The concept

The system to culture and harvest ascidians from the sea where the process gives several environmental and economical benefits:

  1. When our biomass is digested it produces a renewable energy source in the form of biogas
  2. Harvest of our marine biomass produces a net uptake of nutrients from the sea for a low cost per removed kilogram of nitrogen and phosphorus.
  3. The rest product, digestate, is a valuable fertilizer for agriculture.


The background of the project is the need of feedstock for a planned biogas production plant owned by local waste and energy companies at the Swedish west coast (RAMBO AB and Uddevalla Energi AB). The companies are prospecting a large scale production of biogas as car fuel.

Based on marine technological and biological expertise Marine Biogas AB developed a culture system of ascidians as a solution for their needs. An added value is that the harvest of marine biomass also removes nutrients from the sea which is of great importance in combating the large scale eutrophication of coastal waters. Before the system was presented a Swedish patent application was filed. The patent is now published as SE535011.

The concept has received great interest from several Swedish municipalities and sewage treatment plants. The benefits of ascidian culturing, compared with previous mussel culturing, was so crucial that the Swedish Environmental Board granted 450 000 $ for a three year study of its potential, ecological impact and nutrient removal.

The main benefits are:

  1. A high yield of biomass per area and year gives a cost effective removal of nutrients compared to conventional removal of nitrogen and phosphorus.
  2. Ascidians cultured for biomass production is not sold as human food. This means the biomass can be cultured in polluted waters. The cultures need no extra fertilizers or pesticides.
  3. The ascidian Ciona intestinalis is easily digested into biogas.
  4. Ascidians only consist of soft tissue which enables an industrial processing.

The need for biomass for production of biogas is said to increase in line with higher demand for biogas fuel. There is already a competition in that biomass with a yield of biogas is highly demanded by industrial producers of biogas. There is also an unfortunate conflict in use of arable land for production of biogas and ethanol feedstock and the production of food. By localizing the feedstock production to the sea, the competition with arable land is avoided.

As a production system using the ascidian Ciona intestinalis has several benefits. It can be cultured and harvested using regular and proven techniques for blue mussels. The system has also a large potential for improvements to lower the production- and transportation costs.