Kinetics of Ozonation of Typical Sulfonamides in Water

Biomed Environ Sci, 2011; 24(3): 255-260255Original ArticleKinetics of Ozonation of Typical Sulfonamides in Water*SUI MingHaol.", XING SiChul", ZHU ChunYan, SHENG Li', LU KeXiang' , and GAO NaiYun'1.State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science andEngineering, Tongji University, Shanghai 200092, China; 2. School of Mechanical and Instrumental Engineering,Xi 'an University of Technology, Xi 'an 710048, Shanxi, ChinaAbstractObjective To investigate the kinetic rate constants ozone and hydroxyl radicals towards two groups ofantimicrobials - sulfadiazine (SD) and sulfamethoxazole (SMX).Methods The solute consumption method was used to detect the rate constants of ozone alone withsulfadiazine and sulfamethoxazole, and tertiary butanol was selected as a scavenging agent and pH wasadjusted to 2.5 by adding orthophosphate buffers (OB); and the competition kinetics studyingmethodwith nitrobenzene as a reference was applied to measure the rate constants of hydroxyI radicalstowards sulfadiazine and sufamethoxazole, and pH was adjusted to 7.0 by ading OB.Results. The rate constants of SD and SMX with ozone alone were 261 mor' . dm3.s' and 303 moll .dm3 .st by calculating in low reaction system. The rate constants of hydroxyl radicals with SD and SMXwere 2.2x1010 molf' . dm' .s and 2.7x1010 mol' . dm'●s , respectively. Moreover, the rate constantsof hydroxyl radicals with SMX were found to have increased from 3.6x109 mol' . dm' .s' to 2.8x1010molrl. dm3.s' with pH value rising from 5.0to 7.8.Conclusion SMX and SD are both refractory to ozone oxidation alone, and are liable to be degraded byhydroxyl radicals, and the rate constants of SMX with the hydroxyl radical slightly increases with pH rise.Key words: Antibiotics; Sulfadiazine; Sulfamethoxazole; Kinetics; Rate constant; Ozone; HydroxylradicalsBiomed Environ Sci, 2011; 24(3);:255- 260 dol:10.3967/0895-3988.2011.03.008ISSN:0895-3988www.besiourmol.com(full text)CN: 11-2816/QCopyright ⑥2011 by China CDCINTRODUCTIONthey may be persistent in aquatic systems2.Recently, various antibiotics have been detected inntibiotics have been successfully and widelyground. water， surface water or even drinkingAused to control and treat human diseases, aswaterlt54. The long term exposure of human beingswell as in veterinary practice since theto antibiotics even in trace amount has arouseddiscovery of penicllin in 1929. However, antibioticsconcern since they have the potential to negativelyare unable to be completely metabolized in humanaffect non-target living organisms. The presence ofor animal bodies, and the treated subjects excrete aantibacterial agents in water represents the gravestfraction of the administered dose as the unalteredconcern owing to a possibility of leading, to theparent compounds or acetylated metabolites".development of bacteria with resistant genes'S andConsequently, these parts of antibacterial agents arethe development of allergenic responses!".eventually discharged into the environment whereSulfonamides (SAs), a series of drugs containing'The project was supported by Natural Science Foundation of China (Grant 50708067, 51078281), and the Foundationfor the Author of the National Excellent Doctoral Dissertation of China (Grant 2007B48)."Correspondence should be addressed to either SUl MingHao or XING siChu. Tel: 86-21-65982691. Fax:86-21-65986313. E-mail: suiminghao.sui@gmail.com (SUI MingHao) or中国煤化工。majoring inBiographical note of the first author: Sul MingHao, female, bmunicipal engineering, research field: advanced water treatment.TYHCNMHGReceived: May 14, 2010;Accepted: November 3, 2010256Biomed Environ Sci, 2011; 24(3): 255-260the chemical structure of sufanillic amide (Figure 1a),MATERIALS AND METHODSare a widely consumed class of administeredantibacterial agents in animal husbandry asReagents and Materialspreventive and therapeutic agents for bacterialThe SD and SMX standards were purchasedinfections due to their low cost, broad spectrum offrom National Institute for the Control ofactivity and effectiveness in growth promotion'toiPharmaceutical and Biological Products both withDue to their persistence in the environment antheir relatively high mobility, SAs have been found inthe purity of 99.9%. Nitrobenzene， sodiumwater sources at concentrations of tens to hundredsthiosulfate, potassium iodide and tert-butanol,obtained from Sinopharm Chemical Regent Co,of ng/L"I.To assure