5 surprising uses for recycled poo

The average person produces about a pound of poo a day. Where is all this going? The answer depends on where you live. If you have flush toilets, your metabolic output spirals down underground pipes to huge sewage treatment plants that clean the water and dispose of the rest as best they can, either destroying it or burying it. In places where flushing systems are not possible, residents construct cesspools and outhouses, where sludge collects and eventually needs to be emptied.

Because feces spread disease, people go to great lengths to get rid of it as quickly as possible. But now scientists and engineers tell us that we are wasting our own waste. When properly recycled, this cheap, fully renewable and readily available substance, regularly produced by the 7 billion of us living on this planet, can produce food, cook food, power cars and generate electricity. . Here are some cutting-edge technologies that are already recycling people’s poop and may soon join you.

1. Cook your dinner with shit

Urban settlements in Kenya’s capital, Nairobi, are so overcrowded that there is no space to build toilets, including the simplest outdoor latrines. But people still have to go somewhere. So locals relieve themselves in plastic bags, dumping them on the side of the road where they pile up, spread and float away the next time a torrential downpour floods the area. The bag phenomenon even has a name: it’s called “Kenya’s flying toilets”.

At the same time, Kenya has a huge deforestation problem. Wood is the only source of energy available to most, so people cut down trees and convert the wood into charcoal, used for everything from cooking dinners to drying tea leaves for the tea industry. from the country.

A startup named Sanivation stepped in to solve both problems with the same substance. Sanitation provides low-income households with small portable potties that accumulate waste in hygienic containers under toilet seats, which a service team then collects and takes to their reuse site. Human feces contain a lot of lignin, a complex organic polymer that comes from the cell walls of the plants we eat. When heated, this lignin turns poop into a sticky substance. If you throw more combustible fibers, such as sawdust or agricultural waste, into this sticky mixture, the result can be shaped and dried into fuel briquettes. Demand from factories is huge, according to Sanivation founder Emily Woods – in their fourth month of selling “shitty logs” they sold 50 tons. “We are only limited by the amount we can produce,” she says.

2. Make a Plant Health Sewage Smoothie

Turning manually collected excrement into firewood is unlikely to find a big market in the western world, but there are other ways to reuse our metabolic output here. Ajay Singh, a scientist from the University of Waterloo in Ontario, noticed many big trucks buzzing around his town on a regular basis. It turned out that the trucks were carrying human waste. Typically, this wastewater is then dewatered and this water is purified enough to be returned to nature, but the remaining biosolids are a tricky problem. Often, biosolids are dumped in landfills or incinerated, contributing to greenhouse gas emissions. And in some places they are funneled into so-called “lagoons” – essentially massive cesspools slowly bubbling under their PVC covers.

Biosolids are kind of a hot potato in the wastewater world: no one wants them because they’re too grimy, big, and stinky to pump or purify like a liquid. But they are also rich in nutrients like nitrogen and phosphorus, which are excellent fertilizers.

Along with a colleague, Singh figured out a way to puree the biosolids into a “sewage smoothie.” They built an industrial-size mixer that whips the biosolids into the consistency of a milkshake. (To test the idea, they first experimented with a regular kitchen blender, but please don’t try this at home!) With an ultra-sharp blade that spins so fast it shears bacterial cells present in the sludge, the mixer solves two problems at once: it kills pathogens and homogenizes the mixture to the point that it can be pumped into trucks which take it to farmland and inject it into ground. Today, their company Lystek turns biosolids into a bio-fertilizer blend called LysteGro, a nutrient-dense health food for plants.

3. Microbial Munchers convert poo into methane

DC Water, the sewage treatment plant in our nation’s capital, has another kitchen-inspired approach to recycling poo, not in a blender but in a pressure cooker. The factory uses 24 colossal pressure cookers to simmer the city’s production at 320°F and six times the normal atmospheric pressure you feel right now for half an hour. At the end of this cycle, all pathogens are dead and the wastewater stew is loaded into huge concrete tanks called biodigesters, where multitudes of microbes chew up (or “digest”) the sludge. In the process, they spew methane gas, which the company collects and burns to spin the plant’s electric turbines.

Prior to digestion, DC Water produced 1,100 tonnes of biosolids per day. Now the powerful microbes are reducing it to around 450 tons per day, with the difference being converted into gas for green energy production. Some of the carbon is sent back to the earth where it came from: at the end of their feast, the microbes leave behind a form of black gooey compost, which is dehydrated and dried in an organic fertilizer packaged in neat bags and called Bloom. , available for purchase by everyone from farmers to landscapers to gardeners. It’s a perfect example of why we shouldn’t waste our waste, says Christopher Peot, director of resource recovery at DC Water: “There is no waste, only wasted resources.

4. Furnishing fertilizer to grow your own food

A huge pressure cooker is not something the average household can afford, but there are smaller and cheaper biodigester options. Israeli company HomeBiogas makes affordable personal biodigesters that can “digest” food scraps in the same way. They can also be attached to pump toilets, which use manual pumps to flush and therefore require much less water. The digesters, which look a bit like camels on the ground, are seeded with specific microbes that break down biomass and turn it into methane, which travels through a pipe to a stove or water heater. And from the back of the digester drips the other precious product – a brown, viscous liquid that can be a powerful fertilizer and slowly accumulates in a bucket.

For countries where energy is expensive, HomeBiogas digesters (costing around $600 to $700) can offer real savings, according to one of the company’s founders, Yair Teller. For the United States, where energy is cheap, biodigesters can be a source of cheap organic fertilizer. And they can also be a boon to off-grid communities, regardless of their geographic location. Imagine growing your food and cooking it with your own manure!

5. Technology to turn poo into oil

Besides stoves, feces can power just about anything, including cars. Metro Vancouver’s wastewater treatment plant in British Columbia is testing a new technology that converts wastewater into a form of crude oil. Developed at Pacific Northwest National Laboratories (PNNL), one of the United States Department of Energy’s laboratories, the centerpiece of the complex device is a smooth silver serpentine pipe. When loaded inside the pipe, the sludge is heated to approximately 660°F and crushed at 200 times normal air pressure.

These hellish conditions, called hydrothermal liquefaction (HTL) in scientific terms, mimic those that have forged oil and gas at the bottom of the world’s oceans over millions of years. At such temperatures and pressures, mud does not cook itself, but its long organic molecules split into shorter, smaller carbon compounds, which include oil and gas. The difference is that Mother Nature takes millions of years to do this while PNNL technology takes 15 minutes. Essentially, you load in stinky black goo and extract stinky black goo, but the difference is that the outgoing goo has a high economic value.

It still needs to be refined like any oil, says Paul Kadota, Metro Vancouver’s program manager, but it helps with sewage disposal and reduces the amount of oil that needs to be extracted from the earth, because we depend always fossil fuels. The project is in a pilot phase, but if it works, Vancouver residents would literally be fueling their cars with yesterday’s dinner.