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Waste becomes biogas and biofertiliser

Zhao Wang

“Forsbacka biogas plant is a good example of a collaboration between the University of Gävle and the surrounding society,” Zhao Wang and Sandra Carlos Pinedo, researchers at the University of Gävle, says.

On 12 September, the Forsbacka biogas plant will open ceremoniously. It is a 45-metre-long reactor in which our food waste will be turned into enough biogas to power 2300 cars, or all of the buses in Gävle, during one year.

Biogas is formed naturally when biological material degrades; it is a renewable energy source which is part of the natural cycle. Apart from biogas, biofertilisers are also formed. These return nutrients to the agricultural land by replacing artificial fertilisers in farming.

Entirely new technology

Producing biogas from dry waste, so called large-scale dry digerstion, is a new technology. Forsbacka biogas plant will become the second one in Sweden, and in the whole of Europe there are only a handful.

“We have to carry out more research and build new knowledge concerning this technology to optimise the process and gain a stable and greater production of biogas,” says Zhao Wang, researcher at the University of Gävle.

“We meet people from the plant regularly and we suggest ideas and gain data that we need in our modelling. This is because the research is completely new, not only here, but in the whole world,” PhD student Sandra Carlos Pinedo says.

How to find renewable energy

A very important issue in today’s world is how to find a more sustainable way to handle our waste. Another issue is how we are to find new sources for renewable energy which can replace fossil fuels.

Biogas plants provide:

  • A new source of energy for the vehicle fleet
  • An environment-friendly way to handle waste
  • Bio-fertilisers which replace artificial fertilisers

Phosphor is a finite resource used as an artificial fertiliser. It is estimated that it will last for another 50-60 years, so we need to find new sources. Moreover, phosphor, which can be used to make fertilisers, becomes the end product after the biogas process.

Safer and much cleaner

Above all, it is the technique which is the novelty. The old technique, wet digestion, uses sewage sludge from sewage treatment plants as a substrate. Both techniques demand heating, but if there is a great amount of water, more energy is required to heat up the reactor.

Zhao Wang claims that that we can produce more biogas with dry digestion, maybe even to a lower energy cost. Moreover, it becomes much easier to transport the end product, the biofertilisers, to famers, because the wet sewage sludge from the wet digestion is much heavier.

“The Dry digestion process is also a much more controlled process to effectuate this fermentation. We do not get as much interference from hard metals, poisonous substances and chemicals. What comes out, the bio-fertiliser, is much safer and much cleaner,” Sandra Carlos Pinedo says.

Connected to education

Zhao Wang explains that this is research which can continue for a long time and many, new similar plants are now being built in Sweden.

“In this type of reaction, one is completely dependent on microorganisms, small bacteria, and they are very sensitive to their environment. If the environment isn’t optimal, the process stops and, as a result, the production of biogas stops.”

Zhao Wang says that this is very interesting, not just to him as a researcher, but also to lecturers in our Environmental engineering programme. This plant will create a great demand for recruiting new lecturers, new students and, as a result, a connection will be established to teaching and to the programme.

Zhao Wang and Sandra Carlos Pinedo have an academic background as chemical/technical engineer and environmental engineer respectively. He has his doctoral degree from KTH, while she has her master’s degree from Mexico.

They both have earlier relevant experience in this kind of research and believe that they will be able to contribute to this biogas plant at an industrial level.


For more information, please contact:
Zhao Wang, senior lecturer in environmental engineering at the University of Gävle
Phone: 076-648103
e-mail: Zhao.Wang@hig.se

Sandra Carlos Pinedo, PhD student in energy systems at the University of Gävle
Phone: 076-8953144
e-mail: Sandra.Carlos-Pinedo@hig.se

Text: Douglas Öhrbom
Photo: Ove Wall

Published by: Douglas Öhrbom Page responsible: Anders Munck Updated: 2017-09-25
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