International Conference on: Pollution Control & Sustainable Environment

Transcription

1 International Conference on: Pollution Control & Sustainable Environment Water treatment containing organic compounds by coupling adsorption éa and electrochemical degradation at BDD anode: Sawdust adsorption performance for the treatment of dilute phenol solutions Ines BOUAZIZ KARIME, Morched HAMZA, Ahmed SELLAMI, Ridha ABDELHEDI, André SAVALL, Karine GROENEN SERRANO April 25-26, 216 Dubai, UAE 1

2 1 Introduction-Context 2 setups

3 Introduction-Context setups Treatment 3

4 Introduction-Context Phenolic compounds Origin :pharmaceutical, pesticides, oil, textiles, painting, dyes, plastic, detergent industries Dangers: Highly toxic, highly oxygen demanding, Carcinogenic, mutagenic, and can cause a severe health hazard to human beings. 4

5 Introduction-Contexte Dispositif Expérimental Démarche de l étude Résultats et discussions et perspectives Main reagent : the electron Biological Complete oxidation (Mineralization) : possible - Phenolic compounds are generally Non-biodegradable Transformation of organic pollutants Waste into water biodegradable products: possible treatment processes Chemical Physical cost, secondary waste Electrochemical 5

6 Introduction-Contexte Dispositif Expérimental Démarche de l étude Résultats et discussions et perspectives Electrochemical Degradation of organic compounds(r) Anode material Choice of the anode material: high oxygen overpotential Competing Reactions: overvoltage for different anode materials 1 A m-2 in sulfuric acid Anode material Overpotential (V) Pt PbO 2 SnO 2 BDD,27,5,67 1,27 6

7 Introduction-Contexte Dispositif Expérimental Démarche de l étude Résultats et discussions et perspectives Electrochemical Low current efficiency for the treatment of dilute solutions Mass transfer limitations Not economically viable Coupling of electrochemical processes with a pre-concentration step is needed How? Adsorption- electochemical oxidation coupling 7

8 Introduction Commercial activated carbon Origin: wood Particles size:.4 mm Specific area: 98 m 2 /g PH PZC = 8,9 Red wood sawdust Origin : Coniferous trees (by-product of furniture industry) Specific area:.4 m 2 /g Particles size: mm 8

9 Introduction Phenol OH 9

10 Introduction-Contexte Dispositif Expérimental Démarche De l étude Résultats et discussions et perspectives Batch adsorption Column adsorption Electrochemical degradation Conditions: Anode: boron doped diamond (BDD) Cathode: cylindrical mesh of platinum Electrolyte: Na 2 SO 4 1

11 Introduction High Performance Liquid Chromatography (HPLC) Phenol and its oxidation intermediates Automated gas sorption system Cyclic voltammetry BET surface Electrochemical behavior of the activated carbon paste 11

12 Introduction General approach Adsorption Desorption Electrolysis Kinetics study adsorption isotherms Saturation of adsorbents Study of the pollutants desorption without polarization Electro-oxidation of pollutants Study of the pollutants desorption under polarization Electrochemical regeneration of adsorbent 12

13 Desorption rate (%) Introduction Desorption studies Quantify the long term desorption without polarization. Simple Multiple desorption Stirring Loaded adsorbent Desorption equilibrium Stirring Desorption kinetic of phenol adsorbed Time (min) Dosage of desorbed pollutant! Volume of the solution for each step = 1/4 of the simple desorption volume In the case of sawdust : Solution used : Na 2 SO 4 (neutral ph) In the case of activated carbon: Solution used : Na 2 SO 4 + NaOH (ph=13) The process was repeated 4 times 13

14 Desorption rate (%) Introduction Electrochemical degradation of phenol Desorption equilibrium Desorption of the pollutant Desorption kinetic of the pollutant 2 4 Time(min) Electrochemical degradation Electrolysis conditions: Anode: BDD Cathode: cylindrical mesh of platinum Electrolyte: Na 2 SO 4 (,1M) of desired ph 14

