Page 259 - AWSAR 2.0

when they possess a positive surface charge. The IONPs solution is added to the microalgae culture and mixed thoroughly for sufficient interactions between the algae and IONPs. This creates an electrostatic attraction between the microalgae and IONPs causing them to bind and form complexes. These complexes are immediately attracted to the bottom of the flask under the influence of a magnetic field within 60 seconds leaving the clear culture medium above as supernatant. This clear culture medium is carefully decanted leaving only the microalgae and IONPs complexes at the bottom. Thus, successfully harvesting the microalgal culture within a minute. Upon harvesting, the complexes can be detached and the IONPs can be reused for harvesting consecutive batches. This process is several times more convenient than most other existing procedures.
The second part of the project involved increasing the lipid production
by strategically changing the
nutrients of the culture medium
during the growth phase. The
first six days were subjected
to usual growth using the
normal BG 11 culture medium
composition. However, after
six days, the microalgal
species was harvested and
reconstituted in a culture
medium totally deprived of
nitrogen and, simultaneously,
in culture medium completely
deprived of nitrogen and
composed of excess carbon
in the form of citrate, sodium
acetate, sodium carbonate and
sodium potassium tartrate for
two to ten days. Such a growth
creates stress conditions for
the microalgae due to complete absence of nitrogen. Since proteins cannot be synthesized,
Ms. Supriya Bharte || 235
it begins to synthesize lipids in large quantities which increases the lipid productivity by activating specific pathways.
After a growth period of about eight to ten days, it was observed that, there is increased lipid production during nitrogen deprivation and even more lipids are produced under nitrogen deprivation combined with excess carbon. Of the four carbon sources provided, sodium acetate was the best source, which accumulated maximum lipids upto 25% for both organisms, followed by citrate. Sodium carbonate and sodium potassium tartrate did not show any significant increase in lipid production and, hence, cannot be considered as great carbon sources for biofuel production. The obtained lipids were converted to fatty acid methyl esters (FAMEs) by acidic transesterification and were biodiesel quality as estimated by GC-MS analysis.
Thus, our research work achieved the aim of enhancing the steps involved in biodiesel production by improving the harvesting by using IONPs and increasing the lipid productivity by manipulating the carbon- nitrogen ratio. These results are extremely helpful for the microalgae industry and can help in making the process cost
effective.
The microalgae industry
holds a huge potential for the future generations for research as well as its value- added products along with the environmental benefits it provides. Further research is necessary to make large- scale production feasible and affordable. Most of the current
research focusses on designing suitable reactors for maximum sunlight capture. Though,
For use as a source of biofuel, many universities and research organizations are working on a variety of easy-to-manipulate microalgae, for increased lipid production. Our research work was focussed on improving the various steps involved in microalgal biofuel production and, thereby, enhancing the productivity. Microalgal biofuel production consists of four major steps: cultivation, harvesting, lipid extraction and transesterification.