Nutrients for microalgae bio-oil production at a pulp and paper mill site, experiences from a pilot plant
2015 (English)Conference paper, Abstract (Refereed)
Microalgae are a possible source of bio-oil, for example renewable biodiesel. Micro algae gives higher production capacity per area than any other oil producing crop (Chisti 2007). To become competitive with fossil fuel, the bio-oil production must be efficient and cheap. An algae production pilot plant has been running for two years at the site of Nordic Paper Bäckhammar mill in mid Sweden. The purpose is to develop a competitive production process for bio-oil. The challenge is to achieve an economically competitive process that includes, gaining high production rate even though Sweden is a comparably dark and cold country.
The solar radiation is strong enough for algae growth in at least eight months of the year. Radiation inhibition that will be found in other countries closer to the equator can be avoided at this location. However, the low temperature will slow the production rate down during four of these eight months. The possibility to use the excess heat to prolong the growth season is therefore the mayor benefit of growing algae close to a pulp and paper mill. Another benefit is the closeness to the carbon dioxide rich exhaust gas from the recovery boiler. This pilot plant consists of one 25m2 raceway pond and eight smaller pools. The microalgae Scenedesmus Dimorphus is grown in wastewater from the mill. The pools are all covered with a plastic tent to maintain a carbon dioxide rich atmosphere above the surface. However the pulp and paper mill effluent is low in nutrients. The aim with this study is to find efficient and cheap nutrients for algae production, close to the pulp and paper mill site.
Tested nutrients were: the pulp and paper mill effluent, bio-sludge from the pulp and paper mill wastewater treatment plant, digester reject from a close by municipal treatment plant and digester reject from algae residue anaerobic digestion. The residues are collected after the bio-oil has been extracted. In order to see if the nutrients are available for the microalgae Scenedesmus dimorphus, have the different nutrients been tested in small-scale 100 ml growth trials. Scenedesmus Dimorphus was also used in the pilot plant. Cost and energy were used to evaluate the different nutrient sources tested. Algae residues from the pilot plant were anaerobically digested in batch tests to produce the algae digester reject. The biogas potential was determined as input for the evaluation. Costs for transportation and decreased cost for energy and chemicals in the municipal wastewater treatment plant were included to evaluate the municipal digester reject.
Nutrients from all tested sources, except the one from the bio-sludge, were available for microalgae growth. The concentrations of nutrients were to low in the pulp and paper wastewater to enable growth in one batch. The both rejects contain high concentrations of nutrients. The transportation costs made the municipal reject less suitable. The algae residues will give 250 nml3 methane/gVS. The contribution of energy in form of biogas is almost as large as the energy of the bio-oil. Therefore gave the reject from anaerobically digested algae residues the best results. An efficient system can be algae grown in pulp and paper wastewater complemented with recirculate nutrients from the energy recovery of the residues from the bio-oil production.
Place, publisher, year, edition, pages
bio-oil; microalgae; nutrients; pulp and paper mill.
Engineering and Technology
Research subject Environmental and Energy Systems
IdentifiersURN: urn:nbn:se:kau:diva-39213OAI: oai:DiVA.org:kau-39213DiVA: diva2:899871
5th International Conference on Biorefinery - towards Bioenergy University of British Columbia, Aug 10-12
ProjectsAlgodling hos massa- och pappersbruk för hållbar produktion av bioolja