16604984
Electrolytic extraction drives volatile fatty acid chain elongation through lactic acid and replaces chemical pH control in thin stillage fermentation
BackgroundVolatile fatty acids (VFA) are building blocks for the chemical industry. Sustainable, biological production is constrained by production and recovery costs, including the need for intensive pH correction. Membrane electrolysis has been developed as an in situ extraction technology tailored to the direct recovery of VFA from fermentation while stabilizing acidogenesis without caustic addition. A current applied across an anion exchange membrane reduces the fermentation broth (catholyte, water reduction: H2O + e− → ½ H2 + OH−) and drives carboxylate ions into a clean, concentrated VFA stream (anolyte, water oxidation: H2O → 2e− + 2 H+ + O2).ResultsIn this study, we fermented thin stillage to generate a mixed VFA extract without chemical pH control. Membrane electrolysis (0.1 A, 3.22 ± 0.60 V) extracted 28 ± 6 % of carboxylates generated per day (on a carbon basis) and completely replaced caustic control of pH, with no impact on the total carboxylate production amount or rate. Hydrogen generated from the applied current shifted the fermentation outcome from predominantly C2 and C3 VFA (64 ± 3 % of the total VFA present in the control) to majority of C4 to C6 (70 ± 12 % in the experiment), with identical proportions in the VFA acid extract. A strain related to Megasphaera elsdenii (maximum abundance of 57 %), a bacteria capable of producing mid-chain VFA at a high rate, was enriched by the applied current, alongside a stable community of Lactobacillus spp. (10 %), enabling chain elongation of VFA through lactic acid. A conversion of 30 ± 5 % VFA produced per sCOD fed (60 ± 10 % of the reactive fraction) was achieved, with a 50 ± 6 % reduction in suspended solids likely by electro-coagulation.ConclusionsVFA can be extracted directly from a fermentation broth by membrane electrolysis. The electrolytic water reduction products are utilized in the fermentation: OH− is used for pH control without added chemicals, and H2 is metabolized by species such as Megasphaera elsdenii to produce greater value, more reduced VFA. Electro-fermentation displays promise for generating added value chemical co-products from biorefinery sidestreams and wastes.
3180327
Biotechnology-a sustainable alternative for chemical industry.
This review outlines the current and emerging applications of biotechnology, particularly in the production and processing of chemicals, for sustainable development. Biotechnology is "the application of scientific and engineering principles to the processing of materials by biological agents". Some of the defining technologies of modern biotechnology include genetic engineering; culture of recombinant microorganisms, cells of animals and plants; metabolic engineering; hybridoma technology; bioelectronics; nanobiotechnology; protein engineering; transgenic animals and plants; tissue and organ engineering; immunological assays; genomics and proteomics; bioseparations and bioreactor technologies. Environmental and economic benefits that biotechnology can offer in manufacturing, monitoring and waste management are highlighted. These benefits include the following: greatly reduced dependence on nonrenewable fuels and other resources; reduced potential for pollution of industrial processes and products; ability to safely destroy accumulated pollutants for remediation of the environment; improved economics of production; and sustainable production of existing and novel products.
11417035
Microbial electrosynthesis — revisiting the electrical route for microbial production
Microbial electrocatalysis relies on microorganisms as catalysts for reactions occurring at electrodes. Microbial fuel cells and microbial electrolysis cells are well known in this context; both use microorganisms to oxidize organic or inorganic matter at an anode to generate electrical power or H2, respectively. The discovery that electrical current can also drive microbial metabolism has recently lead to a plethora of other applications in bioremediation and in the production of fuels and chemicals. Notably, the microbial production of chemicals, called microbial electrosynthesis, provides a highly attractive, novel route for the generation of valuable products from electricity or even wastewater. This Review addresses the principles, challenges and opportunities of microbial electrosynthesis, an exciting new discipline at the nexus of microbiology and electrochemistry.
138237654
Separation and Purification Technologies in Biorefineries
Separation and purification processes play a critical role in biorefineries and their optimal selection, design and operation to maximise product yields and improve overall process efficiency. Separations and purifications are necessary for upstream processes as well as in maximising and improving product recovery in downstream processes. These processes account for a significant fraction of the total capital and operating costs and also are highly energy intensive. Consequently, a better understanding of separation and purification processes, current and possible alternative and novel advanced methods is essential for achieving the overall technoeconomic feasibility and commercial success of sustainable biorefineries.
85953041
What is vital (and not vital) to advance economically-competitive biofuels production
Since biofuels is a hot topic, many researchers new to this field are eager to propose different solutions while they often seem not to have full understanding of the current status of technologies and numerous (hidden) constraints. As a result, the general public, policymakers, academic researchers, and industrial developers have been assaulted by a wave of biased, misinterpreted, or outright false information. In reality, only a small fraction of exploding biofuels RD instead, it is a typical goal-oriented (engineering) project because so many constraints prevent economically competitive production of most advanced biofuels and are expected to do so in the future. In this opinion paper, I present some basic rules and facts in thermodynamics, physical chemistry, and special constraints in the transport sector, sort through and challenge some claimed breakthroughs or new directions, and identify vital topics to advance biofuels in the short and long terms. Simply speaking, energy efficiency is the most important long-term criterion whereas cost is the most important short-term criterion; eventually thermodynamics determines economics. For light-duty passenger vehicles, which consume ∼60% transportation fuels, cellulosic ethanol and butanol are the best short- and middle-term biofuels, whereas sugary hydrogen would be the ultimate biofuel in the long term. The top three priorities of biofuels R&D are (i) cost-effective release of sugars from lignocellulose, (ii) co-utilization of lignocellulose components for the production of value-added compounds that subsidize whole biorefineries, and (iii) enhancing the biomass-to-kinetic energy efficiency from conversions to prime movers through a potential evolutionary scenario from ethanol or butanol/internal combustion engines (ICE) to ethanol/hybrid diesel-like ICE to sugar hydrogen fuel cell vehicles.
22012578
Biowaste biorefinery in Europe: opportunities and research & development needs.
