For the past six years, Northumbrian Water has been using sewage to produce gas and electricity that can supply up to 7,000 homes.
The sewage from its 418 treatment plants is separated so the liquid can be treated and returned to the environment, while the solids are turned into sludge, which is processed through anaerobic digestion plants to produce biomethane.
Northumbrian Water, which provides sewerage and water services to 1.3m people in the north-east of England, uses some of the resulting gas to generate its own electricity, while selling most of it to the national grid to heat local homes. This process of turning waste into energy turns a cost into an income — saving the company about £15m per year and helping it to meet its net zero emissions target by 2027.
So far, Northumbrian Water is the only water and sewerage company in the UK to use all of its sludge to generate biogas. But other utilities worldwide are racing to catch up as they seek to shift from collecting effluent to turning it into saleable products — such as fertiliser or energy — and helping combat climate change.
Christopher Gasson, chief executive of Global Water Intelligence, a data provider and magazine, says the conversion of sewage to energy could be a game-changer for the industry.
Water and wastewater utilities use large amounts of power, consuming around 3.7 per cent of the world’s annual energy, according to GWI. But, by using waste more effectively, they can combine economic and environmental benefits, Gasson argues.
“Most low- and middle-income countries can’t afford to treat wastewater despite its impact on the environment and public health,” he explains. “Biogas production could transform the economics of good sanitation and deliver a huge net benefit in terms of greenhouse gas emissions.”
Anaerobic digestion — the process of turning waste into energy — was first developed in Victorian times as a means of stopping the build-up of sewage and preventing the spread of disease. A century later, the essential technology remains the same but has been improved.
Cambi, a Norwegian company that listed on the Oslo stock exchange earlier this year, sells the technology behind thermal hydrolysis plants. These apply high temperatures and pressure to sewage sludge, or other types of wet organic waste, to produce bigger quantities of gas than conventional anaerobic digestion plants. There are 77 Cambi plants worldwide, in locations ranging from Brussels and Bydgoszcz in Poland to Beijing, Hong Kong and Sydney.
“Sludge and waste just aren’t being valued sufficiently so there’s room for a lot of expansion,” says Bill Barber, technical director at Cambi. “The world’s population is increasing so there is simply more sludge to deal with.”
Barber says that every person produces around 30g to 80g of useful dried material a day — enough to drive a biogas bus for about 50 metres or to keep LED lights on in a room throughout the day.
Cambi’s biggest market, so far, has been the UK, where the rollout has been aided by financial incentives from water regulator Ofwat. The regulator has also introduced measures to encourage trading in sludge between companies, so that they can produce economies of scale.
Cambi’s US market has also grown since it opened a plant outside Washington DC in 2013. In the past seven years, nine more have opened in North America, although the region is still behind the UK, where there are 25.
According to Water UK, which represents water utilities across England, the 17 large water and sewerage companies have increased their biomethane production in the past two years from 382GW-hours to 477GW-hours — enough to power 40,000 homes.
But while this may help the water companies and the environment, it is not a solution to potential energy shortages in the UK. Even if all of the UK’s sewage sludge was turned into energy, it would meet only 1 per cent of total UK energy demand, Barber says.
Nor will the process generate sufficient income for water companies to pay for the overhaul of sewage treatment works needed to stop the regular flows of storm water and effluent into the UK’s rivers and seas — a problem that has made headlines in the UK in recent months.
How far a biogas bus could travel on the fuel generated from one person’s daily waste material
“It won’t make our rivers swimmable but it could make our water more affordable,” says Gasson.
It makes the water companies more self-sufficient, too. Severn Trent, which services 4.4m UK homes and businesses, already generates the equivalent of half the energy it needs from renewable sources — mainly from anaerobic digestion and biogas.
Severn Trent also plans to recycle waste into fertiliser at a treatment works near Birmingham. This project aims to combine carbon dioxide with ammonia to create saleable fertiliser. It is being partly funded by the UK’s Department for Business, Energy and Industrial Strategy, which supports commercial-scale demonstrations of new technologies that help reduce carbon emissions.
Rich Walwyn, head of asset intelligence and innovation at Severn Trent, says that the move will take us “a step closer to making sure absolutely nothing is wasted in the sewage treatment process”.