Tide on Their Side
Nitrification problem avoided with mixing system
Red Valve Co.
700 North Bell Ave. * P.O. Box 548 * Carnegie,
Most distribution reservoirs have a short-circuiting problem
caused by a common inlet/outlet.
This type of design keeps newly added water from mixing with
water already in the reservoir. This stratification could lead to diminished
water quality, such as loss of disinfectant residual, bacteria regrowth,
disinfection byproduct formation, nitrification, biofilm and algae growth, and
unpleasant taste or odor.
The Calleguas Municipal Water District, which serves an area
of approximately 350 sq miles in southern Ventura County, Calif., wanted to be
proactive and avoid a potential nitrification problem in its Newbury Park
Reservoir. The reservoir is a 145 ft diameter welded steel tank that holds four
million gallons of finished water.
The District turned to Perliter & Ingalsbe Consulting to
find a solution. P&I determined that the installation of a custom-designed
Tideflex Mixing System manufactured by Red Valve Co., Inc., could help to avoid
In the typical ground level water storage tank, the common
inlet/outlet tank penetration is either horizontally through the shell or
vertically through the floor.
Prior to installing the Tideflex Mixing System, the method
used to separate the inlet/outlet pipe included a separate pipe around the
perimeter of the tank or under the floor. This required two penetrations, the two
pipes to be joined in a vault outside the tank, extra fittings, isolation
valves, etc. As can be expected, this method involves unnecessary expenses.
Conversely, the Tideflex Mixing System is cost-effective
because the system is connected to the tank penetration via a flanged fitting
or coupling. A manifold pipe with the system’s inlet valves is laid along
the floor on pipe supports to the side opposite the penetration. A set of
outlet valves is installed on the side of the tank near the penetration.
Field data has shown that a typical Tideflex Mixing System
installation results in increased and more consistent disinfectant residuals
throughout the water volume. The typical tank common inlet/outlet pipe is of a
diameter that only generates 2-4 fps jet velocity at average fill rates.
The Tideflex Mixing System is generally sized for 8-10 fps jet velocity.
In Calleguas’ Newbury Park Reservoir installation, a
new 24-in. PVC manifold replaced the common inlet/outlet. The manifold spanned
most of the tank and utilized four patented Tideflex inlet valves on the far
side and four Tideflex outlet valves near the side wall penetration. This
configuration improved mixing and circulation, and optimized the turnover rate
and detention time. The duckbill design of the Tideflex check valve had no
moving parts and operated solely on the differential pressure already present
to drain/fill the tank.
According to Steve Fiori, project manager for the Calleguas
Municipal Water District, the system works great and will be considered in the
future for other storage tank projects.