Novel approaches based on ultrasound for treatment of wastewater containing potassium ferrocyanide

Industrial wastewaters containing biorefractory compounds like cyanide offer significant environmental problems attributed to the fact that the conventional methods have limited effectiveness and hence developing efficient treatment approaches is an important requirement. The present work investigates the use of novel treatment approach of ultrasound (US) combined with advanced oxidation techniques for the degradation of potassium ferrocyanide (KFC) for the first time. An ultrasonic bath equipped with longitudinal horn (1 kW rated power and 25 kHz frequency) has been used. The effect of initial pH (2-9) on the progress of degradation has been investigated initially and subsequently using the optimized pH, effect of addition of hydrogen peroxide (ratio of KFC:H2O2 varied over the range of 1:0.5-1:5) and TiO2 in the presence of H2O2 (1:1 ratio by weight of TiO2) as process intensifying approach has been studied. Combination of ultrasonic irradiation with ozone (O3) (100-400 mg/h) and ultraviolet irradiation (UV) has also been investigated. Use of combination of US with H2O2, H2O2 + TiO2 and ozone resulted in extent of KFC degradation as 54.2%, 74.82% and 82.41% respectively. Combination of US with both UV and ozone was established to be the best approach yielding 92.47% degradation. The study also focused on establishing kinetic rate constants for all the treatment approaches which revealed that all the approaches followed first order kinetic mechanism with higher rate constants for the combination approaches. Overall, it has been conclusively established that ultrasound based combined treatment schemes are very effective for the treatment of KFC containing wastewaters.