Performance of mesophilic anaerobic granules for removal of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from aqueous solution

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<ul><li><p>Journal of Hazardous Materials 179 (2010) 526532</p><p>Contents lists available at ScienceDirect</p><p>Journal of Hazardous Materials</p><p>journa l homepage: www.e lsev ier .com</p><p>Perform fooctahy e (</p><p>Chun-jia onga Department ob Faculty of Eng 0A2c Sino-Canada niversid Department o , PR Ch</p><p>a r t i c l</p><p>Article history:Received 11 NReceived in reAccepted 6 MaAvailable onlin</p><p>Keywords:Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(HMX)DegradationMesophilic anaerobic granulesMetabolic inhiEnrichment cu</p><p>erobindere of rcontreare</p><p>HMX could be biodegraded by anaerobic granules as the sole substrate. After 16 days of incubation,99.04% and 96.42% of total HMX could be removed by 1g VSS/L acclimated and unacclimated granules,respectively. Vancomycin, an inhibitor of acetogenic bacteria, caused a signicant inhibition of HMX bio-transformation, while 2-bromoethanesulfonic acid, an inhibitor of methanogenic bacteria, only resultedin a slight decrease ofmetabolic activity. The presence of the glucose, as a suitable electron donor and car-bon source, was found to enhance the degradation of HMX by anaerobic granules. Our study showed that</p><p>1. Introdu</p><p>Octahydconsiderablmanufacturcompoundity and detoas 2,4,6-trintriazine (RDtesting, andcontaminatenergetic chand terrestrnervous sysby U.S. EPAincreased bgreat quantrisk for envi</p><p> CorresponE-mail add</p><p>0304-3894/$ doi:10.1016/j.bitorlture</p><p>sulfate had little adverse effects on biotransformation of HMX by anaerobic granules. However, nitratehad signicant inhibitory effect on the extent of HMX removal especially in the initial period. This studyoffered good prospects of using high-rate anaerobic technology in the treatment ofmunitionwastewater.</p><p> 2010 Elsevier B.V. All rights reserved.</p><p>ction</p><p>ro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is ofe industrial importance as themain rawmaterial in theing of explosives and propellants [1]. As a heterocyclicwith eight-membered ring, HMX shows higher stabil-nation power than other conventional explosives, suchitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-X). Large amounts of HMX waste from manufacturing,demilitarizing processes have resulted in widespreadion of the environment [2]. The toxicity caused by suchemical has been well documented in different aquaticial species [3]. HMX has adverse effects on the centraltem, and has been classied as a class D carcinogen[4]. Recently, concerns over HMX contamination haveecause this explosive has been produced and used inities during the past decades andpresented a signicantronment and human health. There is an urgent need for</p><p>ding author. Tel.: +1 306 585 4095; fax: +1 306 585 4855.ress: gordon.huang@uregina.ca (G.-h. Huang).</p><p>effective and safe treatment strategies for such toxic compound.Biological removal of explosives has been proven feasible in</p><p>many laboratory studies. Although HMX and RDX have simi-lar chemical structures, HMX, with the unique heterocyclic ringand stable crown conformation, has shown more resistance tobiological and chemical degradation than RDX [5]. In several pre-vious studies, biodegradation of explosives has been demonstratedunder aerobic conditions [5,6]. But these compounds have oftenbeen shown to be more recalcitrant under oxygen-enriched con-ditions compared to oxygen-limited environments [7]. As a moreprominent alternative, biodegradation of HMX under anaerobiccondition has been extensively reported [710]. The likely mecha-nism of HMX biotransformation was proposed to be similar to thesequential reduction process of RDX and TNT [11]. Although manyresearches onHMXeliminationhavebeen reportedbefore, particu-larly on aspects relating to degradation pathways in pure bacterialcultures, investigations on anaerobic HMX removal in bioreactorsystems are relatively limited in scope.