22 February 2023

Toilets may provide an alternative to chemical fertilizers


By recycling human manure it is possible to produce natural fertilizers that provide identical yields as chemical equivalents, a German research has found. No risk of drug contamination, the authors explain. But further studies are needed

by Emanuele Isonio


The answer to the demand for natural, low-cost fertilizers could lie in our toilets, according to a German research published in the journal Frontiers in Environmental Science. Human excreta – when properly treated – represent an excellent and safe resource for crops, the authors say, thanks to the abundance of essential elements such as nitrogen and potassium, boron, zinc, phosphorus, calcium and magnesium, which are capable of feeding the soil.

Franziska Häfner, a young researcher at the University of Hohenheim, Germany and co-author of the research, is convinced of this. Products derived by recycling our “waste,” she explains in a press release, “are viable and safe fertilizers,” which don’t pose “any risk regarding transmission of pathogens or pharmaceuticals.”

The research on fertilizers

Working on cabbage crops at an experimental site characterized among different kind of soils (sandy, loamy and silty) at the Leibniz Institute of Vegetable and Ornamental Crops in Großbeeren, near Berlin, the authors applied three different recycling fertilizers: “Two nitrified urine fertilizers (NUFs) and one fecal compost were applied alone or in combination, and compared against the commercial organic fertilizer vinasse.”

The two nitrate-containing substances, the study says, “resulted in marketable yields similar to those of vinasse in all soil types. Combining fecal compost with a NUF led to increased marketable yield compared to compost alone. The highest yield was recorded from the sandy soil, where vinasse and NUF treatments led to comparable yields, as expected in organic productions systems.” In conclusion, the authors note, “NUF alone appears to be a promising successful fertilizer substitute in horticultural food production.”

No real risk to human health according to the authors

During the investigation, scientists also tested the safety of products. Among the NUFs, in particular, they examined Aurin, a product recently approved for use in agriculture in Switzerland, Liechtenstein and Austria, and CROP (Combined Regenerative Organic Food Production), a product developed by the Institute of Medicine of the German Aerospace Center to recycle wastewater on on Moon bases.

Aurin production involves filtering and removing traces of most drugs and pathogens found in human urine. The purification system used to produce CROP, the authors say, is still under development. Therefore, a special version derived from sterile synthetic urine was used during the experiment.

Analysis of the fecal compost revealed a minimal presence of some drugs. Two of these, ibuprofen, a painkiller, and carbamazepine, a mood stabilizer, were detectable in the edible parts of the cabbage but at definitely low concentrations, ranging from 1.05 to 2.8 micrograms per kg. “This means that more than half a million cabbage heads would need to be eaten to accumulate a dose equivalent to one carbamazepine pill,” the scientists explained.

A circular solution (but new studies are needed)

According to the authors, the development of this kind of fertilizer would represent a typical solution based on circularity. “Recycling nutrients is essential for closing nutrient loops within a circular economy”, the research states. “Using locally available resources such as human excreta to produce bio-based recycling fertilizers can substitute mineral fertilizers and thereby promote environmentally friendly food production.”

According to Ariane Krause, one of the study’s authors, the proven effectiveness of these products could inspire strong growth in their use in the future. “If correctly prepared and quality-controlled, up to 25% of conventional synthetic mineral fertilizers in Germany could be replaced,” she explained in the released by Frontiers.

In any case, the authors admit, new research is now needed. The risk to human health, as mentioned, seems low. But the impact on the soil of trace drugs in fertilizers, albeit to a small extent, still needs to be investigated. “The consequences of long-term application of fecal compost requires further investigation, particularly regarding the preservation of soil multi-functionality,” the study concludes.