• Guest


    Has anyone tried putting charcoal somewhere (top or bottom) in the biosand filter? What were the results?

  • Eric


    We did use a layer of charcoal in drum filters we made in South Sudan years ago – I know it can improve colour and taste a bit but we did no testing.

  • Guest


    Just a note…don’t confuse “charcoal” with “activated carbon.” Charcoal can be the products of burning at just about any condition and does not necessarily have a lot of capacity to take up water-born contaminants. Activated carbon, used in what are sometimes called “charcoal filters,” is organic matter from a variety of sources which is oven-treated with a controlled temperature and gaseous environment to make it porous at a microscopic level. The huge internal area, like a molecular sponge, is what makes the activated carbon work well. A teaspoon of activated carbon actually has internal surface area equal to the size of a football field, and it can all be used to hold contaminants that get into the pores.
    So the question is, can this kind of carbon be made easily in a developing world facility? Or, is there any kind of charcoal from open fires that has this kind of capacity? It is not likely. The activation is actually a highly controlled two or three stage process, and it also requires either the addition of a synthetic chemical or direct injection of CO2 or O2 during the activation firing. Charcoal that is not activated by such a process will still take up some contaminants, but it will not last very long because its capacity is lower and will be used up. Perhaps there is a way to do an activation process in a low-tech facility that may not provide the highest capacity but will be good enough – that would be a good research project (or maybe it has been done, sometime and somewhere, over the century of activated carbon’s development). The other issue is getting people to replace carbon in a filter and how they even know when this is necessary.
    Steve Dentel

  • Guest


    Dear Mr.Steve,

    Thank you for the clraification between charcol and activated charcol. I think it is auseful piece of information.

    Also charcol in whatever form would be bio-degradable esily , hence I personally dont it is a good idea to add it to sand and gravel layers.


  • Guest


    Since the people that these sand filters are directed toward are also commonly using wood burning fires (or dried manure), it would be a great touch to spend a little time looking into this further.

    I could easily image (and will pursue) a secondary filter that the water exiting the sand filter then goes through. It should be quite easy to replace the media and easy to do so on a daily basis. If it can improve water taste and quality, you’ve not only made the people healthier but also happier. There is value in that, too 😉

  • Eric


    Quite right about the differences between activated carbon and charcoal – activated carbon is much more effective. In fact we don’t really know the effectiveness of adding charcoal at all. It would therefore be interesting to have someone do some research into filters with and without a charcoal layer.

    However, I think we should keep in mind that most raw water would be adequately treated by aeration and filtration alone – for example some bad taste and odour is easily removed by adding oxygen and waiting a while, and taste coming from organic matter may reduce when this is degraded within the filter bed. I guess that is why so far there has been no charcoal in any of the official CAWST or designs.

  • Abhijeet Mairal


    Hi All,

    We have a recommendation to install charcoal slow sand filters (CSF) to contain microbes from the waste water generated from our bioprocess lab. We are already steam autoclaving before discharging the effluent to environment. Is the CSF really required?

    The recommendation from our safety contractor is that the microbes need to be contained in the bio lab itself. Microorganisms which are researched are type BSL-2 microorganisms. Is it mandatory to contain the microbes in the bioprocess lab itself since we are already having SBR reactor, activated carbon filter and pressure sand filter in our ETP unit but it is located around 150-200 m from our bioprocess lab.


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