Treatment of methylamine containing wastewater using combined processes based on ultrasound

Methylamine (MA) degradation has been studied using different processes based on cavitation and oxidants such as hydrogen peroxide (H2O2), Fenton's reagent (H2O2/Fe2+), ozone (O3), and potassium persulfate (KPS, K2S2O8). Effects of different operating parameters such as treatment temperature, US power, pH of the solution, and oxidant loading on the extent of degradation have been studied. Acoustic power of 100 W with a frequency of 22 kHz and duty cycle of 70 % (7 s ON, 3 s OFF) were elucidated as the best treatment conditions for only ultrasound induced degradation (US). Amongst all the combined approaches, US+KPS scheme was the most efficient and economical treatment scheme for the highest removal of MA (97.3 %) within 2 h of treatment. The optimized US+KPS scheme at conditions of pH of 10, KPS loading of 0.5 g/L, and temperature of 30 °C was exploited for MA degradation at a pilot level using a longitudinal horn based sonoreactor at a capacity of 4 L, which resulted in 94 % of MA removal. Cavitational yield for longitudinal horn (1.23 × 10−3 mg/J) was almost 4 times higher than that seen in a simple US horn (0.33 × 10−3 mg/J) under similar conditions. Additionally, it was shown that a combined strategy based on cavitation and oxidants is preferred compared to an individual approach involving ultrasound or oxidants. Overall, the longitudinal horn reactor in combination with KPS was shown to be the most energy-efficient and economical treatment method, giving 94 % of degradation at an operating cost of 0.03 $/L.