Modeling the spreading and remediation efficiency of slow-release oxidants in a fractured and contaminated low-permeability stratum.

Traditional remediation technologies cannot well remediate the low permeability contaminated stratums due to the limitation in the transport capacity of solute. The technology that integrates the fracturing and/or slow-released oxidants can be a new alternative, and its remediation efficiency remains unknown. In this study, an explicit dissolution-diffusion solution for the oxidants in control release beads (CRBs) was developed to describe the time-varying release of oxidants. Together with advection, diffusion, dispersion and the reactions with oxidants and natural oxidants, a two-dimensional axisymmetric model of solute transport in a fracture-soil matrix system was established to compare the removal efficiencies of CRB oxidants and liquid oxidants and to identify the main factors that can significantly affect the remediation of fractured low-permeability matrix. The results show that CRB oxidants can achieve a more effective remediation than liquid oxidants under the same condition due to the more uniform distribution of oxidants in the fracture and hence a higher utilization rate. Increasing the dose of the embedded oxidants can benefit the remediation to some extent, while at small doses the release time over 20 d has little impact. For extremely low-permeability contaminated stratums, the remediation effect can be significantly improved if the average permeability of the fractured soil can be enhanced to more than 10-7 m/s. Increasing the injection pressure at a single fracture during the treatment can enlarge the influence distance of the slow-released oxidants above the fracture (e.g., 0.3-0.9 m in this study) rather than below the fracture (e.g., 0.3 m in this study). In general, this work is expected to provide some meaningful guidance for the design of fracturing and remediating low permeability contaminated stratums.

Applications of functional nanoparticle-stabilized surfactant foam in petroleum-contaminated soil remediation.

Surfactant foam (SF) can be used to remediate petroleum-contaminated soil because of its easy transfer to inhomogeneous and low-permeability formations. Nanoparticles (NPs) not only stabilize SF under extreme conditions but also impart various functions, aiding the removal of petroleum contaminants. This review discusses the stabilization mechanisms of nanoparticle-stabilized SF (NP-SF) as well as the effects of NP size, chargeability, wettability, and NP-to-surfactant ratio on foam stability. SF stabilized by inert SiO2 NPs is most commonly used to remediate soil contaminated with crude oil and diesel. Low dose of SF stabilized by nano zero-valent iron is cost-effective for treating soil contaminated with chlorinated organics and heavy metal ions. The efficiency and recyclability of Al2O3/Fe3O4 NPs in the remediation of diesel and crude oil contamination could be enhanced by applying a magnetic field. This review provides a theoretical basis and practical guidelines for developing functional NP-SF to improve the remediation of petroleum-contaminated soils. Future research should focus on the structural design of photocatalytic NPs and the application of catalytic NP-SF in soil remediation.

Approximate analytical model for transient transport and oxygen-limited biodegradation of vapor-phase petroleum hydrocarbon compound in soil.

Volatile organic compounds (VOCs) contamination may occur in subsurface soil due to various reasons and pose great threat to people. Petroleum hydrocarbon compound (PHC) is a typical kind of VOC, which can readily biodegrade in an aerobic environment. The biodegradation of vapor-phase PHC in the vadose zone consumes oxygen in the soil, which leads to the change in aerobic and anaerobic zones but has not been studied by the existing analytical models. In this study, a one-dimensional analytical model is developed to simulate the transient diffusion and oxygen-limited biodegradation of PHC vapor in homogeneous soil. Laplace transformation and Laplace inversion of the Talbot method are adopted to derive the solution. At any given time, the thickness of aerobic zone is determined by the dichotomy method. The analytical model is verified against numerical simulation and experimental results first and parametric study is then conducted. The transient migration of PHC vapor can be divided into three stages including the pure aerobic zone stage (Stage I), aerobic-anaerobic zones co-existence stage (Stage II), and steady-state stage (Stage III). The proposed analytical model should be adopted to accommodate scenarios where the transient effect is significant (Stage II), including high source concentration, deep contaminant source, high biodegradation capacity, and high water saturation. The applicability of this model to determine the breakthrough time for better vapor intrusion assessment is also evaluated. Lower first-order biodegradation rate, higher source concentration, and shallower source depth all lead to smaller breakthrough time.

