Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico‐chemical and biological technique for the removal of NO_x from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO₃^?, NO₂^?, NO via N₂O to N₂ in this unusual medium. This was done in batch experiments at 30 °C with 25 mmol dm^?3 FeEDTA solutions (pH 7.2 ± 0.2). Also Ca²⁺ (2 and 10 mmol dm^?3) and Mg²⁺ (2 mmol dm^?3) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl‐complex Fe(II)EDTA–NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 °C than NO reduction at 30 °C. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron‐mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. Copyright © 2004 Society of Chemical Industry     

Start‐up and enrichment of a granular anammox SBR to treat high nitrogen load wastewaters

BACKGROUND: Landfill leachate is characterized by low biodegradable organic matter that presents difficulties for the complete biological nitrogen removal usually performed by conventional biological nitrification/denitrification processes. To achieve this, the anaerobic ammonium oxidation (anammox) process is a promising biological treatment. This paper presents an anammox start‐up and enrichment methodology for treating high nitrogen load wastewaters using sequencing batch reactor (SBR) technology. RESULTS: The methodology is based on the gradual increase of the nitrite‐to‐ammonium molar ratio in the influent (from 0.76 to 1.32 mole NO₂^?‐N mole^?1NH₄⁺‐N) and on the exponential increase of the nitrogen loading rate (NLR, from 0.01 to 1.60 kg N m^?3 d^?1). 60 days after start‐up, anammox organisms were identified by polymerase chain reaction (PCR) technique as Candidatus Brocadia anammoxidans. After one year of operation, NLR had reached a value of 1.60 kg N m^?3 d^?1 with a nitrogen (ammonium plus nitrite) removal efficiency of 99.7%. The anammox biomass activity was verified by nitrogen mass balances with 1.32 ± 0.05 mole of nitrite removed per mole of ammonium removed and 0.23 ± 0.05 mole of nitrate produced per mole of ammonium removed. Also, enrichment of anammox bacteria was quantified by fluorescence in situ hybridization (FISH) analysis as 85.0 ± 1.8%. CONCLUSIONS: This paper provides a methodology for the enrichment of the anammox biomass in a SBR to treat high nitrogen loaded wastewaters. Copyright © 2007 Society of Chemical Industry     

RDX biodegradation column study: influence of ubiquitous electron acceptors on anaerobic biotransformation of RDX

A series of column studies, with aquifer material from the former Nebraska Ordinance Plant (NOP), were performed to explore the phenomenon of electron competition from ubiquitous inorganic electron acceptors (nitrate and sulfate) present in contaminated groundwater. Acetate was used as a source of readily biodegradable carbon in all of the treatment‐column systems. Influent hexahydro‐1, 3, 5‐trinitro‐1, 3, 5‐triazine (RDX) concentrations (1–1.8 mg dm^?3) were completely removed to below detection levels of 20 µg dm^?3 in all treatment‐column systems without any nitroso‐metabolites. In the control‐column system (with no carbon amendment) significant levels (～30% of the inlet molar RDX) of nitroso‐substituted RDX derivates were observed in the effluent stream. The estimated first‐order biodegradation rate coefficient for RDX was highest (0.79 h^?1) in the treatment‐column system where acetate was the only amendment, about 52 times higher than the rate coefficient (0.015 h^?1) obtained in the control‐column system. The presence of sulfate (100 mg dm^?3) in influent groundwater temporarily delayed the onset of RDX biotransformation without any adverse effects on overall RDX biotransformation. Coexistence of low (100 mg dm^?3) nitrate levels in the influent feed water reduced the first‐order biodegradation rate coefficient obtained in the absence of nitrate by about 80% to 0.16 h^?1. These nitrate levels, however, were low to halt the RDX biodegradation probably because the available carbon levels were high enough to exceed the demands for nitrate reduction. High levels of nitrate (500 mg dm^?3) initially halted RDX removal, and significantly reduced the rate of RDX biotransformation by about 98% to 0.02 h^?1, thereby increasing the half‐life from 0.9 h in the absence of nitrate to about 32 h, with noticeable levels of untreated RDX in the effluent stream. Contrary to the expectations, the presence of ammonium in conjunction with acetate resulted in a lower (0.09 h^?1) biodegradation rate coefficient as compared with the one obtained in the absence of ammonium. Copyright © 2003 Society of Chemical Industry     

