Use In Permeable Reactive Barriers Research Articles

Chemical aging of biochar-zero-valent iron composites in groundwater: Impact on Cd(II) and Cr(VI) co-removal

Biochar (BC), zero-valent iron (ZVI), and their composites are promising materials for use in permeable reactive barriers, although further research is needed to understand how their properties change during long-term aging in groundwater. In this study, BC, ZVI and their composites (4BC-1ZVI) were subjected to the chemical aging tests in five media (deionized water, NaCl, NaHCO3, CaCl2 and a mixture of CaCl2 and NaHCO3 solutions) for 20 days. After treatment, the microscopic analysis and performance tests for the co-removal of Cd(II) and Cr(VI) were carried out. The results indicated that the removal of Cd(II) by aged 4BC-1ZVI followed a pseudo-second-order model, whereas the removal of Cr(VI) was better fitted with a pseudo-first order model. The aging mechanism of 4BC-1ZVI was primarily governed by iron corrosion/passivation, the reduction of soluble components, and the formation of carbonate minerals. Less Fe3O4/ γ-Fe2O3 was formed during aging in deionized water, NaCl and CaCl2 solutions. The corrosion products, Fe3O4/ γ-Fe2O3, FeCO3 and α/γ-FeOOH, were observed after aging in NaHCO3 and a mixture of NaHCO3 and CaCl2 solutions. The decrease in the soluble components of biochar led to a decrease in cation exchange, while carbonate minerals contributed to Cd(II) precipitation. This work provides insights into the aging processes of BC-ZVI composites for long-term groundwater remediation applications.

Iron-modified biochar-based bilayer permeable reactive barrier for Cr(VI) removal

Iron (Fe)-modified biochar (FeBC) has been developed to remove hexavalent chromium (Cr(VI)) from groundwater and is suitable for use in permeable reactive barriers (PRBs). However, Cr(VI) removal behavior and chemical processes in FeBC-based PRBs are not fully understood, and the potential for Fe release has not been addressed. In this study, three FeBC-based PRBs were assessed in column experiments for 563 days with respect to their ability to remove Cr(VI). Bilayer column filled with FeBC+limestone and BC+limestone in two separate layers (FeBC_Ca_BC) showed the best performance in terms of Cr(VI) removal with a low treatment cost. The corrosion of FeBC was mainly related to pH and Cr(VI) concentration rather than flow rate. Leached Fe was attenuated by BC and limestone and reutilized in FeBC_Ca_BC. Cr(VI) was reduced to Cr(III) and then adsorbed or precipitated on the biochars. Cr and Fe formed inner-sphere complexes and then transformed from double corner sharing to edge sharing. During the reaction, Cr penetrated from the surface to the interior of the biochars and became a more stable species. This study provides evidence of the effectiveness of a new combination of biochars for Cr(VI) removal and insights into the reaction mechanisms.

Activated bamboo charcoal in water treatment: A mini-review

Increased consumption and demand for freshwater has resulted to massive production of wastewater, which has toxins and is harmful to the environment if not treated. The use of permeable reactive barriers using activated carbon has proven to be a low cost and environmental friendlier solution to the problem compared to conventional methods. This minireview demonstrated the use of bamboo activated carbon, which is mesoporous in treating wastewater pollutants through adsorptive processes. The paper discusses the chemical and physical processes involved in activation and carbonization of bamboo charcoal, its adsorptive and structural characteristics. Case examples of its application in wastewater treatment based on literature review are also evaluated. Overall, bamboo is a viable renewable biomass material used in wastewater treatment compared to alternative carbon-based materials such as wood charcoal, coconut shell activated charcoal and carbon nanotubes.

