Advanced Oxidation Process for DNAN Using UV/H2O2

2,4-Dinitroanisole(DNAN)is an important component of insensitive munitions that is anticipated to replace 2,4,6-trinitrotoluene(TNT)in munitions formulations.Photocatalyzed hydrogen peroxide(H2O2)oxidation experiments and chemical analyses were conducted to study the effect of initial pH and H2O2 dosage on the kinetics of DNAN decomposition and the reaction pathways.The results show that DNAN degradation followed zero-order kinetics when a 250 ppm DNAN solution was treated with ultraviolet(UV)light and 1500–4500 ppm H2O2 in an initial pH range of 4–7.However,when the H2O2 concentration was 750 ppm,DNAN degradation followed pseudo-first-order kinetics.The results indicate that DNAN can easily be oxidized by UV/H2O2 treatment.When the H2O2 dosage was 1500 ppm and the initial pH was 7,DNAN was reduced from 250 ppm to less than 1 ppm in 3 h.However,the total organic carbon(TOC)and total carbon(TC)concentrations were reduced slowly from 100 to less than 70 ppm carbon(C)in 3 h,and decreased to about 5 ppm after 9 h of treatment,suggesting the formation of other organic compounds.Those reaction intermediates were oxidized to carbon dioxide(CO2)at a slower rate than the oxidation of DNAN.CO2 was emitted from the solution because the solution pH decreased rapidly to about 3 during the UV/H2O2 oxidation.Most of the nitrogen in DNAN was converted to nitrate by UV/H2O2 oxidation after 9 h of treatment.The research results indicate that UV/H2O2 oxidation is a promising technique for the treatment of DNAN in wastewater.

Decolorization of Methyl Orange by a new clay-supported nanoscale zero-valent iron:Synergetic effect,efficiency optimization and mechanism

In this study, a novel nanoscale zero-valent iron（n ZVI） composite material was successfully synthesized using a low-cost natural clay, ＂Hangjin 2~#clay＂（HJ clay） as the support and tested for the decolorization of the azo dye Methyl Orange（MO） in aqueous solution by n ZVI particles. According to the characterization and MO decolorization experiments, the sample with 5：1 HJ clay-supported n ZVI（HJ/n ZVI） mass ratio（HJ-n ZVI5） showed the best dispersion and reactivity and the highest MO decolorization efficiency. With the same equivalent Fe0 dosage, the HJ-n ZVI1 and HJ-n ZVI5 samples demonstrated a synergetic effect for the decolorization of MO： their decolorization efficiencies were much higher than that achieved by physical mixing of HJ clay and n ZVIs, or the sum of HJ clay and n ZVIs alone. The synergetic effect was primarily due to the improved dispersion and more effective utilization of the n ZVI particles on/in the composite materials. Higher decolorization efficiency of MO was obtained at larger HJ-n ZVI dosage, higher temperature and under N2 atmosphere, while the MO initial concentration and p H were negatively correlated to the efficiency. HJ clay not only works as a carrier for n ZVI nanoparticles, but also contributes to the decolorization through an ＂adsorption-enhanced reduction＂ mechanism. The high efficiency of HJ-n ZVI for decontamination gives it great potential for use in a variety of remediation applications.

Effect of phosphate releasing in activated sludge on phosphorus removal from municipal wastewater

Aluminum and ferric salts are commonly used in municipal wastewater treatment plants（WWPTs） for phosphorus（P） removal. In this study, on-site jar tests were conducted to determine the removal of different P species from the fresh samples in the presence and absence of activated sludge（AS） with different doses of alum, poly-aluminum chloride,and ferric chloride at different p H. The soluble P（SP） concentration in the samples was about 0.63 mg/L. When the mixed liquor containing AS was treated with 8 mg/L of Al, SP could be reduced to 0.13 mg/L, while it was reduced to 0.16 mg/L with only 1 mg/L of Al after sedimentation removal of AS from sample. Chemical analysis determined that AS contained 59.8 mg-P/g-TSS and 43.8 mg-Al/g-TSS and most of the P was associated with the aluminum hydroxide. We discovered that the phosphate in the AS could readily be released from it, which was mainly responsible for ineffective removal of P to low levels in mixed liquor even with very high alum dose. This study provides new insight into the behavior and fate of P in the wastewater treatment plants that use alum to enhance P removal in the final effluent.

Recent advances in SERS detection of perchlorate

Perchlorate has recently emerged as a wide- spread environmental contaminant of healthy concern. Development of novel detection methods for perchlorate with the potential for field use has been an urgent need. The investigation has shown that surface-enhanced Raman scattering （SERS） technique has great potential to become a practical analysis tool for the rapid screening and routine monitoring of perchlorate in the field, particularly when coupled with portable/handheld Raman spectrometers. In this review article, we summarize progress made in SERS analysis of perchlorate in water and other media with an emphasis on the development of SERS substrates for perchlorate detection. The potential of this technique for fast screening and field testing ofperchlorate-contaminated environmental samples is discussed. The challenges and possible solutions are also addressed, aiming to provide a better understanding on the development directions in the research field.

