At sewage school, it is time to make sewage soup. This is not difficult. All it takes is suggestions for what goes down a sewer: shampoo, soap, car grease, number one (lime cordial), number two (an oat biscuit soaked in water). The pupils are from a local primary school in Birmingham, UK. The class is funded by one of the UK’s wastewater utilities, in an attempt to make people understand its largely invisible job. The soup is mixed, and now it comes to cleaning it. The procedure is a version of one used in most wastewater treatment plants: let the larger solids settle, and remove them (they are then called sludge). Add some bacteria to eat the rest. Expel the cleaned effluent into the nearest watercourse. But what about the sludge?
Find a farmer. Sewage sludge is rich with nutrients that crops need. The price of phosphorus – a vital fertilizer – has risen 50 percent in some parts of the world, as phosphate reserves dwindle (and could be gone in 100 years). So farmers love it. Two thirds of British and American fields are fertilized with a by-product of your bowels. Anyway, that’s almost the only option. Ocean dumping of sludge is banned; incineration is unpopular with the public; landfills are filling up. The fields seem like a perfect solution. It would be, if sewage were pure human excrement, if it didn’t contain heavy metals, pharmaceuticals and other contaminants that end up in sewers. People living near fields covered in sludge say it gives them respiratory distress, headaches, Staphylococcus and seizures.
You can get used to anything. Even to be at home with shit.
Maybe DIY sludge is better. Composting toilets are simple to construct and easy to buy. Add sawdust or ash to your excrement and wait six months to destroy any possible pathogens. The resulting compost – also known as “humanure” – is purer and safer, say fans, than sludge. In Shaanxi province, China, Zhang Min Shu and his wife, Wu Zhaoxian installed a composting toilet in 2007. They were suspicious enough to have it installed outside, in their yard, but “now we wish we had it next to the kitchen.” It doesn’t smell, and the compost grows crunchier apples, with sweeter juice. Of course, composting requires unhooking from the sewage system. It is unlikely to happen any time soon. You may find it weird for your shit to sit there after years of watching it flush. But humans used to think differently about shit – the Romans, who defecated in company; or the Californians who ate sewage-fed walnuts – and they can do so again. Petter Jenssen, a Norwegian expert on “sustainable sanitation” such as composting, tells of a friend who had installed a composting toilet. When his children started kindergarten and encountered a flush toilet, they were horrified. “They could see shit in the water and they were used to a black hole. You can get used to anything.” Even to be at home with shit.