the safety of drinking water, seriouswere all of analytical grade and used withoutefforts have been made to remove the antibacterialfurther purification. Formic acid (>98.0% CNWagents from the water source or drinking water inTechnologies GmbH) and acetonitrile(CNW Technologiesrecently years. Ozone, due to its high oxidationGmbH) were of HPLC grade. All solutions werepotential, has been proven to be effective toprepared with water purified by a Millipore Mili-Qdegrade or remove the organic pollutants in water. ItUV Plus system (R=18.2 MQ.cm).AlI glassware were dipped in the acidicis suggested that ozone.. could also degradepotassium dichromate solution overnight, and thenpharmaceuticals in waterl12-3). Nevertheless, till now,rinsed with tap water and pure water repeatedly.few researches on the kinetics of ozonation ofantbatrial agents have been reported, and as a Experimental Equipmentresult the practical application of ozonation for thedegradation of these agents has stagnated.The ozonation experiments were carried out inTwo groups of SAs, sulfadiazine (SD), andsemi-continuous mode. The cylindrical reactorsulfamethoxazole (SMX)， were chosen as model(Figure 2) was made of glass with the insideantibacterial agents (Figure 1b and Figure 1c)diameter 50 mm, length of 700 mm, which wasThe present study is aimed to investigate theenclosed with sintered paper to avoid threaction rate constants of ozone and hydroxyllight-decomposition effect. Ozone was generated byradicals (the decomposition product of ozone ina corona discharge ozone generator (DHX-1, Harbinwater) towards SAs, and meanwhile to observe theJiujiu Electrochemistry Technology Co. Ltd. China)effect of pH on the rate constants.using air as feed gas. The ozone gas concentrationwas 0.45 mg/min with the constant flow rate of 400mL/min at 293 K. The ozone was introduced into theH,N--NH2reactor through a porous titanium sand plate laid atHN--NH(6)①|4H,C-QHi品(cFigure 2. Schematic diagram of ozonationFigure 1. Thchemical structuresystem.①Ozonation reactor ②Aerationsulfonamides.(a) sulfanilic amide; (b)plate③Ozone generator❹Sampling pointsulfadiazine; (C) sulfamethoxazole.中国煤化工"TYHCNMHGBiomed Environ Sci, 2011; 24(3): 255-26025750 mm height higher than the bottom. The off gasO3+HO;→*OH+O; +02(2was adsorbed by the potassium iodide solution.kz =2.8x10*M's1Before the experiment operation, 500 mL of pure03+SAs→SAs-0; .(3water was first added into the reactor, and thenozonized for 5.5 min, which was proven to reach the°OH+ SAS + SAs" +H,0/OH~(4constant ozone concentration in aqueous solution inThe rate of depletion of SAs therefore is thethe pre-test. The SA solution then was immediatelyconsequence of its second order parallel reactionadded into the ozonated solution with the volume ofwith dissolved ozone and with hydroxyl radicals:less than 5 mL water samples were withdrawn at_d[SAs]l= K,s[SASsS[O,I4k,o,h, [SAsI["OH] (5)specific intervals for ozone concentrationdtmeasurement and SA qualfication. For the samplesWhere ko, se and k.ous stand for the rateused for SA qualification, sodium thiosulfate wasconstants of ozone with SAs and hydroxyl radicalsused to quench further oxidation.towards SAs, respectively. And [SAs] stands for theAnalytical Methodconcentration of SAs, [03] stands for the concentrationof ozone, [OH] stands for the concentration ofA High Performance Liquid ChromatographyhydroxyI radicals, and t stands for the reaction time.system (HPLC, Waters UV/Visible 2489， WatersThe kinetics of a gas-liquid ozonation processe2695 Separation Module, Welch Materials, Inc.)depends on the relative rates of physical absorptionand a 150 mm x 4.6 mm C18 5 um reversed-phaseand chemical reaction. The kinetic regime iscolumn (Ultimate AQ-C18，Hypersil Gold, Supelco,determined by the Hatta number, which representsInc, Bellefonte, PA) were used to detect SD, SMX,the maximum rate of chemical reaction relative toand nitrobenzene. SD, SMX, and NB were analyzed atthe maximum rate of mass transfer. For a second265 nm with the mobile phase of 0.1% formic acidorder reaction the Hatta number is:and acetonitrile (70:30, ratio by volume). The flowHa,= k.D.Cc(6rate was 1 000 uL/min, and the retention times fork;SD, SMX, and NB were 3.5, 5.2, and 12.3 min, respectively.In which kz is the decomposition rate constant ofThe concentrations of ozone in the gas and aqueoussolution were determined by the iodometric titrationozone, DA is the diffusivity of ozone in water, CBb ismethod