Bioalcohol Production Research Articles

A review on the design and fabrication of polydimethylsiloxane thin-film composite membranes (TFCMs) for alcohol permselective pervaporation

Pervaporation-based membrane technology have gained increasing interest due to their energy efficiency and environmental sustainability. Polydimethylsiloxane (PDMS) thin-film composite membranes (TFCMs) have emerged as promising candidates for alcohol permselective applications. Compared to the development of pervaporation membrane for water purification, the optimization progress with the ethanol recovery membrane has been fairly slow and fails to meet requirements of bio-alcohol production. Despite the continuous efforts on membrane materials, the role of structural, physicochemical properties for the forming progress of selective layer on substrate is not a well-attended topic. This paper summarized the design and construction considerations of PDMS composite membranes for pervaporation from the viewpoint of the transport resistance model, including the effect of selective layer, support layer, and intermediate layer, to deeply understand and precisely regulate the preparation process. We high light the key role of crosslinking and spreading of PDMS on porous support layer in membrane fabrication. The structure-activity relationship between the separation performance of transport structure with the membrane solution properties, substrate pore structure, and the fabrication methods was discussed in detail. It was indicated that the challenges for the TFCMs applied on a pilot or industrial scale include the thickness control, coating and curing time optimization, and solvent issue. Finally, it was expected for further research to optimize the membrane fabrication process, develop novel advanced membrane materials and to explore complex and potential applications the new requirements in industry.

Improved 2,3-Butanediol Production Rate of Metabolically Engineered Saccharomyces cerevisiae by Deletion of RIM15 and Activation of Pyruvate Consumption Pathway.

Saccharomyces cerevisiae is a promising host for the bioproduction of higher alcohols, such as 2,3-butanediol (2,3-BDO). Metabolically engineered S. cerevisiae strains that produce 2,3-BDO via glycolysis have been constructed. However, the specific 2,3-BDO production rates of engineered strains must be improved. To identify approaches to improving the 2,3-BDO production rate, we investigated the factors contributing to higher ethanol production rates in certain industrial strains of S. cerevisiae compared to laboratory strains. Sequence analysis of 11 industrial strains revealed the accumulation of many nonsynonymous substitutions in RIM15, a negative regulator of high fermentation capability. Comparative metabolome analysis suggested a positive correlation between the rate of ethanol production and the activity of the pyruvate-consuming pathway. Based on these findings, RIM15 was deleted, and the pyruvate-consuming pathway was activated in YHI030, a metabolically engineered S. cerevisiae strain that produces 2,3-BDO. The titer, specific production rate, and yield of 2,3-BDO in the test tube-scale culture using the YMS106 strain reached 66.4 ± 4.4 mM, 1.17 ± 0.017 mmol (g dry cell weight h)-1, and 0.70 ± 0.03 mol (mol glucose consumed)-1. These values were 2.14-, 2.92-, and 1.81-fold higher than those of the vector control, respectively. These results suggest that bioalcohol production via glycolysis can be enhanced in a metabolically engineered S. cerevisiae strain by deleting RIM15 and activating the pyruvate-consuming pathway.

Lignocellulosic ethanol and butanol production by Saccharomyces cerevisiae and Clostridium beijerinckii co-culture using non-detoxified corn stover hydrolysate

Considering global economic and environmental –benefits, green renewable biofuels such as ethanol and butanol are considered as sustainable alternatives to fossil fuels. Thus, developing a co-culture strategy for ethanol and butanol production by Saccharomyces cerevisiae and Clostridium beijerinckii has emerged as a promising approach for biofuel production from lignocellulosic biomass. This study developed a co-culture of S. cerevisiae and C. beijerinckii for ethanol and butanol production from non-detoxified corn stover hydrolysate. By firstly inoculating 3 % S. cerevisiae and then 7 % C. beijerinckii with 8–10 h time intervals, the optimized co-culture process gave 24.0 g/L ABE (20.8 g/L ethanol and 2.4 g/L butanol), obtaining ABE yield and productivity of 0.421 g/g and 0.55 g/L/h. The demonstrated co-culture strategy made full use of hexose and pentose in hydrolysate and contributed to total yield and efficiency compared to conventional ethanol or ABE fermentation, indicating its great potential for developing economically feasible and sustainable bioalcohols production.

