The textile industry is a source of major environmental pollutants. Its global presence means it is a global problem. The major source of emissions orginates from fabric printing where a decorative design or text is applied to fabric products by various screen printing methods. This process leads both to recalcitrant molecules in the production waste water and as Volatile Organic Content (VOC) gas. Surging environmental restrictions require effective treatment of these air or water streams in order to secure a healthy work environment and avoid polluted water recipients. In many facilities, jeans or other clothes are commonly bleached to create a "washed" look.

All of the above in the textile industry can be achieved with ozone treatment, which presents and effective way of reducing operational costs and lower environemental emissions compared to traditional techniques.

Overview of the screen printing process

• Roller
• Flat screen printer
• Rotary screen printer.

In the roller process, print paste is applied to an engraved roller after which fabric is pressured by the roller, creating a printed design.

In rotary screen printing, print paste is distributed inside tubular screens and is printed on the fabric between a rubber belt and the tubular screen. Print paste is pumped to the rotary screen and a dispenser distributes the paste while fabric is continually fed from a roll. The continuous belt collects excess solvent and water wash.For flat screen printing, fabric is pressured onto a screen which has been prepared with print paste.

Prior to collected dry printed fabric, the fabric is dried which vents solvent and water.

Treatment methods

Typical pollutant load from the textile industry

The solvent used to produce printing paste will be wasted during the drying or printing process, generating VOC and wastewater containing organics which are difficult to treat. On average, screen printing runs may require up to 1,200 kg of organic solvents, most of which are emitted as VOC from the dryer process. Up to 80 kg of organic solvents can be emitted in the wastewater. The US EPA has estimated the following potential emissions in various forms from textile printing, based on information directly from the textile industry. Similar printing processes exist in the carpet textile industry.

Average emissions from a 10,000 m textile printing run for various printing techniques (kg).

Emission constituents

Both VOC and aqueous waste from the printing process contain various organics such as alcohols, dyes and aromatics. The table below displays common emission constituents in the wastewater and VOC.

Wastewater and VOC emissions from various sources.

Ozone treatment for screen printing emissions

Wastewater

Ozone technology is an effective method to treat the compunds both in the wastewater and the VOC by effective oxidation of organic molecules. Wastewater typically contains high levels of COD with a COD:BOD ratio of 4:1 to 5:1. Not only does ozone oxidize the organic pollutants, it is capable of converting non-biodegradable COD to readily biodegradable BOD, lowering the COD:BOD ratio for subsequent biological treatment. Depending on the COD and BOD concentration, ozone can oxidize the majority of the compunds which lowers the wastewater load to acceptable regulatory levels. An ozone system for textile wastewater may save significant operational costs and footprint.

Estimates on operational costs and footprint of different treatment technologies for textile wastewater*

*depends largely on load, indications only

Ozonetech has successfully treated screen printing wastewater from a large international clothing supplier, reducing COD levels from 700 mg/L to 100 mg/L and BOD levels from 150 mg/L to 50 mg/L using our compact systems. The full scale system will treat 20 m3/hr of organic wastewater per day to comply with local regulations.

We welcome you to read more about how we treat BOD and COD with ozone-based treatment systems. Read more about this here!

VOC ozone treatment

Destroying VOC fugitive gases by burning is an effective but very costly method. Ozone treatment may reduce the operational costs 1000-fold by avoiding the substantial energy demand associated incineration.

Compared to typical treatment by incineration of hazardous volatile compunds, ozone effectively reacts with these pollutants in gas phase. This eliminates the major energy demands that follows incineration. For VOC gases, ozone is typically combined with an active carbon filter where ozone treatment reduces VOC gases up 90% with secondary polishing to reduce completely the fugitive gases. Please visit the VOC treatment application page to read more.

Textile bleaching by ozone

In modern designer clothing production, fabrics such as jeans are bleached using oxidation by chemicals to create a washed look. The highly oxidative characteristics of ozone enable a sustainable bleaching method without excessive chemical handling or costs. In addition, ozone leaves no by-products which need to be treated. Please go to our Bleaching application page for more information.

Ozone color removal

Textile wastewater is often treated on-site using biological wastewater treatment processes. This may provide around 90% reduction of the incoming COD and BOD. The remaining COD and BOD may still constitute major environmental loads. Typically it is not possible to remove the discoloration of the wastewater originating from the textile production described above. Ozone is a very effective color removal technology as a part the tertiary treatment step. Complete colour removal can be achieved in 5-15 minutes of ozone exposure depending on ozone capacity. At the same time, COD and BOD can be treated to achieve near-zero emissions from any textile factory using ozone.

Applicable Ozonetech ozone systems

For ozone treatment from a textile factory, Ozonetech employs our RENA Tellus X series, which is our tailored solution for large loads. Click here to read more about this system.

Contact us today

Don't hesitate to contact Ozonetech to find out how we can solve your specific needs for treating your industrial textile waste issues. We provide the safest possible method to help you reach regulatory compliance at lowest possible operational costs at a small environmental footprint. Give us a call or send us en email to come in contact with our experienced engineers. We look forward to hearing from you.