The modularity of the skid enabled the entire plant design to be completed in less than four months.
Click here to enlarge imageFor Azusa, each of six skids will contain 132 modules, arranged in two 66-module arrays. Interchangeable steel frames that meet seismic 4 building code are supplied for each array and then bolted together to form a skid. Manifolds are then assembled on each end of the skid with interconnecting piping held on the skid frame. The end manifolds contain all required valves and instrumentation.
In the future, expansion can be accomplished in one of two ways. First, an array of modules can be added onto each skid. To do so, an end manifold would be removed, additional pipe headers installed and the same manifold reinstalled. In this expansion option, each new array need not mirror the initial array containing 66 modules, but can house the number of modules needed to reach the capacity goals (60 to 108 modules). Alternatively, an additional full skid can be installed to mirror the original skids. Since Azusa plans for expansion to 16 mgd, this was a key element in its design concept.
Operation
The system operates with a pressurized feed distributed among the 132 modules in each of the six skids. Water flows in an outside-in pattern across the membrane fibers from the shell side to the internal area, called the lumen. Any particle larger than 0.04 microns is retained on the fiber surface.
Compared to conventional systems, the footprint is greatly reduced. The total plant area of the current Canyon Filtration Plant is 45 percent larger than the new 12 mgd membrane plant footprint. The overall membrane area for the new facility is approximately 55 feet by 18 feet.
In comparison to other pressure membrane technologies, energy use will be reduced. The new system operates to a trans-membrane pressure of 22 psi, versus 30 to 40 psi for some pressure systems, yet achieves similar recovery and chemical cleaning intervals.
The backwash is fully automated and initiated at pre-set intervals, with the ability for operators to make modifications if required. An optimized backwash process using minimal air and water scours the membranes, removing solids that have built up on the fibers. Compared to other pressure membrane systems, the amount of air required for this operation is reduced by nearly 70 percent. Combined with lower trans-membrane pressures, the resulting overall energy savings is nearly 30 percent.
In comparison to submerged systems, waste generation is decreased by approximately 5 percent, resulting in an overall plant recovery of 98 percent. This increased recovery reduces disposal costs and/or the cost of second-stage recovery systems.
About the Authors
Steve Seffer is the water treatment plant operator for the Canyon Filtration Plant in Azusa, Calif. Ron Henderson is a vice president with Black & Veatch in Walnut Creek, Calif. Roger Kohne is a project engineer with Black & Veatch, also located in Walnut Creek. Lisa Sorgini is the global brand manager for the Memcor product line of USFilter, a part of Siemens Water Technologies, and is based out of Sturbridge, Mass.