Clustering hybrid regression: a novel computational approach to study and model biohydrogen production through dark fermentation

Clustering hybrid regression (CHR) approach was developed and evaluated using data from H(2)-producing glucose-based, suspended-cell bioreactor operated for 5 months. The aim was to describe the relationship between metabolic end products and H(2)-production rate. Self-organizing maps (SOM) were used to better visualize the dataset and to detect main metabolic patterns in bioprocess data. SOM detected three distinct metabolic patterns with butyrate, acetate and ethanol as dominant metabolites, respectively. Butyrate dominated metabolism was related to high H(2) production, while acetate and ethanol dominated metabolisms resulted in low H(2) production. CHR models performed well [mean square error (MSE) 0.55 and 0.56] in modeling the H(2)-production rate. The results validate the suitability of the CHR approach in describing the bioprocess behavior and in the modeling of H(2) production rate. The developed model can help in discovering key metabolic interactions and suitable process parameters from complex datasets, and increase the understanding of the bioprocesses occurring in engineered and natural environments.     

Dark fermentation on biohydrogen production: Pure culture

Biohydrogen is regarded as an attractive future clean energy carrier due to its high energy content and environmental-friendly conversion. While biohydrogen production is still in the early stage of development, there have been a variety of laboratory- and pilot-scale systems developed with promising potential. This work presents a review of literature reports on the pure hydrogen-producers under anaerobic environment. Challenges and perspective of biohydrogen production with pure cultures are also outlined.     

Improvement of biohydrogen production using a reduced pressure fermentation

Bioprocess and Biosystems Engineering - This study investigated the effect of reduced pressure on biohydrogen production in an upflow anaerobic sludge blanket (UASB) reactor from whey permeate. The...     

Effects of key operational parameters on biohydrogen production via anaerobic fermentation in a sequencing batch reactor

In this study, a series of tests were conducted in a 6 L anaerobic sequencing batch reactor (ASBR) to investigate the effect of pH, hydraulic retention time (HRT) and organic loading rate on biohydrogen production at 28 °C. Sucrose was used as the main substrate to mimic carbohydrate-rich wastewater and inoculum was prepared from anaerobic digested sludge without pretreatment. The reactor was operated initially with nitrogen sparging to form anaerobic condition. Results showed that methanogens were effectively suppressed. The optimum pH value would vary depending on the HRT. Maximum hydrogen production rate and yield of 3.04 L H₂/L reactor d and 2.16 mol H₂/mol hexose respectively were achieved at pH 4.5, HRT 30 h, and OLR 11.0 kg/m³ d. Two relationships involving the propionic acid/acetic acid ratio and ethanol/acetic acid ratio were derived from the analysis of the metabolites of fermentation. Ethanol/acetic acid ratio of 1.25 was found to be a threshold value for higher hydrogen production.     

Integrated system approach to dark fermentative biohydrogen production for enhanced yield,energy efficiency and substrate recovery

The challenges of climate change, dwindling fossil reserves, and environmental pollution have fuelled the need to search for clean and sustainable energy resources. The process of biohydrogen has been highlighted as a propitious alternative energy of the future because it has many socio-economic benefits such as non-polluting features, the ability to use diverse feedstocks including waste materials, the process uses various microorganisms, and it is the simplest method of producing hydrogen. However, the establishment of a biohydrogen driven economy has been hindered by low process yields due to the accumulation of inhibitory products. Over the past few years, various optimization methods have been used in literature. Among these, integration of bioprocesses is gaining increasing prominence as an effective approach that could be used to achieve a theoretical yield of 4 mol H₂ mol^?1 glucose. In batch integrated systems, dark fermentation is used as a primary process for conversion of substrates into biohydrogen, carbon dioxide, and volatile fatty acids. This is followed by a secondary anaerobic process for further biohydrogen conversion efficiency. This review discusses the current challenges facing scale-up studies in dark fermentation process. It elucidates the potential of batch integrated systems in biohydrogen process development. Furthermore, it explores the various integrated fermentation techniques that are employed in biohydrogen process development. Finally, the review concludes with recommendations on improvement of these integrated processes for enhanced biohydrogen yields which could pave a way for the establishment of a large-scale biohydrogen production process.     