Treatment of ampicillin‐loaded wastewater by combined adsorption and biodegradation

BACKGROUND: This study investigated the treatment of ampicillin (AMP)‐loaded wastewater in airlift reactors where biofilms were developed on granular activated carbon (GAC). A series of batch experiments were thus carried out in order to differentiate potentials of adsorption and biodegradation which would jointly contribute to the AMP removal. RESULTS: Results showed that almost all influent AMP was removed in two reactors supplemented with 4 and 8 mg L^?1 AMP, respectively. Batch experiments revealed that the percentage of the AMP removed through biodegradation increased along with the development of biofilms on GAC. For the mature biofilm‐covered GAC, adsorption accounted for about 60% of the observed AMP removal, whereas the other 40% could be attributed to biodegradation. Possible degraders of AMP were also identified, such as Acinetobacter sp., Flavobacterium sp., Pseudoxanthomonas sp., Delftia sp. and Sphingobium sp. CONCLUSION: The airlift biofilm reactor with GAC as carrier would be a feasible technology for treating AMP‐loaded wastewater due to the joint action of adsorption and biodegradation of AMP by the biofilm‐covered GAC. Copyright © 2010 Society of Chemical Industry     

The effects of nitrate and nitrate‐supplemented leachate addition on methanogenesis from Municipal Solid Waste

The recirculation of nitrified leachate through landfill sites, followed by in situ denitrification, represents a novel and more sustainable approach for the removal of ammonia from leachate, prior to discharge. The effects of nitrate and leachate supplementation on methanogenesis in Municipal Solid Waste (MSW) were studied in batch cultures. The addition of a range of nitrate concentrations to MSW samples had an inhibitory effect on methanogenesis. The effects were dose‐dependent, such that recovery of methane production was recorded within 5 and 23 days with added 100 and 750 mg NO₃ dm^?3, respectively. Even after 24 days, no recovery was observed in cultures challenged with 1000 mg NO₃ dm^?3. The enumeration of denitrifying bacteria in a range of fresh, actively methanogenic and aged, well‐decomposed MSW confirmed the potential of MSW for rapid denitrification. Methanogenesis was not inhibited by the addition of leachate (20–100% strength) that contained high concentrations of VFAs. However, when the same leachate was supplemented with nitrate (250 mg NO₃ dm^?3), methanogenesis was inhibited by the addition of leachate concentrations ≥20%, which was attributed to inhibition of denitrification by VFAs. Propionate accumulated, confirming the importance of methanogenesis as an electron sink. With the removal of nitrate and the recovery of methanogenesis, net propionate concentrations decreased. Copyright © 2004 Society of Chemical Industry     

Nitrate‐dependent degradation of 17α‐ethinylestradiol by acclimated activated sludge under anaerobic conditions

BACKGROUND: The synthetic estrogen 17α‐ethinylestradiol (EE2) is of great environmental concern. Batch experiments were conducted to investigate the removal of EE2 by activated sludge under anaerobic conditions with or without nitrate. The effect of temperature on EE2 removal was also estimated. RESULTS: No biodegradation of EE2 was observed in the absence of nitrate; owing to sorption onto the activated sludge, the overall removal EE2 rate was 62%; the sorption was fitted to both Freundlich and linear sorption models; the sorption rate decreased with the increase temperature. In the presence of nitrate, the overall removal rate of EE2 was greater than 97% after 72 h, mostly from biodegradation (95%); the biodegradation could be described by first‐order reaction kinetics with average rate constant of 0.0344 h^?1; increasing temperature enhanced the rate constant and the removal rate could be as high as 96–98% in the temperature range 10–30 °C. CONCLUSION: EE2 was removed by activated sludge under anaerobic conditions. In the absence of nitrate, the removal of EE2 was a result of sorption onto activated sludge. In the presence of nitrate, biodegradation was the dominant process for EE2 removal. Higher temperature improves biodegradation rate, but reduces the sorption of EE2 onto activated sludge. Copyright © 2009 Society of Chemical Industry     