This review aims to explore the needs and opportunities of research & development in the field of biowaste biorefinery in Europe. Modern industry in recent years is giving its close attention on organic waste as a new precious bioresource. Specific biowaste valorisation pathways are focusing on food processing waste, being food sector the first manufacture in Europe. Anyway they need to be further tested and validated and then transferred at the larger scale. In particular, they also need to become integrated, combining biomass pretreatments and recovery of biogenic chemicals with bioconversion processes in order to obtain a large class of chemicals. This will help to (a) use the whole biowaste, by avoiding producing residues and providing to the approach the required environmental sustainability, and (b) producing different biobased products that enter different markets, to get the possible economical sustainability of the whole biorefinery. However, the costs of the developed integrated processes might be high, mostly for the fact that the industry dealing with such issues is still underdeveloped and therefore dominated by high processing costs. Such costs can be significantly reduced by intensifying research & development on process integration and intensification. The low or no cost of starting material along with the environmental benefits coming from the concomitant biowaste disposal would offset the high capital costs for initiating such a biorefinery. As long as the oil prices tend to increase (and they will) this strategy will become even more attractive.
9443396
Waste to bioproduct conversion with undefined mixed cultures: the carboxylate platform.
Our societies generate increasing volumes of organic wastes. Considering that we also need alternatives to oil, an opportunity exists to extract liquid fuels or even industrial solvents from these abundant wastes. Anaerobic undefined mixed cultures can handle the complexity and variability of organic wastes, which produces carboxylates that can be efficiently converted to useful bioproducts. However, to date, barriers, such as inefficient liquid product separation and persistence of methanogens, have prevented the production of bioproducts other than methane. Here, we discuss combinations of biological and chemical pathways that comprise the 'carboxylate platform', which is used to convert waste to bioproducts. To develop the carboxylate platform into an important system within biorefineries, we must understand the kinetic and thermodynamic possibilities of anaerobic pathways, understand the ecological principles underlying pathway alternatives, and develop superior separation technologies.
10416178
Carboxylate Platform: The MixAlco Process Part 1: Comparison of Three Biomass Conversion Platforms
To convert biomass to liquid fuels, three platforms are compared: thermochemical, sugar, and carboxylate. To create a common basis, each platform is fed “ideal biomass,” which contains polysaccharides (68.3%) and lignin (31.7%). This ratio is typical of hardwood biomass and was selected so that when gasified and converted to hydrogen, the lignin has sufficient energy to produce ethanol from the carboxylic acids produced by the carboxylate platform. Using balanced chemical reactions, the theoretical yield and energy efficiency were determined for each platform. For all platforms, the ethanol yield can be increased by 71% to 107% by supplying external hydrogen produced from other sources (e.g., solar, wind, nuclear, fossil fuels). The alcohols can be converted to alkanes with a modest loss of energy efficiency (3 to 5 percentage points). Of the three platforms considered, the carboxylate platform has demonstrated the highest product yields.
106645140
Bioprocessing for value-added products from renewable resources : new technologies and applications
I. Enabling Technologies II. Cultures for Bioprocessing III. Unconventional and Novel Bioprocesses IV. Feedstock Utilization Index
21411095
Recovery of carboxylic acids produced by fermentation.
Carboxylic acids such as citric, lactic, succinic and itaconic acids are useful products and are obtained on large scale by fermentation. This review describes the options for recovering these and other fermentative carboxylic acids. After cell removal, often a primary recovery step is performed, using liquid-liquid extraction, adsorption, precipitation or conventional electrodialysis. If the carboxylate is formed rather than the carboxylic acid, the recovery process involves a step for removing the cation of the formed carboxylate. Then, bipolar electrodialysis and thermal methods for salt splitting can prevent that waste inorganic salts are co-produced. Final carboxylic acid purification requires either distillation or crystallization, usually involving evaporation of water. Process steps can often be combined synergistically. In-situ removal of carboxylic acid by extraction during fermentation is the most popular approach. Recovery of the extractant can easily lead to waste inorganic salt formation, which counteracts the advantage of the in-situ removal. For industrial production, various recovery principles and configurations are used, because the fermentation conditions and physical properties of specific carboxylic acids differ.
10186123
Clostridium kluyverii, an Organism Concerned in the Formation of Caproic Acid from Ethyl Alcohol
When ethyl alcohol is acted upon by the methane-producing organism, Methanobacterium omelianskii, acetic acid is the sole oxidation product (Barker (1939-40, 1941)). But with alcoholcontaining enrichment cultures for the same organism it often happens that acetic acid is formed in only relatively small amounts, while most of the alcohol is converted into caproic and butyric acids (Barker (1937)). In some cultures as much as 75 per cent by weight of the volatile acid is caproic. Microscopic examination has shown that such caproic-acidproducing enrichment cultures always differ from those forming only acetic acid by containing, besides M. omelianskii, considerable numbers of a large, motile, spore-forming bacterium. The conclusion seemed justified that this latter organism either itself produces or at least helps to produce the caproic acid. However, direct proof of the participation of the spore-forming bacterium in caproic acid formation can be obtained only by studying the organism in pure culture. This communication describes the isolation, the general morphological and physiological characteristics and certain growtlh requirements of this bacterium. Also, evidence is presented which demonstrates that it is responsible for the conversion of ethyl alcohol to caproic acid. Enrichment and isolation. To obtain the caproic acid-producing organism, Clostridium kluyverii,1 the following enrichment medium (no. 1) made with tap water is used: C2H5OH 1 vol. per cent; K2HPO4 0.5 per cent; MgSO4 7H20 0.01 per cent; (NH4)2 SO4 0.03 per cent; FeSO4 .77H20 0.002 per cent; yeast autolysate 0.5
97035594
Chain elongation with reactor microbiomes: upgrading dilute ethanol to medium-chain carboxylates
Ethanol distillation in the biofuel industry is energetically expensive because ethanol is completely miscible in water. Upgrading ethanol into a hydrophobic chemical that is easier to separate would circumvent current fossil-fuel consumption for distillation. Here, we shaped a reactor microbiome to sequentially elongate carboxylic acids with 2-carbon units from dilute ethanol in yeast-fermentation beer. Our continuous bioprocess produced n-caproic acid, a 6-carbon-chain carboxylic acid that is more valuable than ethanol. No antimicrobials to inhibit methanogens were necessary. In-line product extraction achieved an n-caproic acid production rate exceeding 2 grams per liter of reactor volume per day, which is comparable to established bioenergy systems with microbiomes. Incorporation of other organics found in beer increased the mass of carbon in n-caproic acid by 10% compared to ethanol.
