Production of Microalgal Lipids as Biodiesel Feedstock with Fixation of CO2 by Chlorella vulgaris

Globalno su zatopljenje i nedostatak energije najveće zapreke razvoju društva. Smanjenjem se emisije ugljičnog dioksida i zamjenom konvencionalnog dizel goriva biodizelom ti problemi mogu učinkoviti riješiti. U radu je ispitana proizvodnja lipida što se koruste kao sirovina za biogorivo s pomoću slatkovodne mikroalge Chlorella vulgari, koja fiksira ugljični dioksid. Rezultati pokazuju da nedostatak dušika, volumni udjel CO2 i duljina fotoperioda utječu na nakupljanje lipida u mikroalgi C. vulgaris. Pri 5 % CO2, 0,75 g/L NaNO3 i fotoperiodu od 18 h svjetlosti i 6 h tame udjel je lipida dosegao 14,5 %, a produktivnost 33,2 mg/(L·dan). Predložena je metoda poboljšanja proizvodnje lipida iz mikroalge C. vulgaris aktivacijom acetil-CoA karboksilaze. Utvrđeno je da se limunska kiselina i ioni Mg2+ mogu učinkovito upotrijebiti kao aktivatori enzima, pa je tako dodatkom 150 mg/L limunske kiseline proizvedeno 39,1, a dodatkom 1,5 mmol/L MgCl2 38,0 mg lipida po litri podloge po danu, što je gotovo dvostruko više nego u kontrolnom uzorku. Dokazano je da se lipidi mogu proizvesti na jednostavan način s pomoću slatkovodne mikroalge koja fiksira ugljični dioksid, što predstavlja moguće rješenje problema globalnog zatopljenja i nedostatka energije.The global warming and shortage of energy are two critical problems for human social development. CO2 mitigation and replacing conventional diesel with biodiesel are effective routes to reduce these problems. Production of microalgal lipids as biodiesel feedstock by a freshwater microalga, Chlorella vulgaris, with the ability to fixate CO2 is studied in this work. The results show that nitrogen deficiency, CO2 volume fraction and photoperiod are the key factors responsible for the lipid accumulation in C. vulgaris. With 5 % CO2, 0.75 g/L of NaNO3 and 18:6 h of light/dark cycle, the lipid content and overall lipid productivity reached 14.5 % and 33.2 mg/(L·day), respectively. Furthermore, we proposed a technique to enhance the microalgal lipid productivity by activating acetyl-CoA carboxylase (ACCase) with an enzyme activator. Citric acid and Mg2+ were found to be efficient enzyme activators of ACCase. With the addition of 150 mg/L of citric acid or 1.5 mmol/L of MgCl2, the lipid productivity reached 39.1 and 38.0 mg/(L·day), respectively, which was almost twofold of the control. This work shows that it is practicable to produce lipids by freshwater microalgae that can fixate CO2, and provides a potential route to solving the global warming and energy shortage problems