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ELECTROCOAGULATION / ELECTROOXIDATION. Dr. Manuel A. Rodrigo Department of Chemical Engineering. Facultad de Ciencias Químicas. Universidad de Castilla.

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Presentation on theme: "ELECTROCOAGULATION / ELECTROOXIDATION. Dr. Manuel A. Rodrigo Department of Chemical Engineering. Facultad de Ciencias Químicas. Universidad de Castilla."— Presentation transcript:

1 ELECTROCOAGULATION / ELECTROOXIDATION. Dr. Manuel A. Rodrigo Department of Chemical Engineering. Facultad de Ciencias Químicas. Universidad de Castilla La Mancha. Campus Universitario s/n Ciudad Real. Spain. Department of Chemical Engineering. Universidad de Castilla La Mancha. Spain ESSEE 4 4th European Summer School on Electrochemical Engineering Palić, Serbia and Montenegro 17 – 22 September, 2006

2 CONTENTS 1.ELECTROCHEMICAL WASTEWATER TREATMENT TECHNOLOGIES 1.1 What happens inside an electrochemical cell during the electrolysis of a wastewater? 1.2 Types of electrochemical wastewater treatment technologies 1.3 Advantages of electrochemical technologies in environmental remediation 2.ELECTROCOAGULATION 2.1 What is coagulation? 2.2 The electrochemically-assisted coagulation: fundamentals ANODE MATERIALS ELECTRODISSOLUTION ELECTROLYTIC GENERATION OF OXYGEN AND HYDROGEN MAIN PROCESSES INVOLVED IN THE ELECTROCHEMICALLY ASSISTED TECHNOLOGIES FOR COLLOID-POLLUTED WASTES 2.3 Electrochemical cells TANK CELLS FLOW CELLS PROMOTION OF THE ELECTROFLOTATION PROCESS OTHER PROCESSES 2.4 Electrocoagulation of soluble organics and break-up of emulsions. Removal of phosphates 2.5 Advantages and disadvantages of electrocoagulation 3.ELECTRO-OXIDATION 3.1 Fundamentals 3.2 Electrode materials 3.3 Electrochemical cell IS IT RECOMMENDED THE USE OF DIVIDED CELLS? STIRRED-TANK CELLS SINGLE-FLOW CELLS FILTER-PRESS CELLS OTHER CELLS 3.4 Indirect electrochemical oxidation processes 3.5 Advantages of the electrooxidation technologies 3.6 Combined processes

3 e - e - Anode Cathode Power supply e - e - influent effluent Red Ox Red Ox M M n+ M 1. Electrooxidation 2. Electroreduction 3. Electrodissolution 4. Electrodeposition 5. Migration of anions 5. Migration of cations 1.1 What happens inside an electrochemical cell during the electrolysis of a wastewater?

4 Anions Cations Feed solution Diluted solution Concentrated solution cathodeanode Cathionic membrane Anionic membrane Anionic membrane anode Electrolyte flux metal Rotational cathode electrodialysis Electro-oxidation electrocoagulation Electrodeposition 1.2 Types of electrochemical wastewater- treatment technologies

5 1.3 Advantages of electrochemical technologies in environmental remediation Environmental compatibility: “the main reagent used is the electron” No residues are formed. Versatility:  Many processes occur simultaneously in any electrochemical cell. Plethora of reactors, electrode materials, shapes, configuration can be utilized and allow to promote different kinds of treatment technologies.  Point-of-use production of chemicals is facilitated by electrochemical technology  Volumes of fluid from microliters to thousand of cubic meters can be treated Processes work at room temperature and atmospheric pressure Selectivity: the applied potentials can be controlled to selectively attack specific compounds. Easy operation. Amenability to automation. Cost effectiveness

6 Dissolved comp. Colloids Suspended solids 0.1 nm 1 nm 10 nm100 nm 1 micra10 micras100 micras1 mm 1 cm Pollutants size Typical hydraulic residence time of a settler for wastewater treatment 2.1 What is coagulation? Sludge effluent influent 2. ELECTROCOAGULATION

