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Scientists explore human waste as substitute for polluting fertilisers

New research has ascertained that yields from crops fertilised with human faeces and urine rival those produced by organic methods, with no risk of transmitting disease.

If you’d told me a few years ago that human waste would eventually be used as a food-safe fertiliser, I likely would’ve found it impossible to hide my disgust.

These days, with the threat of the climate crisis keeping me up almost every night, I’ll take any solution to slowing down our planet’s deterioration that I can get.

That’s why, upon hearing that scientists have successfully yielded crops using our faeces and urine with no risk of transmitting disease, my response was one of excitement rather than revulsion.

According to the new research, which was conducted by a team at the University of Hohenheim in Germany, fertilisers derived from recycled human waste are just as effective as the conventional nitrogen-based types.

The long, noble and stinky quest to make human shit useful | WIRED UK

That, and they’re far more sustainable, given they aren’t manufactured via an energy-intensive process which uses natural gas as a raw material.

It may seem unappetising, but the stuff we repeatedly flush down our toilets and into the sewage system is actually great for growing fruits and veggies, as it contains the key nutrients they need to flourish, including phosphorus, iron, magnesium, calcium, and potassium.

In fact, the practice of fertilising crops this way has been around since the prehistoric era, and although it’s still pretty common in low-income countries due to its affordability and obvious accessibility, it’s been largely abandoned in the West.

This is because human waste, if untreated, can carry infection-inducing pathogens and parasites. It’s this exact health concern that the study set out to address by applying the compost to cabbages and analysing the presence of pharmaceuticals in the plants.

Human waste could help tackle a global shortage of fertiliser | New Scientist

The results showed that only non-edible parts had taken up the added ibuprofen and carbamazepine at significant levels, with the drugs only detectable in the edible parts at such low concentrations you’d have to eat over half a million cabbage head to accumulate a dose equivalent to a single pill.

‘The fertilisers from nitrified human urine gave similar yields as a conventional fertiliser product and did not show any risk regarding transmission of pathogens or pharmaceuticals,’ says lead co-author, Franziska Häfner.

‘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.’

She estimates that, if correctly prepared and quality controlled, up to 25% of synthetic mineral fertilisers in Germany could be replaced by ones made out of faeces and urine.

Cabbage-growing experiment shows human waste can be good to use as fertiliser | Soil | The Guardian

‘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,’ concludes Häfner.

Simply put, the yield for faecal compost from the experiment was on average 20-30% lower than usual, though it bolstered soil carbon meaning fertility could be maintained long term and, as a result, the most sustainable option is to mix urine fertiliser and faecal compost together.

If we can all be convinced to overcome our squeamishness, this would be a huge step towards creating a circular economy free from the extreme quantity of pollution we’re currently generating and the damage to the environment it’s causing.

But in case you were beginning to get any ideas about starting a vegetable garden in the summer while we wait for this to come to fruition, let’s be sure to leave the technicalities up to the experts, yeah?