Study of the degradation of sodium dodecyl sulfate surfactant from hydrodynamic cavitation coupled to oxygen injection generated by a low-cost electrolytic cell using solar energy

Anionic surfactants such as sodium dodecyl sulfate (SDS), when present in wastewater, are harmful to humans and ecosystems. For this reason, several strategies have been developed to remove these contaminants from the environment (Nguyen et al., 2016; Mondal et al., 2019; Aboulhassan et al., 2006). However, conventional remediation methods, such as biological and physical-chemical processes, do not provide a definitive solution for the treatment of wastewater containing these compounds, as they use chemical reagents for the process, which in turn also raises additional concerns when deposited in rivers and lakes (Mondal et al., 2019; Mirbahoush et al., 2019; Saha et al., 2020; Kim and Park, 2021). Therefore, in this work we propose a treatment solution for this contaminant through hydrodynamic cavitation coupled with oxygen injection. The objective was to remove SDS through an effective and sustainable method without introducing any new chemicals and therefore not affecting the environment. Electrolytic cells were designed and built to produce oxygen by alkaline water electrolysis and solar energy. A central composite design was proposed to obtain the best pressure, pH and surfactant concentration conditions for the treatment of water by hydrodynamic cavitation. High SDS degradation rates (>98 %) were transported in strongly acidic conditions. The increase in pressure also contributed positively to the increased removal of this contaminant. Surfactant concentration was not considered a significant variable. The optimal values of pressure and pH obtained were 5.5 bar and 2.03, respectively. These experimental conditions were used in the surfactant treatment by 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 contaminant removal was 5 % higher than the degradation obtained using cavitation alone. In contrast, the injection of 175 ml/min of oxygen did not significantly increase the kinetic constant of the reaction and consequently the surfactant degradation. Studies indicate that a minimum amount of gas must be added to obtain significant degradations. [Display omitted] •The k constant increased 41.68 % with the injection of 350 ml/min of O2 into process.•The removal of SDS with O2 was about 5 % higher than that achieved using HC alone.•High SDS degradation rates (>98 %) w