7 Electrostatic repulsion energy: Ea Van der Waals attraction energy: Eb Resulting energy : Ea+Eb Interaction energy Distance between particles Ea Eb Ea+Eb Diffuse layer Negatively charged particle Bulk solution Distance from the surface -(electrostatic potential) Zeta potential Surface potential Coagulation is a chemical treatment which consists of the addition of chemical reagents to reduce the electrical repulsion forces that inhibit the aggregation of particles. Hydrolysing metal salts (iron, aluminium)

8 Compression of the diffuse layer by an increase of the ionic strength Neutralization of superficial charges by adsorption of ions Precipitation Charge Neutralization Particles stabilized by electrostatic repulsion forces Interparticle bridging Enmeshment in a precipitate

9 Conventional Chemical Coagulation consists of the direct dosing of a coagulant solution to the wastewater. flocculation coagulation Inlet Chemical reagent sedimentation Flocculation is a physical treatment in which the collision of coagulated colloids is promoted in order to make possible the formation of larger particles. The result of both processes is a wastewater in which the size of the particles is enough to be separated by a settler or a flotation unit. Sludge Outlet

10 pH Log [Al x (OH) y 3x-y ] / mol dm -3 Al 3+ Al(OH) 4 - Al(OH) Al(OH) 2+ Al T OH - /Al pH Nitrate media Sulphate media z1z1 z2z2 z3z3 z4z4 Coagulation by hydrolysing aluminium salts Concentration of monomeric hydrolysis products of Al(III) in equilibrium with the amorphous hydroxides at zero ionic strength at 25ºC Typical titration curve for neutralization of aluminium salt solutions Monomeric species Polymeric species Precipitate

11 Al i /Al T ,544,5 monomers [Al 13 O 4 (OH) 24 ] 7+ [Al 2 (OH) 2 ] 4+ [Al(OH) 3 ] * [Al 2 (OH) x ] (6-x)+ pH h= OH/ Al T 0,25122,22,25

12 pH Log [Fe(OH) y 3x-y ] / mol dm -3 Fe 3+ Fe(OH) 4 - Fe(OH) Fe(OH) 2+ Coagulation by hydrolysing iron salts Concentration of monomeric hydrolysis products of Fe(III) in equilibrium with the amorphous hydroxides at zero ionic strength at 25ºC

13 Electrochemical processes involved: Electrodissolution Electrolytic generation of oxygen and hydrogen coagulation Electro-dissolution e-e- + M n+ M colloids macromolecules emulsions Unstabilized small particles flocculation Aggregated particles An alternative to the direct use of a solution containing the coagulant salts, is the in situ generation of coagulants by electrolytic oxidation of an appropriate anode material (e.g. iron or aluminium). This process is called electrocoagulation or electrochemically assisted coagulation. Electrocoagulation 2.2 The electrochemically assisted coagulation: fundamentals

14 coagulation Electro-dissolution e-e- + M n+ M ANODE MATERIAL Aluminium Iron

15 2.2.2 ELECTRODISSOLUTION Faradaic Efficiencies can be over 100% Electrochemical process Chemical process Influence of pHInfluence of current density Faraday’s value Chemical dissolution Experimental

16 AnodeAnode pH profile Direction of electrolyte flux pH profile in the electrochemical cell CathodeCathode

17 e-e- Anodic processes H20H20 O2O2 H2OH2O H2H2 Cathodic processes + - e-e ELECTROLYTIC GENERATION OF OXYGEN AND HYDROGEN

18 Air-dissolved flotation Bubbles diminish the overall density of the system and the particle floats

19 turbulence Oxygen and hydrogen bubbles Promotes soft mixing conditions and improves flocculation processes Electrochemically assisted flocculation (electroflocculation) Gaseous microbubbles link to pollutant particles. Consequently, the density of the new species decreases and this promotes the flotation of the particle Electrochemically assisted flotation (electroflotation) adhesion

20 MAIN PROCESSES INVOLVED IN THE ELECTROCHEMICALLY ASSISTED TECHNOLOGIES FOR COLLOID-POLLUTED WASTES

21 2.3 Electrochemical cells Type of cells Only electrodissolution Electrocoagulation/electroflocculation Electrocoagulation/electroflocculation electroflotation purpose