</p><p>Anaerobic granules are widely used in various high-rate anaer-obic treatment systems, such as upow anaerobic sludge blanket(UASB) and expanded granular sludge bed (EGSB) reactors. Theseaggregates may degrade organic pollutants through synergetic</p><p>see front matter 2010 Elsevier B.V. All rights reserved.jhazmat.2010.03.035ance of mesophilic anaerobic granulesdro-1,3,5,7-tetranitro-1,3,5,7-tetrazocin</p><p>ng Ana,b, Yan-ling Hea, Guo-he Huangb,c,, Yong-hf Environmental Engineering, Xian Jiaotong University, Xian 710049, PR Chinaineering and Applied Science, University of Regina, Regina, Saskatchewan, Canada S4SResearch Academy of Energy and Environmental Studies, North China Electric Power Uf Environmental and Chemical Engineering, Xian Polytechnic University, Xian 710048</p><p>e i n f o</p><p>ovember 2009vised form 10 February 2010rch 2010e 12 March 2010</p><p>a b s t r a c t</p><p>The performance of mesophilic anatetrazocine (HMX) was investigated uthat anaerobic granules were capablBoth biotic and abiotic mechanismsmesophilic conditions. Adsorption app/ locate / jhazmat</p><p>r removal ofHMX) from aqueous solution</p><p>Liud</p><p>ty, Beijing 102206, PR Chinaina</p><p>c granules to degrade octahydro-1,3,5,7-tetranitro-1,3,5,7-various conditions. The results of batch experiments showedemoving HMX from aqueous solution with high efciency.ibuted to the removal of HMX by anaerobic granules underd to play a signicant role in the abiotic process. Furthermore,</p></li><li><p>C.-j. An et al. / Journal of Hazardous Materials 179 (2010) 526532 527</p><p>Table 1Batch experimental conditions.</p><p>Batch Sludge type Sludge concentration Additional substrate</p><p>HMX as sole substrate Acclimated and unacclimated 1 and 2g VSS/L /Effect of me g VSSEffect of add g VSSEffect of add g VSS</p><p>interactionslayered grabeing exporate anaeroactivity of aconventionthat high-raof some poHowever, dstudies havogy of HMXhigh-rate recleanup of c</p><p>In thisbic granuleBatch testsboth physicremoval. WHMX undeto developfurther achwastewater</p><p>2. Materia</p><p>2.1. Biomas</p><p>The anareactor treation for 6 yesludge aggreters betweto remove tin the batch</p><p>2.2. Medium</p><p>Anaerobanaerobic csisted of th(0.2), MgSOments, withSantos [14](1.1), ZnCl2O244H2O ((0.05), Na2buffered wigranules wcentration fpH in the re</p><p>2.3. Abiotic</p><p>In orderthe removaconditionsacclimation</p><p>al prcclims. Hevingby ined Ht wasmeanulper l00mbottluritydarkas 16ermitionwdsord cruescenma euentdditiyingHMX</p><p>odeg</p><p>ch bbic ceswtrati. The, excect oe batavedabioth exp. AddMXmittwitcont</p><p>alyt</p><p>X wa(HPLSA), w50mconsitabolic inhibitors Acclimated 1itional electron donor Acclimated 1itional electron acceptors Acclimated 1</p><p>among a variety of bacterial groups. Meanwhile, thenular structure can also protect anaerobic bacteria fromsed directly to inhibitory and toxic compounds. High-bic reactors, based on the well settleability and highnaerobic granules, have many advantages over otheral processes [12]. Previous studies have demonstratedte anaerobic systems were effective for the treatmentlycyclic and heterocyclic aromatic hydrocarbons [13].espite this prevalence and concern in the literature, fewe focused on thehigh-rate anaerobic treatment technol-pollutant. With large amounts of contaminated water,actor treatment would be advantageous for eld-scaleontaminated water and soil.paper, we investigated the performance of anaero-s for HMX degradation under mesophilic conditions.were conducted to determine the contributions ofochemical and biological processes involved in HMXe studied the ability of anaerobic granules to degrader various conditions, so that the data can be usedanaerobic granule-based bioreactor technology, andieve complete removal of explosive compounds from.