Life-Cycle Assessment of Potential Algal Biodiesel Production in the United Kingdom: A Comparison of Raceways and Air-Lift Tubular Bioreactors

Abstract

Life-cycle assessment has been used to investigate the global warming potential (GWP) and fossil-energy requirement of a hypothetical operation in which biodiesel is produced from the freshwater alga Chlorella vulgaris, grown using flue gas from a gas-fired power station as the carbon source. Cultivation using a twostage method was considered, whereby the cells were initially grown to a high concentration of biomass under nitrogen-sufficient conditions, before the supply of nitrogen was discontinued, whereupon the cells accumulated triacylglycerides. Cultivation in typical raceways and air-lift tubular bioreactors was investigated, as well as different methods of downstream processing. Results from this analysis showed that, if the future target for the productivity of lipids from microalgae, such as C. vulgaris, of ∼40 tons ha -1 year -1 could be achieved, cultivation in typical raceways would be significantly more environmentally sustainable than in closed air-lift tubular bioreactors. While biodiesel produced from microalgae cultivated in raceway ponds would have a GWP ∼ 80% lower than fossil-derived diesel (on the basis of the net energy content), if air-lift tubular bioreactors were used, the GWP of the biodiesel would be significantly greater than the energetically equivalent amount of fossil-derived diesel. The GWP and fossil-energy requirement in this operation were found to be particularly sensitive to (i) the yield of oil achieved during cultivation, (ii) the velocity of circulation of the algae in the cultivation facility, (iii) whether the culture media could be recycled or not, and (iv) the concentration of carbon dioxide in the flue gas. These results highlight the crucial importance of using life-cycle assessment to guide the future development of biodiesel from microalgae.

Economical Wet Extraction of Lipid from labyrinthula Aurantiochytrium limacinum by Using Liquefied Dimethyl Ether

“…Several step processes were also required when these solvents were employed as extraction media. They are as follows: drying of starting materials, cell disruption as a pre-treatment, evaporation of extraction solvents by heating, and condensation of them by cooling [10][11][12]. Fig.…”

Hydrothermal Conversion of Lipid-Extracted Microalgae Hydrolysate in the Presence of Isopropanol and Steel Furnace Residues

“…Only slightly better results were obtained by Clarens et al, who calculated energy returns of investment ranging from 0.65 to 1.13 for a biodiesel production process, combined with AD, depending on the source of carbon and other nutrients [36]. In contrast, Stephenson et al estimated a fossil-energy requirement reduction of 85% and global warming potential reduction of 78% compared to fossilderived diesel [37]. In all these studies, the major contributors to the overall lifecycle burden are the algae cultivation and pretreatment steps, and therefore further energy recovery of the lipid-extracted algal residue is highly beneficial.…”

Load following with Small Modular Reactors (SMR): A real options analysis

“…It includes the following sub-steps: oil refining, two-step transesterification, biodiesel purification, glycerin purification (glycerin is a saleable co-product of this chemical reaction), methanol recovery and waste water treatment [62,63]. The input data of this phase are: the crude oil yield from the oil extraction, process efficiency and power consumption.…”

“…There may be a "static mode" to perform the load following that does not imply any production switch option: e.g. every night, 0 (Flocculation requires only pumping water, which is already counted in the cultivation phase) Centrifugation (2%e12%) [53,60] 90% [23] 1 kW/m 3 [60] (electric energy) Filtration e press (12%e27%) [53,60] 90% [67] 0 [62] 200 MJ/ton (electric) 1600 MJ/ton (thermal) [63] Ethanol production (via fermentation) 6.27 MJ/L [42] form 2 a.m. to 6 a.m. it is decided that two SMR are dedicated to water desalination. In this "static mode", the plant does not have any degrees of freedom, therefore there is no option to exercise.…”