(I did recreational water quality management eaons ago, we even tested our own samples for total coliforms, fecal coliforms, enterococci, E. coli.)
The crazy thing is they have tested (and maybe still do test? I don’t know, I was there almost 20 years ago (!!!)) against water quality standards exactly like a conventional wastewater treatment plant, and the “processed” water consistently exceeded the standards for DRINKING WATER. And we use constructed wetlands to help “process” overland flow into natural bodies of water all the time (well, “all the time” might be an overstatement, but it is done). Plus conventional wastewater treatment uses aerobic and anaerobic digestion as part of their processes. And yet, because no chemicals are used, it can’t be certified and is basically a test case that has not garnered widespread adoption (although I am sure there are other facilities that utilize a similar system, but again, probably as “test cases”).
I suppose there is a higher chance of something going “wrong” in such a system, and would require a different sort of mindset to manage, but come on. Think how far we could have come in 20 freaking years!