Escherichia coli displays a conserved membrane proteomic response to a range of alcohols

BackgroundAlcohol is a good and environment-friendly fuel that can be microbially produced, capable of eliminating many of the limitations of the present-day fossil fuels. However, the inherent toxic nature of alcohols to the microbial cells leads to end-product inhibition that limits large-scale alcohol production by fermentation. Fundamental knowledge about the stress responses of microorganisms to alcohols would greatly facilitate to improve the microbial alcohol tolerance. The current study elucidates and compares the changes in the membrane proteome of Escherichia coli in response to a range of alcohols.ResultsAlthough alcohol toxicity increased exponentially with alcohol chain length (2–6 carbon), similar stress responses were observed in the inner and outer membrane proteome of E. coli in the presence of 2-, 4- and 6-carbon alcohols at the MIC50. This pertains to: (1) increased levels of inner membrane transporters for uptake of energy-producing metabolites, (2) reduced levels of non-essential proteins, associated with anaerobic, carbon starvation and osmotic stress, for energy conservation, (3) increased levels of murein degrading enzymes (MltA, EmtA, MliC and DigH) promoting cell elongation and 4) reduced levels of most outer membrane β-barrel proteins (LptD, FadL, LamB, TolC and BamA). Major outer membrane β-barrel protein OmpC, which is known to contribute to ethanol tolerance and membrane integrity, was notably reduced by alcohol stress. While LPS is important for OmpC trimerisation, LPS release by EDTA did not lower OmpC levels. This suggests that LPS release, which is reported under alcohol stress, does not contribute to the reduced levels of OmpC in the presence of alcohol.ConclusionsSince alcohol primarily targets the integrity of the membrane, maintenance of outer membrane OmpC levels in the presence of alcohol might help in the survival of E. coli to higher alcohol concentrations. The study provides important information about the membrane protein responses of E. coli to a range of alcohols, which can be used to develop targeted strategies for increased microbial alcohol tolerance and hence bioalcohol production.

Fouling of Polyalkylmethylsiloxane Composite Membranes during Pervaporation Separation of ABE-Fermentation Mixtures

Production of bio-alcohols is one of the approaches used in the development of alternative energy. Pervaporation is a promising option for the separation of bio-alcohols from the fermentation mixture. A serious problem in the process of continuous extraction of biobutanol from the fermentation broth is the contamination of the membrane, which leads to a decrease in its permeability over time. In this work, the transport properties of composite membranes based on polyheptylmethylsiloxane (PHeptMS), polydecylmethylsiloxane (PDecMS), and a commercial membrane MDK-3 were studied during separation of a real ABE-fermentation broth in vacuum pervaporation mode. The study was performed before and after continuous contact of the membranes with the fermentation broth for one month. Visually and by scanning electron spectroscopy, the presence of membrane surface residue and its effect on the wettability of the membrane selective layer by the components of the ABE broth were determined. The sediment composition was evaluated by energy dispersive analysis and infrared spectroscopy. According to the pervaporation separation of the ABE-broth using PHeptMS, PDecMS, and MDK-3 membranes, the butanol flux was 0.029, 0.012, and 0.054 kg/(m2·h), respectively. The butanol-water partition factor was 41, 22, and 13 for PHeptMS, PDecMS, and MDK-3, respectively. After one month of incubation of the membranes in ABE-fermentation broth during the separation of the model mixture, a decrease of 10 and 5% in permeate flux and separation factor, respectively, was observed for all membranes. Temperature dependences (30–60 °C) of permeate flux, permeability, and selectivity were obtained for the membranes after clogging. The most promising in terms of minimal negative changes as a result of fouling was demonstrated by the PHeptMS membrane. For it, the clogging dynamics during separation of the real fermentation broth for 216 h were investigated. Two characteristic steps of decrease in transport and separation properties were observed, after 28 and 150 h of the experiment. After 216 h of experiment, a 1.28-fold decrease in total flux through the membrane, a 9% decrease in butanol permeability, and a 10% decrease in n-butanol selectivity were found for PHeptMS.

Inhibitions of microbial fermentation by residual reductive lignin oil: Concerns on the bioconversion of reductive catalytic fractionated carbohydrate pulp