98639658
Biological formation of caproate and caprylate from acetate: fuel and chemical production from low grade biomass
This research introduces an alternative mixed culture fermentation technology for anaerobic digestion to recover valuable products from low grade biomass. In this mixed culture fermentation, organic waste streams are converted to caproate and caprylate as precursors for biodiesel or chemicals. It was found that acetate, as the main intermediate of anaerobic digestion, can be elongated to medium chain fatty acids with six and eight carbon atoms. Mixed microbial communities were able to produce 8.17 g l−1 caproate and 0.32 g l−1 caprylate under methanogenesis-suppressed conditions in a stable batch reactor run. The highest production rate was 25.6 mM C caproate per day with a product yield of 0.6 mol C per mol C. This elongation process occurred with both ethanol and hydrogen as electron donors, demonstrating the flexibility of the process. Microbial characterization revealed that the microbial populations were stable and dominated by relatives of Clostridium kluyveri.
206132456
High rate heptanoate production from propionate and ethanol using chain elongation.
Heptanoate (or enanthate), a saturated mono-carboxylate with seven carbon atoms, is a commercially produced biochemical building block with versatile applications. Currently, heptanoate is mainly derived from the oxidation of heptaldehyde, which can be obtained after pyrolysis of castor oil. The objective of this investigation was to achieve efficient high rate heptanoate production using a mixed culture chain elongation process based on propionate and ethanol. An efficient high rate heptanoate production using chain elongation could offer an alternative for heptanoate production from castor oil. The investigation was performed in an upflow anaerobic filter with a hydraulic retention time of 17 h. A heptanoate production rate of 4.5 g l(-1) d(-1) was achieved with a heptanoate concentration of 3.2 g l(-1). These results show sufficient potential to consider this approach as an alternative for heptanoate production from castor oil. Future research should make heptanoate production from propionate and ethanol more cost-effective.
13012812
Chain elongation in anaerobic reactor microbiomes to recover resources from waste.
Different microbial pathways can elongate the carbon chains of molecules in open cultures of microbial populations (i.e. reactor microbiomes) under anaerobic conditions. Here, we discuss three such pathways: 1. homoacetogenesis to combine two carbon dioxide molecules into acetate; 2. succinate formation to elongate glycerol with one carbon from carbon dioxide; and 3. reverse β oxidation to elongate short-chain carboxylates with two carbons into medium-chain carboxylates, leading to more energy-dense and insoluble products (e.g. easier to separate from solution). The ability to use reactor microbiomes to treat complex substrates can simultaneously address two pressing issues: 1. providing proper waste management; and 2. producing renewable chemicals and fuels.
14284304
In-line and selective phase separation of medium-chain carboxylic acids using membrane electrolysis.
We had extracted n-caproate from bioreactor broth. Here, we introduced in-line membrane electrolysis that utilized a pH gradient between two chambers to transfer the product into undissociated n-caproic acid without chemical addition. Due to the low maximum solubility of this acid, selective phase separation occurred, allowing simple product separation into an oily liquid containing ∼90% n-caproic and n-caprylic acid.
13396340
Substrate Preference in a Strain of Megasphaera elsdenii, a Ruminal Bacterium, and Its Implications in Propionate Production and Growth Competition
The NIAH 1102 strain of Megasphaera elsdenii utilized lactate in preference to glucose when the two substrates were present. Even when lactate was supplied to cells fermenting glucose, the cells switched substrate utilization from glucose to lactate and did not utilize glucose until lactate decreased to a low concentration (1 to 2 mM). Since substrate utilization was shifted gradually without intermittence, typical diauxic growth was not seen. The cyclic AMP content did not rise markedly with the shift in substrate utilization, suggesting that this nucleotide is not involved in the regulation of the shift. It was unlikely that propionate was produced from glucose, which was explicable by the fact that lactate racemase activity dropped rapidly with the exhaustion of lactate and cells actively fermenting glucose did not possess this enzyme. A coculture experiment indicated that M. elsdenii NIAH 1102 is overcome by Streptococcus bovis JB1 in the competition for glucose, mainly because M. elsdenii NIAH 1102 is obliged to utilize lactate produced by S. bovis JB1; i.e., glucose utilization by M. elsdenii NIAH 1102 is suppressed by the coexistence of S. bovis JB1.
5353714
In Situ Biphasic Extractive Fermentation for Hexanoic Acid Production from Sucrose by Megasphaera elsdenii NCIMB 702410
Hexanoic acid production by a bacterium using sucrose as an economic carbon source was studied under conditions in which hexanoic acid was continuously extracted by liquid–liquid extraction. Megasphaera elsdenii NCIMB 702410, selected from five M. elsdenii strains, produced 4.69 g l−1 hexanoic acid in a basal medium containing sucrose. Production increased to 8.19 g l−1 when the medium was supplemented by 5 g l−1 sodium butyrate. A biphasic liquid–liquid extraction system with 10 % (v/v) alamine 336 in oleyl alcohol as a solvent was evaluated in a continuous stirred-tank reactor held at pH 6. Over 90 % (w/w) of the hexanoic acid in a 0.5 M aqueous solution was transferred to the extraction solvent within 10 h. Cell growth was not significantly inhibited by direct contact of the fermentation broth with the extraction solvent. The system produced 28.42 g l−1 of hexanoic acid from 54.85 g l−1 of sucrose during 144 h of culture, and 26.52 and 1.90 g l−1 of hexanoic acid was accumulated in the extraction solvent and the aqueous fermentation broth, respectively. The productivity and yield of hexanoic acid were 0.20 g l−1 h−1 and 0.50 g g−1 sucrose, respectively.
