Chlorella for protein and biofuels: from strain selection to outdoor cultivation in a Green Wall Panel photobioreactor

Abstract

BackgroundChlorella is one of the few microalgae employed for human consumption. It typically has a high protein content, but it can also accumulate high amounts of lipids or carbohydrates under stress conditions and, for this reason, it is of interest in the production of biofuels. High production costs and energy consumption are associated with its cultivation. This work describes a strategy to reduce costs and environmental impact of Chlorella biomass production for food, biofuels and other applications.ResultsThe growth of four Chlorella strains, selected after a laboratory screening, was investigated outdoors in a low-cost 0.25 m2 GWP-II photobioreactor. The capacity of the selected strains to grow at high temperature was tested. On the basis of these results, in the nitrogen starvation trials the culture was cooled only when the temperature exceeded 40°C to allow for significant energy savings, and performed in a seawater-based medium to reduce the freshwater footprint. Under nutrient sufficiency, strain CH2 was the most productive. In all the strains, nitrogen starvation strongly reduced productivity, depressed protein and induced accumulation of carbohydrate (about 50%) in strains F&M-M49 and IAM C-212, and lipid (40 - 45%) in strains PROD1 and CH2. Starved cultures achieved high storage product productivities: 0.12 g L−1 d−1 of lipids for CH2 and 0.19 g L−1 d−1 of carbohydrates for F&M-M49. When extrapolated to large-scale in central Italy, CH2 showed a potential productivity of 41 t ha−1 y−1 for biomass, 16 t ha−1 y−1 for protein and 11 t ha−1 y−1 for lipid under nutrient sufficiency, and 8 t ha−1 y−1 for lipid under nitrogen starvation.ConclusionsThe environmental and economic sustainability of Chlorella production was enhanced by growing the organisms in a seawater-based medium, so as not to compete with crops for freshwater, and at high temperatures, so as to reduce energy consumption for cooling. All the four selected strains are good candidates for food or biofuels production in lands unsuitable for conventional agriculture. Chlorella strain CH2 has the potential for more than 80 tonnes of biomass, 32 tonnes of protein and 22 tonnes of lipid per year under favourable climates.

Lactic acid fermentation of Arthrospira platensis (spirulina) biomass for probiotic-based products

“…The fermentation broth was serially diluted (1:10) in Maximal Recovery Diluent (Sigma-Aldrich, Ireland) before plating. The plates were incubated at 37°C for 36-48 h. The average weight of a L. plantarum cell was determined by growing LAB 8014 cultures (1 mL of thawed stock culture) in 100 mL of MRS broth incubated at 37°C for 48 h. The cell number was determined by total counts with an Improved Neubauer counting chamber for bacteria, and the biomass dry weight was determined following the method reported by Guccione et al (2014) using membranes with 0.22 μm porosity (Millipore, USA). The average weight of LAB 8014 cells was then calculated by dividing the biomass dry weight by the cell number.…”

Chlorella vulgaris as Protein Source in the Diets of African Catfish Clarias gariepinus

“…Algae are at the base of the aquatic food chain and food resources that fish eat are produced there [7]. Microalgae are source of protein and lipids depending on the species [8,9]. It may be possible to substitute fishmeal with algal protein meal in production of aquafeed.…”

Microalgal growth with intracellular phosphorus for achieving high biomass growth rate and high lipid/triacylglycerol content simultaneously

“…Besides phosphorus deprivation, nitrogen deprivation was also an efficient trigger for microalgal lipid/TAGs accumulation (Guccione et al, 2014;Li et al, 2010a;Sheehan et al, 1998;Yang et al, 2013). However, compared with phosphorus deprivation, the significant difference between algal density growth rate and biomass growth rate was scarcely reported under nitrogen deprivation.…”

“…Nutrient deprivation is considered as an efficient approach to increase the lipid content in microalgal biomass, especially the deprivation of nitrogen (Guccione et al, 2014;Li et al, 2010a;Ren et al, 2013). It was found that when the initial nitrogen concentration in culture medium decreased from 25 to 2.5 mg L À1 , the lipid content in Scenedesmus sp.…”