The nutrient cycle
The nutrient cycle is nature's recycling system. Sunlight gives plants energy to grow and plants extract nutrients from soil. Plants are harvested or browsed and eaten by animals who use the energy and nutrients. The animal poops and pees, which decomposes and assimilates nutrients into the soil and completes the cycle, by feeding the plants.
Unfortunately man has broken the nutrient cycle by not returning our waste to the soils that grew our food, denying our soils the nutrients essential for plant growth.
Humanity has turned a blind eye to the sustainability of the ecosystem in which we live. We remove nutrients from the soil with our crops and our waste is not returned to those soils. Instead, our waste is piped to a centralised sewage treatment plant, that then discharges to water bodies like our seas, rivers and lakes. The result is excess nutrients in our waterways, resulting in algal blooms and death of aquatic life, along with reduced fertility in our crop soils.
Agri-business models of soil management that use synthetic fertilisers to maintain soil fertility only exacerbate the problem by disguising this fundamental break in the nutrient cycle. That is, we mine or synthesize the nutrients required to be able to continue growing crops. This system is not sustainable.
Human waste actually degrades into humus and plant nutrients that can be returned to the soil and used to maintain soil fertility. Solutions are required that don't break the nutrient cycle.
However, solutions must also involve sanitation. Pathogens must be removed before human waste can be used on food crops. Nature offers some very powerful tools that provide safe recycling of nutrients.
Decentralised treatment offers the best opportunity to reinstate the nutrient cycle. Vermifiltration offers a low cost, effective and safe means of returning waste back into soils for crops that feed those who choose to be part of the nutrient cycle.
See the nutrient cycle (Wikipedia)