A novel approach for adding smart functionalities to cellulosic fabrics

A water soluble nanocomposite, based on Ag-nanoparticles (Ag-NPs) loaded on hyperbranched poly (amide-amine, HBPAA) was prepared, characterized and utilized in functional finishing as well as in combined reactive dyeing/and functional finishing of linen, cotton and viscose fabrics. Incorporation of the nanocomposite alone and in combination with reactive dyes in easy care finishing formulations brought about an outstanding antibacterial functionality of the finished and the dyed/finished fabrics even after 15 laundering cycles along with a slight negative impact on other performance properties. Improvement or decrement in the functional, comfort, and dyeing properties is governed by the type of cellulosic substrate.     

Isolation of cellulose-hydrolytic bacteria and applications of the cellulolytic enzymes for cellulosic biohydrogen production

Nine cellulolytic bacterial strains were isolated from soil sample taken in southern Taiwan. Through 16S rRNA sequence matching; eight of those isolates belong to Cellulomonas sp., while the other one belongs to Cellulosimicrobium cellulans. The activity of cellulolytic enzymes (cellulases and xylanase) produced from those strains was mainly present extracellularly and the enzyme production was dependent on cellulosic substrates (xylan, rice husk and rice straw) used for growth. HPLC analysis confirmed the bacterial hydrolysis of these cellulosic substrates for soluble sugars production. The efficiency of fermentative H₂ production from the enzymatically hydrolyzed rice husk was examined with seven H₂-producing pure bacterial isolates. With an initial reducing sugar concentration of 0.36 g l⁻¹, only Clostridium butyricum CGS5 exhibited efficient H₂ production from the rice husk hydrolysates with a cumulative H₂ production and H₂ yield of 88.1 ml l⁻¹ and 19.15 mmol H₂ (g reducing sugar)⁻¹ (or 17.24 mmol H₂ (g cellulose)⁻¹), respectively.     

Multicomponent cellulase production by Cellulomonas biazotea NCIM‐2550 and its applications for cellulosic biohydrogen production

Among four cellulolytic microorganisms examined, Cellulomonas biazotea NCIM‐2550 can grow on various cellulosic substrates and produce reducing sugar. The activity of cellulases (endoglucanase, exoglucanase, and cellobiase), xylanase, amylase, and lignin class of enzymes produced by C. biazotea was mainly present extracellularly and the enzyme production was dependent on cellulosic substrates (carboxymethyl cellulose [CMC], sugarcane bagasse [SCB], and xylan) used for growth. Effects of physicochemical conditions on cellulolytic enzyme production were systematically investigated. Using MnCl₂ as a metal additive significantly induces the cellulase enzyme system, resulting in more reducing sugar production. The efficiency of fermentative conversion of the hydrolyzed SCB and xylan into clean H₂ energy was examined with seven H₂‐producing pure bacterial isolates. Only Clostridiumbutyricum CGS5 exhibited efficient H₂ production performance with the hydrolysate of SCB and xylan. The cumulative H₂ production and H₂ yield from using bagasse hydrolysate (initial reducing sugar concentration = 1.545 g/L) were approximately 72.61 mL/L and 2.13 mmol H₂/g reducing sugar (or 1.91 mmol H₂/g cellulose), respectively. Using xylan hydrolysate (initial reducing sugar concentration = 0.345 g/L) as substrate could also attain a cumulative H₂ production and H₂ yield of 87.02 mL/L and 5.03 mmol H₂/g reducing sugar (or 4.01 mmol H₂/g cellulose), respectively. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Biological hydrogen production by dark fermentation: challenges and prospects towards scaled-up production

