Study of preozonation influence on the physical-chemical treatment of textile wastewater

Physical-chemical and biological processes are the most common methods for the textile effluents treatment. However, in many occasions the pollutants removal efficiency can be increased through the combination of these conventional methods with advanced ones. In this paper, initially the ozonation influence on the coagulation-flocculation process has been studied in textile wastewater from a dyeing, printing and finishing industry. Thus, several jar-tests were carried out using wastewater before and after an ozonation process, with reaction times of 30 and 60 min. It can be highlighted that a short time preozonation enhanced the coagulation process, achieving after sedimentation COD and turbidity reductions of 57% and 95%, respectively. After that, two different NF membranes were tested using as feeding stream the wastewater after the ozone and physical-chemical stages in order to reduce the water conductivity and COD. NF experiments were carried out in a laboratory plant containing a plane module with an effective area of 120 cm(2). The membranes tested were Desal DK-5 from Osmonics and NF-90 from Dow Chemical. The results showed that the COD and conductivity of the nanofiltration permeates were around 100 mg/L and 0.5 mS/cm, respectively with NF-90 membrane.