Biotechnology in China III: Biofuels and Bioenergy

Second-generation bioethanol made from lignocellulosic biomass is considered one of the most promising biofuels. However, the enzymatic hydrolysis of the cellulose component to liberate glucose for ethanol fermentation is one of the major barriers for the process to be economically competitive because of the recalcitrance of feedstock. In this chapter, the progress on the understanding of the mechanisms of lignocellulose degradation, as well as the identification and optimization of fungal cellulases, cellulolytic strains, and cellulase production is reviewed. The physiologic functions and enzymatic mechanisms of two groups of enzymes involved in lignocellulose degradation, cellulases and hemicellulases, are discussed, and the synergism of the cellulase components during lignocellulose degradation is addressed. Furthermore, the methods for screening filamentous fungal strains capable of degrading lignocellulose are evaluated and the production of cellulases by these fungal strains is discussed. Aside from traditional mutagenesis for improving the secretion level and enzymatic activities of cellulases from filamentous fungal species, genetic engineering of strains and protein engineering on cellulase molecules are also highlighted.

China is suffering from a sustained shortage of crude oil supply, making fuel ethanol and other biofuels alternative solutions for this issue. However, taking into account the country’s large population and dwindling arable land due to rapid urbanization, it is apparent that current fuel ethanol production from grain-based feedstocks is not sustainable, and lignocellulosic biomass, particularly agricultural residues that are abundantly available in China, is the only choice for China to further expand its fuel ethanol production, provided economically viable processes can be developed. In this chapter, cutting edge progress in bioethanol is reviewed, with a focus on the understanding of the molecular structure of the feedstock, leading pretreatment technologies, enzymatic hydrolysis of the cellulose component and strategies for the co-fermentation of the C5 and C6 sugars with engineered microorganisms. Finally, process integration and optimization is addressed with a case study on the COFCO Corporation’s pilot plant, and challenges and perspectives for commercial production of bioethanol are highlighted.

At present, traditional fossil fuels are used predominantly in China, presenting the country with challenges that include sustainable energy supply, energy efficiency improvement, and reduction of greenhouse gas emissions. In 2007, China issued The Strategic Plan of the Mid-and-Long Term Development of Renewable Energy, which aims to increase the share of clean energy in the country’s energy consumption to 15% by 2020 from only 7.5% in 2005. Biodiesel, an important renewable fuel with significant advantages over fossil diesel, has attracted great attention in the USA and European countries. However, biodiesel is still in its infancy in China, although its future is promising. This chapter reviews biodiesel production from conventional feedstocks in the country, including feedstock supply and state of the art technologies for the transesterification reaction through which biodiesel is made, particularly the enzymatic catalytic process developed by Chinese scientists. Finally, the constraints and perspectives for China’s biodiesel development are highlighted.

Algal feedstock is the foundation of the emerging algal biofuel industry. However, few algae found in nature have demonstrated the combination of high biomass accumulation rate, robust oil yield and tolerance to environmental stresses, all complex traits that a large-scale, economically competitive production scheme demands. Therefore, untangling the intricate sub-cellular networks underlying these complex traits, in one or a series of carefully selected algal research models, has become an urgent research mission, which can take advantage of the emerging model oleaginous microalgae that have already demonstrated small, simple and tackleable genomes and the potential for large-scale open-pond cultivation. The revolutions in whole-genome-based technologies, coupled with systems biology, metabolic engineering and synthetic biology approaches, would enable the rational design and engineering of algal feedstock and help to fill the gaps between the technical and economical reality and the enormous potential of algal biofuels.