An overview of the permeable reactive barrier as part of water remediation system in tropical countries

Natural resources are widely used for daily life, but due to poor utilization it can cause natural disasters. Disasters can occur due to several circumstances, such as flooding, which is caused by a malfunction of the drainage system. Floods may contain some bad compounds; therefore, proper solutions are needed to prevent soil pollution. Permeable reactive barrier or PRB can be a solution to this problem. There are various ingredients and benefits of Permeable Reactive Barriers, such as the addition of carbon particles, which will filter water containing petroleum when water passes through PRB. With the help of porous concrete, the water will flow into the permeable reactive barrier and then flow into the bio pores, so that it can make the surrounding soil more fertile. This paper review aims to discuss the use of permeable reactive barriers for soil remediation in tropical countries.

The Effectiveness of Reactive Materials for Contaminant Removal in the Process of Coal Conversion

ABSTRACT The technology of permeable reactive barriers (PRB) is one of the most frequently developed methods for protecting soil and water from pollution. These barriers are zones filled with reactive material in which contaminants are immobilized and/or their concentration is reduced to the limit values during the flow of contaminated groundwater. This article presents a study on the efficiency of the removal of contaminants from the post-processing water from the underground coal gasification (UCG) process. The tests were carried out in a laboratory using a flow-through reactor design. The post-processing water came from a UCG experiment carried out in the Barbara mine, Mikołów, Poland. Activated coal, zeolite, and nano-iron were used as the reactive materials in the experiment. The obtained results were compared to tests carried out with reference water (artificial) with strictly defined characteristics. Research has shown that activated carbon is the most effective material used in the reaction zone for removing organic contaminants from groundwater generated during the coal conversion process. A new feature is the use of PRB in a georeactor zone during the UCG process to limit the potential risk of contamination spreading in the case of uncontrolled and unpredictable operation, in emergency situations related to gas leaks into the environment, during underground fires, and for water polluted by high-toxicity substances.

Application of enhanced electrokinetic approach to remediate Cr-contaminated soil: Effect of chelating agents and permeable reactive barrier

Enhanced electrokinetic (EK) technique was employed to remediate Cr-contaminated soil using a permeable reactive barrier (PRB) and chelating agents. Synthesized nanomagnetic Fe3O4 was used as a reactive material in PRB. Moreover, EDTA and citric acid (CA) were used as chelating agents. Sequential extraction method (SEM) was employed to determine Cr-elimination mechanism during the EK process. The results revealed that EDTA (78% Cr removal) was more effective than CA (54% Cr removal) in eliminating Cr from the contaminated soil during the EK process. The application of PRB in combination with EDTA was able to reduce the Cr removal rate to 70 and 66% by locating PRB in the middle section and near the anode/cathode reservoir, respectively. The use of PRB coupled with EDTA near the anode and cathode led to a more uniform Cr removal from the soil during the EK process. The highest energy consumption was 0.12 KWh during the EK remediation using PRB. Traditional EK remediation could only remove exchangeable and carbonate fractions of Cr. The use of chelating agents led to a significant (more than 90%) increase in Cr removal from the following fractions: exchangeable phase, carbonate phase, and bond to Fe–Mn oxides. In addition to electromigration (EM) mechanism, electroosmotic flow (EOF) played an important role in Cr removal during the EK process, especially when coupled with PRB.

Reductive transformation of perfluorooctanesulfonate by nNiFe0-Activated carbon

Degradation of linear (L) and branched (Br) perfluorooctanesulfonate (PFOS) using nNiFe° particles supported on activated carbon (AC) and heat is demonstrated for the first time and with several lines of evidence. At 60 °C, PFOS degradation plateaued at 50 ± 6%, while at 50 °C, 94 ± 4.1 % PFOS transformed. The accelerated iron corrosion at the higher temperature is attributed to the lower PFOS transformation at 60 °C. However, at both temperatures, ≥ 97 % of the PFOS transformed was accounted for by the moles of fluoride generated. At 60 °C, PFOS degradation rates were estimated at 0.028 ± 0.003 h−1 and fluoride and sulfite generation rates of 0.70 ± 0.165 h−1 and 0.62 ± 0.157 h−1, respectively, with no differences between L-PFOS and total Br-PFOS. Using time-of-flight mass spectrometry, some organic products were identified in the particle extracts from the 60 °C reaction. Products included single-bonded C8 polyfluoroalkyl sulfonates (F16 to F7) and alkyl acids (PFCAs, C4-C8) and one perfluorinated C8 desulfonated product supporting both defluorination and desulfonation pathways. Most of the organic products were gone after the first 25 h. High PFOS mineralization using nNiFe°-AC technology warrants further investigation for its use in permeable reactive barriers.