Reductive catalytic fractionation (RCF) is an emerging biomass valorization strategy with high atom economy, which primarily outputting extensively depolymerized reductive lignin oil and highly delignified pulp. In downstream processes, the polysaccharide rich pulp can be potentially transferred into various value-added biochemicals through fermentation. In this study, the negative influences of the residual lignin oil that remaining on the surface of the RCF pulp towards different industrial microbes (total 9 species, categorized into eukaryotes, Gram-negative, and Gram-positive strains) was investigated. Results indicated the reduced lignin fractions were the key inhibitors in the RCF lignin oil, whilst the polarities, molecular weight, and the substitution groups of lignin possessed significant impacts on the growth of strains. Meanwhile, the resistance to RCF lignin oil by different category of industrial strains was analyzed. Generally, eukaryotes exhibited better resistance than the Gram-negative and Gram-positive strains. Took bioethanol and acetone-butanol-ethanol fermentation as examples, the negative influence of the lignin oil on biochemicals production using the RCF pulp as substrate was explored. Batch fermentation results revealed that the RCF lignin oil limited both the sugars (glucose and xylose) metabolism and the pathways toward bio-alcohols production of the microorganism. Therefore, it is vital to take continuous technical improvement in order to minimize the negative influences of the residual lignin oil on downstream biotransformation of the RCF pulps.

Technoeconomic analysis and environmental sustainability estimation of bioalcohol production from barley straw

European Union bioeconomy policy emphasizes that the production of renewable transportation fuels should replace fossil fuels as much as possible. In particular, the utilization of waste or side-stream lignocellulosic materials for fuel production is highly recommended. Moreover, future crises forcing a reliance on locally available sources for fuels and energy may become increasingly common. Barley straw, a common agricultural residue in northern Europe, is a potential raw material for bioalcohol production via fermentation. In this study, the technoeconomic and environmental sustainability of bioethanol and biobutanol production from barley straw were evaluated. When compared with fossil gasoline production and use, the greenhouse gas emissions reduction 77.6% and 72.1% were achieved for ethanol and butanol production, respectively. Thus, the emission reduction of 65% for biofuels demanded by the European Union renewable energy directive was achieved in both biofuel production processes evaluated. However, our results indicated that ethanol production from barley straw, a well-known and mature technology, was an economically feasible process (NPV positive, IRR 20%) but that butanol production with Clostridium species through acetone-butanol-ethanol fermentation has still technoeconomic challenges to overcome (NPV negative, IRR below 10%). This was mainly due to the low yield and high recovery costs of butanol.

The use of banana peels as raw materials of bio-alcohol production

Indonesia’s energy demand has increased in recent years in line with the increase in economic growth and population in Indonesia. Most of this energy is derived from non-renewable sources such as oil, natural gas, and coal. These trends will have a significant impact on energy depletion. One solution to overcome this problem is developing alternative energy resources to replace petroleum, such as bio-alcohol. The objective of this study was to analyze the potential of bio-alcohol production from organic waste, that is, banana peel. This research is experimental. Bio-alcohol was obtained through a fermentation process of 3 types of banana peels waste, including Raja banana (Musa acuminata×M. balbisiana) peel, Agung banana (Musa paradisiaca) peel, and Nangka banana (Musa acuminata×M. balbisiana) peel. Fermentation was conducted using variations of Saccharomyces cerevisiae of 1%, 3%, and 5% with a fermentation time of 5 days. All experiments were performed in duplicate. The results showed that the highest value of bio-alcohol was produced from the waste of Raja Nangka peel at a concentration of 5% Saccharomyces cerevisiae, which was 1.70% (p-value <0.05). This study suggests the potential of banana peel waste in producing bio-alcohol as alternative energy in the future.

Polyhydroxyalkanoates production from syngas fermentation effluents: Effect of nitrogen availability

Syngas fermentation is a promising technology for bioalcohols production even though some produced volatile fatty acids (VFA) may remain unconsumed in the effluent. The present research explored the production of polyhydroxyalkanoates (PHA) from the remaining VFA of the syngas fermentation effluents in fed-batch bioreactors so that bioalcohols and biopolymers could be obtained in a combined way. In order to perform these PHA accumulation tests, two different syngas fermentation effluents, composed mainly of a mixture of VFA and alcohols, were used as substrate. Those effluents were characterized by different nitrogen availabilities, one being N-rich and the other N-limited. A mixed microbial culture (MMC) with a maximum PHA storage ability of 53.6% was used as inoculum. The microorganisms of the MMC mainly consumed the VFA rather than the alcohols, allowing the latter to accumulate as end product, besides PHA. However, when the N-rich effluent was used as substrate, the consumption rate of alcohols was 20 times higher (0.040 Cmmol-Alcohol Cmmol-X-1 h-1) compared to the N-limited effluent (0.002 Cmmol-Alcohol Cmmol-X-1 h-1). Despite not observing large differences in the maximum amount of accumulated PHA (40.5 – 41.5%), there was a decrease in the PHA content after reaching its maximum peak when the N-rich effluent was used as substrate. This trend was not observed with the N-limited effluent, in which the maximum PHA peak exactly matched with the end of the experiment.

