The conventional approach to human waste is to flush it away and pay someone else to deal with it. Municipal sewer systems collect waste from thousands of households, transport it through a vast network of pipes using enormous quantities of water, and treat it in centralized facilities that consume significant energy and chemicals before releasing treated effluent into waterways. This system is both ecologically wasteful and practically fragile: a single infrastructure failure can leave entire neighborhoods without sewer service.

In a regenerative building, human waste is not a disposal problem. It is a resource management challenge. The nutrients in human waste — nitrogen, phosphorus, potassium — are valuable agricultural inputs. The water used to transport waste can be harvested rainwater that, after treatment, is used again in the landscape. The biological energy in the waste can feed microbial communities that do the work of treatment without chemical inputs. When you design a building as a closed-loop system, liquid waste treatment is simply the final stage of the water cycle.

The botanical treatment system developed by Earthship Biotecture and refined by Pangea is the most complete and tested approach to on-site liquid waste treatment at the residential scale. It is covered in full detail in Book 6 of this series, Liquid Waste Water Treatment. This chapter introduces the principles and the system architecture.