There are many secrets hidden beneath the surface of the sea. One of the creatures dwelling there is the ascidian – and Fredrik Norén, PhD and founder of the company Marin Biogas, has more knowledge about it than most people.

marinbiogas1”Carl von Linné described the species in 1767. He called it Ascidia intestinalis; the species name, intestinalis, refers to its intestine-like shape. Its current name is Ciona intestinalis – literally meaning “pillar of intestines” – or vase tunicate. It is a generalist species, thriving in waters of varying salinity and temperature, and is common along the Swedish west coast, all the way down to Kullaberg, Skåne. The ascidian seems to prefer moderately streaming water, and often grows in dense aggregations on submerged structures like vertical rock surfaces, cables and pilings, 15-25 meters below the surface”, Fredrik says.

The EU and the Swedish Energy Agency recently invested 23 MSEK in Marin Biogas. The aim is to commercialise the production of biogas from the ascidian via Falkenberg Biogas, a subsidiary of utility company E.ON.

Triple environmental advantage

The ascidians are invertebrate filter feeders. Just like clams, they feed by straining plankton and bacteria from the surrounding water, absorbing substantial amounts of nutrients. When they are harvested, the nitrogen and phosphorus incorporated in the ascidian tissue is removed, which cleans the water from eutrophication. Unlike clams, the ascidians consist entirely of soft tissue, with an outer tunic similar to cellulose. This simplifies the technical process of digesting the harvested biomass and produce biogas.

”The organisms benefit the environment three times; they reduce eutrophication, produce renewable energy, and the rest product from the digestion becomes a valuable fertilizer for agriculture. We are basically using the same methods to culture ascidians as mussels, and we are now about to prove that large-scale culturing is feasible. We have already established that the harvest is an excellent biomass for biogas digestion”, Fredrik Norén says.

Opportunities and challenges

”The project is a proof of concept, and will run for three years. The culturing and harvest will be handled by Scanfjord, a mussel cultivator in Mollösund. Like the mussels, the ascidians are grown attached to ropes suspended from floating barrels. They can be harvested from the same boats harvesting mussels. The biomass is first harvested, dewatered and ground, then transported to Falkenbergs Biogas for digestion. Falkenbergs Biogas AB is a joint venture between E.ON, Falkenberg municipality and Gekås Ullared. E.ON is also one of the participants in the three-year project”, says Olle Stenberg, CEO at Marin Biogas.

”We see a lot of opportunities and a few challenges ahead”, Fredrik Norén says. The benefits of the project are several:

  • A high yield of biomass per area and year gives a cost effective removal of nutrients compared to conventional removal of nitrogen and phosphorus. A surface of one hectare can remove 26 tonnes of nitrogen and 2 tonnes of phosphorus every year.
  • Ascidians cultured for biomass production are not sold as human food. This means the biomass can be cultured in polluted waters. The cultures need no extra fertilizers or pesticides.
  • The ascidian Ciona intestinalis is easily digested into biogas. A one hectare culture can produce an energy amount equal to 60 000 liters of gasoline.
  • Ascidians only consist of soft tissue which enables an industrial processing.

”There are certain questions we are trying to answer”:marinbiogas2

  • Profitability still remains to be verified. With current CNG-gas prices, operations have to be scaled up to be competitive. It would also help if the nutrient uptake could generate revenue; the Swedish Environmental Protection Agency has suggested a system of tradable nitrogen certificates, but it has not yet been established.
  • It is essential that the nutrients taken from the sea can be distributed as an organic fertilizer. The substrate has to be formally approved.
  • Harvesting needs to be faster.
  • Larger cultures face an increased risk of disease and parasites.

”The lives of these creatures have been studied ever since Linné described them in the eighteenth century. But there is still a lot to be learned”, says Fredrik Norén.

The article was published in April 2016.