Advanced Oxidation Technology for COD and BOD reduction in wastewater treatment. Pure Tech India, A-5, Trec step, Thuvakudi, Trichy Telephone: ; Telefax: website:

Introduction: Waste water treatment in general involves removal of Suspended Solids, Oil & Greases, BOD, and COD. The removal of all contaminants except COD is by and large common using conventional Physio Chemical Separations. COD is the abbreviation for Chemical Oxygen Demand which requires specific technologies for removal from wastewater.

COD: Oxygen demand for the survival of species in water sources is limited by place for discharge of treated wastewater. This is normally in the range of 25 – 250 ppm. Oxygen demand basically consists of Bio degradable or Bio chemical oxygen demand( BOD) and Non bio degradable or Chemical Oxygen Demand (COD). BOD reduces due to compounds readily absorbing atmospheric oxygen on contact. COD is chemically stable and the compounds needs Physical, chemical or Biological activation and oxidation. COD reduction is met by Photo Chemical Oxidation using Advanced Oxidation Technology in our process which is highly advantageous for modern waste management scenario.

Advanced Oxidation Technology (AOT): Introduction: Photo Chemical Oxidation/Advanced Oxidation is a generic name for a family of oxidation technologies that use ultra violet light in conjunction with standard oxidant such as hydrogen peroxide, chlorine etc. to achieve greater treatment performance over that obtained with oxidants alone. A typical Photo Chemical Oxidation: Hydrogen Peroxide is a good Oxidising agent. When it is mixed with wastewater, it breaks into water and Nascent oxygen to effect oxidation of Non biodegradable COD causing compounds. When Hydrogen Peroxide is mixed with wastewater in the presence of UV Light, it dissociates into 2 Hydroxyl (OH) radicals. OH has higher oxidation energy and potential than Nascent oxygen. In addition to the creation of OH radicals, UV light actuates the molecules present in COD causing compounds and converts complex molecules into simpler molecules for easy oxidation.

Advanced Oxidation Technology (AOT) Processes: Photolysis: Photolysis involves the interaction of light with molecules to bring about its disassociation into fragments. The absorption of a photon molecule by the COD compound causes photolysis since the photon energy exceeds the energy for the bond to be broken. This requires that the wavelength be in the ultra violet region of the spectrum for most photolytic reactions and also as per laws of photo chemistry the chemical effect of light, as a rule, is proportional to the light intensity and exposure time. Compounds that absorb ultra violet light and have high quantum yields of photolysis are good candidates for photo degradation. Examples of these classes of compounds include N – nitroso di-mythyl amine (NDMA) and various chlorinated alkanes and aromatics. Direct photolysis is especially important for refractory compounds such as carbon tetra chloride, chloroform, chlorinated alkanes, which react relatively slowly with hydroxyl radicals alone. Destruction by photolysis highlights the importance of using ultra violet lamps with the highest possible output in the ultra violet region, where most organic toxins strongly absorb light energy and where the photolysis quantum yield (i.e. a measure of tendency to change structure) is typically higher.

Advanced Oxidation Technology (AOT) Processes: Oxidation: Oxidation is the chemical conversion of a contaminant to more oxygenated forms by means of reactions with oxidizing agents, such as oxygen (O2), ozone (O3), hydrogen peroxide (H2O2), or sodium hypochlorite (NaOCl). The following equation represents a general oxidation process: Chlorinate O2, O3 Oxygenated Organic ->->->-> Intermediates Molecules H2O2 or NaOCl Oxygenated O2, O3 CO2+H2O+Cl Intermediates ->->->-> H2O2 or NaOCl The multiple arrows indicate multi-step processes. Simple oxidation involves the addition of oxidizing agents such as O2, O3, H2O2, or NaOCl; however, the overall oxidation rates are usually too slow and the chemical consumptions are too high to be applied broadly for wastewater treatment to change structure is typically higher.

Advanced Oxidation Technology (AOT) Processes: Photolysis of Hydrogen Peroxide: In the UV/Peroxide process, a high-powered lamp emits UV radiation through a Polymer tube into the contaminated water. UV light excites the molecular bonds, and makes the molecule amenable to the attack by the hydroxyl radicals. H 2 O 2 +hv-  2.OH The following equation represents the simplified statement of the oxidation process: Chlorinated O 2 Intermediates O 2 Organic Molecule  (aldehydes/  CO 2 +H 2 O+Cl OH Carboxylic acid) The final products of the oxidation reaction are carbon dioxide and water and the extent of reaction depends on the peroxide dosage. Typically, the reaction is allowed to proceed to an extent such that all the complex compounds are broken down into simple structures. These simple compounds can then be absorbed in an activated carbon column. This oxidative treatment is called mineralization of the dissolved contaminants and means that secondary pollution or waste disposal is not required.

Photo Chemical Reactor: Waste water passes through advanced fluoro polymer tubes. UV light acts from outside the tubes. Hydrogen peroxide dosing is done at the inlet to the reactor. Photo chemical oxidation takes place for COD reduction.

A Typical PCR Illustration:

A Typical PCR Treatment System Illustration:

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Since it is possible to generate hydroxyl radicals without UV light (for example, ozone/peroxide), what are the reasons for using UV light? Photolysis: It is possible to photolyze compounds directly. This is very important for compounds that react slowly with hydroxyl radicals. Avoids the use of ozone: Ozone increases capital costs, complexity, and health and environmental concerns and requires air permits. Increased reaction rate constants: This results in “instantaneous” reactions and hence negates the need for large holding tanks and makes the systems very compact. Avoids drastic pH changes: Ozone may require significant changes in pH to be effective. This adds operating and capital costs as well as complexity. Increase flexibility: Can use a variety of oxidants and conditions when light is used. Lower operating cost: due to lower power consumption to generate hydroxyl radicals as long as the peroxide absorbs most of the light. A UV/Oxidation system can be designed to meet any discharge requirement. Advantages of Photochemical Oxidation:

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