Polyaluminium chloride (PAC) dosing
Continuous coagulation with polyaluminium chloride has long been recommended by PWTAG – especially in the light of the threat from Crytposporidium. Like all coagulants PAC works by extracting and then clumping together dissolved, colloidal and suspended matter. The resulting floc is then trapped on the filter.
Dosing rate
PAC is directly and continuously dosed from the containers in which it is delivered at a rate of about 0.1ml/m3 of the circulation flow. (It is very important that it is not diluted with water as it will form a gel.)
This must be mixed as evenly as possible throughout the water flow.
Where to dose
Following dosing, coagulation of pollutants happens quite quickly. Flocculation is a slower process, where the coagulated particles come together in flocs, so it is important that there is sufficient time before the water reaches the filter media.
At least 10sec is recommended, at a flow velocity not exceeding 1.5m/sec. This can normally be achieved in the space in the filter above the filter media.
But to ensure the best possible mixing, PAC should be injected as far before the filters as possible – but after the place where the sample for the chemical controller is taken.
How to dose
For a pool with a capacity of 450m3 and a turnover period of 2 hours the circulation rate is 225m3 per hour.
The PAC dosing rate for this pool would be 22.5ml per hour. This is a very small quantity (two and a quarter 10ml test tubes per hour) and is difficult to dose accurately.
Most chemical dosing pumps used for dosing the other chemicals used in swimming pools are not capable of adding this small quantity accurately and continuously. The most suitable type of dosing pump is a peristaltic pump.
Please simply fill out the Inquiry form, or Email us to serve you today!
