Description-Sediment Filter Backwash
Turbidity is a measure of water clarity how much the material suspended in water decreases the passage of light through the water. Suspended materials include soil particles (clay, silt, and sand), algae, plankton, microbes, and other substances. These materials are typically in the size range of 0.004 mm (clay) to 1.0 mm (sand). Turbidity can affect the colour of the water.
Higher turbidity increases water temperatures because suspended particles absorb more heat. This, in turn, reduces the concentration of dissolved oxygen (DO) because warm water holds less DO than cold. Higher turbidity also reduces the amount of light penetrating the water, which reduces photosynthesis and the production of DO. Suspended materials can clog fish gills, reducing resistance to disease in fish, lowering growth rates, and affecting egg and larval development. As the particles settle, they can blanket the stream bottom, especially in slower waters, and smother fish eggs and benthic macroinvertebrates. Sources of turbidity include:
- Soil erosion
- Waste discharge
- Urban runoff
- Eroding stream banks
- Large numbers of bottom feeders (such as carp), which stir up bottom sediments
- Excessive algal growth.
Turbidity can be measured using either an electronic turbidity meter or a turbidity tube. Both methods have advantages and disadvantages, as shown below. Turbidity is usually measured in nephelometric turbidity units (NTU) or Jackson turbidity units (JTLJ),
The two units are roughly equal.
Removing Turbidity with an automatic backwash filter.
Sediment (floating particulates, sand, clay, etc.) and turbidity (suspended solids that cause cloudiness) are common problems in a wide variety of water situations. Removal of these contaminates provides clearer, cleaner water that is more appealing to the eyes.
Backwashing sediment filters offer a distinct advantage over typical cartridge filter systems with significantly reduced maintenance requirements. Since the system automatically backwashes itself there are no filters to change, which not only cuts down on maintenance time but costs as well.
Typical Filtration Sand Specification
Density: 100 lbs per cubic foot
Size: 0.20 – 3.0 millimeters
Acid Solubility: <1.0%
Specific Gravity: 2.67 > 2.60
Hardness: 6.0 – 8.0 on MOH scale
UC: 1.30 – <1.65
Uniformity Coefficient (U.C.) – The ratio of the sieve size opening from which 60 percent of the sand, by weight, will pass divided by the sieve size opening from which 10 percent of the sand, by weight, will pass.