Enhanced delivery of amendments in fractured clay sites based on multi-point injection: An analytical study.

Fracturing technology that can enhance the delivery of amendments has attracted attention in the remediation of low-permeability contaminated sites. However, there are few works on the enhanced delivery of amendments based on multi-point injection in a fracture-matrix system. This study develops a two-dimensional analytical model for enhanced delivery of amendments in a finite-domain low-permeability matrix through multi-point injection in a natural, hydraulic or pneumatic fracture. The mechanisms of advection, diffusion, dispersion, sorption and degradation are considered in the model and any injection form (e.g., pulse injection, periodic injection or slow-release injection) can be embedded to obtain a specified solution. Then, a new linear factor R*, which is the ratio of the peak concentration to the trough concentration on the same plane, is introduced to evaluate the concentration fluctuation in the fracture and matrix. Results show that with a stronger line source formed in the fracture right after injection (corresponding to a small R*), the concentration distribution of amendments in the matrix is more uniform at each depth resulting in a smaller residual rate, i.e., (R*-1) × 100%. If the injection wells have been installed unreasonably (e.g., a too large spacing), the continuous injection time is an effective controllable parameter to compensate for this defect. Moreover, a controlled slow-release system can maintain a more stable concentration distribution in the fracture than continuous injection and periodic injection systems, giving a longer residence time. Overall, this work is expected to provide some interesting guidelines for the design of multi-point injection in the fracturing low-permeability sites to enhance the remediation of contaminated soil.

Two-dimensional analytical solution for subsurface volatile organic compounds vapor diffusion from a point source in layered unsaturated zone.

Although migration of subsurface volatile organic compounds (VOCs) from contaminant sources in unsaturated soil widely exists, the related analytical models are quite limited. A two-dimensional analytical solution is hence developed to simulate vapor diffusion from the subsurface contaminant source in the layered unsaturated zone. The contaminant source is simplified as a point source leaking at a constant rate. The influences of several important factors, including thickness of stagnant air layer, depth of groundwater table, source characteristics and soil layering characteristics, on vapor migration in subsurface soil are comprehensively investigated by the present model. Soil type does not affect the normalized vapor concentration profile for homogeneous soil, which is not valid for layered soil. The width and effective diffusivity of the upward diffusion pathway and downward diffusion pathway are favorable indexes to evaluate the intensity of subsurface vapor horizontal diffusion. The single-layer capillary fringe assumption overestimates the vapor plume, the assumption can give acceptable result for coarse soil while it is recommended to divide the soil into several layers based on the water-filled porosity profile for fine soil.

An analytical model for one-dimensional diffusion of degradable contaminant through a composite geomembrane cut-off wall.

A one-dimensional analytical model is proposed to analyze contaminant diffusion through a composite geomembrane cut-off wall (CGCW) composed of a geomembrane (GMB) and a bentonite cut-off wall (BCW). The model considers degradation process of contaminant and time-dependent inlet boundary condition which are common in engineering practices. Moreover, two limiting scenarios of the exit boundary condition (EBC) of CGCW for field conditions are taken into account, including the flushing and non-advective semi-infinite aquifer EBCs. The influence of boundary conditions and performance of CGCW are comprehensively investigated. The results show that the upper and lower limits of the mass flux of the exit face of CGCW can be obtained by the models with flushing EBC and the model with non-advective semi-infinite aquifer EBC, respectively. In addition, degradation has substantial influence on the contaminant migration, and smaller half-life in BCW results in smaller contaminant leakage. The performance of CGCW can be improved by embedding GMB at a proper location which is related to the type of contaminant and EBC. Furthermore, thickening HDPE GMB or adopting a coextruded EVOH GMB is efficient to improve the performance of CGCW. The present model can be used as an applicable tool for rational design of CGCW.

