AWWA WQTC62478

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2) is intended to improve control of Cryptosporidium through watershed control programs, improved removal processes or the use of alternative disinfectants (U.S. Environmental Protection Agency, 2003). Large systems may satisfy LT2 requirements by switching to ultraviolet (UV) disinfection; however, small treatment systems may not have the capabilities to implement this technology. Adenovirus, which is on the Contaminant Candidate List, is highly UV resistant (Gerba et al., 2002). Also, certain bacteria can photoreactivate after treatment with UV (Harris et al., 1987) contributing to the challenge of properly applying UV disinfection. Utilities using chlorine alone may not be able to simultaneously meet LT2 and disinfection byproduct regulations because C. parvum is highly resistant to chlorination (Driedger et al., 2000). An alternative is the use of multiple disinfectants which can enhance inactivation (Corona-Vasquez et al., 2002). Sonication is an innovative chemical free disinfectant that should be considered. Ultrasonic waves create pressure variations in time and space that ultimately lead to cavitation. Collapsing bubbles cause dramatic increases in fluid velocity and temperature on a microscopic scale, increasing velocity to near the speed of sound and temperatures to 3,000 K or more (Riesz et al., 1985). When used in combination with a second disinfectant, the stresses on cell membranes can cause an increase in microorganism sensitivity such that inactivation is greater than would be predicted based on additive effects (Phull et al., 1997; Jyoti and Pandit, 2003). In addition, sonication can reduce the required dose or contact time of a second disinfectant while still achieving the same inactivation (Burleson et al., 1975). The objective of this study was to quantify the synergistic impact of ultrasound treatment on chlorination for the disinfection of drinking waters. This technology was studied for potential application at small utilities that currently use chlorine for primary disinfection and need to enhance levels of inactivation in order to meet the LT2 requirements. Laboratory experiments were performed to quantify the inactivation of E. coli and MS2 coliphage (as representative bacterial and viral indicator organisms, respectively) through combined disinfection with chlorine and sonication. Three separate sets of experiments were conducted. The first two, which tested sonication alone and chlorination alone, were used to determine benchmark inactivation levels. In the third set of experiments, the two disinfectants were applied simultaneously. Includes 10 references, tables.