"A one dimensional, multiple reaction pathway model of the dechlorination reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) as these species pass through a zero valent iron permeable reactive barrier (PRB) was produced. Three different types of rate equations were tested; first order, surface controlled with interspecies competition, and surface controlled with inter and intra species competition. The first order rate equations predicted the most accurate results when compared to actual data from permeable reactive barriers. Sensitivity analysis shows that the most important variable in determining TCE concentration in the barrier is the first order rate constant for the degradation of TCE. The velocity of the water through the barrier is the second most important variable determining TCE concentration. For PCE the concentration in the barrier is most sensitive to the velocity of the water and to the first order degradation rate constant for the PCE to dichloroacetylene reaction. Overall, zero valent iron barriers are more effective for the treatment of TCE than PCE. "

Permeable reactive barriers (PRBs) are one of the leading technologies being developed in the search for alternatives to the pump-and-treat method for the remediation of contaminated groundwater. A new optimising design methodology is proposed to aid decision-makers in finding minimum cost PRB designs for remediation problems in the presence of input uncertainty. The unique aspects of the proposed methodology are considered to be: design enhancements to improve the hydraulic performance of PRB systems; elimination of a time-consuming simulation model by determination of approximating functions relating design variables and performance measures for fully penetrating PRB systems; a versatile, spreadsheet-based optimisation model that locates minimum cost PRB designs using Excel's standard non-linear solver; and the incorporation of realistic input variability and uncertainty into the optimisation process via sensitivity analysis, scenario analysis and factorial analysis. The design methodology is developed in the context of the remediation of nitrate contamination due to current concerns with nitrate in New Zealand. Three-dimensional computer modelling identified significant variation in capture and residence time, caused by up-gradient funnels and/or a gate hydraulic conductivity that is significantly different from the surrounding aquifer. The unique design enhancements to control this variation are considered to be the customised down-gradient gate face and emplacement of funnels and side walls deeper than the gate. The use of velocity equalisation walls and manipulation of a PRB's hydraulic conductivity within certain bounds were also found to provide some control over variation in capture and residence time. Accurate functional relationships between PRB design variables and PRB performance measures were shown to be achievable for fully penetrating systems. The chosen design variables were gate length, gate width, funnel width and the reactive material proportion. The chosen performance measures were edge residence, centreline residence and capture width. A method for laboratory characterisation of reactive and non-reactive material combinations was shown to produce data points that could realistically be part of smooth polynomial interpolation functions. The use of smooth approximating functions to characterise PRB inputs and determine PRB performance enabled the creation of an efficient spreadsheet model that ran more quickly and accurately with Excel's standard non-linear solver than with the LGO global solver or Evolver genetic-algorithm based solver. The PRB optimisation model will run on a standard computer and only takes a couple of minutes per optimisation run. Significant variation is expected in inputs to PRB design, particularly in aquifer and plume characteristics. Not all of this variation is quantifiable without significant expenditure. Stochastic models that include parameter variability have historically been difficult to apply to realistic remediation design due to their size and complexity. Scenario and factorial analysis are proposed as an efficient alternative for quantifying the effects of input variability on optimal PRB design. Scenario analysis is especially recommended when high quality input information is available and variation is not expected in many input parameters. Factorial analysis is recommended for most other situations as it separates out the effects of multiple input parameters at multiple levels without an excessive number of experimental runs.

The purpose of this study was to use controlled release technology combining with in situ chemical oxidation (ISCO) and permeable reactive barrier (PRB) to remediate TCE-contaminated groundwater. In this study, potassium permanganate (KMnO4) releasing material was designed for potassium permanganate release in groundwater. The components of potassium permanganate releasing material included poly (£`-caprolactone) (PCL), potassium permanganate, and starch with a weight ratio of 2:1:0.5. Approximately 63.8% (w/w) of potassium permanganate was released from the material after 76 days of operation. The released was able to oxidize contaminant in groundwater. Results from the solid oxidation demand (SOD) experiment show that the consumption rate increased with increased contaminant concentration. TCE removal efficiency increased with the increased TCE concentration. The second-order rate law can be used to simulate the TCE degradation trend. In the column experiment, results show that the released MnO4- could oxidize TCE and TCE degradation byproducts when 95.6 pore volume (PV) of contaminated groundwater was treated. More than 95% of TCE removal can be observed in the column study. Although the concentration of manganese dioxide (MnO2) began to rise after 8.8 PV of operation, TCE removal was not affected. Results also show that low level of hexavalent chromium was detected (< 0.05 mg/L). Results from the scanning electron microscope (SEM) and energy-dispersive spectroscope (EDX) analyses show that the amounts of manganese and potassium in the materials decreased after the releasing experiment. Results indicate that the concentration of TCE and SOD need to be analyzed before the releasing materials are applied in situ. In the practical application, the releasing materials will not become solid wastes because they are decomposed after use. If this slow-releasing technology can be combined with a permeable reactive barrier system, this technology will become a more economic and environmentally-friendly green remedial system.

