Permeable Reactive Barrier System Research Articles

Covalent organic polymer-based sodium alginate composite beads: Decontamination of ciprofloxacin micro-polluted groundwater in a PRB system

The ecological threat posed by ciprofloxacin (CIP) contaminated groundwater could be settled by permeable reactive barriers (PRB) technology. However, exploiting proper and recyclable backfill medium was a major challenge for a PRB system. Herein, a novel three-component covalent organic polymer (SLEL-7) was synthesized by a solvothermal method for the adsorptive purification of CIP in groundwater, followed by the successful introduction into sodium alginate to acquire excellent recyclable beads (SLEL-7@SA beads) achieving enhanced adsorption behaviors. Plausible adsorption mechanisms were proposed through characterizations and adsorption studies in addition to the main controlling factors, including pore filling effect, hydrogen bonding and π-π EDA interaction, of course, hydrophilic-lipophilic balance and electrostatic interaction also took part in. Aside from that, a laboratory PRB column loading SLEL-7@SA beads as backfill medium was established which could continuously treat 60 bed volumes (BVs) of CIP (500 μg·L–1). And to be more specific, the Thomas, Yoon-Nelson and Adams-Bohart models were applied to predict the dynamic behaviors of CIP adsorption in the column. Overall, this work emphasized the structural and functional design of three-component COPs and the great potential of macroscopic COP@SA composite beads for in-situ remediation of CIP micro-polluted groundwater.

Facile fabrication of shapeable three-component hydrogen-bonded covalent-organic aerogel as permeable reactive barrier material for efficient in-situ fluoroquinolone contaminated groundwater remediation

Fluoroquinolones (FQs) antibiotics found in groundwater pose hazardous impacts to organisms and humans. Moreover, permeable reactive barrier (PRB) is reckoned as an effective in-situ remediation technique for FQ-contaminated groundwater, in which PRB materials with high adsorption capacity and moldability are severely desired. Herein, a shapeable three-component hydrogen-bonded covalent-organic aerogel with sulfonic acid (SLEL-3) was fabricated based on a multiple-component method. The appraisal of SLEL-3 for the capture of levofloxacin (LVF) and ciprofloxacin (CIP) was evaluated systematically through kinetics and isotherms, which exhibited satisfactory adsorption performance in the following aspects: amended adsorption capacity, acceptable removal depth and resistance to ions and acidity/alkalinity. The proposed adsorption mechanisms involved a combination of pore filling effect, electrostatic effect, hydrogen bonding, π-π/n-π electron-donor–acceptor (π-π/n-π EDA), Lewis acid-base and hydrophobic/hydrophilic interaction. More importantly, in view of self-shaping ability, adaptability to harsh conditions, high swellability as well as felicitous hydraulic conductivity, novel PRB systems integrating SLEL-3 into 1-D column and 2-D tank in lab-scale study were developed for the capture of LVF, achieving impressive removal efficiencies of 86% and 92.65% over a 72-h period, respectively. Thus, this study provides a new notion of contriving a shapeable, eco-friendly and practicable covalent-organic polymer for potentially efficient in-situ remediation of FQ contaminated groundwater with a large area.

Characteristics of Zinc Adsorption onto Biochars Derived from Different Feedstocks

Human activities such as the discharge of urban sewage, garbage, and industrial waste have seriously affected the quality of groundwater sources for human consumption. The potential for using biochar as a reactive medium in a permeable reactive barrier (PRB) was explored for Zn-contaminated groundwater treatment in this study. Four different types of biochar produced from wood, coconut shell, rice straw, and fruit shell were used. The production temperature of these biochars were 600 °C, 550 °C, 500 °C, and 500 °C, respectively. The samples were coded with the initials of the biochar source and the production temperature as WD600, CS550, RS500, and FS500. The results of various batch adsorption studies show that equilibrium solution pH has a great effect on the maximum adsorption capacity in the pH range of 2–7. The adsorption of Zn on biochars follows the Freundlich model and fits well with the pseudo-second-order model. The fixed-bed column test data were well fitted to the Dose–Response model. The adsorption capacities of WD600, CS550, RS500, and FS500 were 24.91, 15.87, 9.25, and 46.71 mg/g, respectively. The removal rate of FS500 can reach a maximum of 98.87%. FS500 is considered to be a potential reaction medium for treating Zn-contaminated groundwater in a PRB system. This work provides a new option for converting biomass waste into an adsorbent for zinc in wastewater. The results of this study are expected to provide a solid theoretical basis for the further application of biochar in groundwater pollution remediation.

