Effect of low temperature on abiotic and biotic nitrate reduction by zero-valent Iron.

The effect of low temperatures on abiotic and biotic nitrate (NO3-) reduction by zero-valent iron (ZVI) were examined at temperatures below 25 °C. The extent and rate of nitrate removal in batch ZVI reactors were determined in the presence and absence of microorganisms at 3.5, 10, 17, and 25 °C. Under anoxic conditions, NO3- reduction rates in both ZVI-only and ZVI-cell reactors declined as temperature decreased. In ZVI-only reactor, 62% and 17% of initial nitrate concentration were reduced in 6 days at 25 and 3.5 °C, respectively. The reduced nitrate was completely recovered as ammonium ions (NH4+) at both temperatures. The temperature-dependent abiotic reduction rates enabled us to calculate the activation energy (Ea) using the Arrhenius relationship, which was 50 kJ/mol. Nitrate in ZVI-cell reactors was completely removed within 1-2 days at 25 and 10 °C, and 67% of reduction was achieved at 3.5 °C. Only 18-25% of the reduced nitrate was recovered as NH4+ in the ZVI-cell reactors. Soluble iron concentrations (Fe2+ and Fe3+) in the ZVI reactors were also measured as the indicators of anaerobic corrosion. In the ZVI-cell reactors, soluble iron concentrations were 1.7 times higher than that in ZVI-only reactors at 25 °C, suggesting that the enhanced nitrate reduction in the ZVI-cell reactors may be partly due to increased redox activity (i.e., corrosion) on iron surfaces. Anaerobic corrosion of ZVI was also temperature-dependent as substantially lower concentrations of corrosion product were detected at lower incubation temperatures; however, microbially induced corrosion (MIC) of ZVI was much less impacted at lower temperatures than abiotic ZVI corrosion. This study demonstrated that ZVI-supported microbial denitrification is not only more sustainable at lower temperatures, but it becomes more dominant reaction for nitrate removal in microbial-ZVI systems at low temperatures.

A pilot-scale, bi-layer bioretention system with biochar and zero-valent iron for enhanced nitrate removal from stormwater.

Nitrogen (N) removal in conventional bioretention systems is highly variable owing to the low nitrate (NO3-) elimination efficiency. We hypothesized that amending bioretention cells with biochar and zero-valent iron (ZVI) could improve the NO3- removal performance. A well-instrumented, bi-layer pilot-scale bioretention cell was developed to test the hypothesis by investigating its hydrologic performance and NO3- removal efficacy as affected by biochar and ZVI amendments. The cell containing 18% (v/v) wood biochar in the vadose zone and 10% (v/v) ZVI in the saturation zone was monitored for 18 months of field infiltration tests using synthetic stormwater amended with bromide (tracer) and NO3-. Compared to the Control cell without amendments, the Biochar/ZVI cell increased water retention by 11-27% and mean residence time by 0.7-3.8 h. The vadose zone of the Biochar/ZVI cell removed 30.6-95.7% (0.6-12.7 g) of NO3-N from the influent, as compared with -6.1-89.6% (-0.1-2.9 g) by that of the Control cell. While the performance varied with synthetic storm events and seasons, in all cases the Biochar/ZVI cell resulted in greater NO3- removal than the Control cell. This improvement was presumably due to biochar's ability to improve water retention, facilitate anoxic conditions, increase residence time, and provide electrons for microbial denitrification. The saturation zone with ZVI amendment further promoted NO3- removal: removal was 1.8 times greater relative to the control in the first infiltration test, but was minimal in following tests. The reduction in performance of the ZVI amendment in subsequent tests might be due to diminished NO3-N input to the saturation zone after treatment by the biochar-amended vadose zone. The redox potential and dissolved oxygen content at the vadose/saturation zone interface also indicated more favorable denitrification conditions in the Biochar/ZVI cell. Biochar amendment demonstrated significant promise for increasing nitrate removal in bioretention systems.

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.