and indigo method, respectivelypHthe function of chemical and mass transfer of thewas adjusted by phosphate buffer and monitored byorganic compound.Metrohm pH Meter (Switzerland).When Haz < 0.3, the reaction belongs to the slowspeed reaction system; 0.3 < Ho2 <3, the reactionKinetics Studying Methodbelongs to the medium speed reaction system; Haz >3,the reaction belongs to the fast speed reaction system.The solute consumption method and competitionkinetic methodlb切 were used to study the kineticsKinetics of Ozone Molecule with SAsof ozone molecule and hydroxyl radicals with SAs.To ensure that the ozone molecule acted as theNitrobenzene was chosen as reference compound.The rate constants of nitrobenzene with ozone moleculesole oxidant, pH of the solution was adjusted to 2.5,and hydroxyl radicals were reported to be 0.09土0.02and the 25 mg/L of tert-butanol was added tomor. dm' .s and 3.9x 10 molr'. dm'5141819].prohibit the hydroxyl radicals reaction. During theozonation process, ozone was continuously purgedRESULTSinto the solution to keep the ozone concentrationconstant; therefore the reaction could be simplifiedIn aqueous solution, ozone will be decomposedas the pseudo-first order reaction. It was alsointo hydroxyl radicals (OH) (see Equation 1-2indicated that the reaction belonged to the slow(unless under strong acidic pH condition), then inspeed reaction system with Haz < 0.1. Accordingly,ozonation SAs should be oxidized by ozone ancthe Eq. 5 can be rewritten as fllows:hydroxyl radicals will react with SAs in water (see(7Equation 3-4).[SAs]。O,0H~ -→HO2 +02(1)Here. [SAsla and [SAs1. renresent the initial and tk = 70Mr~'s-中国煤化工the apparentTYHCNMHG258Biomed Environ Sci, 2011; 24(3): 255-260rate constant (k' = kos,s[031), the data represented calculated based on Equation 7, which is diferentin Figure 3 and Figure 4 alw the calculation offrom the ozone alone system.apparent rate constant of ozone molecule with SAs,which yields 261 mor'. dm .s and 303 mor'. dm'Ha.=↓(+10+)→(8for ko3.sD and ko3.smw respectively, which are relativelylow constants for the direct ozonation reaction. AsIn which km is the decomposition rate constantis customary， the boundaries represent 95%of ozone, CH2o2 is the concentration of hydrogenconfidence intervals. To further verify the accuracyperoxide, Do3 is the diffusivity of ozone in water, K isof the experimental system, the kinetic of ozone the aqueous transfer cofficient. From Equation 7,molecule oxidization of nitrobenzene was also the Hatta number is the function of solution pH and，studied in the same experimental condition with thethe concentration of H2O2. Under the condition ofSAs tests. The value obtained in this work for thepH 7.0 and with the concentration of H2O2 1 mmol/L,the Hatta number equals to 0.006, and it belongs torate constant of ko, Nitrobenzene was 0.12 moldm'. s , which indicated that the kinetic data forthe slow speed reaction system. Under this pHcondition, hydrogen peroxide will be decomposedozonation of SAs were creditable.into HO2, and then the reactions occurring in the5.0 .O3/H2O2 oxidation systems are shown as Equation9-11, while the reaction shown in Equation 1 could; 4.(= 0.4709x.be ignored due to its low reaction rate constant.3.0R2=0.993+ 0.067H2O2←→0HOz +H*(9pK。=. 11.82.HO2 +O3→HO2.+ Oz(10)kg= 2.2x10 mor'. dm'.s'1.03+H2O2-→H2O + 202(11)0.0 .ka <102 mol'. dm3-s'0..04.8.010.0As recommended by von Gunten and Elovitz, aFigure 3. Pseudo first order kinetic plot ofRet value can be utilized to describe the molarconcentration ratio of' 'OH to ozone duringoxidation reaction of sulfadiazine by ozonealone.ozonation process as described in Equation 1220 ,and under different reaction conditions, including pH,5.0 1alkalinity, DOC, temperature and others, the Rtvalue is in the range of 10° -104. Consequently,.0 ty= 0.5456x - 0.398the concentration of SAs and NB at a specificR'= 0.9967reaction time (t) can be described by Equation 13-14.Then the reaction rate constant of SAs could bederived from Equation 15-16. Through ftting the2.0 1experimental data shown in Figure 5 and Figure 6.0 -with the above mathematical model, the rateconstants of hydroxyl radicals with SD (korso) andSMX (kousod under pH 7.0 are 2.2 x 10" mor'l . dm'.s'0.02.(4.06.(10.0 12.0and 2.7x 10^0 mor'. dm3.s', respectively.f["OH]dtFigure 4. Pseudo first order kinetic plot of(12)oxidation reaction of sulfamethoxazole byf[o,)dtozone alone._InIAS),=kowsnRa [],)(13)Kinetic of Hydroxy/ Radicals with SAs(SAs]oIn this experiment, the O3/H2Oz system was used-(14)[NB]。