Energy efficient biogas production by recirculation of nutrients and complete ulilisation of resources (COMPLETE)

At the 2nd September 2018 the Norwegian company Biokraft AS opened the worlds´s largest factory for production of liquid biogas fuel at Skogn in Trøndelag. This fuel is sold to Aga and will be applied as engine fuel in the Norwegian and Scandinavian transport sector, among other in busses, ferries and heavy transport vehicles. The biogas is produced from waste from food industry, agriculture, aquaculture and paper production and as a zero-emission fuel it contributes to our future energy mix, in the zero-emission society. In the IPN-project COMPLETE, financed by Biokraft AS and the Norwegian Research Council through the ENERGIX-program, the main goal is to investigate various approaches to make production of biogas even more climate friendly. One such approach is to investigate how better to recirculate nutrients in the waste material used for production of biogas either directly in the biogas production processes and/or in other production processes, such as bioproduction. In biogas production a nutrient rich digestate will also be among the products, and as this is especially rich in nitrogen the project will test the solid phase as feed in cultivation of protein rich brush worms (polychaetes) and the liquid phase as growth medium or fertilizer in cultivation of lipid rich microalgae. The organisms will in turn have applications as ingredients in salmon feed. The bio-production in COMPLETE represents a new way of protein and lipid production through re-circulation of nutrients. It also represents CO2-capture, as the algae utilize CO2 from the environment for the building of biomass. The research partners in COMPLETE are SINTEF, NTNU, NIBIO and Scandinavian Biogas Fuels and the project will last for 2016-2018. For exploitation of the solid fraction of the digestate cultivation trials with brush worms from the Trondheimsfjorden are carried out to identify the best conditions for growth and optimum feed consumption with the digestate as feed. The experiments show that brush worms accept digestate as feed, but in varying degree. This challenge is further studied in ongoing activities and it is now shown that the acceptance of digestate increases significantly if sludge from smolt farms are blended into the digestate. Further, microalgae cultivation trials with the liquid digestate as nutrient medium have shown that the algae grow well in this medium. The need for addition of extra vitamins and micronutrients for optimised growth and biomass production is now being studied, together with analysis of the nutrients removal from the digestate by the algae. The techno-economic analysis show that cultivation of phototrophic microalgae in Mid-Norway will be expensive due to the need for artificial light, and another effluent water from the process at the factory are now tested as potential nutrient medium for microalgae. Further, algal species rich in pigments are studied in these growth experiments. As extra substrate supply for the biogas production at Skogn Biokraft plans to utilize residuals from processing of seaweed cultivated close to the factory. The initial focus was on process water from protein extraction, but due to a low market price on protein concentrate and a relatively low biogas potential in the process water the focus has shifted to extraction of high-value compounds, in collaboration with the Nordic center of excellence NordAqua. Mathematical modelling has been used to identify the cultivation areas outside Biokraft and Norske Skog Skogn, as well as the seaweed production potentials in these. It is shown that the production potential is very low at Skogn compared to the open coastal areas outside Trondheimsfjorden. CAMBIs Solid Stream process (Steam Explosion + Thermal Hydrolysis) has the potential to both reduce the net amount of cake produced and increase the overall biogas yield. The nutrient surplus of the liquid digestate could thus find productive use if new substrates, like hardwood and straw, with deficit of these nutrients are treated with the CAMBI process before blending with the nutrient rich digestate prior to anaerobic digestion. Preliminary tests have been conducted, indicating interesting Bio Methane Potentials for such mixtures. Research in COMPLETE is also directed to maximizing the overall energy efficiency in the factory. CO2 is an available by-product from the biogas plant, and if mixed with Hydrogen, synthetic methane could be produced in a process commonly known as Power-to-Gas. This process is exothermic and a significant thermal synergy will be available for Steam Explosion and Anaerobic Digestion. This process could be a kind of regional kick-start for the Hydrogen Economy in Mid-Norway.

COMPLETE revealed that several concepts for new resource use, bioproduction and substrate supply are highly interesting for implementation at Skogn. The liquid digestate as a nutrient source in the digestion of steam exploded lignocellulosic hydrolysate as well as in the aerobic wastewater treatment for production of bacterial biomass was demonstrated to work well. Salmon sludge was confirmed as a good biogas substrate in the factory and mixed with solid digestate also a feed for brush worms. COMPLETE suggests two options for profitable bioproduction at Skogn: 1) to further develop microalgae cultivation based on the liquid digestate fraction using surface reactors for production of a biomass with high-value product potential, or 2) to start aquaculture of organisms that are already well established in the world market, such as e.g. tropical shrimp, that have a high price, can utilize Skogn's resources and last but not least have well-known production protocols.

Biokraft AS has started the building of Stage 1 of an anaerobic digestion (AD) plant at Skogn, north of Trondheim, with a designed capacity output of 12,5 MNm3 per year of liquid biomethane, making it the largest in Scandinavia. To meet the increasing demand for bioenergy, the company envisages a further doubling of the production capacity to 25 MNm3 per year. A significant increase in resource utilization and feedstock supply will thus be needed. To meet these challenges, COMPLETE seeks to develop technology and biological processes to enable a total utilization of the feedstocks through recirculation of nutrients in the residual digestate for new bioproduction as well as an introduction of new biogas substrates from Norwegian aquaculture and new bioproduction industry at Skogn. The major bottle neck for a biogas plant of the size under construction is the utilization of the digested sludge, which traditionally is allocated for use as low valued fertilizer in agriculture. With COMPLETE, Biokraft will focus on the development of new bioproduction of high-value protein- and lipid rich bristle worms and microalgae for increased utilization of solid and dissolved waste fractions, respectively. The project will also evaluate whether a macroalgae farm to produce protein-rich biomass while the residuals are utilized as substrate for renewable biogas production can be setablished outside the factory. This farm could also utilize nutrients released to the recipient. Macroalgae biomasses will be evaluated as fish feed ingredients or as feedstock for production of high-value products like pigments and bioactive compounds. With COMPLETE, Biokraft aims to develop a new standard for climate friendly and sustainable biogas production. The project will contribute to increased resource utilization through the development of innovative solutions for recirculation of nutrients and complete use of resources in biogas production yielding a positive climate impact both through energy savings and production of more renewable energy and new biomasses.