| This. Sometimes decentralized solutions are great, but most people don't want to become experts at the sanitary biological processing of human waste (especially inside their own home). For safety and efficiency reasons it makes sense to aggregate that at the community scale. Think of it like the local sewage treatment plant. Actually it's better than a conventional sewage treatment plant, because * it safely recycles fertility (interrupting the fecal-oral route, unlike "night soil"), providing a sustainable alternative to phosphorus mining and other fossil fertilizers * it doesn't discharge fertilizer into waterways where it causes eutrophication and "dead zones" * it produces biogas energy rather than being a large energy consumer * it doesn't squander potable water to transport human waste, and * it doesn't require a huge network of underground pipes, which have enormous embodied energy and replacement cost. If your city can't afford to replace the underground pipes, your water system is insecure and unsustainable for that reason alone. Here's another large scale biogas digestor operation (this one's for food waste): https://www.nytimes.com/2017/02/15/magazine/the-compost-king... |