Performance Of Permeable Reactive Barrier Research Articles

Quantitative assessment of the impact factors upon remediation performance of the PRB technique in conjunction with pumping/recharge

Installation of pumping/recharge wells adjacent to contaminant plume and permeable reactive barrier (PRB) can effectively improve PRB's performance by artificially altering groundwater flow field attracting more contaminants to pass through PRB within a shorten time. However, the impact factors affecting the performance of PRB in conjunction with pumping/recharge (abbreviated as PRB-PR technique) have not been quantitatively assessed. In this study, numerical approach was adopted and multiple scenarios were implemented based on the developed MODFLOW and MT3MDS models to quantitatively evaluate the influences of impact factors on PRB-PR's remediation performance over a hypothetical contaminated site. Simulation results indicated that: (1) PRB should be installed nearby the downstream boundary of contaminant plume; (2) PRB's contaminant removal efficiency (η), pumping/recharge rate (Q), and aquifer hydraulic conductivity (K) affect PRB-PR's performance significantly, and a linear relationship exists between contaminant removal rate (R) and the product of K and Q no matter η changes (a series of fitting equations representing the linear relationship between R and KQ under various η were yielded based on data fitting); and (3) PRB's hydraulic conductivity, pumping/recharge wells' locations, and pumping/recharge wells' quantity do not affect PRB-PR's performance seriously. The equations indicating PRB-PR's remediation performance and key impact factors can be utilized to calculate the minimum values of Q and η that can meet the requirements of remediation objectives of real contaminated sites, contributing to supervising the installation and operation of the PRB-PR technique accordingly.

Investigating the sustainable performance of a nanoscale zerovalent iron permeable reactive barrier for removal of nitrate, sulfide, and arsenic

Abstract The quality of groundwater resources is at catastrophic risk. The proper performance of iron nanoparticles has made a permeable reactive barrier (PRB) an alternative to conventional filtration methods. The performance of nanozerovalent iron (nZVI) PRBs is limited by particle aggregation, instability, and phase separation, even at low iron concentrations. Therefore, the precipitation of reactive materials and a decrease in the longevity of PRB are fundamental challenges. A laboratory setup is used to compare the performance of bare nZVI and xanthan gum (XG)-nZVI + Mulch PRB to simultaneously remove nitrate, sulfide, and arsenic in groundwater. nZVI (average diameter of 35–55 nm) particles are used as reactive media. The objectives are (1) to develop a method for treating nitrate, sulfide, and arsenic simultaneously in groundwater using organic mulch and XG-nZVI; and (2) to evaluate the longevity performance of the XG-nZVI + Mulch and bare nanoparticles treatment system over 10 days. The results showed that the XG-nZVI + Mulch barrier's performance for eliminating NO3-, As, and S2− was generally improved compared to the bare nZVI barriers by 5.7, 19.2, and 10.9%, respectively. Finally, despite the need for long-term sustainability assessment, XG-nZVI PRB performance is impressive, and this stability promises to improve the longevity of nanoparticles while used in PRBs.

A Review of the Hydraulic Performance of Permeable Reactive Barriers Based on Granular Zero Valent Iron

Permeable reactive barriers (PRBs) based on the use of zero valent iron (ZVI) represent an efficient technology for the remediation of contaminated groundwater, but the literature evidences “failures”, often linked to the difficulty of fully understanding the long-term performance of ZVI-based PRBs in terms of their hydraulic behavior. The aim of this paper is to provide an overview of the long-term hydraulic behavior of PRBs composed of ZVI mixed with other reactive or inert materials. The literature on the hydraulic performance of ZVI-based PRBs in full-scale applications, on long-term laboratory testing and on related mathematical modeling was thoroughly analyzed. The outcomes of this review include an in-depth analysis of factors influencing the long-term behavior of ZVI-based PRBs (i.e., reactive medium, contamination and the geotechnical, geochemical and hydrogeological characteristics of the aquifer) and a critical revision of the laboratory procedures aimed at investigating their hydraulic performance. The analysis clearly shows that admixing ZVI with nonexpansive granular materials is the most suitable choice for obtaining a long-term hydraulically efficient PRB. Finally, the paper summarizes a procedure for the correct hydraulic design of ZVI-based PRBs and outlines that research should aim at developing numerical models able to couple PRBs’ hydraulic and reactive behaviors.

