In a “closed” ecosystem like the Planet Earth, there is no such thing as “Waste” only a redistribution of nutrients.
Animals (people) extract oxygen from an atmosphere consistting of almost 90% nutrogen, a vital nutrient we can only get through nitrogen-fixing bacteria in the soil. That nitrogen passes through plants to us.
Plants take in what we breathe out, carbon dioxide, keep the carbon and pass the oxygen back into the atmosphere.
A lot of our food is power-grown like, fast using ‘artificial’ PKN fertilizers made up of Phosphorus (P) Potassium (K) and Nitrogen (N) but there are at least eleven more nutrients that plants need to thrive and also pass on to us, like nitrogen and must be in the soil, as well as the bacteria and fungi that are part of the Biosphere we are of!