Xinqiang Du

Surface clogging process modeling of suspended solids during urban stormwater aquifer recharge

Aquifer recharge, which uses urban stormwater, is an effective technique to control the negative effects of groundwater over-exploitation, while clogging problems in infiltration systems remain the key restricting factor in broadening its practice. Quantitative understanding of the clogging process is still very poor. A laboratory study was conducted to understand surface physical clogging processes, with the primary aim of developing a model for predicting suspended solid clogging processes before aquifer recharge projects start. The experiments investigated the clogging characteristics of different suspended solid sizes in recharge water by using a series of one-dimensional fine quartz sand columns. The results showed that the smaller the suspended particles in recharge water, the farther the distance of movement and the larger the scope of clogging in porous media. Clogging extents in fine sand were 1 cm, for suspended particle size ranging from 0.075 to 0.0385 mm, and 2 cm, for particles less than 0.0385 mm. In addition, clogging development occurred more rapidly for smaller suspended solid particles. It took 48, 42, and 36 hr respectively, for large-, medium-, and small-sized particles to reach pre-determined clogging standards. An empirical formula and iteration model for the surface clogging evolution process were derived. The verification results obtained from stormwater recharge into fine sand demonstrated that the model could reflect the real laws of the surface clogging process.

Potential Clogging and Dissolution Effects During Artificial Recharge of Groundwater Using Potable Water

To avoid the water quality deterioration that are caused by artificial recharge (AR) of groundwater, potable drinking water has been used as one of the source water for AR to control the side effects caused by the over-exploitation of groundwater. Chemical clogging problems can still be caused by certain chemical components, especially Fe and Al, and a lower concentration of these elements can cause a notable decrease in hydraulic conductivity at the top layer of the infiltration medium. Some components in AR source water can be obstructed by the clogging layer, leading to a change in water quality. The accumulation of total suspended solids (TSS) at the clogging layer can cause physical clogging and worsen the degree of chemical clogging. Although clogging and the related change in water quality were the dominant issues that affect the infiltration rate and health risks during the AR process, the dissolution of the aquifer matrix should also be taken into account. This dissolution contributed to not only the hydraulic conductivity of the infiltration medium but also the potential change in water quality during the aquifer recharge, storage and recovery processes.

Mathematical Modeling of Differentiation Processes in Porous Media During Soil Vapor Extraction (SVE) Remediation of Contaminated Soil/Water

Soil vapor extraction (SVE) is one of the most effective remediation technologies for soil and groundwater contamination. Soil particles can be mobilized by air perturbation during SVE, resulting in the differentiation of porous media, which has not been well addressed. This paper developed a numerical method to study the flow pattern and quantify the change of porous media for the first time. Based on the mass equilibrium and Darcy’s law, a two-phase water–air flow model was constructed with integration of saturation, relative permeability, and capillary pressure during SVE. Relationship between porosity and saturation was deduced and coupled with the two-phase flow model for quantifying change of porous media in real time. Results reveal that both porosity and permeability increase sharply in the early stage of SVE then gradually to a quasi-steady state. These increases in vadose zone tapered off with distance from the SVE screen and the steady period occurred later as well. The influence radius of a single SVE well and the change degree in porosity and permeability of media were proportional to the extraction vacuum and the driving coefficient C, which is more sensitive than extraction vacuum according to the simulation results. Knowledge from this modeling exercise provides a useful tool to estimate the change of remediated zone and assess the environmental risk of remedial activities at real-world contamination sites.

Study on Clogging Mechanism and Control Methods of Artificial Recharge

The severe global fresh water shortage, the over-exploitation of groundwater and its related ecological environment geology problems, the global climate change, all of them are stimulating the study and practice of artificial recharge. But the clogging problem during artificial recharge is always to be the most common obstacle, it can reduce the recharge rate, increase the maintenance cost and shorten the longevity of the recharge facilities. The present paper analyzed the mechanism and characteristics of different clogging types, introduced the common methods for clogging control. Based on lots of experiments, a new method emphasis on engineering structure was proposed to prevent spread basin from clogging.