Simultaneous removal of perchlorate and energetic compounds in munitions wastewater by zero-valent iron and perchlorate-respiring bacteria.

Ammonium perchlorate is one of the main constituents in Army's insensitive melt-pour explosive, PAX-21 in addition to RDX and 2,4-dinitroanisole (DNAN). The objective of this study is to develop an innovative treatment process to remove both perchlorate and energetic compounds simultaneously from PAX-21 production wastewater. It was hypothesized that the pretreatment of PAX-21 wastewater with zero-valent iron (ZVI) would convert energetic compounds to products that are more amenable for biological oxidation and that these products serve as electron donors for perchlorate-reducing bacteria. Results of batch ZVI reduction experiments showed that DNAN was completely reduced to 2,4-diaminoanisole and RDX was completely reduced to formaldehyde. Anaerobic batch biodegradation experiments showed that perchlorate (30 mg L(-1)) in ZVI-treated PAX-21 wastewater was decreased to an undetectable level after 5 days. Batch biodegradation experiments also confirmed that formaldehyde in ZVI-treated wastewater was the primary electron donor for perchlorate-respiring bacteria. The integrated iron-anaerobic bioreactor system was effective in completely removing energetic compounds and perchlorate from the PAX-21 wastewater without adding an exogenous electron donor. This study demonstrated that ZVI pretreatment not only removed energetic compounds, but also transformed energetic compounds to products that can serve as the source of electrons for perchlorate-respiring bacteria.

The removal of 1,4-dioxane from polyester manufacturing process wastewater using an up-flow Biological Aerated Filter (UBAF) packed with tire chips.

1,4-Dioxane is one of the by-products from the polyester manufacturing process, which has been carelessly discharged into water bodies and is a weak human carcinogen. In this study, a laboratory-scale, up-flow biological aerated filter (UBAF), packed with tire chips, was investigated for the treatment of 1,4-dioxane. The UBAF was fed with effluent, containing an average of 31 mg/L of 1,4-dioxane, discharged from an anaerobic treatment unit at H Co. in the Gumi Industrial Complex, South Korea. In the batch, a maximum of 99.5 % 1,4-dioxane was removed from an influent containing 25.6 mg/L. In the continuous mode, the optimal empty bed contact time (EBCT) and air to liquid flow rate (A:L) were 8.5 hours and 30:1, respectively. It was also found that the removal efficiency of 1,4-dioxane increased with increasing loading rate within the range 0.04 to 0.31 kg 1,4-dioxane/m(3)·day. However, as the COD:1,4-dioxane ratio was increased within the range 3 to 46 (mg/L COD)/(mg/L 1,4-dioxane), the removal efficiency unexpectedly decreased.

Detoxification of PAX-21 ammunitions wastewater by zero-valent iron for microbial reduction of perchlorate.

US Army and the Department of Defense (DoD) facilities generate perchlorate (ClO(4)(-)) from munitions manufacturing and demilitarization processes. Ammonium perchlorate is one of the main constituents in Army's new main charge melt-pour energetic, PAX-21. In addition to ammonium perchlorate, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4-dinitroanisole (DNAN) are the major constituents of PAX-21. In order to evaluate microbial perchlorate reduction as a practical option for the treatment of perchlorate in PAX-21 wastewater, we conducted biodegradation experiments using glucose as the primary sources of electrons and carbon. Batch experiments showed that negligible perchlorate was removed in microbial reactors containing PAX-21 wastewater while control bottles containing seed bacteria and glucose rapidly and completely removed perchlorate. These results suggested that the constituents in PAX-21 wastewater may be toxic to perchlorate reducing bacteria. A series of batch toxicity test was conducted to identify the toxic constituents in PAX-21 and DNAN was identified as the primary toxicant responsible for inhibiting the activity of perchlorate reducing bacteria. It was hypothesized that pretreatment of PAX-21 by zero-valent iron granules will transform toxic constituents in PAX-21 wastewater to non-toxic products. We observed complete reduction of DNAN to 2,4-diaminoanisole (DAAN) and RDX to formaldehyde in abiotic iron reduction study. After a 3-day acclimation period, perchlorate in iron-treated PAX-21 wastewater was rapidly decreased to an undetectable level in 2 days. This result demonstrated that iron treatment not only removed energetic compounds but also eliminated the toxic constituents that inhibited the subsequent microbial process.

