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The Sand Filter system is a variation of the Watersave system, as designed by GRS. Greywater is first directed to a 1200 x 1200 mm sedimentation tank and then passes through a stone and sand filter before it is pumped through a subsurface dripper system. The pump chamber is on top of a sand-stone filter.
Sand Filter System
In the GRS Sand Filter Irrigation System, the greywater enters the bottom of the tank, is spread through the floor via 100 mm drain coil pipe and then proceeds to move upwards through the stone and sand layers. The sand is coarse river sand which has been shown to contain 83% of particles 0.5 to 2 mm, and smaller percentages of slightly larger grains and silt. Its red colour suggests an iron content, which is expected to remove some phosphate from the wastewater.
Figure 1. Filling the sand filter tank with coarse river sand.
The effective volume of stone and sand is about 225 L each. This is adequate to filter the greywater to enable effective suspended solids removal for irrigation via drippers. The sand and stone filter (450 L) is only a secondary filtration system - to ensure that blockage of the dripper system does not occur. However, a standard in-line irrigation filter is also placed before the dripper system to remove any sand which may be inadvertently pumped from the tank.
Figure 2. The first tank is a sedimentation tank, and the second tank is the combined sand filter and pump chamber.
The remainder of the tank is the pump chamber. It is estimated that the capacity will be about 750L, of which 600 L will be pumped at any one time. A submersible pump with float switch, such as those produced by Davey or Grunfos, will be used.
Figure 3. Typical sand filter and pump chamber.
Irrigation System
The recycled greywater will be pumped to areas of the garden through standard irrigation pipe to a network of subsurface drippers as part of the Netafim pipe Uniram (purple dripperline, also known as Unibioline). Drippers at set at 300 mm and 2.3 L/h. Tiran 17 pipe has a dripper rate of between 8 and 10 L/h. A 100 mm layer of mulch is placed on top of the irrigation pipe.
Each line (lateral) will have a flushing valve on the end of the line to flush residual solids. At least one vacuum breaker should also be installed at the highest point in the irrigation layout.
Figure 4. Typical layout for dripper irrigation system.
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GRS Sand Filter System 
