Water recycle in biomass production processes

Various aspects of process water recycle in a continuous flow fermentation process are analyzed. Simple mass balance equations in terms of product and feed components for a single-stage reactor producing biomass are developed. Constraints on the recycle ratio, imposed by the efficiency of the dewatering stage, are examined. The recycle analysis is extended using a kinetic growth model incorporating water soluble product formation and growth inhibition. The potential effect of recycle on substrate conversion and product accumulation is also examined and the concept of a critical recycle ratio in fermentation processes is developed.     

Fermentation at non-conventional conditions in food- and bio-sciences by the application of advanced processing technologies

The interest in improving the yield and productivity values of relevant microbial fermentations is an increasingly important issue for the scientific community. Therefore, several strategies have been tested for the stimulation of microbial growth and manipulation of their metabolic behavior. One promising approach involves the performance of fermentative processes during non-conventional conditions, which includes high pressure (HP), electric fields (EF) and ultrasound (US). These advanced technologies are usually applied for microbial inactivation in the context of food processing. However, the approach described in this study focuses on the use of these technologies at sub-lethal levels, since the aim is microbial growth and fermentation under these stress conditions. During these sub-lethal conditions, microbial strains develop specific genetic, physiologic and metabolic stress responses, possibly leading to fermentation products and processes with novel characteristics. In some cases, these modifications can represent considerable improvements, such as increased yields, productivities and fermentation rates, lower accumulation of by-products and/or production of different compounds. Although several studies report the successful application of these technologies during the fermentation processes, information on this subject is still scarce and poorly understood. For that reason, the present review paper intends to assemble and discuss the main findings reported in the literature to date, and aims to stimulate interest and encourage further developments in this field.     

Paper pulpmill sludge utilization: techno-economic potential for fuel ethanol, methane and scp production

Various processes have been developed or proposed for converting cellulosic residues from pulp and paper mills into products which can be used for fuel or food. Among the promising practical possibilities are processes for ethanol, methane and microbial protein production by fermentation technology. Given the current Canadian financial climate and product demand, the results of techno-economic sensitivity analyses of these three process options indicate that microbial protein production for animal food applications is the most attractive followed by methane then ethanol, the last being quite uneconomical at present. Ironically, research emphasis seems to be placed in the reverse order. It is evident that the relevant costs of upstream and downstream processing in the various process proposals have not been adequately addressed. Case studies of several scenarios illustrate the problems.     

Process design and economic studies of alternative fermentation methods for the production of ethanol

Cell recycle and vacuum fermentation processes are described for the continuous production of ethanol. Preliminary process design studies are employed to make an economic comparison of these alternative fermentation schemes with continuous and batch fermentation technologies. Designs are based on a production capacity of 78,000 gal 95% ethanol (EtOH)/day employing molasses as the fermentation substrate. The studies indicate that a 57% reduction in fixed capital investment is realized by continuous rather than batch operation. Further decreases in required capital investment of 68 and 71% over batch fermentation were obtained for cell recycle and vacuum operation, respectively. However, ethanol production costs were dominated by the cost of molasses, representing over 75% of the total manufacturing cost. But, when a reasonable yeast by-product credit was assumed, the net production cost for 95% ethanol was estimated at 82.3 and 80.6 cent/gal, for the cell recycle and vacuum processes, respectively.     

An integrated approach: advances in the use of Clostridium for biofuel

Almost 90% of our energy comes from fossil fuels, which are both limited and polluting, hence the need to find alternative sources. Biofuels can provide a sustainable and renewable source of energy for the future. Recent significant advances in genetic engineering and fermentation technology have made microbial bio-based production of chemicals from renewable resources more viable. Clostridium species are considered as promising micro-organisms for the production of a wide range of chemicals for industrial use. However, a number of scientific challenges still need to be overcome to facilitate an economically viable production system. These include the use of cheap non-food-based substrates, a better understanding of the metabolic processes involved, improvement of strains through genetic engineering and innovation in process technology. This paper reviews recent developments in these areas, advancing the use of Clostridium within an industrial context especially for the production of biofuels.     

Process engineering for a membrane recycle fermentor

Membrane recycle fermentors are used successfully on laboratory scale to increase the efficiency of fermentation processes. The design of a process on larger scale however is obstructed by the lack of relevant data in literature. Compared to a stand-alone fermentor a membrane recycle fermentor presents new features which must be considered in the design. These features include the use of high density cultures, the additional volume in the membrane section and the circulation of the broth. In this theoretical study these aspects are analyzed with the characteristic time concept, in case of an ethanol fermentation integrated with microfiltration. The analysis shows that depending on the reactor configuration used concentration gradients can be expected. These gradients may decrease the efficiency of the fermentation, or can be advantageous, for example by letting the substrate conversion approach completion in the membrane section.     

