Abstract:Biofuels and bioenergy not only benefit independence of energy supply, but also mitigate CO2 emissions. This special issue includes review reports and research articles involving various biofuels and bioenergy products and systems such as fuel ethanol, biodiesel, biogas, biohydrogen, microbial fuel cells and microbial electrolysis cells. Both fundamental research and technology development are highlighted. And in the meantime, challenges for large scale production and application of biofuels and bioenergy are discussed. Taking advantages of modern biotechnology advances, solutions to address these challenges are envisioned.

Abstract:The availability of crop residues in China is reviewed in this article. The definition of crop residues is clarified as the total byproducts of field production and processing industry thereafter, and methodology for evaluating crop residues is discussed. Based on literature, the progress on the crop residue assessment is addressed. The annual field crops residues in China from 1991 to 1999 were estimated between 6.0?6.8 hundred million tons, while the data for the process residues were not available. From 2000 to 2007, the annual crop residues were estimated between 5.9?7.3 hundred million tons, while the processing residues at the range of 0.9?1.1 hundred million tons. The reasons for the significant variations are due to the disagreement on crop residue definition, different, even inaccurate residue to grain ratio data used in the estimations, and the lacking of clear understanding on the statistical analysis and grain outputs related to the crop residue evaluation. With the complete statistic analysis method, the author’s group evaluated the residues in 2006 and 2007 to be 7.4 hundred million tones in total, including 6.5 hundred million tons for field crop residues and 0.9 hundred million tons for process residues. Moreover, the geographic distribution of the field crop residues was analyzed based on the harvest indices (HI) tested within the near 5 years.

Abstract:Biofuels and bio-based chemicals from lignocellulosic biomass are sustainable, making them alternatives to petroleum-derived fuels and chemicals to address the challenges of the shortage of crude oil supply and climate change resulted from the overconsumption of petroleum-based products, particularly in China. However, high cost in liberating sugars from lignocellulosic biomass is still the bottleneck of the commercialization of biofuels and bio-based chemicals. In this article, the major components of cellulases and their synergistic role in the hydrolysis of pre-treated biomass is reviewed, followed by how to evaluate the enzymatic hydrolysis. With the elucidation of the underlying mechanism of the conformations of the enzyme molecules and their effectiveness in attacking cellulose substrate, more efficient enzymes are expected to be developed. Using the high production strain Penicillium decumbens, the on-site production of cellulases for cellulose ethanol production is discussed.

Abstract:Ethanol production from lignocelluloses of consolidated bioprocessing (CBP) is a system in which cellulase and hemicellulase production, substrate hydrolysis, and fermentation are combined or partially combined by ethanologen microorganisms that express cellulolytic or hemicellulolytic enzymes or engineering cellulolytic microorganisms with ethanol production properties. Due to its potential for significant cost reduction, CBP is receiving more and more attention. In this review article, we discuss the factors that influence the expression level of cellulases in Saccharomyces cerevisiae and updated progress in bioethanol production from lignocellulose by the CBP strategy using the yeast species.

Abstract:Biofuels are renewable and environmentally friendly, but high production cost makes them economically not competitive, and the development of robust strains is thus one of the prerequisites. In this article, strain improvement studies based on the information from systems biology studies are reviewed, with a focus on their applications on stress tolerance improvement. Furthermore, the contribution of systems biology, synthetic biology and metabolic engineering in strain development for biofuel production is discussed, with an expectation for developing more robust strains for biofuel production.

Abstract:The regions suitable for growing cassava include 5 provinces in Southern China, with Guangxi alone accounting for over 65% of the total cassava production in the country. In this article, the state-of-the-art development of fuel ethanol production from cassava in China is illustrated by the construction of the cassava fuel ethanol plant with its annual production capacity of 200 000 metric tons. And in the meantime, problems and challenges encountered in the development of China’s cassava fuel ethanol are highlighted and the strategies to address them are proposed.

Abstract:Biodiesel is renewable and environmentally friendly; however, there are still many challenges for its commercial production as an alternative of petroleum-based transportation fuels, particularly in China with very limited resources for its biofuels development. In this article, the update progress of biodiesel R & D and production is reviewed, with a focus on its feedstock supply, manufacturing processes, quality control and byproduct utilization. It is concluded that the strategy of biorefinery to ultimately explore feedstock potentials will make biodiesel production more economically competitive.

