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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Photofuel (Biocatalytic solar fuels for sustainable mobility in Europe)

Teaser

Summary

The EU Horizon2020 project â€˜Photofuelâ€™ seeks to study and advance the biocatalytic production of alternative liquid transportation fuels, using only sunlight, CO2, and water. The goal is to engineer microbial cells to directly excrete hydrocarbon and long chain alcohol fuel compounds to the medium from which they can be separated, without the need to harvest biomass. This strategy significantly improves the costs and energy balances of solar biofuels as only a minimum of nutrients is required for self-replication of the biocatalyst, whilst cell harvesting, drying, and lipid extraction is omitted. Such minimum-input systems are compatible with operation on non arable, degraded or desert land. This next generation biofuel technology has the potential to significantly contribute to mitigation of climate change but avoids the pitfalls of most of the currently available biofuel technologies. The products are drop-in fuels that fully or partially replace their fossil counterparts without the need for new infrastructure and uncompromised food production.
The challenge is to advance the base technology of microalgae cultivation in closed bioreactors by enabling phototrophic algae or cyanobacterial microorganisms to produce hydrocarbons and alcohols, which are excreted to the culture broth for direct separation without cell harvesting. This thereby turns the microbial cells into self-reproducing biocatalysts as illustrated.

Work performed

Biocatalyst development
Three groups from the universities in Uppsala, Bielefeld, and the Imperial College London work in Photofuel in parallel on the advancement of 3 different biocatalytic solar fuel production systems. This multi group approach was chosen because it is difficult to predict the success and effect of the planned bioengineering approaches and measures on the production rates from a single system. The work on butanol production in Synechocystis was very successful. In the first 12 months the best 1-butanol strain was, during the most productive period, able to surpass the target productivity of 34 mg/L/day. This peak production clearly exceeds the objective for M12 and gives confidence concerning achievement of the 100 mg/L/day milestone with butanol production in a laboratory PBR.

The production of undecane and octanol in Synechocystis or Synechococcus was not yet successful. However, production and secretion of intermediary free fatty acids (FFA) has recently been demonstrated at rates close to the benchmark. These FFA form visible flakes, separation requires low efforts and HEFA-upgrading to biofuel is commercially applied. If the Photofuel consortium decides to change to FFA as target instead of undecane and octanol, it seems highly likely that the productivity key performance indicator will be exceeded by a further improved biocatalyst.

The production of the branched alkene bisabolene, a terpenoid of the fir tree, in the green algae Chlamydomonas reinhardtii was achieved already in the first months of the Photofuel project. Previously, nuclear transgene expression in this algal had been met with low success for large nuclear gene constructs. Several breakthroughs in engineering large transgene expression have been achieved with this eukaryotic microalgal host in this work, which has allowed the reliable expression of heterologous terpene synthase transgenes and consequent production of (E)-Î±-bisabolene from this host. However, the produced amounts are so far limited, probably due to long and peripheral nature of the anabolic pathway. If different strategies to improve production remain unsuccessful, a change of target compound might be considered.

Scale-up and solar fuel production
The University of Florence, the Imperial College and the algae-biotech SME A4F collaborate in scale-up of biocatalytic fuel production. Experiments with the wild-type strains, the biocatalyst systems and reference strains (Botryococcus braunii as natural hydrocarbon secreting algae and Nannochloropsis oceanica as lipid-accumulating algae) have been carried out to tune the mineral medium, optimize the growth conditions, and adapt the cells from batch cultivation to continuous, large-scale production under the varying outdoor conditions. A flat-plate photobioreactor-system was set up in chemostat-mode for continuous production. For separation of the biofuel product, it was connected to a cross-flow reactor for accumulation and separation of hydrocarbons and other hydrophobic products via an organic overlay (dodecane). Next steps target the validation of biocatalyst performance in 120 L photobioreactors as first milestone prior to outdoor solar fuel production in 5 mÂ³ volume.

Fuel blending and engine testing
Considerations on upgrading needs, fuel performance and expected feedstocks for fuel blending in the future were discussed between IFPEN, Neste, VW, Volvo and the Fiat research centre. First materials for upgrading trials to be performed in the second period were purchased. Next steps will be an agreement on the composition of the fuel blends expected for the future, blending with Photofuel-components and engine tests.

Assessment
The lay-out of the Life Cycle Assessment (LCA) was designed, processes sketched and frame conditions defined to prepare for data collection and modeling.

Final results

Photofuel progressed well and all three target compounds were produced on levels close to or exceeding those published as state of the art in biocatalytic production of solar fuels. Taking into account the level of technical maturity in this research and innovation action, the consortium expects that significant impacts can be achieved on mitigation of climate change, rural development and sustainable biofuel production.

New biofuel feedstock sources without competition to food
A major impact of the development of biocatalysts for the direct production of fuel components from sunlight, water and CO2 is in the option to reclaim marginal or degraded land, which is not suitable for agriculture or forestry due to salinization, soil erosion or draught. Use of such areas for fuel production in closed photobioreactors would offer reliable employment and income in areas which suffer from rural depopulation and would be free of competition to forestry and food production.

Favourable energy balance
Current microalgae based biofuel production relies on input of large amounts of power, fertilizer and construction materials for the cultivation of biomass, cell harvesting, lipid extraction and purification, which may amount to totals exceeding the produced bioenergy. The biocatalytic fuel synthesis and direct excretion to the surrounding medium requires only a minimum of fertilizer for makeup of the biocatalysts, as the fuel products are composed only of C, H and O obtained from CO2 and water. Such biocatalytic behaviour was for the first time in Photofuel observed in butanol-production without growth over the course of 8 days in a lab-scale experiment.
The highly energy intensive processing to biofuel is replaced by fuel separation directly from the medium as e.g. in a cross-flow reactor with an organic overlay implemented on lab-scale for bisabolene and free fatty acids. Bisabolene and free fatty acids require hydrogenation (HEFA-process) as applied on a scale of 2 million tonnes per year in Nesteâ€™s NEXBTL-plants. A detailed calculation of the contribution of the Photofuel-project towards achievement of this impact is scheduled for the last period.