(768c) From Microalgal Starch to Biobutanol Production – a Combined Experimental and Computational Study

Industrial-scale production of biobutanol, a sugar-based biofuel and a long-term promising gasoline replacement, has so far been restricted by the use of typical food-based or lignocelllosic feedstocks which either raise the food vs fuel debate or compete for arable land (Kumar and Gayen, 2011). Recently, microalgal biomass has been considered as a suitable fermentable feedstock for the production of biobutanol due to its ability to accumulate high contents of starch, a polymeric carbohydrate. Studies have further shown that nitrogen and/or phosphorus stress can significantly enhance starch production in microalgal cells (Markou et al., 2012). Microalgal cultivation strategies in terms of nutrient availability can thus be established to generate “starch-enriched” algal biomass, but such strategies should be robust enough to be capable of: i) preventing a decrease in overall biomass growth, and ii) portraying the distribution of the intracellular carbon pool, which is simultaneously directed to not only starch, but also lipid formation.

In order to establish the best microalgae-to-biobutanol route, we have previously developed a multi-parameter kinetic model capable of predicting the dynamics of biomass, starch, and lipids as a function of nutrient availability and subject to mixotrophic growing conditions (Figueroa-Torres et al., 2017). Our proposed model, responsive to the concentrations of nitrogen (N), and acetate (A) as carbon source, was successfully validated against experimental data obtained from various nutrient-stressed lab-scale cultures of Chlamydomonas reinhartii CCAP 11/32c. In this work, “starch-enriched” microalgal biomass, as obtained from a model-based cultivation strategy maximising starch formation, has been evaluated as a potential feedstock for biobutanol production. Thus, a kinetic model has been developed in combination with a range of lab-scale batch fermentation experiments with the wild-type strain Clostridium acetobutylicumDSM 792 (at 37 °C under anaerobic conditions) to: i) establish optimal operating conditions for biobutanol production, ii) identify optimal pre-treatment steps required to adequately use “starch-enriched” microalgal biomass as a fermentable feedstock, and iii) establish the kinetics of bio-butanol production from “starch-enriched” algal biomass.

References

Figueroa-Torres, G., Pittman, J., Theodoropoulos, C., 2017. Kinetic Modelling of starch and lipid formation during mixotrophic, nutrient-limited microalgal growth. Bioresource Technology (Submitted).

Kumar, M., Gayen, K., 2011. Developments in biobutanol production: New insights. Appl. Energy 88, 1999–2012. doi:10.1016/j.apenergy.2010.12.055

Markou, G., Angelidaki, I., Georgakakis, D., 2012. Microalgal carbohydrates: an overview of the factors influencing carbohydrates production, and of main bioconversion technologies for production of biofuels. Appl. Microbiol. Biotechnol. 96, 631–645. doi:10.1007/s00253-012-4398-0