17977702
Quantitative analysis of growth and volatile fatty acid production by the anaerobic ruminal bacterium Megasphaera elsdenii T81
Megasphaera elsdenii T81 grew on either dl-lactate or d-glucose at similar rates (0.85 h−1) but displayed major differences in the fermentation of these substrates. Lactate was fermented at up to 210-mM concentration to yield acetic, propionic, butyric, and valeric acids. The bacterium was able to grow at much higher concentrations of d-glucose (500 mM), but never removed more than 80 mM of glucose from the medium, and nearly 60 % the glucose removed was sequestered as intracellular glycogen, with low yields of even-carbon acids (acetate, butyrate, caproate). In the presence of both substrates, glucose was not used until lactate was nearly exhausted, even by cells pregrown on glucose. Glucose-grown cultures maintained only low extracellular concentrations of acetate, and addition of exogenous acetate increased yields of butyrate, but not caproate. By contrast, exogenous acetate had little effect on lactate fermentation. At pH 6.6, growth rate was halved by exogenous addition of 60 mM propionate, 69 mM butyrate, 44 mM valerate, or 33 mM caproate; at pH 5.9, these values were reduced to 49, 49, 18, and 22 mM, respectively. The results are consistent with this species’ role as an effective ruminal lactate consumer and suggest that this organism may be useful for industrial production of volatile fatty acids from lactate if product tolerance could be improved. The poor fermentation of glucose and sensitivity to caproate suggests that this strain is not practical for industrial caproate production.
5098223
Electrolytic membrane extraction enables production of fine chemicals from biorefinery sidestreams.
Short-chain carboxylates such as acetate are easily produced through mixed culture fermentation of many biological waste streams, although routinely digested to biogas and combusted rather than harvested. We developed a pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification. Carboxylate-rich broths are electrolyzed in a cathodic chamber from which anions flux across an anion exchange membrane into an anodic chamber, resulting in a clean acid concentrate with neither solids nor biomass. Next, the aqueous carboxylic acid concentrate reacts with added alcohol in a water-excluding phase to generate volatile esters. In a batch extraction, 96 ± 1.6% of the total acetate was extracted in 48 h from biorefinery thin stillage (5 g L(-1) acetate) at 379 g m(-2) d(-1) (36% Coulombic efficiency). With continuously regenerated thin stillage, the anolyte was concentrated to 14 g/L acetic acid, and converted at 2.64 g (acetate) L(-1) h(-1) in the first hour to ethyl acetate by the addition of excess ethanol and heating to 70 °C, with a final total conversion of 58 ± 3%. This processing pipeline enables direct production of fine chemicals following undefined mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide.
100943796
Integrated Production, Extraction, and Concentration of Acetic Acid from CO2 through Microbial Electrosynthesis
Using carbon dioxide for bioproduction combines decreased greenhouse gas emissions with a decreased dependence on fossil carbon for production of multicarbon products. Microbial electrosynthesis (MES) enables this, using renewable energy to drive the reduction of CO2 at the cathode of an electrochemical cell. To date, low product concentrations preclude cost-effective extraction during MES. Here we present an approach that couples production and recovery of acetate in a single, three-chamber reactor system. Acetate was produced at 61% Coulombic efficiency and fully recovered as an acidified stream containing up to 13.5 g L–1 (225 mM) acetic acid, the highest obtained thus far. In contrast to previous MES studies, a single separated acidic product was generated through in situ membrane electrolysis enabling further upgrading.
38420638
Alcohol production through volatile fatty acids reduction with hydrogen as electron donor by mixed cultures.
In this research we demonstrated a new method to produce alcohols. It was experimentally feasible to produce ethanol, propanol and butanol from solely volatile fatty acids (VFAs) with hydrogen as electron donor. In batch tests, VFAs such as acetic, propionic and butyric acids were reduced by mixed microbial cultures with a headspace of 1.5 bar of hydrogen. Observed alcohol concentrations were 3.69+/-0.25 mM of ethanol, 8.08+/-0.85 mM of propanol and 3.66+/-0.05 mM of n-butanol. The conversion efficiency based on the electron balance was 55.1+/-5.6% with acetate as substrate, 50.3+/-4.7% with propionate and 46.7+/-2.2% with n-butyrate. Methane was the most predominant by-product in each batch experiment, 33.6+/-9.6% of VFA and hydrogen was converted to methane with acetate as substrate; which was 27.1+/-7.1% with propionate and 36.6+/-2.2% with n-butyrate. This VFAs reducing renewable fuel production process does not require carbohydrates like fermentable sugars, but uses biomass with high water content or low sugar content that is unsuitable as feedstock for current fermentation processes. This so-called low-grade biomass is abundantly present in many agricultural areas and is economically very attractive feedstock for the production of biofuels.
31568483
Microbial electrocatalysis to guide biofuel and biochemical bioprocessing
131 ISSN 1759-7269 10.4155/BFS.12.93 © 2013 Future Science Ltd Microbial electrocatalysis During the last 10 years, research on bioelectrochemical systems with alive microbes on anodes or cathodes (electrodes) has blossomed. We refer to microbial activity on electrodes as microbial electrocatalysis, especially when no artificial mediators are added to the cultures. Initially, researchers focused on converting organic materials in sediments or wastewater into spontaneous electric power production with microbial fuel cells. Researchers shaped an open culture of mixed microbial consortia to utilize the anode as a solid-state electron acceptor with, for example, a platinum-coated cathode for abiotic oxygen reduction. Over the years, vast leaps in current densities were made and recently a value of approximately 300 A/m was reported with 3D electrodes [1]. Others successfully used microbes as biocatalysts at the cathode to circumvent platinum. Still, the low value of electric power and the high investment and operating costs has prevented a sustainable economic model [2]. The low value of electric power can also be turned around as an advantage by using a power source to manipulate electrode potentials and to enforce higher current densities (rates). This has already resulted in microbial electrolysis cells with acetate production at the cathode via microbial electrosynthesis from CO 2 [3]. Others are exploring the use of electrodes to manage surpluses or shortages of reducing equivalents in anaerobic fermentations (guiding fermentation) [4]. This article will unveil the possible uses of electrodes in biotechnology applications.
