Optimization of organosolv pretreatment of rice straw for enhanced biohydrogen production using Enterobacter aerogenes

Synthetic Lignin Oligomers: Analytical Techniques, Challenges, and Opportunities

Lignin is the second most abundant renewable material after cellulose. However, its economic use is currently relegated to low-value energy production. This biomaterial holds great potential as a source of renewable biofuels, bio-based chemicals, advanced materials, and integrated biorefineries. Fractionation and depolymerization methods yield liquid repositories of promising aromatic monomers and lignin oligomers (LO) that retain many of the structural components found in the native material. However, analyzing this complex mixture is challenging due to the wide range of molecular sizes and heterogeneous chemical structure, which makes their structural elucidation a critical obstacle - unlocking the full potential of lignin hinges upon developing appropriate standards and analytical methods to address existing knowledge gaps. This review provides a comprehensive examination of current analytical techniques for elucidating the chemical structure of lignin oligomers, exploring synthesis methods, molecular structures, and their advantages and limitations. Built upon these findings, opportunities for synergy between synthetic oligomers and lignin utilization can be revealed, such as bioactive compound production and biorefinery integration. Moreover, we underscore the need for standardized analytical methods to facilitate the design of lignin oligomer standards and their diverse applications.

Isolation and characterization of novel bacterial strain from sewage sludge and exploring its potential for hydrogen production

Hydrogen (H2) energy has garnered significant attention due to its numerous advantages. Nonetheless, for future commercialization, it is imperative to screen and identify strains with enhanced H2-producing capacities. In order to attain a high and consistent production performance, the conversion of biomass sources into H2 requires careful selection of the most appropriate H2-producing bacteria. This study aimed to isolate and identify a highly effective H2 producing bacteria from local sewage sludge and assess its fermentability for H2 production. The isolate was first identified by means of morphological, phenotypic, biological, and 16 S rRNA investigations. A facultative anaerobe that produces H2 and is gram-negative was identified as Alcaligenes ammonioxydans strain SRAM. For the purpose of determining whether the isolate could produce H2 using glucose as the substrate, its fermentability was evaluated in 500 mL serum bottles. This strain demonstrated the ability to produce H2 from glucose under anaerobic environment, achieving a maximum H2 yield of 2.9 mol H₂/mol of glucose. The highest rate of H2 production, 9.261 mmol H₂/ g dry cell weight per hr, was attained at 37 °C and an initial pH of 6.8. This work effectively illustrated the use of a novel locally isolated strain in the biotechnological conversion of glucose to H2. This strategy offers an effective remedy for the world's energy instability in addition to addressing environmental issues related to industrial operations.

In vitro effects of alginate lyase SG4 + produced by Paenibacillus lautus alone and combined with antibiotics on biofilm formation by mucoid Pseudomonas aeruginosa

Alginate is a major extra polymeric substance in the biofilm formed by mucoid Pseudomonas aeruginosa. It is the main proven perpetrator of lung infections in patients suffering from cystic fibrosis. Alginate lyases are very important in the treatment of cystic fibrosis. This study evaluated the role of standalone and in conjugation, effect of alginate lyase of SG4 + isolated from Paenibacillus lautus in enhancing in vitro bactericidal activity of gentamicin and amikacin on mucoid P. aeruginosa. Using Response Surface Methodology (RSM) alginate lyase SG4 + production was optimized in shake flask and there 8.49-fold enhancement in enzyme production. In fermenter, maximum growth (10.15 mg/ml) and alginate lyase (1.46 International Units) production, 1.71-fold was increased using Central Composite Design (CCD). Further, fermentation time was reduced from 48 to 20 h. To the best of our knowledge this is the first report in which CCD was used for fermenter studies to optimize alginate lyase production. The Km and Vmax of purified enzyme were found to be 2.7 mg/ml and 0.84 mol/ml-min, respectively. The half-life (t 1/2) of purified alginate lyase SG4 + at 37 °C was 180 min. Alginate lyase SG4 + in combination with gentamicin and amikacin eradiated 48.4- 52.3% and 58- 64.6%, alginate biofilm formed by P. aeruginosa strains, respectively. The study proves that alginate lyase SG4 + has excellent exopolysaccharide disintegrating ability and may be useful in development of potent therapeutic agent to treat P. aeruginosa biofilms.

Effect of deep eutectic solvent pretreatment on biohydrogen production from corncob: pretreatment temperature and duration

Deep eutectic solvent pretreatment with different temperatures and durations was applied to corncob to increase hydrogen yield via photo-fermentation. The correlation of composition, enzymatic hydrolysis, and hydrogen production in pretreated corncobs, as well as energy conversion was evaluated. Deep eutectic solvent pretreatment effectively dissolved lignin, retained cellulose, and enhanced both enzymatic hydrolysis and hydrogen production. The maximum cumulative hydrogen yield obtained under a pretreatment condition of 50°C and 12 h was 677.45 mL; this was 2.72 times higher than that of untreated corncob, and the corresponding lignin removal and enzymatic reduction of sugar concentration were 79.15% and 49.83 g/L, respectively; the highest energy conversion efficiency was 12.08%. The hydrogen production delay period was shortened, and the maximum shortening time was 18.9 h. Moreover, the cellulose content in pretreated corncob was positively correlated with both reducing sugar concentration and hydrogen yield and had the strongest influence on hydrogen production.

Effect of nano-metal doped calcium peroxide on biomass pretreatment and green hydrogen production from rice straw

In this study, calcium peroxide was modified and doped with metal-based nanoparticles (NP) to enhance the efficiency of pretreatment and biohydrogen generation from RS. The findings revealed that the addition of MnO2-CaO2 NPs (at a dosage of 0.02 g/g TS of RS) had a synergistic effect on the breakdown of biomass and the production of biohydrogen. This enhancement resulted in a maximum hydrogen yield (HY) of 58 mL/g TS, accompanied by increased concentrations of acetic acid (2117 mg/L) and butyric acid (1325 mg/L). In contrast, RS that underwent pretreatment without the use of chemicals or NP exhibited a lower HY of 28 mL/g TS, along with the lowest concentrations of acetic acid (1062 mg/L) and butyric acid (697 mg/L). The outcome showed that supplementation of NP stimulated the pretreatment of RS and improved the formation of acetic and butyric acid through the regulation of metabolic pathways during acidogenic fermentation.

