Influence of reaction conditions on the ozonation process

Transcription

1 Ifluece of reactio coditios o the ozoatio process Leka Sumegová, Já Derco, Michal Melicher Faculty of Chemical ad Food Techology, Slovak Uiversity of Techology, Radliského 9, Bratislava, Slovakia leka.sumegova@stuba.sk Abstract: This paper is focused o the ifluece of graulated activated carbo (GAC) ad zeolite as catalysts as well as iflueces of temperature ad ph o the ozoatio process. From obtaied results it ca be cocluded that the additio of graulated activated carbo ad zeolite to model wastewater has a positive effect o the efficiecy ad degradatio rate of methylee blue oxidatio with ozoe. The highest oxidatio efficiecy was observed i the alkalie ph rage for which radical reactio mechaism of ozoe is characteristic. From the results obtaied durig the study of the effect of temperature o the ozoatio process it follows that both the efficiecy ad the rate of oxidatio of methylee blue grow with icreasig temperature. Keywords: ifluecig factors ad variables, kietics, methylee blue, ozoatio Itroductio The ozoatio process is oe of possible methods for removal of resistat, toxic ad priority substaces. Ozoatio process is expesive, both i capital as well as i operatioal costs. Thus combiatios of ozoe with other processes are ivestigated i order to reduce the operatig cost. A importat role i the ozoatio process plays the temperature. It iflueces solubility of ozoe i water. O the temperature depeds also the value of the rate costat of the reactio. I compariso to oxyge, ozoe reacts with may substaces also at ormal temperature. Aother factor ifluecig the efficiecy of ozoatio process is ph. The ph value iflueces the mechaism of the reactio ad also the type of created products. At low ph, direct reactios are prevailig. The usual ed products of direct reactios are carboxylic acids ad aldehydes. At higher ph values, radical reactio mechaism is domiatig (Dřímal, 1997). The idirect reactio mechaism is the most frequet. Decompositio of ozoe to hydroxyl radicals is typical for these oselective reactios. The presece of a catalyst also iflueces sigificatly the mechaism ad efficiecy of the ozoatio process. Catalytic ozoatio is a effective procedure for removal of slowly degradable orgaic substaces from water also i the presece of scavegers which reduce the effectiveess of pollutio degradatio process (Peixoto et al., 2009). Catalytic ozoatio ca be carried out i two ways, either as homogeeous, where suitable catalysts are metal ios or as a heterogeeous, where metal oxides ad active carbo are used as appropriate heterogeeous catalysts. Use ozoatio with activated carbo sigificatly improves the coversio of total orgaic carbo, compared to aloe ozoatio ad the sorptio o activated carbo (Alvarez et al. 2009). Time of ozoatio is importat for optimizig the amout of ozoe delivered. Sufficiet time is importat for trasfer of ozoe from gas to liquid phase. Durig optimal cotact time ehaced biodegradability of pollutats ca be achieved, which ca reduce the dosage of ozoe because the mieralizatio ca be achieved biologically (Arsla-Alato, 2003). Materials ad methods I Fig. 1, the scheme of laboratory ozoatio equipmet is show. Experimets were carried out i a reactor with the volume of 500 ml. Ozoe was produced from oxyge i a laboratory ozoe geerator. The measuremets were performed with a model wastewater which cotaied 200 mg.l 1 of methylee blue (MB). A mixture of oxyge ad ozoe was itroduced ito the ozoatio reactor through a porous frit ad it was mixed with model wastewater by a magetic stirrer. The reactor was filled with model wastewater to volume of 450 ml. Experimets were carried out at a costat flow of oxyge 40 l.h 1 ad costat output of the geerator of ozoe equal to 20 % of the maximum power. This geerator power correspods to the ozoe productio 5 g.h 1. The costat flow of oxyge was maitaied usig a laboratory flowmeter. Cocetratio of ozoe i the gas phase at the ilet ad outlet of the reactor was measured usig a laboratory ozoe UV detector. Aalytical methods The cocetratio of methylee blue was determied spectrophotometrically at the wavelegth 660 m. Sulfuric acid was used for adjustmet 168 Acta Chimica Slovaca, Vol. 6, No. 2, 2013, pp , DOI: /acs

