Biosand Filter FAQs Common questions about how biosand filters work, how to build and operate them, and how to keep them performing well.
Basics (71) Can biosand filters be used for greywater treatment? Can biosand filters be used in emergencies? Can I build a biosand filter to use in North America or Europe? Can I buy one or a few HydrAid filters? Can I create a "community size" biosand filter just by building a large biosand filter ? Can I make smaller holes in the diffuser to reduce the flow rate? Can I make the diffuser plate out of metal instead of plastic? Can I use weaved mesh for sieving sand and gravel as oppsed to welded mesh? Can round river sand be used? Is there a way to clean it? Can the biosand filter remove iron? Is it possible that the iron has penetrated deep into the sand and is supporting bacteria colonies (iron oxidizing critters)? Can the biosand filter remove mercury? Can the BSF remove algae and plankton blooms containing toxins (such as cyanobacteria)? Can the BSF remove arsenic? Can the BSF remove VOCs, insecticides, herbicides, heavy metals, or industrial pollutants, such as lead and cadmium? Can we use calcium chloride to accelerate the concrete setting time of the biosand filter? Can you build the lids out of concrete instead of wood? Can you make the mold out of aluminum rather than steel? Can you recommend a preferred concrete mix? Could arsenic in the river sediments be a contamination problem for the sand used in the BSF? Do we need approval to build the BSFs? 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? Does the biosand filter remove all bacteria and viruses? Does the biosand filter remove calcium from the water? Does the biosand filter remove salt from sea water? What about pesticides, industrial contaminants or other chemicals? How about sealing the diffuser plate in place? How can I prevent cracking in the concrete of the filter body? How do I learn about the Biosand Filter? How do I learn about the Kanchan filter? How do you build a biosand filter? How do you calculate the appropriate flow rate (particularly when designing a non-standard biosand filter)? How does the biosand filter remove contamination? How much does a HydrAid filter cost? How was the biosand filter pore volume determined? I have heard that sea shells contribute to cleaning water, so could I add a layer of sea shells above the gravel layer? In the Kanchan filter, how long should the water be in contact with iron? Is it possible to get a vibrator attachment that fits into the wall section of the mold? Is there any way to reduce the amount of water required for washing the sand? Should I attend a training workshop? Should we use copper, polyethylene, or PVC tubing? The concrete breaks when we try to remove the filters from the mold. What should we do? The concrete seems to be drying too quickly and cracking. We would like to commercially produce the BSF. What are some concerns of using a plastic container for a biosand filter? What are some ways to ensure the sand is washed to achieve the target 400 ml/minute flow rate? What are the main differences between a biosand filter and a slow sand filter? What diameter of outlet tube does a biosand filter use? What does the biolayer look like? What is the difference between a rectangular and cylindrical biosand filter? What is the diffuser plate / diffuser basin? What is the minimum depth of filtration sand, underdrain gravel and separating gravel? (particularly when designing a non-standard biosand filter) What is the per unit cost of the plastic biosand filters? What should I do if the edges and top of my filters are discolored and crumbly? What temperature is ideal for curing the filter after construction? What types of tubing can I use for the outlet tube in the Version 10 Biosand filter? What will happen if the sand sieve analysis results are too high or too low? When designing a non-standard biosand filter (e.g. PVC or plastic), does it matter where the pipe is placed (inside or outside)? When designing a non-standard biosand filter (e.g. PVC or plastic), how high should the reservoir be? When designing a non-standard biosand filter (e.g. PVC or plastic), what is more important, the height or the volume of sand inside the filter? Where are HydrAid filters manufactured? Where can I can find the latest Biosand Filter (BSF) Construction Manual ? Where can I find information on the wood mold? Where can I get training on the biosand filter? Where can I see the biosand filter videos? Why don’t you use activated carbon in the biosand filter? Why not make the biosand filter body out of plastic? Why not make the mold four separate pieces? Why not put the pipe inside the container? Why not put the pipe outside the concrete wall? Will the biosand filter take out parasites? Would the addition of a layer of natural coagulant (like say moringa seeds) below the diffuser plate improve the effectiveness of the biosand filter ? Would the addition of a silver coated screen located near the bottom of the fine sand or between gravels improve the pathogen remove in the filter? Operation (19) Are the filters placed inside or outside of people’s homes? Can I restart a biosand filter that was abandoned? Can one achieve the same effect by pre-filtering water through four layers of t-shirts (knit jersey) as through four layers of Sari cloth? How fast should the water flow from the biosand filter? How is the biosand filter used? How long does the biosand filter really take to ripen? How often can water be poured through the biosand filter? If I fill the reservoir at the top of the filter with dirty water, how long will it take for the entire amount to be purified? What are the most common errors made by new users of the biosand filter? What does a properly installed and properly maintained biosand filter look like? What is a cheap way to remove iron before pouring water into the BSF? What is the flow rate per surface area for the BSF? What is the recommended flow rate for Version 10? What kind of raw water could be treated by the filter? What will tell me if a biosand filter is working well? When should the flow rate be measured? Why does CAWST recommend not exceeding a flow rate of 0.4 m3/m2/hour? Why is the flow rate important for the biosand filter? Will chlorine (such as in city tap water) destroy the biolayer in the BSF? Maintenance (12) How often should the sand be replaced? I have seen small worms crawling on the top of the sand in my biosand filter. What should I do? Is disinfecting the outlet tube something that needs to be done by the user or the Community Health Promoter? The local health department has tested the BSF outlet water and it’s more contaminated than the source. There is an earthy smell coming from the filtered water that isn’t getting flushed out. What do I do if my filter is dry? What if the flow from the biosand filter is very slow? What if the water has lots of lime? Where does the water level stand, during maintenance, in a Slow Sand Filter? Why is our biosand filter giving off a bad smell? With the smaller diameter water tube, is blockage from sand or grit a problem? Would it be more effective to mostly clean the sand and not wash it thoroughly till it runs clear, leaving some dirty water in the top layer so the biofilm can recover more rapidly? Safe water (6) Can I install a hose from the filter spout to the storage container? Can I install a valve on the filter outlet? How do I store the water once it’s been through the biosand filter? How should water from the biosand filter be stored? Why does the filtered water need to be disinfected? Isn't the filter enough? Will any material from the biosand filter dissolve into the water and cause a health problem?