Update May 5, 2014:
This filter is still functional after 2 and a half years of operation. It was frozen solid this winter (until Feb. 2014) for 2 months. Temperatures were down to 10 degrees F. for several days, and below freezing day and night for weeks at a time. It has taken about 6 weeks of running to overcome the effects of being totally frozen. The re-circulation pump needed some cleaning but other than that, there was no visible damage to the filter system from the freezing weather here in western Washington state.
Update October 22, 2013:
This filter is still working after 2 years of continuous operation. The filter has been monitored regularly, and as a result, a potential issue with the sand has been discovered. The bottom layer is too coarse, and takes up too much room. There should be more fine sand and less coarse sand to produce exceptionally clear water. If the depth of the.45 mm effective size sand on the bottom layer is reduced considerably, and the .25 mm effective size layer depth increased accordingly, this filter will produce higher quality water at a reduced flow rate. Reduce the depth of the .45 mm sand to a maximum of 6 inches, and increase the depth of the .25 mm sand as much as the bottom layer has been reduced, so the overall depth of sand is the same as the original design. Note that your flow rate will be reduced, but the quality of the water will increase.
Know that flow rate depends on the turbidity of your input water. Highly turbid input water will clog the filter very quickly. If you have any doubts about your input water turbidity, set up a small test filter in a 5 gallon bucket and watch the flow over a period of several months. You may need to set up a roughing filter.
A new filter has been put together here. This is Filter 4.
AS OF FEBRUARY 8, 2012, THE OUTPUT OF THIS FILTER HAS BEEN TESTED. THE FILTER IS WORKING.
IT WAS STARTED ON NOV. 13, 2011 AND MODIFIED ON NOV 22, 2011 THEN RESTARTED ON NOV 22, 2011; THEN MODIFIED AGAIN ON DECEMBER 14, 2011 AND RESTARTED AT THAT TIME. The tests were done by an EPA certified lab here in the Seattle area. Note that it will be at least 3 weeks from Nov. 22 (weather permitting )before the tests go in and then another 3 weeks until the results are obtained. This means it may be the middle of January 2012 before we know for sure that this design works.
The input section of this filter is an adaptation of
the filter shown by ArashiNage Thank you ArishiNage!!! I suggest viewing his video – its excellent.
Below are some screenshots of the assembly procedure. The bottom level of sand used is .45 mm effective size, the top 3 inches is .25mm effective size. The pvc is half inch. The drill size for the baffle is a #45 and the size for the drain is 5/32 inch.
When you put a small slow sand filter together remember this: add the sand and gravel to the water – don’t add the water to the sand and gravel – fill the container first at least half way full. Here is why: as water is added to fine grain dry sand in a container, often small air pockets form (air pockets can even form in wet sand if it is just dumped in the barrel without water in there first). The sand does not get saturated with water in places and this will cause bacteria to die and horribly foul the filter. There will be a most horrific odor and the filter will produce toxic water. This will require shoveling out all the sand and sterilizing it and then putting it back in, or worse, replacing all the sand. Don’t even go there – just be sure the sand is added to water that covers it when it is added to the container. I have already been through this – and it is a huge pain to replace the sand in one of these filters. Its much easier just to have water in the container first. Don’t put chlorine in the filter – ever. Don’t clean the sand with chlorine unless you make sure to remove ALL of the toxic chemical before you put the sand into the filter. Chlorine will keep the beneficial bacteria from growing. Its ok to sterilize the container and pipes with chlorine, but be absolutely sure to get it all out before you start the filter. A better choice for sterilizing would be hydrogen peroxide – 3 percent solution – just don’t get it on your hands. The bacteria on TOP of the sand and in the top 4 or 5 centimeters needs to stay on top – that is where it works to stop pathogens. “Clean” the filter by “wet harrowing” – agitate the water on top while avoiding direct contact with the sand surface, and drain off the resulting murky water while adding water to keep the sand surface covered. No need to remove sand and add new.