Microbial community analysis of perchlorate-reducing cultures growing on zero-valent iron.

Anaerobic microbial mixed cultures demonstrated its ability to completely remove perchlorate in the presence of zero-valent iron. In order to understand the major microbial reaction in the iron-supported culture, community analysis comprising of microbial fatty acids and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) techniques was performed for perchlorate reducing cultures. Analysis of fatty acid methyl esters (FAMEs) and subsequent principal component analysis (PCA) showed clear distinctions not only between iron-supported perchlorate reducing culture and seed bacteria, but also among perchlorate-reducing cultures receiving different electron donors. The DGGE pattern targeting the chlorite dismutase (cld) gene showed that iron-supported perchlorate reducing culture is similar to hydrogen-fed cultures as compared to acetate-fed culture. The phylogenetic tree suggested that the dominant microbial reaction may be a combination of the autotrophic and heterotrophic reduction of perchlorate. Both molecular and chemotaxonomic experimental results support further understanding in the function of zero-valent iron as an adequate electron source for enhancing the microbial perchlorate reduction in natural and engineered systems.

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

Microbial reduction of nitrate in the presence of nanoscale zero-valent iron (NZVI) was evaluated to assess the feasibility of employing NZVI in the biological nitrate treatment. Nitrate was completely reduced within 3d in a nanoscale Fe(0)-cell reactor, while only 50% of the nitrate was abiotically reduced over 7d at 25 degrees C. The removal rate of nitrate in the integrated NZVI-cell system was unaffected by the presence of high amounts of sulfate. Efficient removal of nitrate by Fe(II)-supported anaerobic culture in 14 d indicated that Fe(II), which is produced during anaerobic iron corrosion in the Fe(0)-cell system, might act as an electron donor for nitrate. Unlike abiotic reduction, microbial reduction of nitrate was not significantly affected by low temperature conditions. This study demonstrated the potential applicability of employing NZVI iron as a source of electrons for biological nitrate reduction. Use of NZVI for microbial nitrate reduction can obviate the disadvantages associated with traditional biological denitrification, that relies on the use of organic substrates or explosive hydrogen gas, and maintain the advantages offered by nano-particle technology such as higher surface reactivity and functionality in suspensions.

Enhanced reduction of nitrate by zero-valent iron at elevated temperatures.

Kinetics of nitrate reduction by zero-valent iron at elevated temperatures was studied through batch and column experiments. It was hypothesized that under increased solution temperatures, the zero-valent iron may accelerate the reduction of nitrate by overcoming the activation energy barrier to nitrate reduction. The results of the batch experiment showed the synergistic effects of elevated temperature (75 degrees C) and a buffered condition (pH 7.4 with 0.1 M HEPES) to enhance the rate of nitrate reduction by zero-valent iron from 0.072+/-0.006 h(-1) ((0.35+/-0.03) x 10(-4) L m(-2) h(-1)) at room temperature to 1.39+/-0.23 h(-1) ((1.03+/-0.07) x 10(-3) L m(-2) h(-1)). Complete nitrate removal was obtained in a Fe(0) column after 30 min under both buffered and unbuffered conditions at 75 degrees C. These results indicate that a temperature increase could overcome the energy barrier. We suggest that an iron reduction process at moderately elevated temperature (50-75 degrees C) may be a suitable method for removing nitrate from industrial discharges.

Microbial reduction of perchlorate with zero-valent iron.