93386153
Global potential bioethanol production from wasted crops and crop residues
Abstract The global annual potential bioethanol production from the major crops, corn, barley, oat, rice, wheat, sorghum, and sugar cane, is estimated. To avoid conflicts between human food use and industrial use of crops, only the wasted crop, which is defined as crop lost in distribution, is considered as feedstock. Lignocellulosic biomass such as crop residues and sugar cane bagasse are included in feedstock for producing bioethanol as well. There are about 73.9 Tg of dry wasted crops in the world that could potentially produce 49.1 GL year −1 of bioethanol. About 1.5 Pg year −1 of dry lignocellulosic biomass from these seven crops is also available for conversion to bioethanol. Lignocellulosic biomass could produce up to 442 GL year −1 of bioethanol. Thus, the total potential bioethanol production from crop residues and wasted crops is 491 GL year −1 , about 16 times higher than the current world ethanol production. The potential bioethanol production could replace 353 GL of gasoline (32% of the global gasoline consumption) when bioethanol is used in E85 fuel for a midsize passenger vehicle. Furthermore, lignin-rich fermentation residue, which is the coproduct of bioethanol made from crop residues and sugar cane bagasse, can potentially generate both 458 TWh of electricity (about 3.6% of world electricity production) and 2.6 EJ of steam. Asia is the largest potential producer of bioethanol from crop residues and wasted crops, and could produce up to 291 GL year −1 of bioethanol. Rice straw, wheat straw, and corn stover are the most favorable bioethanol feedstocks in Asia. The next highest potential region is Europe ( 69.2 GL of bioethanol), in which most bioethanol comes from wheat straw. Corn stover is the main feedstock in North America, from which about 38.4 GL year −1 of bioethanol can potentially be produced. Globally rice straw can produce 205 GL of bioethanol, which is the largest amount from single biomass feedstock. The next highest potential feedstock is wheat straw, which can produce 104 GL of bioethanol. This paper is intended to give some perspective on the size of the bioethanol feedstock resource, globally and by region, and to summarize relevant data that we believe others will find useful, for example, those who are interested in producing biobased products such as lactic acid, rather than ethanol, from crops and wastes. The paper does not attempt to indicate how much, if any, of this waste material could actually be converted to bioethanol.
15904889
Composition of corn dry-grind ethanol by-products: DDGS, wet cake, and thin stillage.
DDGS and wet distillers' grains are the major co-products of the dry grind ethanol facilities. As they are mainly used as animal feed, a typical compositional analysis of the DDGS and wet distillers' grains mainly focuses on defining the feedstock's nutritional characteristics. With an increasing demand for fuel ethanol, the DDGS and wet distillers' grains are viewed as a potential bridge feedstock for ethanol production from other cellulosic biomass. The introduction of DDGS or wet distillers' grains as an additional feed to the existing dry grind plants for increased ethanol yield requires a different approach to the compositional analysis of the material. Rather than focusing on its nutritional value, this new approach aims at determining more detailed chemical composition, especially on polymeric sugars such as cellulose, starch and xylan, which release fermentable sugars upon enzymatic hydrolysis. In this paper we present a detailed and complete compositional analysis procedure suggested for DDGS and wet distillers' grains, as well as the resulting compositions completed by three different research groups. Polymeric sugars, crude protein, crude oil and ash contents of DDGS and wet distillers' grains were accurately and reproducibly determined by the compositional analysis procedure described in this paper.
98561798
Towards integrated biorefinery from dried distillers grains: Evaluation of feed application for Co-products
Abstract In this paper, we presented an integrated C5-based biorefinery concept to produce C5-platform of biofuels and biochemicals using corn fiber from Dried Distillers Grains (DDG). The process utilizes a selective hydrolysis process to generate a xylose-rich hydrolyzate stream and two co-product streams: fine fraction generated during mechanical pretreatment of DDG using Mesh 20 sieve and residual fiber after hydrolysis. Utilization of these two co-product streams is critical to the success of the biorefinery. This paper discusses how the two streams are generated, their composition, and their potential value in animal feed applications. Composition analysis of the first co-product stream showed that it is enriched in proteins compared to original DDG (11% higher crude protein content; 36% higher lysine content). The second co-product stream has 113% higher fat content compared to original DDG, as well as 15% higher total digestible nutrients, and 15% higher digestible energy. The results of this study suggest that these co-product side streams can be potentially applied as additives in animal feed, allowing for cost-effective utilization of DDG for bio-products without negatively impacting feed markets associated with DDG.
13152499
Fundamentals, present and future perspectives of electrocoagulation.
Electrocoagulation is an electrochemical wastewater treatment technology that is currently experiencing both increased popularity and considerable technical improvements. There has been relatively little effort to better understand the fundamental mechanisms of the processes, particularly those that could provide design parameters to optimize the performances of this relatively simple and inexpensive technique. In a research programme to delineate the mechanisms of the fundamental processes involved in, the authors have realized that the technology has been insufficiently reviewed with emphasis on the fundamentals and their relationship to the performance of this technology. This paper presents an in-depth discussion and consideration of the factors that need to be addressed for optimum performance of this technology. Recent improvements of this technique and the theoretical model studies are also reviewed.
2932331
Carbon and electron fluxes during the electricity driven 1,3-propanediol biosynthesis from glycerol.
1,3-Propanediol (1,3-PDO) can be produced biologically through glycerol fermentation. While such a process typically involves a pure culture system, particularly for crude glycerol, there would be operational advantages if a mixed population could be used. However, in the latter case the yield is typically low. Here, we use electrical current as the driving force for a mixed population fermenting glycerol in the cathode of a microbial bioelectrochemical system (BES). The carbon and electron flows were monitored by a titration and off-gas analysis (TOGA) sensor, and the syntrophic interactions in the BES were also investigated. Results show that on a carbon yield basis, current enhanced 1,3-PDO production from 24.8% (without current) to 50.1% (with a polarized biocathode at -0.9 V versus standard hydrogen electrode, SHE). Flux analysis indicated that the reductive current can be integrated into glycerol metabolism to enhance 1,3-PDO yield and that glycerol metabolism was redirected from propionate fermentation to 1,3-PDO production. A polarization of -0.6 V (vs SHE) resulted in more fermentative hydrogen production (from 2.7% to 8.0% on electron basis). 1,3-PDO production was also enhanced with hydrogen supply (37.7% on carbon basis), by suppressing hydrogen fermentation. Moreover, interspecies hydrogen transfer encouraged hydrogenotrophic methanogenesis, which was also accelerated by the cathodic polarization.
