Valorization of carob waste: Definition of a second-generation bioethanol production process

High-Pressure Water Jet System Treatment of Argan Nut Shell and Enzymatic Hydrolysis for Bioethanol Production

Argan nut shell represents the most generated by-product during the process of the extraction of argan oil. For the first time, argan nut shell was characterized and assessed as a new potential feedstock for bioethanol production using a combination of mechanical and enzymatic pretreatment. Argan shell samples were first disintegrated using the Star Burst system, which involves a high-pressure water jet system. Then, the pretreated argan nut shell was subjected to enzymatic hydrolysis using Viscozyme L (30 FBGU/g). Afterwards, the fermentation of the hydrolysate by Saccharomyces cerevisiae was investigated. Argan nut shell, as a feedstock plentiful in carbohydrates, conferred a high yield of saccharification (90%) and an optimal ethanol bioconversion (45.25%) using Viscozyme L (30 FBGU/g) at 2%w/v of argan feedstock.

Bioconversion of the Brown Tunisian Seaweed Halopteris scoparia: Application to Energy

The brown Tunisian seaweed Halopteris scoparia was used as a feedstock for producing renewable bioethanol, biogas, and biodiesel to demonstrate the proof of concept for the North African energy sector. A quantitative and qualitative quantification of H. scoparia composition using different colorimetric methods was completed to highlight its bioconversion potential. These substrate inputs were subjected to anaerobic fermentation by Saccharomyces cerevisiae to produce bioethanol. The materials were also used to generate bio-hydrogen and volatile fatty acids during dark fermentation by a bacterial consortium and using the oleaginous yeast Yarrowia lipolytica. The lipids were extracted and trans-esterified to Fatty Acid Methyl Esters (FAMEs), and their profiles were then analyzed with gas chromatography (GC). A significant ratio of the bioethanol, e.g., 0.35 g ethanol/g DW substrate, was produced without pretreatment, consistent with the theoretical Gay-Lussac yield. The production of the biohydrogen and lipids were up to 1.3 mL H2/g DW substrate and 0.04 g/g DW substrate, respectively, from the raw biomass. These results were higher than those reported for other well-studied seaweeds such as L. japonica. Overall, this work contributes to the current investigations in Tunisia for producing alternative energies from algae and finding new solutions to the current energy situation and environmental challenges in Maghreb.

Biomass utilization and production of biofuels from carbon neutral materials

The availability of organic matters in vast quantities from the agricultural/industrial practices has long been a significant environmental challenge. These wastes have created global issues in increasing the levels of BOD or COD in water as well as in soil or air segments. Such wastes can be converted into bioenergy using a specific conversion platform in conjunction with the appropriate utilization of the methods such as anaerobic digestion, secondary waste treatment, or efficient hydrolytic breakdown as these can promote bioenergy production to mitigate the environmental issues. By the proper utilization of waste organics and by adopting innovative approaches, one can develop bioenergy processes to meet the energy needs of the society. Waste organic matters from plant origins or other agro-sources, biopolymers, or complex organic matters (cellulose, hemicelluloses, non-consumable starches or proteins) can be used as cheap raw carbon resources to produce biofuels or biogases to fulfill the ever increasing energy demands. Attempts have been made for bioenergy production by biosynthesizing, methanol, n-butanol, ethanol, algal biodiesel, and biohydrogen using different types of organic matters via biotechnological/chemical routes to meet the world's energy need by producing least amount of toxic gases (reduction up to 20-70% in concentration) in order to promote sustainable green environmental growth. This review emphasizes on the nature of available wastes, different strategies for its breakdown or hydrolysis, efficient microbial systems. Some representative examples of biomasses source that are used for bioenergy production by providing critical information are discussed. Furthermore, bioenergy production from the plant-based organic matters and environmental issues are also discussed. Advanced biofuels from the organic matters are discussed with efficient microbial and chemical processes for the promotion of biofuel production from the utilization of plant biomasses.

Optimization of Bioethanol Production from Enzymatic Treatment of Argan Pulp Feedstock

Argan pulp is an abundant byproduct from the argan oil process. It was investigated to study the feasibility of second-generation bioethanol production using, for the first time, enzymatic hydrolysis pretreatment. Argan pulp was subjected to an industrial grinding process before enzymatic hydrolysis using Viscozyme L and Celluclast 1.5 L, followed by fermentation of the resulting sugar solution by Saccharomyces cerevisiae. The argan pulp, as a biomass rich on carbohydrates, presented high saccharification yields (up to 91% and 88%) and an optimal ethanol bioconversion of 44.82% and 47.16% using 30 FBGU/g and 30 U/g of Viscozyme L and Celluclast 1.5 L, respectively, at 10%w/v of argan biomass.

