Questions & Answers

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# Question Answer
8490

Where can I see the biosand filter videos?

The English version of the biosand filter videos can be seen on youtube:
https://www.youtube.com/watch?v=icLOgAkofUk&list=PL9v91TA8WG-bNNQR2TKqxdi3zTrCGEa0U

To see other CAWST videos, such as webinars or links to videos on water, sanitation, or hygiene made by other organizations but which we like, visit CAWST's youtube channel here: 
https://www.youtube.com/channel/UCSN24sOUXbvLWlJcvm-F_2w
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8489

Can I build a biosand filter to use in North America or Europe?

The biosand filter, in the versions supported by CAWST, is a technology addressing the great need for potable water in the developing world. The filter does not provide microbiological treatment up to the water quality standards of developed nations, nor does it remove most chemical contaminants.

The biosand filter is most appropriate for use in areas where people do not have access to piped, potable water to their home; pathogens in the water are making, or could make, people sick; there is limited or no access to electricity; and resources and access are so limited that people are unable to purchase or maintain more sophisticated home treatment technologies.


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8475

Why does CAWST recommend that filters be ripened for 1 month, when other organizations recommend 2 weeks?

One of the ways by which the biosand filter removes bacteria and viruses is through biologically mediated mechanisms, such as predation and adsorption onto biofilms. In addition, some virus removal is thought to be due to attraction to positively charged ions which accumulate on the negatively charged sand particles. However, these processes take time to develop. A newly installed biosand filter typically removes only about 0.3 log, or about 50%, of E. coli. This increases over the following weeks as the biolayer develops and the filter “ripens”. However, the exact amount of time required to ripen a BSF is highly variable.


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7899

What types of tubing can I use for the outlet tube in the Version 10 Biosand filter?

The tubing used in the Version 10 Biosand filter can be polyvinyl chloride, polyurethane or polyethylene – as long as it is safe (for drinking water), flexible (won’t give kinks) and has an inner diameter greater than or equal to 6mm, and an outer diameter less than or equal to 9mm.
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7898

Can I use weaved mesh for sieving sand and gravel as oppsed to welded mesh?

Typically weaved mesh will have smaller openings so ensure that the one that you buy will give the right size sand particle (e.g <0.7mm for the filter medium). Weaved mesh will also tend to be heavier and more expensive. Other than that there shouldn’t be any problems
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7862

Can I restart a biosand filter that was abandoned?

There are many things that are unknown about the biosand filter, and the effect restarting a filter that has not been in use for some time is one of them. This is an area that is currently being researched.


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5668

I have seen small worms crawling on the top of the sand in my biosand filter. What should I do?

It isn’t so unusual to have worms living in the filter. It isn't necessarily a bad thing. The filters are complex aquatic ecosystems, and there are lots of creepy crawlies who can make their home in the filter. In conventional slow sand filters, little critters are even considered a good thing as they can ensure aeration. They generally stick to the surface so a complete re-install isn’t be necessary.
 

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4661

Does the biosand filter add minerals to the water? Specifically, if the water has been through a reverse osmosis process can the biosand filter return some healthy minerals to the water?

To our knowledge, there has not been any research on the topic.
 
However, it is known that, for the first year at least, water that flows through the biosand filter increases in pH and total dissolved solids.  This is due to the water dissolving minerals from the sand (and concrete, in the case of a concrete filter). This effect wears off over time as the readily dissolvable minerals on the sand surface get used up.
 

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4646

Where can I find a BSF mold manufacturer in country X ?

We maintain a list of Concrete Biosand Filter mold manufacturers here: http://biosandfilters.info/moldmakers  

If you know a reliable mold manufacturer that is not listed. You can submit their details using this form: http://biosandfilters.info/node/add/mold-maker




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4533

What will happen if the sand sieve analysis results are too high or too low?

The sieve analysis tells you important things about the sand you are using.  The effective size of the sand is the diameter for which 10% of the sand is smaller, and 90% is bigger.  The uniformity coefficient describes how similar in size the sand particles are.  The silt content is the percentage of sand with a diameter < 0.1 mm. 
 
If your effective size is below 0.15 mm, that means too much of the sand is very small sand particles. This will lead to a low flow rate.  If the effective size is greater than 0.20 mm, then there aren't enough small sand particles and the flow rate will probably be too high. 
 

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