Coupling of electrocoagulation and ozone treatment for textile wastewater reuse

Industrial textile wastewater is usually characterized by high pH, intense color and extremely high salinity, especially in case of wastewater generated after dyeing. Due to the complex matrix of textile wastewater, the selection of an appropriate treatment method can be a challenge. This paper presents the advantages of coupling electrocoagulation (EC) and ozonation (O-3) as one-step (EC + O-3) and two-step (EC -> O-3) operations. The combination of EC and O-3, which both worked well in salty environment, gave very good results in the case of aqueous solutions and real industrial wastewater containing Reactive Black 5 (RB5). Very high color removal, more than 95%, was achieved in a very short treatment time (less than 18 min, while ca. 60 min was required in the case of individual O-3). At the same time the applied ozone dose was reduced from 1.69 g/L, when using O-3 only, to less than 0.3 g/L for EC -> O-3. The results of color removal and mineralization analysis indicated the high efficiency of both the EC + O-3 and EC -> O-3 processes; however, the cost evaluation revealed that the EC -> O-3 treatment was more advantageous. EC preformed as a single treatment resulted in an increase in toxicity, but coupling EC with O-3 reduced this undesirable effect. Very promising results were obtained in recycling trials. The color difference (DEcmc, according to ISO 105-J03) of textiles dyed with purified wastewater (brine) were between 0.28 and 0.98 (below the limiting value of 1.5).