Most people don’t give a second thought to the poo they flush away. But perhaps they should, because the energy contained within our repellent remains is impressive.
If you let poo fester – and you probably shouldn’t in polite company – bacterial digestion will produce a methane-rich ‘biogas’ that can be harnessed for energy. You can also dehydrate a deuce to make powdery fuel or combustible bricks with a similar energy content to coal. These schemes may sound outlandish, but wastewater plants all over the developed world take advantage of this salvageable energy to subsidise their operations. One treatment plant in Twickenham, for example, gets 50 per cent of its power using poop.
Now, similar ventures are cropping up in the developing world, offering a means not just of producing “renewable” energy, but dealing with problematic sanitation issues, too. Overflowing and mismanaged sewage leads to the contamination of water supplies, impacting people’s health and that of local ecosystems.
For city dwellers in the developed world, a flushed poo finds its way through a complex series of sewage tunnels until it reaches a wastewater treatment plant. Once there, it goes through filters and a grit chamber where various solids are removed, leaving behind wastewater.
That fluid is then allowed to sit, segregating the lighter “scum” and the denser “sludge” from the water. While the scum and sludge are broken down by microorganisms, the water itself is assailed by filtration technology, chemicals, and still more bacteria, until ultimately you wind up with water clean enough to be returned to the environment. During this process, the microbial digestion also generates biogas.
These types of treatment systems aren’t nearly as ubiquitous in the developing world. According to the World Health Organization, 2.3 billion people do not have basic sanitation facilities, and 892 million people still practice open defecation. Just 2.9 billion people, or 39 per cent of the global population, use a non-shared toilet or latrine attached to a proper sewage disposal and treatment system.
Back in 2015, a UN report saw a potential solution to humanity’s widespread waste problem. It calculated that if the poop produced by those practising open defecation was harvested, it could generate at least £153 million in methane production alone and power up to 10 million homes, with solid residue adding to that considerably.
The report cited Uganda as a potentially model example. And indeed, the country has been working on a variety of poo power schemes for some time now, from turning uncollected garbage into fuel with kilns to biogas production at local businesses, including several slaughterhouses.
Jennifer Musisi, the first executive director (equivalent to mayor) of the Ugandan capital city of Kampala from 2011 to late-2018, explained how schools there began turning their toilets into energy-producing units back in 2014. Previously, many schools had used firewood for cooking and electricity, which was both expensive and unsustainable. The city authorities reached out to various partners to fund a school biogas scheme, including several private telecommunications companies. They agreed to fund a waste-to-energy scheme for ten schools, and as more funding becomes available, the hope is that this self-contained power production model will spread to dozens more across the city.
Daniel Ddiba, a research associate at the Stockholm Environment Institute, cites other examples. Uganda’s National Water and Sewerage Corporation recently signed a memorandum of understanding with global non-profit group Water For People to turn the faecal sludge in the treatment plants in Kampala into combustible briquettes.
European wastewater treatment plants regularly produce biogas that can be used, say, in public transportation. A new plant in Uganda has recently opted up to do the same, although it will be providing electricity to the local grid instead. “This is something more African cities will start to experiment with in the future,” Ddiba said.
Similar schemes can be found in neighbouring Kenya, where one company in Nakuru is opting to bring faecal matter to a processing plant and drying it to turn it into a charcoal-like fuel source for cooking and heating. Another scheme in the slums of Nairobi, where folks lacking toilets toss bags of poo right into the street, is turning to bio-digesters, where methane is collected within a centralised, toilet-containing facility and sold back to locals as biogas.
Ddiba says that there has been an uptick in poop-based waste-to-energy schemes in the past decade or so, but “the idea that human waste has energetic value goes far back into human history.” There’s even a reference to it in the Bible, he points out: Ezekiel chapter 4, verse 12, extols the virtues of using human excrement as cooking fuel.
Old as the idea may be, actually implementing it is often challenging. “Pooping is easy,” said Chelsea Wald, a science and environmental journalist who is working on a book tentatively titled Pipe Dreams: Transforming the Toilet. For those trying to harness poo for energy, everything that comes after is more complicated.
Take, for instance, pit latrines, a common toilet in the developing world. Plenty of trash gets mixed up with the poo. From a fuel perspective, the quality can vary a lot. “There’s a whole area of science that assesses the quality of the faecal sludge in pit latrines,” Wald said, noting that the energy content depends on how long the poo sits in the latrine, and how leak-proof each latrine is. The amount of water a poo contains is critical, as it needs to be removed if you’re making a dry fuel, and that takes considerable energy.
You also need a way to suck the poo out, which is easier said than done. Next, it needs to be transported to treatment sites, whose technology must be maintained by people with the appropriate expertise.
