Treatment of real dairy wastewater by electrolysis and photo-assisted electrolysis in presence of chlorides.

The efficiency of electrolysis (EC/Cl2) and photo-assisted electrolysis (EC/UV/Cl2) methods, in the presence of chloride, for the abatement of real dairy waste from a producer in the Triangulo Mineiro region of Brazil, was evaluated. A complete 23 factorial design was performed for the variables time, pH and current. After determining the ideal pH, a Central Compound Design (CCD) was performed, where the applied current (533.42 mA) and treatment time (60.45 minutes) were maximized. The effluent was subsequently submitted to prolonged EC/Cl2 and EC/UV/Cl2 treatment in order to evaluate the behaviour of specific environmental parameters over time. The EC/UV/Cl2 method was more efficient than simple EC/Cl2 treatment. The EC/UV/Cl2 method resulted in a reduction of all environmental parameters investigated to levels within legal standards for effluent discharge. A relatively low cost of treatment is obtained with Energy per Order (EEO) values of 0.89 and 1.22 kWh m-3 order-1 for the EC/UV/Cl2 and EC/Cl2 treatments, respectively. The electrochemical production of free chlorine species followed by subsequent photolysis and production of radical species can convert a simple electrochemical process into an advanced oxidation process (AOP).

Experimental-design-guided approach for the removal of atrazine by sono-electrochemical-UV-chlorine techniques.

The aim of the present study was to investigate the electrochemical formation of free chlorine species (HOCl/ClO-) and their subsequent use for the degradation of the pesticide atrazine. Initially, the process of electrochemical-free chlorine production was investigated using a bench-scale electrochemical flow-cell. The most significant variables (electrolyte concentration ([NaCl]) and inter-electrode gap) of the process were obtained using a 23 factorial design and the optimum process conditions (1.73 mol L-1 and 0.56 cm) were determined by a central composite design. Following optimization of free chlorine production, three degradation techniques were investigated, individually and in combination, for atrazine degradation: electrochemical, photochemical and sonochemical. The method using the techniques in combination was denominated sono-photo-assisted electrochemical degradation. Constant current assays were performed and the sono-photo-assisted electrochemical process promoted more efficient removal of atrazine, achieving total organic carbon removal of ∼98% and removal of atrazine to levels below the detection limit (>99%) in under 30 min of treatment. Furthermore, the combination of three techniques displayed lower energy consumption, and phytotoxicity tests (Lactuca sativa) showed that there was no increase in toxicity.