Illustration by Anette Moi
In order for crops to grow, you need shit—literally, agriculture requires some sort of fertilizer. Traditionally, farmers have used cow manure because it contains tons of life-giving nutrients, including phosphorus. However, these days there are not enough cow chips to go around, so some places, including Sweden, have taken to replacing it with sewage sludge, which is the cleaned-up version of the gross slurry containing everything we flush down our toilets—cleaning products, medicines, puke, and so on. That’s convenient, because Sweden produces 250,000 tons of this type of sludge a year, and mixed in with this icky garbage is (literally) tons of phosphorus.
“By returning the phosphorus in the sludge to the fields, we can replace 40 percent of Sweden’s use of chemical fertilizers,” is how Mattias Persson, an engineer who works for the local government in Örebro, phrased it in a press release.
Using sludge to grow crops has dredged up a lot of controversy in Sweden. Scientists disagree about the long-term effects the substance has on the environment—some studies in the US have shown that people who live near land fertilized by sludge have suffered symptoms like burning in their eyes and rashes, and activists claim the chemicals left in sludge cause cancer. Switzerland and the Netherlands have banned using sludge to grow crops, while the USA’s EPA is totally cool with it. Sweden is on the fence.
“Heavy metals are already stored up in our soil,” said Urban Boije af Gennäs at the Swedish Chemicals Agency, a government organization. “We should avoid adding more.”
Others are concerned about the residue of drugs that stays in sludge even after it’s been cleaned at treatment plants. Removing some of these highly soluble chemicals from wastewater is notoriously difficult, and they can have negative effects on wildlife. For instance, a study done this year by researchers at Umeå University in Sweden found that fish are more erratic and vulnerable to predators because of antidepressants and sedatives that get into waterways via sewage.
Hans Winsa, a scientist who studies the use of sludge as a fertilizer in forests, thinks that some of those concerns are overblown and that, though there are still tests to be done, so far it’s “100 percent safe” to use cleaned-up waste to grow trees.
There’s also the argument that Swedish sludge is better than other European waste. “We have Europe’s strictest requirements for recycling,” Lisa Osterman, an Örebro government official, said.
Even if sludge isn’t as safe as its proponents say, treatment plants have to do something with it. “The only resources big cities produce are crap and children,” Hans told me. “Both are very important resources that need to be part of the major cycle of things.”
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