Everything has its uses
The search for alternative and environmentally friendly energy sources has turned up some surprising possibilities. Human waste may not be as inspiring as water and wind, but it can be an effective step in creating energy neutral communities.
Story by Ellie van Baaren
It’s not usually a subject you bring up in polite company; you need to tread very car fully if you want to introduce it to the dinner table conversation. But emerging technology is showing that by letting our waste (the bodily kind) languish in sewage treatment plants we are overlooking a valuable resource.
Yes you heard me right. The search for alternative, environmentally friendly energy sources has led us to our own toilet bowls.
Processing our waste in the right way can produce biogas, which can then be used to for heating, cooking and electricity. It’s already being used in far-flung countries around the world, including Rwanda, India, Canada and the United Kingdom.
We’re not the first to come up with this. Not by a long shot. Experts believe the Assyrians were using biogas to heat bath water as far back as the 10th century BC, as were the Persians in the 16th century. In the 13th century AD Marco Polo noted the Chinese were using covered sewage tanks to generate power, and the 17th century author Daniel Defoe referred to biogas technology. In 1859 an anaerobic digestion plant was built to process sewage at a Bombay leper colony and in Victorian Britain human waste was used to power gas street lamps.
In the modern world, biogas is commonly produced by anaerobic digestion as part of the treatment process in municipal wastewater and sewage treatment plants. Technology can take that a step further so that biogas can be used on-site for electricity or exported to other areas.
Biogas from anaerobic digestion can be used to produce heat for the digestion process itself, or for heat and electricity in other parts of the plant. It can be upgraded to “natural gas” quality and fed into a local utility network. It can also be used directly as a fuel in a number of different types of plants.
Biogas is typically composed of 60 per cent methane and 40 per cent CO2, similar to natural gas, which is composed of 99 per cent methane. While methane is a greenhouse gas, combustion turns it into CO2, reducing its environmental impact by more than 20 times. It’s considered carbon neutral because carbon emitted by its combustion comes from carbon that is then fixed by plants, ie it’s part of the natural carbon cycle.
For countries such as India, the process can also provide an answer to two issues – the lack of sewage infrastructure in many villages and lowering their contribution to climate change. Private digesters, which the government there has recently agreed to subsidise, effectively provide the residents with a hygienic sewerage system while also using that waste to supply electricity and gas. All of which creates energy-neutral communities.
On a larger scale, most of the biogas currently produced powers small communities or specific institutions which, collectively, helps ease electricity demand on the national grid and lowers green- house emissions. For instance half the prisons in Rwanda operate biogas facilities that use the electricity produced to cook the prisoners’ meals and light the buildings. In the UK the Didcot sewage works in Oxfordshire went online in October 2010 supplying up to 200 homes with biogas made from human waste.
In New Zealand, several councils generate biogas through sewage and wastewater treatment plants, as well as landfill. There is potential for its use in transport, and the country’s first biogas-powered rubbish truck hit the road in November 2010 (although at this stage the biogas comes from Redvale Energy Park landfill site, rather than directly from sewage).
Biogas from human waste is by no means the silver bullet when it comes to finding a replacement for fossil fuels. We humans naturally produce a finite amount of waste – although that does increase as the population rises – and our stomachs are so efficient that human waste doesn’t produce as much biogas per cubic tonne as animal waste does. However, the more communities and high-energy users that can become self-sustaining, the less demand there is on the national grid.
AROUND THE WORLD
CANADA – Saanich Peninsula Thermal Energy Recovery Plant
Commissioned in early 2001, this plant was built by Opus DaytonKnight Consultants Ltd, the Canadian arm of New Zealand success story Opus International Consultants. Its thermal energy recovery system extracts energy from the effluent of a wastewater treatment plant and, in its first phase, uses it to heat a leisure centre swimming pool.
Based in British Columbia, the Saanich Peninsula Thermal Energy Recovery Plant was a North American first and is a great example of the potential for facilities to benefit from a single closed energy system – feeding in surplus heat or drawing it out depending on requirements.
The closed loop system is efficient and doesn’t need additional energy to operate unlike in more open systems where pumps are required. It is also low-temperature so the piping doesn’t require insulation against energy loss.
Already, the Panorama Recreation Centre has reported cost savings of almost NZ$93,500 and an estimated reduction in greenhouse gas emissions of 560 tonnes.
The whole loop was designed with future expansion in mind. Phase two for the project will see the introduction of an ice rink, and future phases could provide for a local primary school, Centre for Plant Health, the treatment plant itself and nearby residents.
Panorama Recreation Commission’s vice-chair, Marilyn Loveless, is excited about the project’s wider objectives of advocating efficient energy use within communities.
“I believe the value of our facility, the pool in particular, is increased significantly by thermal energy recovery it receives from Saanich Peninsula Wastewater Treatment Plant. We work to make our society healthy, inclusive and sustainable and this project has done much to further these goals.”
The Didcot sewage works in oxfordshire supplies up to 200 homes with biogas made from human waste as part of a pilot programme.
More than 30 million households in china have biogas digesters, biogas accounts for about 1.2 per cent of china’s total energy use.
Half the country’s prisons power their cooking and lighting via biogas made from the prisoners’ waste.
The government has agreed to subsidise private digesters, to get human waste off the streets and power local communities.
Several councils use wastewater and sewage treatment plants, or landfill to create biogas, plus the country’s first biogas-fuelled rubbish truck hit the road in 2010.
Originally published in IN-Business March/April 2012