22 The process combines Coagulation/flocculation Sedimentation/flotation TANK CELLS Mixing can be accomplished either by mechanical stirrers or by the evolved gases Contrarily to electrooxidation processes, mass transport does not control the overall rate of the process

23 Hydrogen evolution can disturb the sedimentation process. For this reason, if possible, it is better to separate the cathodic process from the sedimentation The activity of the anode can decrease with time due to the formation of insoluble hydroxides or sludge layer. These can be avoid by using motion electrodes or by using turbulence promoters

24 HydroShock™ ElectroCoagulation

25 Multiple channels Single channel Electrode configuration in cells for aluminium dose The activity of the electrodes can be decreased by passivation. To solve this problem reverse of polarity (the anode acts as a cathode during a small period) are advised. This can be easily done in a cell designed with the only purpose of aluminium dosing… FLOW CELLS Normally, these cells do not promote the electroflocculation and the electroflotation processes except for especial designs. Hence its main goal is the electrodissolution and the electrocoagulation

26 Cathodes (-) Anodes (+) Bipolar electrodes anode + - cathode … and both, monopolar and bipolar connections, allow this change of polarity! However, it is more complex for cells that combine electrocoagulation and electroflotation in different compartments

27 Horizontal flow Vertical flow The turbulence generated by the evolved gases can be used in both types of flow. However, vertical flow allows to improve the separation by electroflotation as compared with horizontal flow.

28

29 e-e- - Current density (j) influences on both: number of bubbles and the average size of bubbles e-e- - Flow rate can also be used to control the average bubble size If electroflotation processes have to be promoted it has to be taken into account that: PROMOTION OF THE ELECTROFLOTATION PROCESS

30 Power supply Separator Efluent EC EF Divided electrocoagulation/ electroflotation Combined electrocoagulation/ electroflotation And also that the electroflotation can be carried out in the same or in a different cell Power supply Separator Efluent EC EF

31 air influent OTHER PROCESSES

32 Coalescence of phases 2.4 Electrocoagulation of soluble organics and break-up of emulsions. Removal of phosphates Emulsion stabilized by electrostatic repulsion forces Compression of the diffuse layer by an increase of the ionic strength Neutralization of superficial charges by adsorption of ions Inter-droplet bridging

33 Dissolved organic matter Enmeshment in a precipitate HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N M 3+ HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N Binding of monomeric cationic species to anionic sites of the organic molecules, neutralising their charge and resulting in reduced solubility compounds Binding of polymeric cationic species to anionic sites of the organic molecules, neutralising their charge and resulting in reduced solubility compounds Adsorption on a superficially charged precipitate HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N HO OH SO 3 - NO 2 N N

34 Precipitation of phosphates clarifier Treated wastewater wastewater Electrodissolution cell AlPO 4 FePO pH Log dissolved P

35 1) A promotion in the flocculation process due to the movement of the smallest charged colloids inside the electric field generated in the electrochemical cell and also to the turbulence created by the bubbles (electroflocculation process) 2) A promotion in the separation process due to the hydrogen bubbles produced in the cathode during the electrolysis, which can carry the solids to the top of the solution, where they can be easily collected and removed (electroflotation process) 3) A more compact residue, as it is reported that the electrocoagulation process produces a smaller amount of sludge that the chemical coagulation, and that the solids produced are more hydrophobic 4) A more easy operation mode as no mixing of chemicals is required, the dosing of coagulants can be easily controlled by manipulating the cell voltage (or the current density), and thus the operating costs are much lower compared with most of the conventional technologies 5) Very simple. Suitable for small WWTP 6) Lower operating cost. However, higher investment In literature some advantages are reported for electrocoagulation processes including: 2.5 Advantages and disadvantages of electrocoagulation

36 3.ELECTRO-OXIDATION Wastewater polluted with soluble organic pollutants Is it possible the recovery of the pollutant as a valuable product? High calorific power? Non AOP oxidation AOP oxidation Electrochemical oxidation Biodegradable? no When can be applied? 3.1 Fundamentals