Efficient production of n-caproate from syngas by a co-culture of Clostridium aceticum and Clostridium kluyveri

In recent years, the possibility of merging technologies for waste recovery such as those based on syngas fermentation and chain elongation has been studied for the production of medium chain fatty acids (MCFAs) and bioalcohols, in an attempt to integrate the concept of circular economy in the industry. Nevertheless, one of the main issues of this approach is the pH mismatch between acetogens and chain elongating microorganisms. This work reports, for the first time, the suitability of a co-culture of C. aceticum and C. kluyveri metabolizing syngas at near neutral pH in stirred tank bioreactors. For this purpose, bioreactor studies were carried out with continuous syngas supply. In the first experiment, maximum concentrations of n-butyrate and n-caproate of 7.0 and 8.2 g/L, respectively, were obtained. In the second experiment, considerable amounts of n-butanol were produced as a result of the reduction, by C. aceticum, of the carboxylates already formed in the broth. In both experiments, ethanol was used as an exogenous electron agent at some point. Finally, batch bottle assays were performed with a pure culture of C. aceticum grown on CO in presence of n-butyrate to assess and confirm its ability to produce n-butanol, reaching concentrations up to 951 mg/L, with a n-butyrate conversion efficiency of 96%, which had never been reported before in this species. Therefore, this work contributes to the state of the art, presenting a novel system for the bioproduction of MCFAs by combining syngas fermentation and chain elongation at near neutral pH, as opposed to the acidic pH range used in all previously reported literature.

Synthetic Biology and Metabolic Engineering Employing Escherichia coli for C2-C6 Bioalcohol Production.

Biofuel production from renewable and sustainable resources is playing an increasingly important role within the fuel industry. Among biofuels, bioethanol has been most widely used as an additive for gasoline. Higher alcohols can be blended at a higher volume compared to ethanol and generate lower greenhouse gas (GHG) emissions without a need to change current fuel infrastructures. Thus, these fuels have the potential to replace fossil fuels in support of more environmentally friendly processes. This review summarizes the efforts to enhance bioalcohol production in engineered Escherichia coli over the last 5 years and analyzes the current challenges for increasing productivities for industrial applications.

A novel hybrid digestion-gasification process integrated with membranes for efficient conversion of biomass to bio-alcohols

There is an urgent need to develop technologies which enable the conversion of biomass into liquid biofuels to fill the gap between limited fossil fuel supplies and increasing worldwide demand. In order to achieve the EU 2030 vision of at least 15% of the fuels used in the road transportation sector will be biofuels derived from non-food biomass feedstocks, the R&D of clean, inexpensive, highly end-user compatible biofuels from a virtually inexhaustible source of biomass should be pursued to make breakthroughs in cost-effective biomass to liquid biofuels (BTL) technologies. Thus, an innovative, consolidated, and sustainable technology using a hybrid digestion-gasification process integrated with membranes to produce next generation bio-alcohols from different biomass feedstocks was designed. The proposed concept was theoretically estimated to achieve an overall BTL efficiency of 44% and a cost reduction for bioalcohol production of 18.6%. Moreover, this technology can potentially achieve an overall CO2 emission reduction of > 75% for road transport based on the preliminary analysis.

Arbuscular Mycorrhiza Enhances Biomass Production and Salt Tolerance of Sweet Sorghum.

Arbuscular mycorrhizal (AM) fungi (AMF) are widely known to form a symbiosis with most higher plants and enhance plant adaptation to a series of environmental stresses. Sweet sorghum (Sorghum bicolor (L.) Moench) is considered a promising alternative feedstock for bioalcohol production because of its sugar-rich stalk and high biomass. However, little is known of AMF benefit for biomass production and salt tolerance of sweet sorghum. Here, we investigated the effects of Acaulospora mellea ZZ on growth and salt tolerance in two sweet sorghum cultivars (Liaotian5 and Yajin2) under different NaCl addition levels (0, 0.5, 1, 2, and 3 g NaCl/kg soil). Results showed AMF colonized the two cultivars well under all NaCl addition levels. NaCl addition increased mycorrhizal colonization rates in Yajin2, but the effects on Liaotian5 ranged from stimulatory at 0.5 and 1 g/kg to insignificant at 2 g/kg, and even inhibitory at 3 g/kg. High NaCl addition levels produced negative effects on both AM and non-AM plants, leading to lower biomass production, poorer mineral nutrition (N, P, K), higher Na+ uptake, and lower soluble sugar content in leaves. Compared with non-AM plants, AM plants of both cultivars had improved plant biomass and mineral uptake, as well as higher K+/Na+ ratio, but only Yajin2 plants had a low shoot/root Na ratio. AM inoculation increased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and soluble sugar content in leaves. Overall, both cultivars benefited from mycorrhization, and Yajin2 with less salt tolerance showed higher mycorrhizal response. In conclusion, AMF could help to alleviate the negative effects caused by salinity, and thus showed potential in biomass production of sweet sorghum in saline soil.

