Mitigating Cryptosporidium Risk in Source Water

The City of Moline, Ill., is located in the heart of the Midwest, tucked between the banks of the Mississippi and Rock River in Rock Island. Moline is one of four cities that make up the Quad Cities, which include Rock Island, Ill., and Bettendorf and Davenport, Iowa.

Challenge

The Water Division provides continuous high-quality water to the approximately 43,500 people who call Moline home. It utilizes the Mississippi River as its source to treat, pump, and meter water to over 17,000 homes and businesses.

The variable quality of the water in the Mississippi source poses unique treatment challenges to the Water Division. Moline’s LT2 water study revealed that significant levels of cryptosporidium are periodically present in the source water. However, the Water Division staff believes that this level was actually under-­reported due to limitations in sampling and detection methods. Knowing that its drinking water supply system must function dependably and continuously, the city took immediate action to protect public health.

The Solution

After carefully examining a variety of alternate disinfection methods, including ozone and membrane technologies, the city selected ultraviolet (UV) technology as a more economical option in terms of capital and annual operating costs.

Cryptosporidium is effectively deactivated using UV disinfection, which has become an important barrier both in the U.S. and globally to ensure that drinking water is healthy and free from harmful organisms, particularly those resistant to chlorine like cryptosporidium and giardia.

The city chose to add validated UV systems from Evoqua to provide an additional barrier for the filtered water, which will improve water quality and ensure that chlorine-tolerant organisms are not present. The ETS-UV™ systems are third-party validated in accordance with the U.S. EPA Guidance Manual and are manufactured in Beaver Dam, Wis.

A total of eight SX-635-16 UV systems were selected to be installed into the existing filter gallery. When a low water transmittance of 70 percent is recorded, all eight UV systems will operate. When the water quality improves to a transmittance of 80 percent, six UV systems will operate at an average flow rate of 1.2 MGD and it is anticipated each filter will run up to 2 MGD to allow for future growth. The systems are validated to achieve a 2.5 log removal of cryptosporidium.

As often is the case with drinking water filter galleries, space was very tight. The design of the manifold pipework to house the UV system was a concern, as was the location of the butterfly valve. To understand the impact of the design of the installation on the performance of the UV system, Evoqua carried out extensive computational fluid dynamics (CFD) modeling to demonstrate that the UV system would match the performance of the validation when installed.

“The city is pleased to have Evoqua as our partner for this important project,” said Greg Swanson, general manager of Moline Utilities. “We have found the Evoqua ETS-UV team to be knowledgeable, responsive, and goal oriented during the multi-year process that led to the selection of the systems for our demanding drinking water application. Their technical expertise and dedication have played a crucial role in working with our consultant partner and satisfying the design requirements of our primacy agency.” WW

Evoqua Water Technologies is exhibiting at AWWA’s ACE18 expo in booth 20031. Learn more at evoqua.com.

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