Human waste could assist tackle world fertilizer scarcity

Fertilizer derived from human urine and feces is safe and may help lower food prices, tests on cabbage plants show

go through Bryan Owens

Fertilizer derived from recycled human urine and feces is as safe and effective as conventional fertilizers, according to tests on cabbage plants. Using human waste in this way could help alleviate fertilizer shortages that drive up food prices — if people can be persuaded to use them.

Nitrogen fertilizer Made in energy intensive process With natural gas as raw material. Human waste can be a good source of plant nutrients like nitrogen and phosphorus, but it can also harbor disease-causing pathogens and parasites, so it needs to be handled carefully to keep it safe. It is still used—sometimes untreated—as a fertilizer in some low-income countries, but has largely been abandoned in high-income countries.

Franziska Hefner At Agroscope in Zurich, Switzerland, she and her colleagues compared cabbage grown using organic fertilizer derived from distillers grains, a by-product of ethanol production, with fertilizers made from processed human urine and feces.

The yield of cabbage grown with nitrifying urine fertilizer (NUF) was comparable to that of cabbage grown with distiller’s grains. The study found that cabbages grown with manure compost or compost with NUF had lower yields, but the fertilizer may increase the carbon content of the soil in the long run.

The researchers also tested more than 300 chemicals in the manure compost, including pharmaceuticals, flame retardants and insect repellants. Only 6.5 percent of them were detected, and all at very low concentrations. Of the 11 drugs detected in the compost, only two were found in the edible parts of the cabbage: the pain reliever ibuprofen and the anticonvulsant and mood-stabilizing drug carbamazepine. But the concentration of the latter is so low that you’d need to eat half a million cabbages to get a single dose.

“Products derived from recycled human urine and feces are viable and safe nitrogen fertilizers for cabbage cultivation,” Häfner said in a statement. “Their yields were similar to conventional fertilizer products and did not present any risk of spreading pathogens or drugs.”

The researchers estimate that up to 25 percent of traditional synthetic mineral fertilizers in Germany could be replaced by fertilizers recycled from human urine and feces if properly prepared and quality controlled. In some places, this trend has already begun. One NUF they tested is called Aurin, which is approved for use in agriculture in Austria, Switzerland and Liechtenstein.

benjamin wilde At ETH Zurich, when He tested NUF in field trials in South Africa. But getting people to use them may take some convincing. Like farmers from many cultures, the Zulu farmers he worked with had strong social taboos about human waste. However, long discussions about the process of making this fertilizer and field trips until this happened helped them overcome these problems. “Once farmers see that something is working, they’re very pragmatic,” he said, although farmers point out that they may have a harder time convincing clients.

If people can be persuaded to overcome their squeamishness, fertilizer derived from recycled human waste could seriously alleviate fertilizer shortages. There are billions of people in the world with high levels of available nitrogen, Wilde said.