Long-term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation – A mechanistic approach

Permeable reactive barriers (PRBs) are used for groundwater remediation at contaminated sites worldwide. This technology has been efficient at appropriate sites for treating organic and inorganic contaminants using zero-valent iron (ZVI) as a reductant and as a reactive material. Continued development of the technology over the years suggests that a robust understanding of PRB performance and the mechanisms involved is still lacking. Conflicting information in the scientific literature downplays the critical role of ZVI corrosion in the remediation of various organic and inorganic pollutants. Additionally, there is a lack of information on how different mechanisms act in tandem to affect ZVI-groundwater systems through time. In this review paper, we describe the underlying mechanisms of PRB performance and remove isolated misconceptions. We discuss the primary mechanisms of ZVI transformation and aging in PRBs and the role of iron corrosion products. We review numerous sites to reinforce our understanding of the interactions between groundwater contaminants and ZVI and the authigenic minerals that form within PRBs. Our findings show that ZVI corrosion products and mineral precipitates play critical roles in the long-term performance of PRBs by influencing the reactivity of ZVI. Pore occlusion by mineral precipitates occurs at the influent side of PRBs and is enhanced by dissolved oxygen and groundwater rich in dissolved solids and high alkalinity, which negatively impacts hydraulic conductivity, allowing contaminants to potentially bypass the treatment zone. Further development of site characterization tools and models is needed to support effective PRB designs for groundwater remediation.

Eight-year performance evaluation of a field-scale zeolite permeable reactive barrier for the remediation of ammonium-contaminated groundwater

Groundwater, which is one of the main sources of water for cities in northern China, is strongly influenced by surface water, particularly in riverside areas. To remediate ammonium-contaminated groundwater in riverside source fields, a zeolite permeable reactive barrier (PRB) was constructed in Shenyang, China. In this study, groundwater monitoring data from 2012 to 2019 were collected, and an eight-year performance evaluation of the zeolite PRB was conducted with respect to ammonium-nitrogen (NH4+-N) treatment and the corresponding removal mechanism. Groundwater monitoring results showed that NH4+-N removal was divided into stable (2012–2015), semi-stable (2016–2017) and unstable stages (2018–2019). During the stable stage, the NH4+-N concentration in the monitoring well located in the hydraulic down-gradient of the PRB decreased below the national standard limit of 0.5 mg/L with a higher removal efficiency (52%–97%), which was mainly owing to the strong adsorption capacity of the zeolite for NH4+-N. During the semi-stable stage, although the NH4+-N concentration in the down-gradient monitoring well of the PRB fluctuated greatly (0.18 mg/L−1.45 mg/L), the PRB system maintained a relatively high NH4+-N removal efficiency (16%–72%) because of strong nitrification. However, the zeolite in the PRB reached adsorption saturation after 2016, which resulted in NH4+-N desorption when less NH4+-N-contaminated groundwater flowed through the PRB. Then, a NH4+-N concentration in the down-gradient monitoring well of the PRB exceeding 0.5 mg/L has been observed during the unstable stage. Gene analysis results provided evidence that stronger denitrification and weaker nitrification capacity existed in the PRB system in 2018. The weaker nitrification was not enough to convert all the desorbed NH4+-N into NO3−-N, which led to an increase in the down-gradient NH4+-N concentration of the PRB from 2018 to 2019. Overall, time-dependent decay in the PRB performance for NH4+-N removal was noticeable after operating for 4–5 years and thus it is necessary to consider and conduct subsequent microbially mediated zeolite regeneration in the zeolite PRB.

