Standards and pool water filtration

 by Dr.Howard Dryden Nov 2014

The requirement for safe swimming pool water with a low concentrations of disinfection by-products is essential for the health and wellbeing of the public, pool staff and ultimately for the viability of the UK pool industry.

Chlorine disinfection by-products and the off-gas nitrogen trichloride causes stress corrosion cracking of building infrastructure, steel work, ventilation systems and is a huge cost to the industry. The application of efficient water treatment system managed by proficient and well qualified pool staff is absolutely essential in order to help with the mitigation of these issues.

Pool standards

At Dryden Aqua we have always been an advocate of the German DIN standard, the UK is the only country in Europe that does not have a formal standards for pool water quality, atmospheric air quality or the design of pool water treatment systems. The German DIN standard is not perfect and Dryden Aqua is helping to modify parts of the standard, but it is a great deal better than the current situation in the UK, which leaves pool operators open to litigation. It is a requirement for all pool operators to have a COSSH risk analysis and this includes water and air quality. If a standard or WEL (Work Exposure Limit) does not exist in the UK the default position is European standard. How many pool operators have a risk analysis for nitrogen trichloride, THMs and cyanogen chloride and monitor these parameters in air?  This is a requirement by decree in France, especially if you operate a pool with UVc irradiation. If a standard or limit is not available in the UK, the default position is a European standard in the event of an incident.

At Dryden Aqua most of our work is in Switzerland, Germany and Austria because these countries have formal standards and countries are dedicated to providing the best water and air quality.  It also makes economic sense; if you have deficient water treatment system then chlorine consumption and acid consumption increase, to prevent building corrosion and protect staff health ventilation systems need to be turned up, water needs to be dumped to try and maintain water quality, so more cost and energy, chemicals and water is expended.  Instead, the emphasis should be on improving performance, reducing operating costs and entering the circular economy by the prevention of waste and inefficiencies. This is the focus of Dryden Aqua and the reason for us to be working in continental Europe with the DAISY system approach.

DAISY Dryden Aqua Integrated System

Water treatment systems and chemicals need to work together. Only products that have been certified and homologated in Europe should be used in the UK. DAISY stands for Dryden Aqua Integrated System and comprises of a complete integrated system process that can be retrofitted to upgrade any pool water treatment system, or it can be the basis of a new pool installation.


DAISY comprises of a multi spectrum flocculent APF (All Poly Floc) that is injected into a cavitating static mixer ZPM for coagulation and flocculation reactions. The water then enters the filters containing (AFM Activated Filter Media).  After the filters the water flows through a second ZPM which smashes up any bacterial floc that have escaped the filter, this then allows the chlorine to work much quicker to reduce the risk of bacterium reaching the pool.  ACO (Active Catalytic Oxidation) works with APF to create a heavy stable floc that can be removed by AFM. ACO also works with UVc irradiation to reduce the concentration for THMs and cyanogen chloride formed by the UVc unit.

AFM activated Filter Media

Any product used by the water or pool industry should be fit for purpose. Certification of products by the UK Drinking Water Inspectorate under Reg 31 certifies that a product will do not harm, but it is not verification that it is actually fit for purpose. You can therefore have a situation where you have two similar products, both certified under UK regulations but one works and the other does not. In order to try and rectify this inconsistency, Dryden Aqua is working with the Scottish Hydro Nation committee to help develop a new ISO standard is association with Brussels called ETV Environmental Technology Verification.


As a first stage in ETV Dryden Aqua was used as a test case for the water filter media AFM.  The most proficient accredited independent laboratory in Europe for testing filter media is IFTS (Institute of Filtration and Technical Services) in France.  AFM was tested by IFTS under a complete range of ISO procedures for run phase performance, backwash and pressure differentials. Many thousands of measurement were taken, however in order to benchmark AFM, tests also had to be conducted against sand and other filtration media available to the water industry.  The sand used was Leighton Buzzard from the UK, considered to be the best filter grade sand in Europe.  All tests were conduced with new filter media, however it should be considered that sand will become a biofilter and performance will gradually deteriorate in a swimming pool system.

AFM grade 1 has the same particle size range as standard 16 x 30 grade sand.  AFM grade 0 has a smaller particle size and should only be used for pools that do not use coagulation and flocculation.

The graph shows that AFM grade 1 will remove 97% of all particles down to 5 microns whereas sand removed 72%. In terms of what remains in the water, with AFM it was 3% and sand 28%, so effectively AFM is performing 10 times better than sand at removing particles down to 5 micron.

Turbidity in pool water is caused by particles that are sub 5 microns; the particles are dead bacteria and bits of bacterial cell wall. While the bacteria are non viable, they are almost as dangerous as living bacterium because cell components and their contents are toxic.  Pool water should have 25m visibility; it is not acceptable just to be able to see the base of the pool as per the UK guidelines. When AFM is combined with a ZPM with proper coagulation and flocculation, this is an effective barrier to the passage of cryptosporidium oocycts, especially when the filtration velocity is reduced to 20m/hr..

The other products tested included granular glass products as well as glass spheres, Leighton buzzard filter sand performed better than all of the glass filter media tested with the exception of AFM. ETV Environmental Technology Verification provides end users, decision makers and specifies with the information required to make a valued judgement regarding the choice of products.

Key points to take away.

  1. Training of pool plant operators to a high standard is essential
  2. The UK should adopt formal standards such as the German DIN standard
  3. All products purchased should have been through homologation or certification; it is not ideal but much better than using products that have not been through any formal testing.
  4. AFM has been through ETV this is an ideal standard for individual products, but we are still several years away from it being a formal European standard.

By removing particles down to sub 5 microns using AFM as part of the DAISY system, water will sparkle and appear blue, chlorine demand and by products will be reduced by more than 50% and the water will be biologically safe. The staff will also have a much safer working environment and pool operators will be in compliance with their duty of care.

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