Poo Zoo truck

Endangered faeces: zoo turns to ass poo for power

Image credit: Paul Collins/Marwell Wildlife

Marwell Zoo in Hampshire has announced that it will heat its largest buildings using waste collected from its residents, including endangered species. This will conserve the equivalent of 220 tonnes of CO2 each year.

Human and other animal faeces is generally considered waste, but – like forestry and agricultural waste, landfill gas, and sewage sludge – it can be repurposed as a fuel. As bacteria digest faeces, they produce a methane-rich biogas that can be burned for energy. Alternatively, faeces can be dehydrated and packed to produce combustible bricks (biochar or hydrochar) with a similar energy content to coal. ‘Poo power’ is an established technology in wastewater plants all around the world.

At Marwell Zoo in Hampshire, waste from a range of the zoo’s endangered species – including Grevy’s zebra, the scimitar horned oryx, and the Somali wild ass – will be used as feedstock for biofuel. The fuel will be used to heat the zoo’s largest buildings, including its tropical house.

The “Energy for Life” scheme, which will save the equivalent of 200 tonnes of CO2 annually, is a key part of its aim to become carbon neutral by next year.

The zoo will be the first of its kind to generate renewable energy from animal waste.

“Using heat in this way from our own animals is unique in the UK and, as far as we know, across the world,” said Dr Duncan East, head of sustainability at Marwell Zoo. “The urgent need to reduce the burning of fossil fuels and leave these high-carbon sources in the ground means we can’t act soon enough to replace the oil-fired heating systems in these buildings.”

East explained that the zoo had been conscious of the carbon emissions associated with waste management: “Previously, 600 tonnes of animal waste was taken off site to be composted, and this came with a significant carbon transport cost. We came up with the idea of biomass heat generation to reduce our carbon footprint and turn a previous waste stream into a valuable resource, achieving cost savings in the process.”

Each morning, the animal waste is swept up from the animal enclosures and transported to the Energy Centre for shredding and mixing. Next, it is dried and pressed into briquettes. These are used to power a biomass boiler and feed hot water into a 15,000L thermal store, from which it flows underground to heat the zoo’s tropical house.

The tropical house (the Energy for Life: Tropical House) contains exhibits on climate change and sustainability, and provides a humid home to free-flying tropical bird species, crocodile monitor lizards and a Linne’s two-toed sloth. Its roof offers natural light, good insulation, and collects rainwater to sustain the tropical vegetation inside.

According to Marwell Zoo, it has been working since its tropical house opened in 2018 to build a solution to repurpose its unique animal waste as fuel for its biomass boiler. Next, it plans to use its biomass system to heat other buildings across the zoo, providing warmth for primates, okapi, and zoo staff.

East added: “Replacing oil-fired heating systems with heat generated from waste from our own animals will hugely reduce our carbon footprint. What better way than to make use of a material which is in abundant and continuous supply?”

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