When rain falls, the water has a naturally aggressive, slightly acidic nature. This water then dissolves chalk and/or metallic deposits present in the local rock strata, resulting in ground and borehole water containing elements that would not normally be present in mains water. Contaminants such as Iron and Manganese can cause problems such as poor tasting (and potentially harmful) drinking water & staining of appliances and equipment.
Iron and Manganese can be removed from water by using media that encourages the reaction between the contaminant and oxygen present in the water. This reaction forms an insoluble precipitate which can then be filtered out by the media bed. The media acts “catalytically”, which means that although it triggers the reaction it is not used up as part of the process, thus giving long life from a single filter. A choice of media is available, Pyrolox, Filox & Birm. All are based on Manganese Dioxide but with Pyrolox and Filox having more active sites.
In order to remove accumulated deposits from the filter bed, the water flow through the filter is reversed (back washed). Water is run to drain at a high flow rate to separate the deposits from the filter media. The control valve completes the backwash cycle automatically at the intervals and times set during the installation.
Precipitation starts to occur which can then be removed using a multi-media filter before the water reaches the main catalytic filter.
BIRM, which gives good removal at a relatively low cost. Generally suited to waters that would be considered hard in nature, its performance is
adversely affected by the presence of chlorine, organic contaminants, and some chemical treatments.
FILOX R, has a much higher level of activity
than BIRM and is more suitable across a greater range of waters. It is chlorine resistant and can be used to help in the removal of hydrogen
sulfide (the bad egg smell that is sometimes encountered).
MANGANESE GREENSAND, generally only used in industry for iron and manganese removal, as it requires chemical regeneration
(with Potassium Permanganate) to restore its activity.
General turbidity removal at high flows can be achieved satisfactorily down to low micron levels using a multimedia filter with a layered bed of gravel, filter sand, garnet and anthracite or Filter AG media. Other specialist media may need to be added to the filter bed to improve polishing with certain types of water.
In order to remove accumulated deposits from the filter bed, the water flow through the filter is reversed (back washed). Water is run to drain at a high flow rate to separate the deposits from the filter media. The control valve completes the backwash cycle automatically at the intervals and times set during installation. The backwash and rinse cycle takes approximately 20 minutes, although these can be altered to suit individual conditions.
The presence of Nitrates in water causes many problems, ranging from blue baby syndrome (if fed to babies under six months old) to contamination of poultry if used as feed water for farmed birds. The source of Nitrate in groundwater is usually from farming fertilizers. The EEC permitted maximum is 50mg/l with an advisory maximum of 25mg/l. Nitrate dissolved in water is not able to be removed by simple filtration. It can only be reduced by either regenerable or disposable cartridge type ion exchange systems or eliminated by Reverse Osmosis (RO). RO systems can be used to treat all of the water for
a specific application or to just remove the Nitrates from a drinking water supply in the kitchen. For single dwellings with one drinking water tap and low water consumption, a point of use system provides efficient reduction at a low cost. For large or multiple properties, commercial and industrial applications, regenerable ion exchange systems will be preferred.
Ion exchange Nitrate removal is a similar process to water softening, using slightly different polymer resin. The resin removes the Nitrate (and Sulphate due to its chemical similarity) from the water and replaces them with Chloride ions. Once the resin bed is nearly exhausted of Chloride ions, the control valve
carries out a regeneration of the bed.
This is achieved by passing a Chloride rich brine solution (made up of common salt dissolved in water) through the resin bed, which flushes out the Nitrate and Sulphate to drain, replacing them with Chlorides again. After a final rinse to remove excess brine the unit is automatically put back into service
again. The only input required by the user is to ensure that the brine tank is kept topped up with salt. For fixed or consistent flow rates a simple timer-controlled valve will suffice. This will affect the regeneration of the resin bed at a pre-set time interval. For varying demands a water meter controlled unit is more suitable, regenerating only after a set volume of water has been passed through the resin bed. With applications that require continuous high flows
a duty standby “duplex” system will be required.
The choice of valve is entirely dependent upon the application, water use rate, and severity of Nitrate contamination. Your water treatment specialist will be able to advise on the best option for your particular problem. Top of range microprocessor controlled units use a very little salt, are able to cope easily with varying demand, and remove 90 to 93% of the Nitrates present in the water. Simpler, lower specification valves remove between 80 to 85% of the Nitrate present, can be purchased in either metered or timelock control, and are normally suited to most domestic applications with a Nitrate level not in excess of 100mg/l.
Acidic water results in corrosion of pipework, heating cylinders, and equipment. Any Iron and Manganese present will result in poor tasting drinking water, in addition to staining baths, basins, and any appliances with which the water may come into contact. These problematic waters can be treated with a Triplex system to both raise the pH and remove the Iron and Manganese. Firstly the water is passed through an aerator contact assembly which entrails air into the water to encourage the initial precipitation of the contaminants. This has the effect of reducing the overall load on the filter media, making the complete removal of the contaminants much more efficient. The Triplex vessel uses a unique blend containing a pH correction media, an Iron and Manganese removal media, and a physical filter media. This works in three ways and has the combined effect of raising the pH of the water (eliminating the acidity), precipitating any dissolved Iron and Manganese in the water, and finally filtering out this precipitate. Clean treated water is then passed to service ready for use. Unlike other Iron and Manganese removal systems, the Triplex filter has an equal backwash and service flow. This means
that the load on the borehole pump is minimized, with no requirement for backwash booster pumps. This makes Triplex ideally suited to domestic and light
commercial applications with flow rates up to 4m3 per hour.
A pH value below 7 is considered to be acidic, and corrosion accelerates at pH levels below 6.5, with levels below 6.0 considered to be extremely aggressive. It is usually difficult to remove iron and manganese from acidic water, so often the first step in the process is to raise the pH. The simplest and safest way to raise the pH is to run the water through a pressure vessel containing a bed of specially activated limestone. This is a mixture of calcium and magnesium salts, which are the salts found in waters of pH greater than 7.0. This limestone gradually dissolves increasing the pH level of the water. As the limestone dissolves, it will need refilling periodically. Refilling is straightforward as the media is inert and easy to handle. To treat waters that are otherwise clean
and pure, a basic up-flow system is all that is required. For water with iron, manganese, or turbidity problems, automatic backwashing down flow system will be needed to remove accumulated debris. Water with a pH below 5.0 is uncommon and is unsuitable for this type of treatment. The contact time of the water with the pH correction media is important in achieving consistent results.
Here are some data files on various well, borehole, and surface water treatment and filtration methods.