The use of the Fenton's process for the depuration of a post-biological treated milk whey wastewater was studied, aiming to achieve adequate operational conditions for a cost effective treatment to generate a suitable effluent to be directly discharged into the natural water courses. A design of experiments was implemented in order to understand the role of the independent parameters and their combinations over the treatment process. From our results the hydrogen peroxide concentration and the ratio between [H2O2]:[Fe2+] as well as their interaction were statistically important concerning both TOC and COD removal. The experiments performed at the highest value of [H2O2] and at the lowest level of [H2O2]:[Fe2+] lead to effluents accomplishing the environmental legislation. Moreover, toxicological tests revealed that the treated effluent was harmless to the ecosystems. A cost estimation analysis was performed and the catalytic activity of the remaining sludge from the homogeneous process was checked. This activity decreases with the number of reuses which reduces the possibility of the direct utilization of the sludge.
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