37 Electro-oxidation technologies: use of an electrolytic cell to oxidize the pollutants contained in a wastewater 1. Direct electrolysis Oxidation of the pollutant on the electrode surface 2. Advanced oxidation processes With some anode materials it is possible the generation of OH· 3. Chemical oxidation On the electrode surface several oxidants can be formed from the salts contained in the salt e-e- + OH· pollutant H2OH2O PO 4 3- P 2 O 8 4- pollutant

38 e-e- e-e- Organic pollutant intermediates (aromatics, carboxylic acids) +... CO 2 H2OH2O O2O2 Cl - Cl 2 Direct electrolysis consists of the direct oxidation of a pollutant on the surface of the anode. To be oxidized the organic must arrive to the anodic surface and interact with this surface. This means that electrocatalytic properties of the surface towards the oxidation of organics can play an important role in the process. Likewise, it means that in certain conditions mass transfer can control the rate and the efficiency of the electrochemical process

39 e-e- e-e- Organic pollutant intermediates (aromatics, carboxylic acids) +... CO 2 H2OH2O O2O2 The potentials required for the oxidation of organics are usually high. This implies that water can be oxidized and the generation of oxygen is the main side reaction. This is a non desired reaction and it influences dramatically on the efficiencies Cl 2 Cl -

40 e-e- e-e- Organic pollutant intermediates (aromatics, carboxylic acids) +... CO 2 H2OH2O O2O2 Frequently the potential is high enough to promote the formation of stable oxidants, through the oxidation of other species contained in the wastewater. This can have a beneficial effect on the efficiency as these oxidants can oxidize the pollutant in all the volume of wastewater Cl 2 Cl -

41 3. The presence of compounds in the wastewater that can be transformed into oxidants, promoting mediated electrochemical oxidation processes e-e- e-e- Organic pollutant +... CO 2 H2OH2O O2O2 Cl 2 Organic pollutant 2. Mass transport, which can be promoted by a proper cell design 1. Electrode material, which influences on the nature of the products and on the importance of the side reactions Cl -

42 3.2 Electrode material MECHANICAL STABILITY. CHEMICAL STABILITY MORPHOLOGY. ELECTRICAL CONDUCTIVITY CATALYTIC PROPERTIES RATIO PRICE/ LIFETIME. MECHANICAL STABILITY. CHEMICAL STABILITY MORPHOLOGY. ELECTRICAL CONDUCTIVITY CATALYTIC PROPERTIES RATIO PRICE/ LIFETIME. DESIRABLE PROPERTIES

43 Typical materials include low efficiency electrodes High efficiency electrodes material Metals Carbon oxides Platinum Stainless stell Grafite Doped diamond DSA Ti/SnO 2 Ti/PbO 2

44 e-e- + SOFT OXIDATION CONDITIONS Many intermediates Small conversion to carbon dioxide Slow oxidation rates Small current efficiencies Formation of polymers from aromatic pollutants is favoured phenol Quinones, polymers, carboxylic acids Mediated oxidation by a higher oxidation state of the species that conforms the electrode surface? Pt IrO 2 Fouling by polymers Low efficiency electrodes

45 e-e- + HARD OXIDATION CONDITIONS few intermediates Large conversion to carbon dioxide Large current efficiencies only limited by mass transfer phenol Carbon dioxide OH· generation? Confirmed for conductive-diamond Suggested for PbO 2 /SnO 2 High efficiencies electrodes BDD Ti/PbO 2

46 Active electrodes Non-active electrodes Ti/SnO 2 Ti/ PbO 2 Doped diamond Pt Stainless steel DSA Drawbacks of non-active electrodes: Conductive diamond: large price >6000 euros/sqm PbO 2 /SnO 2 : Dissolution of toxic species

47 Anode (+) e - R RO R Mass Transport Electrochemical Reaction Interfase Electrolyte Anode (+) e - Mass Transport Electrochemical Reaction Interfase Electrolyte R RO R H 2 O OH · Anode (+) e - Mass Transport Electrochemical Reaction Interfase Electrolyte RO R Cred Cox Direct oxidation process Mediated oxidation process Electrochemical oxidation ROLE OF THE HYDROXYL RADICALS Kinetic or mass transport controlled Kinetic controlled