to represent the hydroxyl radical reaction process,and pH was adjusted to 7.0 with phosphorous buffer.n [SAs, /r [NB],(15)In O3/H2O2 system, the Hatta number value is中国煤化工MHCNMHGBiomed Environ Sci, 2011; 24(3): 255-260259Kouse x(I[SAsI. /In[N8B],)(16)DISCUSSION[sAsh" [NB]From the experimental data, it can beconcluded that sulfadiazine and sulfamethoxazoley=0.1762x + 0.3077are more liable to be oxidized by hydroxyI radicals,R'=0.9338as compared with ozone alone oxidation. Althoughozone has strong oxidative ability for its high里0.6oxidative potential of 2.07 V, it is inferior to04两hydroxyl radicals. Hydroxyl radicals are one of themost reactive free radicals and are deemed as oneof the strongest_ oxidants with the oxidative0.potential of 2.85 V48. And ozone, being a kind ofpowerful oxidant, is highly selective and reacts0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0slowly with some organic compounds, and theLn([SD]/SDI)reaction rate constants are typical in the range ofko3= 1.0- 10' mol' . dm' . s ; while hydroxyI radicalsFigure 5. The relationship between In(S]/[D])react non-selectively and immediately (koH= 10* -and In([NB]/[NB]o).1010 molr'. dm3 .s") with organic compoundsh1o.20l.The reaction of ozone with aromatic ring systemis highly electrophilic and selective, and the benzene0.8y=0.146x + 0.3085ring is relatively reactive. From the structure ofR-0.9834sulfanilamide (Figure 1)， -NH2 serves as an0.6electron-donor group, which results in thepromotion of the reaction activity of benzene rings 0.4with ozone; while -SO2 is an electron-withdrawinggroup, and the weakening of the electron density ofthe benzene ring will lead to the prohibition of the0.0 .reaction activity. Based on the experimental data, it.5 1.0 1.52.0 2.5 3.0 3.5 4.0is deduced that the weakening effect may beLn(SD/SD)b)stronger than the promoting effect. For SD and SMX,the methyl group on SMX is relatively reactive andFigure 6. The relationship betweenhas electron donor effect, so SMX reacts faster withn((SMX]/[SMX]o) and In([NB]/[NB]o).ozone than SD.For the process of oxidizing SD and SMX withEffect of pH on Rate Constants of Hydroxy/ Radicalshydroxyl radicals, the fast reaction rate constantswith SAsshould be attributed to the unselective reactionThe rate constants of hydroxyl radicals with SAspathway and the high oxidizing oxidative ability ofwere observed under diferent pH conditions usinghydroxyl radicals. Further, the hydroxyl radicals mayphosphate as buffer, and the calculating results wereinitiate the inert hydrogen on benzene ring andsummarized in Table 1. The rate constant obviouslygenerate some organic radicals by dehydrogenation2,augmented with pHincrease, though in aslight way.the formed organic radicals may participate in theTable 1. Rate Constants of HydroxyI Radical Reactionfurther oxidizing of the SD and SMX, which may alsounder different pH Conditionscontribute t its fast reaction. The effect of pH onthe reaction rate constants of hydroxyl radicals withRate Constants (mor'. dm'.s)SAs is due to the fact that the deprotonated SMZpHSDRSMXR'species, known to have higher reactivity towards5.03.6x10'0.9681.6x10ozone compared to protonated species" , becomes5.1.2x10"00.9892.0x10'0predominant as the pH increases. In addition, from6.51.7x1000.9732.3x10*00.988Equation 1 and 9, it can be seen that more hydroxyl7.2.2x10100.9932.7x10*90.983radicals willhe goneratad with the increase of pH. As2.8x10*00.9964.0x10"00.994repor中国煤化工sition rate ofYHCNMHG260Biomed Environ Sci, 2011; 24(3): 255-260ozone will increase by two orders of magnitude2008; 1200, 1455.10. Sukul P, Lamshoft M, Zoihlke s, et al. Sorption and desorptionwhen pH increases by one unit from pH 4.0.of sulfadiazine in soil and sil-manure systems. Chemosphere,2008; 73, 1344-50.CONCLUSIONS11.Sun L Chen LG, sun x, et al. Analysis of sulfonamides inenvironmental water samples based on magnetic mixedhemimicelles solid-phase extraction coupled with HPLC-UVUsing solute consumption and competitivedetection. Chemosphere, 2009; 77, 1306-12.kinetic methods, the kinetics of ozonation of SAswere studied. It is evident that sulfadiazine anpharmaceuticals, endocrine disruptors and pesticides duringsulfamethoxazole are refractory by ozone aloneoxidation, but are prone to be oxidized by hydroxylendocrine-disruptor，pharmaceutical, and personal careradicals. 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