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In this study, a specific fraction of food waste, i.e. depackaging waste, was studied as substrate for hydrogen production by dark fermentation. During storage and transport of this liquid mixture, inhibitory compounds like acids or alcohol might be produced by endogenous flora. A factorial fractional design based on the composition of the substrate was used to determine the best condition to convert this substrate into hydrogen. First results indicated that the consortium used might convert high quantity of lactate into hydrogen. A batch culture confirmed that lactate was used as the main carbon source and a global yield of 0.4mol H2 ·mol lactate -1 was obtained. This study demonstrated the ability of the consortium tested to convert different carbon sources (carbohydrates or lactate) with good efficiency. These data represented an important parameter in the prospect of using an industrial substrate whose composition is liable to vary according to the conditions of storage and transport., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The aim of this work was to study an externally-submerged membrane bioreactor for the cyclic extraction of volatile fatty acids (VFAs) during anaerobic fermentation, combining the advantages of submerged and external technologies for enhancing biohydrogen (BioH2) production from agrowaste. Mixing and transmembrane pressure (TMP) across a hollow fiber membrane placed in a recirculation loop coupled to a stirred tank were investigated, so that the loop did not significantly modify the hydrodynamic properties in the tank. The fouling mechanism, due to cake layer formation, was reversible. A cleaning procedure based on gas scouring and backwashing with the substrate was defined. Low TMP, 10(4)Pa, was required to achieve a 3Lh(-1)m(-2) critical flux. During fermentation, BioH2 production was shown to restart after removing VFAs with the permeate, so as to enhance simultaneously BioH2 production and the recovery of VFAs as platform molecules., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The effect of γ-alumina as a fermentation advancing tool and as carrier for culture immobilisation, regarding VFAs and ethanol production during acidogenic fermentation of glucose, was examined at various process conditions (sugar concentration, pH) and operation modes (continuous with and without effluent recirculation and batch). The results showed that at high initial pH (8.9) the continuous acidogenic fermentation of glucose led to high yields of VFAs and favoured the accumulation of butyric acid. The batch process on the other hand at pH 6.5, favoured the ethanol-type fermentation. The results indicate that in the frame of technology development for new generation biofuels, using γ-alumina as a process advancing tool at optimum process conditions (pH, initial glucose concentration and mode of operation), the produced VFAs profile and ethanol concentration may be manipulated., (Copyright © 2014. Published by Elsevier Ltd.)

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Recent developments in industrial biotechnology have resulted in the exploitation of new and undiscovered microorganisms and the devising of improved methods for enzyme production, which have led to increased yields of the enzyme, thus making a viable industrial process feasible. This review tracks the developments in the field of acidic and neutral protease production with regard to the producers, methods of production and their improvement, the product and its applications. [ABSTRACT FROM AUTHOR]

Gluconic acid is a mild organic acid derived from glucose by a simple oxidation reaction. The reaction is facilitated by the enzyme glucose oxidase (fungi) and glucose dehydrogenase (bacteria such as Gluconobacter). Microbial production of gluconic acid is the preferred method and it dates back to several decades. The most studied and widely used fermentation process involves the fungus Aspergillus niger. Gluconic acid and its derivatives, the principal being sodium gluconate, have wide applications in food and pharmaceutical industry. This article gives a review of microbial gluconic acid production, its properties and applications. [ABSTRACT FROM AUTHOR]