Enhancing bio-alcohol production from volatile fatty acids by suppressing methanogenic activity in single chamber microbial electrosynthesis cells (SCMECs)

This study explored alcohol production from volatile fatty acids (VFAs) in single-chambered microbial electrosynthesis systems (MES) under continuous pH control (≤pH 5.5) for methanogen inhibition. MES with 2 g-COD/l VFA could produce highest current of 5.3 mA followed by 3.6 mA in 6 g-COD/l and 0.44 mA in 8 g-COD/l, implying active bioelectrochemical reactions of microorganisms on the electrodes. Ethanol, methanol and propanol were detected as fermented bio-alcohols without methane production, and ethanol was the main product with a cumulative recovery of 7.14 mM in 2 g-COD/l, 13.6 mM in 6 g-COD/l and 17.9 mM in 8 g-COD/l. Maximum bio-alcohol yield of 0.71 g-CODAlcohols/g-CODVFAs with a recovery efficiency of 35% was obtained from MES under 2.0 g-COD/l, followed by 6 and 8 g-COD/l. The results demonstrate that pH adjustment method is an effective strategy to suppress methanogens for improved bioelectrochemical performance of alcohol production from VFAs in MES.

Bioalcohol production from acidogenic products via a two-step process: A case study of butyric acid to butanol

This article presents the full study (lab-scale experimental study and large-scale techno-economic analysis) results of a two-step catalytic process for the conversion of organic waste–derived butyric acid to butanol. The two-step process consists of the (1) esterification of butyric acid to methyl butyrate and (2) hydrogenolysis of this methyl butyrate to butanol. The first reaction, esterification of butyric acid, was optimized using carbon-based catalysts. The production of butanol from methyl butyrate via hydrogenolysis was investigated using bimetallic Pt–Co catalysts. The hydrogenolysis of methyl butyrate on these catalysts under optimal conditions of 250 °C, 5 MPa H2, and a feed/catalyst weight ratio of 11.2 led to 54.1% selectivity toward 1-butanol. Based on the experimental results, an integrated process simulation model was developed to determine the economic potential of the two-step production of butanol from butyric acid. Using this model, the techno-economic feasibility of the two-step process was analyzed. The minimum selling price (MSP) of 1-butanol produced from butyric acid using this process was US$ 3.388 per gallon of gasoline equivalent (GGE). This MSP is in the range of recent biofuel market prices of US$ 2.03/GGE to US$ 3.83/GGE.

Production of bioalcohols and antioxidant compounds by acid hydrolysis of lignocellulosic wastes and fermentation of hydrolysates with Hansenula polymorpha.

The effect of the H2SO4 concentration in the hydrolysis of sunflower-stalk waste, at 95ºC and using a liquid/solid relation of 20, was studied. In a later stage, the hydrolysates were fermented at different temperatures with the aim of ethanol and xylitol production. A total conversion of the hemicellulose at the acid concentration of 0.5mol/L was achieved; whereas an acid concentration of 2.5mol/L was needed to reach the maximum value in the conversion of the cellulose fraction. The analysis of the hydrolysis kinetics has enabled to determine the apparent reaction order, which was 1.3. The hydrolysates from hydrolysis process with H2SO4 0.5mol/L, once detoxified, were fermented at pH 5.5, temperatures 30, 40, and 50ºC with the yeast Hansenula polymorpha (ATCC 34438), resulting in a sequential uptake of sugars. In relation to ethanol and xylitol yields, the best results were observed at 50°C( =0.11g/g; =0.12g/g). Instantaneous xylitol yields were higher than in ethanol, at the three temperatures essayed. Different phenolic compounds were analyzed in the hydrolysates; hydroxytyrosol was the most abundant (3.79mg/L). The recovery of these compounds entails the elimination of inhibitors in the fermentation process and the production of high value-added antioxidant products.

