Characterization of microalgae native to Quebec for biofuel production

Biodiesel production using microalgae is attractive in a number of respects.  Through the first chapter, a number of pros and cons for using microalgae for biofuels production are reviewed.  Algal cultivation can be carried out using non-arable land and non-potable water with simple nutrient supply. The biomass productivity is much higher than those of vascular plants. Several species produce and store lipids in the form of triacylglycerols (TAGs), which can correspond from 30% to 40% of the biomass dry weight. The algal TAGs are very similar with those of oilseeds.  On the other hand, practical, cost-effective production of biofuels from microalgae requires that a number of obstacles be overcome. These include the development of low-cost, environmental friendly and efficient growth systems, harvesting techniques, and methods for lipid.  The second chapter explores one of the important issues raised in chapter one: the selection of a strain for cultivation. A strain collection of freshwater microalgae native to Quebec was established and examined for physiological diversity.  This collection consisted in 100 strains, which appeared very heterogeneous in terms of growth when they were cultured at 10±2 °C or 22±2 °C on the secondary effluent from a municipal wastewater treatment plant (WW) and defined BBM medium. Scatterplots were used to examine the diversity in physiology that might be present in the collection.  These showed a number of interesting results.  There was a fair amount of dispersion in growth rates by media type independent of temperature.  Surprisingly considering that all the isolates had been initially enriched on BBM, the distribution was quite symmetrical around the iso-growth line, suggesting that enrichment on BBM did not seem to bias the cells for growth on this medium versus WW.  As well, considering that all the isolates had been initially enriched at 22 °C, it is quite surprising that the distribution of specific growth rates was quite symmetrical around the iso-growth line with roughly equal numbers of isolates found on either side.  Thus enrichment at 22 °C does not seem to bias the cells for growth at this temperature versus 10°C.  The scatterplots obtained when the percentage lipid of cultures grown on BBM were compared with cultures grown on WW at either 10 °C or 22 °C made it apparent that lipid production was favored by growth on WW at either temperature and that lipid production does not seem to be particularly favoured by one temperature over the other.  When the collection was queried for differences with respect to sampling location, statistical analysis showed that roughly the same degree of physiological diversity was found with samples from the two different aggregate locations.  The third chapter continued the assessment of algal culture in Quebec. Some industrial wastes are rich in mineral nutrients and carbon sources, and can be used to increase the final microalgal biomass and lipid yield. This could be a low cost strategy to make algal biofuel technology viable. Using strains from the microalgal collection of the Université de Montréal, this chapter shows for the first time that microalgal strains can be grown on xylose, the major carbon source found in wastewater streams from pulp and paper industries, with an increase in growth rate of 2.8 fold in comparison to photoautotrophic growth, reaching up to µ=1.1/day. On glycerol, growth rates reached as high as µ=1.52/day. Lipid productivity increased up to 370% on glycerol and 180% on xylose for the strain LB1H10, showing the suitability of this strain for further development for biofuels production through mixotrophic cultivation.   The addition of xylose into algal cultures showed some unexpected effects. The fourth chapter of this work focused to understand these effects on microalgal growth and lipid production. Four wild-type indigenous strains were monitored daily, before and after xylose addition, using flow-cytometry. With some Chlorella strains xylose addition induced a rapid increase in lipid accumulation (up to 3.3 fold) during the first six to twelve hours. At later times cells showed a decrease in chlorophyll content, cell size and cell counts. On the other hand, the one member of the Scenedesmaceae family was able to profit from the presence of this carbon source during mixotrophic or heterotrophic cultivation without apparent negative effects.  These results suggest that xylose could be used prior to harvesting to boost the lipid content of algal cultures in either continuous or two-stage systems growing and carrying out bio-remediation of wastewater from the pulp and paper industry.  The fifth chapter addresses another important industrial waste: carbon dioxide and flue-gases. More than half of the CO2 that is emitted into the atmosphere every day is released by stationary process, either for generation of electricity or industrial manufacturing. The CO2 exhaustion from theses sources could be attenuated through bioremediation with microalgae, a putative feedstock for biofuels. Nevertheless, every flue has a different gas, and algal strain selection is vital. This work proposes to use a particular site condition for bioprospection of the algal strain to be used in the bioremediation process. This work showed that using a simple enrichment process at the isolation stage can select strains that were in average 43.2% better performing in biomass production than the strains isolated through the traditional methods. The strains isolated in this work were capable of assimilating carbon dioxide at an above average rate, according to recent the results in the literature.

Keyphrases: Biofuels, Algal biodiesel, Oil Extraction, Sustainability, Algae, Wastewater treatment, Biodiesel, Xylose, CO2 capture, Carbon dioxide, Durable