• Production of 2G bioethanol remains technologically challenging. • 2G bioethanol production is increasing but still less than 3% of total bioethanol. • The biochemical route must tackle with both pentose and hexose conversion. • The evaluation of a treatment pathway includes process simulation. • Agro-resource renewal and soil impacts are added for a complete LCA. The advancements in second-generation bioethanol produced from lignocellulosic biomass, such as crops residues, woody crops or energy grasses are gaining momentum. Though, they are still representing less than 3% of total bioethanol production, the GHG reduction potential is higher than for 1G-bioethanol. The environmental impacts of bioethanol production are totally dependent on feedstock availability and conversion technology. The biochemical conversion route must overcome several technological and economical challenges such as pre-treatment, fermentation, hydrolysis process and separation. A completely mature technology is still to be developed and must adapted to the nature of the feedstock. Nevertheless, using process simulation software, Life Cycle Assessment and integrating the different steps of bioresource harvesting and treatment processes, including the energy balances and the water requirements, it is shown that 2G bioethanol production will reduce environmental impacts provided the evaluation addresses a long-time perspective, including all conversion steps and the regeneration of the bioresource. [ABSTRACT FROM AUTHOR]

Batch cultivation of an anaerobic consortium fed with glucose as sole carbon source showed a sharp decrease of the hydrogen productivity when volatile fatty acids (VFA) concentration exceeded 12.5 g L −1 . To avoid VFA accumulation, fermentative batch cultures were thereafter carried out with a submerged membrane anaerobic bioreactor to continuously remove hydrogen fermentation co-products, while retaining the biomass. The membrane made it possible to separate the residence times of bacterial biomass and hydraulic part. With this technology, average and maximal productivities reached 0.75 and 2.46 L H2 L −1 h −1 , corresponding to an increase of 44 and 51% in comparison to the control, respectively. By removing the VFAs from the cultivation medium, H 2 -producing pathways were favored, confirming the metabolic inhibitory effects of co-product accumulation in fermentation medium. Such hydrogen productivity is one of the highest values encountered in the literature. Readily implementable, such technology offers a good opportunity for further developing high rate hydrogen fermentation bioprocesses. [ABSTRACT FROM AUTHOR]

Hydrogen production by dark fermentation (DF) from wastewater, food waste, and agro-industrial waste combines the advantages to be renewable, sustainable and environmentally friendly. But this attractive process involves a three-phase gas-liquid-solid system highly sensitive to mixing conditions. However, mixing is usually disregarded in the conventional strategies for enhancing biohydrogen productivity, even though H 2 production can be doubled, e.g. versus of reactor design (0.6–1.5 mol H 2 /mol hexose). The objective of this review paper is, therefore, to highlight the key effects of mixing on biohydrogen production among the abiotic parameters of DF. First, the pros and cons of the different modes of mixing in anaerobic digesters are described. Then, the influence of mixing on DF is discussed using recent data from the literature and theoretical analysis, focusing on the multiphase and multiscale aspects of DF. The methods and tools available to quantify experimentally the role of mixing both at the local and global scales are summarized. The 0-D to 3-D strategies able to implement mixing in fermentation modeling and scale-up procedures are examined. Finally, the perspectives in terms of process intensification and scale-up tools using mixing optimization are discussed with the issues that are still to be solved. [ABSTRACT FROM AUTHOR]

The use of microbial consortia and industrial effluents for the production of biohydrogen by dark fermentation is seen as a key strategy in an attempt to overcome the economic and technical drawbacks of this potential technology. Three mesophilic microbial consortia were sampled and identified. Fermentation was carried out in a vinasse-based medium supplemented with pure or complex carbon sources under different conditions of H 2 partial pressure. Consortia LPBAH1 and LPBAH2 were predominantly composed of Oxalobacteraceae and Lactobacillaceae , while LPBAH3 was rich in sporulating Lactobacillaceae (>96%). Each consortium presented specificities related to biohydrogen and VFAs production: (i) the highest biohydrogen yield was achieved with LPBAH1 (>50% Oxalobacteraceae ) in a vinasse medium supplemented with sugarcane juice (1.59 ± 0.21 mol H2 /mol glucose ); (ii) The lower H 2 yields were achieved with LPBAH3, which otherwise produced the highest amount of butyric acid (up to 10 g L −1 ); (iii) LPBAH2 presented great stability in H 2 production in different conditions of H 2 partial pressure. [ABSTRACT FROM AUTHOR]