Modeling and simulation of a sawdust mixture-based integrated biorefinery plant producing bioethanol

The design, modeling and simulation of an integrated biorefinery plant assumed to convert different forestry assortments such as sawdust or shavings (sawmill waste) into bioethanol from cellulose and hemicellulose as the main product, and lignin as the most valuable co-product, was carried out. The proposed lignocellulosic ethanol biorefinery plant was simulated with ProSimPlus. The model was based on experimental results and includes an Organosolv pretreatment, enzymatic hydrolysis, fermentation and distillation to obtain bioethanol. The investigated plant size processed 70,088 tons of biomass/year, with a production capacity of 11,650 tons ethanol/year. Ethanol productivity reached 351 L/ton of dry feedstock. Considering water consumption, approximately 4.8 L of water were needed to produce a liter of ethanol. Finally, the energy targeting through conventional pinch analysis lead to 16.4 MW and 16.07 MW of hot and cold utility energy demand for the entire process respectively with the cogeneration of electricity.

Hydrolysis and fermentation steps of a pretreated sawmill mixed feedstock for bioethanol production in a wood biorefinery

The aim of this work was to demonstrate the feasibility of second-generation bioethanol production using for the first time a sawmill mixed feedstock comprising four softwood species, representative of biomass resource in Auvergne-Rhône-Alpes region (France). The feedstock was subjected to a microwave-assisted water/ethanol Organosolv pretreatment. The investigation focused on enzymatic hydrolysis of this pretreated sawmill feedstock (PSF) using Cellic® Ctec2 as the enzyme, followed by fermentation of the resulting sugar solution using Saccharomyces cerevisiae strain. The cellulose-rich PSF with 71% w/w cellulose content presented high saccharification yields (up to 80%), which made it perfect for subsequent fermentation; this yield was predicted vs. time up to 5.2% w/v PSF loading using a mathematical model fitted only on data at 1.5%. Finally, high PSF loading (7.5%) and scaleup were shown to impair the saccharification yield, but alcoholic fermentation could still be carried out up to 80% of the theoretical glucose-to-ethanol conversion yield.

A closed-loop biorefinery approach for polyhydroxybutyrate (PHB) production using sugars from carob pods as the sole raw material and downstream processing using the co-product lignin

A novel closed-loop biorefinery model using carob pods as the feed material was developed for PHB production. The carob pods were delignified, and as the second step, sugars present in the delignified carob pods were extracted using water. Ralstonia eutropha and Bacillus megaterium were cultivated on the carob pod extract and its performance was evaluated using Taguchi experimental design. R. eutropha outperformed the B. megaterium in terms of its capability to grow at a maximum initial sugar concentration of 40 g L^-1 with a maximum PHB production of 12.2 g L^-1. Finally, the concentrated lignin from the first step was diluted with different proportion of chloroform to extract PHB from the bacterial biomass. The PHB yield and purity obtained were more than 90% respectively using either R. eutropha or B. megaterium. Properties of the PHB produced in this study were examined to establish its application potential.

Production of Lactic Acid from Carob, Banana and Sugarcane Lignocellulose Biomass

Lignocellulosic biomass from agricultural residues is a promising feedstock for lactic acid (LA) production. The aim of the current study was to investigate the production of LA from different lignocellulosic biomass. The LA production from banana peduncles using strain Bacillus coagulans with yeast extract resulted in 26.6 g LA·L⁻¹, and yield of 0.90 g LA·g⁻¹ sugars. The sugarcane fermentation with yeast extract resulted in 46.5 g LA·L⁻¹, and yield of 0.88 g LA·g⁻¹ sugars. Carob showed that addition of yeast extract resulted in higher productivity of 3.2 g LA·L⁻¹·h⁻¹ compared to without yeast extract where1.95 g LA·L⁻¹·h⁻¹ was obtained. Interestingly, similar LA production was obtained by the end where 54.8 and 51.4 g·L⁻¹ were obtained with and without yeast extract, respectively. A pilot scale of 35 L using carob biomass fermentation without yeast extract resulted in yield of 0.84 g LA·g⁻¹ sugars, and productivity of 2.30 g LA·L⁻¹·h⁻¹ which indicate a very promising process for future industrial production of LA.

Using CO2 as an Oxidant in the Catalytic Pyrolysis of Peat Moss from the North Polar Region

As global warming and climate change become perceived as significant, the release of greenhouse gases (GHGs) stored in the earth's polar regions is considered a matter of concern. Here, we focused on exploiting GHGs to address potential global warming challenges in the north polar regions. In particular, we used CO₂ as a soft oxidant to recover energy as syngas (CO and H₂) and to produce biochars from pyrolysis of peat moss. CO₂ expedited homogeneous reaction with volatile matters from peat moss pyrolysis, and the mechanistic CO₂ role resulted in the conversion of CO₂ and peat moss to CO at ≥530 °C. Steel slag waste was then used as an ex situ catalyst to increase reaction kinetics, addressing the issue of the role of CO₂ being limited to ≥530 °C, with the result where substantial H₂ and CO formation was achieved at a milder temperature. The porosity of biochars, a solid peat moss pyrolysis product, was modified in the presence of CO₂, with a significant improvement in CO₂ adsorption capacity compared to those achieved by N₂ pyrolysis. Therefore, CO₂ has the potential to serve as an initial feedstock in sustainable biomass-to-energy applications and biochar production, mitigating atmospheric carbon concentrations.

