At the end of 2015, the first results from the unique project Bäckhammars Algbruk (Bäckhammar’s Algae Factory), run by SP, were presented. ”For the last three years, we have used waste from Bäckhammar’s pulp and paper mill to produce biomass at the test bed. The aim has been to make use of excess resources to produce algae biomass in a sustainable way, in order to extract refinable bio-oils”, Niklas Strömberg, researcher at SP, says.

Mikroalger växer på rökgas och överskottsvärme från Nordic Papers massa- och pappersbruk.

The microalgae grow on flue gas and excess heat from Nordic Paper’s pulp and paper mills.

”There are several factors making algae cultivation promising for the Nordic countries, and the concept is gaining interest. We may not have the same access to sunlight as southern countries, but we have plenty of nutrients, heat and carbon dioxide – the very growth factors of the algae.  Aquatic microalgae are very productive in the proper environment, and their growth produce fat, oils, carbohydrates and proteins. The result can be bio-oils suitable to be refined into bio-plastics, biodiesel and lubricating oils. Algae can even be turned into food and cosmetics”, Niklas says.

Climate clever cultivation

The SP researchers developed a climate clever way to cultivate algae, making use of excess heat, carbon dioxide and nutrients from the waste water of Bäckhammar’s pulp and paper mill. The idea was to use local resources in an energy efficient way. Water was taken from the wastewater treatment facility at the mill, providing the algae with enough nutrients to grow and multiply. The 35 degree water was exchange heated to the proper temperature for algae growth.

The culturing also provided an opportunity to use the carbon dioxide in the mill flue gas as a resource. The flue gas was led in tubes from the chimney to the ten ponds.

”The combination of nutrients, heat and carbon dioxide is excellent for the algae. The microscopic plants clean the waste water and remove nitrogen and phosphorus, and they prevent carbon dioxide emissions which would otherwise affect the climate. Reducing the carbon footprint is important not only for a mill but for many industries. This method of cultivation is truly unique, producing both business value and environmental advantage. The environment benefits because the mill produces more green products and less waste” Niklas Strömberg asserts.

It was Niklas who made the drawings for the test bed, and he also developed the one step process in which the cultivation, sedimentation and drying of the algae is carried out. The flue gas infusion is stopped during the night, making the algae sink to the bottom of the ponds. The next day, new flue gas is added. As the process is repeated, a sediment of algae is gradually accumulated. At the end of each culturing cycle, the water is removed and the remaining sediment is dried for a couple of days with the help of sunlight and waste heat.

”The end result is a dry material with an energy content of between 23 and 25 megajoule per kg. It is comparable to peanuts, an energy dense foodstuff. From this dry material, bio-oil can be extracted. So far, we have been able to produce 25 kg of dry biomass every year – but the amount of nitrogen and phosphorus available in the mill waste water would allow for a much larger production. Naturally, larger ponds would be required. In this project, we have had access to ten circular ponds (Tethys reactors) with a combined area of 36 square meters, plus a single oblong 21 square meter raceway, where a paddle wheel has kept the water in circulation. The unicellular strain of algae Scenedesmus dimorphus was inoculated into the ponds, but it turned out that local strains thrive as well: Monoraphidium, Chlorella, Scenesemus quadricauda and others”, says Niklas.

Energy efficient cultivation

The overall results from the three-year long test bed project show that the concept is very efficient with respect to energy consumption and the labour needed. The project shows:

  • High yield; 1 hectare algae cultivation is equivalent to more than 5 hectares rape in the same location.
  • Positive energy balance; more than 4 times more energy out than the energy used to run the cultivation.
  • Using carbon dioxide (flue gas) from heavy industry for the production of oil projects works well.
  • Algae cultivation is possible on unusable land.

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”We are very pleased with the results so far. The energy efficiency is hardly surprising, since the system was designed with energy-saving in mind. We did not anticipate the yield to be so high, however. More details will be available once the results have been reviewed externally. Large-scale culturing is definitely possible but is likely to be years in the future. We would like to see a second phase of the project with a larger pilot facility, before moving on to a demonstration installation”, says Niklas Strömberg.

The article was published in February 2016.