Comparison of cleaning the Manz Slow Sand FilterTM (MSSF)
and the Traditional Slow Sand Filter (TSSF)

Normal cleaning of the MSSF:

Backwashing removes particulate material that had blocked flow from top of media.
1. Filtered water is added into bottom of filter backwash flow
2. Backwash begins - surface layer of media is fluidized and expanded.
3. Only the layer of fine filtering media expands and captured particles are flushed from it.
4. Backwash flow is stopped and media settles back into position. Smallest particles coated with biofilm remain at surface. Top layer collapses to original depth.
5. Water containing all of the captured material is discharged from filter. Discharged water is sent to waste. Note that the wastewater does not represent a biohazard or a disposal problem if chemicals are NOT used. Recycling wastewater may be practical.
6. Discharge is complete. Biolayer has not been removed and does not need to reform.
7. Filter is put into production without filter-to-waste cycle.

The entire cleaning process takes less than 30 minutes for very large filters.
No media is removed or needs to be replaced.

In comparison, cleaning of a traditional slow sand filter:

Must be scraped to remove particulate material that had blocked flow from top of media.  Scraping removes the biolayer, which needs time to reform.

Successive scrapings reduce the filter media level to the minimum depth and the filter must be re-sanded, a lengthy and expensive process.

Cleaning the Manz Slow Sand FilterTM (MSSF) - detail

Flow to filter is stopped

Backwash is started and bed fluidizes

Backwash continues as long as required to flush particles blocking flow from filter

Particles blocking flow from filter are now in water above media

Backwash stops. Particles coated with biofilm settle into original pre-backwash position - on the surface of the media

Water containing suspended particles is discharged

State of filter after backwash and discharge complete.  Note that the particles with biofilm are at the surface

Filtration resumes

Oasis Filter International Ltd.
2525 Macleod Trail SW
Calgary, Alberta, Canada T2G 5J4

Phone: 1-403-269-1555
Fax: 1-403-264-6244

Last updated Saturday November 27, 2010
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