Fluorine contamination, mobility, and risks in soils at a phosphate-gypsum waste landfill: a new analytical method and comparison with previous methods.

This study used a new X-ray fluorescence (XRF)-based analytical method with better precision and sensitivity to evaluate the fluorine concentrations in soil. It was hypothesized that the XRF method with a pellet-synthesizing procedure may effectively analyze the fluorine concentrations in soil with ease and reliability. The total fluorine concentrations determined using XRF were compared with those determined using three different types of analytical protocols-incineration/distillation, alkaline fusion, and aqua regia extraction procedures. Among the three procedures, the incineration/distillation procedure did not show reliable precision and reproducibility. In contrast, the total fluorine concentrations determined using the XRF analysis were linearly correlated with those determined using the alkaline fusion and aqua regia extraction procedures. Based on the results of the Korean waste leaching procedure and toxicity characteristics leaching procedure, the leachability of fluorine from soil and waste was not directly related to total fluorine concentrations in soil. Risk assessment also revealed that the fluorine-rich soils did not show non-carcinogenic toxic effects, despite exceeding the regulation level (800 mg/kg) in South Korea for total fluorine concentrations in soil. Our results suggest that XRF analysis in combination with the newly developed pretreatment method may be a promising alternative procedure for easily and rapidly determining the total fluorine concentration in soil. However, further efforts are needed to evaluate fluorine leachability and its associated risks in fluorine-contaminated soils.

Biodegradable dust suppressants prepared from biomass-based materials: The role of viscosity and suppressed particles.

In this study, biodegradable dust suppressants were prepared using glycerol and biomass-based oily compounds, including palm oil, biodiesel, and soybean oil. The suppressing ability of the glycerol and the oily compound mixture was evaluated using wind tunnel tests, and factors affecting the suppression of the particles were determined. The replacement of sodium dodecyl sulfate with coco glucoside and lauryl glucoside significantly enhanced the biodegradability of the suppressants (2.02 vs. 9.01 and 8.54 mg/L of BOD5). The glycerol and soybean oil mixture exhibited excellent performance owing to the relatively high viscosity of the suppressants, and the optimal dilution ratio was 1:50 and 1:1000 for sand and granite-weathered soil, respectively. More than 98% of suppression was obtained under the optimal conditions. The effect of the particle properties (particularly permeability) was significant, even though the viscosity of the suppressants was responsible for the suppression of the particles. Our results suggest that the mixture of glycerol and biomass-based oily compounds could be a promising suppressant for reducing the mobility of ultrafine particles in the atmosphere.Implications: Since the early 2010s, anthropogenic fugitive dust from industrial activities has become a serious environmental issue due to its serious hazards to the environment and human health in South Korea. So far, several dust suppressants (mostly salts) were made and used for field application. However, due to their toxic effects, it is necessary to develop a new eco-friendly suppressant that can be biodegraded in the soil and that is not hazardous to human health or the environment. Previously we have developed an eco-friendly dust suppressant with low toxicity and high suppression ability using ingredients and by-products of biodiesel production, marine biomass, and commercial vegetable oils (Tsgot and Oh 2021, J. Air Waste Manag. Assoc. 71:1386-1396). However, due to the low biodegradability of surfactant, the synthesized dust suppressants showed limited biodegradability. As a follow-up to our previous study, we employed readily biodegradable surfactants as additives to enhance the biodegradability of the dust suppressants with the same excellent suppressing ability. To determine the optimal conditions, the synthesis and preparation of the dust suppressants was conducted using biodegradable surfactants, including coco glucoside and lauryl glucoside. The factors affecting the suppressing ability of the suppressants were examined via wind tunnel tests. These factors include the dilution factors, the viscosity of the suppressants, and the type of suppressed particles. Possible suppressing mechanisms were also discussed.

Degradation of phenol by perborate in the presence of iron-bearing and carbonaceous materials.

