Evan Stephens

An economic and technical evaluation of microalgal biofuels

In her News Feature “Biotech’s green gold”, Emily Waltz details the ‘hype’ being propagated around emerging microalgal biofuel technologies, which often exceeds the physical and thermodynamic constraints that ultimately define their economic viability. Our calculations counter such excessive claims and demonstrate that 22 MJ m−2 d−1 solar radiation supports practical yield maxima of ∼60 to 100 kl oil ha−1 y−1 (∼6,600 to 10,800 gal ac−1 y−1) and an absolute theoretical ceiling of ∼94 to 155 kl oil ha−1 y−1, assuming a maximum photosynthetic conversion efficiency of 10%. To evaluate claims and provide an accurate analysis of the potential of microalgal biofuel systems, we have conducted industrial feasibility studies and sensitivity analyses based on peer-reviewed data and industrial expertise. Given that microalgal biofuel research is still young and its development still in flux, we anticipate that the stringent assessment of the technologys economic potential presented below will assist R&D investment and policy development in the area going forward.

Future prospects of microalgal biofuel production systems.

Climate change mitigation, economic growth and stability, and the ongoing depletion of oil reserves are all major drivers for the development of economically rational, renewable energy technology platforms. Microalgae have re-emerged as a popular feedstock for the production of biofuels and other more valuable products. Even though integrated microalgal production systems have some clear advantages and present a promising alternative to highly controversial first generation biofuel systems, the associated hype has often exceeded the boundaries of reality. With a growing number of recent analyses demonstrating that despite the hype, these systems are conceptually sound and potentially sustainable given the available inputs, we review the research areas that are key to attaining economic reality and the future development of the industry.

RNAi Knock-Down of LHCBM1, 2 and 3 Increases Photosynthetic H2 Production Efficiency of the Green Alga Chlamydomonas reinhardtii

Single cell green algae (microalgae) are rapidly emerging as a platform for the production of sustainable fuels. Solar-driven H2 production from H2O theoretically provides the highest-efficiency route to fuel production in microalgae. This is because the H2-producing hydrogenase (HYDA) is directly coupled to the photosynthetic electron transport chain, thereby eliminating downstream energetic losses associated with the synthesis of carbohydrate and oils (feedstocks for methane, ethanol and oil-based fuels). Here we report the simultaneous knock-down of three light-harvesting complex proteins (LHCMB1, 2 and 3) in the high H2-producing Chlamydomonas reinhardtii mutant Stm6Glc4 using an RNAi triple knock-down strategy. The resultant Stm6Glc4L01 mutant exhibited a light green phenotype, reduced expression of LHCBM1 (20.6% ±0.27%), LHCBM2 (81.2% ±0.037%) and LHCBM3 (41.4% ±0.05%) compared to 100% control levels, and improved light to H2 (180%) and biomass (165%) conversion efficiencies. The improved H2 production efficiency was achieved at increased solar flux densities (450 instead of ∼100 µE m−2 s−1) and high cell densities which are best suited for microalgae production as light is ideally the limiting factor. Our data suggests that the overall improved photon-to-H2 conversion efficiency is due to: 1) reduced loss of absorbed energy by non-photochemical quenching (fluorescence and heat losses) near the photobioreactor surface; 2) improved light distribution in the reactor; 3) reduced photoinhibition; 4) early onset of HYDA expression and 5) reduction of O2-induced inhibition of HYDA. The Stm6Glc4L01 phenotype therefore provides important insights for the development of high-efficiency photobiological H2 production systems.

Expanding the microalgal industry--continuing controversy or compelling case?

Herein we examine the potential role that microalgae might play in the approaching challenges of energy and fuel security, and food and water supply. Microalgal production systems remain the subject of controversy however, generally consisting of arguments about the economic and environment sustainability of these systems. We discuss these aspects and draw some parallels with other systems to highlight real advantages and obstacles to expanding the modern microalgal industry. Emerging alternative production models and the relatively early developmental state of the microalgal biofuels industry provide room for extensive innovation that has the potential to bring the technology to a highly productive maturity.