Agro-waste to sustainable energy: A green strategy of converting agricultural waste to nano-enabled energy applications

The rising demands of the growing population have raised two significant global challenges viz. energy crisis and solid-waste management, ultimately leading to environmental deterioration. Agricultural waste (agro-waste) contributes to a large amount of globally produced solid waste, contaminating the environment, and raising human-health issues on improper management. It is essential for a circular economy to meet sustainable development goals and to design strategies to convert agro-waste into energy using nanotechnology-based processing strategies, by addressing the two significant challenges. This review illustrates the nano-strategic aspects of state-of-the-art agro-waste applications for energy harvesting and storage. It details the fundamentals related to converting agro-waste into energy resources in the form of green nanomaterials, biofuels, biogas, thermal energy, solar energy, triboelectricity, green hydrogen, and energy storage modules in supercapacitors and batteries. Besides, it highlights the challenges associated with agro-waste-to-green energy modules with their possible alternate solutions and advanced prospects. This comprehensive review will serve as a fundamental structure to guide future research on smart agro-waste management and nanotechnological innovations dedicated to its utilization for green energy applications without harming the environment. The nanomaterials assisted generation and storage of energy from agro-waste is touted to be the near-future of smart solid-waste management strategy for green and circular economy.

Simultaneous removal of microplastics and benzalkonium chloride using electrocoagulation process: statistical modeling and techno-economic optimization

Microplastics and benzyldimethyldodecylammonioum chloride (DDBAC) enter the environment more frequently during the COVID-19 pandemic and their co-occurrence will be a potential threat to the environment in the post-pandemic era. This study investigates the performance of an electrochemical system for the simultaneous removal of microplastics and DDBAC. During experimental studies, effects of applied voltage (3-15 V), pH (4-10), time (0-80 min), electrolyte concentration (0.01-0.0.09 M), electrode configuration, and perforated anode were investigated to identify their influence on DDBAC and microplastics removal efficiency. Eventually, the techno-economic optimization yielded to evaluate the commercial feasibility of this process. The central composite design (CCD) and analysis of variance (ANOVA) are employed for evaluation and optimization of the variables and response, DDBAC-microplastics removal, and for determining the adequacy and significance of mathematical models proposed by response surface methodology (RSM). Experimental results indicate that optimum conditions are pH = 7.4, time = 80 min, electrolyte concentration = 0.05 M, and applied voltage = 12.59, in which the removal of microplastics, DDBAC, and TOC reached the maximum level, which was 82.50%, 90.35%, and 83.60% respectively. The results confirm that the valid model is adequately significant for the target response. Overall, financial and energy consumption analyses confirmed that this process is a promising technology as a commercial method for the removal of DDBAC-microplastics complexes in water and wastewater treatment.

Optimization and Evaluation for the Capacitive Deionization Process of Wastewater Reuse in Combined Cycle Power Plants

Combined cycle power plants (CCPPs) use large amounts of water withdrawn from nearby rivers and generate wastewater containing ions and pollutants. Despite the need for wastewater reclamation, few technologies can successfully convert the wastewater into make-up water for CCPPs. Therefore, this study aimed to apply capacitive deionization (CDI) for wastewater reclamation in CCPPs. Using a bench-scale experimental unit, which included ion exchange membranes and carbon electrodes, response surface methodology (RSM) was used to optimize the operating conditions of the CDI process to increase the total dissolved solids (TDS) removal and product water ratio. The optimal conditions were found to be a voltage of 1.5 V, a flow rate of 15 mL/min, and an adsorption/desorption ratio of 1:0.8. The changes in CDI performance with time were also studied, and the foulants on the membranes, spacers, and electrodes were examined to understand the fouling mechanism. The TDS removal decreased from 93.65% to 55.70% after 10 days of operation due to the deposition of scale and organic matter. After chemical cleaning, the TDS removal rate recovered to 93.02%, which is close to the initial condition.

Pretreatments of lignocellulosic and algal biomasses for sustainable biohydrogen production: Recent progress, carbon neutrality, and circular economy

Lignocellulosic and algal biomasses are known to be vital feedstocks to establish a green hydrogen supply chain toward achieving a carbon-neutral society. However, one of the most pressing issues to be addressed is the low digestibility of these biomasses in biorefinery processes, such as dark fermentation, to produce green hydrogen. To date, various pretreatment approaches, such as physical, chemical, and biological methods, have been examined to enhance feedstock digestibility. However, neither systematic reviews of pretreatment to promote biohydrogen production in dark fermentation nor economic feasibility analyses have been conducted. Thus, this study offers a comprehensive review of current biomass pretreatment methods to promote biohydrogen production in dark fermentation. In addition, this review has provided comparative analyses of the technological and economic feasibility of existing pretreatment techniques and discussed the prospects of the pretreatments from the standpoint of carbon neutrality and circular economy.

Process optimization for biosynthesis of pyruvate decarboxylase (PDC) and Neuberg’s ketol (PAC) from a novel Pichia cecembensis through response surface methodology

Purpose

Phenylacetylcarbinol (PAC) is an intermediate for the synthesis of several active pharmaceutical ingredients (ephedrine, pseudoephedrine, norephedrine, etc.) used for the production of antiasthematics and decongestants. An efficient biosynthesis of PAC through condensation of benzaldehyde and acetaldehyde catalyzed by a solvent tolerant pyruvate decarboxylase (PDC) is being reported. A process for the biosynthesis of PAC was designed and optimized through response surface methodology (RSM) in the present study.

Methods

The effects of incubation time (8–18 h), incubation temperature (30–38 °C), medium pH (4–10), and inoculum size (4–10%) on PAC yield, sugar consumption, and PDC activity were determined through submerged fermentation using a newly isolated potent yeast strain of Pichia cecembensis. PAC was quantified spectrophotometerically and through HPLC. PDC produced was exposed to 40 mM benzaldehyde as whole cells, crude extract, and partialy purified preparation to check its stability against the said solvent.

