The water clarity of the output from filter 4 has been getting worse and worse up until 2 days ago. An air vent on the top of the barrel was added after I noticed the output pulsing while the pump was in operation. I realized at that time that the pump was actually drawing water from the filter’s output because the water had reached the top of the barrel beyond the overflow drain just below the top and was forming a seal so as to allow the pump drawing water to create a vacuum strong enough to briefly cause water to be forcefully drawn through the filter much faster than it could handle. This was (apparently) causing the increased turbidity and (possibly) the biological contamination of the output water. So. . . know that:
The storage container, especially when used with a pump, must be vented above the water level in the container or the pumping action from the small recirculation motor (or any pumping action) will actually forcefully draw water from the filter at a destructive rate.
We operate a large organic dairy farm, and are looking for a system to purify water. We consume 300 gallons/day.
Is there a Biosand application that would work for us?
Probably, depending on how turbid your input water is, and how much storage volume you have, and maximum instantaneous flow rate you require directly from the filter system. Storage will allow higher instantaneous flow rates. Storage is necessary, as slow sand filters do not provide “water on demand” like rapid sand filters.
The two filters described here, filter 2 and filter 3, on one of the accompanying web sites to this blog, supply 70 liters per hour continuously from a shallow well, this flows into the cistern. The two barrels are hooked in parallel and feed into one pipe that flows into the cistern. 70 liters per hour is slightly over 18 gallons per hour (about 432 gallons per day). 300 gallons per day is about 12.5 gallons per hour continuously. You will probably want redundancy so have 4 of them set up with 2 each started several months apart so you will have water when one system needs cleaning. As long as your input water is fairly non turbid this would work. Also if you are in a location where winters are severe, you will want to have the filters protected from freezing, also if the water is to be used for consumption there should be tests done regularly by qualified health officials.