The Study On The Treatment Of Refractory Chemical Industrial Organic Wastewater By An Electrochemical Oxidation

The electrochemical oxiadation processes have attracted a great deal of attentionbecause of their versatility, environmental compatibility, and especially, destruction oftoxic and non-biodegradable organics by direct or indirect anodic oxidation. In fact,the main reagent used at electrochemical oxiadation of organics is electron, which is aclean reagent and therefore there is no need for additional chemicals. In recent years,it is much more cried for electrochemical methods that have been successfully appliedin the purification of several industrial wastewaters, landfill leachate, tannery wastes,textile wastes, oil refinery wastewaters, etc. However, there are many desiderativeproblems solved for the application of electrochemical oxidation process. The aim ofthe work was to investigate the electrochemical oxidation degradation mechanisms,processes of organic pollutants, anode materials and the practical problems ofelectrochemical treatment of organic wastewater.The current efficiency has directly connections with anodic oxidation reaction oforganic wastewater and selectivity of anode. The studies of anodic oxidation of indigocarmine at Ti/SnO₂-Sb₂O₃/PbO₂ anode, the electrochemical oxidation degradationmechanisms were demonstrated. The studies of the catalysis of several anodematerials, it demonstrated that the effects of anode materials on electrochemicaldegradation of organic were greater. The major reason for this effect is the differencein hydroxyl radicals produced on the anode suface. The performance of Ti/SnO₂anode preparated by cathodal deposit, anodic oxidation and thermal decomposition isan anode with higher oxygen evolution over-potential and with higher catalyticcapability. The anode is one of the present best anode materials in make use of organicelectrochemical degradation, but its stability is poor, and the lifetime of the anode isnot long enough to apply for the application. The performance ofTi/SnO₂-Sb₂O₃/PbO₂ anode preparated by brush coating thermal decomposition andanode deposit is one of the present best anode materials in make use of organicelectrochemical degradation, and its stability is fine. Ti/SnO₂-Sb₂O₃/PbO₂ anode withhigher oxygen evolution over-potential and longer lifetime is the present mostpromising anode material for electrochemical wastewater treatment. The performanceof Ti/RuO₂ anode with adulterated TiO₂ and preparated by brush coating thermaldecomposition possesses higher oxygen evolution over-potential and the lifetime ofTi/RuO₂ anode is long enough to apply for the application.In the electrochemical process, the pollutants are destroyed by either direct or indirect oxidation process, but the two processes are not isolated. In definiteconditions, the direct or indirect oxidation process may be simultaneous carry out. Ithas been demonstrated using Ti/SnO₂+Sb₂O₃/β-PbO₂ anodes for treatment of indigocarmine.In this work, the electrochemical oxidation process characterizations andcorrelative problem were studied using several anodes for treatment of characteristicorganic pollutants, such as isothiazolin-ones and characteristic effluents, such asbactericide effluent, curatorial effluent, and pesticide effluent The results have shownthat electrochemical oxidation degradation of organic mainly occur directly on theanode, in the absence of NaCl. The key of oxidation is the production of hydroxylradicals on the anodes. Organics are easily oxided on the high oxygen over-voltageanodes, but low oxygen over-voltage anodes.The thesis has demonstrated that the addition of chloride ions in the electrolytecaused an increase in removal efficiency, and the complete degradation of pollutantscan be performed due to the participation of active chlorine, in the form of chlorine,regenerated on anode surface in the electrochemical oxidation. The chloride ions arecatalysis intermediary. In the presence of chloride ions indirect oxidation of organicsoccurs, but also direct oxidation of organics occurs at the same time. The completeremoval of ammonia and coluor was achieved using Ti/RuO₂. The anode materialshave great effect on direct oxidation of organics, but indirect oxidation of organics.The electrochemical oxidation reactions and reaction intermediates ofisothiazolin-ones using a Ti/SnO₂-Sb₂O₃/PbO₂ were investigated usingUv-spectroscopy and mass spectrum (MS) in the study. By the analysis of MS, it maybe considered as the electrochemical oxidation route of isothiazolin-ones, Thepathway for isothiazolin-ones was the dissociation from chlorine, ring openingthrough the nitrogen-sulphur bond, and loss of sulfur and methyl, leading to1-nitro-2-crylic-acetone, acetic acid and formic acid, and then the organic acids wereoxidated into CO₂ and H₂O, along with the formation of SO₄^2-, NO₃^- ions and Cl₂gas.The reaction of electrochemical oxidation of isothiazolin-ones follows apseudo-first-order kinetics, and the process of anodic oxidation of isothiazolin-onessolution is a diffusion controlled process.It has demonstrated that electrochemical oxidation is an effective method whichdegraded toxic and non-biodegradable organics applied in the purification of industrial wastewaters.In electrochemical oxidation process of curatorial effluent contained higher salinityusing a Ti/RuO₂, organics, ammonia and colour in solution were removed effectively.The removal rates of COD, ammonia and colour were 71.3%, 96.74% and 95% inelectrochemical time of 120 min, at current density of 114.29 mA.cm^-2 respectively.In electrochemical oxidation process of curatorial effluent which dealed withmicroorganism, using a Ti/RuO₂, organics, ammonia and colour in solution wereremoved effectively. The removal rates of COD, ammonia and colour were 74.2%,98% and 90 %, and the concentrations of COD, ammonia and colour were 80 mg·L^-1,2 mg·L^-1 and 10 multiple (diluted multiple) in electrochemical time of 150 min, atcurrent density of 10 mA·cm^-2 respectively. The indexes of effluent were lower thanthe indexes of "effluent standard of primary water contamination in chemicalindustry".In the paper, the combined process of electrochemical oxidation and biologicaltreatment of bactericide effluent was studied. The purpose of this study was toevaluate the effectiveness of combined process. COD, S^2-and isothiazolin-onesremovals of 99.6%, 99.9% and 100% were also achieved by the overall combinedprocess of chemical coagulation, electrochemical oxidation and membrane bioreactor(MBR) adding powder activated carbon (PAC) respectively. It was concluded that thetoxicity and non-biodegradable organic pollutant were removed and destroyed mucheffectively in pretrcatment of chemical coagulation, electrochemical oxidation. Andthe concentration of COD was much effectively decreased by adding PAC in MBRtreatment. And this combined process of chemical coagulation, electrochemicaloxidation and MBR adding PAC was successfully employed and was highlypracticable.The conclusion was successfully applied in the treatmeng of bactericide effluent,curatorial effluent, and pesticide effluent etc. It has been showed that theelectrochemical oxidation process is promising for industrial wastewater treatmentand reuse.