“I’m going to talk to you about a fascinating subject that concerns us all. Because everyone poops, right?” Smiling at her webcam, Daniel Ddiba questions a mosaic of black screens. The Ugandan engineer and researcher based in Sweden speaks during a Stockholm Environment Institute (SEI) videoconference. Around 1.3% of global greenhouse gas emissions come from sanitation and wastewater management systems, and therefore toilets. “It is more or less the equivalent of the emissions of the global aviation sector, but in the discourse on climate change, we hardly talk about sanitation,” the researcher is surprised.
World Toilet Day, Tuesday November 19, provides an opportunity to rejoice in the improvement, throughout the world, in access to toilets. But this undeniable progress in public health has been accompanied by a spectacular increase in greenhouse gas emissions that are particularly harmful to the climate: methane and nitrous oxide, respectively 28 and 273 times more “warming”. “ than CO2 in the atmosphere.
In India, where access to toilets increased by 14% between 2015 and 2020, methane emissions from pit latrines – a hole dug in the ground – increased fourfold, according to the SEI (available PDF). In China, methane emissions from wastewater exploded by 90% between 2000 and 2020, reports Science Direct. Finally, according to the American Agency for International Development, cited by the IISD think tank, these emissions could increase by 60% by 2030 in sub-Saharan Africa, boosted by urbanization and the generalization of access to small corners. “What to do then? Holding back from going to the bathroom?jokes the researcher. “No, rest assured. The solutions already exist, he promises. All that remains is to deploy them.”
Emissions linked to sanitation have long been underestimated, or even ignored. “We don’t care what happens after we flush the toilet”summarizes Daniel Ddiba. As for areas of the world that are not connected to sewers and use, for example, septic tank systems emptied by truck“too few studies make it possible to precisely evaluate their emissions”. But one point is beyond doubt, the scientist continues: “As soon as there are human excrement in large quantities under anaerobic conditions [sans contact avec l’oxygène]methane is generated.”
With a much shorter lifespan in the atmosphere than CO2 (around twenty years), methane “has a disproportionate impact on temperature in the short term”, writes the IPCC. Reducing these emissions quickly and drastically is therefore imperative to limit global warming to 1.5°C by 2100, as enshrined in the Paris agreement. Following this logic, 158 countries have committed to reducing methane emissions by 30% in 2030 compared to 2020, by signing the Global Methane Pledge at COP26. “To meet these two challenges, we must address the issue of sanitation.”hammer Daniel Ddiba, conceding that‘”there is no universal solution, which would work in Stockholm as in Kampala”.
“Toilets as we know them in Europe, with the flush that takes our small business through a network to a large treatment plant, should not be considered as a reference that should be deployed everywhere. “
Daniel Ddiba, researcher at the Stockholm Environment Instituteat franceinfo
In the absence of sewers, as is often the case in emerging and developing countries“we can already ensure that pit latrines are built above the level of the water tables, explains Daniel Ddiba. This prevents them from filling with water, which reinforces anaerobic conditions and increases methane emissions.” Without excessive investments or revolutionary technologies, simply emptying septic tanks more often helps reduce their methane emissions, according to a study published in the journal Environmental Science & Technology by researchers who were studying this problem in Vietnam, where 90% of the population relies on this type of device.
Finally, “Ideally, all wastewater treatment facilities should be equipped with a capture plant that transforms methane, instead of releasing it into the atmosphere.” In Stockholm, 300 buses run using biomethane obtained from sludge of the sanitation plant which treats the excrement of the inhabitants of the Swedish capital. In Europe as in India or China, projects are multiplying and raising the annoying question: that of financing, or rather, investments.
Because for specialists, these technologies can respond to both the energy crisis and the climate crisis. Practical, especially since “the sanitation sector is very energy intensive”, supports Alexis de Kerchove, director of customer sustainability at Xylem, an American company specializing in water management. “Today, the sector uses around 20% of renewable energy globally, so it emits indirectly due to its energy needs. But the other problem is that the process itself, the one that which has always been used to treat wastewater, unfortunately also generates methane and nitrous oxide. continues the specialist.
Discharging dirty water into nature is not an option, recovering these greenhouse gases “fugitives” produced by the processing activity allows their impact to be reduced and significant savings to be made, he argues.
“Wastewater is considered a waste, but if we look more closely, it is a resource: it is rich in carbon, nitrogen, phosphorus and, above all, water!”
Alexis de Kerchove, Director of Customer Sustainability at Xylemat franceinfo
“We can recover resources from wastewater and produce added value, such as fertilizers for agriculture, or biochar”a black material resulting from a process called pyrolysis, “and thus store the carbon in solid form”, he explains, enthusiastic at the idea of seeing these rejects become part of a virtuous circle.
At the Swedish University of Agricultural Sciences, researchers have developed technology capable “to separate urine from excrement, to make urine into a powder essentially composed of nutrients, all in a machine the size of a washing machine”describes Daniel Ddiba. This powder can be used for example in the manufacture of fertilizers. And removing urine from wastewater helps reduce nitric acid production during treatment.
“When we talk about sanitation and global warming, the water sector tends to focus on adaptation, on making our systems more resilient to disasters, like floods or droughts,” notes Alexis de Kerchove. “It’s essential,” he believes, recalling the events which have affected Europe this year, in particular the recent floods which have plunged Spain into mourning. “But what’s the point if we continue to emit tons of greenhouse gases which only fuel global warming? he asks. We must fight this war on both fronts.” Including on the throne.
