Biological sand water filters (otherwise known as slow sand filters) are becoming popular. To all those people who have put up YouTube videos claiming to have built a slow sand filter that can be backwashed by forcing water into the output and churning up the sand from the bottom up – I say you are wrong; totally wrong. There are hundreds of studies that have been done on these filters that show beyond any reasonable doubt that backwashing a biological slow sand filter will destroy it, and most likely mix harmful bacteria and helminths (small worms) far down into the sand layers resulting in horrifically toxic water output.
I hope people actually read some real studies with documented results before they actually try to build one of those filters and use it because even watering vegetables with the water from one of these ill-designed filters would be dangerous – after several backwash events the entire filter would be filled with toxic bacteria. The aggressive bacterial action occurs at the top of the filter because the sand forms its own layers due to the action of water and gravity the bad stuff is removed at the top – it needs to stay there along with the beneficial life – backwashing will mix the bacteria, including the nasty stuff too far down in the filter as the sand layers are disrupted. But don’t believe me, or the hundreds of others, try it; just let sand sit for five or six months in a container with water flowing through it and then try to dig it out – it gets compacted and layered. Be very suspicious and wary of information you find on the internet. Some of it can be really great and some is just plain bs. And while I’m at it let me say, if anyone finds errors in any of the observations or test result interpretations on any of my sites, please let me know, I will respond and do my best to fix the errors – however; please back up your information with test results and documented observations or scholarly peer reviewed articles. Opinions or beliefs won’t cut it. and And again, let me remind readers: the filters I have tested and described on my sites and here are NOT recommended for producing potable water.
The internet is amazing; so much information is available. Unfortunately a lot of it is not what it appears to be. When we are talking about science things get even more precarious. When you read a scientific article or something on the internet that purports to be science, always, if possible, follow the money trail and /or check to see if you can determine what the author’s motives are for sure. Check to see if the information is either peer reviewed, or backed up by citations of peer reviewed scholarly articles; or at the very least check to see if others have done similar work and obtained similar results.
Now where is the “money trail” for my stuff? That is covered on the websites. The funding is unconditional and private – there is no funding from any political, religious, educational or environmental group. What are my motives? I’ve already stated them: Water is not a luxury or something that should be marketed, patented and owned by multinational corporations or anyone, for that matter.Clean water should be freely available to all people. My study, hopefully, is a good starting place. I encourage others to improve on my study, but do so in an honest open way. Some have already done this – thank you!!