Om V. Singh and Steven P. Harvey

Introduction

Even given the seemingly unlikely near-term resolution of issues involving atmo­spheric CO2 levels and their effect on the climate, the adoption of global conser­vation measures, and the stabilization of fossil fuel prices, it is still a certainty that global oil and gas supplies will be largely depleted in a matter of decades. That much is clear from even a cursory comparison of the independent estimates of the world’s oil and natural gas reserves and the respective data on their consumption, as published regularly on the internet by the US Government Energy Information Administration [1]. Nature of course, offers abundant renewable resources that can be used to replace fossil fuels but issues of cost, technology readiness levels, and compatibility with existing distribution networks remain. Cellulosic ethanol and biodiesel are the most immediately obvious target fuels, with hydrogen, methane and butanol as other potentially viable products. Other recent reports have cov­ered various aspects of the current state of biofuels technology [2-4]. Here we continue to bridge the technology gap and focus on critical aspects of lignocellu — losic biomolecules and the respective mechanisms regulating their bioconversion to liquid fuels and value-added products of industrial significance.

The lignocellulosic structure does not readily yield its component five — and six- carbon sugars so the efficient biological conversion of biomass typically requires a pretreatment step to render the polysaccharide molecules accessible to enzymes. Several thermochemical or biochemical approaches are currently in various stages of development, and have the potential for major impact on the economics of biofuel

O. V. Singh (b)

Division of Biological and Health Sciences, University of Pittsburgh, 300 Campus Drive, Bradford, PA 16701 USA

e-mail: ovs11@pitt. edu, ovs11@yahoo. com S. P. Harvey (в)

U. S. Army Edgewood Chemical Biological Center, AMSRD-ECB-RT-BC, Bld E3150, 5183 Blackhawk Rd, Aberdeen Proving Ground, MD 21010-5424, USA e-mail: steve. harvey@us. army. mil

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production. In order to derive a stable and cost-effective approach, a greater fun­damental understanding is needed of the exact effects of these processes on plant anatomy. These are difficult experiments to conduct and in Chapter 1 “Heat and Mass Transport in Processing of Lignocellulosic Biomass for Fuels and Chemicals”, Viamajala et al. provide an in-depth report on the effects of heat and mass transport on the efficiency of biomass conversion. Further, Wu et al. in Chapter 2 “Biofuels from Lignocellulosic Biomass”, give the matter a more detailed consider­ation by comparing thermochemical and biochemical approaches to the production of biofuel from lignocellulosic biomass.

As compared to gas and oil, relatively greater potential reserves exist for both coal and uranium (probably on the order of a century) but neither is renewable and each is associated with its own environmental conundrum (carbon release and waste storage, respectively). Linus Pauling expressed a particular concern for the destruc­tion of the element uranium, saying “In a thousand or ten thousand years the world may require uranium for a purpose about which we are currently ignorant.” [5]. Looking beyond the immediate temporal horizon, we are unavoidably confronted with the need to develop permanently renewable sources of energy.

Earth’s most plentiful and renewable energy resources typically include sunlight, wind, geothermal heat, water (rivers, tides and waves), and biomass. All of these are suitable for the generation of electricity but biomass is the current main renewable feedstock for the production of “liquid” fuels — typically ethanol, and biodiesel and possibly to include butanol, hydrogen and methane. These liquid fuels, or energy carriers lie at the heart of the solution to the global energy problem, since they are the materials currently most suitable for use in the transportation sector and for the direct replacement of the immediately endangered fossil resources of oil and gas. Vasudevan et al. in Chapter 3 “Environmentally Sustainable Biofuels — The Case for Biodiesel, Biobutanol and Cellulosic Ethanol” provide a detailed dis­cussion of the case for ethanol, butanol and biodiesel. Significantly, a potential technical hurdle confronting the production of biofuels is the efficiency of utiliza­tion of hemicellulose-derived sugars. In Chapter 4 “Biotechnological Applications of Hemicellulosic Derived Sugars: State-of-the-Art”, Chandel et al. examine the challenges associated with the successful utilization of this second most abundant polysaccharide in nature.

Energy-yielding materials are found in various guises, one of which is garbage. Although not always classified as a resource, garbage clearly is renewable (increas­ingly so, in fact), and processes that convert it into energy are obviously dually beneficial. In Chapter 5 “Tactical Garbage to Energy Refinery (TGER)”, Valdes and Warner present a hybrid biological/thermochemical system designed for the conversion of military garbage into ethanol and electricity, with clear potential for applications in the civilian sector.

Agricultural waste (e. g. livestock, manure, crop residues, food wastes etc.) is a high impact feedstock with particular utility in the production of bio­gas. In Chapter 6 “Production of Methane Biogas as Fuel Through Anaerobic Digestion”, Yu and Schanbacher discuss the anaerobic conversion of biomass to methane. Untreated wastewater also contains biodegradable organics that can be used to produce hydrogen or methane. In Chapter 7 “Waste to Renewable Energy: A Sustainable and Green Approach Towards Production of Biohydrogen by Acidogenic Fermentation”, Mohan provides a detailed review of the state of the art with regard to biological hydrogen production using waste and wastewater as substrates with dark fermentation processes.

Many biological processes use mixed cultures operating under non-sterile con­ditions (e. g. biological hydrogen and methane production, as discussed above). Watanabe et al. in Chapter 8 “Bacterial Communities in Various Conditions of the Composting Reactor Revealed by 16S rDNA Clone Analysis and Denaturing Gradient Gel Electrophoresis” demonstrate the utility of 16S rRNA analysis and denaturing gradient gel electrophoresis (DGGE) techniques for tracking microbial communities within a mixed and changing culture. Their work uses a composting process, which offers a typically cost-effective alternative to incineration for the remediation of contaminated soil.