Abstract A novel process of combining electrokinetic remediation and nano-sized iron wall was used for studying its effectiveness of treating nitrate-containing soil. Nitrates and nitrites are commonly found in surface water and groundwater. These substances, in general, could pose a threat to both organisms in the water bodies and human health. Traditionally, nitrogen oxides in various water bodies are treated by biological denitrification processes. However, it would take a longer time to yield a satisfactory result as compared with physicochemical processes. In recent years, permeable reactive barriers (PRBs) using zero-valent iron have been successfully used for degradation of various compounds including nitrates. Electrokinetic processing (EK) also is considered as an effective in-situ technology for removing both inorganic and organic substances from the treatment zone. In this work, the synthesized nano-scale iron particles were incorporated into a PRB, which was further combined with EK to form a novel process for the degradation of nitrates. Various operating parameters were studied in this work. The nano-sized iron particles were determined to be ranging from 50-80nm in size and having specific surface area of 37.83m2. The isoelctric point of these nanoparticles was found to be at pH 7.3. Experimental results have shown that the best location of the iron wall was 5cm from the anode reservoir. Also, the optimal treatment time would be six days in this study. The treatment efficiency was found to increase with increasing dose of nano-sized iron particles in the PRB. Operating with the polarity reverse would slightly increase the overall treatment efficiency as compared with the case of no polarity reverse (92.38% versus 88.34%). An electric gradient of 1.5V/cm was determined to be the optimal electric field strength in this study. In this work, it was also found that 2.5g nano-scale iron particles outperformed 20g micro-scale iron particles (75-150&#x00B5;m) in terms of nitrate degradation. In a study of using an extended treatment time up to 20 days, the black colored iron wall would fade away becoming a rusty plume toward the cathode as the treatment time elapsed. Furthermore, the Fe2+ concentration was elevated throughout the soil column after the 20-day treatment. Therefore, it is evident that nano-sized iron particles would migrate when they are subjected to EK. Based on the research findings obtained, the novel process employed in this study was found to be an effective one for in-situ treatment of nitrate-containing soil.

Abstract Permeable reactive barrier technology is a cost effective means of treating near surface groundwater contaminant plumes. However, current reactive barrier technology lacks the capacity to manipulate flow rates and thus hydraulic retention time (HRT) within the barriers in order to maximize the effectiveness and longevity of the media. This study examines the effectiveness of tile drains as passive controls on the flow rate of ground-water through an existing wood particle media permeable reactive barrier treating agricultural nitrate. The use of upgradient and downgradient tile drains allowed HRT to be increased from 4.5 to 10 days in one trial and then to be decreased from 11.1 to 0.8 days in a second trial. Influent groundwater NO3-N concentrations of ~100 mg/L were attenuated to detection limit (0.02 mg/L) only 12% of the 4 m long barrier with HRTs of 4.5 to 10 days. During the second trial, HRT was decreased to 0.8 days and NO3-N penetrated to the downgradient edge of the PRB at 1.8 mg/L. The behaviour of SO4 in the PRB was also affected by flow rate. SO4 entered the PRB at 60 to 71 mg/L during the first trial. Under a HRT of 10 days it was depleted to detection limit after traveling through only 13% of the barrier. When HRT was decreased to 4.5 days, SO4 was able to penetrate the downgradient edge of the PRB at concentrations from 4 to 6 mg/L. With a 0.8 day HRT SO4 reduction was highly restricted as calculations showed 90% of available carbon in the PRB was being used to reduce NO3-N, compared to 7.5% being used for SO4 reduction at that time. In comparison, at the 10 day HRT, 61% of carbon being used for NO3-N reduction, 8.7% for SO4 reduction, 0.7 for dissolved oxygen and 29% was lost through DOC leaching. These calculations suggest that barrier efficiency can be greatly enhanced by manipulation of HRT through use of tile drains.

