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How sewage water helps with the energy transition

In False Creek, a waterfront community in Vancouver, Canada, the energy used to heat homes comes from an unlikely source.

Instead of a boiler, each building’s hot water comes into underground pipes from a city power plant, a system called district heating. A growing number of municipalities are incorporating this strategy into their plans to reduce fossil fuel consumption, using renewable energy sources such as geothermal or solar energy instead of oil or natural gas.

But in the case of False Creek, they use sewage.

It turns out that the water flowing from your sink, washing machine, shower, dishwasher (and yes, toilet) is warmer than when it first shows up in your home. Wastewater flowing through municipal sewer pipes can maintain a temperature between 10°C and 20°C even in the coldest months.

So instead of wasting that heat, False Creek uses it. In 2022, the local utility said it generated 23,441 megawatt hours of thermal energy from sewage – enough to heat 3,000 residential apartments for a year. “What we’re doing is turning wastewater into a resource,” says Derek Pope, community energy manager for Vancouver. “That way we can warm up an entire neighborhood.”

As the energy transition falls behind and global warming continues to accelerate, cities are looking for ways to bridge the gap. Wastewater is one of many alternative energy options being exploited.

According to a 2022 report from the European Investment Bank, 380 billion cubic meters of municipal sewage is produced annually worldwide. As cities grow, this is expected to increase by 51% by 2050. According to the U.S. Department of Energy, a year’s worth of U.S. wastewater contains an estimated 350 terawatt hours of energy, which can heat 30 million homes. In other words, that’s a lot of unused heat.

The energy used to heat homes and workplaces is one of the largest contributors to an individual’s carbon footprint. Gas boilers and wood-burning stoves emit huge amounts of carbon dioxide, while electric stoves are only as green as their energy source, often gas or coal. Globally, heating is responsible for 40% of all energy-related emissions.

It may come as no surprise that, according to a 2023 report from global engineering firm Danfoss, excess heat is the world’s largest untapped energy source. In the European Union alone, approximately 2,860 terawatt hours of waste heat are generated annually, almost the same as the area’s total energy demand for heat and hot water in residential and service sector buildings.

Bloomberg

A global effort to capture this heat could help prevent the burning of nearly 30 million barrels of oil per day, or 650 billion cubic meters of natural gas per year, the report said. That is about four times as much as what the EU imported from Russia in 2021.

“This isn’t just about reducing greenhouse gas emissions; it is also about rethinking the way we look at waste heat sources like sewage,” says Pope. “Around every city there are several waste heat sources that systems like ours can tap into, and we need to start thinking about it seriously.”

Aaron Gillich, professor of building decarbonisation at London South Bank University, says initiatives like False Creek’s make it easier to introduce stricter building greenhouse gas limits and achieve more sustainable urban planning. In Vancouver, a big part of that is reducing dependence on natural gas. “We use so much that nothing can replace it on its own,” Gillich says. Wastewater “is potentially a very important ingredient in squaring that circle.”

Wastewater is an attractive energy source because the supply and temperature are stable. This means that the pumps that transfer heat to clean water can operate in winter, when the demand for heating is greatest. But how exactly does this all work?

To start, a liquid refrigerant is passed through an evaporator, which turns it into a gas that is sent to pipes surrounded by waste water. The gas absorbs the heat of the water and is then passed through a compressor to make it even hotter: up to 80°C. The hot gas is then circulated around pipes containing clean water. As that water flows through insulated distribution pipes to individual buildings, the gas returns to its liquid form. Although such heat pumps consume a certain amount of electricity, they are four times more efficient than boilers or electric heaters. And in False Creek, the pumps get their power from hydroelectric dams.

The practice of heat extraction from waste water has been adopted in many European countries. Switzerland started extracting heat from sewage as early as the 1980s, and German company Uhrig says it has built more than 100 wastewater heat projects, both in Germany and abroad. In Britain, the method has become an “emerging sector,” says Antoine Reguis, a renewable energy expert at Edinburgh Napier University. Gillich estimates that the energy in Britain’s 4.2 billion liters of daily wastewater could provide space heating and hot water for up to 1.6 billion liters of water. million homes.

