For neutralising acidic waters or re-mineralising very pure waters
As supplied by your distributor, water should have a pH value of no less than 6.5 and no more than 8.5. In other words water should neither be too acid nor too alkaline. Acid water causes accelerated corrosion of pipework and heating cylinders. In addition it increases the 'plumbosolvency' of the water and can lead to high (and potentially dangerous) levels of lead in drinking water. Water which is neutral has a pH value of 7. The maximum permitted pH value for distribution is 9.5, which is alkaline.
A pH value below 7 is considered to be acid, and accelerated corrosion starts at levels below 6.5. A pH value below 6 is extremely aggressive. It is also difficult to remove Iron and Manganese from acid water, so often the first stage of Iron and Manganese removal is to raise the pH.
For waters in which the pH is not below 5 the simplest and safest method to raise the pH is to run it through a pressure vessel containing a bed of specially activated dolomitic limestone, a mixture of calcite and magnacite. The limestone gradually dissolves, increasing alkalinity.
Periodically the dolomitic limestone will need to be topped up as its level decreases. The medium itself is inert and easy to handle.
For waters that are otherwise clean and pure a basic up-flow system is all that is required. For water with Iron or turbidity problems, a backwashing downflow system will be needed to remove accumulated debris.
Water with a pH of 5 and below is uncommon, but when it occurs, it needs correcting with a liquid alkaline solution such as caustic soda or soda ash which requires accurately controlled chemical dosing and continuous monitoring (see section on 'Chemical dosing & control').
Specifying and Sizing
The contact time of the raw water with the pH correction media is most important for safety performance. Take advice on the recommended maximum service flows for each system.
For every 10 mg/L CO2, alkalinity and total hardness will be raised by approximately 18 mg/L as CaCO3. Consumption - for each 10 mg/l CO2 removed, there will be a consumption of approximately 12 mg/L of media.
System Management - upflow
Upflow 'manual' pH correction units are used for raising pH of otherwise clean water or for the re mineralising of pure water produced by Reverse Osmosis or desalination. For water with significant Iron and Manganese levels an auto-backwashing or combination system will be required. Domestic units up to 13" include service flow controller and quick release couplings (QRCs) for ease of refilling. Larger industrial systems of 14" diameter and above use top and bottom entery vessel for maximum flow. These do not include flow controllers or QRCs. With certain waters periodic manual high volume flushing will be needed in a 'manual' system to break up any Calcium Carbonate that has re-deposited onto the pH correction media bed. A manually operated flushing system can be incorporated into the unit in the factory.
Technical details and model numbers - upflow
Available on request.
System Management - backwashing systems
Backwashing systems include service and drain line flow controllers. NB Backwash flow per vessel is 1.5 times the service flow. Therefore where possible use two or more small units instead of one large one to reduce the pumping requirement. In areas of high media usage, special vessels can be supplied with an additional filling port eliminating the need to remove the backwashing valve during media replenishment.
Technical details and model numbers - backwashing systems
Available on request.
NB To prevent damage to the vessel these filters must be protected from negative pressure from the drain or supply. A vacuum relief valve is recommended on the inlet supply and is supplied with all vessels from 370mm diameter upwards.
High efficiency British made media uses less mineral volume to correct pH than conventional systems. Replacement media is convenient and safe to handle.