Adsorption and recovery of phosphate from water by amine fiber,effects of co-existing ions and column filtration

A weak-base adsorption fiber,acrylic amine fiber(AAF),was prepared for removal and recovery of phosphate from water.The adsorption properties of the AAF for phosphate and effects of co-existing ions were investigated using batch and column filtration experiments,scanning electron microscope,and Fourier transform infrared techniques.Experimental results showed that AAF had a high phosphate adsorption capacity of 119 mg/g at pH 7.0.The effects of calcium,sulfate,carbonate,nitrate,and fluoride showed that sulfate and calcium inhibited phosphate adsorption.However,AAF showed higher binding affinity toward phosphate than sulfate.Column filtration results showed that AAF could filter 1420 bed volumes of tap water containing 1.0 mg-P/L of phosphate.The saturated AAF could be regenerated using 0.5 mol/L hydrochloric acid solution and reused.After desorption,phosphate was recovered through precipitation of hydroxyapatite(Ca5(PO4)3OH).The easy of regeneration,good adsorption performance,and the fiber morphology of AAF make it an attractive alternative for phosphate recovery from multiple water sources.

Fluoride removal by Al,Ti,and Fe hydroxides and coexisting ion effect

Batch experiments were conducted to evaluate fluoride removal by Al,Fe,and Ti-based coagulants and adsorbents,as well as the effects of coexisting ions and formation of aluminum–fluoride complexes on fluoride removal by co-precipitation with alum（Al_2（SO_4）_3·18H_2O）.Aluminum sulfate was more efficient than the other coagulants for fluoride removal in the pH range between 6 and 8.Nano-crystalline TiO_2 was more effective for fluoride removal than Al and Fe hydroxides in a pH range of 3–5.Coexisting anions in water decreased the removal of fluoride in the order：phosphate（2.5 mg/L） 〉 arsenate（0.1 mg/L） 〉 bicarbonate（200 mg/L） 〉sulfate（100 mg/L） = nitrate（100 mg/L） 〉 silicate（10 mg/L） at a pH of 6.0.The effect of silicate became more significant at pH 〉 7.0.Calcium and magnesium improved the removal of fluoride.Zeta-potential measurements determined that the adsorption of fluoride shifted the PZC of Al（OH）_3 precipitates from 8.9 to 8.4,indicating the chemical adsorption of fluoride at the surface.The presence of fluoride in solution significantly increased the soluble aluminum concentration at pH 〈 6.5.A Visual MINTEQ modeling study indicated that the increased aluminum solubility was caused by the formation of AlF^（2＋）,AlF^（＋2）,and AlF_3complexes.The AlF_x complexes decreased the removal of fluoride during co-precipitation with aluminum sulfate.

SERS detection of arsenic in water:A review

Arsenic（As） is one of the most toxic contaminants found in the environment. Development of novel detection methods for As species in water with the potential for field use has been an urgent need in recent years. In past decades, surface-enhanced Raman scattering（SERS）has gained a reputation as one of the most sensitive spectroscopic methods for chemical and biomolecular sensing. The SERS technique has emerged as an extremely promising solution for in-situ detection of arsenic species in the field, particularly when coupled with portable/handheld Raman spectrometers. In this article, the recent advances in SERS analysis of arsenic species in water media are reviewed, and the potential of this technique for fast screening and field testing of arsenic-contaminated environmental water samples is discussed. The problems that remain in the field are also discussed and an outlook for the future is featured at the end of the article.

Adsorption of Ca2+on single layer graphene oxide

Graphene oxide（GO） holds great promise for a broad array of applications in many fields,but also poses serious potential risks to human health and the environment.In this study,the adsorptive properties of GO toward Ca^（2＋） and Na＋were investigated using batch adsorption experiments,zeta potential measurements,and spectroscopic analysis.When pH increased from 4 to 9,Ca^（2＋）adsorption by GO and the zeta potential of GO increased significantly.Raman spectra suggest that Ca^（2＋）was strongly adsorbed on the GO via –COO Ca~＋ formation.On the other hand,Na＋was adsorbed into the electrical diffuse layer as an inert counterion to increase the diffuse layer zeta potential.While the GO suspension became unstable with increasing pH from 4 to 10 in the presence of Ca^（2＋）,it was more stable at higher pH in the NaC l solution.The findings of this research provide insights in the adsorption of Ca^（2＋）on GO and fundamental basis for prediction of its effect on the colloidal stability of GO in the environment.