Results

The highest PDC activity and PAC yield during present study were found to be 56.27 U/ml and 8.44 g/l, respectively. The yield of PAC was increased by 71% (2.22 to 8.44 g/l) after process optimization through RSM with incubation time of 13 h, incubation temperature of 33 °C, and 18% total sugar as significant factors (P-values, 0.902, 0.260, and 0.247, respectively). R-squared value of 0.770 and Adeq Precision value of 4.888 show the goodness of fit of the process design. PDC is used in the form of Pichia cecembensis whole cells revealed higher stability towards benzaldehyde and elevated temperature as compared to partially purified PDC. Whole cells and partially purified PDC showed half-lives of 240 and 72 h at 4 °C, whereas 33 and 28.5 h at 25 °C. PAC was purified though HPLC with a purity level of 76.18%.

Conclusion

Incubation time, temperature, and sugar concentration were found to be significant factors for the biosynthesis of PAC. A newly isolated Pichia cecembensis produced a highly active, solvent, and temperature-tolerant pyruvate decarboxylase (PDC) which is superior to its counterpart being presently used in the industry. Hence, this novel yeast species is a promising candidate for commercial production of PAC and other related APIs owing to its highly stable PDC.

Green hydrogen production through consolidated bioprocessing of lignocellulosic biomass using nanobiotechnology approach

The main objective of this study was to develop a sustainable process for hydrogen production by implementing nanotechnology in combination with consolidated bioprocessing (CBP) approach from lignocellulosic biomass (LCB). Peroxidase mimicking CeFe₃O₄ nanoparticles (NPs, 4.0 g/L) were applied for degradation of lignin from raw corn cob (CC) biomass for generation of cellulose-hemicellulose fractions amenable towards Clostridium cellulovorans during fermentation process. NP-treated biomass exhibited 43.26 % lignin removal from raw CC which was further employed for hydrogen fermentation by C. cellulovorans through CBP method. The strain yielded maximum 78.45 mL of cumulative hydrogen with hydrogen production rate of 1.55 mL/h using NP-treated CC. To the best of our knowledge, this is the first study on enhanced hydrogen production using NP-treated CC biomass in single pot fermentation which can prove to be a simpler, easier, and more economical process.

The comprehensive characterization of Prosopis juliflora pods as a potential bioenergy feedstock

The production of renewable and sustainable biofuels using inevitable wastes is a promising alternative to the alarming depletion of fossil fuels. Significantly, the sustainable biorefinery of lignocellulosic waste, as an alternative fuel source, is a prognosticating approach to tackle many agricultural/forestry residues and offers a circular economy as well as environmental benefits. But, the heterogeneity of lignocellulosic biomass is one of the major bottlenecks in lignocellulosic biorefinery. Thus the characterization of lignocellulosic biomass is essential to understanding the feedstock's nature, composition and suitability for biofuel production. The present study taps evergreen spiny non-edible pods of Prosopis juliflora (Pj) as an energy feedstock. Proximate, ultimate and biochemical characterization of Pj pods were conducted, and thermal behaviour and calorific values were determined. Cellulose and hemicellulose were isolated and characterized by reliable methods. The overall characterization has revealed the Pj pods as a potential feedstock for bioenergy. The collected Pj pods contain (% w/w) moisture 7.89 ± 0.002, volatile matter 87.67 ± 0.002, ash 0.21 ± 0.002, fixed carbon 4.23 ± 0.002 with a calorific value of 17.62 kg/MJ. The CHNS content was (w/w %) carbon 41.77, nitrogen 3.58, sulfur 26.3 and hydrogen 6.55. The biochemical composition analysis yields (% w/w) on a dry basis; cellulose 26.6 ± 0.18, hemicellulose 30.86 ± 0.27, lignin 4.71 ± 0.12, protein 11.63 ± 0.12 and starch 1.1 ± 0.06 and extractives 30.56 ± 0.008. The isolated cellulose and hemicellulose were analyzed and confirmed by CP/MAS &¹H NMR, FTIR, TG-DSC, SEM, XRD, and TGA. The present results revealed that the tested biomass, Prosopis juliflora, could be used as a feedstock in biorefinery for bioenergy.

Intensification of Acidogenic Fermentation for the Production of Biohydrogen and Volatile Fatty Acids—A Perspective

Utilising ‘wastes’ as ‘resources’ is key to a circular economy. While there are multiple routes to waste valorisation, anaerobic digestion (AD)—a biochemical means to breakdown organic wastes in the absence of oxygen—is favoured due to its capacity to handle a variety of feedstocks. Traditional AD focuses on the production of biogas and fertiliser as products; however, such low-value products combined with longer residence times and slow kinetics have paved the way to explore alternative product platforms. The intermediate steps in conventional AD—acidogenesis and acetogenesis—have the capability to produce biohydrogen and volatile fatty acids (VFA) which are gaining increased attention due to the higher energy density (than biogas) and higher market value, respectively. This review hence focusses specifically on the production of biohydrogen and VFAs from organic wastes. With the revived interest in these products, a critical analysis of recent literature is needed to establish the current status. Therefore, intensification strategies in this area involving three main streams: substrate pre-treatment, digestion parameters and product recovery are discussed in detail based on literature reported in the last decade. The techno-economic aspects and future pointers are clearly highlighted to drive research forward in relevant areas.

Optimization of ethanol-extracted lignin from palm fiber by response surface methodology and preparation of activated carbon fiber for dehumidification

Lignin is a renewable bioresource that can be used for a variety of value-added applications. However, the effective separation of lignin from lignocellulosic biomass remains an ongoing challenge. In this study, lignin was extracted from waste palm fiber and successfully converted into a dehumidifying material. The following four process parameters of lignin extraction from palm fiber were optimized systematically and comprehensively using the response surface methodology: reaction time, extraction temperature, ethanol concentration and solid/liquid ratio. The results revealed that under the optimum processing conditions (111 min of extraction at 174 °C using 73% ethanol at 1/16 g/mL solid/liquid ratio), the extraction yield of lignin was 56.2%. The recovery of ethanol solvent was as high as 91.8%. Further, the lignin could be directly used without purification to produce lignin-based activated carbon fibers (LACFs) with specific surface area and total pore volume of 1375 m2/g and 0.881 cm3/g, respectively. Compared with the commercial pitch-based activated carbon fiber, the LACF has a higher specific area and superior pore structure parameters. This work provides a feasible route for extracting lignin from natural palm fiber and demonstrates its use in the preparation of activated carbon fiber with a remarkable performance as a solid dehumidification agent.

