Estudo da degradação do surfactante dodecil sulfato de sódio a partir da cavitação hidrodinâmica acoplada à injeção de oxigênio gerado in loco por eletrólise alcalina da água induzida por energia solar fotovoltaica

Abstract

Anionic surfactants such as Sodium Dodecyl Sulfate (SDS) are harmful to humans and ecosystems. Conventional remediation methods do not provide a definitive solution for treating wastewater containing these compounds. Thus, it was proposed to treat solutions of this contaminant through hydrodynamic cavitation coupled to oxygen injection by alkaline water electrolysis and solar energy. First, electrolytic cells were designed and built to produce oxygen from the electrolysis of water and solar energy. The results modified that the highest oxygen productions were obtained at the highest currents and the highest electrolyte (KOH) solutions. The energy efficiency and capacity of these cells connected in series were investigated. The most efficient configurations were not those that produced the greatest amounts of oxygen gas, but those that produced the greatest amount of oxygen per unit of energy consumed. The most efficient arrangement referred to 5 cells connected in series, with a concentration of 7 mol/L and an oxygen flow rate of 175 mL/min. The flow of 350 mL/min of gas was obtained with a configuration of 4 cells connected in series, with an electrolyte concentration of 7 mol/L and a current of 13.5 A. A central composite design was proposed to obtain the best conditions for pressure, pH and surfactant concentration for the treatment of hydrodynamic cavitation. High SDS degradation rates (greater than 98%) were transported in strongly acidic conditions. The increase in pressure also contributed positively to the increase in removal. Surfactant concentration is not shown to be a significant variable. The optimum values of pressure and pH obtained were 5.5 bar and 2.03, respectively. These experimental conditions were used in the treatment of hydrodynamic cavitation coupled with oxygen injection. Two oxygen flows were analyzed: 175 and 350 mL/min. The introduction of the highest gas flow into the system increased the reaction kinetic constant from 50.43 · 10−3 to 71.45 · 10−3 . The removal of the contaminant was 5% higher, when comparing the degradation obtained only with cavitation. However, the injection of 175 mL/min did not result in a significant increase in the kinetic constant of the reaction and, consequently, in the degradation of the surfactant Studies indicate the existence of a minimum amount of gas to be added to obtain significant degradations. The analysis of the addition of oxygen was also carried out under non-optimized conditions, using solutions with neutral pH. At the end of 120 min of treatment, the removal of SDS with the addition of 350 mL/min of oxygen was about 7% higher, when compared to the removal obtained only with hydrodynamic cavitation.