Abstract Permeable reactive barrier technology is a cost effective means of treating near surface groundwater contaminant plumes. However, current reactive barrier technology lacks the capacity to manipulate flow rates and thus hydraulic retention time (HRT) within the barriers in order to maximize the effectiveness and longevity of the media. This study examines the effectiveness of tile drains as passive controls on the flow rate of ground-water through an existing wood particle media permeable reactive barrier treating agricultural nitrate. The use of upgradient and downgradient tile drains allowed HRT to be increased from 4.5 to 10 days in one trial and then to be decreased from 11.1 to 0.8 days in a second trial. Influent groundwater NO3-N concentrations of ~100 mg/L were attenuated to detection limit (0.02 mg/L) only 12% of the 4 m long barrier with HRTs of 4.5 to 10 days. During the second trial, HRT was decreased to 0.8 days and NO3-N penetrated to the downgradient edge of the PRB at 1.8 mg/L. The behaviour of SO4 in the PRB was also affected by flow rate. SO4 entered the PRB at 60 to 71 mg/L during the first trial. Under a HRT of 10 days it was depleted to detection limit after traveling through only 13% of the barrier. When HRT was decreased to 4.5 days, SO4 was able to penetrate the downgradient edge of the PRB at concentrations from 4 to 6 mg/L. With a 0.8 day HRT SO4 reduction was highly restricted as calculations showed 90% of available carbon in the PRB was being used to reduce NO3-N, compared to 7.5% being used for SO4 reduction at that time. In comparison, at the 10 day HRT, 61% of carbon being used for NO3-N reduction, 8.7% for SO4 reduction, 0.7 for dissolved oxygen and 29% was lost through DOC leaching. These calculations suggest that barrier efficiency can be greatly enhanced by manipulation of HRT through use of tile drains.

Soil and groundwater at many existing and former industrial areas and disposal sites is contaminated by halogenated organic compounds that were released into the environment. Halogenated organic compounds are heavier than water. When they are released into the subsurface, they tend to adsorb onto the soils and cause the appearance of DNAPL (dense-non-aqueous phase liquid) pool. Among those halogenated organic compounds, trichloroethylene (TCE), a human carcinogen, is one of the commonly observed contaminants in groundwater. Thus, TCE was used as the target compound in this study. The objective of this study was to develop the emulsified carbon-releasing substrate and apply it as the filling material in the permeable reactive barrier to remediate TCE-contaminated groundwater. In this study, the developed emulsified carbon-releasing substrate contained soybean oil, lactate, biodegradable surfactant (Simple GreenTM and lecithin), and nutrients. Results of emulsion test show that up to 90% of the emulsified carbon-releasing substrate was distributed effectively in the soil pores. The emulsified carbon-releasing substrate was able to provide carbon for the enhancement of in situ anaerobic biodegradation for a long period of time. A pilot-scale study was operated at a TCE-contaminated site located in southern Taiwan. Emulsified carbon-releasing substrate emulsion was pressure-injected into the remediation wells. A total of 120 L of emulsified carbon-releasing substrate was injected into the test site. Based on the groundwater analytical results, dissolved oxygen, oxidation-reduction potential, and sulfate concentrations decreased after injection. However, the anaerobic degradation byproduct, acetic acid, increased after injection. Results also show that the total viable bacteria increased in the upgradient injection (remediation) well. Decrease in TCE concentration (dropped to below 0.01 mg/L) was also observed after substrate injection, and TCE degradation byproducts, cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) were also observed. Result of microbial analyses show that various TCE-degrading bacteria exist in the groundwater samples including Ralstonia sp., Clostridium sp., Uncultured Burkholderiales bacterium, Hydrogenophaga sp., Acidovorax sp., Zoogloea sp., Hydrocarboniphaga sp., Uncultured Curvibacter sp., Pseudomonas sp., Comamonas sp., Aquabacterium sp., and Variovorax strains. This reveals that the anaerobic dechlorination of TCE is a feasible technology at this site. Slug test result show that only a slight variation in soil permeability of the injection well was observed. This indicates that the substrate injection would not cause clogging of the soil pores. Results from the cost analysis show that the total cost for the test site remediation was approximately USD13,442 per year. This indicates that the developed system has the potential to be developed into an environmentally, economically, and naturally acceptable remedial technology. Knowledge obtained from this study will aid in designing a carbon-released substrate biobarrier system for site remediation.