Automated nutrient screening system enables high-throughput optimisation of microalgae production conditions.

BackgroundMicroalgae provide an excellent platform for the production of high-value-products and are increasingly being recognised as a promising production system for biomass, animal feeds and renewable fuels.ResultsHere, we describe an automated screen, to enable high-throughput optimisation of 12 nutrients for microalgae production. Its miniaturised 1,728 multiwell format allows multiple microalgae strains to be simultaneously screened using a two-step process. Step 1 optimises the primary elements nitrogen and phosphorous. Step 2 uses Box-Behnken analysis to define the highest growth rates within the large multidimensional space tested (Ca, Mg, Fe, Mn, Zn, Cu, B, Se, V, Si) at three levels (−1, 0, 1). The highest specific growth rates and maximum OD750 values provide a measure for continuous and batch culture.ConclusionThe screen identified the main nutrient effects on growth, pairwise nutrient interactions (for example, Ca-Mg) and the best production conditions of the sampled statistical space providing the basis for a targeted full factorial screen to assist with optimisation of algae production.

Algae Fuels as an Alternative to Petroleum

Here we examine the scale of petroleum consumption and the current lack of scalable petroleum alternatives. We highlight the contribution that macroalgae and microalgae can collectively make as feedstocks in the future energy mix, discuss recent advancements and current development pathways, and consider the potential and the limitations of these production systems for economic and environmental sustainability moving towards a scale of 10-20% of global petroleum consumption.

Surveying a Diverse Pool of Microalgae as a Bioresource for Future Biotechnological Applications

Resource limitation is an escalating concern given human expansion and development. Algae are increasingly recognised as a promising bioresource and the range of cultivated species and their products is expanding. Compared to terrestrial crops, microalgae are very biodiverse and offer considerable versatility for a range of biotechnological applications including the production of animal feeds, fuels, high value products and waste-water treatment. Despite their versatility and capacity for high biomass productivity on non-arable land, attempts to harness microalgae for commercial benefit have been limited. This is in large part due to capital costs and energy inputs remaining high, the necessity of identifying ‘suitable’ land with proximal resource and infrastructure availability and the need for process and strain optimisation. Microalgae represent a relatively unexplored bioresource both for native and engineered strains. Success in this area requires (1) appropriate methods to source and isolate microalgae strains, (2) efficient maintenance of motherstocks, (3) rapid strain characterisation and correct matching of strains to applications, (4) ensuring productive and stable cultivation at scale, and (5) ongoing strain development (breeding, adaptation and engineering). This article illustrates a survey and isolation of over 150 local microalgae strains as a bioresource for ongoing strain development and biotechnological applications.

Genetic Engineering for Microalgae Strain Improvement in Relation to Biocrude Production Systems

An advanced understanding of the genetics of microalgae and the availability of molecular biology tools are both critical to the development of advanced strains, which offer efficiency advantages for primary production, and more specifically in the context of production for biocrude and renewable energy. Consequently, we outline the current state of the art in microalgal molecular biology including the available genome sequences, molecular techniques and toolkits, amenable strains for transformation of nuclear and plastid genomes, and the control of transgenes at both transcriptional and translational levels. We also examine some strategies for improvement of expression and regulation. We suggest the primary strategies in strain improvement that are most relevant to biocrude applications; briefly illustrate the process of photosynthesis to enable identification of targets for improvement of net photosynthetic conversion efficiency in mass cultivation; and further discuss how improvement of metabolic systems may also be achieved and benefit production models. Finally, we acknowledge the aspects of prudent risk assessment and consequent regulation that are developing and how our knowledge of natural algae in existing ecosystems, and GM work in conventional agriculture both contribute lessons to these discussions. We conclude that if properly managed, these developments provide significant potential for increasing global capacity for renewable fuel production from microalgae and that these developments could also have benefits for other applications.

Microalgal biofuel systems: Climate change, fuel supply and economic opportunities for sustainable development

The development of carbon neutral fuels for the future is one of the most urgent challenges facing our society for three reasons – to minimise the effects of climate change, to protect against fuel price shocks and to provide a secure basis for economic growth.