We investigated the oxidation of phenol by perborate-a newly proposed oxidant-in the presence of iron-bearing and carbonaceous materials through batch experiments. We hypothesized that the oxidation of phenol by perborate was enhanced due to the formation of reactive oxygen species (ROS) in the presence of iron-bearing or carbonaceous materials. Zero-valent iron and ferrous iron (Fe2+) promoted the oxidation of phenol by perborate. Biochar, granular activated carbon, an anode carbonaceous material recovered from a spent Li-ion battery, and graphite also accelerated the oxidation of phenol by perborate. Quenching experiments with radical scavengers and electron paramagnetic resonance (EPR) analysis revealed that hydroxyl (˙OH) and superoxide (O2˙-) radicals were generated and enhanced the degradation of phenol in the perborate systems. Singlet oxygen (1O2) was involved in the iron-bearing material-perborate systems. Moreover, we found that Persil®, a commercial perborate detergent, enhances the oxidation of phenol in the presence of iron-bearing and carbonaceous materials. Our results suggest that perborate can be used for advanced oxidation processes to remediate recalcitrant organic contaminants in natural environments and engineered systems.

Energy recovery and waste treatment using the co-pyrolysis of biomass waste and polymer.

The pyrolysis of spent coffee grounds (SCG) and polymers was examined as a waste treatment option for energy recovery and carbon sequestration. Rice straw-derived biochar was used as control biochar to evaluate the sorption capacity and energy production capability of SCG-derived biochar. SCG are characterised by high levels of volatile matter, rendering them suitable as an energy source. SCG were converted to biochar, bio-oil, and syngas via pyrolysis, with yields of 22%, 33%, and 45%, respectively. The high heating value (HHV) of the biochar and bio-oil was 20.6 and 22.9 MJ kg-1, respectively, indicating that they could be used as supplementary fuels. Co-pyrolysis with polymers (20 v v%-1) increased the HHV of biochar. Accordingly, the maximum production of CH4 and H2 increased from 0.3 and 0.04 mmol g-1 to 3.4-6.3 and 0.8-1.3 mmol g-1, respectively. Polystyrene most strongly enhanced the yields of CH4 and H2, followed by polypropylene and polyethylene; this order was likely to be in accordance with the number of carbon and hydrogen atoms present in the monomers. Similar to rice straw-derived biochar, the biochar produced from SCG demonstrated a high sorption capacity for 2,4-dinitrotoluene and chromate due to its high carbon content and anion exchange capacity, respectively. Laboratory pot tests revealed that the coffee grounds-derived biochar was able to increase the growth of young radish. Our results suggest that the pyrolysis of SCG and polymer may be a promising option for waste treatment, energy production, and carbon sequestration.

Co-pyrolysis of rice straw with industrial wastes: Waste disposal and environmental remediation.

To reduce waste volumes and recover valuable products, char was synthesized via co-pyrolysis of rice straw (RS) with spent tires, sulfur wastes, and CO2. The inclusion of wastes and CO2 in pyrolysis of RS was hypothesized to enhance the sorption ability of char for various contaminants, including 2,4-dinitrotoluene (DNT), 2,4-dichlorophenol (DCP), lead, barium, chromate (CrO42-), and selenate (SeO42-). Using a lab-scale electrical furnace, the co-pyrolysis was conducted, and the soprtion capacity of char was evaluated via a series of batch sorption experiments. The maximum sorption capacity of spent tire-RS char for DNT was 16.8 ± 0.2 mg g-1, much higher than that of RS biochar (10.1 ± 0.3 mg g-1) due to increasing carbon content from the spent tires. The sorption of DCP to the spent tire-RS char was also enhanced via hydrophobic sorption to carbon residues, although not to the same degree of DNT due to deprotonation of the DCP. Compared with RS biochar, co-pyrolysis with raw sulfur wastes and CO2 enhanced sorption of lead, barium, and chromate, which can be attributed to increased cation and anion exchange capacities resulting from developments of oxygen or sulfur-containing functional groups. Sorption of selenate was strongly affected by pH. The results suggest that co-pyrolysis of agricultural and industrial wastes and CO2 is a promising option for the final waste disposal and the production of valuable char, which can be selectively customized for various types of contaminants as sorbents.