China initiated its acetone–butanol–ethanol (ABE) industry in the 1950s; it peaked in the 1980s, and ended at the end of the last century owing to the development of more competitive petrochemical pathways. However, driven by the high price of crude oil and environmental concerns raised by the over-consumption of petrochemical products, biofuels and bio-based chemicals including butanol have garnered global attention again. Currently, butanol produced from ABE fermentation is mainly used as an industrial solvent or a platform chemical for several bulk derivatives, and is also believed to be a potential biofuel. A number of plants have been built or rebuilt in recent years in China for butanol production with the ABE process. Chinese researchers also show great interest in the improvement of the production strains and corresponding processes. They have applied conventional mutagenesis methods to improve butanol-producing strains such as the Clostridium acetobutylicum mutant strains EA2018 (butanol ratio of 70%) and Rh8 (butanol tolerance of 19 g/L). The omics technologies, such as genome sequencing, proteomic and transcriptomic analysis, have been adapted to elucidate the characteristics of different butanol-producing bacteria. Based on the group II intron method, the genetic manipulation system of C. acetobutylicum was greatly improved, and some successful engineering strains were developed. In addition, research in China also covers the downstream processes. This article reviews up-to-date progress on biobutanol production in China.

China’s energy requirements and environmental concerns have stimulated efforts toward developing alternative liquid fuels. Compared with fuel ethanol, branched-chain higher alcohols (BCHAs), including isopropanol, isobutanol, 2-methyl-1-butanol, and 3-methyl-1-butanol, exhibit significant advantages, such as higher energy density, lower hygroscopicity, lower vapor pressure, and compatibility with existing transportation infrastructures. However, BCHAs have not been synthesized economically using native organisms, and thus their microbial production based on metabolic engineering and synthetic biology offers an alternative approach, which presents great potential for improving production efficiency. We review the current status of production and consumption of BCHAs and research progress regarding their microbial production in China, especially with the combination of metabolic engineering and synthetic biology.

Biogas technology has been practiced for over a century and is widely used in full-scale facilities in China. However, there are still many technological and economic barriers to be overcomed in its applications. Recent advances and multi-disciplinary cooperations in microbiology, biochemistry, and engineering science are bringing new promises of a better understanding and control of the anaerobic digestion processes, and thus a renaissance of this technology. In particular, great progress in biogas technology has been achieved in China in the approach to larger-scale and more widespread applications. This chapter overviews the recent advances in biogas technology in China, evaluates the current challenges, and discusses the emerging technologies and future perspectives.

Significant progress has been achieved in China for biohydrogen production from organic wastes, particularly wastewater and agricultural residues, which are abundantly available in China. This progress is reviewed with a focus on hydrogen-producing bacteria, fermentation processes, and bioreactor configurations. Although dark fermentation is more efficient for hydrogen production, by-products generated during the fermentation not only compromise hydrogen production yield but also inhibit the bacteria. Two strategies, combination of dark fermentation and photofermentation and coupling of dark fermentation with a microbial electrolysis cell, are expected to address this issue and improve hydrogen production as well as substrate utilization, which are also discussed. Finally, challenges and perspectives for biohydrogen production are highlighted.

Microbial fuel cells (MFCs) have been progressing at an amazing speed in the past few years, with higher power density but lower cost being continuously achieved. However, most of the studies to date have been conducted at laboratory scale, and many technological and economic barriers remain to be overcome prior to large-scale application of the MFC technique. In recent years, China has been playing an increasingly important role in this field, and has contributed considerably to moving MFCs forward toward large-scale implementations for both power generation and extended applications. Nevertheless, the development of MFCs is still in its infancy, the power density needs to be further improved, the cost reduced and a better understanding gained on the underlying mechanisms of electron generation and flow. All these warrant further investigations at both laboratory and pilot levels, and more cooperation of scientists and engineers from different disciplines and countries. In this review, we highlight the progress achieved to date in MFC technology, especially in China, and discuss the challenges and future opportunities.

Industrial processes of lignocellulosic material have made use of only the hexose component of the cellulose fraction. Pentoses and some minor hexoses present in the hemicellulose fraction, which may represent as much as 40% of lignocellulosic biomass, have in most cases been wasted. The lack of good methods for utilization of hemicellulose sugars is a key obstacle hindering the development of lignocellulose-based ethanol and other biofuels. In this chapter, we focus on the utilization of hemicellulose sugars, the structure of hemicellulose and its hydrolysis, and the biochemistry and process technology involved in their conversion to valuable fuels and chemicals.