Improved utilization of waste resources from the pulp and paper mill Nordic Paper Bäckhammar and isolation of local freshwater microalgae species

Abstract

This master thesis was performed during a full academic year and aimed at investigating the possibilities in utilizing otherwise discarded biosludge as a source of nutrients for algal cultures. This work was done as a part of a project cofounded by Vinnova and ÅF in collaboration with the Swedish pulp and paper mill Nordic Paper Bäckhammar (NPB) and SP, Technical Research Institute of Sweden (SP). Biosludge was chosen as a possible source as it is produced in situ en masse and contained a large mass fraction of nitrogen (2.8 % g/g). Biosludge was pre-treated with acids, bases and ultrasonication prior to experiments to determine an effective method for nutrient leaching. Acid pre-treatment showed promising results and was chosen as a suitable method for further development during this project. A screening was performed to evaluate the effect of heat and time versus leached nutrient concentrations from biosludge in HCl-solutions. The results indicated that a high temperature, 120 °C and a long reaction time, 24 h, reached the highest concentrations of NH4+ (19 mg/l) and PO43- (60 mg/l). The highest concentration of NO3- was 64 mg/l, reached after 170 h at 25 °C. The volume was kept constant during all leaching experiments. Water samples were collected at NPB for isolation of microalgae, which were cultivated and stored in minimal laboratory medium, 3N-BBM+V. Algae monocultures were isolated via serial dilution and plate streaking. Based on a visual examination, 7 different morphologies were found among the isolated cultures: Phormidium sp, Oscillatoria sp, Coenococcum sp, Scenedesmus dimorphus, Scenedesmus quadricauda, Chlorella vulgaris and Monoraphidium contortum. S. quadricauda and C. vulgaris could grow in treated biosludge-based medium. C. vulgaris, S. dimorphus and M. contortum showed fast growth rates in 3N-BBM+V medium and 15 % CO2, with growth rates of 0.065, 0.064 and 0.054 h-1 respectively. The total lipid content were determined for the algae strains in selected conditions and it was found that M. contortum could contain as much as 45 % lipids with a fatty acid composition suitable for biofuel production.