A new mold has been developed for fabrication of the Version 10 biosand filters. The fabrication instructions are included in an updated version of the biosand filter manual.
For clients wishing to implement Version 10 there are several options:
1. Fabricate new molds
Option 1 is the preferred option, but given the cost of molds it may not be a good option for some clients. The Version 10 fabrication instructions are now available in the new biosand filter manual.
2. Modify the exterior mold and build a new interior mold
Existing exterior molds can be modified by changing the "nose panel". The other three panels remain the same. To change the nose panel:
- Remove the existing nose piece
- Weld a 6 mm plate to fill the original cut-out hole
- Cut a new hole in the panel for the new nose piece
- Cut the new nose pieces
- Assemble and weld the new nose pieces
- Fabricate a new interior mold. Ensure that the ledge for the diffuser plate is 10 cm higher.
Complete instructions are provided in the biosand filter manual.
3. Modify the exterior mold and use the existing interior mold with a diffuser box instead of a diffuser plate
Modify the exterior mold by changing the "nose panel" (see Option 2 above for instructions).
Use the existing interior mold and install filters with a diffuser box instead of a diffuser plate. If diffuser boxes are used, then the diffuser ledge is no longer needed, therefore it is not necessary to modify the existing interior mold.
A diffuser box is often preferred because diffuser plates can become bent or broken or do not fit properly. This allows fast moving water to go around the plate and disturb the biolayer at the top of the sand. This disturbance can allow the contaminated water to 'bypass' the biolayer, potentially reducing the effectiveness of the filter. Diffuser boxes prevent this since the water can only flow through the small holes at the bottom.
The diffuser box is more costly than the diffuser plate since it uses about 4 times more galvanized sheet metal and often requires a local sheet metal worker (or equivalent trained worker) to fabricate the box.
Complete instructions for building a diffuser box are provided in the biosand filter manual.