Monitoring the performance of permeable reactive barriers constructed in acid sulfate soils

Two pilot-scale permeable reactive barriers (PRBs) were installed in an acidic terrain to treat contaminated groundwater with low pH and high concentrations of Al and Fe. The first pilot-scale barrier (PRB-1) was installed in 2006 using recycled concrete aggregates (RCA) as the reactive material, and the second barrier (PRB-2) was installed in late 2019 using limestone aggregates (LA) as the reactive material. Although the initial material cost of the recycled concrete aggregates is low, laboratory trials conducted before the field applications deduced that limestone is capable of more reliable and efficient pH neutralisation in the long term, reducing frequent maintenance or material replacement in the PRB. The performance of PRB-1 has been monitored continuously over the past 14 years. In particular, both internal (within PRB) and external (upgradient and downgradient) variations in acidity (pH), ion concentrations, and the flow conditions, including the piezometric heads, have been analysed. These decade long field observations have resulted in a comprehensive understanding of the temporal variations of treatment by RCA along the groundwater flow path through the alkaline granular mass and its biogeochemical clogging. For instance, acid neutralisation at the entrance of PRB-1 decreased by 31% over 14 years, whereas the corresponding reduction at the outlet is only 6%. The non-homogeneous biogeochemical clogging in different PRB zones was evident by a 48% reduction in hydraulic conductivity at the inlet and a 34% reduction at the outlet.

Modeling porosity loss in Fe0-based permeable reactive barriers with Faraday\u2019s law

Solid iron corrosion products (FeCPs), continuously generated from iron corrosion in Fe0-based permeable reactive barriers (PRB) at pH > 4.5, can lead to significant porosity loss and possibility of system’s failure. To avoid such failure and to estimate the long-term performance of PRBs, reliable models are required. In this study, a mathematical model is presented to describe the porosity change of a hypothetical Fe0-based PRB through-flowed by deionized water. The porosity loss is solely caused by iron corrosion process. The new model is based on Faraday’s Law and considers the iron surface passivation. Experimental results from literature were used to calibrate the parameters of the model. The derived iron corrosion rates (2.60 mmol/(kg day), 2.07 mmol/(kg day) and 1.77 mmol/(kg day)) are significantly larger than the corrosion rate used in previous modeling studies (0.4 mmol/(kg day)). This suggests that the previous models have underestimated the impact of in-situ generated FeCPs on the porosity loss. The model results show that the assumptions for the iron corrosion rates on basis of a first-order dependency on iron surface area are only valid when no iron surface passivation is considered. The simulations demonstrate that volume-expansion by Fe0 corrosion products alone can cause a great extent of porosity loss and suggests careful evaluation of the iron corrosion process in individual Fe0-based PRB.

Cement kiln dust-sand permeable reactive barrier for remediation of groundwater contaminated with dissolved benzene

ABSTRACT The interaction of cement kiln dust and simulated acidic groundwater (pH = 3) contaminated with benzene were studied. FTIR results showed that cation−π and H-bonding interactions had a major role in the removal process. The concentration of benzene in the effluent water and hydraulic conductivity of the continuous experiments was used to evaluate the performance of permeable reactive barrier for 60 days. The increase of CKD improves the performance of the bed with efficiency ranged from 40% to 90%, but clear decrease in the hydraulic conductivity was observed due to the accumulation of the benzene in the beginning of the barrier.

Role of Microorganisms in Permeable Reactive Bio-Barriers (PRBBs) for Environmental Clean-Up: A Review

It is an indisputable fact that any environmental clean-up technology generating certain kind of effective result would be easily supported. One of them includes Permeable reactive bio-barrier which is an innovative technology started from 90’s to treat a variety of contaminants along the natural gradient flow of groundwater through immobilization or transformation of pollutants into less toxic and harmful form. Despite of any broad acknowledgement, there are lesser known knowledge about use of microorganisms in permeable reactive barriers, mingling of microorganisms with other reactive media and their effect on each other’s reactivity. The current review deals with an overview of the types of reactive media used in Permeable Reactive Barriers (PRBs) as well as different bio-barriers (PRBBs) utilized for the treatment of various contaminants, long–term performance of permeable reactive barrier and combination of microorganism and reactive media to look forward for their symbiotic relationship in permeable reactive barrier for environmental remediation.

