Hybrid sonolysis application as polishing step for removal of thms generated from the drinking water treatment

Abstract

"Trihalomethanes (THMs) are organic compounds (with toxicity potential) generated during the classical treatment flow of drinking water as a result of reaction between natural organic matter (always present in drinking waters resources) and chlorine, which is the most disinfection reagent on a broad scale, in drinking water treatment plants. Ultrasonic treatment can be feasible for THMs removal for small or medium drinking water treatment plants. This paper emphasyzes the possiblity to use sonolysis (chemical oxidation based on active radicals generated during cavitation process) as polishing step in drinking water treatment flow for trihalomethanes (THMs - trichloromethane, tribromomethane and bromodichloromethane) removal (initial concentrations over the admitted limit - 100 µg THM/l). Four sonolysis systems were tested for synthetic and real surface treated water: direct sonolysis (US), US + H2O2, US + H2O2 + Fe (Fenton sonolysis), US + H2O2 + Fe + UV (low pressure mercury lamp  = 250 - 400 nm). The variation domains of the main process parameters were as following: THMs concentrations 310 ÷ 3615 µg/L, sonolysis time 1 ÷ 60 min., ultrasonic energy 2x106 J - 8x106 J, ultrasonic amplitude 20 ÷ 80%, oxidant dose 0.6 ÷ 2.1 g H2O2/L, catalyst dose 0.25 ÷ 2 mg Fe2+/L. Experimental results showed the evolution of THMs removal depending on sonolysis system: direct sonolysis (US) 56% < sonolysis and hidrogen peroxide (US + H2O2) 59% < foto Fenton sonolysis (US + H2O2 + Fe + UV) 63% < Fenton sonolysis (US + H2O2 + Fe) 73% emphasizing that bromoform are more difficult to remove compared to other."