Microbial reduction of perchlorate in the presence of zero-valent iron was examined in both batch and column reactors to assess the potential of iron as the electron donor for biological perchlorate reduction process. Iron-supported mixed cultures completely removed 65 mg/L of perchlorate in batch reactors in 8 days. The removal rate was similar to that observed with hydrogen gas (5%) and acetate (173 mg/L) as electron donors. Repeated spiking of perchlorate to batch reactors containing iron granules and microorganisms showed that complete perchlorate reduction by the iron-supported culture was sustained over a long period. Complete removal of perchlorate by iron-supported anaerobic culture was also achieved in a bench-scale iron column with a hydraulic residence time of 2 days. This study demonstrated the potential applicability of zero-valent iron as a source of electrons for biological perchlorate reduction. Use of zero-valent iron may eliminate the need to continually supply electron donors such as organic substrates or explosive hydrogen gas. In addition, iron is inexpensive, safe to handle, and does not leave organic residuals in the treated water.

Reduction of acrolein by elemental iron: kinetics, pH effect, and detoxification.

Acrolein is a highly toxic alpha,beta-unsaturated aldehyde that is widely used as a biocide, a cross-linking agent, and an intermediate in the chemical industry, among other applications. In this study we investigated the reductive transformation of acrolein by elemental iron and evaluated the feasibility of using iron to detoxify acrolein. At acidic and neutral pH, acrolein was transformed by iron through reduction of the C=C double bond to propionaldehyde. The reduction appeared to involve the chemisorption of acrolein to the iron surface followed by reduction of adsorbed acrolein. Both the adsorption and reduction rate constants decreased with increasing pH. Between pH 7.0 and 7.4, the acrolein adsorption rate constant decreased precipitously, resulting in a sharp decline in its removal rate. At higher pH, acrolein disappeared rapidly in control without iron, presumably due to reversible, base-catalyzed hydration. At equilibrium, approximately 93% of acrolein was hydrated, corresponding to an equilibrium constant of 13. Acrolein at 25 mg/L completely inhibited aerobic respiration; in contrast, its reduction product propionaldehyde was biodegradable. This suggests that elemental iron may be used to pretreat acrolein-containing wastes prior to aerobic biodegradation. To our knowledge, this is the first report of reduction and detoxification of an alpha,beta-unsaturated aldehyde by elemental iron.

Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system: I. Evaluation of system performance.

The objective of this research is to evaluate an integrated system coupling zero-valent iron (Fe(0)) and aerobic biological oxidation for the treatment of azo dye wastewater. Zero-valent (elemental) iron can reduce the azo bond, cleaving dye molecules into products that are more amenable to aerobic biological treatment processes. Azo dye reduction products, including aniline and sulfanilic acid, were shown to be readily biodegradable at concentrations up to approximately 25 mg/L. Batch reduction and biodegradation data support the proposed integrated iron pretreatment and activated sludge process for the degradation of the azo dyes orange G and orange I. The integrated system was able to decolorize dye solutions and yield effluents with lower total organic carbon concentrations than control systems without iron pretreatment. The success of the bench-scale integrated system suggests that iron pretreatment may be a feasible approach to treat azo dye containing wastewaters.

Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system: II. Effects of physical-chemical parameters.

As part of a study to evaluate an integrated zero-valent iron (Fe(0))-biological oxidation process for treating azo dye wastewaters, we conducted batch and column experiments with the azo dye orange G to assess the effects of solution conditions on the performance of iron pretreatment. The influence of iron type and surface area, solution pH, dissolved inorganic salts, and phosphate ion on the reduction (decolorization) of orange G solution were examined. In batch experiments, increased iron surface area, decreased pH, and chloride and sulfate salts enhanced dye decolorization, whereas high pH (9.9) and phosphate concentrations (> 3 mg/L PO4-P) inhibited dye reduction. Results from batch experiments were confirmed in column experiments. An increase in temperature from 22 to 35 degrees C resulted in a near doubling of the reduction rate constant in a column study. The abiotic reduction results illustrate the feasibility and potential limitations of an integrated iron column, activated sludge treatment process for wastewaters containing azo dyes.

Enhanced reduction of perchlorate by elemental iron at elevated temperatures.

