Microbes feed on organic components of waste until they can no longer derive energy from it.
At this point, sludge consists of mostly cellular material and stable degradation products that are considered safe for application to agricultural or forest lands. If properly managed, land application is an excellent way to dispose of sludge. Waste can be applied at rates to meet crop nutrient requirements without harming the environment. Both the waste generator and the crop producer benefit from this recycling system. Humans and animals are natural waste generators, and land application makes it possible to recover the valuable components of waste as a usable resource.