Water reuse in the L-lysine fermentation process

L-Lysine is produced commercially by fermentation. As is typical for fermentation processes, a large amount of liquid waste is generated. To minimize the waste, which is mostly the broth effluent from the cation exchange column used for l-lysine recovery, we investigated a strategy of recycling a large fraction of this broth effluent to the subsequent fermentation. This was done on a labscale process with Corynebacterium glutamicum ATCC 21253 as the l-lysine-producing organism. Broth effluent from a fermentation in a defined medium was able to replace 75% of the water for the subsequent batch; this recycle ratio was maintained for three sequential batches without affecting cell mass and l-lysine production. Broth effluent was recycled at 50% recycle ratio in a fermentation in a complex medium containing beet molasses. The first recycle batch had an 8% lower final l-lysine level, but 8% higher maximum cell mass. In addition to reducing the volume of liquid waste, this recycle strategy has the additional advantage of utilizing the ammonium desorbed from the ion-exchange column as a nitrogen source in the recycle fermentation. The major problem of recycling the effluent from the complex medium was in the cation-exchange operation, where column capacity was 17% lower for the recycle batch. The loss of column capacity probably results from the buildup of cations competing with l-lysine for binding. (c) 1996 John Wiley & Sons, Inc.     

Solid-state fermentation

Solid-state fermentation has emerged as a potential technology for the production of microbial products such as feed, fuel, food, industrial chemicals and pharmaceutical products. Its application in bioprocesses such as bioleaching, biobeneficiation, bioremediation, biopulping, etc. has offered several advantages. Utilisation of agro-industrial residues as substrates in SSF processes provides an alternative avenue and value-addition to these otherwise under- or non-utilised residues. Today with better understanding of biochemical engineering aspects, particularly on mathematical modelling and design of bioreactors (fermenters), it is possible to scale up SSF processes and some designs have been developed for commercialisation. It is hoped that with continuity in current trends, SSF technology would be well developed at par with submerged fermentation technology in times to come.     

S-腺苷甲硫氨酸的研究进展

S-腺苷甲硫氨酸(SAM)是甲硫氨酸和三磷酸腺苷相结合的代谢物,广泛存在于动植物和微生物体内,参与40多种生化反应,主要作为三种代谢途径(转甲基、转硫基、转氨丙基)的前体,临床上被广泛用于治疗肝病、抑郁症、关节炎等。SAM的制备方法主要有化学合成法、酶促合成法、发酵法三种。化学合成的SAM是消旋体,需进行光学拆分,且存在产率低、原料L-高半胱氨酸价格昂贵和环境污染等问题。酶促合成法合成的SAM纯度高,但原料ATP成本太高。发酵法已成为目前生产SAM最常用的方法,欧洲利用发酵法生产SAM已实现了产业化,但国内的起步较晚,目前还处于实验室研究阶段。因此,应加强发酵法生产SAM的产业化关键技术研究。     

Improvement of microbial strains and fermentation processes

Improvement of microbial strains for the over-production of industrial products has been the hallmark of all commercial fermentation processes. Conventionally, strain improvement has been achieved through mutation, selection, or genetic recombination. Over-production of primary or secondary metabolites is a complex process, and successful development of improved strains requires a knowledge of physiology, pathway regulation and control, and the design of creative screening procedures. In addition, it requires mastery of the fermentation process for each new strain, as well as sound engineering know-how for media-optimization and the fine-tuning of process conditions. This review focuses on the various options that may be employed to improve microbial strains and addresses the complex problems of screening, the tools and technology behind the selection of targeted organisms, and the importance of process optimization. Furthermore, this review discusses new and emerging technologies and designing optimized media for tracking mutants with enhanced productivity or other desired attributes. Received: 7 February 2000 / Received revision: 2 May 2000 / Accepted: 2 May 2000     