Analytical Model for the Design of Permeable Reactive Barriers Considering Solute Transport in a Dual-Domain System

A permeable reactive barrier (PRB) is an effective groundwater in situ remediation technology, and the design methods used for PRBs are significant in ensuring that they meet remediation goals. Steady-state analytical solutions are an effective tool to provide conservative and simple design methods. A steady-state analytical solution is proposed to describe organic contaminant transport through the PRB and aquifer in a PRB and cut-off wall system. The proposed analytical solution may serve as an effective tool to provide conservative and simple design methods. The shape factor (S) is introduced at the PRB-aquifer interface to investigate the effects of a PRB’s layout forms on its performance. The results show that the relative contaminant concentration at the point of compliance for a PRB with S=8 is 11 orders of magnitude larger than that without considering the shape factor. Effects of degradation, dispersion, and advection on PRB design are subjected to dimensionless analysis. Dimensionless analysis shows that degradation plays a key role in decreasing contaminant concentration in the PRB. In addition, increasing advection may promote contaminant transport from the source to the aquifer. Simplified solutions to estimate PRB thickness and source remediation time are derived for the practical design and performance evaluation of the PRB system.

In Situ Bioreduction of Hexavalent Chromium‐Contaminated Water Using a Microbial Culture Barrier

AbstractChromium (Cr) has been extensively used in many industrial applications. Inappropriate disposal of effluent has led to increased Cr concentrations in the environment. As a result, Cr(VI) has been classified under strict control measures by most national and international lists of highly toxic materials. Bioremediation of Cr(VI)‐contaminated effluents appears to be a more economical and environment‐friendly treatment method. This study investigates Cr(VI) removal in a bench‐scale bioreactor using municipal dried sludge as a permeable bioreactive barrier. The 20‐cm‐thick permeable bioreactive barrier with 30 % sludge and 70 % sand was able to achieve 95 % Cr(VI) removal during 90 operational days, demonstrating the effectiveness of the biological permeable reactive barrier system in treating Cr(VI)‐containing process effluent streams.

Soil Based Adsorption Media for Permeable Reactive Barriers to Adsorb Lead (Pb<sup>2+</sup>) & Cadmium (Cd<sup>2+</sup>)

Groundwater contamination is one of the predominant environmental problems in Sri Lanka and it is suspected as one of the unseen factors of the country’s widespread kidney disease. Heavy metals Cadmium (Cd2+) and Lead (Pb2+) are two potentially harmful contaminants found in polluted groundwater samples in Sri Lanka. Permeable reactive barrier (PRB) is an on-site, costeffective and efficient groundwater heavy metal remediation technique. However, the effectiveness of the PRB system is highly dependent on the characteristics of the reactive materials being used. Accordingly, Rendzina soil (Hunugala series), Reddish Brown earth soil (Nonagama series), Reddish brown latosolic soil (Melsiripura series), and Bog Soil (Wagura series) were selected based on the basic soil properties which were found by previous researchers. Sieve analysis, Atterberg limits, and Procter compaction tests were carried out to determine the physical properties of the selected soils. The batch tests were carried out to determine the absorption rate of heavy metals, namely, Lead (Pb2+) and Cadmium (Cd2+), and to assess the effects of pH, contact time, and initial concentration on the adsorption characteristics of the selected reactive materials. The results reveal that the Rendzima soil is the most suitable reactive material out of all the reactive materials tested.

Nitrate removal rates, isotopic fractionation, and denitrifying bacteria in a woodchip-based permeable reactive barrier system: a long-term column experiment.