Optimization of permeable reactive barrier dimensions and location in groundwater remediation contaminated by landfill pollution

One of the well-known methods is the use of permeable reactive barrier (PRB) to treat groundwater. In order to simulate the PRB design due to the complexity of the equations governing hydraulic flow and pollutant transfer and the integration of these two sets of equations, there is need to use simulated flow and pollutant transfer models. MODFLOW as quantitative model for groundwater flow modeling and MT3DMS qualitative model for groundwater contamination modeling as well as GMS software as graphical interface were used. In the optimization section, due to the extent of decision space in the objective function and the need for high reliability of the selective optimization algorithm, metaheuristic algorithm (GA) is used. The model is implemented under the non-barrier condition and then comparing it with the optimum PRB condition indicates that cost of treatment and total costs are reduced despite consideration costs of manufacturing and active materials presented in PRB and then effect of changes in landfill pollution concentration level was studied in different scenarios. Also, the simulation model was used to investigate the effect of changes of PRB’s active material, length, width and height parameters on pollutant concentration and treatment cost. Of the total PRB costs, 37 % is related to manufacturing costs and 63 % to active materials used in PRB. A comparison of the total costs reveals 45 % benefit in the using condition and the optimum barrier width is 3 m, its length is 35 m and its height is 25 m, located 21 m from the well.

Effect of chemical additives on electrokinetic remediation of Cr-contaminated soil coupled with a permeable reactive barrier.

Chromium (Cr) contamination in soil, especially Cr(VI), is a serious threat to the environment and human health. The electrokinetic remediation (EKR) is a promising technology to remediate the Cr(VI). Therefore, in this study, EKR coupled with a permeable reactive barrier (PRB) was used to treat the Cr(VI)-contaminated soil. The CTMAB-Z, a modified zeolite (prepared with cetyltrimethyl ammonium bromide) alone and a mixture of CTMAB-Z and Fe(0) were used as PRB-1 and PRB-2 reactive media, respectively. The effect of chemical enhancers/additives, i.e. DL-tartaric acid and Tween 80 on EKR of Cr(VI) was also analysed in the contrasting experiments. While the effects of repair time, voltage gradient and DL-tartaric acid concentration on Cr(VI) remediation were investigated by using the multifactor orthogonal experiment which was based on contrasting experiments. The contrasting experiment results showed that the highest Cr(VI) removal rate (66.27%) and leaching efficiency (71.29%) were observed in the experimental group which had DL-tartaric acid and PRB-2. Furthermore, the multifactor orthogonal experiment results had depicted that the highest Cr(VI) removal rate (80.92%) and leaching efficiency (85.25%) were achieved after treating the samples at a voltage gradient of 2.5 V cm−1 for 8 days in the presence of 0.15 M concentration of DL-tartaric acid. This study demonstrated that Cr(VI) remediation through EKR process could be significantly enhanced by the use of PRB and additives.

A systematic mapping study on the development of permeable reactive barrier for acid mine drainage treatment

Acid mine drainage is a result of exposure of sulfide ore and minerals to water and oxygen. This environmental pollutant has been considered the second biggest environmental problem after global warming. On the other hand, permeable reactive barrier is an emerging remediation technology which can be used to treat acid mine drainage. However, the effectiveness of this proposed remediation technology greatly depends on the reactive media. Also, treatment of acid mine drainage using permeable reactive barrier is still in the infancy stage, and long-term performance is still unknown. Hence, this study was conducted to identify what have been studied, addressed and what are currently the biggest challenges and limitations on the use of permeable reactive barrier for acid mine drainage treatment. Through systematic mapping approach, the results have shown that the reactive media used in permeable reactive barrier can be categorized into five namely iron-based, organic-based, inorganic minerals-based, industrial waste-based, and combined media. The data revealed that majority of the papers which is about 40% use combined media as the reactive substrate. The future direction is toward the use of combined media as a reactive material for AMD treatment, for instance, use of geopolymer with mine tailings and silts as reactive media in combination with organic-based media

