Microbial Communities Performing Hydrogen Solventogenic Metabolism of Volatile Fatty Acids

Four different physicochemical pretreatments on an anaerobic inoculum used for alcohol production from acetate and butyrate are evaluated. Experiments were conducted in single batches using acetate and butyrate as substrates at 30°C and with a pressurized headspace of pure H2 at 2.15 atm (218.2 MPa). Thermal and acidic-thermal pretreatments lead to higher production of both ethanol and butanol. Modelling shows that the highest attainable concentrations of ethanol and butanol produced were 122 mg L−1 and 97 mg L−1 for the thermal pretreatment (after 17.5 days) and 87 mg L−1 and 143 mg L−1 for the acidic-thermal pretreatment (after 18.9 days). Thermodynamic data indicated that a high H2 partial pressure favoured solventogenic metabolic pathways. Acidic-thermal pretreatment selected a bacterial community more adapted to the conversion of acetate and butyrate into ethanol and butanol, respectively. Thermal-acidic pretreatment was unstable, showing significant variability between replicates. Acidic pretreatment showed the lowest alcohol production.

Acidic pretreatment of cellulose for bio methane production

Present work deals with the exhaustive investigations of rapid de-lignification processes from source-sorted organic fractions that are recalcitrant in nature. Organic solid wastes (OSW) belong to the organic fraction of municipal solid wastes (MSW) and they act as enormous potential substrate for alternative source of energy in the form of bio-fuels. Nevertheless, these substrates are not easily biodegradable and the degree of biodegradability is solely dependent on the composition and characteristic of organic solid wastes in municipal solid wastes. The component responsible for recalcitrance of organic solid wastes is lignin that occurs in variable amounts in different plant residues. In order to remove the recalcitrance from organic fraction municipal solid wastes and to make it more easily degradable by microbial groups, certain pretreatment techniques have been adopted and they are applied either individually or in combined way for enhancement of anaerobic digestion (AD) process. The present work studied the effect of acid treatment with acetic acid on the used substrate, evaluated its effectiveness on biogas production, and studied the concentrations of CH4 and CO2 during the fermentation period, which amounted to 90 days. All results are presented in clear curves for the purpose of facilitating the study.

Production of Green Biocellulose Nanofibers Through Utilizing Agricultural Wastes

In the present study, the green Biocellulose Nanofibers (BC), a vitally emerging biomaterial, was produced by fermentation of wheat straw (WS), as a widely available agricultural waste, using. Two different fermentation methods were used; Separate Hydrolysis and Fermentation (SHF), and Simultaneous Saccharification and Fermentation (SSF). Different acidic and enzymatic WS pretreatment conditions were used to understand the effect of pretreatment conditions on BC production. Afterward, sugar hydrolsates were simultaneously or separately inoculated with Gluconacetobacter Xylinum bacterium (i.e., for SSF and SHF, respectively), at optimum production conditions in shake flasks for 7 days to produce the biocellulose nanofibers. BC productions of 9.7 g/L in SHF and 10.8 g/L in SSF were achieved when WS was pretreated with dilute acids. Enzymatic treatment of WS after acidic pretreatment increased sugars’ concentrations from the hydrolysis, which increased BC production in SHF to 10.6 g/L. However, enzymes in SSF broke cellulose I alpha linkage in BC and decreased its production compared to no enzymatic treatment. Results show that glucose extracted from WS (~55% of total sugars) was found essential for the cellular metabolism, while xylose (~28% of total sugars) was highly consumed during cells growth phase. Generally, increasing thermal treatment, time and temperature, resulted in increasing furfural concentration. This observed to inhibits bacterial cells growth and leads to lower nanofibers yield when exists at concentration higher than 1 g/L threshold. In general, results obtained in the present study demonstrate the ability of utilizing agricultural wastes in the fermentation production of BC. Such a step is expected to eliminate cost of expensive pure sugars as a carbon source in the fermentation. Also the study shows an improved production yield by using effective fermentation techniques as SSF compared to classical methods used in literature.

Production of Green Biocellulose Nanofibers Through Utilizing Agricultural Wastes