This study evaluated the effectiveness of using organic carbon materials (i.e., woodchips) to remove nitrate from groundwater. The results of our flow-through column experiment, which was conducted over 1.6years, suggested that denitrifying bacteria reduce nitrate by using it as an electron acceptor and woodchips as an electron donor. The nitrate removal rates were sufficiently high (0.39-1.04mmol L-1day-1) during the operation of the column. Denitrification process was supported by fractionation of nitrogen and oxygen isotopes (δ15N and δ18O), with the δ15N and δ18O values enriched from 7.4‰ and 22.3‰ to 21.2‰ and 30.4‰, respectively. Enrichment factors ([Formula: see text]) for 15N and 18O were calculated using the Rayleigh fractionation model, with values of - 13.2‰ for ε15N and - 7.1‰ for ε18O. The fractionation ratio of 15N to 18O was 1.9:1, confirming denitrification. The most abundant bacterial genera in the soil used for inoculation were Enterobacter (86.7%), Nitrospira (1.8%), and Arthrobacter (1.5%), while those in the column effluent were Macrococcus (37.1%), Escherichia (14.7%), and Shigella (14.6%), indicating that bacterial communities changed in response to geochemical conditions in the column. This study suggests that nitrate in groundwater can be effectively removed using woodchip-based passive treatment systems and that information on isotopic fractionation and denitrifying bacteria can be key tools to understand denitrification.

Remediation of Contaminated Soil with Compound Heavy Metals Using an Array-Electrode Electrokinetics Coupled with Permeable Reactive Barrier System with Different Electrolytes

Remediation of Contaminated Soil with Compound Heavy Metals Using an Array-Electrode Electrokinetics Coupled with Permeable Reactive Barrier System with Different Electrolytes

Remediation of nitrate contaminated groundwater using a simulated PRB system with an La–CTAC–modified biochar filler

In the present study, the Erigeron canadensis L., a typical invasive plant in Southwest China, was utilized as the raw material to prepare original biochar (ECL), a rare earth element La–modified biochar (La–ECL), and a rare earth element La coupling cationic surfactant [cetyltrimethylammonium chloride (CTAC)]–modified biochar (La/CTAC–ECL). These materials were then added to simulated permeable reactive barriers (PRBs) and their nitrate (NO3−) contaminant remediation performances were evaluated in groundwater. The results show that the breakthrough time for NO3− in a simulated PRB column increases as the concentration of the influent NO3− and the flow rate decreases, whereas with the increases of filler particle size and the height of the filler in the column initially increases, and then decreases. Considering an initial NO3− concentration of 50 mg L−1, and a filler particle size range of 0.8–1.2 mm, the maximum adsorption capacity of the La/CTAC–ECL column for NO3− is 18.99 mg g−1 for a filler column height of 10 cm and an influent flow rate of 15 ml min−1. The maximum quantity of adsorbed NO3− of 372.80 mg is obtained using a filler column height of 15 cm and an influent flow rate of 10 ml min−1. The Thomas and Yoon–Nelson models accurately predict the breakthrough of NO3− in groundwater in the simulated PRB column under different conditions, and the results are consistent with those from dynamic NO3− adsorption experiments. TEM, XRD, FTIR, and XPS analyses demonstrate that the modification using the La and CTAC improves the surface structure, porosity, permeability, and configuration of functional groups of the biochar. The mechanisms of NO3− removal from groundwater using the La/CTAC–ECL include pore filling, surface adsorption, ion exchange, and electrostatic adsorption. The composite La/CTAC–ECL exhibits a superior potential for the remediation of NO3− contaminated groundwater.

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.

Measurement of pore volume, connectivity and clogging of pervious concrete reactive barrier used to treat acid mine drainage.

It has recently been shown that pervious concrete is a promising, effective technology as a permeable reactive barrier system for treatment of acid mine drainage (AMD). However, pore clogging also occurs simultaneously during AMD treatment. In the present study, mixtures of pervious concrete were made and used in a column experiment during which pore clogging occurred in the samples. Pore volume, connectivity and other parameters of pervious concrete were evaluated using five (5) different methods comprising the volumetric method (VM), linear-traverse method (LTM), image analysis (IA), falling head permeability test and X-ray microcomputed tomography. It was found that pervious concrete effectively removed from AMD, about 90 to 99% of various heavy metals including Al, Fe, Zn, Mn and Mg. Cr concentration significantly increased in the treated effluent, owing to leaching from cementitious materials used in mixtures. The VM and LTM gave statistically similar pore volume results, while IA's values were 20 to 30% higher than those of the conventional methods. The falling head permeability test and IA were found to be effective in quantifying pore clogging effects. Pervious concrete exhibited high pore connectivity of 95.0 to 99.7%, which underlies its efficacious hydraulic conductivity.