Inhibition of sulfide on the simultaneous removal of nitrate and p‐cresol by a denitrifying sludge

BACKGROUND: Many industrial discharges, such as those generated from petrochemical refineries, contain large amounts of sulfurous, nitrogenous and organic contaminants. Denitrification has emerged as a suitable technology for the simultaneous removal of these pollutants in a single reactor unit; however, more evidence is demanded to clarify the limitations of denitrification on the simultaneous removal of sulfide and phenolic contaminants and to optimize the biological process. The aim of this study was to evaluate the capacity of a denitrifying sludge to simultaneously convert sulfide and p‐cresol via denitrification. RESULTS: Sulfide was the preferred electron donor over p‐cresol, imposing a 5 h lag phase (required for complete sulfide removal) on organotrophic denitrification. Addition of sulfide (20 mg S^2? L^?1) to p‐cresol‐amended denitrifying cultures also decreased the reduction rate of nitrate and nitrite, as well as the production rate of nitrogen gas. Nitrite reduction rate was the most affected step by sulfide, decreasing from 35 to 21 mg N (g VSS d)^?1. A synergistic inhibitory effect of nitrate and sulfide was also observed on nitrite reduction. Despite the effects of sulfide on the respiratory rates monitored, complete removal of nitrate, sulfide and p‐cresol could be achieved after 48 h of incubation. CONCLUSION: Our results suggest that simultaneous removal of sulfide and p‐cresol could be achieved in denitrifying reactors, but a large hydraulic residence time may be required to sustain an efficient process due to inhibitory effects of sulfide. Copyright © 2008 Society of Chemical Industry     

Insoluble porous conjugated polymer films via phase separation and photo‐crosslinking for the trace detection of 2,4‐dinitrotoluene

A novel conjugated polymer film with microscale/submicroscale porous morphology fabricated from crosslinked poly(fluorene‐co‐carbazole) (PFC1) was developed for the detection of 2,4‐dinitrotoluene (DNT). The fluorescent conjugated polymer PFC1 with pendant photo‐crosslinkable coumarin groups was synthesized by Suzuki coupling polymerization. Taking advantage of the phase separation of PFC1/polystyrene (PS) blends in the film and the solvent‐resistant network, porous structured films were prepared by removal of PS. Films with porous morphologies exhibited marked responsive sensitivity to trace DNT vapor due to the unique porous structure favoring the diffusion of and association with DNT molecules. The formation of a crosslinked network by dimerization of the coumarin moieties may be beneficial for isolating the polymeric backbones, thus to some extent preventing chain aggregation. This facile fabrication method enabled the crosslinked porous films to be efficient fluorescence chemosensors towards the detection of trace amounts of DNT vapor.© 2012 Society of Chemical Industry     

Integration of continuous biological and chemical (ozone) treatment of domestic wastewater: 1. Biodegradation and post‐ozonation