Braskem and Haldor Topsoe start-up demo unit for developing renewable MEG

The use of fermentative microorganisms for efficient C2–C5 alcohol production from renewable feedstocks has been a subject of intense investigation over recent decades. While the physiology of microorganisms involved in alcohol production from first-generation feedstocks is well established, the utilization of microorganisms for the production of second-generation bioalcohols from complex biomass, such as lignocellulose, remains challenging. At present, there are no “all in one” bioprocessing organisms that have been used on an industrial-scale capable of both complex biomass conversions to fermentable substrates and fermentation to alcohols. Extensive investigations on bioalcohol-producing organisms and related processes have targeted challenges ranging from the conversion of feedstock biomass to fermentable substrates, process design, and organism improvements. Recent advances in the production of liquid fuel carriers such as ethanol, propanol, and butanol as well as branched-chain alcohols will be the subject of this chapter.

Gasification of lignin-rich residues for the production of biofuels via syngas fermentation: Comparison of gasification technologies

This paper reports the use of lignin-rich residues from second generation bioethanol production, to produce syngas that can be applied in the gas fermentation process. Three gasification technologies at a different scale were considered in this study. Fixed bed updraft gasification of about 30 kg/h solid feed, bubbling fluidized bed gasification of about 0.3 kg/h solid feed and indirect gasification of about 3 kg/h solid feed. Two lignin-rich residues with different properties were tested and the results were evaluated in terms of feedstock pretreatment (grinding, drying and pelleting) and syngas quality requirements for the fermentation process. The molar H2/CO ratio (ranging from 0.6 to 1.0) and the tar yield (18–108 g/Nm3) obtained from the three gasification technologies was quite different. For the syngas fermentation process, low H2 to CO ratio is preferred, as most of the organisms grow better on CO than H2. Furthermore, different contents of impurities that can reduce the fermentability of the gas (such as hydrocarbons, HCN, HCl, NH3, COS and other organic S- compounds) were detected in the product gas. The concentration of these compounds in the syngas is related to the content of the corresponding compounds in the original feedstock. The different characteristics of the lignin-rich feedstocks are related to the specific pre-treatment technologies for the (hemi)cellulose extraction. By tuning the pre-treatment technology, the properties of the feedstock can be improved, making it a suitable for gasification. Tar and unsaturated hydrocarbon compounds need to be removed to very low levels prior to the fermentation process. As a next step, the combination of the gasification and the appropriate product gas cleaning, with the syngas fermentation process for the production of bio-alcohols will be evaluated and the overall efficiency of the gasification-fermentation process will be assessed.

Review: Biofuel Production from Plant and Algal Biomass

Biofuels are the promising alternative to exhaustible, environmentally unsafe fossil fuels. Algal biomass is attractive raw for biofuel production. Its cultivation does not compete for cropland with agricultural growing of food crop for biofuel and does not require complex treatment methods in comparison with lignocellulose-enriched biomass. Many microalgae are mixotrophs, so they can be used as energy source and as sewage purifier simultaneously. One of the main steps for algal biofuel fabrication is the cultivation of biomass. Photobioreactors and open-air systems are used for this purpose. The formers allow the careful cultivation control, but the latter ones are cheaper and simpler. Biomass conversion processes may be divided to the thermochemical, chemical, biochemical methods and direct combustion. For biodiesel production, triglyceride-enriched biomass undergoes transetherification. For bioalcohol production, biomass is subjected to fermentation. There are three methods of biohydrogen production in the microalgal cells: direct biophotolysis, indirect biophotolysis, fermentation.

Bioalcohol production from spent coffee grounds and okara waste biomass by engineered Bacillus subtilis

Protein biomass is one of the useful biomasses which could be converted to various biochemicals. In this study, protein-rich food wastes such as SCG (spent coffee ground) and okara waste were utilized for production of bioalcohol of ethanol, isobutanol, and methylbutanols by engineered Bacillus subtilisΔcodYΔbkdBΔrelA. Protein biomass is composed of amino acids, and some are depleted in the early phase of biotransformation process. This causes cellular stress and low growth rate of host B. subtilis strains leading to low productivity of biochemicals. To overcome this nutritional stress, B. subtilis host strain was engineered to restore nutritional stress by inactivation of RelA regulatory protein with additional supplement of lysine and cysteine. Finally, the engineered B. subtilis ΔcodYΔbkdBΔrelA showed the highest bioalcohol production of 0.59 ± 0.09 g/L and 0.43 ± 0.03 g/L from SCG and okara protein resources, respectively.