Sodium alginate/graphene oxide hydrogel beads as permeable reactive barrier material for the remediation of ciprofloxacin-contaminated groundwater

The wide occurrence of antibiotics in groundwater has raised serious concerns due to their impacts on humans and the ecosystem. Most of the research in groundwater remediation focuses on the exploitation of nano-materials. However, nano-materials have several disadvantages such as high production cost, rapid reduction in permeability, disposal problems, and high sensitivity to environmental conditions. To solve these issues, novel sodium alginate/graphene oxide hydrogel beads (GSA) were synthesised and their effectiveness as permeable reactive barrier (PRB) backfill material in the remediation of ciprofloxacin (CPX)-contaminated groundwater was tested. The adsorption of CPX onto GSA followed the pseudo-second-order kinetic model. The isotherm data followed the Freundlich model. The maximum adsorption capacity was 100 mg g−1 at pH 7.0. The adsorption process was sensitive to contact time, initial CPX concentration and ionic strength. However, it was not pH sensitive. Hydrophobic interaction, electrostatic interaction, ion exchange, H-bonding, and pore filling were proposed to be the main adsorption mechanisms. The effects of flow rate, influent CPX concentration, and ionic strength on the performance of PRB were confirmed through flow-through column experiments and by using a chemical non-equilibrium two-site model. Accordingly, a proper PRB was designed based on hydrogeological conditions. Finally, the lifetime and cost of the PRBs were calculated. The results obtained provided concrete evidence that GSA is a promising adsorbent material for PRBs applications in the remediation of CPX-contaminated groundwater.

Nitrate removal by a permeable reactive barrier of Fe0: A model-based evaluation

Permeable reactive barrier (PRB) filled with zero valent iron (ZVI, Fe0) can be an effective option to remove nitrate from contaminated groundwater. The long-term performance of such PRBs, however, might be compromised by the problem of declining reactivity and permeability, which could cause a decrease in the nitrate removal efficiency. In this study we explored suitable model formulations that allow for a process-based quantification of the passivation effect on denitrification rates and tested the model for a 40 years long operation scenario. The conceptual model underlying our selected formulation assumes the declining reactivity of the ZVI material through the progressing passivation caused by the precipitation of secondary minerals and the successive depletion of the ZVI material. Two model scenarios, i.e., the base model scenario which neglects the explicit consideration of the passivation effect and one performed with the model in which the impact of the passivation effect on denitrification was considered, were compared. The modeling results illustrate that nitrate removal in the model of considered passivation started to be incomplete after 10 years, and the effluent nitrate concentration of PRB rose up to 86% of the injected water concentration after 40 years, in contrast to the base scenario, corresponding well with the field observations of successively declining nitrate removal efficiencies. The model results also showed that the porosity of the PRB increased in both models. In order to improve and recover the reactivity of ZVI, pyrite was added to the PRB, resulting in completely nitrate removal and lower consumption of ZVI.

Role of Humic Substances on Cr(VI) Removal from Groundwater with Pyrite

Groundwater composition may have a pronounced impact on long-term performance of permeable reactive barriers (PRBs). Here, batch and column experiments were conducted to investigate the effects of humic acid (HA) on Cr(VI) removal by pyrite in systems containing cations such as Ca2+ and Mg2+. HA was observed to have inhibitory effect on Cr(VI) uptake by pyrite under the experimental conditions studied (e.g., pH 3 to 8). HA sorbed onto pyrite surface and thus (1) competed against Cr(VI) for pyritic surface sites and/or (2) increased electrostatic repulsion between Cr(VI) and pyrite. In systems with HA and Ca2+/Mg2+, the Cr(VI) uptake by pyrite decreased drastically relative to HA alone due to the aggregation of HA with Ca2+/Mg2+. The formation of such HA aggregates/precipitates blocked Cr(VI) ions to reach its binding sites, thereby resulting in a substantial decrease in Cr(VI) uptake. Overall, the results have major implications for proper design and operation of PRBs with pyrite as the reactive material.

Stabilization of Iron (Micro)Particles with Polyhydroxybutyrate for In Situ Remediation Applications

Groundwater is an extremely important resource that may, however, contain a variety of toxic and bioaccumulative contaminants. Traditional “Pump and Treat” technologies for treating contaminated groundwater are no longer time- or cost-effective; therefore, new technologies are needed. In this work, we synthesized core–shell materials of micrometric dimensions based on the interaction of iron particles (the core) and fermentable biopolymers such as polyhydroxybutyrate (PHB, the surrounding shell) to be used in permeable reactive barriers for the removal of chlorinated pollutants from contaminated groundwater. The materials were prepared by precipitation techniques that allowed stable preparations to be obtained, whose chemico-physical properties were thoroughly characterized by scanning electron microscopy, porosimetry, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses, disc centrifuge analysis, and dynamic light scattering. The properties of the prepared materials are very promising, and may enhance the performance of permeable reactive barriers towards chlorinated compounds.