Biodegradation of petroleum hydrocarbon by indigenous microorganisms isolated from an oil contaminated groundwater site

Bioremediation of petroleum contaminated land and groundwater has been an interesting area in recent years. A microbial study was carried out at a petroleum contaminated groundwater site to have successfully isolated eight dominant strains of oil degradation from the oil contaminated groundwater samples. The results showed that the Prokaryotic actinomycetes possessed the best degradation rate, followed by other bacteria and fungi. Pairwise orthogonal combination showed obvious better degradation rates than single bacteria, indicating the presence of synergies. Mixed strains expressed poorer degradation rates, revealing the antagonistic effect. Dynamics experiment demonstrated TPH degradation curve conformed to the first-level reaction kinetics equation, degradation rate was in order of SF2>;SX3>;SZ1>;mixed bacterium. The half-life of petroleum contamination was 18.0, 16.4, 19.9 and 21.3 h respectively with the treatment of SX3, SF2, SZ1 and mixed bacteria, which displayed limited life cycle of the microorganisms. Supplement of additional inorganic nutrient and carbon sources raised their degradation ability. For specific compounds, alkane exhibited the similar degradation to TPH; refractory non-hydrocarbon compounds showed lower degradation rate, it was concentrated later since the transformation of alkanes, little change in benzene. The microbial activity experimental results showed that the biomass and dehydrogenase activity correlated with the biodegradation positively. This can provide an important evidence for remediation strategy of the contaminated site.

Retraction Note to: Fate and Transport of EDCs in Soils: Estrone and its Sulfate Conjugate's Adsorption from Mediator Solutions

The fate and transport of emerging contaminants have been major concerns for ecoenvironment and human health. This study presents the adsorption behavior of an endocrine disrupting chemical estrone (E1) and its sulfate conjugate estrone-3-sulfate (E1-3S) that are released to the environment via animal waste in significant amounts and direct exposures in grazed pasture systems. Both compounds have been shown to potentially contribute to endocrine disruption in wildlife, and knowledge about the adsorption behavior of these compounds is necessary for a sound environmental risk assessment. For labile compounds such as E1 and E1-3S, however, the standard protocols might overestimate adsorption by not considering metabolite formation or allowing for equilibration that exceeds the commonly reported half-lives of these compounds. Modified batch adsorption experiments with mediator solution of 0.005 M calcium chloride (CaCl2) and artificial urine (AU) solution were, therefore, conducted to determine the influence of these mediator solutions on the adsorption of E1 and E1-3S in three agricultural soils from Nasarawa State of Nigeria. Adsorption isotherms of both compounds were nonlinear, and the Freundlich equation was found adequate to describe the isotherms. The calculation of concentration-dependent effective distribution coefficients (K d eff) revealed that for a range of realistic exposure concentrations in a grazed farming system, the common approach of using CaCl2 would deliver incorrect information for a sound risk assessment.

Dynamics of Photodecomposition Biodegradation and Volatilization Behaviors of Petroleum on Soil Surface

petroleum contamination is a very common environmental problem. Soil as the protective of groundwater, its remediation relates the security of groundwater, so we simulated the remediation of surface soil. From the experiment, we found that the natural attenuation of contaminated soil is a complicated process. The more processes contained, the easier petroleum attenuated. These processes can accelerate some of components reduce. Volatilization can only attenuate 24.85% petroleum, but if volatilization is coupled with biodegradation, that 89.99% petroleum can be attenuated. With the help of photodecomposition, 97.26% petroleum can be consumed. Volatilization action is a kind of physical attenuation mode, and it may not make some of components which are hard to volatilize into the air. Biodegradation action is a kind of biologic process which depend on the activity of bio-enzyme, and it need microbe compose a steady population. Photodecomposition is a kind of photochemical attenuation mode. If there are three or more attenuation processes exist, the powerful process will play a lead role, such as photodecomposition and biodegradation. From the result we can obtain that 59.83% contribution rate was caused by photodecomposition, and it can decay more petroleum than biodegradation and volatilization.

The Characteristic of Petroleum Contaminant Adsorption Materials and the Estimation of Adsorption Attenuation

Based on the experiment in lab and the investigation in study site, we have studied the adsorption of fine sand, medium sand and coarse sand which composes the aquifer. The different types soil is different to the petroleum adsorption, the adsorptive capacity of fine sand is strongest, the coarse sand adsorption is worst. The adsorptive capacity of Sandy in 33.8% to 46.1%, adsorptive capacity of gravel is 9.2%. Freundlich model is more accurate to explain the sorption of the sands. The adsorption reaction of sand is very rapid, and it often only needs less than a day to reach adsorption reaction balance. The pollution levels are underestimated, and has been underestimated approximately 37.1% to 41.4%, and adsorption attenuation is a main action in study site.