Multi-media sand filters
Sand filters are the oldest and most basic form of water filtration and originally consisted of large volumes of sand through which water simply percolated. Modern systems however now include various media layers which allows much more efficient filtration in smaller vessels.
Multi-media sand filters normally consist of three media layers (ie. support base gravel, micro screened sand and anthracite) and are a very economical means of primary filtration to remove the bulk of suspended solids. They are particularly efficient on surface waters for the removal of grit, sediment, turbidity and organic matter but also widely used on oxidised iron ('rust') and other precipitated contaminants such as manganese or scale particles.
Multi-media filters are periodically backwashed (either automatically or manually) by simply reversing the flow and this flushes to waste the accumulated sediment and also regrades the filter media layers.
Operation and maintenance is extremely simple. After initial set-up, the system is virtually self sustaining. With the Performa Head, back-flushing and clearing of trapped contaminates occurs automatically.
Activated Carbon Filters
Activated carbon filters are generally employed in the process of removing organic compounds and/or extracting free chlorine from water, thereby making the water suitable for discharge or use in manufacturing processes. Eliminating organics in potable water, such as humic and fulvic acid, prevents chlorine in the water from chemically reacting with the acids and forming trihalomethanes, a class of known carcinogens.
Activated Carbon (AC) filtration, as with any water treatment method, is not capable of removing every possible type of contaminant. For example, sodium, microbes, fluoride, and nitrates cannot be removed with AC filtration. Water softening also cannot be achieved with AC filters. In addition, heavy metals, such as lead, can only be removed with a very specific kind of activated carbon water treatment, which is typically used only in residential point-of-use filters.
Coconut shells and coal (anthracite or bituminous) are both organic sources of activated carbon. Carbon forms when an organic source is burned in an environment without oxygen. This process leaves only about 30% of the organic mass intact, driving off heavy organic molecules. Prior to being used for water treatment, the organic mass must then be "activated." The process of activation opens up the carbon's massive number of pores and further drives off unwanted molecules. The open pores are what allow the carbon to capture contaminants, known as "adsorption". The rate of adsorption for a surface area of a just one pound of AC is equal to 60-150 acres!
How it Works
Activated carbon water treatment is basically used for two water treatment purposes and each work in totally different ways.
1. Chlorine Removal: Activated carbon may be used to remove chlorine with little degradation or damage to the carbon. Dechlorination occurs rapidly and flow rates are typically high. However, this process requires an extensive amount of surface area, and organics in the water will eventually fill up and block the pores of the carbon. Ultimately, the AC filter will need to be replaced as its ability to dechlorinate the water will slowly decline. Spent carbon can be re-activated; however, re-activated filters should only be used in waste-water treatment applications. One advantage to using AC is its low operating cost and virtual "fail safe" operation once installed. One disadvantage is that as the chlorine is removed from the topmost layer of the media, the AC provides a damp environment ideal for the growth and proliferation of bacteria. Bacteria can cause problems in medical applications, or when using carbon as a pretreatment to reverse osmosis.
2. Removal of Organic Matter: As water passes through an activated carbon filter, organic particles and chemicals are trapped inside through a process known "adsorption". The adsorption process depends upon 5 key factors: 1) physical properties of the activated carbon (surface area and pore size distribution); 2) the chemical makeup of the carbon source (amount of hydrogen and oxygen); 3) the chemical makeup and concentration of the contaminant; 4) water pH and temperature; and 5) the length of time the water is exposed to the activated carbon filter (called empty bed contact time or EBCT).
Technical parameters sheet for Mechanical sand carbon filter
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