Oxidative and Photochemical Processes for Soft Drink–Industry Wastewater Treatment

Soft drinks–industry wastewater (SDIW) contains high concentrations of sugar (420–487 mg/L) and sodium (320–397 mg/L), has high pH (∼9), and contains biorefractory pollutants. Therefore, rapid and effective techniques are required for its treatment. In the present study, SDIW was subjected to microwave (MW) photocatalysis (PC) using electrodeless discharge lamps, and the outcomes were compared with other oxidative and photochemical advanced oxidation processes, including oxidation, MW oxidation (MWO), and ultraviolet–titanium dioxide PC, in terms of the removal efficiency of organics based on chemical oxygen demand (COD), total phosphate (TP), and total nitrogen (TN). The mineralization of organics was ∼3.5 times higher in the MWPC and MWO systems compared to the oxidation and PC systems. The COD removal efficiency after 60 min using the oxidation, PC, MWO, and MWPC systems was 22.7%, 25.41%, 79.36%, and 87.3%, respectively. Direct photolysis using UV (using 486 kJ/mole of energy) and photocatalytic degradation using increased hydroxyl radicals in the presence of MWs was the primary degradation mechanism in the MWPC system. The TP removal efficiency in the oxidation, PC, MWO, and MWPC systems was 15%, 40%, 50%, and 60%, respectively. The respective TN removal efficiencies for the four systems were 40%, 58%, 82%, and 85%. The main mechanism for organics, TP, and TN removal in the MWPC system involved the direct disruption of the chemical bonds of the organic molecules, photocatalytic phosphate reduction, and breaking of the primary amine bond in the organic nitrogen using the high-energy plasma and hotspots that formed in the MW-based systems. The electrical energy consumed by the systems [electrical energy per order (EEO)] occurred in the order PC > MWO > MWPC, with respective values of 14,614, 6,919, and 4,526 Rs/kg COD removal.