This work deals with the analysis and the optimization of a dual-impeller design in terms of mixing, hydrodynamics, mass transfer properties and power input in a mechanically stirred digester devoted to biohydrogen production through acidogenic fermentation of lignocellulosic waste. Various mixer designs involving Rushton turbines, an Elephant Ear impeller and a marine propeller, were compared. Experimental data were successfully confronted to CFD-based simulations used to reveal the respective roles of impeller type, geometry and clearance. The results showed that the flow pattern was strongly influenced by the off-bottom and inter-impeller clearances, and by the size and type of the lower impeller. Straw suspension was enhanced by a small disk turbine with a low off-bottom clearance and a large inter-impeller clearance that promoted an axial flow circulation together with a small mixing time due to the interaction with the larger turbine used as the upper impeller. Conversely, k L a evolution was weakly dependent on impeller design, position, and rotation speed until a deep vortex formed on the free surface, showing that power input was too weak to enhance liquid-to-gas mass transfer. Finally, the design including an Elephant Ear turbine as the upper impeller and a smaller Rushton turbine as the lower impeller was selected as the best compromise between distributive and dispersive mixing, while the objective of a power input lower than 10 W/m 3 was achieved. [ABSTRACT FROM AUTHOR]

This work deals with the optimization of mixing in an anaerobic submerged membrane bioreactor (AnMBR) devoted to the production of biohydrogen as a 2nd generation biofuel using the dark fermentation process from lignocellulosic waste. The AnMBR consists of an unbaffled mechanically-stirred tank equipped with a two-stage radial impeller which is coupled to an external hollow fibre membrane module placed in a forced circulation loop with permeate suction. In the tank, mixing conditions must enable the suspension of solid waste, homogenize local concentrations, and enhance hydrogen desorption simultaneously. For optimizing reactor design, mixing was investigated both experimentally and numerically. The computational strategy consisted in the combination of 1D and 3D methodologies including single-phase and two-fluid CFD models. The experimental approach encompassed RTD and mixing time measurements, the analysis of vortex formation and the description of solid suspension using straw as waste. The results showed that a laminar flow pattern prevailed in the recirculation loop and the membrane unit, while turbulent flow was observed in the stirred tank in which mixing time was far smaller than residence time in single-phase flow. A compromise was defined using CFD, which prevented vortex formation and promoted homogeneous suspension, by optimizing impeller position and rotation speed. The positions of the inlet and the outlet of the forced circulation loop in the tank were deduced from CFD simulations and validated by experimental data. Finally, this work confirms the potential interest of AnMBR for biohydrogen production and the applicability of CFD for the optimization of abiotic factors. [ABSTRACT FROM AUTHOR]

Abstract: VFAs can be obtained from lignocellulosic agro-industrial wastes, sludge, and various biodegradable organic wastes as key intermediates through dark fermentation processes and synthesized through chemical route also. They are building blocks of several organic compounds viz. alcohol, aldehyde, ketones, esters and olefins. These can serve as alternate carbon source for microbial biolipid, biohydrogen, microbial fuel cells productions, methanisation, and for denitrification. Organic wastes are the substrate for VFA platform that is of zero or even negative cost, giving VFA as intermediate product but their separation from the fermentation broth is still a challenge; however, several separation technologies have been developed, membrane separation being the most suitable one. These aspects will be reviewed and results obtained during anaerobic treatment of slaughterhouse wastes with further utilisation of volatile fatty acids for yeast cultivation have been discussed. [Copyright &y& Elsevier]

Abstract: There is an increasing demand for cellulases in the market for various applications, among which the bioconversion of lignocellulosic biomass for ethanol production is the major one. Improvements in the titers as well as specific activities of cellulases are highly desired for its use in bioethanol production as well as in other applications. This review deals with developments in bioprocess technologies, solid-state and submerged fermentation as well as on the strategies adopted for improving cellulase production or properties, including engineering the genes or designing enzyme cocktails. It also gives a brief overview of commercially available cellulase preparations. [Copyright &y& Elsevier]