Recent advances in biofuel production through metabolic engineering

Rising global energy demands and climate crisis has created an unprecedented need for the bio-based circular economy to ensure sustainable development with the minimized carbon footprint. Along with conventional biofuels such as ethanol, microbes can be used to produce advanced biofuels which are equivalent to traditional fuels in their energy efficiencies and are compatible with already established infrastructure and hence can be directly blended in higher proportions without overhauling of the pre-existing setup. Metabolic engineering is at the frontiers to develop microbial chassis for biofuel bio-foundries to meet the industrial needs for clean energy. This review does a thorough inquiry of recent developments in metabolic engineering for increasing titers, rates, and yields (TRY) of biofuel production by engineered microorganisms.

A Novel Endophytic Trichoderma longibrachiatum WKA55 With Biologically Active Metabolites for Promoting Germination and Reducing Mycotoxinogenic Fungi of Peanut

Plant residuals comprise the natural habitat of the plant pathogen; therefore, attention is currently focusing on biological-based bioprocessing of biomass residuals into benefit substances. The current study focused on the biodegradation of peanut plant residual (PNR) into citric acid (CA) through a mathematical modeling strategy. Novel endophytic Trichoderma longibrachiatum WKA55 (GenBank accession number: MZ014020.1), having lytic (cellulase, protease, and polygalacturonase) activity, and tricalcium phosphate (TCP) solubilization ability were isolated from peanut seeds and used during the fermentation process. As reported by HPLC, the maximum CA (5505.1 μg/g PNR) was obtained after 9 days in the presence of 15.49 mg TCP, and 15.68 mg glucose. GC–MS analysis showed other bioactive metabolites in the filtrate of the fermented PNR. Practically, the crude product (40%) fully inhibited (100%) the growth and spore germination of three mycotoxinogenic fungi. On peanuts, it improved the seed germination (91%), seedling features, and vigor index (70.45%) with a reduction of abnormal seedlings (9.33%). The current study presents the fundamentals for large-scale production in the industry for the sustainable development of PNR biomass as a natural source of bioactive metabolites, and safe consumption of lignocellulosic-proteinaceous biomass, as well. T. longibrachiatum WKA55 was also introduced as a novel CA producer specified on PNR. Application of the resulting metabolite is encouraged on a large scale.

Microbiomes of biohydrogen production from dark fermentation of industrial wastes: current trends, advanced tools and future outlook

Biohydrogen production through dark fermentation is very attractive as a solution to help mitigate the effects of climate change, via cleaner bioenergy production. Dark fermentation is a process where organic substrates are converted into bioenergy, driven by a complex community of microorganisms of different functional guilds. Understanding of the microbiomes underpinning the fermentation of organic matter and conversion to hydrogen, and the interactions among various distinct trophic groups during the process, is critical in order to assist in the process optimisations. Research in biohydrogen production via dark fermentation is currently advancing rapidly, and various microbiology and molecular biology tools have been used to investigate the microbiomes. We reviewed here the different systems used and the production capacity, together with the diversity of the microbiomes used in the dark fermentation of industrial wastes, with a special emphasis on palm oil mill effluent (POME). The current challenges associated with biohydrogen production were also included. Then, we summarised and discussed the different molecular biology tools employed to investigate the intricacy of the microbial ecology associated with biohydrogen production. Finally, we included a section on the future outlook of how microbiome-based technologies and knowledge can be used effectively in biohydrogen production systems, in order to maximise the production output.

Simulation and optimization of organosolv based lignocellulosic biomass refinery: A review

Organosolv pretreatment can be considered as the core of the lignocellulosic biomass fractionation within the biorefinery concept. Organosolv facilitates the separation of the major fractions (cellulose, hemicelluloses, lignin), and their use as renewable feedstocks to produce bioenergy, biofuels, and added-value biomass derived chemicals. The efficient separation of these fractions affects the economic feasibility of the biorefinery complex. This review focuses on the simulation of the organosolv pretreatment and the optimization of (i) feedstock delignification, (ii) sugars production (mainly from hemicelluloses), (iii) enzymatic digestibility of the cellulose fraction and (iv) quality of lignin. Simulation is used for the technoeconomic optimization of the biorefinery complex. Simulation and optimization implement a holistic approach considering the efficient technological, economic, and environmental performance of the biorefinery operational units. Consequently, an optimized organosolv stage is the first step for a sustainable, economically viable biorefinery complex in the concept of industrial ecology and zero waste circular economy.

Optimisation of Propane Production from Hydrothermal Decarboxylation of Butyric Acid Using Pt/C Catalyst: Influence of Gaseous Reaction Atmospheres

The displacement and eventual replacement of fossil-derived fuel gases with biomass-derived alternatives can help the energy sector to achieve net zero by 2050. Decarboxylation of butyric acid, which can be obtained from biomass, can produce high yields of propane, a component of liquefied petroleum gases. The use of different gaseous reaction atmospheres of nitrogen, hydrogen, and compressed air during the catalytic hydrothermal conversion of butyric acid to propane have been investigated in a batch reactor within a temperature range of 200–350 °C. The experimental results were statistically evaluated to find the optimum conditions to produce propane via decarboxylation while minimizing other potential side reactions. The results revealed that nitrogen gas was the most appropriate atmosphere to control propane production under the test conditions between 250 °C and 300 °C, during which the highest hydrocarbon selectivity for propane of up to 97% was achieved. Below this temperature range, butyric acid conversion remained low under the three reaction atmospheres. Above 300 °C, competing reactions became more significant. Under compressed air atmosphere, oxidation to CO2 became dominant, and under nitrogen, thermal cracking of propane became significant, producing both ethane and methane as side products. Interestingly, under a hydrogen atmosphere, hydrogenolytic cracking propane became dominant, leading to multiple C–C bond cleavages to produce methane as the main side product at 350 °C.

