A new study has shown that modern ‘green’ products recycled from human excreta are excellent, and safe, fertilisers for agriculture.
Franziska Häfner, a PhD student at University of Hohenheim, Stuttgart, Germany, said, “Here we show that products derived from recycling human urine and faeces are viable and safe nitrogen fertilisers for cabbage cultivation. The fertilizers from nitrified human urine gave similar yields as a conventional fertilizer product and did not show any risk regarding transmission of pathogens or pharmaceuticals.
“The combined application of nitrified urine fertilizers and faecal compost led to slightly lower crop yields but may increase soil carbon content in the long term, promoting climate-resilient food production.”
They compared the marketable crop yield of white cabbage at the Leibniz Institute of Vegetable and Ornamental Crops on plots with sandy, loamy, or silty soil enriched with four recycled fertilisers, compared to commercially available organic vinasse, produced through the fermentation of biomass residues from bioethanol production. They also tested two so-called ‘nitrified urine fertilizers’ (NUFs), modern products synthetized from human urine that has been collected separately from faeces, in which nitrogen-bearing compounds are converted by microbes into valuable ammonium and nitrate.
The highest yields were obtained from the NUF fertilisers or the vinasse, with the lowest from faecal compost alone. The authors also screened for the presence of 310 chemicals in the faecal compost, from pharmaceuticals to rubber additives, flame retardants, UV filters, corrosion inhibitors, and insect repellents.
“In general, the risk for human health of pharmaceutical compounds entering the food system by means of faecal compost use, seems low,” concluded the researchers.
Lead scientist Dr Ariane Krause, from the Leibniz Institute of Vegetable and Ornamental Crops in Großbeeren in Germany, said, “Our study results demonstrate that nitrified urine fertilizers such as Aurin and CROP have a huge potential as fertilizer in agriculture. They argue for a greater use of these recycled products in the future.
“If correctly prepared and quality-controlled, up to 25% of conventional synthetic mineral fertilizers in Germany could be replaced by recycling fertilizers from human urine and faeces. Combined with an agricultural transition involving the reduction of livestock farming and plant cultivation for fodder, even less synthetic fertilizer would be necessary, resulting for example in lower consumption of fossil natural gas.”