After reading website after website on how to build a biological slow sand filter, I have come to the conclusion that people need to learn more about how they actually work. Here are 50 references to studies on slow sand filters, roof water harvesting and related information
Read them. Most of the studies have 50 or 60 references to other studies on the same topic, that makes hundreds of studies. Read those too.
Now let’s clear the air about the ninnies who throw around their “beliefs” like they are facts. I could get into a long philosophical argument – with people who deliberately prevaricate science – about the validity of scientific inquiry and peer reviewed scientific writing. I have seen this ludicrous situation between “climate change deniers” and those who back up their claims with research that has thousands of other people supporting it; and it makes me sick. Here’s the deal. People do studies; they know what works from experience, watching for results, and the use of high tech equipment. There are hundreds of studies ( some of them are listed on the above page ) that have been done on biological sand water filters (slow sand filters, bio sand filters). These studies have used instruments that can measure and detect things that are impossible to detect with the human eye. The studies are done by people who KNOW what they are doing and they KNOW HOW TO USE THE equipment. There are thousands of biosand filters in use around the world (mostly outside of the USA) and they work. The information in these studies I have mentioned is available for anyone who has access to a public library or a public university library. Now, it is true that there are lots of people who don’t have that access. It is therefore the responsibility of those of us who do, to accurately report the information from the studies, and to NOT distort the facts. There are those who throw some sand in a bucket and call it good. I have no problem with this and sharing ideas and experience is a very good thing, but so many of them come across as if they are the final word with nothing but bluster and fancy graphics to back it up. PLEASE before you come up with your own ideas about how the thing works, READ THE STUDIES, and learn some biology and some science and take your output water to an epa approved lab and have it tested – and learn what to test for. Now enough of that.
A biological sand water filter works because of microscopic life. This life consists of bacteria, zooplankton, diatoms, and algae. There are hundreds of different types of each.
The top 5 – 10 centimetres of sand are the most active, but biological activity occurs as far down as 40 centimetres from the surface of the sand; and, over time, naturally formed layers of sand make the filtering process more effective. The sand must be at least 65 cm deep ( about 25 inches) . The organisms that make a slow sand filter work are aerobic and aquatic- they must have oxygen and be under water to survive. Most of these organisms are harmless to people. Because they are alive, they must eat something to survive. They will ( and do ) consume pathogens ( bacteria and viruses that make people sick ) in water. All that is left in the water is harmless minerals. A layer of organic “goo” forms on the surface of the sand – it is not necessarily visible. This traps particulate matter and living organisms. The water that emerges from a functioning slow sand filter is purified – pathogens are REMOVED not just killed. A biological sand filter is not the end all solution to clean water supply. And there are problems with these filters. Those problems are also listed in the studies, and also on this page:
Read them. Then build your filter and test it.