It is not surprising that critics of biofuels are skeptical about (or hostile to) further research into bioproduction routes, especially from food crop sources, because the proponents of biofuels have often confounded two quite separate issues:

1. Plant biomass as a supply of feedstocks for fuels for automobiles owned and operated by private drivers

2. Plant biomass as a source of industrial chemicals to replace petrochemicals “eventually” or “sooner or later”

Biofuels need not be manufactured from food crops, but both biofuels and biore­fineries must utilize lignocellulosic substrates to satisfy the massive demand that is presently met worldwide by a very large manufacturing sector, that is, the oil, gas, and petrochemical industries, based on an unsustainable basis (fossil fuels).

In addition, biofuels may be a poor choice in the long term when compared with photovoltaic cells to capture solar energy and the plethora of “renewable” (wind, wave, geothermal, etc.) energy sources, alternatives that have many dedicated publicists.

Further scientific research from a biotechnological perspective is unlikely to stumble on arguments to convince the critics of biofuels to radically revise their position or dubious investors to reassess the risks. Based on the material presented in this and the preceding seven chapters, however, a priority list can be assembled for bioenergy aims that are achievable within the next three to four decades (chapter 5, section 5.6), that is, before oil depletion becomes acute — viewed not purely as the narrow biofuels agenda but as part of the unavoidable need to develop a viable biocommodity production system within that time.

First, biohydrogen is the sole means of breaking any dependence or “addiction” to CO2 cycles in the industrial world. Is either photoproduction or “dark” bacterial fer­mentation energetically sufficient and cost-efficient to seriously rival solar-powered or chemical routes to generate the enormous quantities required for fuel cell technol­ogies on a global scale? Critics of fuel cell-powered mass transportation point to the cost of the units and the practical problems inherent in supplying inflammable H2. In October 2007, however, a report appeared of an elegant solution to both issues: a fuel cell designed for automobiles without any expensive platinum catalyst and capable of using hydrazine (N2H4) as a convenient liquid form of H2.101 The production of hydrazine has a total energy efficiency of 79% and the refilling energy efficiency of hydrazine is higher than of H2 because energy is required to compress gaseous H2. Whether this direct hydrazine fuel cell proves to be the final form of a vehicle — compatible fuel cell, a similar design is likely to evolved within the next 20-50 years. A viable technology to bioproduce H2 will, therefore, be highly desirable on an industrial scale to eliminate reliance on natural gas as the major long-term source of H2 for this supposedly zero-carbon fuel.

Second, lignocellulosic biomass is the main biological source of fuel ethanol (and/or other biofuels) on a truly mass-sufficient basis to displace (or replace) gaso­line. Can bioprocesses achieve the volumes of product required to displace up to 30% of gasoline demand before 2030, with or without tax incentives, as a nascent biocommodity sector seeking funding, with multiple, rival microbial catalysts and possible substrates, and with significant governmental guidance (or interference) to ensure continual development despite any short-term fluctuations in oil price or availability? Lignocelluloses remain refractory — this is particularly obvious when compared with the ease of processing of sugarcane and corn grains — and biotech­nology might profitably be applied to optimizing the use of clostridial microbes that have evolved during a billion years or more precisely to utilize the food resource that cellulose presents. Clostridial cellulases are a much-undervalued source of novel biocatalysts.102,103 Fungal cellulases can, as a further innovation, be incorpo­rated into bacterial cellulosomic structures with enhanced activity toward cellulosic substrates.104 Clostridia can even perform the ultimate in resource-efficient biofuels production, transforming domestic organic waste to ethanol and butanol.105,106 As arguments rage over the use of food crops and agriculturally valuable land for bio­fuels production, exploiting what the global ecosphere offers in efficient microbial biocatalysts adept at recycling the mountains of waste produced by human com­munities remains not only environmentally attractive but could, as the twenty-first century progresses, make overwhelming economic sense.

Third — and crucial to the success of biofuels production and biorefineries — have the best sources of the optimal choice of carbohydrate polymer — and lignin­degrading enzymes been located? The identification, gene mining, characterization, and successful manufacture of complex mixtures of enzymes to pretreat efficiently, rapidly, and without generating any unwanted or toxic products and the full range of mechanically disintegrated biomass feedstocks that could be available (on a seasonal or serendipitous or opportunistic basis) are essential to the rise of the much-antici­pated biobased economy. Unconventional and little-researched microorganisms are still fertile grounds for exploring even as intensively investigated enzymes as cel — lulases but artificially designed, multiple enzyme mixtures still appear to mimic the natural microbial world in offering the highest bioprocessing capabilities.107

Fourth, lignins cannot be eliminated (as essential components of terrestrial plant structure), but their carbon is underused and undervalued. Can laccases and other enzymes or whole wood-rotting cells be developed to liberate the benzenoid struc­tures that are presently petrochemical products? Lignins can also be inputs for hydro — processed high-octane fuels.108 Could they be enzymically processed at sufficiently rapid rates and with high carbon recoveries to enter the list of biorefinery resources? Broadening the question of the likely feedstocks for the hypothetical future biorefiner­ies, can new procedures (based on enzymes or mild chemical treatments or a mixture of both) define better ways of separating and fractionating plant biomass constitu­ents, that is, are presently operated feedstock pretreatment techniques for bioethanol production (some of which have been known and discussed for decades) only crude approximations to what is required for fully developed biorefinery operations?109111

Fifth, optimizing the interface between biorefineries and “traditional” fermen­tation manufacture will smooth the transition to the biobased economy. Can exist­ing fermentation processes operated at commercial scales of production be adapted to at least comparable yields and economic cost with novel sources of ingredients for microbial media presented by refineries?112,113 The industrial fermentation sector evolved under conditions where the supply of inputs usually mirrored products for the food industry (glucose syrups, soybean oil, soybean protein, etc.). Locating the manufacture of fine chemicals alongside the primary processing facilities for biore­fineries allows economies of scale and shared use but will require the rethinking and reformulation of media, nutrient supply, and feeding strategies to efficiently utilize the sugar units and other plant-derived product streams that will be available on an increasingly large scale.

Finally, harmonizing agronomy and biotechnology will accelerate the approach to the biorefinery model of the future commodity chemicals market. Plant biotechnol­ogists view the woefully low efficiency of capture of solar energy as a prime target for genetic therapy, and this issue may still limit greatly how much of the world’s present lavish energy use could be met by biomass as the ultimate bioenergy source.114 At the same time, the debate over the ecological desirability of monoculture plantations as sustainably supplying biomass for biofuels production remains a pointed argument — grassland pastures may simply outperform any dedicated “energy crops.”115

In the prelude to the establishment of a biorefineries for advanced biofuels, com­modity chemicals, or both, however, there is still time to resolve an equally per­tinent conundrum: should reliable crop as biorefinery inputs be (quickly) defined, relevant processing technologies fixed, products and coproducts agreed (nationally, if not internationally), and the various interdependent operations of a biorefinery be designed around those agronomic choices?116,117 Or is the clearly most energy-effi­cient route of choice for biomass use that of thermochemical decomposition (domesti­cally and in localized industry via wood-burning stoves of high energy conversions)? Biomass gasification dovetails very well into the existing oil and natural gas sectors and their chemistries, and in the first half of the twenty-first century Fischer-Tropsch liquid fuels remain an obvious short-term choice. Syngas is highly versatile, but can expanding the knowledge base fully exploit this versatile carbon and energy source? In particular, can syngas-based fermentations be the optimum biomass conversion methodology for bioethanol production?118