The continuous treatment of domestic wastewater by an activated sludge process and by an integrated biological–chemical (ozone) oxidation process were studied in this work. Chemical oxygen demand (COD), biochemical oxygen demand (BOD), absorbance at 254 nm (UV₂₅₄) and nitrogenous compound content were the parameters followed in order to evaluate the performance of the two processes. Experimental data showed that both UV₂₅₄ and COD reductions are improved in the combined biological–chemical oxidation procedure. Thus, reductions of 59.1% and 37.2% corresponding to COD and UV₂₅₄, respectively were observed after the biological process (hydraulic retention time = 5 h; mixed liquor volatile suspended solids concentration = 3142 g m⁻³) compared with 71.0% and 78.4% obtained when a post‐ozonation step ( D _O3 = 41.7 g m⁻³) was included. During conventional activated sludge treatment, appropriate nitrification levels are only achieved with high hydraulic retention time and/or biomass concentration. Ozonation after the secondary treatment, however, allows improved nitrogen content reduction with total nitrite elimination. Post‐ozonation also leads to a higher biodegradability of the treated wastewater. Thus, the ultimate BOD/COD ratio goes from 0.16 after biological oxidation to 0.34 after post‐ozonation with 41.7 g O₃ m⁻³. © 1999 Society of Chemical Industry     

Comparison of different treatment alternatives for removal of pesticide from water solution

BACKGROUND: Removal of recalcitrant chemicals is an essential step in conventional wastewater treatment plants. Among these, pesticides are of great environmental concern. Different treatment options were compared in this work: the combination of advanced oxidation processes (AOPs) with biological treatment, an aerobic process and anaerobic biological treatments. The role of chemical processes in improving solution biodegradability was verified. Oxidation by‐products were identified and biological process kinetics are reported. The performance of biological processes and their kinetics were studied. RESULTS: Chemical oxidation increased the solution biodegradability index to 0.25. Oxidation by‐products were identified as maleic acid, phenol and a mixture of catechol, resorcinol and hydroquinone. The combined processes resulted in 98% organic matter removal. Pesticide degradation followed pseudo‐first‐order kinetics with a rate constant in the range 0.5–1.2 L g^?1TVSS h^?1. An anaerobic process was found to be an attractive option with 92% removal efficiency. The aerobic process had a long adaptation time (>200 days), 80% removal efficiency and an average pseudo‐first‐order rate constant of 0.18 L g^?1TVSS h^?1. CONCLUSION: Comparison of the investigated processes favoured the use of combined AOPs and biological and/or aerobic biological treatment due to its practical operating conditions. Copyright © 2009 Society of Chemical Industry     

Evaluation of heterotrophic nitrite removal by a sulphide and acetate oxidizing mixed culture originated from an oil reservoir

BACKGROUND: Shortcut biological nitrogen removal (SBNR) has attracted much attention in recent years due to lower aeration and chemical oxygen demand (COD) requirements, shorter residence time and smaller biomass production. In this work an oil reservoir denitrifying culture, with the ability to function under autotrophic and heterotrophic conditions was used for heterotrophic denitritation. Using freely suspended cells, effects of nitrite concentration (10–50 mmol L^?1) and temperature (15–35 °C) on the kinetics of denitritation were investigated and a kinetic model was developed. Potential for enhancement of nitrite removal rate, and impacts of nitrite concentration and loading rate were investigated in a continuous biofilm reactor. RESULTS: Nitrite did not impose any inhibitory effect, even at the highest applied concentration of 50 mmol L^?1. Increase of temperature in the range 15–35 °C enhanced the reduction rate significantly. Fitting the experimental data into the model developed, values of biokinetic coefficients (µ_max?NO2, K_S?NO2, Y_X?NO2, Y_X?Ace?NO2 and Eµ‐_NO2) were determined. In the biofilm reactor increases in nitrite loading rate (through flow rate or feed nitrite concentration) led to a linear increase of nitrite removal rate, with the highest removal rate of 140.6 mmol L^?1 h^?1 achieved with a residence time of 0.19 h. CONCLUSION: The enrichment culture used in this study is not only a superior biocatalyst for simultaneous removal of sulphide, nitrate and BOD, it could also be used effectively in the denitritation step of an SBNR process. The kinetic model developed would certainly have beneficial applications in the design, operation and control of the SBNR process. Copyright © 2011 Society of Chemical Industry     

