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From sewage sludge to renewable energy

At an office with its own laboratory in Solna, South African process engineer Jennifer van Niekerk works and studies how sewage sludge can best be converted into renewable biofuel, so-called hydrochar. “Here I feel I can truly make a difference,” she says. 

Jennifer van Niekerk, Process engineer from South Africa.
Jennifer van Niekerk, Process engineer from South Africa.

Ten different languages are spoken at C-Green’s offices in Solna. In addition to Swedish English, German, Spanish, and Persian can also be heard. And yet the workforce is not large – only 25 people.

“The international dimension at the office is just another reason why I like it here,” Jennifer notes, adding that she has been in Sweden since 2019. She earned her Master’s degree at the University of Cape Town.

“It’s crucial to find the right expertise for the company. And it’s not always available in Sweden,” explains Michael Sjöberg, C-Green’s CEO since summer 2021.

But the idea behind the technology that C-Green’s business is built upon is Swedish. In 2014 the company’s three founders, who all still work at the company, began developing the technology to convert sewage sludge into renewal biofuel. A year later, when they saw the commercial potential of the technology, the company C-Green Technology was founded.

“The company’s technology is based on old, proven technology that has been modified and combined in a novel way. The process has been made more energy-efficient and thereby practically applicable, which wasn’t the case previously,” says Michael Sjöberg, adding that C-Green has eight patents in its portfolio.

“Which means that our unique process is protected,” he notes.

Michael Sjöberg, CEO of C-Green
Michael Sjöberg, CEO of C-Green

Has left start-up phase

The company’s commercial potential is evidently something that has become apparent for many external investors , and to date the company has raised about 230 million Swedish kronor (22 million euros). Last year SEB Greentech, a unit in the bank that invests venture capital in green technologies, became one of C-Green’s investors. 

“It’s the combination of green technology that benefits the environment and the potential for a high return, I think, that is attracting investors,” says Michael Sjöberg, who is an engineer from the Royal Institute of Technology (KTH), but also has a degree from the Stockholm School of Economics.

With full-scale production of biofuel at one C-Green biorefinery, an additional couple of reference biorefineries in the pipeline, and recently started international collaborations, Sjöberg says the company has now reached a crucial point.

“We are transitioning from being a start-up company to a company with a functioning and unique production process that will make us a world leader in sludge handling,” he says.

Above all, Sjöberg wants to highlight the company’s two international collaborations.

“These will mean a lot both for C-Green’s global establishment and for our ability to increase our production volume,” he notes, explaining that the company’s collaboration partners consist of a world-leading water purification technology group and REYM Rotterdam, one of the largest waste management companies in the Netherlands.

Naturally, increasing the pace of the establishment process will require greater resources, and in 2022, C-Green will be bringing in new capital.

It’s crucial to find the right expertise for the company. And it’s not always available in Sweden.
Michael Sjöberg, CEO of C-Green
Lab image of “raw material” called sludge.
C-Greens “raw material” is sludge. Sludge consists of organic residues from wastewater treatment. As a result, sludge is produced as a byproduct and over time accumulates in many types of operations. These can be wastewater treatment plants, but also various manufacturing industries.

Residual products from wastewater treatment…

C-Green’s “raw material” is sludge. Sludge consists of organic residues that are collected from wastewater treatment. As a result, sludge is produced as a byproduct and over time accumulates in many types of operations. These can be wastewater treatment plants, but also various manufacturing industries.

In Sweden, sludge has long been used as fertiliser in agriculture. In connection with the decomposition process that sludge undergoes before it is spread on fields, methane gas is produced, which is 30 to 40 times more harmful for the climate than carbon dioxide.

…are converted to biofuel

“By converting sludge into hydrochar, the decomposition process can be avoided, which entails a major benefit for the climate,” explains Sjöberg and at the same time notes that hydrochar can also be used as renewable biofuel, which in turn can accelerate the phase-out of fossil fuels.

In the future, C-Green expects that the company’s biorefineries, where sludge is converted into hydrochar, will be located near or directly adjacent to customers’ operations, for example near a wastewater treatment plant or a pulp mill. Since the collection and transportation of sludge is often associated with high cost and environmental impact, this means significant savings for client companies when transports become shorter and more efficient.

Generally, C-Green’s biorefinery is sold directly to the customer, which then becomes the owner of the biorefinery. C-Green handles the installation and often the maintenance.

“In addition to the sales revenue for the actual refineries, this will give us an extra revenue stream,” says Sjöberg, who also emphasizes the economic gains for customers.

“Since our biorefineries have low investment and operating costs, the customer’s repayment period for the biorefinery is relatively short. In most cases, not longer than four to five years.”

Close up image in the C-Green laboratory
C-Green conducts sludge analyses at its laboratory in Solna, which has all of the subcomponents of the process, like a biorefinery in mini-format.

Plant in Finland operating

C-Green conducts sludge analyses at its laboratory in Solna, which has all of the subcomponents of the process, like a biorefinery in mini-format.  

But in Heinola, Finland, C-Green has built up a full-scale biorefinery. It is situated at Stora Enso’s pulp and paper mill and converts sludge from packaging material production into hydrochar, which in turn is used to produce energy for the mill. This achieves a kind of instant recycling. Since the hydrochar replaces peat, which is classified as a fossil fuel, it is also helps accelerate the necessary transition from fossil fuels to renewables.

C-Green has several biorefineries in the pipeline, including a reference plant for municipal sewage sludge at Roslagsvatten’s Margretelund wastewater treatment plant in Åkersberga, Sweden. The target group here is municipal wastewater treatment plants. Another reference biorefinery – this one for recycling companies – will treat various types of municipal sludge. It is planned to be situated at one of the recycling company Ragn-Sells’ facilities in Sweden and is expected to be operational in early 2023. In the case of Ragn-Sells, C-Green will own the facility and charge a fee per tonne of sludge converted. The Swedish Energy Agency is providing 40 million kronor in funding for this project.  

Sights on markets outside the Nordic countries

The biorefineries that C-Green is now building up in Sweden and Finland will primarily serve as reference plants for potential customers both in and outside the Nordic countries.

“For obvious reasons, population size is decisive for our type of operations, more people mean more sludge and thus also a greater need to recycle sludge. This is why we are looking at the markets in the rest of Europe, the USA and Japan with great interest. It is important to have operational biorefineries that we can demonstrate for potential customers,” says Michael Sjöberg, who is not alone in his optimistic view of the company’s future.

Jennifer van Niekerk infront of the computer.
“We have a very strong position. There’s no one else doing what we are doing here,” says Jennifer van Niekerk, who both believes and hopes she will still be at C-Green in five years. 

The office in Solna is bustling with activity. Among other things they are studying and analysing various types of sludge and learning which types are best-suited to be used to make hydrochar. They are constantly developing and refining the technology.

“We have a very strong position. There’s no one else doing what we are doing here,” says Jennifer van Niekerk, who both believes and hopes she will still be at C-Green in five years. 

“Yes, definitely! I am helping to develop the company and the company is developing me.”

Read more about C-Green at: www.c-green.se


Article published on April 14, 2022

Text: Pär Krause
Photo: Joel Sherwood

This is SEB Greentech

SEB Greentech is a unit within SEB that invests in green technology, focusing on transformative ideas that promise substantial impact in reducing greenhouse gas emissions or in preventing transgression of the planetary boundaries. They can invest in hardware, software and technology platform solutions, in sectors ranging from renewable energy, energy storage, water and agricultural technology, circular business models, to waste management.