The modernized world is over-consuming low-cost energy sources that strongly contributes to environmental stress. As a consequence, the interest for environmentally friendly alternatives has increased immensely. One such alternative is utilizing the diazotrophic nature of the heterocystous filamentous cyanobacteria Nostoc sp. as feedstock for biodiesel and hydrogen production using pulp and paper wastewater – a phosphorous and nitrogen deficient medium. In this work, biodiesel and hydrogen production was studied with respect to three main aspects: biodiesel quality properties, lipid content and hydrogen production coupled with a preliminary study investigating the luminous effects on the biomass and biodiesel quality properties when exposed to low (50 μEm-2s-1), medium (150 μEm-2s-1) and high light (300 μEm-2s- 1).
The preliminary study showed that an increase of light intensity was associated with parabolic results for biomass following the 10-day cultivation period, with the medium light intensity showing an average dried weight of at the most 203% greater than the two other light intensities. When analysing the FAME- composition, similar results were demonstrated for the fatty acid constituents preferred for biofuel applications, C18:1 and C18:2 fatty acids, where the low, medium and high light showed an accumulative 34.65, 43.1 and 31.6 dwt % respectively.
The strain could be of interest as feedstock for biodiesel when cultivated in pulp and paper wastewater, due to the positive results pertaining to the lipid content and biodiesel quality properties. Following the 10-day cultivation period the lipid content obtained was 35.9 dwt %. The biodiesel quality properties were tested to assess the strains suitability for biodiesel and were tested to ensure its accordance to the standards on commercial biodiesel quality; European Standard for Biodiesel as heating oil (EN 14213) and European Biodiesel Standard (EN 14214). The critical parameters tested were the regulated (iodine value, cetane number, density, viscosity, pour point, cold filter plugging point, oxidative stability) and unregulated (FAME-composition) fuel properties. Results obtained showed values within the regulated values set by the different standards. However, due to a high saturated fatty acid content, the strain showed inadequate low temperature flow properties (cloud point, pour point and the cold filter plugging point).
This study shows that this strain has a low potential for hydrogen production, with a hydrogen production of 0.13 nmol/mg dry wt/h following the 10-day cultivation period. This low hydrogen production could be attributed to the among other things the current growth phase of the cyanobacteria.
Chemical analyses were conducted for revealing the total nitrogen, total phosphorus and chemical oxygen demand (COD) content. Following the 10-day cultivation period, the samples showed a 22% decrease in phosphorous concentration, 11% decrease in COD concentration and 51% increase of nitrogen concentration. The probable causes for this increase is the Nostoc’s diazotrophic nature and the ammonium excretion nitrogen fixation entails, as well as the nitrogen release following the final algal growth phase – the death phase.
In conclusion, the results showed great potential, however, further studies are recommended investigating the changes that occurs during cultivation period to further assess the strains potential as well as assessing the continuity of the results with a greater initial cellular concentration. Nonetheless, due to the positive results obtained regarding the nutrient uptake, biodiesel and hydrogen production, this study shows potential for further optimization for the use of Nostoc grown in pulp and paper wastewater for wastewater treatment, biodiesel and/or hydrogen production.