Effects of lower body positive pressure treadmill on functional improvement in knee osteoarthritis: A randomized clinical trial study.

BACKGROUND: Knee joint pain and stiffness are the two main symptoms of knee osteoarthritis (OA) and thus restrict a patient's activities, such as walking and walking up and downstairs. The lower body positive pressure (LBPP) treadmill as one of the emerging body weight support system devices brings new hope for exercise-related rehabilitation for knee OA patients. AIM: To investigate the biomechanical effects and the subjective clinical assessment of LBPP treadmill walking exercise when compared with conventional therapy in mild to moderate knee OA patients. METHODS: Eighteen patients with mild-to-moderate knee OA were recruited in this randomized controlled trial (RCT) study. The eligible knee OA patients were randomly assigned to two groups: LBPP and control groups. The patients in the LBPP group performed an LBPP walking training program for 30 min/session per day, 6 d per week for 2 wk whereas the patients in the control group performed walking on the ground for the same amount. All patients underwent clinical assessments and three-dimensional gait analysis at pre- and 2-wk post-treatment. RESULTS: The Western Ontario and McMaster Universities Arthritis Index and visual analog scale scores in both the LBPP group and control group were found to decrease significantly at the post-treatment point than the pre-treatment point (LBPP: 70.25 ± 13.93 vs 40.50 ± 11.86; 3.88 ± 0.99 vs 1.63 ± 0.52; control: 69.20 ± 8.88 vs 48.10 ± 8.67; 3.80 ± 0.79 vs 2.60 ± 0.70, P < 0.001). Moreover, compared with the control group, the LBPP group showed more improvements in walking speed (P = 0.007), stride length (P = 0.037), and knee range of motion (P = 0.048) during walking, which represented more improvement in walking ability. CONCLUSION: The results of our RCT study showed that the LBPP group has a greater effect on improving gait parameters than the conventional group, although there was no significant advantage in clinical assessment. This finding indicates that LBPP treadmill walking training might be an effective approach for alleviating pain symptoms and improving lower extremity locomotion in mild to moderate knee OA patients.

Analytical model for organic contaminant transport through GMB/CCL composite liner with finite thickness considering adsorption, diffusion and thermodiffusion.

A new analytical model for organic contaminant transport through GMB/CCL (geomembrane and compacted clay liner) composite liner is developed, which can consider adsorption, diffusion and thermodiffusion processes and is applicable for typical bottom boundary conditions. The separation of variables method is adopted to derive the solution. The present model is first verified against experimental results and a numerical model. The influence of thermodiffusion on organic contaminant transport in composite liner is then investigated. Toluene is adopted as the representative organic contaminant. The results reveal that when the Soret coefficient ST is not less than 0.01 K-1, the effect of thermodiffusion should be taken into account on the contaminant transport in GMB/CCL composite liner in wet landfills. When the Soret coefficient ST is 0.03 K-1, the breakthrough time of a GMB + 0.75 m CCL composite liner and a 2 m CCL would be overestimated by 20% to 76% due to omitting of the effect of thermodiffusion. Namely, the barrier performance would be greatly overestimated if the effect of thermodiffusion is neglected in these cases. In other aspects, the thermal conductivity of GMB and CCL has little effect on the contaminants transport in GMB/CCL composite liners, so there is no need to modify the materials for this parameter. The present model is an applicable tool for evaluating the barrier performance of the GMB/CCL composite liner, and can provide valuable advices for improving the liner materials.

Two-dimensional analytical solution for VOC vapor migration through layered soil laterally away from the edge of contaminant source.

