Treatment of wastewater containing printing dyes: summary and perspectives

Abstract

Synthetic dyes are widely used in textile, printing, leather tanning, cosmetic, drug and food processing industries. The printing and dyeing industry is considered as one of the most polluting industrial sectors. The printing process is very versatile and includes printing on paper as well as printing on textile, plastic and other materials. After the printing process is completed, various chemicals such as ethers, alcohols, phenols, aldehydes, ketones, benzene, and esters are used in the cleaning procedure. Resulting wastewater often contains a variety of solvents, surfactants, dyes, and other chemicals, thus greatly increasing the difficulty of wastewater treatment. Improper discharge of printing and dyeing wastewater into water bodies will have several effect, beginning with aesthetical issues followed by destruction of the aqueous ecosystem due to light attenuation, oxygen consumption and toxicity effects. Therefore, it is very important to find out and optimize printing and dying wastewater treatment techniques. Processes for dye removal from wastewater can be physical, chemical, biological and more recently hybrid treatments. Physical processes such as adsorption, based on mass transfer mechanism, are commonly used method mainly due to ease of operation and high efficiency. Chemical processes including coagulation and flocculation, advanced oxidation processes and electrochemical treatment are usually more expensive due t chemicals use, equipment requirements and electrical energy consumption. However, these techniques are destructive and may lead to total mineralization of dye molecules and accompanying pollutants. Biological treatment is a low-cost and environmentally friendly process that produces less sludge. This method has significant advantages but dye molecules are less prone to this kind of treatment as they are made to be stable and reluctant. So, the adjustment and optimization of biological treatment, for dye removal, is an ongoing field of research. In recent studies hybrid processes are gaining more attention, combining different techniques. Integrating treatments, as a cost-saving and time-saving process, can represent optimal solution for printing wastewater treatment.