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Nutrient recovery from the liquid fraction from anaerobic digestion

Organisation: Biovakka Suomi Oy

Time: 3/1/2013 – 12/31/2015



Biovakka Suomi Oy is a leading biogas plant operator in Finland. Biovakka has two centralised biogas plants in operation in the southwest of Finland (Vehmaa, Turku) with a total treatment capacity of around 200 000 tons/year.

Anaerobic digestion is well-suited for controlled treatment of organic materials while minimising their emissions, enhancing their fertiliser value and eliminating pathogens. Thus, biogas technologies meet the requirements of renewable energy production, reduced greenhouse gas emissions, and production of safe, recycled organic fertilisers and soil conditioners. However, one of the main challenges in environmentally and economically efficient material flow management through biogas plants is the digestate management. Nowadays in general, post-processing of the digestate is usually only mechanical separation of the digestate into liquid and solid fractions which divides the nitrogen and phosphorous roughly into the different fractions (P/solid fraction and N/liquid fraction), but volumes to be transported for final use or disposal stay the same. Moreover, the land application can cause similar environmental problems as manure and digestate as such, e.g.nutrient leaching to waters, if not implemented properly with care.

Biovakka Suomi Oy commits to develop a concept for efficient nutrient recovery and concentration from the digestate liquid fraction originating from the treatment of various organic materials in the biogas plants. The developed concept will enable nutrient recovery (P, N, K and trace elements) efficiency of >99% and production of recycled nutrient products for industrial use, e.g. for forest industry waste water treatment. Simultaneously, half of the initial liquid volume can be discharged on-site as purified waste water.

The developed concept will provide a solution for sustainable nutrient recycling by enabling transfer of excess nutrients in a concentrated form, e.g. from the areas of intensive animal farming to industrial use, and thus reduce the risk of nutrient leakage to the Baltic Sea.

The objective of the Commitment is to reduce eutrophication in the Baltic Sea.