Those hoping to connect energy production to flushable toilet systems also face considerable challenges. In 2014, when a major faecal sludge treatment plant opened up in Ugandan capital city of Kampala, the capacity was exceeded within the first month. Wastewater treatment plants are expensive to build and operate, and with limited funds and considering Kampala’s population is expected to rise from 3 to 7 million by 2050, “the infrastructure cannot cope”, Dbida said.
Poop-to-power schemes may help change that, where an ideally revenue-generating system can take the pressure off the struggling, pre-existing infrastructure. Sadly, the financial support for them is inadequate at the moment. In 2017, private investors initially keen on placing their chips on waste-to-energy tech in the city got cold feet after feasibility studies suggested the city’s waste requires more energy to heat up than would be generated.
While various groups attempt to tackle the obstacles of integrating poo-to-power schemes into today’s infrastructure, some entrepreneurs are betting big on decidedly futuristic pieces of poo-powered tech.
Peter Janicki, co-founder and CEO of Janicki Industries, is one of them. Aided by the Bill and Melinda Gates Foundation, his company has designed the Omni Processor, which can separate clean, potable water from human waste. The prototype model comes in at around 13,000 square feet, and can potentially churn through 66 tonnes of biosolids and around 5,800 gallons of water per day, enough to service around 100,000 people. The dehydrated fuel is burned, powering a steam engine which generate electricity within the system itself. Some of this steam can be used to power the drying process. The net capacity of the plant is between 100 and 200 kilowatts, enough to power nearly 170 average American households.
A pilot scheme in the Senegalese capital city of Dakar, largely managed by local staff, has been operating for around four years or so on a near-daily basis, and during that time, the technology’s efficiency has risen considerably, Janicki said. In the early stages, the unit managed to achieve an ideal processing performance 80 to 85 per cent of the time; now, it operates at maximum efficiency at 95 to 100 per cent of the time. Although the first was not designed to assess the Omni Processor’s economic feasibility, a second pilot plant soon to be shipped to the country will be as it’s run by a private Senegalese sanitation company.
The economics are what many schemes live or die by. Low-tech or high-tech, however you turn poop it into fuel, you need a market for it. What if you want to supply poop power to the entire district, “but there’s no grid to hook it up to? What if you bottle up biogas, and no-one wants to buy it?” Wald asked. Or what if the state holds a monopoly on the energy sector, making it impossible for a private company to sell its energy? These are real barriers parts of the developing world face, even if there’s a need to come up with solutions to human waste.
Linda Strande, senior scientist at Eawag, the Swiss Federal Institute for Aquatic Science and Technology, pointed out that if even the market exists, you need to efficiently produce poop-based fuel to make any scheme viable. This is tricky for many developing countries, where “very small fractions of fecal sludge are actually being managed,” she said. “If you have a large industrial customer, you might not be able to generate enough product for them.”
From Uganda to Kenya to Senegal, perception of the maturity of these schemes is another key issue too for potential investors. “You can buy a car or a house and finance it, because banks know how cars and houses work,” said Janicki. Right now, though, big investors don’t see waste-to-energy programs in the same manner.
Even with some success stories, it’s clear that huge infrastructural and technological obstacles stand in the way of a meteoric, money-making proliferation. “Profits are elusive,” said Wald. “The world is still waiting on a successful business model.”
Perhaps the scheme that offers the most hope at the moment is biogas-producing wastewater plants, like the high-tech one that recently appeared in Kampala. Funded by the Ugandan government, with additional support from the African Development Bank, the European Union and the Frankfurt-based KfW development bank, it’s expected to treat around 12 million gallons of wastewater daily and generate over 630 kilowatts of energy – enough to power 530 US households – as a result. Ddiba expects it to do well, financially speaking, as it relies on water tariffs and follows a business model similar to European utilities that also produce biogas.
Although a renewable resource in the sense that, well, humans are always pooing, burning poo isn’t what you’d call a “clean” source of energy, from a climate perspective. More research needs to be done to quantify the carbon footprint of the various schemes, but it’s safe to say that all methods generate carbon emissions.
There are good arguments, however, in favour of poop over more traditional forms of energy. Extracting methane from biogas could reduce the need for fracking, which brings a plethora of threats to human health and the environment. By replacing wood burning, it may also help prevent deforestation in some places, which in turn would help to balance out the emissions it generates.
Ddiba points to a major study that looked into the long-term use of biogas for, among other things, vehicle fuel. Assuming that the transportation sector widely adopted biogas, the study estimated that the sector’s greenhouse gas emissions could be reduced anywhere between 49 and 84 per cent compared to the use of fossil fuels.
Climate change certainly plays a role in poop-to-power decision making; Musisi mentioned that climate resilience was one of the reasons Kampala started to take these schemes seriously. At the end of the day, though, the most immediate environmental benefits will be realised on the smallest of scales. And those shouldn’t be discounted.
“In my mind, these schemes aren’t solutions for energy problems,” said Wald. “They’re often solutions for sanitation problems. If you can put poop to work, then great: that means it’s not sitting around and contaminating the environment and making people sick.”