Preparations and application of dust suppressants from biomass-based materials.

Both natural and anthropogenic fugitive dust can cause serious hazards to the environment and human health. In this study, the development of biodegradable dust suppressants and their environmental impacts were evaluated. Biodegradable dust suppressants were prepared using various biomass-based polymeric materials such as crude glycerol (a by-product of biodiesel manufacturing), biodiesel, palm oil, cooking oil, seaweed mixtures, wakame (Undaria pinnatifida), and red algae. The results of wind-tunnel tests with Korean standard sand demonstrated that spraying diluted mixtures of crude glycerol and biomass materials can significantly reduce the generation of dust. The optimal molar mixing ratio of crude glycerol and the biomass materials was 1:1, and the optimal dilution concentration was determined to be 100 times for the mixture of crude glycerol and biodiesel, palm oil, and cooking oil and 50 times for the mixture of crude glycerol with a seaweed mixture, wakame, and red algae. The suppression ability was 83.4%, 60.4%, 99.5%, and 98.1% for the mixtures of glycerol with soybean oil, palm oil, wakame, and red algae, respectively. The mixtures of glycerol plus wakame or red algae were the most efficient suppressants; they also have substantial biodegradability. Our results suggest that the mixture of crude glycerol with the various oils or the seaweeds may be a promising option to develop nontoxic biodegradable dust suppressants.Implications: Since the early 2010s, anthropogenic fugitive dust from industrial activities has become a serious environmental issue due to its serious hazards to the environment and human health in South Korea. The origin and responsibility of the dusts is still disputable to prepare appropriate actions to take, which could be solved by scientific collaboration with surrounding countries. Regardless, domestic efforts to reduce the generation of fine dust from various sources should also be made. So far, several dust suppressants (mostly salts) were made and used for field application. However, due to their toxic effects, it is necessary to develop a new eco-friendly suppressant that can be biodegraded in the soil and that is not hazardous to human health or the environment. In this study, we try to develop an eco-friendly dust suppressant with low toxicity, to evaluate various potential dust suppressants, and to propose promising candidate products for commercialization and mass production. Ingredients and by-products of biodiesel production, marine biomass, and commercial vegetable oils were selected for the synthesis of suppressants. The optimal mixing ratio was determined, and the suppression ability was evaluated via wind tunnel tests. Considering biodegradability, the most effective suppressants were determined.

Anode carbonaceous material recovered from spent lithium-ion batteries in electric vehicles for environmental application.

Recycling opportunities for graphitic carbon from lithium-ion battery (LIB) anodes have been neglected owing to the relative low value of application. In this study, the potential methods for removing toxic metals (lead, barium, and cadmium) and organic compounds (2,4-dinitrotoluene [DNT], 2,4,6-trinitrotoluene [TNT], hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX], and 2,4-dichlorophenol [DCP]) with anode carbonaceous material (ACM) obtained from the anodes of spent LIBs were evaluated. The sorption ability of ACM for lead is higher (the maximal sorption capacity is 43.5 mg/g) than for barium and cadmium. Similarly, the maximal sorption capacity of ACM for DCP is 6.5 mg/g, which is higher than those for TNT and DNT (2.6 and 2.3 mg/L, respectively). As a catalyst, ACM significantly enhances oxidation by persulfate with zero-valent iron and reduction by dithiothreitol (DTT) and hydrogen sulfides for nitro compounds. In addition, the graphitic properties enhance the redox reactions. The results suggest that ACM from spent LIBs may be an effective sorbent and catalyst in redox processes for the remediation of contaminated water and soil.

Environmental monitoring of toxic metals in roadside soil and dust in Ulsan, South Korea: pollution evaluation and distribution characteristics.

