Advanced Oxidation Process
Process Description of Ozonation System in STP
Ozone plays very important role in Sewage Treatment Plants. When biological treatment is used in secondary stage, there is a carryover of micro Organisms in tertiary stage. Ozone being a very strong oxidizing agent can effectively & quickly disinfect the Treated sewage water. Post reaction, Byproduct& unused residual ozone are safe to be disposed without any further treatment. Ozonation in waste water treatment is universally accepted & new mended by pollution control boards.
The effectiveness of the ozone depends on multiple factors:
Advantages of Advance Oxidation Process:
• Target microorganisms load
• Other pollutant like H2S, Ammonia etc.
• Organic Load
• Inorganic load
• Non-biodegradable organism
• COD & BOD
• Ozone contact time
• Ozone concentration
• Induced ozone dose
• Ozone mass transfer (dissolving) efficiency
• Purity of feed gas etc.
In waste water Ozonation the amount of ozone which gets dissolved in waste water is the only reactive ozone & effective on pollutants & contaminants. This reactive ozone when reacts with the pollutants in waste water gets consumed. So efficiency of Ozonation process also depends upon the efficiency of core waste water treatment & effective reduction in pollutants.
Generally waste water contains diversified constituents/pollutants, out of them ozone reacts with many of them and in the process gets consumed. The ozone reacts on micro-organisms, color, odor, COD, BOD, organics, inorganic, heavy metals, oil & grease, total organics carbon (TOC), volatile organic compound (VOC) etc.
Advance Oxidation Process (AOP) for STP
Spectrum Coverage(Graph) – UV | Ozone | AOP
Due to extensive use of personal care products (PCPs) & non-biodegradable biocides, endorinediscruptors (EDCs), pharmaceutical products & other emerging contamination, domestic waste water becomes more complex & challenging in treating with conventional techniques. At the same time current & future regulation demands for better quality of recycled waste water for reuse.
The current conventional biological or membrane base [MBR] domestic waste water treatment cannot cope up with this demand of emerging contamination. This results in drop in efficiency & increase in indicative COD & BOD in waste water units.
To take care of these conditions one requires highest degree of oxidation potentials, 2.8mV of hydroxyl radicals (OH), which is more than any one individual form. Advance oxidation
is the best option so called “Best Available Technology” (BAT).
Advance oxidation process is an extended treatment of Ozonation, where Ozone & 253.7 nm wavelength of UV radiation creates hydroxyl radicals to optimize the capital & operational cost. It is a smart way to use AOP with moderate dose of Ozone rather than using high dose on only ozone giving saturated result. In this UV + Ozone process, photons in the UV light convert Ozone in the presence of water to oxygen & peroxide. The peroxide then reacts with the Ozone to form hydroxyl radical, please check below reaction.
O3 + H2 O -----------> O2 + H2 O2 (in the presence of UV light)
2O3 + H2 O2 -----------> 2 OH + 3O2
Only Ozone at time becomes performance / oxidation saturated, where increases in Ozone Dose cannot further reduce / oxidize pollutant.
Below one can notice the spectrum coverage of different technologies on various pollutants
Technological Spectrum coverage:- UV | Chlorine | Ozone | AOP :
• AOP covers maximum pollutant spectrum.
• AOP is extremely quick in oxidation.
• To oxidize complex organic constituents to simpler end products.
• Primary degradation- structural change in the parent compound.
• Accepted degradation – structural change in the parent compound to the extent that toxicity in reduced / eliminated.
• Ultimate degradation : (Mineralization) conversion of organic carbon to CO2