untreated domestic sewage

There are six polluted  rivulets spaced an average of 150 meters of each other, three of which have a wider catchment area, though I believe that is only domestic waste.

I would like to get some idea if it’s possible to treat the water locally, and if it’s possible to do it in an environmental way , with reed beds for example, using the existing topography, and what kind of areas that would require.

Treating the sewage water would mitigate the foul smells specially strong in the summer months and work as a model on how to treat sewage at local scale without the requirement of large scale plants. It’s worth noting that the river Douro (which all this flows into) has closed  its fluvial beaches due to water pollution so these local measures would have a wider potential benefit.