The idea of using human sewage to fertilise the land has been poo-pooed for too long. As a global food crisis looms and fertiliser costs soar, isn’t it time for us to get over our squeamishness, asks Daniel Selwood

We’re “sleepwalking” towards an age of avoidable food crisis.

That was the warning from Oxfam this week as it predicted food prices would double in the next 20 years. “The food system must be overhauled,” it said.

Even the most bullish expert would admit that’s a tall order. Yet, every day we are flushing away one possible solution to the problem. Literally. Human faeces is a rich source of organic nutrients and a growing number of experts believe we should give serious thought to using it on food crops. It won’t avert the looming crisis, they say, but it will alleviate it.

In short, it’s time to wake up and smell the sewage. Not that you’d actually be able to smell it. Things have moved on considerably since the days of Tudor England, when ‘gong farmers’ had the unenviable task of collecting ‘night soil’, so-called because of a rule dictating it could only be spread on fields after dark to save residents from its foul stench.

Thankfully, those days are over. “There is no obnoxious smell,” says Yorkshire-based beekeeper Graham Wiles of the 8,000 tonnes of treated sewage he spreads on his land near Wakefield every year. “Nobody would ever imagine where it came from. It looks like very good quality soil, which is what it is.”

Sewage has been a boon for the Able Project, his not-for-profit sustainable farming initiative, and its bees. Wiles began spreading sludge on his land to fertilise willow for use as a biofuel. Trouble was, it worked a little too well, causing any seed that fell to the ground to sprout. The riot of growth strangled about 80% of the willow saplings, but all was not lost. The local bees began to thrive, so the project increased its hives. Now they produce 2,000 jars of honey a year.

Honey is one thing, though, fruit and veg quite another. The link between fertiliser and food is that much closer, which is partly why such crops have largely missed out. There are also regulatory barriers. The Safe Sludge Matrix guidelines set out by the BRC and Water UK bans the direct application of treated sludge to fruit, salad and veg, although in some cases it can be used if there is enough of an interval between application and harvest.

However, many experts are calling for this guidance to be reviewed. “The Safe Sludge Matrix is a few years old now,” says Nicola Campbell, environmental policy advisor at the NFU, which supports the use of human waste. “A lot of the problem is perception. As soon as you say the word ‘sewage’ people get a bit squeamish. Looking again at the Safe Sludge Matrix could help enhance people’s perceptions.”

The other concern that needs to be addressed if human exrement is to be used as fertiliser is contamination. For the past 40 years, treated sewage or biosolids (1% sulphur, 4% nitrogen and 5% phosphorus) has been used on British farms as a fertiliser for non-food crops and as a means of improving soil structure and drainage.

In principle, Tim Lang, professor of food policy at City University is in favour of using human waste on food crops. But, he warns, it is not as easy as it sounds. “By mixing human waste with everything that comes from streets and industrial outlets, we have, by having one sewage system, created problems for the potential to recycle,” he says.

When introduced to soil in significant quantities, heavy metals such as zinc, mercury and nickel from industry and road run-off can lead to reduced plant growth and pose a threat to human health.

“You’re then into very big issues about what sort of bioengineering would be necessary,” says Lang. “Can we just modify existing sewage systems or do we have to completely re-engineer them? Or do we have to treasure human waste and re-engineer what we do in our houses?’

The concept of ‘treasuring’ waste is a startling one, but one we may have to get our heads around and quickly. Some already have and believe they’ve tackled the contamination issue to boot.

As part of a Europe-wide project, Harper Adams University, Cranfield University and United Utilities have been conducting trials of an odourless pellet derived from treated sewage sludge on a Cheshire farm. They claim to have created a fertiliser so advanced that its nutrient levels can be adjusted to meet the specific needs of different commodity crops such as barley, wheat and maize.

“Heavy metals such as zinc used to be a problem, but we’re finding now that we’re having to add zinc to it,” says Charles Murray, field trials manager at Harper Adams University. “There is no practical reason it can’t be used on food crops.”

Isobel Tomlinson, policy and campaigns officer at the Soil Association, agrees. “It’s clear that it’s very well-processed stuff and safe,” she says.

Despite such assurances, retailers remain to be convinced. “Treated compost (sludge) isn’t used as a fertiliser on any farms growing produce for us,” says a Waitrose spokesman. Morrisons adopts a similar line: “We await the evidence that shows the safety of these types of fertilisers in the supply chain but at the moment our policy is not to use them.”

Their concern is understandable if consumers don’t buy into the idea, it’ll be the retailers that pay the price. But there’s a PR job to be done and they need to be part of it, says Murray. “Having seen how badly perceptions of GM have been managed we hope we will be able to do a better job with this,” he says. “We will get only one crack of the whip. We have to get this right.”

Fail to do so, warn the experts, and the future of global food supply could be in jeopardy and not many people would say they don’t give a s*** about that.

Waste not want not

By 2030, the proverbial really will have hit the fan. Oxfam believes food prices could well double in the next two decades as the number of mouths to feed on the planet soars and our resources dwindle.

A key factor will be cost of fertilisers. These are set to rise dramatically as traditional sources come under increasing pressure. Indeed, with approximately 160 million tonnes of phosphorous rock being dug from the earth each year, experts say that extraction of the element required by plants to grow will be uneconomic by 2033. 

Synthetic nitrogen fertiliser is also expected to rocket in cost. But there is a solution, believe experts: human faeces. They are rich in phosphorous and nitrogen and to put it bluntly, they’re in plentiful supply.

“We have got to start seeing human waste as a recycling opportunity, just as paper and plastics are,” says Tim Lang, professor of food policy at City University. The question is whether consumers or the food industry can overcome their squeamishness sufficiently to do so.