Sonochemical degradation of ciprofloxacin by hydrogen peroxide and persulfate activated by ultrasound and ferrous ions

Abstract

This paper evaluates the use of various oxidation methods such as ultrasonic/persulfate (US/PS), ultrasonic/hydrogen peroxide (US/H2O2), US/H2O2/Fe2+, US/PS/Fe2+, and the US/PS/H2O2/Fe2+ process and compares their potential in removal of ciprofloxacin (CIP). The results showed that US/PS/H2O2/Fe2+, was the most efficient among the studied processes. In US/PS/H2O2/Fe2+, 100% removal of CIP was achieved at pH 3 and 50 min of treatment when the initial concentration of CIP, H2O2, PS and Fe2+ were 25 mg/L, 4 mM, 6 mM and 1 mM, respectively. The results showed that with increasing ultrasonic power and increasing concentrations of H2O2, PS, and Fe2+, the removal percentage increases. Toxicity of CIP solution was scrutinized by Daphnia magna, and the US/PS/H2O2/Fe2+ process was able to provide toxicity elimination of 100% for the solution. Also, the equilibrium data for all processes followed first-order kinetics with a regression coefficient above 0.9, and the reaction rate constant for the US/PS/H2O2/Fe2+ process was higher than other systems. At 60 min of sonochemical time, the energy consumptions by US/PS, US/H2O2, US/H2O2/Fe2+, US/PS/Fe2+, and US/PS/H2O2/Fe2+ were 105.5, 87.5, 64.7, 41.4 and 16.2 kWh/m3, respectively, suggesting the last one as the most economical. Additionally, for the processes combined with the iron, biochemical oxygen demand/chemical oxygen demand (BOD5/COD) in the CIP solution was above 0.4, which indicated the conversion of non-biodegradable wastewater to biodegradable form. The total organic carbon (TOC) test was performed, and the mineralization percentage by the US/PS/H2O2/Fe2+ process was 82%. Studies conducted for evaluating the effect of scavengers also showed that both sulfate (SO4•−) and hydroxyl (•OH) radicals play an important role in the studied process.