Biotechnological potential of coffee pulp and coffee husk for bioprocesses

Advances in industrial biotechnology offer potential opportunities for economic utilization of agro-industrial residues such as coffee pulp and coffee husk. Coffee pulp or husk is a fibrous mucilagenous material (sub-product) obtained during the processing of coffee cherries by wet or dry process, respectively. Coffee pulp/husk contains some amount of caffeine and tannins, which makes it toxic in nature, resulting the disposal problem. However, it is rich in organic nature, which makes it an ideal substrate for microbial processes for the production of value-added products. Several solutions and alternative uses of the coffee pulp and husk have been attempted. These include as fertilizers, livestock feed, compost, etc. However, these applications utilize only a fraction of available quantity and are not technically very efficient. Attempts have been made to detoxify it for improved application as feed, and to produce several products such as enzymes, organic acids, flavour and aroma compounds, and mushrooms, etc. from coffee pulp/husk. Solid state fermentation has been mostly employed for bioconversion processes. Factorial design experiments offer useful information for the process optimization. This paper reviews the developments on processes and products developed for the value-addition of coffee pulp/husk through the biotechnological means.     

Criteria for lactic acid bacteria screening to enhance silage quality

The main challenge of ensiling is conserving the feed through a fermentative process that results in high nutritional and microbiological quality while minimizing fermentative losses. This challenge is of growing interest to farmers, industry and research and involves the use of additives to improve the fermentation process and preserve the ensiled material. Most studies involved microbial additives; lactic acid bacteria (LAB) have been the focus of much research and have been widely used. Currently, LABs are used in modern and sustainable agriculture because of their considerable potential for enhancing human and animal health. Although the number of studies evaluating LABs in silages has increased, the potential use of these micro-organisms in association with silage has not been adequately studied. Fermentation processes using the same strain produce very different results depending on the unique characteristics of the substrate, so the choice of silage inoculant for different starting substrates is of extreme importance to maximize the nutritional quality of the final product. This review describes the current scenario of the bioprospecting and selection process for choosing the best LAB strain as an inoculant for ensiling. In addition, we analyse developments in the fermentation process and strategies and methods that will assist future studies on the selection of new strains of LAB as a starter culture or inoculant.     

Biodiesel biorefinery: opportunities and challenges for microbial production of fuels and chemicals from glycerol waste

ABSTRACT: The considerable increase in biodiesel production worldwide in the last 5 years resulted in astoichiometric increased coproduction of crude glycerol. As an excess of crude glycerol hasbeen produced, its value on market was reduced and it is becoming a "waste-stream" insteadof a valuable "coproduct". The development of biorefineries, i.e. production of chemicals andpower integrated with conversion processes of biomass into biofuels, has been singled out asa way to achieve economically viable production chains, valorize residues and coproducts,and reduce industrial waste disposal. In this sense, several alternatives aimed at the use ofcrude glycerol to produce fuels and chemicals by microbial fermentation have beenevaluated. This review summarizes different strategies employed to produce biofuels andchemicals (1,3-propanediol, 2,3-butanediol, ethanol, n-butanol, organic acids, polyols andothers) by microbial fermentation of glycerol. Initially, the industrial use of each chemical isbriefly presented; then we systematically summarize and discuss the different strategies toproduce each chemical, including selection and genetic engineering of producers, andoptimization of process conditions to improve yield and productivity. Finally, the impact ofthe developments obtained until now are placed in perspective and opportunities andchallenges for using crude glycerol to the development of biodiesel-based biorefineries areconsidered. In conclusion, the microbial fermentation of glycerol represents a remarkablealternative to add value to the biodiesel production chain helping the development ofbiorefineries, which will allow this biofuel to be more competitive.     

Controlling accumulation of fermentation inhibitors in biorefinery recycle water using microbial fuel cells

Background  

Microbial fuel cells (MFC) and microbial electrolysis cells are electrical devices that treat water using microorganisms and convert soluble organic matter into electricity and hydrogen, respectively. Emerging cellulosic biorefineries are expected to use large amounts of water during production of ethanol. Pretreatment of cellulosic biomass results in production of fermentation inhibitors which accumulate in process water and make the water recycle process difficult. Use of MFCs to remove the inhibitory sugar and lignin degradation products from recycle water is investigated in this study.     