Selenite sorption by carbonate substituted apatite

The sorption of selenite, SeO32−, by carbonate substituted hydroxylapatite was investigated using batch kinetic and equilibrium experiments. The carbonate substituted hydroxylapatite was prepared by a precipitation method and characterized by SEM, XRD, FT-IR, TGA, BET and solubility measurements. The material is poorly crystalline, contains approximately 9.4% carbonate by weight and has a surface area of 210.2 m2/g. Uptake of selenite by the carbonated hydroxylapatite was approximately an order of magnitude higher than the uptake by uncarbonated hydroxylapatite reported in the literature. Distribution coefficients, Kd, determined for the carbonated apatite in this work ranged from approximately 4200 to over 14,000 L/kg. A comparison of the results from kinetic experiments performed in this work and literature kinetic data indicates the carbonated apatite synthesized in this study sorbed selenite 23 times faster than uncarbonated hydroxylapatite based on values normalized to the surface area of each material. The results indicate carbonated apatite is a potential candidate for use as a sorbent for pump-and-treat technologies, soil amendments or for use in permeable reactive barriers for the remediation of selenium contaminated sediments and groundwaters.

Evaluation of a permeable reactive barrier to capture and degrade hydrocarbon contaminants.

A permeable reactive barrier (PRB) was installed during 2005/2006 to intercept, capture and degrade a fuel spill at the Main Power House, Casey Station, Antarctica. Here, evaluation of the performance of the PRB is conducted via interpretation of total petroleum hydrocarbon (TPH) concentrations, degradation indices and most probable number (MPN) counts of total heterotroph and fuel degrading microbial populations. Results indicate that locations which contained the lowest TPH concentrations also exhibited the highest levels of degradation and numbers of fuel degrading microbes, based on the degradation indices and MPN methods selected. This provides insights to the most appropriate reactive materials for use in PRB's in cold and nutrient-limited environments.

Use of permeable reactive barrier to mitigate groundwater nitrate contamination from on-site sanitation

Nearly 50% of India's population depends on variants of pit-toilet systems for human waste disposal. Nitrate contamination of groundwater by pit-toilet leachate is a major environmental concern in the country as it sources a major proportion (50–80%) of potable water from aquifers. Therefore, minimizing nitrate contamination of groundwater due to leachate infiltration from pit-toilet systems is essential. Batch and column experiments demonstrated the capability of bentonite-enhanced sand (BES) specimens to reduce nitrate concentrations in synthetic solutions (initial NO3-N concentration = 22.7 mg/L, C/N = 3) by about 85–90% in 10 to 24 hour by a heterotrophic denitrification process. Based on the laboratory results, it is recommended that use of a BES-permeable reactive barrier layer at the base of pit-toilets will facilitate heterotrophic denitrification and mitigate nitrate contamination of the underlying aquifer.

In-situ Pb(2+) remediation using nano iron particles.

Originally, application of nano zero valent iron (nZVI) particles for the removal of lead (Pb2+) in porous media was studied. At first, stabilized nZVI (S-nZVI) was prepared and characterized, then used in batch and continuous systems. Based on the batch experiments, corresponding reaction kinetics well fitted with the pseudo-first-order adsorption model, and reaction rate ranged from 0.01 to 0.04 g/mg/min depend on solution pH and the molar ratio between Fe and Pb. In batch tests, optimal condition with more than 90% removal efficiency at 60 min was observed at a pH range of 4 to 6 and Fe/Pb ratio more than 2.5. Continuous experiments exposed that Pb2+ remediation was as well influenced by seepage velocity, grain size, and type of porous media. The maximum Pb2+ removal efficiency in batch and bench-scale systems were 97% and 81%, correspondingly. The results have shown the ability of S-nZVI to use in permeable reactive barriers, as an efficient adsorbent for Pb2+, because of its excellent stability, high reducing power, and a large surface area.Electronic supplementary materialThe online version of this article (doi:10.1186/s40201-015-0157-3) contains supplementary material, which is available to authorized users.

