WTP uses UV254 to Help Reduce Coagulant Costs

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The Ridgway WTP receives water from a spring-fed source on Big Mill Creek in rural north-central Pennsylvania near the Allegheny National Forest. Raw water from the creek is fed into the 272 million-gallon H.B. Norton Reservoir before being fed to the WTP. From there, the city’s 2 MGD (7.5 MLD) conventional coagulation, flocculation, sedimentation treatment process handles treatment. Raw water entering the process is dosed with polyaluminum chloride (PAC) for coagulation and soda ash (sodium carbonate) for pH control. Both gas chlorine and permanganate (KMnO4) are also dosed to achieve better organics control in the conventional process. Settled water is then fed to one of five (5) conventional dual-media (sand + anthracite) filters for filtration prior to final stabilization and disinfection before distribution. Overall, the process continues to provide excellent water treatment for its community.

Improving Performance with UV254

Although raw water to the plant is of generally high quality, periodic turbidity spikes and seasonal variation of dissolved organics entering the process have posed operational challenges. Looking for ways to improve performance, Rick McKnight, Ridgway’s Water Plant Supervisor, decided to explore UV254 instruments in the summer of 2012. Before starting to monitor UV254, the plant looked at turbidity on the raw water. “We would have high colour in the water that wasn’t picked up with turbidity” said McKnight “As a result sometimes we were either over-, or under-dosing coagulant which led to filtration and other operating issues.” Based on his research and many years experience operating the plant, McKnight took a proactive approach by putting data from his Real UV254 meter into action. After five (5) years of very promising results the WTP installed a dual-feed Real UV254 analyzer to monitor both raw and settled water in 2017. Now with years of continuous operating data the plant has developed a firm relationship between raw water UV254 and coagulant dose. Being able to monitor organics and adjust their coagulant has made a big impact for the plant.

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