Kinetics of perchlorate reduction by elemental iron was examined at elevated temperatures using microwave heating and conventional block heating. It was hypothesized that increasing the solution temperature may accelerate the reduction of perchlorate by overcoming the high activation energy barrier. Results from microwave heating study showed that 98% of aqueous perchlorate was removed in 1 h at 200 degrees C. Similar results observed in control experiments with a block heater indicated that the enhancement in the extent and rate of perchlorate removal by elemental iron was mostly due to heat energy at high temperature. The rapid and complete reduction of perchlorate by elemental iron at elevated temperatures suggests that iron reduction process at elevated temperature may be an option to consider for complete removal of perchlorate from industrial discharges.

Zero-valent iron pretreatment for enhancing the biodegradability of RDX.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (C3H6N3(NO2)3, royal demolition explosive or RDX) is a common nitramine explosive and one of the major constituents in wastewaters from ammunitions plants. The objective of this study is to investigate zero-valent iron (Fe0) pretreatment for enhancing the biodegradability of recalcitrant RDX. It was hypothesized that iron pretreatment can reductively transform RDX to products that are more amenable to biological treatment processes such as activated sludge. Results of batch and column experiments showed rapid and complete removal of RDX by Fe0 regardless of the buffering capacity. Formaldehyde (HCHO), a major reduction product of RDX, was readily biodegraded by a mixed culture. Respirometric data indicate that iron-treated RDX solution exerted substantially higher biochemical oxygen demand (BOD) than untreated RDX solution. We propose that an integrated iron reduction-activated sludge process may be a feasible option for treating RDX-laden wastewater.

Reductive transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, and methylenedinitramine with elemental iron.

Reductive (pre)treatment with elemental iron is a potentially useful method for degrading nitramine explosives in water and soil. In the present study, we examined the kinetics, products, and mechanisms of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) degradation with elemental iron. Both RDX and HMX were transformed with iron to formaldehyde, NH4+, N2O, and soluble products. The yields of formaldehyde were relatively constant (71% +/- 5%), whereas the yields of NH4+ and N2O varied, depending on the nitramine and the mechanism. The reactions most likely were controlled by a surface process rather than by external mass transfer. Methylenedinitramine (MDNA) was an intermediate of both RDX and HMX and was transformed quantitatively to formaldehyde with iron. However, product distributions and kinetic modeling results suggest that MDNA represented a minor reaction path and accounted for only 30% of the RDX reacted and 14% of the formaldehyde produced. Additional experiments showed that RDX reduction with elemental iron could be mediated by graphite and Fe2+ sorbed to magnetite, as demonstrated previously for nitroaromatics and nitrate esters. Methylenedinitramine was degraded primarily through reduction in the presence of elemental iron, because its hydrolysis was slow compared to its reactions with elemental iron and surface-bound Fe2+. Our results show that in a cast iron-water system, RDX may be transformed via multiple mechanisms involving different reaction paths and reaction sites.

Reduction of nitroglycerin with elemental iron: pathway, kinetics, and mechanisms.

Nitroglycerin (NG) is a nitrate ester used in dynamites, propellants, and medicines and is therefore a common constituent in propellant-manufacturing and pharmaceutical wastewaters. In this study we investigated the reduction of NG with cast iron as a potential treatment method. NG was reduced stepwise to glycerol via 1,2- and 1,3-dinitroglycerins (DNGs) and 1- and 2-mononitroglycerins (MNGs). Nitrite was released in each reduction step and was further reduced to NH4+. Adsorption of NG and its reduction products to cast iron was minimal. A reaction pathway and a kinetic model for NG reduction with cast iron were proposed. The estimated surface area-normalized reaction rate constants for NG and NO2- were (1.65 +/- 0.30) x 10(-2) (L x m(-2) x h(-1)) and (0.78 +/- 0.09) x 10(-2) (L x m(-2) x h(-1)), respectively. Experiments using dialysis cell with iron and a graphite sheet showed that reduction of NG to glycerol can be mediated by graphite. However, reduction of NO2- mediated by graphite was very slow. NG and NO2- were also found to reduce to glycerol and NH4+ by Fe2+ in the presence of magnetite but not by aqueous Fe2+ or magnetite alone. These results indicate that in a cast iron-water system NG may be reduced via multiple mechanisms involving different reaction sites, whereas nitrite is reduced mainly by iron and/ or adsorbed Fe2+. The study demonstrates that iron can rapidly reduce NG to innocuous and biodegradable end products and represents a new approach to treat NG-containing wastewaters.