This study investigated toxic metal distribution in roadside soil and dust in the metropolitan city of Ulsan, South Korea, and the factors affecting distribution, using Korean waste-leaching tests, determination of total concentrations, sequential extraction, and statistical analysis. Composite grab samples were collected from high-traffic roads (7 sites), low-traffic roads (2 sites), and an uncontaminated control area (2 sites) in Ulsan. The pH of roadside soil and dust was slightly alkaline. The concentrations of copper, lead, and zinc in soil as determined by Korean waste-leaching tests decreased as soil depth increased, while those of arsenic, nickel, and chromium increased. Leaching concentrations in dust were lower than in soil, with the exception of copper. Total concentrations decreased as soil depth increased, and total concentrations of metals in dust were higher than in soil. The sampling sites that exceeded the regulation levels of soil contamination in South Korea were 7 points in topsoil, 3 points in middle soil, and 9 points in dust. TCLP tests showed that the concentrations of arsenic, cadmium, and lead in topsoil and dust at Duwang and Myeongchon intersections were higher than regulatory levels. The maximum correlation coefficient among two metals in soil and dust was 0.987 (p < 0.01), for cadmium and lead. Concentrations of cadmium, copper, arsenic, lead, nickel, and mercury, mostly from tire and brake-pad abrasion, were highly correlated. The strong positive correlation between traffic volume and metals in dust suggests that vehicle emissions may be responsible for metal contamination of soil and dust. Pollution indices of topsoil at 4 sites and all dust at 7 high-traffic sites were higher than 1.0, which is consistent with an effect of vehicle traffic on metal contamination in soil and dust.

FeS-biochar and Zn(0)-biochar for remediation of redox-reactive contaminants.

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis. These biochars significantly promoted the removal of 2,4-dichlorophenol (DCP) by means of sorption and reduction. Compared to direct reduction with FeS and Zn(0), the formation of reduction intermediates and product was enhanced from 21% and 22% of initial DCP concentration to 41% and 52%, respectively. 2,4-Dinitrotoluene (DNT), chromate (CrO4 2-) and selenate (SeO4 2-) were also reductively transformed to reduction products (e.g., 2,4-diaminotoluene [DAT], Cr3+, and selenite [SeO3 2-]) after they sorbed onto the biochars including FeS and Zn(0). Mass recovery as DAT, Cr3+ and selenite was 4-20%, 1-3%, and 10-30% under the given conditions. Electrochemical and X-ray analyses confirmed the reduction capability of the biochars including FeS and Zn(0). Fe and S in the FeS-biochar did not effectively promote the reductive transformation of the contaminants. Contrastingly, the stronger reducer Zn(0) yielded faster reductive transformation of contaminants over the Zn(0)-containing biochar, while not releasing high concentrations of Zn2+ into the aqueous phase. Our results suggest that biochars including Zn(0) may be suitable as dual sorbents/reductants to remediate redox-reactive contaminants in natural environments.

Distribution, toxicity, and origins of polycyclic aromatic hydrocarbons in soils in Ulsan, South Korea.

This study was conducted to investigate the concentrations, distributions, toxicities, and sources of polycyclic aromatic hydrocarbons (PAHs) in the soils from different areas in Ulsan, South Korea. Samples were collected from 41 sites, including a waste treatment facilities area (WA), traffic facilities area (TA), child playground area (CA), industrial area (IA), railroad facilities area (RA), ore and iron scraps fields area (OA), and residential area (ReA). Ulsan was chosen for research area because it used to be an environmental hot spot in South Korea, and 16 PAHs in the US EPA priority pollutant list were selected. The concentration of total PAHs (t-PAHs) ranged from 61.7 to 12,421 µg/kg, and the average concentration of t-PAHs was 706.9 µg/kg. The distribution of PAHs by ring number indicated that the portion followed the order of 4 rings > 5 rings > 3 rings > 6 rings > 2 rings. According to PAH origin indices, LMW/HMW (low molecular weight 2-3 ring PAHs over high molecular weight 4-6-ring PAHs), phenanthrene/anthracene ratio and fluoranthene/pyrene ratio, benzo(g,h,i)perylene/indeno (1,2,3-c,d)pyrene ratio, vehicular emissions, and the combustion of fossil fuel were the sources of PAHs. The strong correlation (R2 = 0.995) between t-PAHs and total carcinogenic PAHs (t-PAHcarc) indicated that the concentration of t-PAHcarc increased in proportion with that of t-PAHs. The toxic equivalent concentrations (TEQs) of PAHs in the soils ranged from 44.0 to 1929.9 µg TEQ/kg. It is imperative to set regulatory levels for PAHs for periodic monitoring and rapid remediation action of contaminated soils, because there are no national standards in South Korea for 15 PAHs with the exception of benzo(a)pyrene.

