reporter: zirkulierbar's research happens here, on the edge of eberswalde.is where nutrients such as potassium, phosphorus, nitrogen, and many others that people excrete every day are being recycled, turning the plants that feed us back into fertilizer. the collected fecal matter is composted along with green waste and transformed into humus fertilizer for agricultural use. ariane: why do we want to recycle nutrients? if we look at minerals such as phosphorus or potassium, we typically get them from mines, and when it comes to phosphorus, resources are extremely scarce. nitrogen is another nutrient that we really need to be recycling, because it's an essential nutrient that every plant needs to grow. reporter: and that would normally be extracted in an energy-intensive way. during composting, bacteria create heat. florian: so we're currently at 67 degrees. the goal is to reach 75 degrees, because that's when you have the greatest inactivation rate for pathogens. reporter: killing off the pathogens is key. that's just one of the things monitored by claudia ki