Enhancing Fenton oxidation of TNT and RDX through pretreatment with zero-valent iron.

The effect of reductive treatment with elemental iron on the rate and extent of TOC removal by Fenton oxidation was studied for the explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using a completely stirred tank reactor (CSTR). The results support the hypothesis that TNT and RDX are reduced with elemental iron to products that are oxidized more rapidly and completely by Fenton's reagent. Iron pretreatment enhanced the extent of total organic carbon (TOC) removal by approximately 20% and 60% for TNT and RDX, respectively. Complete TOC removal was achieved for TNT and RDX solutions with iron pretreatment under optimal conditions. On the other hand, without iron pretreatment, complete TOC removal of TNT and RDX solutions was not achieved even with much higher H(2)O(2) and Fe(2+) concentrations. Nitrogen was recovered as NH(4)(+) and NO(3)(-) when Fe(0)-treated TNT and RDX solutions were subjected to Fenton oxidation. The bench-scale iron treatment-Fenton oxidation integrated system showed more than 95% TOC removal for TNT and RDX solutions under optimal conditions. These results suggest that the reduction products of TNT and RDX are more rapidly and completely degraded by Fenton oxidation and that a sequential iron treatment-Fenton oxidation process may be a viable technology for pink water treatment.

Zero-valent iron pretreatment for enhancing the biodegradability of Azo dyes.

Azo dyes are a group of chemicals that are largely resistant to aerobic biodegradation and persist in wastewater treatment processes. This study proposed that zero-valent iron can be used to reduce the azo bond, cleaving the dye molecule into products that are more amenable to mineralization by bacteria in biological treatment processes such as activated sludge. Batch anaerobic reduction experiments were performed using two azo dyes, orange G and orange II, to determine reaction kinetics and to identify reduction products. Iron-treated dye solutions were subjected to batch biodegradation tests and respirometric analyses to screen for enhanced biodegradability over parent dyes. Results indicate that treatment of orange G and orange II with scrap iron produces aniline and sulfanilic acid as significant products that are degraded by an acclimated culture within 24 hours. Respirometric data illustrated that iron-treated dye solutions exert a significantly higher biochemical oxygen demand than the solutions containing orange G and orange II, demonstrating that recalcitrant azo dyes can be aerobically biodegraded after iron pretreatment.

Effect of adsorption to elemental iron on the transformation of 2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine in solution.

The effect of adsorption to elemental iron on the reductive transformation of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (royal demolition explosive [RDX]) in aqueous solution was studied with scrap iron and high-purity iron. In batch experiments with the same total iron surface area and a mixing rate of 100 rpm, TNT and RDX were removed from the solution within 30 min. With high-purity iron, adsorbed TNT was reduced to 2,4,6-triaminotoluene (TAT) rapidly, with little accumulation of intermediates at the surface. With scrap iron, the extent of adsorption of TNT and its daughter products was more significant and reduction of these adsorbed molecules to TAT was slower. Distribution of the intermediates indicated that the reaction with scrap iron occurred primarily through reduction of the ortho nitro group. Kinetic analysis suggests that mass transfer or adsorption of TNT controlled the overall rate of TNT reduction to TAT with pure iron, whereas with scrap iron, the rate of TAT formation was probably limited by other processes. Compared to TNT, transformation of adsorbed RDX was more rapid and less affected by iron type. The RDX was reduced to an unidentified, water-soluble intermediate and NH4+, which accounted for approximately 50% of the RDX nitrogen. No total organic carbon reduction was observed before and after RDX transformation with scrap iron.