Fermentative molecular biohydrogen production from cheese whey: present prospects and future strategy

Waste-dependent fermentative routes for biohydrogen production present a possible scenario to produce hydrogen gas on a large scale in a sustainable way. Cheese whey contains a high portion of organic carbohydrate and other organic acids, which makes it a feasible substrate for biohydrogen production. In the present review, recent research progress related to fermentative technologies, which explore the potentiality of cheese whey for biohydrogen production as an effective tool on a large scale, has been analyzed systematically. In addition, application of multiple response surface methodology tools such as full factorial design, Box-Behnken model, and central composite design during fermentative biohydrogen production to study the interactive effects of different bioprocess variables for higher biohydrogen yield in batch, fed-batch, and continuous mode is also discussed. The current paper also emphasizes computational fluid dynamics-based simulation designs, by which the substrate conversion efficiency of the cheese whey-based bioprocess and temperature distribution toward the turbulent flow of reaction liquid can be enhanced. The possible future developments toward higher process efficiency are outlined.

Strategy for Surface Post-Processing of AISI 316L Additively Manufactured by Powder Bed Fusion Using Ultrasonic Nanocrystal Surface Modification

Ultrasonic nanocrystal surface modification (UNSM) technology was applied to the surfaces of specimens additively manufactured by powder bed fusion (PBF). The changes in roughness and hardness due to the UNSM were set as objective functions, and the optimal conditions for the main parameters were derived through the response surface method (RSM) and Box–Behnken design (BBD). Regression analysis-based mathematical models for predicting the surface hardness and roughness are presented and validated. The RSM results show that the surface roughness is highly dependent on the load and ball tip diameter, and the surface roughness significantly improves as the inter-pass interval and ball tip diameter decrease. Through BBD and ANOVA, the optimal conditions for the improvement of surface characteristics were found to be a load of 40 N, inter-pass interval of 10 μm, and ball tip diameter of 2.38 m. The surface treated under these optimal conditions exhibited a hardness of 497 Hv and surface roughness of 1.32 μm, which were significantly improved compared to the values for an untreated specimen. In addition, it was confirmed that the grains are significantly refined after UNSM, and scratch resistance increases for the top layer of the surface directly affected by the UNSM horn.

Sequential pretreatment of sugarcane bagasse by alkali and organosolv for improved delignification and cellulose saccharification by chimera and cellobiohydrolase for bioethanol production

Sequential pretreatments for sugarcane bagasse (scb) by NaOH followed by organosolv under mild conditions were evaluated for cellulose recovery and dilignification. The best-optimized sequential pretreatment of scb was obtained at 10% (w/v) of raw scb loading at 1% (w/v) NaOH (50 °C, 2 h) followed by treatment with organosolv (85%, v/v phosphoric acid, 50 °C, 1 h) with chilled acetone. This sequentially pretreated scb showed cellulose recovery, 66.1% (w/w) and delignification, 83.2% (w/w). NaOH or organosolv pretreated scb showed lower cellulose recovery 47.4% (w/w) or 54.5% (w/w) with lower delignification, 61% (w/w) or 56% (w/w), respectively. Pretreated solid residue of sequentially pretreated scb was enzymatically saccharified by chimera (β-glucosidase and endoglucanase, CtGH1-L1-CtGH5-F194A) and cellobiohydrolase (CtCBH5A) cloned from Clostridium thermocellum. Enzymatic hydrolysate of best sequentially pretreated scb gave total reducing sugar (TRS) yield, 230 mg/g and glucose yield, 137 mg/g pretreated scb. Only organosolv pretreated scb gave TRS yield, 112.5 mg/g and glucose yield, 72 mg/g of pretreated scb. Thus, sequentially pretreated scb resulted in 37% higher enzymatic digestibility than only orgnaosolv pretreated scb. Higher enzymatic digestibility was supported by higher crystallinity index CrI (45%) than those obtained with only organosolv pretreated (38%) or raw scb (25%). Field Emission Scanning Electron Microscope (FESEM) and Fourier-transform infrared (FT-IR) analyses showed enhanced cellulose exposure in sequentially pretreated scb. Preliminary investigation of bioethanol production at small scale by separate hydrolysis and fermentation (SHF) of enzymatic hydrolysate from best sequentially pretreated scb by Saccharomyces cerevisiae gave maximum ethanol yield of 0.42 g/g of glucose.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02600-y.

Harnessing the biocatalytic attributes and applied perspectives of nanoengineered laccases-A review

In the recent past, numerous new types of nanostructured carriers, as support matrices, have been engineered to advance the traditional enzyme immobilization strategies. The current research aimed to develop a robust enzyme-based biocatalytic platform and its effective deployment in the industrial biotechnology sectors at large and catalysis area, in particular, as low-cost biocatalytic systems. Suitable coordination between the target enzyme molecules and surface pendent multifunctional entities of nanostructured carriers has led an effective and significant contribution in myriad novel industrial, biotechnological, and biomedical applications. As compared to the immobilization on planar two-dimensional (2-D) surface, the unique physicochemical, structural and functional attributes of nano-engineered matrices, such as high surface-to-volume ratio, surface area, robust chemical and mechanical stability, surface pendant functional groups, outstanding optical, thermal, and electrical characteristics, resulted in the concentration of the immobilized entity being substantially higher, which is highly requisite from applied bio-catalysis perspective. Besides inherited features, nanostructured materials-based enzyme immobilization aided additional features, such as (1) ease in the preparation or green synthesis route, (2) no or minimal use of surfactants and harsh reagents, (3) homogeneous and well-defined core-shell nanostructures with thick enzyme shell, and (4) nano-size can be conveniently tailored within utility limits, as compared to the conventional enzyme immobilization. Moreover, the growing catalytic needs can be fulfilled by multi-enzymes co-immobilization on these nanostructured materials-based support matrices. This review spotlights the unique structural and functional attributes of several nanostructured materials, including carbon nanotubes, graphene, and its derivate constructs, nanoparticles, nanoflowers, and metal-organic frameworks as robust matrices for laccase immobilization. The later half of the review focuses on the applied perspective of immobilized laccases for the degradation of emergent contaminants, biosensing cues, and lignin deconstruction and high-value products.