Effects of electrolytes on the reduction of 2,4‐dinitrotoluene by zero‐valent iron

BACKGROUND: Dinitrotoluenes (DNTs) are environmentally persistent, making the remediation of contaminated streams and groundwater difficult. Zero‐valent iron (Fe⁰) can be used as an electron source for the reduction of recalcitrant DNTs in waste‐water and thus enhance their biodegradability. However, little is known about the qualitative effects of major anions and cations present in waste‐water on the reduction of DNTs by Fe⁰. RESULTS: The presence of Na₂SO₄ and NaCl at levels between 0.25 and 2 mmol L^?1 was observed to enhance the reactivity of Fe⁰ towards 2,4‐DNT. The positive effect of K₂SO₄ is stronger than that of Na₂SO₄ at the same level (1 mmol L^?1). Varying (NH₄)₂SO₄ from 0.1 to 1.0 mmol L^?1 improved the efficiency of 2,4‐DNT degradation by Fe⁰. The effects of varying NaNO₃ and NaNO₂ from 0 mmol L^?1 to 4.7 mmol L^?1 and 0 mmol L^?1 to 5.8 mmol L^?1, respectively, were also investigated. Both NaNO₃ and NaNO₂ at low concentration improved the efficiency of 2,4‐DNT degradation by Fe⁰, however, at high concentration, inhibiting effects appeared. CONCLUSION: SO₄^2?, Cl^?, Na⁺, K⁺ and NH₄⁺ notably enhanced 2,4‐DNT reduction by Fe⁰ at the tested concentrations. The positive effect of K⁺, Cl^? was relatively stronger than that of Na⁺ and sulfate (SO₄^2?). However, the effect of NH₄⁺ was relatively weaker at concentrations greater than 1.0 mmol L^?1. The presence of low concentrations of NO₃^? and NO₂^? promoted 2,4‐DNT reduction by Fe⁰ and inhibited the reaction. The results suggest that 2,4‐DNT reduction by Fe⁰ can be controlled by the ions composition of the waste‐water. Copyright © 2010 Society of Chemical Industry     

Particle size distribution based evaluation of biodegradation and treatability for leachate from organic waste

BACKGROUND: The study evaluated the relationship between particle size distribution (PSD) of chemical oxygen demand (COD) and treatability of leachate generated by organic waste. PSD determinations were performed together with physico‐chemical and biological treatability studies. Leachate biodegradation was also evaluated by means of oxygen uptake rate (OUR) profiles and experimental results were used for calibration of the adopted mathematical model. RESULTS: The leachate was characterized by a COD content of 80 000 mg L^?1 in summer. PSD analysis showed a bimodal distribution with around 60% of the COD below 2 nm and 25% above 1600 nm. Chemical treatment by lime and alum provided limited COD removal (30‐35%). The extent of COD removal was higher than the particulate COD fraction above 1600 nm, it also occurred in the soluble range below 2 nm through adsorption. A modeling study indicated three major COD fractions that could be correlated with PSD analysis: readily biodegradable COD and slowly biodegradable COD in the soluble range and hydrolyzable COD fraction in the particulate range. CONCLUSION: PSD‐based COD fractionation adequately explained limitations of chemical treatment efficiency; it was also a reliable complement to the currently used respirometric tests for biodegradation, providing insight to the fate of different COD fractions included in the soluble range (<2 nm) and yielding concrete supporting information on the generation of soluble residual microbial products. Copyright © 2011 Society of Chemical Industry     

Treatment of PAH‐contaminated soil by combination of Fenton's reaction and biodegradation

