Many governments are scrambling to find ways to meet the growing energy needs of their citizens, and biogas from waste and wastewater could be a solution, according to experts.
In the UN's latest World Water Development Report, launched today in Tokyo, Japan, ahead of World Water Day tomorrow, biogas technology is highlighted as a promising way to provide energy, especially in rural areas.
"In developing countries, particularly in warm climates ... generating biogas from wastewater can be very useful," says the report. "This is now a widespread practice in many cities in Africa and in Asia."
But some scientists, environmentalists and businesspeople would like to see even greater global attention given to the sector.
"Biogas is a big opportunity because basically what we have the chance to do is to give people modern energy without using crude oil and other sources that are unsustainable," says Kyle Schutter, founder and managing director of Takamoto Biogas, a Kenyan start-up that provides biogas to farmers.
"This is an opportunity for developing countries to access energy in a way that's sustainable for the environment," a company spokesperson adds.
Methane-rich biogas is produced through the decomposition of organic matter and can be generated from waste, including manure and sewage.
In Takamoto Biogas's reactors, bacteria break down animal waste from farms, producing biogas. Leftover solids can be used as fertiliser.
Biogas can help to meet the energy needs of Sub-Saharan Africa, which is 70 per cent rural, says Michela Miletto, coordinator of the report and the UN's World Water Assessment Programme.
She points out that it is the only region of the world in which the total number of people without access to electricity is rising.
The International Energy Agency, for example, estimates that "without major policy action and increased investment in the electricity sector", 650 million Africans will be living without electricity by 2030, compared with 500 million today.
Globally, 1.3 billion people are not connected to an electric power grid and 768 million have no access to an improved source of clean water, the UN report says.
The report emphasises that water is required to produce nearly all forms of energy and that energy is needed at all stages of water extraction, treatment and distribution. This year's World Water Day has the theme of 'water and energy', with hydropower as well as wastewater also under the spotlight.
Experts from both the energy and water sectors need to work more closely together, Miletto tells SciDev.Net.
Regarding biogas, the UN report highlights Chile's Farfana plant, where half of Santiago's wastewater produces nearly 24 million cubic metres of biogas, which is now used instead of natural gas by 100,000 of the city's residents.
In Stockholm, Sweden, sewage-plant wastewater is used to create biogas that powers taxis and public buses, the report says. And, similar to the farmers in Kenya, families in Maresu, Lesotho, are using biogas from wastewater to cook, the report says.
The production of biogas, along with other forms of renewable energy, can also help women, says Kenya-based scientist Segenet Kelemu, who was named this week (19 March) as the laureate for Africa and the Arab states in the 2014 L'Oréal-UNESCO Awards for Women in Science.
"I grew up in a very rural village in Ethiopia with no electricity, no running water, no indoor plumbing," says Kelemu, a food security expert. "I also went out to collect firewood, to fetch water and to take farm produce to market. Somehow, all the back-breaking tasks in Africa are reserved for women and children."
She says that biogas will not be the solution for all of Africa, but that, alongside solar energy and hydropower, it could "go a long way" to helping the continent and women in particular - saving them the hours spent collecting firewood.