Optimization of sunlight photo-catalytic treatment coupled to a coagulation-flocculation process

Abstract

Abstract The oleic industry is one of the most polluting in food industry sector. Among other harmful by-products, it generates charged sludge. Coagulation–flocculation is a relatively simple physico–chemical technique that ensures excellent separation of solid particles from dissolved ones. To obtain acceptable treated water quality, this method is used along with TiO2-based sunlight photo-catalysis. We optimize this binary process to treat mill wastewater collected from the region of Mahdia, east center of Tunisia, by applying a combination of mixture design (3 components-mixture: lime water, iron solution and cactus mash) and full factorial design 22 (2 process factors: dilution ratio (aqueous solution/water) and used TiO2 mass). Both the phenolic compounds removal and solution decolorization are closely monitored. The quadratic models for those two responses indicate optimum conditions to a coagulation-flocculation performance using a mixture of 48.48% of lime water with 51.52% of cactus mash with low level of dilution rate and high level of TiO2 mass. Experience of those conditions validated calculi, and they give a decolorization of 92.57 ± 0.90% and an organic degradation of 96.19 ± 0.97% in good concordance with the mathematic predictions that yield 93.06% of decolorization and 98.70% of organic degradation.