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.

Assessment of locally available reactive materials for use in permeable reactive barriers (PRBs) in remediating acid mine drainage

The management and treatment of contaminated mine water is one of the most urgent problems facing the South African mining industry. The cost advantage of permeable reactive barriers (PRBs) has seen their increased application as means of passively treating mine drainage. A PRB is built by placing a reactive material in the path of polluted groundwater. As the contaminant moves through the material, reactions occur that transform it into an environmentally acceptable form. Batch tests were carried out on limestone, dolomite, fly ash, concrete and wood chips to find a reactive material and/or reactive mixture, for use in a PRB, which can neutralise acidity, remove metals and is locally abundant. Batch tests involved the leaching of the materials in deionised water to determine the leachable component of each reactive material and the pH that each material could achieve in deionised water. The materials were also tested in acidic water (pH 5.54) to determine the effectiveness of each reactive material in removing contaminants. In terms of the ability to increase the pH, the topperforming reactive materials were limestone and fly ash as they both achieved a pH above 11. Limestone, concrete, fly ash and dolomite successfully removed at least 99% of the iron (Fe) from the mine water. Limestone and fly ash removed at least 99% of manganese (Mn) and magnesium (Mg) from the mine water. While the other reactive materials were ineffective in removing sulphate (SO4 2), limestone and fly ash, respectively, removed 72% and 99.9 % of SO 4 2from the mine water. The study of 3 reactive material mixtures, namely: (i) limestone-wood chips-concrete, (ii) limestone-fly ash, and (iii) fly ashconcrete, showed that all 3 systems were effective in removing heavy metals present in the mine water. All of the mixtures increased the pH to above 11, increased the alkalinity and decreased Fe, Mn, and Mg concentrations to below the prevailing South African discharge criteria of wastewater into a water resource. Reactive Mixtures 2 and 3 successfully removed 99% of SO4 2within 14 days. This study found that the most suitable reactive material for remediating acid mine groundwater was fly ash because it was able to neutralise acidity and remove Fe, Mn, and Mg and SO 4 2-.

Removal of uranium from contaminated drinking water: a mini review of available treatment methods

In the present article, the major treatment methods applied for uranium removal from groundwater, with specific applications in drinking water treatment, are reviewed. These include pump-and-treat technologies, such as membrane filtration methods, anion exchange, and the use of adsorbents, such as iron oxides, or titanium dioxide, as well as the application of coagulation processes with the addition of Fe/Al salts, or by lime softening. In all cases, uranium removal is mainly dependent on its speciation, which is greatly affected by the (usually coexisting) carbonate ions in the contaminated water. Under circumneutral pH values, uranium forms anionic complexes with carbonate of the type UO2(CO3)22-, or UO2(CO3)34-. In situ treatment technologies comprise mainly the use of permeable reactive barriers. These contain reactive materials, such as zero valent iron or hydroxyapatite, and uranium is usually removed by reduction to the respective insoluble products of U(IV); reducing bacteria, when present, can play a supplementary role.

Highly organic natural media as permeable reactive barriers: TCE partitioning and anaerobic degradation profile in eucalyptus mulch and compost

Batch and column experiments were conducted with eucalyptus mulch and commercial compost to evaluate suitability of highly organic natural media to support anaerobic decomposition of trichloroethylene (TCE) in groundwater. Experimental data for TCE and its dechlorination byproducts were analyzed with Hydrus-1D model to estimate the partitioning and kinetic parameters for the sequential dechlorination reactions during TCE decomposition. The highly organic natural media allowed development of a bioactive zone capable of decomposing TCE under anaerobic conditions. The first order TCE biodecomposition reaction rates were 0.23 and 1.2d−1 in eucalyptus mulch and compost media, respectively. The retardation factors in the eucalyptus mulch and compost columns for TCE were 35 and 301, respectively. The results showed that natural organic soil amendments can effectively support the anaerobic bioactive zone for remediation of TCE contaminated groundwater. The natural organic media are effective environmentally sustainable materials for use in permeable reactive barriers.

