AquaGreen – turning sludge into a sustainable resource

Wednesday 04 Dec 19

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Jesper Ahrenfeldt
Senior Scientist
DTU Chemical Engineering
+45 21 32 53 44

DTU spinout AquaGreen has found a way to turn sludge into marketable biochar – a sustainable coal that functions as fertilizer, improves the quality of soil and binds CO2 to the earth for more than 2.700 years. And the customers are lining up.

Sludge as a global problem

Getting rid of sludge is an increasing global challenge. Claus Thulstrup and Henning Schmidt-Petersen, owners and CEOs of AquaGreen, took up this challenge with a great idea and an alliance with researchers from DTU Chemical Engineering. That was the beginning of AquaGreen that was established as a DTU spinout in 2015.

The main problem with sludge is that there is so much of it. It is dangerous for health and environment, and it is full of water that makes the sludge disposal cost very high.

The Solution

AquaGreen's solution for dealing with sludge is a processing plant that can dry and pyrolyze it and, ultimately, turn it into biochar.

The process is pretty straight forward. Their machine dries sludge using overheated steam at 200 degree Celsius. The, now dry, sludge then goes through a pyrolysis oven that heats it up to 650 degree Celsius. This extreme temperature disintegrate all organic material, which releases pyrolysis gas – a combination of combustible gasses.

"If we were to take all sludge from the farming industry and run it through our machine, the farming industry would reach its 2030 goals about a 70% reduction immediately"
Claus Thulstrup, Owner and CEO of AquaGreen

The generated heat from the pyrolysis gas is then used to heat the steam-dryer and the process is thus recirculated. In the end, the only energy used, for keeping the machine going, is the fans that drives the gas, steam and sludge through the system.

The pyrolyzed sludge is reduced to 1/10 in volume. The end product is sanitised, odourless, storage safe, easy to transport and pathogenic bacteria are eliminated.

AquaGreen began in the aqua culture industry, but today they work mostly in municipal wastewater. There is really no limits for where to use the machine. It's just about finding the right market and where it can make the biggest difference.

Reducing CO2 emission

Turning sludge into biochar can reduce CO2 emission drastically as biochar “binds” CO2 to the earth.

Basically, when the biochar is returned to the earth, it takes 2.700 years before the earth’s microorganisms has turned half of it to CO2 again. In comparison, when regular sludge is used as fertilizer, most carbon is released as CO2 again after just 3 years.

“In this way we can reduce CO2 emission very effectively. We are actually binding CO2 in the earth. If we were to take all sludge from the farming industry and run it through our machine, the farming industry would reach its 2030 goals about a 70% reduction immediately”, says Owner and CEO of AquaGreen Claus Thulstrup.

“We already have the technology to reduce CO2 emission – we just have to use it”, he explains. And fortunately for everyone, they already have customers lining up.

“We started going into dialogue with customers in the wastewater industry last year and everyone is interested. The main challenge is choosing the right customer to launch it and we are negotiating several contracts as we speak”, he says

The extent of the technology is huge and something that can really make a difference. “One steam dryer and pyrolysis unit can process what corresponds to a city of 50.000 people’s sludge. And there is going to be models that are 4 times that size”, Claus Thulstrup concludes. 

The company is now situated at DTU Risø Campus. Keep an eye out for AquaGreen in the future – it’s looking very green.

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