Orange peel valorization by pyrolysis under the carbon dioxide environment

To valorize biomass waste, pyrolysis of orange peel was mainly investigated as a case study. In an effort to establish a more sustainable thermolytic platform for orange peel, this study particularly employed CO₂ as reactive gas medium. Accordingly, this study laid great emphasis on elucidating the mechanistic role of CO₂ in pyrolysis of orange peel. The thermo-gravimetric analysis (TGA) confirmed that no occurrence of the heterogeneous reactions between the solid sample and CO₂. However, the gaseous effluents from pyrolysis of orange peel experimentally proved that CO₂ effectively suppressed dehydrogenation of volatile matters (VMs) evolved from the thermolysis of orange peel by random bond scissions. Moreover, CO₂ reacted VMs, thereby resulting in the formation of CO. Note that the formation of CO was being initiated at temperatures ≥550 °C. The two identified roles of CO₂ led to the compositional modification of pyrolytic oil by means of lowering aromaticity.

Kinetic Modeling and Techno-economic Feasibility of Ethanol Production From Carob Extract Based Medium in Biofilm Reactor

In this study, different carob extract-based media containing Medium A (included all ingredients), Medium B (included yeast extract and salts), Medium C (included (NH4)2SO4 and salts), Medium D (included only salts) and Medium E (included no ingredients) were evaluated for ethanol fermentation by Saccharomyces cerevisiae in a biofilm reactor and their results were used for kinetic modeling. The logistic model for cell growth, Luedeking-Piret model for ethanol production and Modified Luedeking-Piret model for substrate consumption were studied. Kinetic parameters were determined by fitting the observed values of the models. The findings indicated that the predicted data with the suggested kinetic model for each medium fitted very well the experimental data. Estimated kinetics were also in good agreement with experimental kinetics. The techno-economic analysis was performed with the unit costs of the components used in the medium and ethanol. Medium-based process economic feasibility proved carob extract-based Medium E and subsequently Medium D as most economical for ethanol production. The present study verified the potential of carob extract-based medium for increased economical production of ethanol. In conclusion, the ethanol production in a biofilm reactor is growth-associated since α (gP/gX) was greater than β (gP/gX.h) and Media D and E increased the economic production of carob extract-based ethanol.

Production of lactic acid from thermal pretreated food waste through the fermentation of waste activated sludge: Effects of substrate and thermal pretreatment temperature

Valorization of organic-rich waste stream to lactic acid by the mixed microbial consortium has attracted tremendous research interests in recent years. In this study, thermal pretreatment was involved in co-fermentation of food waste (FW) and waste activated sludge (WAS) to enhance lactic acid production. First, sole FW was observed as the most suitable substrate employing thermal pretreatment for the generation of lactic acid. The fermentation time for reaching the maximal plateau was significantly shortened at a corresponding thermal pretreatment temperature. The mechanism study found that the enhancement of lactic acid yield was in accordance with the acceleration of solubilization and hydrolysis. Furthermore, the physicochemical characteristics of fermentative substrate and surface morphology of the fermentation mixture varied with the pretreatment temperatures. Further investigations of microbial community structure also revealed that the proportions of key microorganisms such as Bacillus and Lactobacillus were changed by the thermal pretreatment.

The DNA-methyltransferase inhibitor 5-aza-2-deoxycytidine affects Humicola grisea enzyme activities and the glucose-mediated gene repression

Humicola grisea var. thermoidea (Hgvt) is a thermophilic ascomycete that produces lignocellulolytic enzymes and it is proposed for the conversion of agricultural residues into useful byproducts. Drugs that inhibit the DNA methyltransferases (DNMTs) activity are employed in epigenetic studies but nothing is known about a possible effect on the production of fungal enzymes. We evaluated the effect of 5-aza-2'-deoxycytidine (5-Aza; a chemical inhibitor of DNMTs activity) on the secreted enzyme activity and on the transcription of cellulase and xylanase genes from Hgvt grown in agricultural residues and in glucose. Upon cultivation on wheat bran (WB), the drug provoked an increase in the xylanase activity at 96 h. When Hgvt was grown in glucose (GLU), a repressor of Hgvt glycosyl hydrolase genes, 5-Aza led to increased transcript accumulation for the cellobiohydrolases and for the xyn2 xylanase genes. In WB, 5-Aza enhanced the expression of the transcription factor CreA gene. Growth on WB or GLU, in presence of 5-Aza, led to a significant increase in transcripts of the pH-response regulator PacC gene. To our knowledge, this is the first report on the effect of a DNMT inhibitor in the production of fungal plant cell wall degradation enzymes.