In the present work, the degradation of methomyl has been carried out by using the ultrasound cavitation
(US) and its combination with H2O2, Fenton and photo-Fenton process. The study of effect of operating pH
and ultrasound power density has indicated that maximum extent of degradation of 28.57% could be
obtained at the optimal pH of 2.5 and power density of 0.155 W/mL. Application of US in combination
with H2O2, Fenton and photo-Fenton process has further accelerated the rate of degradation of methomyl
with complete degradation of methomyl in 27 min, 18 min and 9 min respectively. Mineralization study
has proved that a combination of US and photo-Fenton process is the most effective process with maximum
extent of mineralization of 78.8%. Comparison of energy efficiency and cost effectiveness of various
processes has indicated that the electrical cost of 79892.34 Rs./m3 for ultrasonic degradation of methomyl
has drastically reduced to 2277.00 Rs./m3, 1518.00 Rs./m3 and 807.58 Rs./m3 by using US in combination
with H2O2, Fenton and photo-Fenton process respectively. The cost analysis has also indicated that
the combination of US and photo-Fenton process is the most energy efficient and cost effective process.