Sustainable biofuels and bioplastic production from the organic fraction of municipal solid waste

Municipal solid waste is an environmental threat worldwide; however, the organic fraction of municipal solid waste (OF-MSW) has a great potential for the generation of fuels and high-value products. In the current study, OF-MSW was utilized for the production of ethanol, hydrogen, as well as 2,3-butanediol, an octane booster, by using Enterobacter aerogenes. Furthermore, a promising alternative to non-biodegradable petrochemical-based polymers, polyhydroxyalkanoates (PHAs), was produced. The OF-MSW was first pretreated by an acetic acid catalyzed ethanol organosolv pretreatment at 120 and 160 °C followed by enzymatic hydrolysis of the residual solids. The residual unhydrolyzed solids resulting from enzymatic hydrolysis were further anaerobically digested for methane production. The enzymatic hydrolysis of the solids prepared at 120 °C for 60 min led to the production of hydrolysate with the highest glucose production yield of 498.5 g/kg dry untreated OF-MSW, which was fermented to 139.1 g 2,3-butanediol, 98.3 g ethanol, 28.6 g acetic acid, 71.4 L biohydrogen, and 40 g PHAs. Moreover, 23.1 L biomethane was produced through the anaerobic digestion of the enzymatic hydrolysis residue solids. Thus, appreciable amounts of energy (8236.9 kJ) and an eco-friendly bioplastic were produced by the valorization of carbon sources available in OF-MSW.

Enhanced (R)-2-(4-Hydroxyphenoxy)Propionic Acid Production by Beauveria bassiana: Optimization of Culture Medium and H2O2 Supplement Under Static Cultivation

(R)-2-(4-hydroxyphenoxy)propionic acid (HPOPA) is a key intermediate for the preparation of aryloxyphenoxypropionic acid herbicides (R-isomer). In order to improve the HPOPA production from the substrate (R)-2-phenoxypropionic acid (POPA) with Beauveria bassiana CCN-A7, static cultivation and H₂O₂ addition were attempted and found to be conducive to the task at hand. This is the first report on HPOPA production under static cultivation and reactive oxygen species (ROS) induction. On this premise, the cultivation conditions and fermentation medium compositions were optimized. As a result, the optimal carbon source, organic nitrogen source, and inorganic nitrogen source were determined to be glucose, peptone, and ammonium sulfate, respectively. The optimal inoculum size and fermentation temperature were 13.3% and 28°C, respectively. The significant factors including glucose, peptone, and H₂O₂, identified based on Plackett-Burman design, were further optimized through Central Composite Design (CCD). The optimal concentrations/amounts were as follows: glucose 38.81 g/l, peptone 7.28 g/l, and H₂O₂ 1.08 ml/100 ml. Under the optimized conditions, HPOPA titer was improved from 9.60 g/l to 19.53 g/l, representing an increase of 2.03- fold. The results obtained in this work will provide novel strategies for improving the biosynthesis of hydroxy aromatics.

Fermentative hydrogen production and bioelectricity generation from food based industrial waste: An integrative approach

In the present study, isolation and identification of hydrogen producing strains from sugar and food industry wastewater were reported. From 48 isolates in both the wastewater, initial batch studies led to the use of four effective strains, which were identified using 16S rRNA gene sequencing as Bacillus thuringiensis-FH1, Comamonas testosteroni-FB1, Klebsiella pneumoniae-FA2 and Bacillus cereus-SB2, respectively. Further optimization studies were done at various pH values (5-8) and wastewater concentrations (10-100%). In the optimized batch experimentation, K. pneumoniae-FA2 excelled with the maximum cumulative hydrogen production of 880.93 ± 44.0 mL/L. A 3 L bioreactor was employed for effective hydrogen production, which conferred that K. pneumoniae-FA2, surpassed the other three with the maximum hydrogen yield of 3.79 ± 0.04 mol H₂/mol glucose. Bioelectricity production by K. pneumoniae-FA2 was also investigated in the microbial fuel cell at the optimized conditions to demonstrate its versatility in energy applications.

Oxidative conversion of lignin isolated from wheat straw into aromatic compound catalyzed by NaOH/NaAlO2

Lignin was isolated from wheat straw via organosolv process and further transferred to monophenolic compounds via oxidative conversion. Wheat straw lignin (WSL) with purity at 91.4 wt% was acquired in the presence of heterogeneous and recyclable catalyst of Amberlyst-45. WSL was characterized by infrared spectrometer (IR), nuclear magnetic resonance spectroscopy (NMR) including 1H NMR and 13C NMR spectra. The results showed that WSL possesses typical syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units, and it is mainly composed of S and G units. The product distribution was dependent on the composition of WSL. Derivatives from S and G units were found to be the main products. The oxidative conversion of WSL was performed by varying oxidant and catalyst. Both the formation of monophenolic compounds and aromatic aldehydes were enhanced by combining oxidants and catalysts. The composite catalyst composed of NaOH/NaAlO2 was effective for the oxidation of WSL in the presence of nitrobenzene and atmospheric pressure air. The total yield of monophenolic compounds reached up 18.1%, and yields at 6.3 and 5.7% for syringaldehyde and vanillin were achieved, respectively.

Investigation of heterogeneous sulfonated graphene oxide to hydrolyze cellulose and produce dark fermentative biohydrogen using Enterobacter aerogenes

The main aim of this work was investigating the potential of sulfonated graphene oxide (sGO) for hydrolysis of cellulosic substrates and dark fermentative hydrogen production from obtained hydrolysates using E. aerogenes. Sulfonation of graphene oxide was performed using chlorosulfonic acid which showed a high acid density of 4.63 mmol/g. Influence of the reaction time (1-5 h), temperature (90-180 °C) and sGO dosage (62.5-500 mg in 25 mL reaction volume) on the hydrolysis of pretreated microcrystalline cellulose was experimented. It revealed that the yield of glucose and total reducing sugars and selectivity can reach 454.4 ± 22.20 mg/g, 682.6 ± 30.67 mg/g and 95.5%, respectively, at 150 °C for 3 h using 250 mg sGO. The maximum hydrogen efficiency of 150.0 ± 5.65 mL/g was achieved under optimized conditions, which was 2.2-fold higher than that from the pretreated MCC substrate as control in the absence of sGO (67.3 ± 8.84 mL/g).

