Assessing the application and downstream effects of pulsed mode ultrasound as a pre-treatment for alum coagulation

• Pulsed mode ultrasound (PMU) as a pre-treatment for alum coagulation was studied.
• PMU pre-treatment increased maximum DOC and turbidity removal.
• PMU pre-treatment decreased the minimum residual dissolved Al.
• PMU pre-treatment increased microbial removal and decreased DBPs.
• PMU improved the settleability of coagulation sludge.

The application of pulsed mode ultrasound (PMU) as a pre-treatment for alum coagulation was investigated at various alum dosages and pH levels. The effects of the treatments on turbidity and dissolved organic carbon (DOC) removal and residual Al were evaluated. Response surface methodology (RSM) was utilized to optimize the operating conditions of the applied treatments. The results showed that PMU pre-treatment increased turbidity and DOC removal percentages from maximum of 96.6% and 43% to 98.8% and 52%, respectively. It also helped decrease the minimum residual Al from 0.100 to 0.094 ppm. The multiple response optimization was carried out using the desirability function. A desirability value of >0.97 estimated respective turbidity removal, DOC removal and Al residual of 89.24%, 45.66% and ∼0.1 ppm for coagulation (control) and 90.61%, >55% and ∼0 for coagulation preceded by PMU. These figures were validated via confirmatory experiments. PMU pre-treatment increased total coliform removal from 80% to >98% and decreased trihalomethane formation potential (THMFP) from 250 to 200 ppb CH3Cl. Additionally, PMU application prior to coagulation improved the settleability of sludge due to the degassing effects. The results of this study confirms that PMU pre-treatment can significantly improve coagulation performance.