Drop of Hope How the BSF operates BioSand Water Filter project introducing Shona Grow and Go childrens curriculum into schools in Zimbabwe

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Drop of Hope - How the BSF operates

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Optional: Download English BioSand Filter PowerPoint - 'BioSand Filter Operations'

How the BioSand Filter Operate?

During the Run (water is flowing)

When water is poured into the filter, the high water level (also called the hydraulic head) pushes the water through the diffuser and filter. The water level in the reservoir goes down as the water flows evenly down through the sand. When the reservoir is full, the flow rate should be 400 mL per minute. The flow rate will slow down as the reservoir empties because there is less pressure to force the water through the filter.

The inlet water contains dissolved oxygen, nutrients and contaminants. It provides some of the oxygen and nutrients required by the micro-organisms in the biolayer.

Larger suspended particles and pathogens are trapped in the top of the sand and they partially plug the pore spaces between the sand grains. This clogging causes the filter's flow rate to slow down over time. Users can periodically perform a Swirl and Dump maintenance procedure to restore the flow rate in the filter.

View on YouTube CAWST English Video #4 'How to use the BSF'

Pause Period (no water is flowing)

The water will stop flowing when the standing water level is at the same height as the end of the outlet tube.

Some oxygen from the air diffuses through the standing water to the biolayer during the pause period.

The pause period allows time for micro-organisms in the biolayer to consume the pathogens and nutrients in the water. Pathogens in the non-biological zone (below the biolayer) die off due to a lack of nutrients and oxygen during the pause period. The pause period should be at least 1 hour.

What Kind of Water Can I Use?

Clear water - The filter will work well. You will not have to clean the top of the sand very often.

Dirty water - After a few weeks, the filter will start to flow slowly. You will have to clean the top of the sand sometimes to make it flow faster.

Very dirty water - The filter will quickly start to flow too slowly. You will have to clean the top of the sand often to make it flow faster.

If the water is very dirty, settle the dirt out of the water by letting it sit in the bucket for a few hours, do not use the dregs from the bottom of the bucket.

Always use the same water source in the filter

HANDOUT:

Optional: Download English 'How the BioSand Filter Operates' Handout #3

(To transate into Shona)

A DROP OF HOPE