Ecological sewage treatment ponds concept

The idea is: several households generate sewage. They use ecologically responsible cleaners that you can eat, and they use flush toilets and they don't bother with separating out grey water. They live in a sufficiently humid climate that they don't have to worry  too much about water efficiency, but they still make sure to soak more water into the ground through swales than they pump from their wells, using wind power to fill a water tower. they don't want to have to smell, see or think about their sewage, but they still want to own their shit, and keep a closed loop system.

So this is my design concept for them. This would be downhill from their dwellings. A pipe with sewage inputs goes into the first pond, the lagoon. The overflow from the lagoon flows through a second pipe the second pond, which is full of algae. The overflow from the algae pond flows to the "higher plants" pond. The overflow from there finally goes to the big ecological pond, through a gravel reed bed. The ecology pond has swale connections, to feed any leftover nutrients to trees. Three large berms protect the residents from the sight and smell of the ponds, and protect the ponds from being gorged by too much runoff water in a storm.

Adding a septic tank at the start of your pond series would, in my opinion, be a good move and make the whole system a lot less likely to start stinking, since you hold the smelliest step in an enclosed area where the smell can't get blown up toward the house, and the 'finishing ponds' only have to deal with very nutrient-rich liquids, rather than entire solids.  

For sewage lagoons, I believe a key part of the system is to /not let unfinished humanure into the ground/ - it has to be processed down by bacteria thoroughly before being allowed to enter the groundwater.
By using a septic tank at the start, you're putting in a safety measure to prevent the spread of disease & smell, and what comes out of that tank would be a lot easier for your other ponds to process.

By using a series of ponds (embankments that can hold standing water for long periods) , rather than bare-ground swales, you're also adding more processing & barriers between the excrement & local animals.

Tbh, you may be able to go directly from Septic Tank to Algae Pond, then right into 'Full Plant & Fish Ecosystem Pond', without that extra dedicated 'reed and gravel' bed in the middle... or make the 'full plant' ecosystem START with a gravel & reed bed, which liquid has to flow through to get to the full-plant ecosystem. Not two seperate ponds, but an intermediate barrier.... though storm runoff/flooding may make that a bad idea, since it'll push 'less finished' waters downstream into the fish ecosystem.
Something to consider, I guess.

Check out these sewage treatment lagoon articles for more ideas:

https://www.omag.org/news/2019/1/2/sewage-lagoon-basics

https://water.mecc.edu/concepts/pondreq.html

https://www.waterworld.com/home/article/16192273/introduction-to-wastewater-treatment-ponds

You'll likely have to deal with fairly high-level regulations about sewage treatment lagoons- how they're constructed, and when the liquids are /physically able/ to sink into the ground. Since human waste is such a big vector of disease that can spread to very wide areas via groundwater/aquifers, many governments tends to strictly crack down on its treatment.