Assessing the performance of a permeable reactive barrier–aquifer system using a dual-domain solute transport model

Transport behavior through a permeable reactive barrier (PRB)-aquifer system is complicated because of the different physical and chemical properties of the PRB and the aquifer. Dual-domain solute transport models are efficient tools for better understanding the various processes and mechanisms of reactive solute transport through a PRB–aquifer system. This study develops a dual-domain analytical model to assess the physical and chemical processes of two-dimensional reactive solute transport through a PRB–aquifer system. The dispersion processes of a dual–domain system on the solute transport are investigated. The results show that the dispersion parameters in a dual-domain system synchronously govern the dynamic shape of the contaminant plume. The low longitudinal and transverse dispersion coefficients of a dual-domain system may restrict the spreading of the plume and elevate the plume’s concentration level. The derived analytical solution is applied to explore how the different reactive transport processes affect the performance of a PRB-aquifer system. The results show that the first-order decay rate constant of the PRB has a critical effect on the performance of the PRB-aquifer system, whereas the effects of the physical dispersion properties on PRB performance are less significant.

Influences of environmental factors on bacterial extracellular polymeric substances production in porous media

Summary Bioclogging of natural porous media occurs frequently under a wide range of conditions. It may influence the performance of permeable reactive barrier and constructed wetland. It is also one of the factors that determine the effect of artificial groundwater recharge and in situ bioremediation process. In this study, a series of percolation column experiments were conducted to simulate bioclogging process in porous media. The predominant bacteria in porous media which induced clogging were identified to be Methylobacterium, Janthinobacterium, Yersinia, Staphylococcus and Acidovorax, most of which had been shown to effectively produce viscous extracellular polymeric substances (EPS). The column in which EPS production was maximized also coincided with the largest reduction in saturated hydraulic conductivity of porous media. In addition, carbon concentration was the most significant factor to affect polysaccharide, protein and EPS secretion, followed by phosphorus concentration and temperature. The coupled effect of carbon and phosphorus concentration was also very important to stimulate polysaccharide and EPS production.

Consideration of grain packing in granular iron treatability studies

Commercial granular iron (GI) is light steel that is used in Permeable Reactive Barriers (PRBs). Investigations into the reactivity of GI have focused on its chemical nature and relatively little direct work has been done to account for the effects of grain shape and packing. Both of these factors are expected to influence available grain surface area, which is known to correlate to reactivity. Commercial granular iron grains are platy and therefore pack in preferential orientations that could affect solution access to the surface. Three packing variations were investigated using Connelly Iron and trichloroethylene (TCE). Experimental kinetic data showed reaction rates 2–4 times higher when grains were packed with long axes preferentially parallel to flow (VP) compared to packings with long axes preferentially perpendicular to flow (HP) or randomly arranged (RP). The variations were found to be explainable by variations in reactive sorption capacities, i.e., sorption to sites where chemical transformations took place. The possibility that the different reactive sorption capacities were related to physical pore-scale differences was assessed by conducting an image analysis of the pore structure of sectioned columns. The analyses suggested that pore-scale factors – in particular the grain surface availability, reflected in the sorption capacity terms of the kinetic model used – could only account for a fraction of the observed reactivity differences between packing types. It is concluded that packing does affect observable reaction rates but that micro-scale features on the grain surfaces, rather than the pore scale characteristics, account for most of the apparent reactivity differences. This result suggests that treatability tests should consider the packing of columns carefully if they are to mimic field performance of PRBs to the greatest extent possible.