Recent advances in organosolv fractionation: Towards biomass fractionation technology of the future

Organosolv treatment is among the most promising strategies for valorising lignocellulosic biomass and could facilitate the transition towards enhanced utilization of renewable feedstocks. However, issues such as inefficient solvent recycle and fractionation has to be overcome. The present review aims to address these issues and discuss the role of the components present during organosolv treatment and their influence on the overall process. Thus, the review focuses not only on how the choice of solvent and catalyst affects lignocellulosic fractionation, but also on how the choice of treatment liquor influences the possibility for solvent recycling and product isolation. Several organic solvents have been investigated in combination with water and acid/base catalysts; however, the lack of a holistic approach often compromises the performance of the different operational units. Thus, an economically viable organosolv process should optimize biomass fractionation, product isolation, and solvent recycling.

Enhanced biohydrogen production from cotton stalk hydrolysate of Enterobacter cloacae WL1318 by overexpression of the formate hydrogen lyase activator gene

BACKGROUND

Biohydrogen production from lignocellulose has become an important hydrogen production method due to its diversity, renewability, and cheapness. Overexpression of the formate hydrogen lyase activator (fhlA) gene is a promising tactic for enhancement of hydrogen production in facultative anaerobic Enterobacter. As a species of Enterobacter, Enterobacter cloacae was reported as a highly efficient hydrogen-producing bacterium. However, little work has been reported in terms of cloning and expressing the fhlA gene in E. cloacae for lignocellulose-based hydrogen production.

RESULTS

In this study, the formate hydrogen lyase activator (fhlA) gene was cloned and overexpressed in Enterobacter cloacae WL1318. We found that the recombinant strain significantly enhanced cumulative hydrogen production by 188% following fermentation of cotton stalk hydrolysate for 24 h, and maintained improved production above 30% throughout the fermentation process compared to the wild strain. Accordingly, overexpression of the fhlA gene resulted in an enhanced hydrogen production potential (P) and maximum hydrogen production rate (R _m), as well as a shortened lag phase time (λ) for the recombinant strain. Additionally, the recombinant strain also displayed improved glucose (12%) and xylose (3.4%) consumption and hydrogen yield Y(H₂/S) (37.0%) compared to the wild strain. Moreover, the metabolites and specific enzyme profiles demonstrated that reduced flux in the competitive branch, including succinic, acetic, and lactic acids, and ethanol generation, coupled with increased flux in the pyruvate node and formate splitting branch, benefited hydrogen synthesis.

CONCLUSIONS

The results conclusively prove that overexpression of fhlA gene in E. cloacae WL1318 can effectively enhance the hydrogen production from cotton stalk hydrolysate, and reduce the metabolic flux in the competitive branch. It is the first attempt to engineer the fhlA gene in the hydrogen-producing bacterium E. cloacae. This work provides a highly efficient engineered bacterium for biohydrogen production from fermentation of lignocellulosic hydrolysate in the future.

Optimization Study of Biomass Hydrogenation to Ethylene Glycol Using Response Surface Methodology

Statistical-based study using response surface methodology (RSM) was conducted to study the effects of process parameters towards biomass hydrogenation. Using Malaysian oil palm empty fruit bunches (EFB) fibres as feedstock, the central composite design (CCD) technique was employed and 18 runs were generated by CCD when four parameters (mass ratio of binary catalyst, hydrogen pressure, temperature and mass ratio of catalyst to feedstock) were varied with two center points to determine the effects of process parameters and eventually to get optimum ethylene glycol (EG) yield. RSM with quadratic function was generated for biomass hydrogenation, indicating all factors except temperature, were important in determining EG yield. Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of >0.98, ensuring a satisfactory prediction of the quadratic model with experimental data. The quadratic model suggested the optimum EG yield should be >25 wt.% and the EG yield results were successfully reproduced in the laboratory.

An Optimized Surfactant-Based PEG-PLCL In Situ Gel Formulation For Enhanced Activity Of Rosuvastatin In Poloxamer-Induced Hyperlipidemic Rats

BACKGROUND

Injectable in situ gel (ISG) systems suffer from high initial drug release that may result in toxic effects.

OBJECTIVE

This work aimed to develop an injectable sustained release rosuvastatin (RSV) ISG formulation with minimum initial drug burst and improved hyperlipidemic efficacy.

METHODS

Six formulation factors that affect RSV release after 0.5, 2 and 24 hrs have been screened and the significant ones were optimized utilizing an experimental design tool. The optimum ISG formulation components were physicochemically characterized. Kinetic treatment, dissolution efficiency and mean dissolution time were investigated for the developed ISG formulations. Pharmacodynamic effects of the optimized ISG formulation were studied and compared to ISG formulation loaded with free RSV and to a marketed oral drug product.

RESULTS

The concentration polylactide-co-ε-caprolactone (25: 75), the surfactant hydrophilic lipophilic balance (HLB) and the ratio of surfactant to polyethylene glycol 400 were significantly affecting the release of RSV during the first 24 h. Physicochemical characterization demonstrated complete dispersion of RSV in the polymeric matrix with slight changes in the drug crystalline structure. The optimized formulation demonstrated acceptable syringeability, good flow rate and was able to extend the in vitro drug release for 34 days. The ISG formulations complied with Weibull model. Pharmacodynamic study revealed a sustained reduction in the lipid profile that lasted for 21 days with a marked decrease in the lipid level during the first 24 hrs from the ISG system loaded with free RSV.

CONCLUSION

The optimized RSV ISG formulation could be considered a promising strategy due to a reduction in dosing frequency and enhancement in hypolipidemic efficacy.

Grid columnar flat panel photobioreactor with immobilized photosynthetic bacteria for continuous photofermentative hydrogen production

A biophotoreactor with a transparent glass flat panel with polymethyl methacrylate (PMMA) grid columnar for enhanced biofilm growth with Rhodopseudomonas palustris GCA009 was developed and tested at 590 nm incident light. Continuous photofermentative hydrogen production from glucose was tested using this novel reactor. At light intensity of 210 W/m², feed substrate concentration of 56.0 mmol/L, and crossflow velocity of 1.68 × 10^-6 m/s, a maximum hydrogen production rate of 32.6 mmol/L-d (3.56 mmol/m²-h), hydrogen yield of 1.15 mol H₂/mol glucose and light conversion efficiency of 5.34% can be achieved. Since the revised grid columnar effectively enlarged the surface area of reactor and enhanced cell attachment, the present reactor design led to higher hydrogen production rates than literature works.