2 ph of samples to 3. For adjustmet to ph = 11 sodium hydroxide was used. Experimetal data were treated usig kietic model of zero (1), the first (2) ad secod (3) orders (Derco, 2009): S t = S 0 k 0 t (1) S t = S 0 exp( k 1 t) (2) S t = S 0 /(1 + S 0 k 2 t) (3) where S 0 [mg.l 1 ] is the iitial cocetratio of substace measured at time 0, S t [mg.l 1 ] is the cocetratio of the substace beig studied at time t ad k 0 /mg.l 1.mi 1, k 1 /mi 1 ad k 2 /mg 1.l.mi 1 are the rate costats for kietic of zero, first ad secod orders. Results ad discussio 1 source of oxyge, 2 ozoe geerator, 3 supply of a mixture of ozoe ad oxyge to the reactor, 4 reactor with model water, 5 ozoe detector, 6 magetic stirrer Fig. 1. Schematic diagram of the experimetal apparatus. Fig. 2 shows the time depedece of the measured ad calculated cocetratios of MB durig ozoatio without catalyst, ozoatio with the additio of GAC ad ozoatio with the additio of zeolite. 71 % efficiecy degradatio of MB was achieve after 10 mi ozoatio. 76 % efficiecy degradatio of MB was achieved by ozoatio with the additio Fig. 2. Time depedeces of experimetal ad calculated values of MB cocetratio. Tab. 1. The values of the rate costat ad of the correlatio coefficiet for the idividual orders of reactio. uits O 3 O 3 + GAC O 3 + zeolite k R 2 YX k R 2 YX k R 2 YX 0 [mg.l 1.mi 1 ] [mi 1 ] [mg 1.l.mi 1 ]

3 of zeolite ad 78 % effeciecy of MB was measured by the ozoatio with the additio of GAC after 10 miutes of both processes. From the results it follows that the presece of a catalyst icreases speed ad efficiecy of the ozoatio process. Zhag et al (2009) achieved 95.4 % efficiet oxidatio MB after 40 miutes ozoatio with the additio of activated carbo. Values of the rate costats ad the correlatio coefficiets obtaied for kietic equatios (1) to (3) ad the experimetal data resulted from performace of ozoatio without catalyst, ozoatio with the additio of GAC ad ozoatio with the additio of zeolite. They are listed i Tab. 1. From comparisom of the correlatio coefficiets for idividual reactio orders it follows that i the case of ozoatio without catalyst ad ozoatio with the additio of GAC the best fit betwee the experimetal ad calculated data was achieved for the first order kietics. I the case of ozoatio with the additio of zeolite the best descriptio of oxidatio of MB correspods to the secod order kietics. The ext series of experimets was focused o the study of ph ifluece o the efficiecy of ozoe utilizatio. Experimets were performed at ph = 3, ph = 7, ad ph = 11. I Fig. 3, the time depedeces of the measured cocetratios of methylee blue for ozoatio carried out at adjustet ph values are show. The highest decrease i the cocetratio of methylee blue was observed after 10 mi of ozoatio. For ozoatio at ph = 3, 66 % efficiecy of MB degradatio was achieved after 10 mi. 71 % efficiecy degradatio of MB was achieved durig 10 mi ozoatio at ph = 7 ad 90 % efficiecy durig 10 mi ozoatio at ph = 11. From these results it follows that the highest efficiecy was observed i the alkalie regio. From compariso of the values of correlatio coefficiets (they are listed i Tab. 2 for the idividual reactio kietic orders) it follows that experimetal data measured durig ozoatio at ph = 3 ad ph = 7 are best described by the first order reactio kietics. I the case of ozoatio carried out at ph = 11 the best descriptio of the experimetal data correspods to the kietics of the first order. Very good fit was obtaied also by usig the secod order kietic model. The effect of temperature o the ozoatio process was also studied. Ifluece of temperature o the Fig. 3. Time depedeces of experimetal ad calculated values of MB cocetratio durig ozoatio at diferet ph values. Tab. 2. The values of the rate costat ad of the correlatio coefficiet for the idividual orders of reactio. uits ph = 3 ph = 7 ph = 11 k R 2 YX k R 2 YX k R 2 YX 0 [mg.l 1.mi 1 ] [mi 1 ] [mg 1.l.mi 1 ]

