Energy efficiency evaluation of lipid production by oleaginous yeast Rhodosporidium toruloides

Mass-energy balance of lipid fermentation by oleaginous yeast Rhodosporidium toruloides Y4 with glucose as sole carbon source was investigated. The elemental composition of the freeze-dried cell samples obtained at different time points was determined using a Vario EL3 analyzer to estimate the biomass energetic yield (eta). Then this work established the biomass energetic yield (eta) to sets of biochemical variables and a new equation was developed to determine eta without elemental composition of biomass. Biomass energetic yield estimated by the new equation was highly in accordance with that based on elemental composition. Bomb-calorimetric measurements were shown to be a direct method of quantifying the energy content of oleaginous yeasts. Combustion heat (Q(c)) of biomass determined experimentally was in consistent with those calculated according to its elementary contents. The relationship between lipid content and Q(c) of the cells was simulated and a new practical equation was developed based on lipid content (Y-L/S) to evaluate Q(c) of biomass. Biomass energetic yield of R. toruloides Y4 could reach higher than 0.8. Combustion heat of biomass obtained after 116 h was 33 (kJ g(-1)) that was about 73% of the combustion heat of diesel. The results revealed that R. toruloides Y4 was an efficient "energy-converter" in lipid production with glucose as the substrate. The results also implied the approaches to estimating eta of fermentation, and Q(c) of single oil cells developed in this study should be valuable to address the overall techno-economical analysis of bio-energy production.