Existing water treatment systems
One of the big problems I have seen with water treatment systems is the companies behind them. Take the biolytix, for instance. Looks like a great technology, and maybe the concept could be used for a self contained toilet. The problem is the company won’t sell the proprietary filter media (I even contacted them, and they never answered,) they just want to sell this one type of system for cottages. And apparently, from reading a few forums, etc., they are lackadaisical about fixing the systems when they break; one guy had the worms die on him and had to wait 6 weeks for the replacement filter media (which you can’t just buy yourself because they won’t sell it to you.)
Same sort of deal with a lot of greywater filtering systems out there; the nubian and the perpetual water (which seems to have gone out of business,) are two. They won’t even tell you how the system works, so I guess you can forget about getting replacement parts for them. Membrane bioreactors, on the other hand, are not actually new, they have been used for more than 30 years for wastewater treatment, and ultrafiltration membranes are just as old, though fortunately they keep being improved (as shown by the lifesaver bottle.)
This is why I like the idea of using standard parts for stuff, and in developing the sort of system anyone could build and maintain. It’s like a Lister (diesel engine you can look up.) They are not fancy, or super efficient or blah blah, but they are incredibly popular and useful because they are simple, easy to maintain, and they area readily available.
Any sort of proprietary technology always costs way too much when it first comes out anyway, usually for many years until the patents expire. That’s fine in that the inventors deserve the profit for their hard work and obviously we need progress like that, but there’s a lot to be said for working with what we already have.