A new flow reactor for the treatment of polluted water with microwave and ultrasound

Microwave (MW) and high-intensity ultrasound (US) provide innovative techniques for the degradation of persistent organic pollutants (POPs). When Fenton's reagent is used to treat industrial wastes, organic pollutants are degraded by highly reactive hydroxyl radicals (HO.) that can oxidize almostany organic compound to carbon dioxide and water. These reactions, when carried out under US or MW, are faster and much more efficient. The present work assesses the combined effect of US and MW using a new flow reactor developed in our laboratory. In this 5 L pilot reactor the liquid was pumped in parallel through a modified domestic MW oven and through a cell where it was irradiated with two US generators working at 20 and 300 kHz, while MW irradiation took place in it modified domestic oven. We studied the degradation of 2,4-dibromophenol (0.1 g L-1 in water) by Fenton's reagent, assessing the contribution of each energy source to the overall effect, and found that MW and US-300 kHz played the main role. A modest amount of oxidant (6 mL 30% H2O2 per 1 L of polluted water) sufficed to achieve complete degradation within 6 h, at which time organic compounds were no longer detectable. Even if no Fenton's reagent was added, about one half of the pollutant was degraded after 3 h irradiation.