At many sites it has become apparent that most chemicals of concern (COCs) in groundwater are persistent and not effectively treated by conventional remediation methods. In recent years, the permeable reactive barrier (PRB) technology has proven to be more cost-efficient in the long-run and capable of rapidly reducing COC concentrations by up to several orders of magnitude. In its simplest form, the PRB is a vertically emplaced rectangular porous medium in which impacted groundwater passively enters a narrow treatment zone. In the treatment zone dissolved COCs are rapidly degraded as they come in contact with the reactive material. As a result, the effluent groundwater contains significantly lower solute concentrations as it re-enters the aquifer and flows towards the plane of compliance (POC). Effective implementation of the PRB relies on accurate site characterization to identify the existing COCs, their interactions, and their required residence time in the PRB and aquifer. Ensuring adequate residence time in the PRB-aquifer system allows COCs to react longer, hence improving the probability that regulatory concentrations are achieved at the POC. In this study, the Park and Zhan solution technique is used to derive steady-state analytical and transient semi-analytical solutions to multispecies reactive transport in a permeable reactive barrier-aquifer (dual domain) system. The advantage of the dual domain model is that it can account for the potential existence of natural degradation in the aquifer, when designing the required PRB thickness. Also, like the single-species Park and Zhan solution, the solutions presented here were derived using the total mass flux (third-type) boundary condition in PRB-aquifer system. The study focuses primarily on the steady-state analytical solutions of the tetrachloroethylene (PCE) serial degradation pathway and secondly on the analytical solutions of the parallel degradation pathway. Lastly, the solutions in this study are not restricted solely to the PRB-aquifer model. They can also be applied to other types of dual domain systems with distinct flow and transport properties, and up to four other species reacting in serial or parallel degradation pathways. Although the solutions are long, the results of this study are novel in that the solutions provide improved modeling flexibility. For example: 1) every species can have unique first-order reaction rates and unique retardation factors, 2) higher order daughter species can be modeled solely as byproducts by neglecting their input concentrations, 3) entire segments of the parallel degradation pathway can be neglected depending on the desired degradation pathway model, and 4) converging multi-parent reactions can be modeled. As part of the study, separate Excel spreadsheet programs were created to facilitate prompt application of the steady-state analytical solutions, for both the serial and parallel degradation pathways. The spreadsheet programs are included as supplementary material.