Abstract:This paper reports the progress of biodiesel production with enzymatic catalysis in Beijing University of Chemical Technology, one of the leaders in biodiesel R & D in China, which includes screening of high-yield lipase production strains, optimization and scale-up of the lipase fermentation process, lipase immobilization, bioreactor development and scale-up, biodiesel separation and purification and the by-product glycerol utilization. Firstly, lipase fermentation was carried out at industrial scale with the 5 m3 stirred tank bioreactor, and the enzyme activity as high as 8 000 IU/mL was achieved by the species Candida sp. 99-125. Then, the lipase was purified and immobilized on textile membranes. Furthermore, biodiesel production was performed in the 5 m3 stirred tank bioreactor with an enzyme dosage as low as 0.42%, and biodiesel that met the German biodiesel standard was produced. And in the meantime, the byproduct glycerol was used for the production of 1,3-propanediol to partly offset the production cost of biodiesel, and 76.1 g/L 1,3-propanediol was obtained in 30 L fermentor with the species Klebsiella pneumoniae.

Abstract:With the dwindling of fossil fuels supply and the urgent need for the development of low-carbon economy, microalgae bioenergy, both renewable and environmentally friendly, has become one of the worldwide focuses. Given its benefit to the security of national energy supply, microalgae energy is particularly significant for China, with more than 50% crude oil imported and limited arable land for grain and edible oil production. In this article, both the advantages of microalgae bioenergy and the challenges of its development are addressed, which involves fundamental research and technology development as well as commercial production. Furthermore, strategies are proposed for China’s microalgae bioenergy development, and its prospects are projected.

Abstract:Butanol is not only an important chemical feedstock but also expected to become a new generation biofuel. Thus, biological butanol production using renewable feedstocks has attracted renewed attention due to the worries of global oil supply and its impact on social and economic development. However, compared with petrochemical-derived butanol, biological butanol production is still not economically competition, because of its major drawbacks: high cost of the feedstocks, low butanol concentration in the fermentation broth and the co-production of low-value byproducts acetone and ethanol. Recently, Shanghai cooperative bio-butanol group (SCBG) developed a simple-to-complex technical route to improve bio-butanol production with a focus on: increasing butanol ratio in the solvent through metabolic engineering of Clostridia spp.; introducing and optimizing the butanol synthetic pathway in the species with high butanol tolerance; overcoming the glucose repression effect to utilize low-cost non-grain based feedstocks. SCBG believes that, through extensive domestic and international industry-university-research cooperation, a sustainable and economically viable process for biological butanol production can be established in the near future.

Abstract:Dwindling supplies of conventional energy sources and the demand to increase the share of renewable energy for sustainability have increased the significance of biogas, the product of synergistic fermentation of biodegrable organic wastes from municipal, agricultural and industrial activities by microbial populations under anaerobic conditions. With extensive research and engineering practice, many technologies and modes have been developed for biogas production and application. Currently, the most widely used mode is the complete-mixing mesophilic fermentation. Europe, especially Germany, is leading the world in the combined heat and power production (CHP) from biogas. In this paper, updated progress in biogas technologies is reviewed, with focuses on anaerobic microorganisms, bioreactor configurations and process development, biogas production and applications, in which perspectives of biogas as a clean and renewable energy are projected.

Abstract:Hydrogen production from lignocellulosic biomass is both sustainable and environmentally friendly, which is garnering more and more attention across the world, with an expectation to challenge the shortage of fossil fuels supply and climate change as well. In this article, the update research progress and technology development of biohydrogen production are reviewed, with a focus on biomass pretreatment, hydrogen-producing microorganisms and process engineering strategies. And in the meantime, a roadmap for more efficient and economic biohydrogen production is envisioned.

Abstract:Microbial fuel cells (MFCs) that can harvest biomass energy from organic wastes through microbial catalysis have garnered more and more attention within the past decade due to its potential benefits to ecological environment. In this article, the updated progress in MFCs is reviewed, with a focus on frontier technologies such as chamber configurations, feedstock varieties and the integration of MFCs with microbial electrolysis cells for hydrogen production. And on the other hand, the challenges like development of cost-effective electrode materials, improvement of biomass energy recovery and power output, design and optimization of commercial MFC devices are presented.

Abstract:The massive water and steam are consumed in the production of cellulose ethanol, which correspondingly results in the significant increase of energy cost, waster water discharge and production cost as well. In this study, the process strategy under extremely low water usage and high solids loading of corn stover was investigated experimentally and computationally. The novel pretreatment technology with zero waste water discharge was developed; in which a unique biodetoxification method using a kerosene fungus strain Amorphotheca resinae ZN1 to degrade the lignocellulose derived inhibitors was applied. With high solids loading of pretreated corn stover, high ethanol titer was achieved in the simultaneous saccharification and fermentation process, and the scale-up principles were studied. Furthermore, the flowsheet simulation of the whole process was carried out with the Aspen plus based physical database, and the integrated process developed was tested in the biorefinery mini-plant. Finally, the core technologies were applied in the cellulose ethanol demonstration plant, which paved a way for the establishment of an energy saving and environment friendly technology of lignocellulose biotransformation with industry application potential.

