Green Sand Filters (GS)

Green sand is a natural glauconitic capable of reducing the aforementioned ions through oxidation and filtration. Once the ions are oxidized and precipitated, they are removed by washing the media again. Once the oxidation capacity has been exhausted, the media can be regenerated using a chlorine or KMnO4 solution. There are two forms of regeneration that can be used as follows:

 1. a. The continuous regeneration is a constant chlorine feed in the middle with the feed water. It is necessary to have 0.5 to 1 ppm of free chlorine (not total) detected in the effluent. Chemical speed is a function of the feed, so the feed rate must be adjusted if the tested free chlorine is outside this range.

 2. b. Batch regeneration is when the system is isolated and washed with KMnO4. The quantity of chemical products and the execution time can be illustrated by the following example:

 Q: What is the proper operating period for water containing 1.0 GPG and 0.015 GPG manganese at a pressure of 4 GPM / Ft2?

        KMn04 demand = (1 x Fe (GPG) + 2 x Mn (GPG); (1 x 1) + (2 x 0.015) = 0.13 GPG

        Normal load = 1.000 grains / ft2 Thus 1000 grains / ft2 ÷ 0.13 GPG = 7.692 Gal / ft2

        @ 4 GPM / ft2 Service fee: 7,692 Gal / ft2. ÷ 4 GPM / ft2 = 1,923 minutes

 A: The frequency of backwash is approximately every 30-36 hours of actual operation.

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What is a Green Sand Filter

The Green Sand Filter (GSF), like any media filter, is composed of a mineral tank (FRP or steel), valve controllers (mounted on the top or sides) or face controllers (Digital Stagers or PLC), medium (gravel or green sand).

A Greensand filter is available in different flow capacities and media volumes. It can be configured to operate as a single independent unit or multiple tanks, which work together or in sequence depending on the application. Smaller units may have valve controllers, such as Fleck® or Clack®, while medium units may have air-operated or electric-operated diaphragm valves (Aquamatic®) controlled by a digital controller. The larger units are usually designed with electric butterfly valves and have a PLC (Siemens® or Allen-Bradley®) as the main controller. It must have a service flow of 2-5 GPM / ft2 and a minimum backwashing speed of 12 GPM / ft2 to ensure that it is running in optimal conditions and to extend the life of the media. The media in the tank should only have a maximum depth level of 50% to allow the green media to increase by 40% during the countercurrent wash mode.

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A Greensand filter system can be used as a direct water filtration to treat water with Fe, Mn and H2S for the supply of potable water applications or it can be used as a pre-treatment for equipment or processes, such as a Reverse Osmosis System, which needs more levels. low of the ions mentioned. This system is normally used in industrial plants, municipal treatment facilities or commercial establishments that need water of better quality than that coming from the city.

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Green sand filter systems are used as pretreatment for OI systems, since OI membranes can only allow a maximum of 0.05 ppm Fe and almost zero amounts of Mg and H2S in the feedwater. A greensand filter ensures that these ions below the minimum level allow the RO system to run without the high risk of premature membrane fouling and system downtime. Also, it could be used for any water treatment application that requires the removal or reduction of iron and manganese.

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