25410743
Dialister micraerophilus sp. nov. and Dialister propionicifaciens sp. nov., isolated from human clinical samples.
Seventeen anaerobic, Gram-negative, tiny coccobacilli were collected in France from various human clinical samples. Biochemical analyses as well as molecular studies, including 16S rRNA and dnaK gene sequencing, affiliated all the isolates to the genus Dialister. However, 16S rRNA and dnaK gene sequence similarities were below 95.2 and 79.7 %, respectively, when comparisons were performed with the currently described species Dialister pneumosintes and Dialister invisus. Two clusters consisting of 13 and four isolates could be differentiated. 16S rRNA- and dnaK-based phylogeny confirmed that these two clusters represent two novel and distinct lineages within the genus Dialister. Finally, phenotypic, genotypic and phylogenetic data supported the proposal of the two novel species Dialister micraerophilus sp. nov. (type strain ADV 04.01T=AIP 25.04T=CIP 108278T=CCUG 48837T) and Dialister propionicifaciens sp. nov. (type strain ADV 1053.03T=AIP 26.04T=CIP 108336T=CCUG 49291T). The G+C content of the DNA of the D. micraerophilus type strain is 36.3 mol%. On the basis of 16S rRNA gene sequence analysis, 11 isolates originating from Canada could also be affiliated to D. micraerophilus sp. nov., and were included in the species description.
29897629
Prevotella, a new genus to include Bacteroides melaninogenicus and related species formerly classified in the genus Bacteroides.
It was recently proposed that the genus Bacteroides should be restricted to Bacteroides fragilis (the type species) and closely related organisms (viz., B. caccae, B. distasonis, B. eggerthii, B. merdae, B. ovatus, B. stercoris, B. thetaiotaomicron, B. uniformis, and B. vulgatus). By contrast, the moderately saccharolytic, predominantly oral Bacteroides species, which include B. melaninogenicus, B. oralis, and related species, form a phenotypically and phylogenetically coherent group of species which differ so significantly from the emended description of the genus Bacteroides that they should not be classified in the same genus. Therefore, we formally propose that these species be reclassified in a new genus, Prevotella. The type species is Prevotella melaninogenica.
86122132
Pectinatus, a New Genus of the Family Bacteroidaceae
The properties of an anaerobic, rod-shaped bacterium having an unusual flagellar arrangement are described. The flagella emanate from only one side of the cell body and are not limited to the center portion as they are with selenomonads. The organism is a gram-negative, nonsporeforming mesophile producing acetic, propionic, and succinic acids and traces of lactic acid from glucose fermentation. The guanine-plus-cytosine content of the deoxyribonuleic acid is 39.8 mol%. The characteristics of this organism indicate that it belongs in none of the presently described genera. For this organism, we propose a new genus, Pectinatus, and a new species, Pectinatus cerevisiiphilus, in the family Bacteroidaceae. The type strain, CCC B-1022, has been deposited in the American Type Culture Collection under the number 29359.
8703162
Pectinatus sottacetonis sp. nov., isolated from a commercial pickle spoilage tank.
A strictly anaerobic, Gram-stain-negative, non-spore-forming, motile bacterium, designated strain FSRU B0405(T), was isolated from a commercial pickle spoilage tank and characterized by biochemical, physiological and molecular biological methods. Analyses of the 16S rRNA gene sequence of strain FSRU B0405(T) showed affiliation to the class Negativicutes in the phylum Firmicutes, with the closest relatives being the type strains of Pectinatus haikarae (96 %) and Pectinatus brassicae (95 %). In maximum-likelihood and neighbour-joining phylogenetic trees, strain FSRU B0405(T) clustered definitively (in 100 % of bootstrapped trees) within the genus Pectinatus, but not specifically with any characterized species within this genus. Strain FSRU B0405(T) was a slightly curved rod, varying from 3 to 30 µm in length, motile with a distinctive X-wise movement, having flagella only on the concave side of the cell. The isolate produced acetate and propionate from fructose and glucose as major metabolites similar to type strains of species of the genus Pectinatus. The major fatty acids were C11 : 0, C13 : 0, C15 : 0, C13 : 0 3-OH, C17 : 1 and C18 : 1ω11t. Strain FSRU B0405(T) differed from the pickle wastewater strain, Pectinatus brassicae TY(T), due to its lack of susceptibility to vancomycin, acetoin production, growth temperature range, acid production from adonitol, erythritol, glycerol, inositol, lactose, maltose, mannose, ribose, salicin, sorbitol, trehalose and xylitol and lack of hydrolysis of milk. Strain FSRU B0405(T) could be differentiated from other species of the genus Pectinatus both phenotypically and genetically. The results indicate that strain FSRU B0405(T) represents a novel species of the genus Pectinatus, for which the name Pectinatus sottacetonis sp. nov. is proposed. The type strain is FSRU B0405(T) ( = ATCC BAA-2501(T) = VTT E-113163(T)). An emended description of the genus Pectinatus is also provided.
8637441
Dynamics of Cathode-Associated Microbial Communities and Metabolite Profiles in a Glycerol-Fed Bioelectrochemical System
ABSTRACT Electrical current can be used to supply reducing power to microbial metabolism. This phenomenon is typically studied in pure cultures with added redox mediators to transfer charge. Here, we investigate the development of a current-fed mixed microbial community fermenting glycerol at the cathode of a bioelectrochemical system in the absence of added mediators and identify correlations between microbial diversity and the respective product outcomes. Within 1 week of inoculation, a Citrobacter population represented 95 to 99% of the community and the metabolite profiles were dominated by 1,3-propanediol and ethanol. Over time, the Citrobacter population decreased in abundance while that of a Pectinatus population and the formation of propionate increased. After 6 weeks, several Clostridium populations and the production of valerate increased, which suggests that chain elongation was being performed. Current supply was stopped after 9 weeks and was associated with a decrease in glycerol degradation and alcohol formation. This decrease was reversed by resuming current supply; however, when hydrogen gas was bubbled through the reactor during open-circuit operation (open-circuit potential) as an alternative source of reducing power, glycerol degradation and metabolite production were unaffected. Cyclic voltammetry revealed that the community appeared to catalyze the hydrogen evolution reaction, leading to a +400-mV shift in its onset potential. Our results clearly demonstrate that current supply can alter fermentation profiles; however, further work is needed to determine the mechanisms behind this effect. In addition, operational conditions must be refined to gain greater control over community composition and metabolic outcomes.
