Water companies use sewage to produce energy

Northumbrian Water has been using sewage to produce gas and electricity that can supply up to 7,000 homes for the past six years.

The sewage from its 418 treatment plants is separated so that 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 1.3 million people in the north-east of England, uses some of the gas to generate its own electricity, while selling most of it to the national grid to heat local homes. The process of turning waste into energy can save the company about 15 m per year and help it meet its net zero emissions target by 2027, as a result of the process of turning waste into energy.

Northumbrian Water is the only water and sewerage company in the UK to use all of its sludge to generate biogas. Other utilities around the world are trying to catch up as they try to shift from collecting effluent into sellingable products — such as fertiliser or energy — and helping combat climate change.

Christopher Gasson, chief executive of Global Water Intelligence, said 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. Gasson argues that by using waste more efficiently, they can combine economic and environmental benefits by using waste more effectively.

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 be a huge net benefit to the environment in terms of greenhouse gas emissions, as well as the economics of good sanitation. 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. The essential technology has been improved a century later.

Cambi, a Norwegian company that listed on the Oslo stock exchange earlier this year, sells the technology behind thermal hydrolysis plants. These high temperatures and pressure are applied to sewage sludge, or other types of wet organic waste, to produce larger amounts 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 aren't being valued sufficiently, so there's room for expansion, says Bill Barber, technical director at Cambi. There is more sludge to deal with because of the increasing population of the world. Barber says that every person produces between 30 g and 80 g 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.

The rollout in the UK has been aided by financial incentives provided by Ofwat, which has helped Cambi's biggest market. 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 grown since it opened a plant outside Washington DC in 2013. Nine more have opened in North America in the past seven years, although the region is still behind the UK, where there are 25.

In the past two years, Water UK, a water and sewerage company in England, has increased their biomethane production from 382 GW-hours to 477 GW-hours - enough to power 40,000 homes, according to Water UK.

This may help the environment and the water companies, but it is not a solution to the potential energy shortages in the UK. Barber says that if all of the UK's sewage sludge was turned into energy, it would meet only 1 per cent of total UK energy demand.

The process will not generate enough income for water companies to pay for the overhaul of sewage treatment works needed to stop the flow 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 would a biogas bus travel on the fuel generated by one person's daily waste material?

Gasson says that it won't make our rivers swimmable, but it could make our water more affordable.

It makes the water companies more self-sufficient. Severn Trent, which serves 4.4 m UK homes and businesses, already generates half of the energy it needs from renewable sources, mainly from anaerobic digestion and biogas.

Severn Trent plans to recycle waste into fertiliser at a treatment works near Birmingham. The goal is to combine carbon dioxide with ammonia to create a saleable fertiliser. It is partly funded by the UK 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 nothing is wasted in the sewage treatment process.