Among different technologies of hydrogen production, bio-hydrogen production exhibits perhaps the greatest potential to replace fossil fuels. Based on recent research on dark fermentative hydrogen production, this article reviews the following aspects towards scaled-up application of this technology: bioreactor development and parameter optimization, process modeling and simulation, exploitation of cheaper raw materials and combining dark-fermentation with photo-fermentation. Bioreactors are necessary for dark-fermentation hydrogen production, so the design of reactor type and optimization of parameters are essential. Process modeling and simulation can help engineers design and optimize large-scale systems and operations. Use of cheaper raw materials will surely accelerate the pace of scaled-up production of biological hydrogen. And finally, combining dark-fermentation with photo-fermentation holds considerable promise, and has successfully achieved maximum overall hydrogen yield from a single substrate. Future development of bio-hydrogen production will also be discussed.     

Semi-continuous biohydrogen production as an approach to generate electricity

In this work, a semi-continuous biological system was established to produce hydrogen and generate electricity by coupling the bioreactor to a fuel cell. Heat and acid pretreatments (at 35 and 55 °C) of a seed sludge used as inoculum were performed in order to increase hydrogen producers. Different initial glucose concentrations (IGC) were tested for heat pretreated inoculum at 35 °C to determine the optimum concentration of glucose that supported the highest hydrogen production. Results showed that the heat pretreated inoculums (35 °C) reached the highest hydrogen molar yield of 2.85 mol H₂/mol glucose (0.014 L/h), which corresponds to the acetic acid pathway. At the optimum IGC (10 g/L, 35 °C) the hydrogen molar yield was 3.6 mol H₂/mol glucose (0.023 L/h). The coupled bioreactor-fuel cell system yielded an output voltage of 1.06 V, power of 0.1 W (25 °C) and a current of 68 mA. The overall results suggest that high hydrogen molar yields can be obtained through the acetic acid pathway and that is feasible to generate electricity using hydrogen from the semi- continuous bioreactor.     

A novel biochemical route for fuels and chemicals production from cellulosic biomass

The conventional biochemical platform featuring enzymatic hydrolysis involves five key steps: pretreatment, cellulase production, enzymatic hydrolysis, fermentation, and product recovery. Sugars are produced as reactive intermediates for subsequent fermentation to fuels and chemicals. Herein, an alternative biochemical route is proposed. Pretreatment, enzymatic hydrolysis and cellulase production is consolidated into one single step, referred to as consolidated aerobic processing, and sugar aldonates are produced as the reactive intermediates for biofuels production by fermentation. In this study, we demonstrate the viability of consolidation of the enzymatic hydrolysis and cellulase production steps in the new route using Neurospora crassa as the model microorganism and the conversion of cellulose to ethanol as the model system. We intended to prove the two hypotheses: 1) cellulose can be directed to produce cellobionate by reducing β-glucosidase production and by enhancing cellobiose dehydrogenase production; and 2) both of the two hydrolysis products of cellobionate--glucose and gluconate--can be used as carbon sources for ethanol and other chemical production. Our results showed that knocking out multiple copies of β-glucosidase genes led to cellobionate production from cellulose, without jeopardizing the cellulose hydrolysis rate. Simulating cellobiose dehydrogenase over-expression by addition of exogenous cellobiose dehydrogenase led to more cellobionate production. Both of the two hydrolysis products of cellobionate: glucose and gluconate can be used by Escherichia coli KO 11 for efficient ethanol production. They were utilized simultaneously in glucose and gluconate co-fermentation. Gluconate was used even faster than glucose. The results support the viability of the two hypotheses that lay the foundation for the proposed new route.     