Enhanced remediation of Cd-contaminated soil using electrokinetic assisted by permeable reactive barrier with lanthanum-based biochar composite filling materials

ABSTRACT Electrokinetic remediation (EK) combined with a permeable reactive barrier (PRB) is a relatively new technique for efficiently remediating Cd-contaminated soil in situ. Eupatorium adenophorum, which is a malignant invasive plant, was used to synthesise biochar and a novel lanthanum-based biochar composite (LaC). The biochar and LaC were used as cheap and environmentally benign PRB filling materials to remediate simulated and real Cd-contaminated soils. The pH and residual Cd concentration in the simulated contaminated soil during remediation gradually increased from the anode to the cathode used to apply an electric field to the EK–PRB system. However, the soil conductivity changed in the opposite way, and the current density first increased and then decreased. For simulated contaminated soils with initial Cd concentrations of 34.9 and 100.6 mg kg−1, the mean Cd removal rates achieved using LaC were 90.6% and 89.3%, respectively, which were significantly higher than those of biochar (P < 0.05). Similar results were achieved using natural soils from mining area and polluted farmland, and the Cd removal rates were 66.9% and 72.0%, respectively. Fourier-transform infrared and X-ray photoelectron spectroscopy indicated that there were many functional groups on the LaC surfaces. The removal mechanism of EK-PRB for Cd in contaminated soil includes electromigration, electroosmotic flow, surface adsorption, and ion exchange. The results indicated that the LaC could be used in the EK–PRB technique as a cheap and ‘green’ material to efficiently decontaminate soil polluted with heavy metals.

Reuse of residues/wastes as a sustainable solution for landfill leachate contaminated groundwater

In order to increase the reuse of wastes and residues, as required by the Waste Framework Directive, the potential use of waste, residue and natural minerals as low-cost permeable reactive barrier (PRB) materials was investigated. The performance of a kitchen waste compost, sepiolite and steel slag was compared with that of volcanic slag, pumice and activated carbon in removing specific contaminants from landfill leachate. The experiments represented that the activated carbon removed 27% of the ammonium (NH4+), 75% of the chemical oxygen demand (COD) and 100% of the phosphate (PO43–), zinc (Zn2+) and nickel (Ni2+) from the landfill leachate. Volcanic slag exhibited removal efficiencies of 50% COD and 100% PO43– and pumice exhibited removal efficiencies of 20% NH4+, 27% Zn2+, 65% COD and 100% PO43–. The reactive materials were also checked for their potential in releasing unwanted constituents and represented different levels of the solute (e.g., PO43–, SO42–, NH4+) release. Among the reactives, sepiolite was found to be the reactive material reflecting a minor release (e.g., Zn2+, Cd2+ and Ni2+), but also delivering removal efficiencies of 40, 50, 65, 95, 97, 98, 98 and 100% for Ni2+, COD, Zn2+, SO42–, Cl–, F–, NH4+ and PO43–, respectively. The results show that the studied materials have the potential as reactives for PRB systems treating high strength contaminant plumes.

Cd(II) removal from aqueous solutions by pomelo peel derived biochar in a permeable reactive barrier: modelling, optimization and mechanism

Biochar can have multiple benefits, such as solid waste recycling, water pollution treatment, carbon fixation and sustainability, and it is green, friendly, inexpensive and highly efficient. Therefore, the present study aimed to investigate Cd(II) removal from aqueous solutions using pomelo peel derived biochar combined with a permeable reactive barrier (PRB). Meanwhile, the materials were characterized using SEM, FIIR, XRD, N2 adsorption, Zeta potential, TGA and XPS. The removal conditions were optimized by a response surface methodology (RSM) and a back propagation combined with genetic algorithm (BP-GA). The results show that there were slight changes in the structure of the pomelo peel derived biochar before and after activation, while the variation was not significant. The specific surface areas of the not activated and activated pomelo peel derived biochars were 3.207 m2 g−1 and 6.855 m2 g−1, respectively. The pore diameter of the former was 4.165 nm and that of the latter was 4.425 nm, indicating that the two materials are mainly mesoporous. BP-GA is more suitable than RSM for optimizing the removal conditions of Cd(II) using the prepared materials combined with PRB. The maximum removal efficiency of Cd(II) was 90.31% at biochar dosage = 4.84, reaction time = 53.75 min, initial Cd(II) concentration = 19.36 mg l−1 and initial pH = 6.07. The verification experiment was 88.74% under these experimental conditions, and the absolute error was 1.57%. The saturated adsorption capacity of quartz sand for Cd(II) is approximately 0.08 mg g−1 when reaching equilibrium. The saturated adsorption capacity of biochar for Cd(II) is approximately 29.76 mg g−1. Pseudo second order kinetics and Langmuir isotherm adsorption were more suitable for describing the Cd(II) adsorbed from an aqueous solution by activated pomelo peel derived biochar. The adsorption process of Cd(II) by the prepared biochar was spontaneous, endothermic and entropy driven. Our results suggest that the modified pomelo peel derived biochar can be regenerated within the fourth cycle and that it has application prospects as a useful adsorbent for water treatment in PRB systems. This finding provides a reference for relieving Cd pollution and for its large scale removal from wastewater when combined with a PRB system.