</p><p>ls and methods</p><p>s sources</p><p>erobic granules were taken from a mesophilic UASBting food wastewater. The reactors had been in opera-arswith an organic loading rate of 5 kg COD/(m3d). Theegates were black and almost spherical, with the diam-en 0.45 and 2mm. The sludge sources were elutriatedhe ne particles and residual carbon source before useexperiments.</p><p>and growth conditions</p><p>ic granules were grown in serum bottles under strictlyonditions. The basal medium used for the study con-e following components (mM): NH4Cl (1.2), K2HPO447H2O (0.05), CaCl22H2O (0.05) and 1mL trace ele-composition modied from the descriptions of dos</p><p>, containing per litre (mM): H3BO3 (0.8), FeCl36H2O(0.3), MnCl24H2O (0.5), CuCl22H2O (0.03), (NH4)6Mo70.02), AlCl36H2O (0.03), CoCl26H2O (1.7), NiCl26H2OSeO35H2O (0.11), EDTA (1.6) and HCl 36% (0.02),th 70mM NaHCO3 at a pH of around 7. The anaerobicere acclimatized with gradual increasing of HMX con-or six months at 35 C under anaerobic condition. Theactor was adjusted to 6.87.2 using NaHCO3.</p><p>removal experiments</p><p>chemicwith atrationautoclaaddedcontainsolvenaqueouobicgr(VSS)then 1serumhigh-pin thetem wfor detin soluHMX aout anwithdby Sipsubseq[17]. Aby varinitial</p><p>2.4. Bi</p><p>BatanaeroGranulconcenimentsculturethe effand thAutoclunderfor eacresultswith Hwere oushedclaved</p><p>2.5. An</p><p>HMraphy(CA, Uumn, 2phaseto estimate the contribution of abiotic mechanisms tol of HMX, batch assays were performed under sterilizedto avoid the inuence of HMX biodegradation. Sinceprocess may cause potential changes in physical and</p><p>rate of 1.0mmonitoredultravioletodically viasterile, 0.2-/L 0.17mM Vancomycin and 50mM BESA/L 1.25mM Glucose/L 2mM Na2SO4 and 3mM NaNO3</p><p>operties of biomass [15], abiotic tests were conductedated and unacclimated granules at different concen-at-treated form of anaerobic granules was prepared bythe sludge at 120 C and 110kPa for 30min. HMX wasjecting a small volume of acetone stock solution, whichMX, into the empty 250mL serum bottles. The organic</p><p>s removed by evaporation prior to the addition of thedium. Autoclaved acclimated and unacclimated anaer-es, at concentrationof1and2gvolatile suspendedsolidsiter, were weighted into the bottles respectively, andL of basal medium as described above was added. Theeswere closedwith butyl rubber stoppers, ushedwithnitrogen and incubated in a rotary shaker (120 rpm)at 35 C. The initial concentration of HMX in the sys-.2M. Blank controls were incubated without sludgening abiotic HMX conversions. The HMX concentrationasdetectedafter 16days. For thepurposeofmeasuring</p><p>bed by anaerobic granules, the wet granules were takenshed by pushing them through a syringe and needledingdiameterunder anaerobic conditions, asdescribedt al. [16]. Residual HMX concentrations in granules foranalysis were determined using U.S. EPAMethod 8330onally, batch adsorption experiments were also studiedthe dose of granular sludge from 0.5 to 5g VSS/L on anconcentration of 16.2M for a contact time of 24h.</p><p>radation batch studies</p><p>iodegradation experiments were performed underonditions,with the sameproceduresasdescribedabove.ere added to 250mL anaerobic serumbottles. The initialon ofHMX in the solutionwas 16.2Mfor all the exper-medium composition was similar to that in growthept MgSO47H2O was omitted in the assays to studyf electron acceptors. Four series of tests were conductedch experimental conditions are summarized in Table 1.controls were used to determine the removal of HMXic conditions. Batch tests were performed in triplicateerimental condition to ensure the reproducibility of theitionally, in the series for detecting gas end productsas the sole substrate, nitrogen-contained compoundsed from themedium. The anaerobic culture bottleswerehhelium to removeoxygen.HMXunamended and auto-rols were used to compare the results.