The nutrient cycle is nature's recycling system. Sunlight gives plants energy to grow and plants extract nutrients from the soil. Plants are harvested or browsed and eaten by animals who use the energy and nutrients. The animal's waste decomposes and assimilates nutrients into the soil and completes the cycle, by feeding the plants. 

Unfortunately we've 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, yet our waste is not returned to those soils. Instead, our cities pump waste to a centralised sewage treatment plant, that then discharges to water bodies like our seas, rivers and lakes. The result is an excess of 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 use synthetic fertilisers to maintain soil fertility, but this only exacerbates the problem by disguising the fundamental break in the nutrient cycle. That is, we mine or synthesise non-renewable nutrients we require to be able to continue growing crops. This system is not sustainable.

Human waste actually degrades into humus and plant nutrients that can and should 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 or around food crops. The World health Organisation recommends wastewater quality to be used in agriculture as 1 intestinal nematode or less per litre, 1000 or less faecal coliforms per 100 ml for irrigation of crops likely to be eaten uncooked*. Luckily, nature offers some very powerful tools to safely recycle nutrients, with vermifiltration at the helm.

Decentralised wastewater treatment offers the best opportunity to reinstate the nutrient cycle. Vermifiltration offers a low cost, effective and safe means of returning human waste back into soils for crops that feed those who choose to be part of the nutrient cycle.

Further reading

See the nutrient cycle (Wikipedia)

*World Health Organisation (1989), Health Guidelines for the use of Wastewater in Agriculture and Aquaculture, WHO Technical Report 778.