6th March 2005 at 12:15 pm #624
About SSFs operating in cold conditions, I quote from Huisman and Wood in the book ‘Slow Sand Filtration’: “In climates where the winters are very cold it may be necessary to install expensive structural precautions against freezing. At the same time the efficiency of purification will be adversely affected by low temperatures. Rapid filters will be equally affected, but because of theis smaller area they are cheaper to cover.”
In an article about removal of microcystins (products from cyanobacterial blooms) in slow sand filters, Grutzmacher et al found that temperature of <4 degrees C was a likely reason for incomplete biodegradation of microcystins.
In an article by Laurent et al on biodegradable organics removal in biological filters, there is a graph that shows biological activity against temperature. At 0-5 degrees C, it seems that there is between 15 and 30% activity in varying bacteria groups – some are more adapted to cold conditions. It can’t be denied then that cold temperatures reduce the efficiency of the sand filtration process.
With this in mind, a household sand filter project would have to ensure that all filters made are kept in the house, for example the kitchen. What is the average temperature in the coldest time of year in an average Badakshan kitchen?
Hope this helps, let me know if you want me to forward other stuff.