Human urine and feces as an alternative to polluting fertilizers

How do you stay if we tell you that our urine and feces could be used to fertilize the vegetables that we eat? This is precisely what a team of researchers whose study has been published in Frontiers in Environmental Science. Scientists have shown that fertilizing with human poop and pee is safe and productive.

Human pee and poop contain most of the nutrients plants need to grow. The urine is rich in nitrogen and potassium and contains traces of boron, zinc and iron. The poop would provide phosphorus, calcium and magnesium. Also organic carbon to the soil.

The scientists compared the yield of a marketable crop of white cabbage grown between June and October 2019 at the Leibniz Institute for Horticultural and Ornamental Crops with four recycled fertilizers, applied gradually throughout the growing season. As a reference fertilizer they used organic vinasse, which can be purchased on the market and is produced by fermenting biomass residues left over from bioethanol production.

Our urine and feces could be used to fertilize the vegetables we eatGetty Images

The team also used of nitrified orine fertilizers, one called Aurin and another CROP. These products are made from human urine that is collected separately from feces. In them, microbes convert nitrogenous compounds into ammonium and nitrate. Aurin fertilizer is already marketed for use in human agriculture in Switzerland, Liechtenstein and Austria. CROP is in the development phase. Nitrified fertilizers were applied to the cabbage crop separately and also combined with fecal fertilizer.

The marketable yield, which is the parts of the cabbages that can be sold, ranged from 35 to 72 metric tons per hectare. This yield was higher in the plots fertilized with Aurin, CROP or vinasse, lower (between 20 and 45% less, depending on the type of soil) in those fertilized only with fecal compost, and intermediate in those fertilized with increased fecal compost. with nitrified urine fertilizers. The results indicate, then, that the same performance in soils fertilized with nitrified urine products as with organic stillagewhich is widely used.

Are there health risks?

The researchers found 310 chemicals in the fecal compost. These included pharmaceuticals, rubber additives, flame retardants, UV filters, insect repellents, and corrosion inhibitors. Analyzing all this, they concluded that only 6.5% of them were present above the detection limit in the compost, albeit in low concentrations, including 11 pharmaceuticals. Among the latter, only ibuprofen and carbamazepine, used to treat bipolar disorder and epileptic seizures, were detectable in the edible parts of cabbages, at very low concentrations (between 1.05 and 2.8 μg per kg). This means that to accumulate in the body a dose equivalent to a pill of carbamazepine would have to eat more than half a million heads of cabbage.

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“In general, the risk to human health from pharmaceutical compounds entering the food system through the use of fecal compost appears low,” the authors say.

“If properly prepared and quality controlled, up to 25% of conventional synthetic mineral fertilizers in Germany could be replaced by recycling fertilizers made from human urine and faeces. Combined with an agricultural transition involving the reduction of livestock and the cultivation of plants for fodder, even fewer synthetic fertilizers would be neededwhich would translate, for example, into a lower consumption of fossil natural gas”, says Dr. Ariane Krause, lead author of the study.

Reference: Häfner, F.; Rodrigo Monzón Díaz, O. et. al. Recycling fertilizers from human excreta exhibit high nitrogen fertilizer value and result in low uptake of pharmaceutical compounds. 2023. Frontiers in Environmental Science. DOI: 10.3389/fenvs.2022.1038175

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