The Westin Maui resort hotel on Hawaii's island of Maui is known for its exotic landscaping. Unfortunately, a filter problem was turning its handsome tropical ponds into a milky and murky mess. The problem needed to be defined and solved quickly.
Defining the Problem
In the filter bed for the Westin Maui's beautiful chain of decorative ponds, the problem proved to be exactly the same one experienced in the process industries, utility companies and wastewater facilities: an interrelated cycle of failure. This cycle included
- leaking media,
- excessive pressure drop, and
- excessive backwash requirements.
In this instance, the cycle failure began with the original installation of PVC laterals.
The Original Installation
The water that flows through the tropical ponds is recycled. The original design required water flow to be clarified through a horizontal sand filter with PVC laterals. These polyvinyl chloride plastic laterals were used to retain the media and slotted to pass the flow of clarified water.
In this case, PVC was not the best choice. It offered good corrosion resistance but poor structural stability. Pressure variations and torque from pumps caused laterals to break off at the threads resulting in high pressure drops and uneven flows.
This situation led to the cycle of failure. High differential pressure on the backwash sequence twisted and broke off the PVC laterals. The media would lodge in and clog the slots of the PVC pipe and escape through broken laterals into the ponds. Even with continual vacuuming and the addition of large quantities of makeup water, the pond water was still milky and murky.
The hotel's facilities managers called in filtration experts to put an end to the problem. After an investigation, the expert demonstrated that the original distribution and flow characteristics of the filter bed had been altered. Therefore, neither filtration nor backwash were effective.
The suggested solution was an upgrade of the filter system. The failing PVC laterals would be replaced with LEEM Filtration Products' Wedge-Flow stainless steel laterals.
Unlike PVC, these laterals are supplied as a permanent assembly. The wires, with triangular-shaped profiles, are wrapped around and welded to stainless steel rods to create a strong, clog-resistant assembly.
For the Westin Maui installation, 2< IPS, 304 stainless steel pipe based Wedge-Flow laterals, with .010< slots, were specified. The laterals were replaced in May and December 1997 and February 1998. All large stock pond filters were retrofitted with the laterals. As a further refinement, the silica sand media was replaced with crushed recycled glass.
Crystal Clear Results
The upgrade effectively solved the facility's problems with pond clarity and high maintenance. Normal maintenance, including minimal vacuuming, keeps the chain of ponds crystal clear. The ease of back washing the stainless steel laterals keeps the filters operating virtually maintenance free.
The end result of this switch is a savings of thousands of dollars each year in labor costs alone, plus the savings inherent in a 50-percent reduction in makeup water consumption.
The Westin Maui management is satisfied with the results after the upgrade. Now, thousands of visitors to the resort hotel can enjoy its chain of tropical ponds, feed the koi and delight in the birdsong-and never dream of the complex problems and solutions underlying their beauty.