48 e-e- e-e- cathode anode H2OH2O 0.5H 2 + OH - Cathodic material Deposit of carbonates OH - + HCO 3 - Increase in the cell potential Increase in the energy consumption e-e- e-e- cathode anode e-e- e-e- cathode H2OH2O 0.5 O 2 + 2H + The organic-oxidation processes that occur in an electrochemical cell are usually irreversible. Hydrogen evolution is the main cathodic reaction. Polarity reversal

49 SIMPLE MECHANICAL DESIGN. SMALL PRICE. EASY TO USE. LOW MAINTENANCE COST. ENHANCED MASS TRANSFER. HOMOGENEOUS CURRENT DISTRIBUTION ON THE ELECTRODES. LARGE DURABILITY SAFETY DESIRED CHARACTERISTICS FOR A ELECTROCHEMICAL CELL 3.3 Electrochemical cell

50 + - Power supply e-e- e-e- Anode Cathode Anolite Catholite Membrane Turbulence promoters IS IT RECOMMENDED THE USE OF DIVIDED CELLS? 1. The membrane increases the cell potential and consequently the operating cost. 2. Most organic-oxidation processes are irreversible 1. The membrane increases the cell potential and consequently the operating cost. 2. Most organic-oxidation processes are irreversible Direction of charge flux V Cell potential Electrolyte ANODECATHODE   a +   diff   a +  +  reaction 

51 3.3.2 STIRRED-TANK CELLS + - Power supply e-e- e-e- anode cathode Turbulence promoters ADVANTAGE: Simplest cell DRAWBACK: Low mass transfer coefficients

52 ANODE CATHODE TURBULENCE PROMOTER Membrane? INLET ANOLYTE INLET CATHOLYTE OUTLET ANOLYTEOUTLET CATHOLYTE SINGLE FLOW CELL

53 3.3.4 FILTER PRESS CELL Large electrode surfaces / volume ratios Small interelectrode gap Plane electrodes

54 Electrolyte flow

55 + + Packed bed cell Steel cathode Steel anode Activated carbon polyuretane Cell with continuous regeneration of the adsorbent OTHER CELLS

56 Rotating electrode cell CATHODE ANODE

57 e - Electrodo Power supply e - pollutant product inert 1 electroactive pollutant Product inert electroactive pollutant Product a) Direct electrolysis b) Indirect electrolysis inert Indirect electrochemical oxidation processes

58 The oxidation is carried out in the whole reaction volume (not limited to the electrode surface) No mass transfer control higher efficiency Both direct and indirect electro-oxidation develop simultaneously in the cell Power supply anodecathode Homogeneous reactions Heterogeneous reactions AB CD e-e- e-e- e-e- IV A B D C e-e- e-e-

59 Without addition of reagents: changes in the pH and temperature to promote the generation of oxidants from the direct oxidation of salts present in the wastewater (in some cases throught hydroxyl radicals) With additions of reagents: in addition to changes in pH and temperature, some salts are added to promote the generation of oxidants Types of mediated electrochemical oxidation processes Production of reagents and treatment of the waste in the same cell Production of reagents and treatment of the waste in different cells

60 Separation of the oxidant or of its reduction product Electrosynthesis of the oxidant Oxidation and electroxidation of the pollutants Electrosynthesis of the oxidant Oxidation and electrooxidation of the pollutants wastewater Treated waste wastewater Treated waste Dosing of reagent Separation of the oxidant or of its reduction product

61 The potential at which the electrogenerated oxidants are produced must not be near the potential for water oxidation, since then a large portion of the current will be employed in the side reaction The rate of generation of the electrogenerated oxidant should be large The rate of oxidation of pollutant by the electrogenerated oxidant must be higher than the rates of any competing reactions. The electrogenerated oxidant must not be a harmful product To take in mind…

62 Ag(I) / Ag(II) Co(II) / Co(III) Ce(III) / Ce (IV) Fe(II) / Fe (III) SO 4 2- / S 2 O 8 2- Reversible oxidant The oxidant can be reduced in the cathode. A divided cell may be considered Irreversible (killers) Cl 2 O3O3 H2O2H2O2 The oxidant is not reduced on the cathode. Non-divided cells are used for their production PO 4 3- / S 2 O 8 4- These oxidants are generated from anions typically present in a wastewater It can be formed by a cathodic process. Extra oxidation efficiency!

