Technical and economic feasibility of polyester dyeing wastewater treatment by coagulation/flocculation and Fenton's oxidation

This study aims to investigate the efficiency of individual and integrated processes applied to organic matter abatement and biodegradability improvement of a polyester dyeing wastewater, namely coagulation/flocculation combined with Fenton's reagent (Approach 1), Fenton oxidation alone (Approach 2) and its integration with coagulation/flocculation (Approach 3). The effects of Fe2+ dose, initial concentration of the oxidant (H2O2) and temperature during Fenton's oxidation were evaluated in Approaches 1 and 2, whereas in Approach 3 the influence of pH and flocculant dose was also assessed, during the coagulation/flocculation stage. Toxicity and biodegradability of the final effluent were also evaluated. After oxidation, a slight increase in the specific oxygen uptake rate of the effluent was observed (from 27.0 up to 28.5-30.0mg O-2/(g(VSS)h)) and the inhibition to Vibrio fischeri was eliminated. An effluent that complies with discharge standards was obtained in all cases; however, Approach 3 revealed to be a promising solution for treating this effluent as it leads to smaller operating costs. Therefore, the use of dissolved iron resulting from Fenton's oxidation as coagulant in the second stage was shown to be an innovative, efficient and economically attractive strategy for treating these effluents.