Factors affecting the sorption of halogenated phenols onto polymer/biomass-derived biochar: Effects of pH, hydrophobicity, and deprotonation.

High-performance biochar synthesized via co-pyrolysis of a polymer and rice straw (RS) was evaluated as a sorbent for ionizable halogenated phenols. Compared with RS-derived biochar, the sorption of 2,4-dichlorophenol (DCP), 2,4-dibromophenol (DBP), and 2,4-difluorophenol (DFP) onto polymer/RS-derived biochar was significantly enhanced by the properties of biochar changing due to polymer residues. According to Langmuir sorption isotherm model maximum sorption capacities for DCP, DBP, and DFP were 25.5-27.8, 22.1-26.5, and 11.5-13.3 mg/g, respectively, 3-5 times higher than those of RS-derived biochar. The removal of the polymer residues and increasing aromaticity of polymer/RS-derived biochar at elevated pyrolysis temperatures affected the sorption capacity of halogenated phenols. The surface charge of biochar and deprotonation of the halogenated phenols according to the solution pH were other factors responsible for sorption onto polymer/RS-derived biochar. Competition with other halogenated phenols, Zn2+, and Cu2+ implied that similar sorption mechanisms existed and that surface complexation and electron donor-acceptor interactions were involved in sorption onto polymer/RS-derived biochar. Our results suggest that co-disposal of thermoplastic and biomass wastes through pyrolysis may be an effective option to produce high-performance upgraded biochar as a sorbent for various types of contaminants.

Upgrading biochar via co-pyrolyzation of agricultural biomass and polyethylene terephthalate wastes.

Spent polyethylene terephthalate (PETE) bottles were collected and co-pyrolyzed with rice straw (RS) to examine the characteristics and performance of biochar as a sorbent for various types of U.S. EPA priority pollutants, including 2,4-dinitrotoluene (DNT), 2,4-dichlorophenol (DCP), Pb, chromate (CrO4 2-), and selenate (SeO4 2-). During sorption of contaminants to PETE/RS-derived biochar, PETE residues from pyrolysis, pH, and pyrolysis temperature greatly affected the sorption process. Depending on the types of contaminants and experimental conditions, co-pyrolysis of PETE and RS may enhance the sorption of contaminants through different sorption mechanisms, including hydrophobicity, electrostatic force, ion exchange, surface complexation, and surface precipitation. Unlike other contaminants, selenate was reductively transformed by delocalized electrons from the graphitic structure in biochar. Our results strongly suggest that co-pyrolysis of PETE and agricultural wastes may be favorable to enhance the properties of biochar. In addition to syn-gas and bio-oil from co-pyrolysis, biochar may be a valuable by-product for commercial use.

Sorption of Nitro Explosives to Polymer/Biomass-Derived Biochar.

Factors affecting the sorptive removal of nitro explosives (2,4,6-trinitrotoluene [TNT] and hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX]) to polymer/biomass-derived biochar were investigated through batch experiments. Compared with that of rice ( L.) straw (RS)-derived biochar, the sorption of TNT and RDX to polymer/RS-derived biochar was greatly enhanced by >2.5 and 4 times, respectively. The type and amount of polymer did not significantly affect the sorption of nitro explosives to polymer/RS-derived biochar. Pyrolysis temperature did not affect the sorption capacity. Surface treatment with acid or an oxidant did not significantly change the sorption capacity, suggesting that polymer residues may be strongly responsible for the enhancement. Possible polymer residues were identified via gas chromatography mass spectrometry analysis. The toxicity characteristic leaching procedure and Microtox bioassay analyses indicated that polymer/RS-derived biochar did not show possible harmful effects. Our results suggest that polymer/RS-derived biochar can be effectively used as a sorbent to remove nitro explosives both in the natural environment and engineered systems.