15 q (mg/g) q (mg/g) Introduction Adsorption kinetics of phenol onto activated carbon and sawdust Activated carbon.5 Sawdust Activated carbon: Activated equilibrium carbon time=3 days Sawdust: equilibrium time=2 min 16 Sawdust 6 14 initial (C ) and final (C f ) 5 12 The rate of adsorption The phenol is adsorption much slower follows for the a pseudo-second activated carbon order kinetic 4 concentrations 1 of MB 3 for both adsorbents 8 V :volume of 6 solution M: weight of 2 adsorbent Internal transport of phenol in the pores of activated carbon reduces the pollutant scavenging rate on the activated carbon adsorption sites. t/q t Time (min) Time (min) Pseudo-second order model t/q t Time (min) Time(min) 15

16 Introduction Adsorption isotherms of phenol at 3 C q (mg/g) 4 2 Ac vated Carbon Langmuir isotherm Sawdust C e /q e (g/l) Linearization of Langmuir equation C e (mg/l) Ce (mg/l) C e : equilibrium concentration of the adsorbate (mg/l) q e :adsorption capacity (mg g -1 ), Equilibrium data are well represented by the Langmuir q m : maximum adsorption capacity (mg g isotherm equation. -1 ) K L : Langmuir isotherm constant (L mg -1 ). 16

17 Introduction Adsorption isotherms of phenol at 3 C Adsorbent Langmuir constants q m (mg/g) K L (L/mg) q m /S (mg/m 2 ) Sawdust 18,2,3 45,5 S=.4 m 2 /g Activated carbon 333,3,2,3 S= 98 m 2 /g q m of the activated carbon is the highest Activated carbon has the highest specific surface The sawdust is capable to adsorb a higher phenol weight per surface unit 17

18 Desorption rate (%) Desorption rate (%) Introduction Phenol desorption Desorption kinetics of phenol Sawdust ph of the solution: neutral Time(min) Activated carbon 15 min 5 min ph of the solution: Time(min) In the case of activated carbon: maximum desorption rate =5% The desorption In the kinetics case of of sawdust: the phenol maximum is very fast. desorption rate=38% The phenol retained by the activated carbon comes in two states: strongly adsorbed Value relatively (chemisorption)and high : phenol weakly is still adsorbed in its undissociated (physisorption) form Solution of ph Hypothesis: an important part of phenol retained on sawdust is rather v weakly Activated adsorbed carbon ph pk a +1 ph ph 18 PZC

19 Desorption rate (%) Introduction Phenol desorption Multiple desorption 6 Phenol desorption during multiple desorption steps The % of the desorbed phenol does not exceed 6% Desorption step A part of the phenol adsorption is rather chemical and irreversible Re-adsorption of phenol on activated carbon obtained after multiple desorption Regeneration efficiency : E = 73% Changes in the properties of activated carbon E obtained Adsorptive capacity of the activated carbon after multiple E (%) = (73%) is higher after contact with NaOH during the desorption than expected (6%) Initial adsorption capacity of the fresh steps activated carbon Fragmentation of the activated carbon particles by stirring * 1

20 [Benzoquinone](mg/L) [Phenol] (mg/l) Introduction Electrochemical degradation of phenol Oxydation of phenol on BDD anode at i=.215 A/cm ` Electrolysis 1 time=: 15 Electrolysis time min) Desorbed phenol in the solution with activated carbon 1 adsorbent 5 under galvanostatic without with activated activated carbon conditions. carbon 5 [Phenol] (mg/l) The experiments of degradation of phenol was carried out in two Electrolysis time =: steps: Simple desorption then Electrolyses Desorbed phenol in the with solution the presence of the with sawdust without sawdust with sawdust Electrolysis time time (min) (min) Electrolysis Electrolysis time (min) time (min) The The total rate of disappearance of the of phenol is alone achieved that in in the the presence of of adsorbents the adsorbent A part of the initially adsorbed phenol was desorbed during electrolysis.

