Two case studies outlining the benefits of using ozone and UV are presented in this paper. They demonstrate the cost effectiveness and robustness that can be observed when the synergies of these two treatment alternatives are utilized. In the first study, ozone and UV disinfection were used at the Weber Basin Water Conservancy District’s Water Treatment Plant No. 3. The ozone system was designed to improve pretreatment, control taste and odor (T&O) compounds, and provide an additional Giardia barrier, while UV was used to provide 2-log of Cryptosporidium inactivation. The capital cost savings obtained by using this option, as opposed to using ozone alone, were nearly 50%. In the second study, the effectiveness of ozone and UV were assessed on the challenging water of Lake Okeechobee. With the goal of meeting all US Primary and Secondary Drinking Water Standards, the data analysis indicated that a combination of ozone and UV disinfection would result in the most cost-effective option. The use of ozone to reduce color and decrease UV transmittance (UVT) resulted in substantial cost savings by decreasing the ozone dose over what would be required to achieve Cryptosporidium disinfection and allowing for the elimination of an ozone contactor. Furthermore, the increase in UVT that was observed resulted in a smaller UV system, thereby reducing the cost of the overall system even further.

The use and selection of microbial surrogates to validate ultraviolet (UV) reactor performance remain a challenge. Proper interpretation of bioassay results requires an appreciation of the relative UV dose–response of the surrogate and target organisms and the limitations surrogates impose. The aim of this study was to improve the understanding of MS2 coliphage's use as a bioassay surrogate for the waterborne pathogen Cryptosporidium parvum. Side‐by‐side MS2 and Cryptosporidium bioassays were performed to directly link MS2 and Cryptosporidium inactivation. At a flow rate of 757 L/min (200 gpm), the low‐pressure, high‐output UV reactor provided > 4.7‐log Cryptosporidium inactivation at an MS2 equivalent dose of 45 mJ/cm2. Although these data support the use of MS2 as a test organism to validate UV reactor performance, MS2 is a very conservative surrogate for Cryptosporidium. Use of a test organism with a more comparable UV dose–response would allow validation of much higher levels of log inactivation.

Due to the development of a new analytical method that lowered the perchlorate detection limit to 4 μg/L, perchlorate has been detected in many drinking water sources. Perchlorate contamination is now recognized as a widespread concern affecting many water utilities. Furthermore, perchlorate is a very stable substance in aquatic systems and is therefore difficult to remove with conventional treatment processes. Magna Water Company in Utah, USA, provides chlorinated groundwater as potable water to the northwest section of Salt Lake County. The groundwater of one of their wells is contaminated with low levels of perchlorate and concentrations are expected to rise due to plume migration. High hardness, alkalinity, and TDS characterize this groundwater. An electrodialysis reversal (EDR) pilot unit was installed at an uncontaminated well. Various perchlorate levels were spiked into the feed water to test the full range of possible perchlorate concentrations. This paper provides EDR performance and cost data for perchlorate treatment. Based on perchlorate removal, the production cost varies between $1.10 and $1.50 per 1000 gal ($0.30 and $0.40/m3). The presented data allow comparison with other treatment processes.