Phosphate recovery from anaerobic digester effluents using CaMg(OH)_4

Dolomite lime（DL）（CaMg（OH）4） was used as an economical source of Mg^2＋for the removal and recovery of phosphate from an anaerobic digester effluent of a municipal wastewater treatment plant（MWWTP） wastewater. Batch precipitation results determined that phosphate was effectively reduced from 87 to less than 4 mg-P/L when the effluent water was mixed with 0.3 g/L of DL. The competitive precipitation mechanisms of different solids in the treatment system consisting of Ca^2＋–Mg^2＋–NH4^＋–PO4^3-CO3^2-were determined by comparing model predictions with experimental results. Thermodynamic model calculations indicated that hydroxyapatite（Ca10（PO4）6（OH）2）, Ca4H（PO4）3·3H2O, Ca3（PO4）2（beta）, and Ca3（PO4）2（am2）were more stable than struvite（MgNH4PO36·H2O） and calcite（CaCO3）. However, X-ray diffraction（XRD） analysis determined the formation of struvite and calcite minerals in the treated effluent. Kinetic experimental results showed that most of the phosphate was removed from synthetic effluent containing NH4^＋within 2 hr, while only 20% of the PO4^3-was removed in the absence of NH4^＋after 24 hr of treatment. The formation of struvite in the DL-treated effluent was due to the rapid precipitation rate of the mineral. The final pH of the DL-treated effluent significantly influenced the mass ratio of struvite to calcite in the precipitates. Because more calcite was formed when the p H increased from 8.4 to 9.6, a pH range of 8.0–8.5 should be used to produce solid with high PO4^3-content. This study demonstrated that DL could be used for effective removal of phosphate from the effluent and that resultant precipitates contained high content of phosphate and ammonium.

Lead removal from water using organic acrylic amine fiber(AAF)and inorganic-organic P-AAF,fixed bed filtration and surface-induced precipitation

Granular porous sorbents were normally used for heavy metals removal from water.To search for the new commercial sorbent and treatment strategy,an organic acrylic amine fiber(AAF)and phosphorus loading inorganic-organic AAF(P-AAF)were prepared and used for lead(Pb)removal from water.A new strategy of inorganic-organic coupling technology was proposed for Pb removal,based on the hypothesis of surface-induced precipitation mechanism.The AAF showed a Pb adsorption capacity of 417 mg/g from the Langmuir fitting,while the column filtration technology was further applied to measure the adsorption edge and applications.Effects of different initial Pb concentrations,hydraulic retention time,and co-existing P were considered in the filtration experiments.The presence of 0.8 mg/L P in water significantly improved the Pb breakthrough point from 15,000 to 41,000 bed volumes of water spiked with 85μg/L Pb,while the P-AAF fixed bed showed better removal of Pb than AAF SEM/EDX and XRD spectra were employed for determining the surface functional groups and the formation of surface-induced precipitation of pyromorphite(Pb_5(PO_4)_3 OH)on AAF.This study verified the application of AAF sorbent for Pb removal and the enhanced effect of coating P on AAF,thus improved our fundamental understanding and application of the surface chemistry process of Pb with P.

Spectrophotometric analyses of hexahydro-1,3,5-trinitro-1,3,5-triazine(RDX) in water

A simple and accurate spectrophotometric method for on-site analysis of royal demolition explosive（RDX） in water samples was developed based on the Berthelot reaction. The sensitivity and accuracy of an existing spectrophotometric method was improved by：replacing toxic chemicals with more stable and safer reagents; optimizing the reagent dose and reaction time; improving color stability; and eliminating the interference from inorganic nitrogen compounds in water samples. Cation and anion exchange resin cartridges were developed and used for sample pretreatment to eliminate the effect of ammonia and nitrate on RDX analyses. The detection limit of the method was determined to be 100 μg/L. The method was used successfully for analysis of RDX in untreated industrial wastewater samples. It can be used for on-site monitoring of RDX in wastewater for early detection of chemical spills and failure of wastewater treatment systems.

Release of Pb adsorbed on graphene oxide surfaces under conditions of Shewanella putrefaciens metabolism

In this study, Pb(Ⅱ) was used as a target heavy metal pollutant, and the metabolism of Shewanella putrefaciens(S. putrefaciens) was applied to achieve reducing conditions to study the effect of microbial reduction on lead that was preadsorbed on graphene oxide(GO) surfaces.The results showed that GO was transformed to its reduced form(r-GO) by bacteria, and this process induced the release of Pb(Ⅱ) adsorbed on the GO surfaces. After 72 hr of exposure in an S. putrefaciens system, 5.76% of the total adsorbed Pb(Ⅱ) was stably dispersed in solution in the form of a Pb(Ⅱ)-extracellular polymer substance(EPS) complex, while another portion of Pb(Ⅱ) released from GO-Pb(Ⅱ) was observed as lead phosphate hydroxide(Pb_(10)(PO_(4))_(6)(OH)_(2))precipitates or adsorbed species on the surface of the cell. Additionally, increasing pH induced the stripping of oxidative debris(OD) and elevated the content of dispersible Pb(Ⅱ)in aqueous solution under the conditions of S. putrefaciens metabolism. These research results provide valuable information regarding the migration of heavy metals adsorbed on GO under reducing conditions due to microbial metabolism.