A two-dimensional analytical solution is developed to simulate vapor migration in layered soil laterally away from the edge of contaminant source and has advantages in considering the vapor concentration profile in a functional form near the source edge. The analytical solution is validated against existing analytical solution, numerical model and experimental results. It has also proved to be an alternative screening tool to evaluate the vapor intrusion (VI) risk by compared with existing VI assessment tools. The influence of the characteristics of contaminant source and soil layer on the VI risk are investigated. The existence of capillary fringe effectively reduces VI risk. Among all the single-layer-soil cases, the lateral inclusion zone for sand is the widest due to the thinnest capillary fringe and the lowest effective diffusivity ratio between soil and capillary fringe. For layered soil, the lower effective diffusivity layer overlying the higher one enhances the horizontal diffusion and extends the lateral inclusion zone. The width of lateral inclusion zone increases logarithmically with increasing source concentration while it increases linearly with increasing source depth. Based on the calculation results, a simplified formula is proposed to preliminarily estimate the width of lateral inclusion zone for the typical single-layer-soil cases considering the capillary fringe.

Numerical model of aerobic bioreactor landfill considering aerobic-anaerobic condition and bio-stable zone development.

Aeration by airflow technology is a reliable method to accelerate waste biodegradation and stabilization and hence shorten the aftercare period of a landfill. To simulate hydro-biochemical behaviors in this type of landfills, this study develops a model coupling multi-phase flow, multi-component transport and aerobic-anaerobic biodegradation using a computational fluid dynamics (CFD) method. The uniqueness of the model is that it can well describe the evolution of aerobic zone, anaerobic zone, and temperature during aeration and evaluate aeration efficiency considering aerobic and anaerobic biodegradation processes. After being verified using existing in situ and laboratory test results, the model is then employed to reveal the bio-stable zone development, aerobic biochemical reactions around vertical well (VW), and anaerobic reactions away from VW. With an increase in the initial organic matter content (0.1 to 0.4), the bio-stable zone expands at a decreasing speed but with all the horizontal ranges larger than 17 m after an intermittent aeration for 1000 days. When waste intrinsic permeability is equal or greater than 10-11 m2, aeration using a low pressure between 4 and 8 kPa is appropriate. The aeration efficiency would be underestimated if anaerobic biodegradation is neglected because products of anaerobic biodegradation would be oxidized more easily. A horizontal spacing of 17 m is suggested for aeration VWs with a vertical spacing of 10 m for screens. Since a lower aeration frequency can give greater aeration efficiency, a 20-day aeration/20-day leachate recirculation scenario is recommended considering the maximum temperature over a reasonable range. For wet landfills with low temperature, the proportion of aeration can be increased to 0.67 (20-day aeration/10-day leachate recirculation) or an even higher value.

Transient analytical solution for one-dimensional transport of organic contaminants through GM/GCL/SL composite liner.

Analytical solution for transport of organic contaminants through composite liner consisting of a geomembrane (GM), a geosynthetic clay liner (GCL), and a soil liner (SL) with finite thickness is presented. The transient diffusion-advection processes in the whole composite liner and adsorption in GCL and SL can be described by the present method. The method is successfully verified against analytical solution to a coupling transient diffusion-advection problem in double-layer porous media. The rationality of the steady-state transport assumption in GM and GCL and the semi-infinite bottom boundary assumption, which are widely adopted in the existing works, is comprehensively investigated. The overestimated zone, underestimated zone and no difference zone caused by the two assumptions under various conditions are identified. With the increase of elapsed time, the overestimated zone disappears, and the underestimated zone becomes smaller and smaller and finally is overwhelmed by the no difference zone. Moreover, the equivalency between GM/GCL/SL and GM/CCL composite liners is also properly assessed by the present method. GM/GCL/SL composite liner performs better than GM/CCL composite liner under high leachate level condition.

A dual-permeability hydro-biodegradation model for leachate recirculation and settlement in bioreactor landfills.

