FILTRATION: High Rate Sand Vs. Regenerative Media

Until the past 5-10 years, pressure high rate sand filtration was installed on the majority of commercia2468-BethelAquaticCent-90l pool applications.  There were and continue to be other types of filtration such as vacuum sand filters, cartridge filters, diatomaceous earth filters, and others.  But often whether it was due to the type of pool, cost, material handling, operations, or other reasons, high rate sand filters were generally the preferred choice.

But in the last 5-10 years, regenerative media filters have gained a significant portion of the market share, especially with the number of projects pursuing LEED certification.  Instead of diatomaceous earth (DE), which creates material handling challenges for operators, the regenerative media filters use perlite.  Perlite is a volcanic ash material and the overwhelming majority of local jurisdictions allow it to be disposed directly to the sewer, unlike DE.

When comparing regenerative media filtration to high rate sand filtration, there are really two main points of consideration.  The first is the first-dollar capital costs.  It’s not uncommon to find a regenerative media filtration system to be double the cost of a traditional high rate sand system.  Depending upon the type, size and quantity of pools this cost differential may be tens of thousands to hundreds of thousands of dollars.  To offset the capital cost increase most commonly seen when using regenerative media filters, the ongoing operational cost should be less than that of a high rate sand.  A majority of this operation savings is from the reduction in water usage, translating into a reduction in pool chemicals.  When including the potential capital cost savings from a reduction in pool mechanical room space (high rate sand filters traditionally result in more floor space as compared to regenerative media), the payback period analysis can be as little as 3 to 5 years.  However, this payback analysis assumes an indoor pool with operations 365 days per year.  When looking at the payback analysis for seasonal outdoor pools, the time period for the reduction in ongoing operational expenses to exceed that of the capital investment can increase to 20 years or greater.

The second consideration when comparing regenerative media filtration to high rate sand filtration is daily operations and routine maintenance.  The extent of high rate sand filter maintenance typical includes semi-weekly or weekly backwashing (frequency depends on bather loads), replacing the sand media every 10 years or so, and servicing laterals inside the filter tanks as needed (this isn’t an issue for many well-constructed commercial filter tanks).  Regenerative media filters require daily “bumping” of the filters.  This process is automated and it takes approximately 5-10 minutes to shake the media off of the filter elements and recoat.  Backwashing is much less frequent than with high rate sand filters and a significantly smaller volume of water is sent to waste.  Every 4-8 weeks approximately, two filter volumes of water will need to be dumped and new media will need to be introduced to the filter system.  Finally, on an annual basis, routine maintenance is suggested which includes inspecting and cleaning (if necessary) the filter elements and checking torques.

For a quick comparison analysis let’s consider an indoor 8-lane 25 Meter Pool.  The below chart indicates the filter payback analysis for hi-rate sane versus regenerative media filtration.


As you can see the comprehensive capital cost increase for use of the regenerative media filter system is nearly $32,000.  However, the yearly operational increase is approximately $5,000.  Therefore, it will take nearly 77 months for savings in operational expenses of the regenerative media system to payback the initial increase in capital cost investment.  As previously mentioned, as the pool type, size and location (indoor versus outdoor) changes, so too will the payback analysis.

While there are many other factors to consider when comparing high rate sand filtration to regenerative media, the capital cost analysis and daily operations and maintenance are often viewed as the primary considerations for a comparative analysis.  Additional considerations such as filter media, filtration quality and disposal of media should not be overlooked.

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