A combination of modified Fenton and biological treatment was used to remove polycyclic aromatic hydrocarbons (PAHs) from creosote oil‐contaminated soil. After modified Fenton reaction the toxicity of column leachate and soil to Vibrio fischeri increased. The number of intact bacterial cells and utilisation of PAHs in PAH utilisation microplate assay decreased after modified Fenton reaction. However, bacteria in chemically treated soil utilised PAHs without addition of other carbon sources. The activity of extracellular esterases increased during incubation of modified Fenton‐treated soil. PAH removal in combined chemical oxidation and incubation (43–59%) was higher than in incubation alone (22–30%). Residual H₂O₂ in soil allowed chemical oxidation of PAHs during incubation. Copyright © 2006 Society of Chemical Industry     

Photocatalytic pretreatment of contaminated groundwater for biological nitrification enhancement

The sequential photocatalytic/biological treatment of a contaminated groundwater from a local industrial site was studied. The ground water contained approximately 100 mg dm^?3 ammonia, as well as mg dm^?3 levels of nitrification‐inhibiting organics such as chlorobenzene. An existing treatment system uses carbon adsorption pretreatment to remove the nitrification inhibitors before the water is treated in a biological nitrification system. Photocatalysis, using a corrugated plate photoreactor, was studied as an alternative to the carbon adsorption system for inhibitor removal. Photocatalytic pretreatment was found to significantly enhance the extent of biological nitrification. An optimal pretreatment time appeared to exist, since further pretreatment resulted in accumulation of nitrite. Although further study is required, there appears to be a potential for using photocatalysis to remove inhibitors from biological nitrification systems. © 2002 Society of Chemical Industry     

Oxidation of phenol in a bioremediation medium using chlorine dioxide

BACKGROUND: High concentrations of phenol in wastewater are difficult to remove by purely biological methods. Chemical oxidation is one way to treat high concentrations of phenol but complete oxidation will make the treatment process uneconomical. For the purpose of integrating chemical and biological treatment, the oxidation of phenol using chlorine dioxide was investigated in a medium suitable for bioremediation. The effects of chlorine dioxide concentration (500 to 2000 mg L^?1), temperature (10 to 40 °C) and pH (3 to 7) on the oxidation of 2000 mg L^?1 of phenol were determined. RESULTS: Chlorine dioxide concentration was found to be the dominant parameter for the removal of phenol in the nutrient rich medium. The optimal concentration of chlorine dioxide to completely oxidize 2000 mg L^?1 of phenol was 2000 mg L^?1. Compared with Fenton's reagent, half as much chlorine dioxide was needed to oxidize 2000 mg L^?1 phenol. The reaction of chlorine dioxide with phenol was very fast and reached equilibrium within 10 min. The main oxidation products were identified as 1,4‐benzoquinone and 2‐chloro‐1,4‐benzoquinone. CONCLUSION: Compared with Fenton's reagent, chlorine dioxide is a superior oxidant for removal of phenol from both pure water and bioremediation medium. Copyright © 2010 Society of Chemical Industry     

Scrap cast iron and copper‐modified cast iron for reductive degradation of 2,4‐dinitrotoluene

BACKGROUND: Little attention has been paid to the use of large‐sized scrap cast iron for reduction of refractory organic pollutants at neutral pH and in the presence of dissolved oxygen (DO). RESULTS: Scrap cast iron and copper‐modified cast iron with fresh surfaces have a high reactivity towards the reduction of 2,4‐dinitrotoluene (2,4‐DNT). The extent of conversion reached around 80% and 97% respectively, though it gradually decreased with repeated reactions to relatively stable values of 63% and 72%, and recovered once the reacted filings were cleaned by dilute acid. After 50 days reaction, no dissolved copper appeared in the copper‐modified cast iron process. The mass loss of copper due to physical detachment reached 1.1% of the total coated copper within the initial 20 reaction days, and only 0.3% appeared in the next 30 days. 2,4‐DNT oxidizes scrap cast iron to generate mainly FeFe₂O₄ with DO, however, it oxidizes scrap copper‐modified cast iron to generate mainly γ‐FeO(OH) and α‐FeO(OH). CONCLUSION: Both samples of cast iron were successfully applied in the treatment of neutral wastewater containing 2,4‐DNT with high reactivity and good repeatable efficiency. Electrode reaction rate was enhanced by the deposited copper, which has strong chemical and physical stability. Copyright © 2011 Society of Chemical Industry     

