Optimization of Ultrasonic Disinfection of Combined Sewage Overflow Water
Abstract:Combined Sewer Overflow (CSO) events are an important problem facing most major cities in the Northeast and Midwestern United States. In these communities, storm and sanitary sewers are connected so that storm runoff and raw sewage can mix together. This mixing often occurs when the sewer system is surcharged (overloaded) due to a storm event. To prevent raw sewage from backing up into homes and businesses, municipalities often divert the excess sewage directly into an open stream or river, thereby creating a CSO event. Because this diverted sewage is untreated, it has high Escherichia Coli (E. Coli.) counts, which adversely effects water quality and poses a significant public health threat. One possible solution is to treat CSO water with ultrasonic disinfection. We investigated the conditions for the optimization of ultrasonic disinfection of CSO water; as well as, whether the addition of TiO2 could strengthen this process. Experimental results indicated that ultrasonic disinfection of CSO was a firstorder process and that more than 95% of E. Coli. in 300ml CSO samples were deactivated after 35 minutes of treatment at 60w. When the treatment time was held constant (20 minutes), increasing the ultrasonic power from 15 to 40.2w increased E. Coli. removal from 40.5% to 85.9%, although ultrasonic power from 40.2 to 70.8w had no significant improvements on E. Coli. reduction. The addition of TiO2 from 0 to 0.05321g/300ml of CSO water actually reduced E. Coli. removal percentage from 76.2% to 55.7% for 20 minutes of treatment; however, when TiO2 was increased to 0.2725g/300ml of CSO water, the percent removal of E. Coli. increased to 83.8%. No significant change to E. Coli. removal was detected for further increases of TiO2 addition. This study showed that ultrasonication could deactivate E. Coli. effectively at room temperature and both ultrasonication time and power could be optimized. However, the addition of TiO2 resulted in different ultrasonic disinfection performance with no significant improvement over pure ultrasonication.
Document Type: Research Article
Publication date: January 1, 2009
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