4 Fig. 4. Time depedeces of experimetal ad calculated values of MB cocetratio durig ozoatio performed at differet temperatures. Tab. 3. The values of the rate costat ad of the correlatio coefficiet for the idividual orders of reactio. uits 7 C 15 C k R 2 YX k R 2 YX 0 [mg.l 1.mi 1 ] [mi 1 ] [mg 1.l.mi 1 ] Tab. 4. The values of the rate costat ad of the correlatio coefficiet for the idividual orders of reactio. uits 20 C 30 C k R 2 YX k R 2 YX 0 [mg.l 1.mi 1 ] [mi 1 ] 1.15* * [mg 1.l.mi 1 ] 1.40* * process of oxidatio of methylee blue was measured at temperatures 7 C, 15 C, 20 C, ad 30 C. After 10 mi of ozoatios carried out at 7 C ad 15 C 55 % ad 71 % efficiecies of oxidatio of MB were achieved. 68 % ad 73 % efficiecy of degradatio of MB were achieved after 10 mi durig ozoatios at 20 C ad 30 C. I Fig. 4, the time depedecies of the experimetal ad calculated cocetratio of methylee blue are preseted at various temperatures. The results of the measuremets show that the efficiecy of the use of ozoe for oxidatio of methylee blue is the highest at 30 C. The values of the rate costats ad of the correlatio coefficiets are listed i Tab. 3 for temperatures 7 C ad 15 C. Similar values are give for temperatures 20 C ad 30 C i Tab. 4. From compariso of the correlatio coefficiets for idividual kietic orders of reactio it follows that at all temperatures the best descriptio of the oxidatio of methylee blue gives the first-order kietics. Coclusios Based o the obtaied results it ca be cocluded that the presece of activated carbo durig ozoatio process has a positive effect o the efficiecy of the process of oxidatio of methylee blue. The whole 171

5 ozoatio process is also accelerated by the additio of activated carbo. The efficiecy of the ozoatio process is sigificatly iflueced by ph. The results show that the highest efficiecy is achieved i alkalie regio for which a radical reactio mechaism of ozoe is characteristic. The highest value of the rate costat was achieved whe the ozoizatio was performed at ph 11. Whe ozoizatio was carried out at ph 3. The lowest rate costat of the ozoatio process, as well as the lowest efficiecy of ozoe oxidatio of methylee blue was observed. From the results of this study it ca be cocluded that the efficiecy ad oxidatio rate of methylee blue depeds remarkably o temperature ad it is highest at 30 C. The lowest rate ad efficiecy of methylee blue oxidatio by ozoe was observed at 7 C. Ackowledgemets The authors wish to thak the support from APVV Grat 0656/12. Refereces Alvárez PM, Beltrá FJ, Masa FJ, Pocostales JP (2009): A compariso betwee catalytic ozoatio ad activated carbo adsorptio/ozoe-regeeratio processes for wastewater treatmet. Appl. Catal. B, 92, Arsla Alato. (2003): The effect of pre-ozoatio o the biocompatibility of reactive dye hydrolysates. Chemosphere, 51 (9), Derco J, Mecáková A, Almásiová B (2009): Využitie ozóu a čisteie priesakovej vody zo skládky komuáleho odpadu. Chem. Listy, 103, Dřímal J (1997): Ozóové techológie, súčasý stav a aplikácie. Ozoia Switzerlad, Peixoto ALC, Silvia MB, Izário Filho HJ (2009): Leachate treatmet process at a muicipial stabilized ladfill by catalytic ozoatio: A exploratory study from taguchi orthogoal array. Brazilia Joural of Chemical Egieerig, 26, No. 3, Zhag J, Lee K-H, Cui L, Jeog T (2009): Degradatio of methylee blue i aqueous solutio by ozoebased processes. Joural of Idustrial ad Egieerig Chemistry, 15,