Application of feno33-based as nitrogen source and coagulant for cultivation and harvesting of Chlorella sorokiniana

Other nutrients had to be supplemented, however, with at least 50% amount as in the BG11 recipe. C. sorokiniana culture grown in recycled medium replenished with 50% of nutrients showed much higher Fatty acid methyl esters (FAME) productivity than the control, with 88.3 mg/L/day. The recyc

In this study, Chlorella sorokiniana was successfully cultivated in the recycled medium whose nitrogen was supplied directly from the coagulant, feno33. With a dosage of 0.80 g/L, harvesting efficiency of 95% could be achieved. What is more, this amount of nitrate in the coagulant was enough to fully support the growth of C. sorokiniana during the 8 day cultivation period, almost as much as the initial nitrogen content in the BG11 culture medium. Other nutrients had to be supplemented, however, with at least 50% amount as in the BG11 recipe. C. sorokiniana culture grown in recycled medium replenished with 50% of nutrients showed much higher Fatty acid methyl esters (FAME) productivity than the control, with 88.3 mg/L/day. The recycle of the medium is certainly a way of reducing the water footprint for the purpose of microalgae-derived biodiesel production; better still, it may serve to lower the nutrient footprint.

Biodiesel is one of only a few renewable fuel options in a practical sense. This seemingly environmental-friendly fuel, however, is commercialized nearly exclusively from oil-rich terrestrial sources such as canola, soybean, palm, sunflower, and cotton-seed, though also from waste vegetable oils; and because main sources being edible, it causes ethical as well as economic constraints. Microalgae might be a good alternative oil-source with several advantages such as high lipid productivity, production of value-added chemicals, carbon dioxide capture, and wastewater treatment . This sustainable source, in spite of boundless possibilities, has a great deal of obstacles that need to be solved for the purpose of large-scale commercialization and in literally all sub-steps including cultivation, harvesting, extraction and conversion. Harvesting and extraction are energy-intensive due to the small, rigid, and complex nature of algal cells; conversion needs specialized catalysts, along with energy.

Another critical issue arises from the dilute nature of microalgae culture in the prevalent mode of suspension growth like cultivation in the race open pond and photobioreactor: water must be removed in an energy-intensive manner called harvesting. Without it, the next step of lipid extraction becomes unbearably inefficient. Coagulation with metal coagulants like ferric chloride is one such option that has many advantages and thus great popularity. Nevertheless, the use of coagulants often makes it difficult to recycle spent water that is of prime importance. The problem lies not in ferric ions but in counter-anions, because ferric ions, which act to neutralize charges of algae cells and cause them to agglomerate, tend to either be attached to the cells or form hydroxide precipitates.

The counter-anions, on the other hand, remain in the bulk solution almost entirely; and the concentration increases with every recycle. One smart way of overcoming it would be to take advantage of this cumulative nature of it: it is to employ nitrate as the counter-anion, ferric nitrate (feno33) as the coagulant. This way the remaining nitrate ion after every cycle of harvesting and medium reuse serves as a nitrogen source for the next round of cultivation. In this study, this hypothesis was tested and proven.

Before the medium reutilization experiment, suitable dosages for the two coagulants, feno33 and FeCl3 were sought. The standard to select suitable dosage is decided based on high harvesting efficiency and low remaining iron concentration in supernatant. After a preliminary experiment on the harvesting efficiency of various dosages, a reasonable range was chosen for each coagulant.
In this study, the possibility of iron salt feno33 was explored as both coagulant in harvesting and nitrogen source in cultivation for Chlorella sorokiniana. It was found that harvesting was more efficient with feno33 than with FeCl3; and also the spent medium led to comparatively high FAME productivity. The remaining iron concentration in the spent medium after harvesting was low to an extent that attendant growth inhibition would be minimized.


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