A dual-permeability hydro-biodegradation model is developed to describe the leachate flow in municipal solid waste (MSW) and predict the long-term settlement induced by biodegradation in bioreactor landfills. The model is verified against Hydrus-1D and a recirculation experiment conducted in a full-scale landfill. Preferential flow and mass transfer between fissure and matrix can be reasonably modeled by the proposed model. A higher recirculation flow rate can speed up the stabilization process of landfill. However, too much recirculation leachate is not economical and environmental friendly. A stabilization speed index and a leachate utilization index are adopted to evaluate the stabilization speed of bioreactor landfill and utilization rate of leachate, respectively, and the optimal recirculation flow rate is estimated. A flow rate of q = 5 × 10-5-5 × 10-4 m/h (equivalent to recirculation intensity of Q = 15-150 L/tonwaste/year) is recommended for recirculation, which has been verified by the field data in numerous bioreactor landfills.

CFD modeling of hydro-biochemical behavior of MSW subjected to leachate recirculation.

The most commonly used method of operating landfills more sustainably is to promote rapid biodegradation and stabilization of municipal solid waste (MSW) by leachate recirculation. The present study is an application of computational fluid dynamics (CFD) to the 3D modeling of leachate recirculation in bioreactor landfills using vertical wells. The objective is to model and investigate the hydrodynamic and biochemical behavior of MSW subject to leachate recirculation. The results indicate that the maximum recirculated leachate volume can be reached when vertical wells are set at the upper middle part of a landfill (H W/H T = 0.4), and increasing the screen length can be more helpful in enlarging the influence radius than increasing the well length (an increase in H S/H W from 0.4 to 0.6 results in an increase in influence radius from 6.5 to 7.7 m). The time to reach steady state of leachate recirculation decreases with the increase in pressure head; however, the time for leachate to drain away increases with the increase in pressure head. It also showed that methanogenic biomass inoculum of 1.0 kg/m3 can accelerate the volatile fatty acid depletion and increase the peak depletion rate to 2.7 × 10-6 kg/m3/s. The degradation-induced void change parameter exerts an influence on the processes of MSW biodegradation because a smaller parameter value results in a greater increase in void space.

[Malaria Epidemic Situation in Rudong County of Jiangsu Province during 1999-2014].

From 1999 to 2014 a total of 23 cases of malaria were reported in Rudong County, Jiangsu Province, comprising one indigenous case of vivax malaria, 9 imported cases of vivax malaria, and 13 imported cases of falciparum malaria. The imported cases accounted for 95.7%(22/23) of all cases. The first diagnosis was mainly made in town hospitals and village clinics, accounting for 60.9%. There was no obvious seasonal variation in disease onset, and all cases reported in 2004 were imported.

Ant colony optimization analysis on overall stability of high arch dam basis of field monitoring.

A dam ant colony optimization (D-ACO) analysis of the overall stability of high arch dams on complicated foundations is presented in this paper. A modified ant colony optimization (ACO) model is proposed for obtaining dam concrete and rock mechanical parameters. A typical dam parameter feedback problem is proposed for nonlinear back-analysis numerical model based on field monitoring deformation and ACO. The basic principle of the proposed model is the establishment of the objective function of optimizing real concrete and rock mechanical parameter. The feedback analysis is then implemented with a modified ant colony algorithm. The algorithm performance is satisfactory, and the accuracy is verified. The m groups of feedback parameters, used to run a nonlinear FEM code, and the displacement and stress distribution are discussed. A feedback analysis of the deformation of the Lijiaxia arch dam and based on the modified ant colony optimization method is also conducted. By considering various material parameters obtained using different analysis methods, comparative analyses were conducted on dam displacements, stress distribution characteristics, and overall dam stability. The comparison results show that the proposal model can effectively solve for feedback multiple parameters of dam concrete and rock material and basically satisfy assessment requirements for geotechnical structural engineering discipline.