Wastewater Colour Removal
The colour caused by organic molecules or substances in water starts to lose its effect by being broken down as soon as it comes into contact with ozone. Ozone applications are great solutions for colour removal in wastewater in many industries.
How does ozone remove color in wastewater?
Ozone can be used to remove color in wastewater through a process known as ozonation. Color in wastewater is often caused by the presence of organic compounds, such as humic and fulvic acids, as well as dyes and other industrial contaminants. Ozone treatment is effective at reducing or eliminating this color for several reasons:
Oxidation: Ozone (O3) is a highly reactive molecule. When ozone is introduced into wastewater, it readily undergoes chemical reactions with organic molecules that contribute to color. Ozone molecules break down into reactive oxygen species, including hydroxyl radicals (OH•) and superoxide radicals (O2•-), which oxidize and degrade the organic compounds responsible for the color.
Decomposition of Organic Chromophores: Many colored organic compounds contain chromophores, which are specific groups of atoms responsible for absorbing light and giving the compound its color. Ozone attacks these chromophores, causing them to break apart and lose their color-producing properties.
Destruction of Aromatic Rings: Some colored compounds in wastewater contain aromatic rings, which are highly stable and contribute to color. Ozone can break the aromatic rings, destabilizing the compounds and reducing color.
Breaking Down Dyes: Industrial wastewater may contain dyes used in various processes. Ozone can break down these dyes into simpler, colorless molecules.
Precipitation and Coagulation: In some cases, ozone treatment can also cause the formation of coagulants that help in the removal of color-causing particles through precipitation and subsequent settling or filtration.
Enhanced Biodegradability: Ozone treatment can make organic compounds more biodegradable by breaking them down into smaller, more easily digestible molecules. This can aid in subsequent biological treatment processes, further reducing color.
It’s important to note that the effectiveness of ozonation in removing color from wastewater can vary depending on the specific compounds present, their concentration, and the overall water quality. Additionally, ozonation is often used in conjunction with other treatment processes, such as biological treatment and filtration, to achieve comprehensive wastewater purification.
Overall, ozonation is a powerful and versatile method for color removal in wastewater, especially when dealing with complex organic contaminants. However, the design and operation of an ozonation system must be tailored to the specific characteristics of the wastewater to achieve optimal results.
Colour Challenge in Textile Wastewater
The textile industry is a sector that contains wastewater with intense colour and COD pollution load. Water treatment plants in textile companies face problems in meeting colour and COD discharge standards. The most widely used method in the textile industry is the aerobic biological treatment method, but this method is generally not effective in removing colour in wastewater containing dyestuffs.
Colouring in textile products is a key factor for commercial success. In addition, the colour on the product is washed, light, dry cleaning sweat, etc. Modifications made to the dyestuff structures to increase their resistance to external factors, that is, their fastness, have caused these dyestuffs to show resistance to traditional wastewater treatment systems as well. (O’Neill et al., 1999, Cooper, 1993)
COD and colour removal in textile wastewater requires a high amount of oxidation. For this reason, if a wastewater project is to be carried out in the textile industry, the ozone generator must meet certain standards.
The treatment of many textile companies works 24 hours a day, 7 days a week, and the daily wastewater capacity of a large-scale textile company can reach figures such as 15,000 m3 / day. If ozone is applied at such high flow rates, the contact time of ozone gas with wastewater will be extremely limited.
For this reason, the ozone gas concentration should not be below 11% in the studies to be carried out in textile wastewater. To reach this concentration, the ozone generator MUST be fed with oxygen generators. No ozone gas can be produced in 11% concentration from dry air with any technique or production method in the world.
There are 3 main reasons why ozone gas is used in textile wastewater. These reasons;
1) COD and BOD removal
2) Colour removal
3) Odour removal
But a good ozone gas project is possible ONLY with a good treatment project. The ozone generator is not a purification solution itself, but a supplementary product.
Due to the strong oxidant nature of ozone gas, the success of colour and odour control methods in drinking water has led to an important market in wastewater treatment.
Ozone systems are very low operating costs, no personnel costs. Ozone systems provide 85-98% success in colour removal and 40-55% success in COD removal.
Today, ozone applications in many countries of the world painting, textile, pharmaceuticals and so on. are one of the preferred methods in industrial plants. Ozone is used as “bleach in pulp and paper production, kaolin production and textile production in addition to the applications mentioned above.
The quality of the ozone treatment effluent in terms of colour control depends on:
- The colour values of the feed
- The ozone dosage
- The wastewater type (Typically colour values do not decrease below 200 Pt-Co units even if an especially high ozone dosage is applied)
- The wastewater temperature (better results with effluent from the existing treatment whose temperature is much lower than the temperature of wastewater from the equalisation tank)
- The values of the other wastewater characteristics that ozone also affects (better results if BOD, COD and SS have already been decreased in a previous treatment level)
The best results concerning colour removal are achieved if the wastewater has been previously treated to lower the values of the other characteristics so that the ozone oxidising effect is “consumed” only or at least at a maximum proportion in colour removal. Additionally, the temperature must be below 30-deg C to achieve the best physical conditions for its solubility.
You can check our ozone generators for colour removal applications for wastewater by clicking here.
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