폐영가철 투수성반응벽체를 이용한 Modified Fenton 산화에 의한 MTBE 처리연구

MTBE (Methyl tertiary-butyl ether) has been commonly used as an octane enhancer to replace tetraethyl lead in gasoline, because MTBE increases the efficiency of combustion and decreases the emission of carbon monoxide. However, MTBE has been found in groundwater from the fuel spills and leaks in the UST (Underground Storage Tank). Fenton's oxidation, an advanced oxidation catalyzed with ferrous iron, is successful in removing MTBE in groundwater. However, Fenton's oxidation requires the continuous addition of dissolved Fe 2+ . Zero-valent iron is available as a source of catalytic ferrous iron of MFO (Modified Fenton's Oxidation) and has been studied for use in PRBs (Permeable Reactive Barriers) as a reactive material. Therefore, this study investigated the condition of optimization in MFO-PRBs using waste zero-valent iron (ZVI) with the waste steel scrap to treat MTBE contaminated groundwater. Batch tests were examined to find optimal molar ratio of MTBE : H2O2 on extent to degradation of MTBE in groundwater at pH 7 with 10% waste ZVI. As the results, the ratio of optimization of MTBE to hydrogen peroxide for MFO was determined to be 1:300[mM]. The column experiment was conducted to know applicability of MFO-PRBs for MTBE remediation in groundwater. As the results of column test, MTBE was removed 87% of the initial concentration during 120days of operational period. Interestingly, MTBE was degraded not only within waste ZVI column but also within sand column. It means the aquifer may affect continuously the MTBE contaminated groundwater after throughout the waste ZVI barrier. The residual products showed acetone, TBF (Tert-butyl formate) and TBA (Tert-butyl acetate) during this test. The results of the present study showed that the recycled materials can be effectively used for not only a source of catalytic ferrous iron but also a reactive material of the MFO-PRBs to remove MTBE in groundwater. Key word : Waste Zero-Valent Iron, MTBE, Modified Fenton Oxidation, PRBs, MFO-PRBs

Ion Exchange Capacity of Sr<sup>2+</sup> onto Calcined Biological Hydroxyapatite and Implications for Use in Permeable Reactive Barriers

With the recent Fukushima incident, there is an urgent need to find cost effective and workable permeable reactive barrier (PRBs) for the remediation/retardation of problematic radionuclides. Catfish bones were calcined at various temperatures (400­1100°C) to remove the organic matter (87.1mg·g ¹1 ) and to change the structural properties of the hydroxyapatite (HAP). Increasing temperatures increased the HAP crystallinity as indicated by a decrease in lattice strain (0.0098 to 0.00135) and an increase in crystallite sizes (5.0 © 10 ¹8 to 7.7 © 10 ¹8 m). There was also an observed decrease in specific surface areas (98.9 to 0.99m 2 ·g ¹1 ) and increase in particle sizes (50 to 1000nm). The sorption densities of Sr 2+ decreased with increasing calcination temperatures, from 0.34 to 0.05mmol·g ¹1 . However, once normalized for surface area, the sorption densities increased from 1.8 to 5.9mmol·m¹2. Overall, this research has important implications for the design of hydroxyapatite PRBs with higher calcination temperatures producing a more reactive material with larger particle sizes for increased permeability. Lower calcination temperatures produced amorphous HAP material, which released more aqueous PO4 3¹ and resulted in the precipitation of strontium phosphates, ultimately reducing the permeability of PRBs. [doi:10.2320/matertrans.M-M2012813]