Slow sand filter construction and operation with roof water harvesting

More information. This is very important. The two most recently set up slow sand filters in operation here have some important lessons to be considered. In extreme cases, a diverter by itself, will not be enough of a pre-filter:

Turbid water from a roof (or anywhere) will clog a slow sand filter within hours. Excessively turbid water comes from roofs when there are lots of trees directly above or within 20 or 30 feet of the roof surface; or when wildlife has access to the roof surface, or both. This turbidity will cause severe problems with the filter. Cleaning will be necessary to the point of preventing the filter from producing purified water. A pre-filtering system is absolutely necessary. Either a dual sand filter system (filters in series) with very coarse sand (.85 mm effective size) in the pre-filter; or an effective screen system to keep fine debris and mud-like substance our of the filter input, or both will be required or the filter will not function and will produce un-usable water. The cleaning will be required so often just to enable throughput that the output water will not be purified. This problem has occurred here with 2 of the filters that are handling roof water with only a diverter as a pre-filter.

The oldest filter here works well with 2 settling barrels acting as pre-fiters following the diverter. This filter has been working flawlessly for 6 years now. Two other filters here processing water from a surface well have been working for 3 years. In both these situations the input water has very low turbidity.

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2 Responses to Slow sand filter construction and operation with roof water harvesting

  1. Paul says:

    You commented somewhere else about the possibility of running two slow sand filters in series to further improve the quality of the filtered water. Have you tried this method? What were the results?

  2. Orpheus says:

    Thank you for reminding us about running filters in series, Paul. Actually, that idea was first suggested by one of the readers of this blog, and not myself. I will search the archives here and post a link when I find it. I have not tried running filters in series yet; although I do use re circulation on 2 of the filters here. This is similar to running water through filters in series, but not exactly the same. Regarding the “filters in series” setup, the schmutzdecke would likely be somewhat different in separate filters, and it would be possible to use a much finer sand in the second filter, if they were run in series.

    Another idea has come to my attention as a result of the experience here with excessively turbid water coming from the roof surface directly shadowed by a massive fir tree. This is to use an upflow filter directly following the first flush diverter, in series with the slow sand filter. This may not be as effective as having 2 ssf units in series.

    As I have been recovering from major surgery since June, I have not been able to do much in the way of helping to build new devices . . . up until now. Hopefully we will be able to set up both situations here – filters in series, and an upflow filter in series with one of the existing slow sand filters. It will likely be early summer before any results are available from this location.

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