23209456
[NiFe] hydrogenases: a common active site for hydrogen metabolism under diverse conditions.
Hydrogenase proteins catalyze the reversible conversion of molecular hydrogen to protons and electrons. The most abundant hydrogenases contain a [NiFe] active site; these proteins are generally biased towards hydrogen oxidation activity and are reversibly inhibited by oxygen. However, there are [NiFe] hydrogenase that exhibit unique properties, including aerobic hydrogen oxidation and preferential hydrogen production activity; these proteins are highly relevant in the context of biotechnological devices. This review describes four classes of these "nonstandard" [NiFe] hydrogenases and discusses the electrochemical, spectroscopic, and structural studies that have been used to understand the mechanisms behind this exceptional behavior. A revised classification protocol is suggested in the conclusions, particularly with respect to the term "oxygen-tolerance". This article is part of a special issue entitled: metals in bioenergetics and biomimetics systems.
14961119
Constructing and testing the thermodynamic limits of synthetic NAD(P)H:H2 pathways
NAD(P)H:H2 pathways are theoretically predicted to reach equilibrium at very low partial headspace H2 pressure. An evaluation of the directionality of such near‐equilibrium pathways in vivo, using a defined experimental system, is therefore important in order to determine its potential for application. Many anaerobic microorganisms have evolved NAD(P)H:H2 pathways; however, they are either not genetically tractable, and/or contain multiple H2 synthesis/consumption pathways linked with other more thermodynamically favourable substrates, such as pyruvate. We therefore constructed a synthetic ferredoxin‐dependent NAD(P)H:H2 pathway model system in Escherichia coli BL21(DE3) and experimentally evaluated the thermodynamic limitations of nucleotide pyridine‐dependent H2 synthesis under closed batch conditions. NADPH‐dependent H2 accumulation was observed with a maximum partial H2 pressure equivalent to a biochemically effective intracellular NADPH/NADP+ ratio of 13:1. The molar yield of the NADPH:H2 pathway was restricted by thermodynamic limitations as it was strongly dependent on the headspace : liquid ratio of the culture vessels. When the substrate specificity was extended to NADH, only the reverse pathway directionality, H2 consumption, was observed above a partial H2 pressure of 40 Pa. Substitution of NADH with NADPH or other intermediates, as the main electron acceptor/donor of glucose catabolism and precursor of H2, is more likely to be applicable for H2 production.
118429
Identifying target processes for microbial electrosynthesis by elementary mode analysis
BackgroundMicrobial electrosynthesis and electro fermentation are techniques that aim to optimize microbial production of chemicals and fuels by regulating the cellular redox balance via interaction with electrodes. While the concept is known for decades major knowledge gaps remain, which make it hard to evaluate its biotechnological potential. Here we present an in silico approach to identify beneficial production processes for electro fermentation by elementary mode analysis. Since the fundamentals of electron transport between electrodes and microbes have not been fully uncovered yet, we propose different options and discuss their impact on biomass and product yields.ResultsFor the first time 20 different valuable products were screened for their potential to show increased yields during anaerobic electrically enhanced fermentation. Surprisingly we found that an increase in product formation by electrical enhancement is not necessarily dependent on the degree of reduction of the product but rather the metabolic pathway it is derived from. We present a variety of beneficial processes with product yield increases of maximal 36% in reductive and 84% in oxidative fermentations and final theoretical product yields up to 100%. This includes compounds that are already produced at industrial scale such as succinic acid, lysine and diaminopentane as well as potential novel bio-commodities such as isoprene, para-hydroxybenzoic acid and para-aminobenzoic acid. Furthermore, it is shown that the way of electron transport has major impact on achievable biomass and product yields. The coupling of electron transport to energy conservation could be identified as crucial for most processes.ConclusionsThis study introduces a powerful tool to determine beneficial substrate and product combinations for electro-fermentation. It also highlights that the maximal yield achievable by bio electrochemical techniques depends strongly on the actual electron transport mechanisms. Therefore it is of great importance to reveal the involved fundamental processes to be able to optimize and advance electro fermentations beyond the level of lab-scale studies.
13073006
The synthesis of n-caproate from lactate: a new efficient process for medium-chain carboxylates production
A unique microbiome that metabolizes lactate rather than ethanol for n-caproate production was obtained from a fermentation pit used for the production of Chinese strong-flavour liquor (CSFL). The microbiome was able to produce n-caproate at concentrations as high as 23.41 g/L at a maximum rate of 2.97 g/L/d in batch trials without in-line extraction. Compared with previous work using ethanol as the electron donor, the n-caproate concentration increased by 82.89%. High-throughput sequencing analysis showed that the microbiome was dominated by a Clostridium cluster IV, which accounted for 79.07% of total reads. A new process for n-caproate production was proposed, lactate oxidation coupled to chain elongation, which revealed new insight into the well-studied lactate conversion and carbon chain elongation. In addition, these findings indicated a new synthesis mechanism of n-caproate in CSFL. We believe that this efficient process will provide a promising opportunity for the innovation of waste recovery as well as for n-caproate biosynthesis.