Abstract:The recalcitrance of lignocellulosic biomass makes its hydrolysis by cellulases less effective, and the consolidated bioprocessing (CBP) strategy that combines enzyme production, cellulose hydrolysis and fermentation, particularly the synergetic role of different microbes in attacking cellulose component could be a solution. In this article, a facultative anaerobe microbial consortium named H was isolated, which exhibited high stability even after 30 subcultures, with pH ranging from 6 to 9. Within three days, 0.5 g filter paper immerged in 100 mL PCS buffer was completely degraded, and 1.54 g/L ethanol was produced, correspondingly. Further analysis on the component of the microbe consortium was carried out though 16S rDNA and DGGE, and Clostridium thermosuccinogene, Clostridium straminisolvens and Clostridium isatidis that can directly convert cellulose to ethanol were identified, indicating that Clostridium spp. played important role in cellulose degradation through the synergistic coordination of different species, and the characterization of the consortium will benefit the analysis of the underlying mechanisms as well as the optimization of the CBP process for more efficient cellulose degradation and ethanol production.

Abstract:A robust strain of the species Saccharomyces cerevisiae CGMCC1949 was screened and identified, and advanced solid state fermentation (ASSF) technology for fuel ethanol production from sweet sorghum stalks was thus developed. The fermentation time was shortened to less than 30 h, and ethanol yield was 92% of its theoretical maximum. And in the meantime, the cost-effective storage was established for sweet sorghum stalks, with less than 5% sugar loss after 200 days of storage, making the plant operation could extend up to 200 days without feedstock shortage. With the fermentation kinetics and heat-mass transfer models, modeling of the ASSF process was investigated, and the rotating drum bioreactor was designed. Furthermore, the ASSF technology was successfully applied in the pilot plant in which the rotating drum bioreactor was scaled up to 127 m3, and ethanol yield of 91% was achieved. At the end, techno-economic analysis (TEA) conducted by ASPEN indicated that ethanol production from sweet sorghum stalks by the ASSF is economically competitive.

Abstract:In order to explore the feasibility of planting sweet sorghum in sugarcane growing area to prolong milling duration for bioethanol production, 15 varieties were sown monthly from March to September in Liuzhou of Central Guangxi Zhuang Autonomous Region. Yields of fresh stem, grain and leave were documented. The results showed that all varieties grew well when sown from March to August, but could not get mature when sown after late September. The high fresh stem yields were observed for the varieties Sart and PT3-S, 79.28 t/hm2 and 78.58 t/hm2 for single growing season, and 157.95 t/hm2 and 155.25 t/hm2 for two growing seasons. Ripening began from the end of June to late December, making the feed stock available for ethanol production from July to the end of December, even January next year.

Abstract:Jerusalem artichoke tubers with inulin as major component are potential feedstock for fuel ethanol production, and Kluyveromyces cicerisporus Y179 expressing high level of inulinase is suitable for ethanol production with this feedstock by simultaneous saccharification and fermentation approach. In this article, the impact of inoculum, aeration and temperature on ethanol production by the yeast was studied. The experimental results illustrated that inoculum with different levels and seed collected at different cultivation times had negligible effect, while anaerobic conditions enhanced ethanol production, and more ethanol was produced by the yeast at 30°C than at 37°C or 42°C. The medium using Jerusalem artichoke tuber meal as sole component with 22% (W/V) total sugars was inoculated with 36 h-precultured seed at 10% (V/V), and the batch fermentation was conducted in a 5 L fermentor at 30°C with a stirring speed of 300 r/min under anaerobic conditions. After 144 h, 12.3% (V/V) ethanol was produced and the yield of ethanol from sugars was 86.9% of its theoretical one, with 93.6% sugars consumed. These results indicate that K. cicerisporus Y179 is a promising candidate for industrial ethanol production using Jerusalem artichoke tuber feedstock.

Abstract:Butanol production from acid hydrolysate of Jerusalem artichoke juice by Clostridium acetobutylicum L7 was investigated, and it was found that natural components of the hydrolysate were suitable for solvent production with the species. With batch fermentation using the medium containing 48.36 g/L total sugars, 8.67 g/L butanol was produced at 60 h, and the ratio of butanol to acetone to ethanol was 0.58:0.36:0.06, which were similar to the fermentation with fructose as carbon source, but both of these two fermentations were slower than that with glucose as carbon source, indicating the fructose transport of the species might not be effective as that for glucose. When the total sugars of the medium were increased to 62.87 g/L, the residual sugars increased slightly from 3.09 g/L to 3.26 g/L, but butanol production of the fermentation system was improved significantly, with 11.21 g/L butanol produced and the ratio of butanol to acetone to ethanol at 0.64:0.29:0.05, which illustrated that an excess in sugars enhanced the butanol biosynthesis of the species by compromising its acetone production. When the sugar concentration of the medium was further increased, much more sugars were remained unconsumed, making the process economically unfavourable.