Sequential treatment of nitrate and phosphate in groundwater using a permeable reactive barrier system

When not properly treated, nitrate and phosphate present in groundwater can damage human health and environments. In this study, laboratory column experiments were performed for sequential treatment of nitrate and phosphate in groundwater. Two columns were set up and connected: one to treat nitrate with organic carbon materials (i.e., woodchips) and the other to treat phosphate with basic oxygen furnace (BOF) slag. The columns were operated for a total of 1.6 years. The results showed that nitrate was removed through denitrification and phosphate was removed by precipitation of the phosphate minerals (e.g., hydroxyapatite). BOF slag was effective at removing phosphate, though the high pH (11–12) of the system's effluent water raised a concern for the downgradient areas. Of the three subsequent experiments performed, pH was near neutral when the effluent of the BOF slag column was passed through local soil. Sparging with CO2 and air, in contrast, resulted in pH levels that were either too low (5 in the case of CO2) or too high (9.5 in the case of air). The study shows that sequential permeable reactive barrier (PRB) systems consisting of woodchips and BOF slag can be effective for removal of nitrate and phosphate in groundwater and they can be a long-term remedial solution for groundwater contaminated with both nitrate and phosphate.

Pilot-Scale Low-Cost Mixed-Media Permeable Reactive Barrier (PRB) System to Treat Heavy Metals in Groundwater Contaminated by Landfill-Leachate

"ENGINEER", established in 1973 by The Institution of Engineers, is a Journal for dissemination of Engineering knowledge, published quarterly.Cover DescriptionCover images show a schematic diagram of a Pumped-Storage Hydroelectricity (PSH) facility and one of the promising sites for PSH in Sri Lanka. The latter image was obtained from the publicly available JICA report on “Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka”. The Institution of Engineers, Sri Lanka acknowledges JICA for the image. If you are interested in contributing an Original Technical Paper based on research by the author(s) (intended for Section I) or an Original Article of Professional or Technical interest related to Engineering. (Section II) to this journal please go through the publication checklist which can be downloaded from here.

Determining the impact of biofilm in the bioaugmentation process of benzene-contaminated resources

Recently, petroleum contamination in groundwater has become one of the most common environmental problems. Bioaugmentation is proposed as a fully functional and economical technology by the addition of microorganisms to remove pollutants. The aim was to study the effect of biofilm formation of different species during the bioaugmentation of benzene removal in a Permeable Reactive Barrier (PRB) system based on calcium peroxide (CaO2) nanoparticles. Therefore, at first 3 strains identified with the ability to form biofilms and benzene degradation were isolated from groundwater. Subsequently, dissolved oxygen (DO), pH, the concentration of benzene, and microbial count of experimental columns were measured. Further, the examination of the biofilm formation on glass bead surfaces in bioaugmented and control reactors was also studied by confocal laser scanning microscopy (CLSM). The results of bioaugmentation show that adding Pseudomonas lini and Pseudarthrobacter polychromogenes can remove almost 80% of benzene from effluent after 70 days. Therefore, the study reveals the effect of bioaugmentation over intrinsic bioremediation. Also, the thicker and concentrated biofilm of Pseudomonas lini can be seen. This system provides a novel environmentally friendly technology for the in situ bioremediation of benzene.

