Fertilisers made from human urine and faeces are ‘safe and productive’ to use in food production, say scientists

The idea of using human urine and faeces as a fertilizer in agriculture is not new. Proponents suggest that to tackle biodiversity loss and pollution, there needs to be move to a circular economy. Why not recycle our own body waste too as fertilizer, provided there is no risk that harmful microbes or traces from pharmaceuticals end up in the consumed crops?

Most nutrients needed for plant growth occur in human urine and faeces. Urine is especially rich in nitrogen and potassium, and contains trace amounts of metals such as boron, zinc, and iron. Faeces could in theory supply other nutrients such as phosphorus, calcium, and magnesium or valuable organic carbon to soils.

Now, a new study in Frontiers in Environmental Science​ claims to show that products derived from recycling human urine and faeces are viable and safe nitrogen fertilizers for cabbage cultivation.

German researchers compared the marketable crop yield of white cabbage grown on soil enriched with conventional fertilizers with modern products already being made from human urine which are turned into ammonium and nitrate.

This included Aurin, which was recently approved for use in agriculture in Switzerland, Liechtenstein and Austria, and CROP (combined regenerative organic food production) developed by the Institute of Aerospace Medicine of the German Aerospace Center to recycle wastewater on Moon or Mars bases.

The effects of these products on cabbage growth were tested both when applied separately to the soil, or in combination with faecal compost, recycled from dry toilets.

‘Huge potential to replace current synthetic products’​

Fertiliser made from human faeces and urine has ‘huge potential’ to replace up to 25% of current synthetic products in some countries, according to the research.

Lead author Dr Ariane Krause, a scientist at 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.”​

‘Low risk of pharmaceutical compounds entering the food system’​

In terms of safety, the study authors reported a low risk from pharmaceuticals in faecal compost.

The authors screened the human waste for 310 chemicals - including rubber additives, insect repellents and pharmaceutical. These were found in 6.5% of the samples examined, but still at low concentrations.

The researchers said only the painkiller ibuprofen and the anticonvulsant and mood-stabilizing drug carbamazepine were detectable in the edible parts of the cabbages, but at markedly low concentrations. More than half a million cabbage heads would need to be eaten to accumulate a dose equivalent to one carbamazepine pill, they reported.

“In general, the risk for human health of pharmaceutical compounds entering the food system by means of faecal compost use, seems low,”​ concluded the authors.

“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,”​ said first author Franziska Häfner, a PhD student at University of Hohenheim, Stuttgart. “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.”​

FoodNavigator asked Dr Ariane Krause if the study would allay fears of unforeseen consequences of using new fertilizers recycled from urine and faeces such as the risk of contamination to the microbiome, be it from pharma residues or other 'novel entities' like microplastics?

“If we collect human excreta separately from other streams of wastewater, microplastics are not an issue,”​ she said. “Microplastics mostly enter the wastewater through greywater from washing machines, rainwater runoff, or wastewater from industry and commerce. So ‘pure’ human excreta usually don’t contain microplastics; only of the food is contaminated like fish.​

“Furthermore, most pharmaceuticals are contained in human urine. During treatment of urine to become a recycling fertilizer, a very important step is filtration. Here, most (<99%) of pharmaceuticals are removed. The faecal part contains less pharmaceuticals, which are partly degraded during composting.​

“Moreover, in most current systems, pharmaceuticals are not removed but released to rivers with the runoff water from the wastewater treatment plant. ​Also conventional synthetic mineral fertilizers are sometimes also not beneficial for the soil biome because their application doesn’t care for the humus content in the soil.”​

She added that recycling all resources was a solution that can potentially tackle global challenges like climate change. “By collecting human waste separately and turning it into fertilizer we aim at three goals, which will be an improvement to the current situation: we will use less water in the toilets, which is relevant in face of climate change; but also, because less dilution makes treatment more effective, which allows us to recycle more nutrients and to remove more pollutants like pharmaceuticals.​

The challenge is that we must adjust our sanitation system, which will be possible step-by-step and with courage and creativity.”​

Reference​

Our toilets can yield excellent alternatives for widespread polluting fertilizers​

Frontiers in Environmental Science​

DOI: 10.3389/fenvs.2022.1038175