Performance of a permeable reactive barrier for in situ removal of ammonium in groundwater

Nitrogen as ammonium (NH4+-N) is one of the most common nitrogen contaminants in groundwater; this is particularly true in the industrial and agricultural regions of northern China, where rapid population growth and economic development have stressed public water supplies and reduced groundwater quality. In this study, we report the performance of a zeolite permeable reactive barrier (PRB) designed to remove ammonium from contaminated river water that infiltrates to a groundwater aquifer that serves as a drinking water supply for the city of Shenyang. Groundwater monitoring data obtained over 5 months of operation indicate that ammonium concentrations in the groundwater decreased from 2–10 mg/L to <0.5 mg/L after the PRB was installed in the vicinity. Data suggest that ammonium removal was mainly due to sorption and ion exchange, with NH4+ exchanged with Na+ and K+ in the zeolite. After more than 1 year of continuous operation, there is no evidence of microbial ammonium oxidation. To our knowledge, this was the first field-scale demonstration of a PRB in China.

Feasibility of using fly ash, lime, and bentonite to neutralize acidity of pore fluids

Acidic groundwater resulting from the poorly planned use of acid sulfate soils has become a major environmental issue in coastal Australia over the last several years. Use of permeable reactive barriers (PRBs) designed to generate alkalinity by promoting sulfate reduction has recently become popular as an alternative solution to this problem. However, recent studies have also revealed that the long-term performance of such PRBs can be significantly undermined by chemical precipitation and clogging of pore space, which would decrease the buffer capacity and hydraulic conductivity of the reactive material. This study seeks to explore the feasibility of using bentonite in addition to lime and fly ash to form mixtures with a high buffer capacity and permeability that would enable groundwater flow through PRBs over a substantial period of time. A series of laboratory experiments, including buffer capacity and leaching tests, were performed on different mixtures of fly ash with lime and bentonite using acidic fluids of low pH. It was found that the ability of such mixtures to neutralize acidic fluids was mostly controlled by the content of lime. Laboratory data also showed that an addition of bentonite to lime—fly ash mixtures could decrease the buffer capacity of soil. Compaction tests indicated that the presence of bentonite would increase the dry density of mixtures at the optimum moisture content. A series of hydraulic conductivity tests were carried out to study changes in the coefficient of permeability of lime—fly ash mixtures with different contents of bentonite permeated with acidic liquids. The obtained results revealed that the coefficient of permeability of the specimens tended to increase over a period of time, likely due to the changes in the diffuse double layer of bentonite particles.

Predicting longevity of iron permeable reactive barriers using multiple iron deactivation models

In this study we investigate the model uncertainties involved in predicting long-term permeable reactive barrier (PRB) remediation efficiency based on a lab-scale column experiment under accelerated flow conditions. A PRB consisting of 20% iron and 80% sand was simulated in a laboratory-scale column and contaminated groundwater was pumped into the column for approximately 1year at an average groundwater velocity of 3.7E−1m d−1. Dissolved contaminants (PCE, TCE, cis-DCE, trans-DCE and VC) and inorganic (Ca2+, Fe2+, TIC and pH) concentrations were measured in groundwater sampled at different times and at eight different distances along the column. These measurements were used to calibrate a multi-component reactive transport model, which subsequently provided predictions of long-term PRB efficiency under reduced flow conditions (i.e., groundwater velocity of 1.4E−3m d−1), representative of a field site of interest in this study. Iron reactive surface reduction due to mineral precipitation and iron dissolution was simulated using four different models. All models were able to reasonably well reproduce the column experiment measurements, whereas the extrapolated long-term efficiency under different flow rates was significantly different between the different models. These results highlight significant model uncertainties associated with extrapolating long-term PRB performance based on lab-scale column experiments. These uncertainties should be accounted for at the PRB design phase, and may be reduced by independent experiments and field observations aimed at a better understanding of reactive surface deactivation mechanisms in iron PRBs.

Performance Prediction of Permeable Reactive Barriers by Three-Dimensional Groundwater Flow Simulation

Various analytical methods for describing the hydraulic behavior of a permeable reactive barrier (PRB) are developed based on a three-dimensional approximation of the groundwater flow system. To simulate the actual geological groundwater system, modeling was proposed in this study. Using MODFLOW module of the GMS software, the groundwater head and contaminants (BTEX; Benzene, Toluene, Ethyl benzene, and Xylene) concentration distribution model was developed. Based on these data and models, the optimal location of PRB installation was selected and the performance of PRB and the future response of Hydrogeological system were predicted by the model.