Abstract:To shorten the cultivation time and reduce the consumption of raw materials for microbial lipid production, oleaginous yeast Rhodosporidium toruloides AS 2.1389 was cultivated using a two-stage culture mode, in which the cell propagation and lipid accumulation were separated. The yeast cells recovered from the propagation culture were re-suspended in glucose solution for lipid accumulation, through which lipid content over 55% of the dry cell weight was achieved, the longer the propagation stage was, the higher the lipid content. Analysis of the lipid indicated that the long-chain fatty acids with 16 and 18 carbon atoms were major components, suggesting that the lipid can be an alternative feedstock for biodiesel production.

Abstract:Tetraselmis subcordiformis, a marine green alga, can produce hydrogen by photobiologically hydrolyzing seawater with hydrogenase. In this study, the preliminary purification of the enzyme was explored by ammonium sulfate precipitation, and the impact of sodium dithionite, b-mercaptoethanol and glycerol on the enzyme stability during the process was investigated. The experimental results illustrated that sodium dithionite provided significant protection on the hydrogenase by depleting oxygen, while glycerol, a protectant against the structure instability of the enzyme, also presented protection. Crude enzyme with specific activity of 0.557 U/mg protein was extracted using 60%?70% saturated ammonium sulfate solution supplemented with 200 mmol/L sodium dithionite and 5% glycerol, and the hydrogenase recovery yield was about 30%.

Abstract:To explore new microbial resources in deep subsurface oil reservoirs, strain DL-7 was isolated with Hungate technology from oil reservoir water sampled from Dagang oilfield, China. Physiological and biochemical examinations showed that H2/CO2 is the unique substrate of the strain, which cannot metabolize formate, methanol, trimethylamine, acetate and other secondary alcohols. The optimum growth conditions were further identified to be 60°C, pH 7.0?7.5 and 0.25% NaCl. Moreover, the strain cannot grow without yeast extract. Analysis of its 16S rRNA sequence indicated that a similarity of 99.7% presents between the strain and the model species M. marburgensis DSM2133T (X15364).

Abstract:Improving stress tolerance of the microbial producers is of great importance for the process economy and efficiency of bioenergy production. Key genes influencing ethanol tolerance of brewing yeast can be revealed by studies on the molecular mechanisms which can lead to the further metabolic engineering manipulations for the improvement of ethanol tolerance and ethanol productivity. Trahalose shows protective effect on the cell viability of yeast against multiple environmental stress factors, however, further research is needed for the exploration of the underlying molecular mechanisms. In this study, the promoter region of the trehalose-6-phosphate synthase gene TPS1 was cloned from the self-flocculating yeast Saccharomyces cerevisiae flo, and a reporter plasmid based on the expression vector pYES2.0 on which the green fluorescence protein EGFP was directed by the TPS1 promoter was constructed and transformed to industrial yeast strain Saccharomyces cerevisiae ATCC4126. Analysis of the EGFP expression of the yeast transformants in presence of 7% and 10% ethanol revealed that the PTPS1 activity was strongly induced by 7% ethanol, showing specific response to ethanol stress. The results of this study indicate that trehalose biosynthesis in self-flocculating yeast is a protective response against ethanol stress.

Abstract:This research aimed to study the effect of distillage recycling on ethanol fermentation, the key glycolytic enzymes and cell composition of the self-flocculating yeast. With the self-flocculating yeast SPSC01 and medium composed of 220 g/L glucose, 8 g/L yeast extract and 6 g/L peptone, continuous ethanol fermentation was carried out at the dilution rate of 0.04 h?1 with a 1.5 L tank bioreactor. Fermentation broth was collected every 3 days, and ethanol and other volatile byproducts were removed by distillation, but the stillage with high boiling byproducts was recycled to prepare the medium instead of fresh water. The system was run for 20 days, during which ethanol and biomass concentrations in the effluent decreased continuously, indicating the significant inhibition of the high boiling byproducts accumulated within the system. Thus, the activities of the key enzymes of the glycolytic pathway: hexokinase, 6-phosphofructose kinase, and pyruvate kinase were analyzed, and it was observed that all of them were inhibited. Furthermore, the biosynthesis of the stress response metabolites glycerol and trehalose was investigated, and it was found that glycerol production that can protect yeast cells against osmotic pressure stress was enhanced, but trehalose biosynthesis that can protect yeast cells against ethanol inhibition was not improved, correspondingly. And in the meantime, the biosynthesis of the major intracellular components proteins and hydrocarbons was adjusted, correspondingly.