The production of liquid fuel from biomass necessitates the consideration of var­ious issues such as the effects on the food supply, the rainforest, and greenhouse gas production, as well as carbon sustainability certification. Some of these issues may require appropriate regulations and in Chapter 9 “Perspectives on Bioenergy and Biofuels”, Scott et al., examine these issues closely.

In addition to its environmental advantages, the use of renewable energy resources offers the potential for stimulation of the economies of the nations where they are produced. The potential products of these renewable materials extend well beyond liquid fuels alone. Owing partly to the enormous volume of their produc­tion, fuels are sold for relatively low prices, and the successful implementation of renewable fuels depends, at least initially, on their ability to compete in the mar­ketplace. To this end, it is particularly important to maximize the efficiency of their production in biorefineries where secondary products would be derived from the same feedstock as the fuels. As an example, petroleum refineries have been in oper­ation for over 150 years and now produce lubricants, plastics, solvents, detergents, etc., all from the starting crude oil [6]. Similarly, biomass, in addition to being used for the production of fuels, can be used as a starting material for the pro­duction of other value-added products of microbial bioconversion processes such as fermentable sugars, organic acids and enzymes. In Chapter 10 “Perspectives on Chemicals from Renewable Resources”, Scott et al. describe how, with the aid of biotechnology, Protamylase® generated from starch production, can be used as a medium for the production of a cynophycin polymer, which is a major source of arginine and aspartic acid for the production of many industrially useful compounds including 1,4-butanediamine and succinic acid. In Chapter 11 “Microbial Lactic Acid Production from Renewable Resources”, Li and Cui describe the production of lactic acid from renewable resources such as starch biomass, cheese whey etc. Lactic acid has recently gained attention due its application to the manufacture of biodegradable polymers. Among other renewable resources, Chapter 12 “Microbial Production of Potent Phenolic-Antioxidants Through Solid State Fermentation”, Martin et al. describe the role of agroindustrial residues including plant tissues rich in polyphenols for the microbial bioconversion of potent phenolics under solid state fermentation conditions. Hence, combined with the economy of scale derived from large refineries, secondary products could be key to bridging the price gap between fossil fuels and renewables.

One critical advantage of biofuels is their potential to achieve a reduction in greenhouse gas releases, since the plants from which they are produced derive their carbon from the atmosphere. The overall balance of greenhouse gases however, depends in large measure on the particular feedstocks used and the methods by which they are produced. Corn ethanol for instance, while being potentially car­bon neutral, is not likely to achieve an overall reduction in greenhouse gas release due to its requirement for nitrogenous fertilizer and the associated release of nitrous oxide [7]. An interesting approach to the production of biodiesel is the use of algae to synthesize oil from the CO2 they capture for growth. Algae cultivation offers a potential low-cost alternative to physical methods of carbon sequestration such as pumping liquid CO2 underground or underwater or chemical methods such as base-mediated capture of CO2 and subsequent burial of the resulting carbonates. The algae, while using CO2 as their sole source of carbon for growth, can produce up to 50% of their weight in oil suitable for conversion to biodiesel. Algae are one of the best sources of plentiful biomass on earth; their potential for biosynthesis of astaxanthin, a red carotenoid nutraceutical responsible for the color of salmon flesh, was explored in Chapter 13 “Photoautotrophic Production of Astaxanthin by the Microalga Haematococcus pluvialis”, Del Rio et al.

In a biological system, the biosynthesis of industrially useful compounds has long been recommended. Heparin, a low-molecular weight highly sulfated polysac­charide represents a unique class of natural products, that has long been used as an anticoagulant drug. Due to recent outbreaks of contamination and seizure of hep­arin manufacturing facilities [8], an efficient bioconversion process of heparin is required. In Chapter 14 “Enzymatic Synthesis of Heparin”, Liu and Liu describe novel enzymatic approaches for the biosynthesis of heparin sulfate that mimic E. coli heparosan.

Discovering new and sustainable resources can help refuel industrial biotech­nology. Adverse environmental conditions which normal earth microbiota do not tolerate, offer potential sites to explore specific sets of microorganisms desig­nated as “Extremophiles”. The discovery of these microorganisms has enabled the biotechnology industry to innovate unconventional bioproducts i. e. “Extremolytes”

[9] . In Chapter 15 “Extremophiles: Sustainable Resource of Natural Compounds — Extremolytes”, Kumar et al. provide an overview of these extreme habitats. The applications of extremophiles and their products, extremolytes, with their possible implications for human use are also discussed broadly.

This book “Sustainable Biotechnology: Sources of Renewable Energy” is a col­lection of research reports and reviews elucidating several broad-ranging areas of progress and challenges in the utilization of sustainable resources of renewable energy, especially in biofuels. This book comes just at a time when government and industries are accelerating their efforts in the exploration of alternative energy resources, with expectations of the establishment of long-term sustainable alter­natives to petroleum-based liquid fuels. Apart from liquid fuel this book also

emphasizes the use of sustainable resources for value-added products, which may help in revitalizing the biotechnology industry at a broader scale.

We hope readers will find these articles interesting and informative for their research pursuits. It has been our pleasure to put together this book with Springer press. We would like to thank all of the contributing authors for sharing their quality research and ideas with the scientific community through this book.