Case Study AZUD Filter in Public Swimming Pools

In 2011, Pfeffer Filtertechnik, as AZUD Distributor for Germany, was asked to consult a engineering firm about the retrofit of the filter system of a large open public pool in the City of Kaiserslautern / Germany. The old sand filter system was not up to standard anymore and the distribution of the chlorine, that was injected for hygienic reasons was not distributed evenly throughout the pool. A better recirculation and distribution of chlorine was needed.

An economical solution was needed for reasons of financial regulations, and it was possible to look for alternative solutions away from a standard sand filter system for pools according to DIN 19643 – German Norm for public swimming pools .

The total volume of the basin is very big with 9000 m3 and 7.400 m2 of water surface. Due to normative regulations a water turnover of once every four hours was designed.

AZUD HELIX Automatic filters with a filter grade of 100 micron and a design flow of 1.680 m3 and 84 filter elements was installed. For a minimal footprint, the AZUD 4DC series with 4 inch twin filters was chosen. New at the time was the availability of filters made completely of Polypropylene that is 100% chlorine resistant and durable. The backflush pressure at that time (2012) was still 4 bar, so special backwash pumps had to be installed in order to achieve a good backflush quality, whilst the filtering pressure was 0,8 bar for minimal energy consumption. Today, AZUD HELIX filters can do a backwash with a pressure of 1,5 bar only which makes separate backwash pressure pumps obsolete.

As it was not expected that a filtration to 100 micron could get the same result in brilliance and clarity of the water as a sand filtration and flocculation can achieve, a small sand filter system and chemical dosing for flocculant was added. This system was intended to close the mathematical “gap” in turnover volume between the AZUD filter installed with 1680 m3/h and the design flow of  “once ever four hours” which is 2250 m3/h. So a “small” sand filter system with a turnover rate of 600 m3/h was installed instead of a system of 2250 m3/h, four times the size and with an enormous need for back flushing water.