</p><p>ical methods</p><p>s analyzed using high-performance liquid chromatog-C). The HPLC instrument, a Varian 210 HPLC systemas equipped with two solvent pumps and a C-18 col-m in length and 4.6mm in internal diameter. A mobilesting of methanol/water (50:50, v/v) was used at a ow</p><p>L/min. The explosive compounds were continuously</p><p>with a Model 320 programmable multi-wavelengthdetector set at 254nm. Samples were collected peri-syringe and needle. All samples were ltered throughm-pore-size PTFElters before injection. Gas products</p></li><li><p>528 C.-j. An et al. / Journal of Hazardous Materials 179 (2010) 526532</p><p>Fig. 1. Remov</p><p>were also asystem coudetail [18,1son with stastandard m</p><p>2.6. Chemic</p><p>HMX wResearch Ior greater.(mononitroUSA). HPLCCo. (NJ, USAwere obtainchemicals u</p><p>3. Results</p><p>3.1. Abiotic</p><p>The remare illustratpercentagewere 92.76samples, thfor acclimatmain part oFurthermorremainingHgranules, w9.28% and 8tively. Thescould causeremaining Hand unacclHMX loss w</p><p>Physicocand oxidatilutants in wof HMX waabiotic remtem. Furthewere obseraqueous so</p><p>dsorp.</p><p>tratiin mal reby</p><p>peratpreitsvedncey 4.8tionstemial fonaerompat grct stlreadoreonce iimatial chhe inremadsotion of HMX with varying sludge dose. The equilibrium dataeentted into the linearizedFreundlichadsorption isotherm,al of HMX by anaerobic granules under different abiotic conditions.</p><p>nalyzed for N2, N2O, CH4 and CO2 by Agilent 6890 GCpled to thermal conductivity detector as described in9]. Identication of the gas was conrmed by compari-ndard reference. VSS was analyzed according to APHAethods [20].</p><p>als</p><p>as obtained from the Xian Modern Chemistrynstitute (Xian, China) and had a purity of 99%Octahydro-1-nitroso-3,5,7-trinitro-1,3,5,7-tetrazocineso-HMX) was obtained from SRI International (CA,grade methanol was obtained from Fisher Scientic). Vancomycin and2-bromo-ethanesulfonic acid (BESA)ed from Sigma Chemical Company (MO, USA). All othersed were of reagent grade quality or higher.</p><p>and discussion</p><p>removal of HMX with anaerobic granules</p><p>aining percentages of HMXat various abiotic conditionsed in Fig. 1. In the aqueous solution, theHMX remainings with 1g VSS/L acclimated and unacclimated granules% and 93.15%, respectively. In the corresponding sludgee HMX remaining percentages were 5.06% and 5.79%ed and unacclimated granules. It was obvious that thef remaining HMXwas in solution, rather than in sludge.</p><p>Fig. 2. Agranules</p><p>concenthe machemiccausedwell-o</p><p>In a76% ofautoclaadhereimateladsorptest sypotent[13]. Aity as cfact thcompabeen acles. Mdiffereunacclpotent[15]. Tabiotic</p><p>Thecentrahavebe, when the sludge concentrations were 2g VSS/L, theMX in solutiondecreased in the testswithbothkindsofhile HMX remaining percentages in sludge increased to.97% for acclimated and unacclimated granules, respec-e results showed that autoclaved anaerobic granulesslight removal of HMX. No signicant differences ofMXwere obtained between the series with acclimated</p><p>imated granules. Additionally, a negligible amount ofas detected in sludge free experiments.hemical mechanisms, such as adsorption, hydrolysis,on, often have important effects on the removal of pol-astewater treatment system. In our study, the decreases observed under various sterile conditions, indicatingoval may contribute to the deduction of HMX in sys-rmore, although different distribution patterns of HMXved in these experiments, the total amounts of HMX inlution and in sludge were all above 96% of initial HMX</p><p>which is of</p><p>ln(</p><p>x</p><p>m</p><p>)= l</p><p>where x is(mol), mis the equiland n are ctionprocessThe result slatedbyFremore thansludge werAs for the uwere 0.18nated that sis limited. Ution isotherms for HMX by acclimated and unacclimted anaerobic</p><p>on for each trial (Fig. 1). Therefore, it is assumed thatechanism for abiotic HMX removal is adsorption andduction is negligible. Addi...</p></li></ul>

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