The coagulation-flocculation process is considered a primary treatment. In this process, chemicals (coagulants/flocculants) are added in the influent wastewater. This makes the colloidal matters in the water form large flocs which then settle down due togravity. This process is used before all treatments processes as it removes most of the bulk materials and the associated organic and nitrogenous pollutants from the influent wastewater. This process has limited impact because of its low decolorization efficiency, large resultant sludge generation and regeneration and dumping problem of the residual sludge.
The biological processes used are usually a combination of anaerobic and aerobic treatment in which an anaerobic process is used to the influent chemical oxygen demand (COD), followed by aerobic method for polishing. This method has benefits as it is eco-friendly, produces less sludge, is cost-competitive, and generates energy in the form of biogas. The problem with these processes is that they do not deliver reasonable results consistently, as some of the dye molecules or other components created or used by textile industry during different stages of operation may be recalcitrant or toxic to biological treatment. In general, it is seen that small size textile manufacturers prefer aerobic treatment over anaerobic treatment due to lower capital cost than the latter, although the operating cost for the aerobic treatment is higher compared to anaerobic treatment due to the cost of aeration energy.