63 Ag(I) / Ag(II) Main drawbacks ions Ag+ are harmful products chlorides can reduce the efficiencies due to precipitates formation silver is very expensive Some pollutants efficiency removed by this technology: Ethylene glycol, isopropanol, acetone, organic acids, benzene, kerosene Co(II) / Co (III) Some pollutants successfully treated: Organic radioactive waste materials, dichloropropanol, ethylene glycol This process has to be carried out in divided cells (Co can be electrodeposited on the cathode surface) Main drawback

64 Phosphate/peroxodiphosphate Large efficiencies with diamond electrodes Its presence is very common: Phosphate salts are frequently present in industrial wastewaters Powerful oxidant (more selective than persulphate). The oxidation carried out by this reagent depends importantly on the pH Less sensitive to temperature Sulphate/peroxodisulphate Large efficiencies with diamond electrodes Its presence is very common: Sulphate salts are frequently present in industrial wastewaters. Very powerful oxidant (non selective oxidation) It decomposes at temperatures above 60ºC

65 selectivity depends on operating conditions. Carbon dioxide can be the final product in the oxidation of organics good efficiencies are obtained for high temperatures and low current densities Electrocoagulation can occur simultaneously Some pollutants treated by this technology: Celluloid materials, fats, urea, cattle manure, sewage sludge, meat packing wastes, ethylene glycol Fe(II) / Fe (III) ?

66 Chloride/ Chlorine It can lead to the formation of organochlorinated compounds The chlorine speciation depends on the pH - Its presence is very common: chloride salts are frequently present in industrial wastewaters. hypochlorite Dosing in channel Dosing in pipe + - Electrochemical cell + NaCl % HClO pH

67 Hydrogen peroxide E 0 = V It can be formed on the cathode by reduction of oxygen However, the main drawback is the decomposition of the hydroperoxide anion that it is favoured at alkaline conditions. To promote the efficiencies it is required : a cathode material with a high overpotential for the reduction of the hydroperoxide anion to water (graphite) Good oxygen transfer rates to the cathode surface To promote the efficiencies it is required : a cathode material with a high overpotential for the reduction of the hydroperoxide anion to water (graphite) Good oxygen transfer rates to the cathode surface Combination of electrooxidation with cathodic generation of hydrogen peroxide allows to obtain current efficiencies over 100%. It is the best way of obtaining a valuable compound from the cathodic reaction in wastewater treatment processes e-e- e-e- cathode anode O2O2 H2O2H2O2 Anodic oxidation processes

68 Ozone E 0 =1.51 V E 0 =1.23 V The oxidation of water to ozone can occur on the electrode surface but it is less favoured than that of oxygen To promote the formation of ozone: Use of anode material with large overpotentials for oxygen evolution Use of very high current densities Use of an adsorbate to block the oxygen evolution process (f.i.F -, BF 4 -, BF 6 - ) Some examples of electrochemical generation of ozone anodeelectrolytecurrent densityyield B-PbO 2 HPF 6 (2M)750 mA cm -2 21% Active carbonHBF 4 (7.3 M)600 mA cm -2 35% Active carbonHBF 4 (62% w/w)200 mA cm -2 45%

69 3.5. Advantages of the electro-oxidation technology Environmental compatibility: “the main reagent used is the electron” No residues are formed. Can be a complementary treatment or a final treatment Operation at room temperature and atmospheric pressure High efficiency if proper anode material is used. The efficiency can be easily increased by promoting indirect processes Easy operation. Amenability to automation.

70 Lower operating cost compared with other AOP Energy consumption during the treatment of an actual industrial waste. Electrochemical oxidation j:30 mA cm -2 ; natural pH; T: 25ºC ; Ozonation pH 12; T: 25ºC 

71 +- Comportment of adjust of the pH Filter Electrochemical Reactor Absorber H2H2 S (S) NaOH Solution Poor Gas H 2 S Rich Gas H 2 S Solution 3.6. Combined processes Treatment of gaseous effluents

72 Combination of electrochemical oxidation with bio-oxidation electrooxidation biooxidation electrooxidation Main drawback: When to change? a) pre-treatment b) post-treatment


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