PI in textile industry
1. GENERAL DESCRIPTION
Azo dyes are the most widely used synthetic dyes in the textile industry. Unfortunately thei release to the environment is very critical.
It can interfere the light penetration in water and furthermore it can disturb the biological activities of aquatic life. Some of the substances are toxic and cause hazardous effects on living organism in aquatic environments. They are also known to be stable in term of their biological or chemical graduation because of their molecular structure. So the dye effluents of the textile industry have to be treated before they are discharged to the water stream.
2. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT
- Electrocoagulation (EC)
It is a very efficient way to treat textile wastewater which contains dyes. The technique uses a current source between metal electrodes which are put into polluted water. The most common materials for the electrodes are aluminium and iron. The metal ions can absorb the dissolved contaminates or can destabilize and aggregate the suspended particles at an appropriate pH. The formed flocs have a large surface- That advantages a rapid adsorption of the soluble organic compounds. Afterwards they can easily be removed from the aqueous medium by sedimentation and flotation. Today the technique of EC is widely used in industry sectors.
Source: Chemical Engineering and Processing: Process Intensification, Volume 49, Issue 11, November 2010, Pages 1176-1182
- Advanced Oxidation Processes (AOPs)
This option enables high removal efficiencies when conventional methods of wastewater treatment such as chemical oxidation, activated carbon adsorption or coagulation/flocculation are not efficient enough. A very common AOP for the treatment of wastewater is the Fenton process. Its reaction uses hydrogen peroxide and ferrous salt to generate hydroxyl radicals. These radicals can attack organic pollutants in water and lead in best case to a total mineralization into carbon dioxide, water and mineral acids. When the Fenton reaction is used in combination with UV (Ultraviolet) radiation we talk about a photo-Fenton process. The main advantages of the use of AOPs are the increase of the reaction rate and the possibility to use solar radiation, a cheap source of energy.
Source: Chemical Engineering and Processing: Process Intensification Volume 47, Issue 2, February 2008, Pages 169-176
- Membrane techniques
Membrane filtration processes are promising options not only for the removal of pollutants but also for the reuse of water and some waste constituents. In the last years many improvements in economical and technical fields have been made. Ultrafiltration is an efficient method for recycling of high molecular weight and insoluble dyes, auxiliary chemicals and water. Efficient colour removal can be realized by nanofiltration and reverse osmosis. The major problem of the use of different membrane techniques is the decline of permeate flux due to the accumulation of molecules on membrane surface. The accumulation (also known as concentration polarisation) causes an increase of membrane fouling.
Reference: Chemical Engineering and Processing: Process Intensification, Volume 41, 2002, Pages 601-609
