It’s no secret that total dissolved solids (TDS) are a growing concern for many aquatic facility operators. Some may argue that using a regenerative media filter instead of a traditional high-rate sand filter will add to TDS levels. High-rate sand filters naturally reduce TDS by regularly dumping considerable amounts of water down the drain during backwash cycles. Regenerative media filters, on the other hand, use a bumping process to regenerate the media daily without wasting any water. The only water wasted with a regenerative media filter is about 2-3 tank volumes worth during a media change.
With water conservation being top of mind these days, using a regenerative media filter can save up to 90% of water going to waste when compared to high-rate sand filters. With all that water savings, TDS may begin to build up over time. Not to worry though, high TDS levels are usually manageable and depend greatly on the TDS level of the local make-up water being used. The Model Aquatic Health Code (MAHC) references maintaining an upper TDS level of 1500 ppm above the site make-up water and mentions there is no known scientific data that supports a maximum TDS level.
Finding the ideal TDS level to maintain will vary from site to site, but there are several ways to manage TDS when using a regenerative media filter. While it may not add up to 90% water savings in a high TDS situation, being able to monitor and control the amount of make-up water used for dilution will equate to overall water savings. Generally with today’s sand filter designs and controls, it is impractical to regulate the amount of water loss due to the necessity of regularly having to backwash.
Other important factors to consider is the quality of the sodium hypochlorite (liquid chlorine) being used or whether calcium hypochlorite (chlorine tablets) is being used in conjunction with high TDS in the make-up water. As sodium hypochlorite ages, the concentration of chlorine will decrease and what’s left behind is mostly an inert saltwater solution that will quickly increase the TDS when added into the pool water. Calcium tablets may be easy to handle and have a longer shelf life than liquid chlorine, but TDS will climb as chlorine is fed.
Another perceived concern is that excessively high TDS levels may decrease effectiveness of primary disinfectants in pools. In a recent study it was shown that a Neptune Benson Defender® Regenerative Media Filter can remove 99% of 5-micron particles compared to 28% with high-rate sand (courtesy of UNC Charlotte). If providing excellent water quality and clarity is a priority, a pool running regenerative media filtration has clear advantages over high-rate sand.
If you wish to discuss TDS concerns at your facility, please contact us at nbsales@evoqua.com or +1-401-821-2200.
