The textile industries of the world release wastes during different stages of production. Water pollution has always been a rising concern, and many new technologies have been introduced to combat the problem of effluent wastes of textile dyeing. The industry is assumed to consume more than 80,000 tons of reactive dyes every year. Stringent laws and increasing ecological awareness is making textile dyeing units, switch to more sustainable options of dyeing and treating waste water to upcycle.
The dyeing of fabrics or fibre uses water to transmit dyes in the form of vapour to heat the treatment baths. Printing being a subset of dyeing also contributes to releasing toxic wastes. Hence textile pre-treatment, printing, dyeing, and finishing processes are responsible for using and discharging all kinds of chemical waste. These processes generate effluents that comprise of high concentration of salts, and demonstrate high biological oxygen demand (BOD) or chemical oxygen demand (COD) values. Water treatment plants and processes must be incorporated by textile industries.
Most of the textile dyeing waste gets discharged into water bodies like lakes and rivers. The waste water disposed reduces the depths of the penetration of sunlight and results in decreasing the process of photosynthesis, and consequently dissolves oxygen. Several techniques are developed to treat water waste and effectively reduce chemicals before releasing them into rivers. The following are a few processes widely used in the textile industry.
Physiochemical effluent treatment, where the first step is to mix and equalize the effluent waste that is released from different stages at different intervals and time. Another primary treatment used is equalization and homogenization, where in waste substances that have similar characteristics in terms of pollution, temperature, and pH are separated. Floatation is a technique that divides fibre from the waste water. This process releases micro-bubbles to form substances in three phases of water, gas, and solids. To remove organic substances coagulation flocculation treatments are used conventionally. This process adequately eliminates insoluble dyes but does not remove soluble dyes.