In Vancouver, a city of 680,000 on Canada’s west coast, buildings are responsible for 57% of greenhouse gas emissions. The False Creek system, which Pope said was the first North American application of heat recovery from raw sewage, was deployed before the 2010 Winter Olympics to provide heat to the athletes’ housing complex.

At the time, the system heated nine buildings; today it serves 46, including 6,000 residential apartments. In 2022, 71% of heating energy in the neighborhood came from renewable energy sources, with sewer heat being the primary source.

The False Creek development in Vancouver

The False Creek development in Vancouver | Bloomberg

But the False Creek project was purpose-built. Installing the necessary infrastructure in existing developments can be prohibitively expensive. Furthermore, the maximum energy recovery from wastewater takes place in or near water treatment plants, where the flow is greatest. Such facilities are usually located on the outskirts of cities, meaning the heated water must travel further.

“Even well-insulated pipes will have some amount of heat loss per meter, so you want the pipes carrying the heated water to run as short as possible,” says Gillich. But according to Nick Meeten, director of New Zealand consultancy Applied Energy, in every city there are places where flow rates are high enough to heat large buildings or even entire city blocks.

In Oslo, renewable energy company Hafslund Oslo Celsio is tapping into a main sewer line that reportedly passes more than a million liters of wastewater per hour. The project provides heat and hot water for 13,000 apartments per year, the company says.

Specific points of high demand can be chosen for localized wastewater heat transfer: a hospital, a train station, a swimming pool or a university campus. In Rockhammar, Sweden, residual heat from the waste water of a paper factory is used, for example, to heat an industrial-scale greenhouse.

“You map the flows of wastewater heat, and you look for where the major users of heat energy are, and you look for a number of similarities,” says Meeten. difficult.”

Wastewater is just one of many strategies used to reduce fossil fuel use in this way. In London’s Islington district, the local authority says it is heating hundreds of homes, a school and two leisure centers using energy generated by the electric motors and brakes of Tube trains. Sanepar, a company in Curitiba, Brazil, combines wastewater and organic waste from a food distribution center to generate biogas for electricity, which is then fed into the grid.

But more often, waste heat recovery relates to the buildings themselves. Typically, warm air from large structures is released into the atmosphere through ventilation shafts. But it can also have its heat removed. The Swedish utility company Stockholm Exergi uses residual heat from supermarkets, ice rinks and data centers. “Wherever we have mechanical work or cooling, we also have excess heat,” says Erik Dahlén, the company’s head of research and development. Through collaboration with retailers and industries, called ‘open district heating’, these companies can also charge for the energy they supply.

Perhaps the most obvious sources of waste heat are the massive data centers proliferating in and around cities. Servers emit enormous amounts of excess heat that can be captured to heat water.

In Greater Helsinki, excess heat from two Microsoft data centers will be routed to more than 250,000 customers, according to Fortum, the Finnish energy company. They will ultimately meet around 40% of the district heating needs of Espoo, Kauniainen and Kirkkonummi, saving around 400,000 tonnes of CO2 emissions annually.

As part of Vancouver’s Climate Emergency Action Plan, the False Creek Neighborhood Energy Utility says it plans to be fully renewable by 2030, with 70% of energy coming from sewage heat, saving an estimated 7,000 tonnes of greenhouse gas emissions annually.

To be fair, it is unlikely that entire cities will soon, if ever, be heated by residual heat. But the race to slow global warming requires exploring every option, says Semida Silveira, a professor of systems engineering at Cornell University. Despite the challenges of harnessing and scaling up such heat sources, it makes sense to invest in the technology because every little bit helps.

And in the case of sewage, it could at least be used to save energy when treating water. “It’s actually surprising that more cities haven’t used this sooner,” says Silveira.

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