The Application of Response Surface Methodology in the Study of Photodegraded Industrial Dairy Effluents by the Photo-Fenton Process: Optimization and Economic Viability

This study presents results from an application of Photo-Fenton process for organic-load reduction in dairy effluents. Process efficiency was evaluated in terms of percentage dissolved organic carbon, chemical oxygen demand, and biochemical oxygen demand (DOC, COD, and BOD, resp.), whose initial values were ？mg？O2？L？1, ？mg？O2 L？1, and ？mg？O2？L？1, respectively. We applied a statistical design represented by Box-Behnken factorial design inclusive of Fenton's reagent, the power of applied radiation (W), and pH factors. The set temperature value was 30°C with a reaction time of 60？min. The maximum efficiency obtained was at , Fenton reagent in the proportion of 35？g H2O2？ ？3.6？g Fe2+, and ultraviolet radiation potency of 28？W. The results obtained for DOC, COD, and BOD were 81%, 90.7%, and 78.8%, respectively. Regarding the cost/benefit evaluation, the variables and their levels should be the following: pH 3.5, 35.0？g H2O2/Fe2+ 3.6？g, and 28？W？UV, obtaining a reduction in concentration of 79.5% DOC. 1. Introduction Dairy industry effluents are characterized by high volumes of water consumption and elevated organic contents and inhibited recalcitrancy for a conventional treatment [1]. The escape into the aqueous environment of such pollutants, defined as industry-relevant organic components and BOD, COD, pH, fats, and phosphates, among others, demands treatment formulas that minimize the devastating impact of effluent pollution inclusive of degraded waterways, harmed environment, and a general detriment to animal and human health [2, 3]. Economically advantageous biological processes are typically used for dairy effluent treatments regardless of a series of practical limitations [4, 5]. A common problem in this methodology is the oscillation of the organic load in the dairy effluent, resulting in expanded sludge volume and compromises to the efficiency of biological processes [5]. POAs are defined as processes with considerable capacity for hydroxyl radical (？OH) production [6, 7]. A high standard reduction potential (see (1)) for this radical is capable of oxidizing a wide variety of organic compounds to CO2, H2O, and inorganic ions from heteroatoms: Among the POAs, the use of Fe2+/Fe3+ in the presence of hydrogen peroxide under irradiation, called a Photo-Fenton reaction, is considered the most promising for remediation of effluents containing a variety of toxic nonbiodegradable organic compounds [8, 9]. Several industrial effluent treatment studies using this process have been made in recent decades [5, 8–11]. Using a process parameter optimization, the