Yes,In fact an older faculty member here specializes in low-energy low maintenace wastewater treatment. Wetlands are a good example of that, but they are usually used after 2ndary treatment. Lagoons, essentially giant basins to dump sewage in, can be designed very effectively to minimize odor and treat a sizeable community. there are many options for those that are looking to construct something "simple" and effective. The only trade off, usually, is energy cost versus footprint. Usually, you can get away with minimal energy cost, but the land needed for it might be large in comparison to a mechanical operation treating the same volums. Maybe for a community of a few dozen houses you could get away with a few acres for your lagoon, oxidation ditch, etc. But that also depends upon the communities conciousness with water use. I can get some references for you, if you're interested.

Drinking water:
You can even get "commercial" treatment facilities for small flows (a few housing units or even one unit), but they're relatively expensive. Their effectiveness also depneds upon the overall quality of the source water. For example, the town Simpsonville, in SC, has just discovered they have a uranium problem in their drinking water. A company donated one treatment unit (used for treatment of 1 house) and it was around 50K, but it was pretty effective.