نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Global water scarcity and the increasing demand from industrial sectors have made wastewater recycling an essential strategy for sustainable resource management. Among various industrial effluents, spent caustic wastewater from petrochemical units is considered one of the most challenging and hazardous streams due to its high alkalinity, high sulfide content, unpleasant odor, and toxicity. Inadequate treatment or disposal of this effluent can severely contaminate water bodies and threaten both human health and aquatic ecosystems. Therefore, the development of efficient, economical, and environmentally friendly methods for sulfide removal has become a critical priority. This study investigated the potential of hydrodynamic cavitation as a treatment technology for sulfide removal from spent caustic wastewater. A semi-industrial pilot reactor equipped with an orifice-plate cavitation device was designed and operated using synthetic wastewater simulating real effluent. The influence of key operating parameters - including inlet pressure (3 to 5 bar), initial temperature (20 to 40°C), residence time (0 to 120 minutes), sulfide concentration (5 to 20 mg/L), and the addition of oxidants (1000 mg/L H2O2 and 45 L/min of air) - was systematically investigated using a single-factor approach. The results indicated that at the optimal pressure of 4 bar and a temperature of 30°C, more than 90% of sulfide removal was achieved in less than 60 minutes, with complete removal achieved within 90 minutes. Increasing the retention time led to a higher number of recirculation cycles (over 70 cycles) and improved removal efficiency. At an initial concentration of 5 mg/L, complete sulfide removal occurred in less than 60 minutes, whereas at 20 mg/L, approximately 50% removal was achieved within the first 30 minutes, with complete removal after 90 minutes. The addition of air or H2O2 alone did not yield significant improvement; the high peroxide dose converted part of the OH• radicals into weaker HO2• species, and excessive aeration reduced the intensity of bubble collapse, thus reducing the system’s oxidative capacity compared to pure HC. The data showed good agreement with zero-order (R2 = 0.89–0.99) and pseudo-first-order (R2 = 0.85-0.98) kinetic models. The cavitation yield was calculated as 0.0025 mg/J, and the treatment cost under optimal conditions was estimated at approximately 44060 Rials per cubic meter of wastewater. The results show that the hydrodynamic cavitation, without the need for chemical additives, is an efficient, cost-effective, and sustainable method for removing sulfide from high-salinity spent caustic wastewater.
کلیدواژهها English
