I wrote last year about my sewage cleaning facility  –click-. I actually designed that system myself, and I think it is a good design for a self-sustainable land plot. For just one person, it would not even need to be as big as mine is, although it is about twice the size on the hypothetical map. Here is what I think would be ideal to do with that space.

1. A 5 m³ underground, anaerobic, 3-chamber septic tank. This is the first stage of cleaning, and it separates all the liquid and water-soluble stuff from insoluble sludge. The sludge needs to be pumped out once a year with three people; with one person, it would last much, much longer. And since this structure is underground, it is not accounted for in the map – only the fourth stage is.
2. An underground sand filter or biofilter. Which one to use depends on the local geography. Sand filters need a bigger slope, and biofilters deal better with being constantly submerged.
3. A 70 m² gravel field sown with reed canary grass, Phalaris arundinacea. Why this particular species and not the common reed Phragmites australis that I use in my own cleaning facility? Because unlike common reed,  reed canary grass can be mown two to three times a year for hay to feed the rabbits, whilst being just as effective at cleaning the water with its roots throughout the year. With a gravel field this big, I think the water would be even cleaner at the end than mine is, which is pretty clean.
4. An 8 to 10 m³ underground cistern, into which goes not only the clean water from the sewage cleaning facility, but also all the rainwater from all the buildings.
5. A small pond between two rows in the coppice, into which would go the overflow from the cistern. If there were a well somewhere on the property, it would need to be at a distance that a hydrologist determines as safe (in my case, 30 m was seen as ample).

That way, the sewage would serve a secondary purpose as a reservoir of utility water (mostly for watering the garden) in a drought.

Removal of insoluble sludge is the one thing that cannot be dealt with legally in a self-sustainable way where I live, but that does not mean it cannot be done safely, just that the laws are a bit overcautious (for good reasons). In the part of the coppice that is furthest from the well (and neighbour’s well), it could be safely disposed of on the ground once a year, ideally in the spring, in a pile of old, dead leaves or wood chips or both. It would be smelly for a bit, but nature is really good at dealing with shit, and one person does not produce so much of it to cause any trouble. After a few months, that pile of leaves would decompose and transform into compost safe enough to recycle nutrients to the fields. Which are the most interesting parts of all this, IMO, so that is the part about which I will write next time.