Since arsenic is chemically bound to the media, no arsenic is removed or desorbed during the backwashing cycle. 
The backwash water typically has very low or non-detectable levels of arsenic. They can have a holding tank to monitor and confirm before discharging the backwash water.

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Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus leo ante, consectetur sit amet vulputate vel, dapibus sit amet lectus.

Effective Size refers to the sieve size opening through which precisely 10% by weight of a representative sample of sand will pass.

The uniformity coefficient is a measure of the ‘degree of sameness’ of media particles. It’s calculated based on the sieve size opening that allows precisely 60% of a representative sample of filter media to pass. This coefficient is defined as the ratio of D60 to D10. The lower the uniformity coefficient, the more uniform particle sizing within the media is.

Measured in kg/m³ according to the Australian Standard Test (AS1141.5), Specific Gravity, also known as particle density, plays a crucial role in filter bed design. It provides insights into the necessary backwash rates for effectively cleaning the media without experiencing losses through the backwash overflow troughs. The lower the Specific Gravity, the less the backwash water required for effective washing of the media. Please note that Specific Gravity is unrelated to filter coal’s hardness.

Backwash Rates are typically measured in cubic metres of water (or air) per square metre of bed area per hour, denoted as m³/m²/hr or m/hr.

Backwash water is sourced from a clean water tank of previously filtered water. Therefore, it’s advisable to maintain backwash rates at a minimum to effectively cleanse the media, conserving clean water and minimising the cost of backwash equipment. Techniques such as air scour and combined air/water backwash are often employed to achieve this goal.

During backwash, the filter bed must become fluidised and expand under vigorous turbulence to effectively cleanse the bed of entrapped particulate matter. A bed expansion of 20% – 30% is considered optimal for adequate media cleansing but can go as low as 15%.

During backwash, the filter media rises within the bed due to bed expansion. Overflow troughs must be positioned at a sufficient height above the filter bed to prevent media carried upward from reaching the height of the washout troughs and carrying over with the dirty washout water. Typically, a height equal to 50% of the media bed depth above the top of the bed depth is considered sufficient.

Run length is the amount of time available between the backwashing of a filter. A longer run length (or filter run) means more water production due to longer filter availability and less wastage of backwash water. It is measured in hours, and 24 – 72 hours is regarded as an effective filter run.

Filter Rates or Throughput is the rate of water flow through the filter during filtration, measured in cubic metres of raw water per square metres of filter bed per hour, denoted as m/hr. This figure determines the size of the filter required to cope with the designated capacity of the water treatment plant and is integral to the overall design of the plant. Rapid flow filters operate at throughputs of 5 – 30m/hr.

Breakthrough is when the water passes through the filter without being cleaned sufficiently to meet the designed quality of effluent. Once breakthrough occurs, backwashing is necessary.

Unit Filter Run Volume (UFRV) defines the volume of water filtered per filter run and is calculated by multiplying Throughput (m³/m²/hr) by Run Length (hrs). It is measured in cubic metres of water filtered per square metres of filter area. This figure is a common gauge for assessing filter performance.

Head loss is measured in millimetres and is an indicator of the restriction of water flow in the filter due to the entrapment of floc and sediment through the depth of the filter bed. Once head loss reaches a pre-determined level, the filter is backwashed. The longest filter runs are achieved when the designed head loss is reached at the same time as the filter breakthrough.

Clean Bed Head loss is measured in millimetres. This is the head loss solely due to the filter media before the bed becomes restricted with entrapped sediment.

A mono media filter is made up entirely of one type of filter media; a highly graded sand that has consistency in both shape and size to ensure successful filtration.

As sand is the only medium used, the largest particles within the grade evenly disperse themselves down within the filter, while the smallest remain on top of the media bed. The result of this dispersion rate throughout the bed is very limited use of the media depth, meaning only a comparatively small part of the bed traps the filterable particles in the smallest voids at the top of the filter bed. Due to this limited use of the whole bed, the filter will run for shorter cycles and will require regular backwashing to avoid anything stopping the flow.

This type of filter is commonly used in swimming pools for both residential and commercial properties.

A dual media filter utilises two layers for the filter process which is known as in-depth filtration. This process uses different layers to screen out or remove any impurities before they reach the filter bed. A dual filter system is commonly used in the industrial water treatment industry and requires proper selection of filter media to suit the filter use.

The ideal top layer for a dual media filter is Anthracite, a filter coal, as it has a greater surface area and can hold more dirt and impurities over sand. Anthracite provides in-depth filtration with its larger storage capacity and thereby retains efficiency due to the high-carbon nature of the media which makes it durable and can resist erosion. Placing sand as the bottom layer of the filter keeps it relatively unpolluted due to the qualities of the Anthracite and enables more effective filtration. As the sand is naturally unpolluted and relatively clean, this layer isn’t as dependent on backwashing and also reduces the chance of it becoming biologically corrupt.

The main benefits of dual media filtration include:

• Extended filter cycles.
• Improved water quality.
• Higher retention of solids.
• Generally lower pressure losses.

Mixed media filter profiles are also known as multi-media filter profiles and they add another layer to the set-up of a dual filter system. They are considered an enhanced in-depth filtration system due to the inclusion of a garnet layer at the bottom of the filter bed. This type of filter profile is commonly used in water treatment plants. The most ideal media combination is anthracite, sand, and garnet; however, it is possible to replace the garnet with graded gravel. It is also possible in a mixed media profile to incorporate a fourth layer, meaning the filter would be made up of anthracite, sand, garnet, and graded gravel.

The three layers of a mixed media filter profile have different densities, with anthracite being the lightest, followed by sand and then the garnet or gravel. By utilising the different densities of the media, it means that during the backwash cycle the lightest media, anthracite, will settle at the top, the sand as the medium media will remain in the middle and the heaviest media, garnet or gravel, will settle at the bottom. These characteristics help to maintain the structure of the filter profile during the backwash cycle and keep the sand from infiltrating any pipes.

This filter set up also assists in trapping the largest contaminants in the anthracite layer at the top, with the smaller debris being caught in the lower layers. Trapping the contaminants in this manner ensures efficiency and longer run times between backwash cycles.

Benefits:

• Due to their design, they can trap and retain larger amounts of contaminants before requiring backwashing.
• Use of the entire bed for filtering out contaminants ensures longer periods of running time.
• Produces high quality, filtered water or potable water at faster flow rates.