In the present study, the green Biocellulose Nanofibers (BC), a vitally emerging biomaterial, was produced by fermentation of wheat straw (WS), as a widely available agricultural waste, using. Two different fermentation methods were used; Separate Hydrolysis and Fermentation (SHF), and Simultaneous Saccharification and Fermentation (SSF). Different acidic and enzymatic WS pretreatment conditions were used to understand the effect of pretreatment conditions on BC production. Afterward, sugar hydrolsates were simultaneously or separately inoculated with Gluconacetobacter Xylinum bacterium (i.e., for SSF and SHF, respectively), at optimum production conditions in shake flasks for 7 days to produce the biocellulose nanofibers. BC productions of 9.7 g/L in SHF and 10.8 g/L in SSF were achieved when WS was pretreated with dilute acids. Enzymatic treatment of WS after acidic pretreatment increased sugars’ concentrations from the hydrolysis, which increased BC production in SHF to 10.6 g/L. However, enzymes in SSF broke cellulose I alpha linkage in BC and decreased its production compared to no enzymatic treatment. Results show that glucose extracted from WS (~55% of total sugars) was found essential for the cellular metabolism, while xylose (~28% of total sugars) was highly consumed during cells growth phase. Generally, increasing thermal treatment, time and temperature, resulted in increasing furfural concentration. This observed to inhibits bacterial cells growth and leads to lower nanofibers yield when exists at concentration higher than 1 g/L threshold. In general, results obtained in the present study demonstrate the ability of utilizing agricultural wastes in the fermentation production of BC. Such a step is expected to eliminate cost of expensive pure sugars as a carbon source in the fermentation. Also the study shows an improved production yield by using effective fermentation techniques as SSF compared to classical methods used in literature.

Effect of Inoculum Pretreatment on Alcohol Production from Volatile Fatty Acids through an Anaerobic Solventogenic Process

1AbstractBackgroundProduction of alcohols from wastes through biological processes is environmentally and economically interesting, since they can be valorized as drop-in liquid fuels, which have a high market value. Using microbial mixed cultures in such processes is of great interest since it confers more stability, a higher resistance to both toxicity and contamination, and an increased substrate flexibility. However, there is still a lack of fundamental knowledge on such microbial populations used as inoculum in solventogenic processes. This work evaluates the effect of four different physicochemical pretreatments (acidic, thermal, acidic-thermal and thermal-acidic) on an anaerobic inoculum used for alcohols production from volatile fatty acids.ResultsAll experiments were conducted in single batches using acetate and butyrate as substrates, at 30°C and with a pressurized headspace of pure H2 at 2182 mBar. Higher productions of both ethanol and butanol were achieved with both thermal and acidic-thermal pretreatments of the inoculum. The highest concentrations of ethanol and butanol produced were respectively of 122 mg.L−1 and 97 mg.L−1 for the thermal pretreatment (after 710 hours), and of 87 mg.L−1 and 143 mg.L−1 for the acidic-thermal pretreatment (after 210 hours). Butyrate was consumed and acetate was produced in all assays. A mass balance study indicated that the inoculum provided part of the substrate. Thermodynamic data indicated that a high H2 partial pressure favored solventogenic metabolic pathways. Finally, sequencing data showed that both thermal and acidic-thermal pretreatments selected mainly the bacterial genera Pseudomonas, Brevundimonas and Clostridium.ConclusionThe acidic-thermal pretreatment selected a bacterial community more adapted to the conversion of acetate and butyrate into ethanol and butanol, respectively. A higher production of ethanol was achieved with the thermal pretreatment, but at a slower rate. The thermal-acidic pretreatment was unstable, showing a huge variability between replicates. The acidic pretreatment showed the lowest alcohol production, almost negligible as compared to the control assay.

Eco-friendly additives in acidic pretreatment to boost enzymatic saccharification of hardwood for sustainable biorefinery applications

Pretreatment of renewable lignocellulosic biomass is essential to produce fermentable sugars and biofuels in a sustainable biorefinery. However, lignin repolymerization during pretreatment was reported to intensify the lignin inhibition on...

Insights on Monosaccharides and Bioethanol Production from Sweet Sorghum Stalks Using Dilute Acid Pretreatment

Sweet sorghum is a unique bioenergy crop that produces stalks with fermentable free sugars. The purpose of this study was to evaluate how the production of hemicellulosic saccharides and bioethanol from sweet sorghum stalks (SSS) can be influenced by a dilute sulfuric acid (H2SO4) pretreatment under different isothermal conditions. The bioethanol production from untreated SSS and pretreated solid phases was achieved through the Simultaneous Saccharification and Fermentation (SSF) process. A good SSS fractionation and an extensive hemicellulose hydrolysis into soluble saccharides were obtained, the most abundant hemicellulose-derived compounds present in the pretreated liquid phase being monosaccharides, with up to 17.22 g/L of glucose and 16.64 g/L of xylose in the pretreatments performed with 3% and 1% H2SO4 for 30 min at 134 °C, respectively. The SSF process of untreated SSS allowed a maximum bioethanol concentration of 9.78 g/L, corresponding to a maximum glucan conversion into ethanol of 49.8%. Bioethanol production from untreated SSS led to a higher bioethanol concentration and conversion than in the case of using acid pretreated solid phases obtained under the most severe conditions (with 3% H2SO4 for 30, 60 and 120 min at 134 °C), suggesting that, in the case of this biomass naturally rich in soluble sugars, the acidic pretreatment could negatively influence the fermentative process.