Integrated ozonation assisted electrocoagulation process for the removal of cyanide from steel industry wastewater

This work focuses on the removal of cyanide, chemical oxygen demand (COD), biological oxygen demand (BOD), and chloride from biological oxidation treated (BOT) effluent of the steel industry by integrated ozonation assisted electrocoagulation method. The removal efficiency of the pollutants was found to be inefficient when the electrocoagulation or ozonation process was performed separately. However, a combination of ozonation and electrocoagulation gives a highly satisfactory result. Such an integrated approach for the treatment of BOT effluent has not been previously investigated. The effects of operating variables viz. ozone generation rate, current density, and analysis time on pollutant removal were primarily analyzed for the hybrid process. The experimental operating condition was optimized and was seen that ozone generation rate of 1.33 mg s^-1, ozonation time of 40 min, a current density of 100 A m^-2, and electrolysis time of 30 min were sufficient for reducing the pollutant concentration below its permissible limits. The removal efficiencies of the combined process at optimum conditions were 99.8%, 94.7%, 95%, and 46.5% for cyanide, COD, BOD, and chloride ions, respectively. A kinetic study was performed for the degradation of the pollutants during ozonation. The pseudo-first-order kinetic model was found to be best suited for the analysis with the highest R² value of 0.99 for cyanide, COD, BOD, and chloride, respectively. The mass transfer study conducted further showed that the volumetric mass transfer coefficient, K_la, was increased with that of the ozone generation rate. Cost estimation of the hybrid process was done and compared with that of the other reported integrated process.