21 Phenol concentration (mg/l) Introduction Electrochemical degradation of phenol Modeling of phenol degradation in the presence of sawdust 3 2 without sawdust with sawdust model of electrolysis without sawdust model Time (min) k=.252 m.min -1 k des =.516 min -1

22 Regeneration efficiency (%) Introduction Adsorption/electrochemical regeneration cycles Regeneration efficiency ( Re) Adsorption/Regeneration Cycles (1) Initial adsorption + (2) Electrochemical degradation + (3) Re-adsorption Repetition: (2) Electrochemical degradation + (3) Re-adsorption sawdust Activated carbon Regeneration/Adsorption cycles Electrolysis conditions: i=.215 A/cm 2 electrolysis time=5 hours Phenol/sawdust Phenol/activated couple carbon couple Regeneration efficiency= efficiency 59,5 1 % after four cycles Sawdust The remaining is more chemisorbed easily regenerated phenol because is not affected of its surface by the properties electrochemical unlike activated regeneration carbon Electrochemical A possible electro-polymerization treatment seems to of activate the phenol sawdust at the by boundary changing of its the physicochemical activated carbon properties grains 22

23 Introduction Electrochemical behavior study of activated carbon by cyclic voltammetry Oxidation of phenol solution on a virgin activated carbon paste CV of phenol in Na 2 SO 4 (.5M) 1 st scan I (µa) 2 nd scan E (mv/esm) The oxidation pic of phenol disappears completely from the second cycle Electro-polymerization of phenol on the surface of activated carbon

24 Introduction Electrochemical behavior study of activated carbon by cyclic voltammetry Electrolyte oxidation on an activated carbon (obtained after multiple desorption) paste electrode CV of electrolyte Na 2 SO 4 (,5M) Hypothesis confirmed: the electropolymerization of the strongly I (µa) 1 st scan adsorbed phenol can explain the deterioration in performance of activated carbon by the obstruction of its pores during the electrolysis. The Search of other nonconductive adsorbents E (mv/esm) The oxidation pic of adsorbed phenol disappears completely during the following cycles Sawdust The deactivation of the activated carbon could be associated to the electropolymerization of the phenol strongly retained by the activated carbon

25 Introduction Adsorption study: Both adsorbents (activated carbon and sawdust) follow a Langmuir adsorption isotherm. The maximum adsorption capacity of the activated carbon is 18 times greater than the one obtained with sawdust. Desorption study: An important part of phenol retained on the activated carbon is rather irreversible. An important part of phenol retained on the sawdust is rather weakly adsorbed. 25

26 Introduction Electrochemical regeneration study: The regeneration efficiency of the activated carbon is only 59% after 1 cycle of adsorption and regeneration: Low reversibility of the adsorption. Electropolymerization of the phenol on the surface of the activated carbon during anodic electrolysis The regeneration efficiency of sawdust is more than 1% at the end of the fourth adsorption-regeneration cycle: Sawdust is easily regenerated because of its surface properties. Electrochemical treatment seems to activate sawdust by changing its physiochemical properties. 26

27 Introduction Perspectives Understanding the mechanism of sawdust activation. The application of this method on other types of organic pollutants. Studying the competition of several organic compounds which may be present in a real effluent on their abilities to be adsorbed, desorbed and oxidized. Development of a reactor (adsorption+regeneration): 27

28 Publications I. Bouaziz, C. Chiron, R. Abdelhedi, A. Savall, K. Groenen Serrano, Treatment of dilute methylene blue-containing wastewater by coupling sawdust adsorption and electrochemical regeneration, Environ. Sci. Pollut. Res., 214, 21, I. Bouaziz, M. Hamza, R. Abdelhedi, A. Savall, K. Groenen Serrano, Treatment of diluted solutions of methylene blue by adsorption coupled with electrochemical regeneration: a comparative study of three adsorbents, ECS Trans., 214, 59(1),

29 Thank you 29