Combination of zeolite barrier and bio sparging techniques to enhance efficiency of organic hydrocarbon remediation in a model of shallow groundwater

Adsorption and bioremediation are effective processes for remediation of benzene, toluene, and ethylbenzene (BTE) through Permeable Reactive Barriers (PRBs). A few researches focus on adsorption of natural zeolite because of its hydrophilic property. On the other hand, PRBs need to be replaced by fresh materials after a while when all the possible absorption positions were filled up. We tried to find a way to increase the efficiency of PRB, elongation of its replacement period and of course decreasing the cost of remediation. Equipping of PRB with microbial degradation system was the idea. The present study describes the performances of natural Clinoptilolite-Heulandite Zeolite (CH-Z) and three new strains (safe and low-cost media) utilized in a PRB for removing BTE from contaminated shallow groundwater. First, batch tests were conducted to recognize the optimal removal conditions for utilization of C-HZ and strains to remediate BTE compounds. Then, an aerobic PRB system filled with a natural zeolite was designed and investigated in a continuous flow sand-tank model to assess the efficiency of combined PRBs (zeolite + biosparging), for BTE-contaminated groundwater. Batch experiments showed that the BTE removal of zeolite was 89%, as well as, a consortium of three bacterial strains, Variovorax sp. OT16, Pseudomonas balearica OT17, and Ornithinibacillus sp. OT18 efficiently removed the BTE mixture. The process of BTE removal in the PRB under continuous-flow condition was divided into three phases: Phase I, in which the barrier was made of the only zeolite, and in Phases II and III the reactor was fed by microorganisms. This experiment revealed that in Phases I, the concentrations of BTE decrease (92%) due to zeolite adsorption. In Phase II and III, the degradation process became the principal removal mechanism (68% and 81%, respectively). Consequently, this research showed high ability of C-HZ in the BTE treatment, and a combination of Natural Zeolite, with a biological degradation system (CH-Z –PRB) improves the efficiency of BTE remediation. However, the slow biodegradation rates and the continuous injection of BTE in the model confirmed that longer time was needed for the PRB to function optimally. Finally, the combined method of CH-Z- BIO PRB showed the great potential in the restriction of the BTE migration that can be used at the field-scale after up-scaling.

Synthesis, characterization, and application of zero-valent iron nanoparticles for TNT, RDX, and HMX explosives decontamination in wastewater

This study has evaluated the efficiency of zero-valent iron nanoparticles (nZVI) for the remediation of soil and groundwater containing 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). It was conducted via different treatment methods (batch experiments, column tests, and a permeable reactive barrier (PRB)) system. The combinative studies could be used to develop a more effective remediation technique. The chemical reactions that occurred upon mixing nZVI and contaminants provided the batch experiments, leading to rapid reduction of the explosives. There was a decrease in the removal efficiency from 95% to less than 30% for the batch experiments, which was due to the lake of stirring facilities in the column test, PRB system, and the interaction of the soil and explosives with nZVI. Kinetics studies indicated a more significant and rapid degradation of TNT than that of RDX and HMX, which was consistent with the lower activation energy of TNT. The X-ray spectroscopy results highlighted that during the reduction process, nZVI was transformed into core-shell structures with Fe(0) core and Fe3O4 shell. High-performance liquid chromatography-mass spectrometry (HPLC/MS) tests depicted the decomposition of explosive contaminants into simple elements, such as carbon dioxide, nitrous oxide, and methane, over cleavage of the ring structure.

Batch-scale remediation of toluene contaminated groundwater using PRB system with tyre crumb rubber and sand mixture

The objective of the study is to examine the potential of TCR (tyre crumb rubber) particles to remediate toluene contaminated aquifers by using them as the reactive constituent of permeable reactive barriers (PRB). The objective is achieved by performing laboratory experiments to identify toluene adsorption capacity and rate of toluene removal of the optimal TCR-sand mix. Adsorption isotherms and Kc-Co relations (Kc: distribution coefficient, Co: initial toluene concentration) identified the optimum mix (2.5 % TCR-97.5 % sand mix) for remediation of toluene contaminated water. Batch experiments showed that toluene adsorption by TCR particles is endothermic and is energetically favoured at higher temperature. Adsorption of the non-polar molecule by TCR particles obeyed bi-linear, pseudo first order kinetics. The carbon-black component of TCR particles adsorbed significant amount of toluene during the initial contact period (10−60 min). Scatchard analysis, Freundlich isotherm and DR (Dubinin-Radushkevich) equation indicated that toluene is adsorbed by van der Waals attraction at energetically heterogenous sites of TCR particles. The near irreversible toluene adsorption in the laboratory experiment is attributed to physical entrapment of the non-polar molecules in the medium and fine pores of TCR particles. Batch experiment results predict that unit PRB column constructed with 2.5 % TCR-97.5 % sand mix can remediate 11,013 K L of toluene contaminated (0.15 mg/L) groundwater near instantaneously.