Comparative sorption isotherms and removal studies for Pb(II) by physical and thermochemical modification of low-cost agro-wastes from Tanzania.

Corn and rice husks, agro-wastes available in large quantities in Tanzania, were used to remove Pb2+ from aqueous solution. Husks were used in raw form, pyrolyzed form, and chemically modified form. Material characterization was carried out using the BET method, FTIR spectroscopy, SEM, pHPZC, and cation exchange capacity analysis. Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Temkin isotherms were used to elucidate Pb2+ sorption mechanisms. The surface area and cation exchange capacity (CEC) of untreated and chemically treated biochars were significantly higher than that of raw husks. Sorption data for Pb2+ for all biosorbents fit the Freundlich and D-R models well with high R2 values. Most of the synthesized biosorbents in this study indicated >90% for Pb2+ removal, with the ZnCl2-treated corn husk biochar sorption capacities ranking highest in all modeling results. Surface morphological features (e.g., micropores and fissures) and acidic and unsaturated functional groups may have significantly contributed to the observed Pb2+ removal efficiencies.

Redox and catalytic properties of biochar-coated zero-valent iron for the removal of nitro explosives and halogenated phenols.

A novel biochar-coated zero-valent iron [Fe(0)], which was synthesized with rice straw and Fe(0), was applied to remove nitro explosives (2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine) and halogenated phenols (2,4-dibromophenol and 2,4-difluorophenol) from contaminated waters. Due to the presence of biochar on the outside, the removal of nitro explosives and halogenated phenols was significantly enhanced via sorption. The sorbed contaminants were further transformed into reductive products, indicating that the inner Fe(0) played the role of a reductant in the biochar-coated Fe(0). Compared to direct reduction with Fe(0), the reductive transformation with biochar-coated Fe(0) was markedly enhanced, suggesting that the biochar in biochar-coated Fe(0) may act as an electron transfer mediator. Further experiments showed that the surface functional groups of biochar were involved in the catalytic enhancement of electron transfer. Our results suggested that biomass could be used to synthesize a novel sorbent and catalyst for treating redox-sensitive contaminants in natural and engineered systems.

Polymer/biomass-derived biochar for use as a sorbent and electron transfer mediator in environmental applications.

Co-pyrolysis of polymer and biomass wastes was investigated as a novel method for waste treatment and synthesis of enhanced biochar. Co-pyrolysis of rice straw (RS) with polypropylene (PP), polyethylene (PE) or polystyrene (PS) increased the carbon content, cation exchange capacity (CEC), surface area and pH of the biochar. As a result, the sorption of 2,4-dinitrotoluene (DNT) and Pb to polymer/RS-derived biochar was markedly enhanced. The increased aromaticity and hydrophobicity may be responsible for enhancing the DNT sorption to the polymer/RS-derived biochar. In contrast, increasing CEC, higher pH, and the newly developed surface area may account for the enhancement in Pb sorption. The addition of polymer to RS did not significantly change the catalytic role of biochar during the reduction of DNT by dithiothreitol. Our results suggest that co-pyrolysis of RS and polymer can improve the biochar properties to enhance the sorption of DNT and Pb.

Reductive removal of 2,4-dinitrotoluene and 2,4-dichlorophenol with zero-valent iron-included biochar.

