Optimization of iron dosage for microalgal biomass production as a feedstock for biofuel

Summary

Biomass and metabolite production of three marine (Tetraselmis sp., Nannochloropsis sp., Chlorocystis sp.) and three freshwater microalgae (Scenedesmus sp., Chlorella sp., Monoraphidium sp.) were studied under different iron concentrations. The biomass concentration in control cultures (i.e., no iron added) was in the range of 291.5 – 707.5 mg/L, suggesting that these microalgae could use dissolved iron in the source water and also the carried over iron from the inoculum. In terms of biomass production, 0.05 mg/L or less Fe³⁺ supplementation was optimum for all the marine microalgae, however addition of iron did not have any significant effect on the biomass yield of freshwater microalgae (P < 0.05). Different iron supplementations, however, resulted in mixed trends in metabolites contents among these strains. Nevertheless, iron uptake by these microalgae was low while extra iron could remain in the culture media or precipitate. The biomass concentrations of Nannochloropsis sp. and Scenedesmus sp. cultures, when grown in outdoor 1000 L raceway tanks without iron supplementation, were 721.5 mg/L and 530 mg/L, respectively. From the indoor and outdoor experiments, it can be concluded that some microalgae have a very low iron requirement.

Keywords:

• Microalgae
• iron
• biomass
• metabolites
• biofuel