Investigating natural organic carbon removal and structural alteration induced by pulsed ultrasound

The application of pulsed ultrasound for DOC removal from natural water samples has been thoroughly investigated in this work. Natural water samples were treated with ultrasound at power levels of 48 and 84 W with treatment times of 5 and 15 min. Chemical fractionation was conducted for both untreated and treated samples to clearly identify the change in DOC structure caused by ultrasonic treatments. Statistical analyses applying 2(3) factorial design were performed to study the behaviour of the response (i.e. DOC removal) under different operating conditions. Overall, ultrasonic treatments resulted in DOC removal of 7-15% depending on the applied operating conditions. The treated water had high microbial loading that interfered with DOC removal due primarily to the release of microbial products when exposed to ultrasound. Pulse ultrasound was found to be more effective than the continuous mode for DOC removal at the same effective power level. A regression model was developed and tested for DOC removal prediction. The model was adequate in predicting DOC removal with a maximum deviation from the experimental data of <11%. Pulsed ultrasound at low power levels and short treatment times was found to be the most energy efficient treatment for DOC removal.