results indicated that four sequent redox zones are appear in pollution plume, and different terminal electron acceptors (they are CO2, Fe3+, NO3- and O2) were used by microbes in different zones; Zones can be named methanogenic zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone correspondingly; the indicator of the different zone is HCO3-, Fe2+, NO2- and DO, and its highest concentration is 10,353 mg/L, 13.61 mg/L, 0.097 mg/L and 5.8 mg/L respectively. OXC of the soil is increased sequentially, its lowest value is 14.18 micromol/g in methanogenic zone and highest value is 24.45 micromol/g in oxygen reduction zone; RDC of the soil is reduced sequentially, its highest value is 14.18 micromol/g in methanogenic zone and lowest value is 24.45 micromol/g in oxygen reduction zone. With the more serious contamination, Fe3+ minerals of the soil are reduced by biogeochemical process, and dissolved Fe2+ is produced. Some of the Fe2+ is released to water and the other is precipitated as sediments. Therefore, it is significant for the in situ remediation and risk assessment of the landfill contaminated site to investigate of the redox zones.

Bioreactor landfill is an emerging landfilling method, which represents the newest developing aspect of Municipal Solid Wastes (MSW) treatment. On basis of analyzing the merits and defects of present bioreactor landfilling methods, the paper improves these methods and combines organically aeration and leachate recirculation into a new reactor (called reactor A), which is contrasted with bare aerobic landfill (called reactor B). During the course of experiment, NH3, CH4, CO2, pH, temperature and electric conductivity in the two bioreactors were controlled and detected, meanwhile, COD, Fe3+, NH4(+) in the leachate were detected and analyzed. The paper researches on the wastes degradation and the COD, Fe3+ and NH4(+) removal of the two bioreactors, probes into the mechanics of wastes and leachate degradation. Finally the paper draws a conclusion that the effect of degrading wastes and leachate of bioreactor A is better than that of bioreactor B.