发酵生物制氢研究进展

综述了近年来发酵生物制氢领域的研究进展?在菌种方面,除了对现有产氢菌种的深入研究外,还采用生物学,分子生物学及生物信息学手段建立产氢菌种库;在氢酶的研究方面,已逐步从基因确定、功能研究拓展到基因工程构建高效产氢菌研究：而在与废弃生物质处理相结合的反应过程方面,研究主要集中在利用不同种类的废弃物的产氢和高效产氢反应器上。此外,还初步总结了目前对发酵制氢可行性和经济性的评价,并对其发展方向提出了新的看法。     

Fermentative biohydrogen production: trends and perspectives

Biologically produced hydrogen (biohydrogen) is a valuable gas that is seen as a future energy carrier, since its utilization via combustion or fuel cells produces pure water. Heterotrophic fermentations for biohydrogen production are driven by a wide variety of microorganisms such as strict anaerobes, facultative anaerobes and aerobes kept under anoxic conditions. Substrates such as simple sugars, starch, cellulose, as well as diverse organic waste materials can be used for biohydrogen production. Various bioreactor types have been used and operated under batch and continuous conditions; substantial increases in hydrogen yields have been achieved through optimum design of the bioreactor and fermentation conditions. This review explores the research work carried out in fermentative hydrogen production using organic compounds as substrates. The review also presents the state of the art in novel molecular strategies to improve the hydrogen production.     

Biohydrogen production from cellulosic hydrolysate produced via temperature-shift-enhanced bacterial cellulose hydrolysis

A “temperature-shift” strategy was developed to improve reducing sugar production from bacterial hydrolysis of cellulosic materials. In this strategy, production of cellulolytic enzymes with Cellulomonas uda E3-01 was promoted at a preferable temperature (35 °C), while more efficient enzymatic cellulose hydrolysis was achieved under an elevated culture temperature (45 °C), at which cell growth was inhibited to avoid consumption of reducing sugar. This temperature-shift strategy was shown to markedly increase the reducing sugar (especially, monosaccharide and disaccharide) concentration in the hydrolysate while hydrolyzing pure (carboxymethyl-cellulose, xylan, avicel and cellobiose) and natural (rice husk, rice straw, bagasse and Napier-grass) cellulosic materials. The cellulosic hydrolysates from CMC and xylan were successfully converted to H₂ via dark fermentation with Clostridium butyricum CGS5, attaining a maximum hydrogen yield of 4.79 mmol H₂/g reducing sugar.     

木质纤维素原料酶水解产乙醇工艺的研究进展

木质纤维素原料预处理后,经水解、发酵等过程,可生产乙醇作为清洁燃料,这大大提高了农业和林业废弃物的利用率,减轻了环境污染,并为经济的可持续发展提供了保证。目前木质纤维素酶水解因其具有明显优势而受到重视,被普遍研究和采用。综述了近年来木质纤维素原料的预处理方法、酶与水解技术、发酵工艺以及发酵耦合分离技术的最新研究成果。     

Anaerobic solid state fermentation of cellulosic substrates with possible application to cellulase production

Summary A solid state fermentation process was developed for the conversion of straw and cellulose under anaerobic conditions by a mixed culture of cellulolytic and methanogenic organisms. The bioconversion rate and efficiency were compared under mesophilic (35° C) and thermophilic (55° C) conditions. Cellulolytic activity was assayed in terms of sugar and overall soluble organic matter (chemical oxygen demand, COD) production. Maximum conversion rates were obtained under thermophilic conditions, i.e. 8.4 g and 14.2 g COD/kg·d, respectively, when wheat straw and cellulose were used as substrates. The cellulolytic activity of the reactor contents (23% dry matter), measured under substrate excess conditions, amounted to 50 g COD/kg·d. As a comparison, the activity of rumen contents (15% dry matter) measured by the same assay amounted to 150 g COD/kg·d. The anaerobic cellulases appeared to be substrate bound. This and the relative low activity levels attained, limit the perspectives of producing cellulase enzymes by this type of process.     

Enhanced production of cellulases byPenicillium citrinum in solid state fermentation of cellulosic residue

Penicillium citrinum, using rice husks in a solid state fermentation, produced maximum cellulase yields (37 Units/g) after 12 days with a cellulose utilization of more than 70%. Enzyme yields were three times higher than in shake-flask cultures.