The U.S. Environmental Protection Agency's (USEPA) Guidance Manual requires both direct
and indirect monitoring of membrane filtration performance by daily integrity testing and
continuous on-line turbidity testing. Some states have accepted the USEPA guidelines; however,
other states require further indirect monitoring and have implemented additional, more stringent
requirements. Many of the regulations and guidelines were promulgated when membrane
filtration technology was in its infancy and only limited or pilot testing data were available.
The City of Kennewick, Washington completed the retrofit of its Water Filtration Plant (WFP)
multi-media filters with a state-of-the-art submerged membrane system. This conversion
doubled the plant's capacity (to 15 million gallons per day [MGD]) within the original footprint.
However, during the startup period, the turbidity and particle counts exceeded the Washington
Department of Health threshold limits. The plant's supervisory control and data acquisition
(SCADA) system showed that spikes occurred after every backwash and after the daily pressure
decay test (PDT). The output from the on-line instruments confirmed that the spikes occurred
approximately 60 seconds after the backwash cycle and continued for up to 20 minutes.
An investigation ensued, and minute air bubbles were observed in the tubing and rotometers that
led to each instrument. It became apparent that entrained/dissolved air was released into the
membrane filtrate, migrated to the instruments, and registered as particles, causing false positive
turbidity and particle count readings.
The challenge of starting up this submerged membrane system was to meet water demands and
maintain regulatory compliance with instrumentation that is so sensitive that a few tiny air
bubbles can trigger an automatic shutdown and indicate that the system is out of regulatory
compliance.
Startup procedures required innovative actions to successfully reduce the influence of entrained
air and to demonstrate to the Department of Health that the membrane filtration system was fully
operational and compliant with state and USEPA guidelines.
This paper summarizes the regulatory guidelines of several states in which membrane filtration is
used and how these rules can affect full-scale operating and reporting parameters during startup.
The regulatory lessons learned at the Kennewick WFP, the largest membrane filtration plant in
the Northwest, are described, as well as lessons learned from other recent membrane plants in the
U.S. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 47 |
| Published : | 06/01/2007 |