The effect of repeated temperature shock on baker's yeast

Summary In a recycle system in which evaporation is used for ethanol recovery during fermentation, temperature changes of the broth in the loop will occur. These repeated temperature shocks may have an effect on the microbial ethanol production rate. In this study such repeated temperature changes were simulated in a recycle system with ethanol production by baker's yeast. The magnitude of the temperature change, as well as the time of exposure to this change were found to have an effect on the ethanol production rate. A temperature increase from 30°C in the fermentor to 35°C or more in the recycle loop led to a significantly lower ethanol concentration in the broth. This effect became negligible at a short exposure time of 18 s of the yeast to the higher temperature. Correspondence to: R. G. J. M. van der Lans     

Fermentative production of butanol--the industrial perspective

A sustainable bacterial fermentation route to produce biobutanol is poised for re-commercialization. Today, biobutanol can compete with synthetic butanol in the chemical market. Biobutanol is also a superior biofuel and, in longer term, can make an important contribution towards the demand for next generation biofuels. There is scope to improve the conventional fermentation process with solventogenic clostridia and drive down the production cost of 1-butanol by deploying recent advances in biotechnology and engineering. This review describes re-commercialization efforts and highlights developments in feedstock utilization, microbial strain development and fermentation process development, all of which significantly impact production costs.     

Broth recycle in a yeast fermentation

Fermentation is a water-intensive process requiring treatment of large amounts of effluent broth. It is desirable to increase the ratio of product produced to the volume of effluent by minimizing the discharge of effluent from the fermentation process. A study of recycling spent fermentation process. A study of recycling spent fermentation broth for the subsequent fermentation was carried out with Apiotrichum curvatum an oleaginous yeast, as the working culture. Spent broth from a defined medium was recycled t replace as much as 75% of the water and salts for subsequent batches and this was repeated for seven sequential batches without affecting cell mass and lipid production. A 64% vlume reduction of wastewater was achieved in this manner. However, when using whey permeate as the medium, lipid production dropped after three consecutive recycle operations at 50% recycle, and after two consecutive recycle operations at 75% and 100% recycle. Accumulation of ions in the broth appeared to be responsible for the inhibition. An ion exchange step was able to eliminate the ion buildup and restore fermentation performance. (c) 1994 John Wiley & Sons, Inc.     

Key technologies for the industrial production of fumaric acid by fermentation

The growing concern about the safety of food and dairy additives and the increasing costs of petroleum-based chemicals have rekindled the interest in the fermentation processes for fumaric acid production. The key problems of the industrial production of microbial fumaric acid are reviewed in this paper. Various strategies, including strain improvement, morphology control, substrate choice, fermentation process and separation process, are summarized and compared, and their economical possibilities for industrial processes are discussed. The market prospects and technological strategies for value-added fumaric acid derivatives are also addressed. The future prospects of microbial fumaric acid production are proposed at the end of this article.     

Functional yeast starter cultures for cocoa fermentation

The quest to develop a performant starter culture mixture to be applied in cocoa fermentation processes started in the 20th century, aiming at achieving high-quality, reproducible chocolates with improved organoleptic properties. Since then, different yeasts have been proposed as candidate starter cultures, as this microbial group plays a key role during fermentation of the cocoa pulp-bean mass. Yeast starter culture-initiated fermentation trials have been performed worldwide through the equatorial zone and the effects of yeast inoculation have been analysed as a function of the cocoa variety (Forastero, Trinitario and hybrids) and fermentation method (farm-, small- and micro-scale) through the application of physicochemical, microbiological and chemical techniques. A thorough screening of candidate yeast starter culture strains is sometimes done to obtain the best performing strains to steer the cocoa fermentation process and/or to enhance specific features, such as pectinolysis, ethanol production, citrate assimilation and flavour production. Besides their effects during cocoa fermentation, a significant influence of the starter culture mixture applied is often found on the cocoa liquors and/or chocolates produced thereof. Thus, starter culture-initiated cocoa fermentation processes constitute a suitable strategy to elaborate improved flavourful chocolate products.     

Microbial production of small peptide: pathway engineering and synthetic biology

Small peptides are a group of natural products with low molecular weights and complex structures. The diverse structures of small peptides endow them with broad bioactivities and suggest their potential therapeutic use in the medical field. The remaining challenge is methods to address the main limitations, namely (i) the low amount of available small peptides from natural sources, and (ii) complex processes required for traditional chemical synthesis. Therefore, harnessing microbial cells as workhorse appears to be a promising approach to synthesize these bioactive peptides. As an emerging engineering technology, synthetic biology aims to create standard, well-characterized and controllable synthetic systems for the biosynthesis of natural products. In this review, we describe the recent developments in the microbial production of small peptides. More importantly, synthetic biology approaches are considered for the production of small peptides, with an emphasis on chassis cells, the evolution of biosynthetic pathways, strain improvements and fermentation.