7559404
Temperature and solids retention time control microbial population dynamics and volatile fatty acid production in replicated anaerobic digesters
Anaerobic digestion is a widely used technology for waste stabilization and generation of biogas, and has recently emerged as a potentially important process for the production of high value volatile fatty acids (VFAs) and alcohols. Here, three reactors were seeded with inoculum from a stably performing methanogenic digester, and selective operating conditions (37°C and 55°C; 12 day and 4 day solids retention time) were applied to restrict methanogenesis while maintaining hydrolysis and fermentation. Replicated experiments performed at each set of operating conditions led to reproducible VFA production profiles which could be correlated with specific changes in microbial community composition. The mesophilic reactor at short solids retention time showed accumulation of propionate and acetate (42 ± 2% and 15 ± 6% of CODhydrolyzed, respectively), and dominance of Fibrobacter and Bacteroidales. Acetate accumulation (>50% of CODhydrolyzed) was also observed in the thermophilic reactors, which were dominated by Clostridium. Under all tested conditions, there was a shift from acetoclastic to hydrogenotrophic methanogenesis, and a reduction in methane production by >50% of CODhydrolyzed. Our results demonstrate that shortening the SRT and increasing the temperature are effective strategies for driving microbial communities towards controlled production of high levels of specific volatile fatty acids.
2473899
A biomolecular isolation framework for eco-systems biology
Mixed microbial communities are complex, dynamic and heterogeneous. It is therefore essential that biomolecular fractions obtained for high-throughput omic analyses are representative of single samples to facilitate meaningful data integration, analysis and modeling. We have developed a new methodological framework for the reproducible isolation of high-quality genomic DNA, large and small RNA, proteins, and polar and non-polar metabolites from single unique mixed microbial community samples. The methodology is based around reproducible cryogenic sample preservation and cell lysis. Metabolites are extracted first using organic solvents, followed by the sequential isolation of nucleic acids and proteins using chromatographic spin columns. The methodology was validated by comparison to traditional dedicated and simultaneous biomolecular isolation methods. To prove the broad applicability of the methodology, we applied it to microbial consortia of biotechnological, environmental and biomedical research interest. The developed methodological framework lays the foundation for standardized molecular eco-systematic studies on a range of different microbial communities in the future.
206851128
Collateral damage from oral ciprofloxacin versus nitrofurantoin in outpatients with urinary tract infections: a culture-free analysis of gut microbiota.
Recent treatment guidelines for uncomplicated urinary tract infections (UTIs) discourage fluoroquinolone prescription because of collateral damage to commensal microbiota, but the ecologic impact of alternative agents has not been evaluated by culture-free techniques. We prospectively collected faecal samples at three time points from ambulatory patients with UTIs treated with ciprofloxacin or nitrofurantoin, patients not requiring antibiotics and household contacts of ciprofloxacin-treated patients. We described changes in gut microbiota using a culture-independent approach based on pyrosequencing of the V3-V4 region of the bacterial 16S rRNA gene. All groups were similar at baseline. Ciprofloxacin had a significant global impact on the gut microbiota whereas nitrofurantoin did not. The end of ciprofloxacin treatment correlated with a reduced proportion of Bifidobacterium (Actinobacteria), Alistipes (Bacteroidetes) and four genera from the phylum Firmicutes (Faecalibacterium, Oscillospira, Ruminococcus and Dialister) and an increased relative abundance of Bacteroides (Bacteroidetes) and the Firmicutes genera Blautia, Eubacterium and Roseburia. Substantial recovery had occurred 4 weeks later. Nitrofurantoin treatment correlated with a reduced relative proportion of the genus Clostridium and an increased proportion of the genus Faecalibacterium. This study supports use of nitrofurantoin over fluoroquinolones for treatment of uncomplicated UTIs to minimize perturbation of intestinal microbiota.
37853114
Introducing mothur: Open-Source, Platform-Independent, Community-Supported Software for Describing and Comparing Microbial Communities
ABSTRACT mothur aims to be a comprehensive software package that allows users to use a single piece of software to analyze community sequence data. It builds upon previous tools to provide a flexible and powerful software package for analyzing sequencing data. As a case study, we used mothur to trim, screen, and align sequences; calculate distances; assign sequences to operational taxonomic units; and describe the α and β diversity of eight marine samples previously characterized by pyrosequencing of 16S rRNA gene fragments. This analysis of more than 222,000 sequences was completed in less than 2 h with a laptop computer.
2639559
UCHIME improves sensitivity and speed of chimera detection
Motivation: Chimeric DNA sequences often form during polymerase chain reaction amplification, especially when sequencing single regions (e.g. 16S rRNA or fungal Internal Transcribed Spacer) to assess diversity or compare populations. Undetected chimeras may be misinterpreted as novel species, causing inflated estimates of diversity and spurious inferences of differences between populations. Detection and removal of chimeras is therefore of critical importance in such experiments. Results: We describe UCHIME, a new program that detects chimeric sequences with two or more segments. UCHIME either uses a database of chimera-free sequences or detects chimeras de novo by exploiting abundance data. UCHIME has better sensitivity than ChimeraSlayer (previously the most sensitive database method), especially with short, noisy sequences. In testing on artificial bacterial communities with known composition, UCHIME de novo sensitivity is shown to be comparable to Perseus. UCHIME is >100× faster than Perseus and >1000× faster than ChimeraSlayer. Contact: robert@drive5.com Availability: Source, binaries and data: http://drive5.com/uchime. Supplementary information: Supplementary data are available at Bioinformatics online.
39278206
Fluorescence in situ hybridization analysis of the prokaryotic community inhabiting crystallizer ponds.
A fluorescence in situ hybridization (FISH) protocol suitable for the identification of prokaryotes inhabiting hypersaline environments was developed and applied to several crystallizer ponds with salinities above 36% from a multipond solar saltern in Alicante, Spain. Two morphotypes were abundant in these environments: rods and square or square-like prokaryotes that could be affiliated to Bacteria and Archaea, respectively, by FISH with domain-specific probes. FISH with a newly designed probe proved that the archaeal 16S rDNA sequence most frequently recovered from the crystallizers, SPhT, originated from the dominant square-like prokaryotes. These uncultured prokaryotes have the morphology of Walsby's square bacteria. Additionally, FISH with a probe targeted to the genus Haloarcula, members of which are frequently isolated from this environment, indicated that this genus accounts for less than 0.1% of the total prokaryotic community.