Removal of high concentrations of H2S from simulated natural gas by Acidithiobacillus ferrooxidans immobilized on polyurethane foam

A chemo‐biochemical process for desulfurization of simulated natural gas containing hydrogen sulfide (H₂S) was investigated. The results showed that using polyurethane foam as a support for immobilization of Acidithiobacillus ferrooxidans obtained good biological oxidation performance and the maximum oxidation rate of ferrous iron was 4.12 kg m^?3 h^?1. Moreover, a semi‐empirical formula was set up for calculating theoretical ferrous oxidation rate as a function of influent Fe²⁺ and Fe²⁺ concentration in the bioreactor. The integrated chemical and biological process achieved removal efficiencies of about 80% when treating high concentrations of H₂S (15 000 ± 100 ppmv). © 2012 Society of Chemical Industry     

Thermal Stability Studies Comparing IMX‐101 (Dinitroanisole/Nitroguanidine/NTO) to Analogous Formulations Containing Dinitrotoluene

The 2,4,6‐trinitrotoluene (TNT) replacement, IMX‐101, containing 43.5 % 2,4‐dinitroanisole (DNAN), 19.7 % 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) and 36.8 % nitro‐guanidine (NQ), has been certified for use as an insensitive munition. IMX‐101 has passed standardized performance, stability, and aging tests but in some categories was not necessarily an improvement over TNT or RDX. This study compared the thermal stability of DNAN and another low‐melting nitroarene, 2,4‐dinitrotoulene (DNT). When examined individually, DNAN was more stable; but formulated in IMX‐101 with NTO and NQ, the opposite was true. In two part mixtures, NQ had a similar acceleratory effect on the decomposition of both nitroarenes, while NTO had a greater impact on DNAN than on NTO. Ammonia, a reported decomposition product of both NQ and NTO, also accelerated the decomposition of both DNAN and DNT, with a larger impact on DNAN. The formation of dinitroaniline, potentially due to the interaction between the nitroarenes and ammonia, was detected by LC/MS as a decomposition product when either nitroarene was combined with NTO and/or NQ, indicating that this molecule may play a significant role in the decomposition mechanism. While not advocating the use of DNT in insensitive munitions formulations, this study addresses the importance of chemical compatibility as a criterion for selecting replacement components in formulations.     

Effect of enzymatic pretreatment on acid fermentation of food waste

Although food waste is a valuable carbon source for biological nutrient removal systems with low organic wastewater because of high C/N and C/P ratios, it must be pretreated to promote the hydrolysis of particulates, which is considered as a rate‐limiting step. This study investigated the effects of enzymatic pretreatment on hydrolytic solubilization of food waste with commercial enzyme. Both acidification efficiency and volatile fatty acid (VFA) production potential of enzymatically pretreated food waste were examined under controlled laboratory conditions. Experimental results indicated that protease exhibited the highest VSS reduction rate among three types of enzymes: carbohydrase, protease and lipase. A mixed enzyme treatment showed better reduction efficiency than a single enzyme treatment, and the highest volatile suspended solids (VSS) reduction was observed at an enzyme mixture ratio of 1:2:1 with carbohydrase:protease:lipase, respectively. It has been noted that pretreatment resulted in both maximum VFA production and the highest VFA content of soluble chemical oxygen demand at an enzyme mixture dosage of 0.1% (v/v). VFA production at this dosage revealed a 3.3 times higher rate than that of no‐enzyme added fermenter. The dominant VFAs were n‐butyrate followed by acetate. Copyright © 2006 Society of Chemical Industry