or, why you don't see more slow sand filters out thereThe traditional water treatment industry has done a great job in promoting their products as the only alternatives to your water treatment issues. This has led to a marketplace full of products that have attached revenue streams. Not so much planned obsolescence as planned dependency on replacement components and mystery chemicals and media blends that require you to have an ongoing financial relationship with your supplier. It's a business model, not a water treatment model.
But, it doesn't have to be that way. In recent years, membrane filtration has been all the rage for basically any problem you can imagine with water. Ultra-fitration, a membrane technology, is pitched as THE solution to surface water treatment. If you look up the regulations though, ultra-filtration isn't listed as one of the approved technologies- it's an alternative technology along with bag filters, cartridges etc. One technology that IS listed as an approved method for treating surface water according to the Surface Water Treatment Rule is also one of the simplest and easiest to maintain- slow sand filtration. And no revenue stream. Once you put ssf in, you maintain it yourself, or hire someone to do it, but you're not joined at the hip indefinitely with your supplier. It's easy to understand why the water treatment industry has not been so interested in slow sand or related more natural systems- no ongoing revenue stream.
Simple biological and physical processes are also great for wastewater treatment and removing metals from groundwater.
Membranes are good at treating brackish waters and seawater, but that is the only area where they excel except in creating a gee whiz factor for engineers and a positive ongoing revenue stream for chemical manufacturers who need to supply all the chemicals required to maintain the membranes. Membranes also waste a lot of water, a problem in an age of shrinking water availability. Membranes should not be the go-to technology for all uses.
The present situation will remain until industry changes the business model which requires an ongoing revenue stream in their designs. There is plenty of need out there. A company selling slow sand filters or related technologies could be selling globally and never run out of new business. The other change agent- educated consumers expecting technology to be more sustainable and less wasteful.
above: a fancy shmancy ion exchange unit.