State of the art and challenges of biohydrogen from microalgae

Biohydrogen from microalgae has attracted extensive attention owing to its promising features of abundance, renewable and self sustainability. Unlike other well-established biofuels like biodiesel and bioethanol, biohydrogen from microalgae is still in the preliminary stage of development. Criticisms in microalgal biohydrogen centered on its practicality and sustainability. Various laboratory- and pilot-scale microalgal systems have been developed, and some research initiatives have exhibited potential for commercial application. This work provides a review of the state of the art of biohydrogen from microalgae. Discussions include metabolic pathways of light-driven transformation and dark fermentation, reactor schemes and system designs encompassing reactor configurations and light manipulation. Challenges, knowledge gaps and the future directions in metabolic limitations, economic and energy assessments, and molecular engineering are also delineated. Current scientific and engineering challenges of microalgal biohydrogen need to be addressed for technology leapfrog or breakthrough.

Continuous production of biohydrogen from brewery effluent using co-culture of mutated Rhodobacter M 19 and Enterobacter aerogenes

This study investigated the biohydrogen production from brewery effluents using free and immobilized co-culture of mutated Rhodobacter M 19 and Enterobacter aerogenes obtained from random mutagenesis with ultra violet (UV) and ethidium bromide (EtBr) treatment. The best mutant for biohydrogen production was screened based on the sugar utilization efficiency. Maximum hydrogen production of 87% was achieved with immobilized EtBr mutated co-culture. The mutant immobilized strains showed around 30% enhanced hydrogen production than wild strains at pH 6.9. Gompertz and Richard's model were used to fit the augmenting biohydrogen production and Logistics equation determines the fitness of biomass growth data. The maximal biomass concentration of co-cultures strains was 3.145 g/L with carrying capacity coefficient 0.137 h^-1. Gompertz model showed the best fit with minimal error in predicting the biohydrogen potential.

Cheese whey to biohydrogen and useful organic acids: A non-pathogenic microbial treatment by L. acidophilus

The burgeoning organic waste and continuously increasing energy demands have resulted in significant environmental pollution concerns. To address this issue, the potential of different bacteria to produce biogas/biohydrogen from organic waste can be utilized as a source of renewable energy, however these pathogenic bacteria are not safe to use without strict contact isolation. In this study the role of safe food grade lactic acid bacteria (Lactobacillus spp.) was investigated for production of biogas from cheese waste with starting hexose concentration 32 g/L. The bacterium Lactobacillus acidophilus was identified as one of the major biogas producers at optimum pH of 6.5. Further the optimum inoculum conditions were found to be 12.5% at inoculum age of 18 h. During the investigation the maximum biogas production was observed to be 1665 mL after 72 hours of incubation at pH 6.5. The biogas production was accompanied with production of other valuable metabolites in the form of organic acids including pyruvate, propionate, acetate, lactate, formate and butyrate. Thus this research is paving way for nonpathogenic production of biohydrogen from food waste.

Enhanced L-methionine production by genetically engineered Escherichia coli through fermentation optimization

Microbial fermentation for L-methionine (L-Met) production based on natural renewable resources is attractive and challenging. In this work, the effects of medium composition and fermentation conditions were investigated to improve L-Met production by genetically engineered Escherichia coli MET-3. Statistical optimization techniques including Plackett-Burman (PB) design and Box-Behnken design (BBD) were adopted first to optimize the culture medium. Results of PB-designed experiments indicated that the culture medium components including glucose, yeast extract, KH₂PO₄, and MgSO₄.7H₂O had significant effects on L-Met biosynthesis. With their best-predicted concentration established by BBD (glucose 37.43 g/L, yeast extract 0.95 g/L, KH₂PO₄ 1.82 g/L, and MgSO₄.7H₂O 4.51 g/L), L-Met titer was increased to 3.04 g/L from less than 2.0 g/L. For further enhancement of L-Met biosynthesis, the fermentation conditions of batch cultivation carried out in a 5-L fermentor were optimized, and the optimum results were obtained at an agitation rate of 300 rpm, medium pH of 7.0, and induction temperature of 28 °C. Based on the optimization parameters, fed-batch fermentation with the modified medium was conducted. As a result, great improvement of L-Met titer (12.80 g/L) and yield (0.13 mol/mol) were achieved, with an increase of 38.53% and 30.0% compared with those of the basal medium, respectively. Furthermore, higher L-Met productivity of 0.261 g/L/h was obtained, representing 2.13-fold higher in comparison to the original medium. The results may provide a helpful reference for further study on strain improvement and fermentation control.

Effects of Phytoremediation Treatment on Bacterial Community Structure and Diversity in Different Petroleum-Contaminated Soils

Increased exploitation and use of petroleum resources is leading to increased risk of petroleum contamination of soil and groundwater. Although phytoremediation is a widely-used and cost-effective method for rehabilitating soils polluted by petroleum, bacterial community structure and diversity in soils undergoing phytoremediation is poorly understood. We investigate bacterial community response to phytoremediation in two distinct petroleum-contaminated soils (add prepared petroleum-contaminated soils) from northwest China, Weihe Terrace soil and silty loam from loess tableland. High-throughput sequencing technology was used to compare the bacterial communities in 24 different samples, yielding 18,670 operational taxonomic units (OTUs). The dominant bacterial groups, Proteobacteria (31.92%), Actinobacteria (16.67%), Acidobacteria (13.29%) and Bacteroidetes (6.58%), increased with increasing petroleum concentration from 3000 mg/kg–10,000 mg/kg, while Crenarchaeota (13.58%) and Chloroflexi (4.7%) decreased. At the order level, RB41, Actinomycetales, Cytophagales, envOPS12, Rhodospirillales, MND1 and Xanthomonadales, except Nitrososphaerales, were dominant in Weihe Terrace soil. Bacterial community structure and diversity in the two soils were significantly different at similar petroleum concentrations. In addition, the dominant genera were affected by available nitrogen, which is strongly associated with the plants used for remediation. Overall, the bacterial community structure and diversity were markedly different in the two soils, depending on the species of plants used and the petroleum concentration.