A Membrane System Retrofit-Rapid Valley Sanitary District Case Study

A Stable, Long-term, and Resilient Solution for Clean Water and Consistent Volume

In 2017, the Rapid Valley Sanitary District was not able to reach its goal to deliver three million gallons per day (3 MGD) of drinking water to the community. The root cause was the unreliable and insufficient capacity from the existing polymeric microfiltration systems, which included a system for treatment of backwash from the three other skids.

Above and beyond the capacity challenge in the winter, where near-freezing feedwater caused shrinkage in the polymeric membranes, the systems were subject to frequent fiber breakage and irreversible fouling. This problem was particularly exacerbated when the plant experienced turbidity spikes on incoming water quality as high as 15 NTU. Additionally, the constant fiber breakage issue required manual maintenance, creating an untenable situation for the operators. With the number of shutdowns for cleaning and maintenance, in addition to erratic feed water quality fluctuations, increasing along with the corresponding costs of chemicals and labor, the Rapid Valley Sanitary District knew they needed to replace rather than repair – but they didn’t want to replace PUF systems only to have the same problem in the future.

After a system audit revealed an opportunity for Nanostone to help improve performance and reliability, the district installed its first set of Nanostone CM-151™ ceramic ultrafiltration membrane modules to replace the difficult-to-treat backwash recovery unit. The unique design of the CM-151 ceramic membrane necessitated fewer chemical cleanings, saving the plant 70% on chemical costs, and at the same time, increased the backwash system recovery rate from 80% to 92%, reducing operational headaches and many hours of labor.

Seeing the success of the backwash recovery system, the district retrofitted two out of the three racks of the main processing system with Nanostone CM-151 modules. The unique, patented monolith design of the CM-151 tolerated higher incoming water variability, helping restore Rapid Valley’s output to 3 MGD with only two systems running, as well as enable the plant to consistently and reliably pass its daily integrity test. The systems have also been able to handle feed water turbidity spikes. With the significant increase of the recovery rate of the backwash system, the recovery rate of the overall plant increased from 95% to over 98%.

Since investing in Nanostone’s CM-151™ ceramic UF system, the Rapid Valley operators have a stable, long-term solution for clean water and consistent volume. When the third rack is changed out, the overall capacity will be expanded to 5 MGD with the same footprint, enabling the community to have a resilient water system for current and future capacity needs.