In order to remediate organic contaminants in natural waters and soils, a novel zero-valent iron [Fe(0)]-included biochar was synthesized via slow pyrolysis. 2,4-Dinitrotoluene (DNT) and 2,4-dichlorophenol (DCP) were removed in water via sorption to the Fe(0)-included biochar. Compared to sorption control without Fe(0), the sorbed DNT and DCP were further transformed to reduction products by Fe(0)-included biochar. Compared to the reduction control with Fe(0), the presence of biochar promoted the reductive transformation of DNT and DCP. Increasing the pyrolysis temperature resulted in enhancing the removal of DNT and DCP, suggesting that the aromaticity of biochar may be responsible for the removal. The yields of the reduction products also indicated that unlike the direct reduction by Fe(0), different reduction pathways existed in the reduction of DNT and DCP with Fe(0)-included biochar. The results suggest that Fe(0)-included biochar is a viable option to immobilize and transform redox-sensitive organic contaminants in natural environments.

Reduction and persulfate oxidation of nitro explosives in contaminated soils using Fe-bearing materials.

The oxidative and reductive transformation of nitro explosives in contaminated soils with Fe-bearing materials and persulfate (S2O8(2-)) was examined via batch experiments. Zero-valent cast iron [Fe(0)], steel dust from a steel manufacturing plant, and FeS rapidly reduced 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in soil under anaerobic conditions as long as a sufficient amount of water was present. The Fe-bearing materials also effectively activated persulfate to enhance the oxidative transformation of TNT and RDX in soil-water systems. Kinetically, reductive and oxidative transformations removed more than 90% of the explosives from a soil-water system within 5 h under the given conditions. Pseudo-first-order rates in the range of 0.7-23.4 h(-1) were observed. By increasing the concentration of persulfate or Fe-bearing materials, the oxidative transformation could be promoted. Treated soils via redox reactions using the Fe-bearing materials did not show significant toxicity, except for the case of TNT-contaminated soils oxidized by FeS-assisted persulfate. Considering the kinetics of explosive degradation and the toxicity of treated wastewaters and soils, Fe(0) or steel dust-assisted persulfate oxidation may be a safe option as an ex situ remediation process for the treatment of explosive-contaminated soils.

Biochar Amendment for Reducing Leachability of Nitro Explosives and Metals from Contaminated Soils and Mine Tailings.

The mobility and bioavailability of nitro explosives (2,4-dinitrotoluene [DNT], 2,4,6-trinitrotoluene [TNT], and hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX]) in biochar-amended soils and toxic metals (As, Cd, Cu, Pb, and Zn) in biochar-amended mine tailings were investigated via various types of leaching procedures in laboratory-scale batch experiments. The results from the toxicity characteristic leaching procedure (TCLP) and hydroxypropyl-ß-cyclodextrin (HPCD) extraction showed that approximately 55 to 95% of the explosives were released from the contaminated soils and would thus be considered as mobile. With the addition of biochar, the extracted concentrations of explosives were reduced to less than 10% of the initial concentrations after 10 d. According to the results from a Korean waste leaching method, the TCLP method, and diethylenetriaminepentaacetic acid (DTPA) extraction, adding biochar to mine tailings reduced the extractability and bioavailability of metals. The chemical forms of the metals, types of extractants, pH, and curing period strongly affected the extractability of metals from mine tailings. The results suggest that biochar is a promising immobilizer of explosives and metals in contaminated soils and mine tailings under limited conditions.

Microbial reduction of nitrate in the presence of zero-valent iron and biochar.

The denitrification of nitrate (NO3(-)) by mixed cultures in the presence of zero-valent iron [Fe(0)] and biochar was investigated through a series of batch experiments. It was hypothesized that biochar may provide microbes with additional electrons to enhance the anaerobic biotransformation of nitrate in the presence of Fe(0) by facilitating electron transfer. When compared to the anaerobic transformation of nitrate by microbes in the presence of Fe(0) alone, the presence of biochar significantly enhanced anaerobic denitrification by microbes with Fe(0). Graphite also promoted the anaerobic microbial transformation of nitrate with Fe(0), and it was speculated that electron-conducting graphene moieties were responsible for the improvement. The results obtained in this work suggest that nitrate can be effectively denitrified by microbes with Fe(0) and biochar in natural and engineered systems.