Groundwater contamination by petroleum hydrocarbons has become one of the serious environmental problems in many countries. The sources of petroleum-hydrocarbon contaminants may be released from above ground and underground storage tanks, and pipelines. Petroleum hydrocarbons are mainly composed of benzene, toluene, ethyl- benzene, and xylems (BTEX), and other constituents such as methyl-tert-butyl ether (MTBE), naphthalene, 1,3,5-trimethylbenzene (1,3,5-TMB), and 1,2,4-trimethylbenzene (1,2,4-TMB). It is generally recognized that petroleum hydrocarbons have high risks to environmental receptors when hydrocarbon releases occur. Various biological, physical, and chemical remediation technologies (e.g. pump and treat, air sparging, enhanced bioremediation, and chemical oxidation) can be used to remediate petroleum-hydrocarbon contaminated groundwater. However, many of these techniques are typically costly or have limited applications. Permeable reactive barriers (PRBs) are a promising technology for the passive and in situ treatment of contaminated groundwater. A PRB can be defined as ¡§an emplacement of reactive materials in the subsurface designed to intercept a contaminant plume, provide a preferential flow path through the reactive media, and transform the contaminant(s) into environmentally acceptable forms to attain remediation concentration goals at points of compliance.¡¨ The oxygen release materials can be emplaced in the PRBs to passive increase dissolved oxygen (DO) in the subsurface to enhance the intrinsic biodegradation of dissolved hydrocarbons. In the first part of this study, guidelines for PRBs installation have been developed for the remediation of petroleum hydrocarbons, heavy metals, and organic solvents contaminated groundwater. PRB is a cost-effective approach for the remediation of contaminated aquifers. As contaminated groundwater moves through a permeable reactive barrier, the contaminants are scavenged or degraded, and uncontaminated groundwater emerges from the downgradient side of the reactive zone. The permeable reactive barrier concept has several advantages over other remediation technologies currently in use (e.g., pump and treat, air sparging), including absence of mechanical facilities and the electric power, no groundwater extraction and reinjection, treatment in situ, and cost-effective. The first part of this study presents the designs, applications, and case studies of PRB systems on groundwater remediation. In the second part of this study, oxygen release materials have been constructed and evaluated for the appropriate components in batch experiments. Microbial degradation of petroleum hydrocarbons in groundwater can occur naturally. Since the petroleum-hydrocarbons are generally degraded faster under aerobic conditions, aerobic bioremediation can be applied to enhance the biodegradation of petroleum-hydrocarbons within of the plume if oxygen can be provided to the subsurface economically. Batch experiments were conducted to design and identify the components of the oxygen-releasing materials. Cement and gypsum were used as a binder in this mixtures experments. (1) using cement as the binding material The mixtures of the oxygen release material were prepared by blending cement, peat, sand, ethylene-vinyl acetate copolymer(EVA), calcium peroxide (CaO2), and water together at a ratio of 1.0¡G0.18¡G0.20¡G0.10¡G1.12¡G1.74 by weight. Cement was used as a binder and regular medium filter sand was used to increase the permeability of the mixture. Calcium peroxide releases oxygen upon contact water. The designed material with a density of 1.9 g/cm3 was made of 3.5 cm cube for the batch experiment. Results show that the oxygen release rate of the material is 0.046 mg O2/day/g rock. The oxygen release material was able to remain active in oxygen release for more than three months. (2) using gypsum as the binding material The mixtures of the oxygen release material were prepared by blending gypsum, CaO2, sand, and water together at a ratio of 1¡G0.5¡G0.14¡G0.75 by weight. Gypsum was used as a binder and regular medium filter sand was used to increase the permeability of the mixture. Calcium peroxide releases oxygen upon contact water. The designed material with a density of 1.1 g/cm3 was made of 3.5 cm cube for the batch experiment. Results show that the oxygen release rate of the material is 0.031 mg/day/g. The oxygen release material was able to remain active in oxygen release for more than three months. In the third part of this study, immobilization technology was applied to produce the low permeability wrapping film for the construction of oxygen-releasing granular materials. The mixtures of the oxygen release material were prepared by blending alginate, CaO2, and sand together at a ratio of 8.3¡G1.0¡G1 by weight. The low permeability wrapping film of the oxygen release material was able to remain active in oxygen release for two months. In the fourth part of this study, a laboratory-scale column experiment was conducted to evaluate the feasibility of this proposed system on the bioremediation of petroleum-hydrocarbon contaminated groundwater. This system was performed using a series of continuous-flow glass columns including four consecutive soil columns. Simulated petroleum-hydrocarbons contaminated groundwater with a flow rate of 0.263 m/day was pumped into this system. In the column experiment, the samples of column influent and specified sampling ports were collected and analyzed for pH, DO, BTEX, MTBE, and microbial populations. Results show that up to 99% of BTEX removal was observed in this passive system. Results from this study would be useful in designing an efficient and cost-effective passive oxygen-releasing and bioremediation system to remediate petroleum- hydrocarbon contaminated aquifer.

Chromium is a common groundwater pollutant originating from industrial processes such as metal plating, leather tanning and pigment manufacturing. Permeable reactive barriers (PRBs) have proven to be viable and cost-effective systems for remediation of chromium contaminated groundwater at many sites. The purpose of this research presented in this thesis is to focus on two parameters that affect the performance of PRB on chromium removal, namely the concentration of reactive media and groundwater flux by analyzing the data obtained from laboratory column studies. Laboratory scale columns packed with different amounts of iron powder and quartz sand mixtures were fed with 20 mg/l chromium influent solution under different fluxes. When chromium treatment efficiencies of the columns were compared with respect to iron powder/quartz sand ratio, the amount of iron powder was found to be an important parameter for treatment efficiency of PRBs. The formation of H2 gas and the reddish-brown precipitates throughout the column matrix were observed, suggesting the reductive precipitation reactions. SEM-EDX analysis of the iron surface after the breakthrough illustrated chromium precipitation. In addition to chromium / calcium and significant amount of iron-oxides or -hydroxides was also detected on the iron surfaces. When the same experiments were conducted at higher fluxes, an increase was observed in the treatment efficiency in the column containing 50% iron. This suggested that the precipitates may not be accumulating at higher fluxes which, in turn, create available surface area for reduction. Extraction experiments were also performed to determine the fraction of chromium that adsorbed to ironhydroxides. The analysis showed that chromium was not removed by adsorption to oxyhydroxides and that reduction is the only removal mechanism in the laboratory experiments. The observed rate of Cr(VI) removal was calculated for each reactive mixture which ranged from 48.86 hour-1 to 3804.13 hour-1. These rate constants and complete removal efficiency values were thought to be important design parameters in the field scale permeable reactive barrier applications.