Microalgae biomass deconstruction using green solvents: Challenges and future opportunities.

Microalgae enablefixation of CO2into carbohydrates, lipids, and proteins through inter and intracellularly biochemical pathways. These cellular components can be extracted and transformed into renewable energy, chemicals, and materials through biochemical and thermochemical transformation processes.However, recalcitrant cell wall andlack of environmentally benign efficient pretreatment processes are key obstacles in the commercialization of microalgal biorefineries.Thus,current article describes the microalgal chemical structure, type, and structural rigidity and summarizes the traditional pretreatment methods to extract cell wall constituents. Green solvents such as ionic liquid (ILs), deep eutectic solvents (DES), and natural deep eutectic solvents (NDESs) have shown interesting solvent characteristics to pretreat biomass with selective biocomponent extraction from microalgae. Further research is needed in task-specific IL/DES design, cation-anion organization, structural activity understanding of ILs-biocomponents, environmental toxicity, biodegradability, and recyclability for deployment of carbon-neutral technologies. Additionally, coupling the microalgal industry with biorefineries may facilitate waste management, sustainability, and gross revenue.

Machine learning in fermentative biohydrogen production: Advantages, challenges, and applications.

Hydrogen can be produced in an environmentally friendly manner through biological processes using a variety of organic waste and biomass as feedstock. However, the complexity of biological processes limits their predictability and reliability, which hinders the scale-up and dissemination. This article reviews contemporary research and perspectives on the application of machine learning in biohydrogen production technology. Several machine learning algorithems have recently been implemented for modeling the nonlinear and complex relationships among operational and performance parameters in biohydrogen production as well as predicting the process performance and microbial population dynamics. Reinforced machine learning methods exhibited precise state prediction and retrieved the underlying kinetics effectively. Machine-learning based prediction was also improved by using microbial sequencing data as input parameters. Further research on machine learning could be instrumental in designing a process control tool to maintain reliable hydrogen production performance and identify connection between the process performance and the microbial population.

A sustainable vanadium bioremediation strategy from aqueous media by two potential green microalgae.

Globally, environmental concerns are rapidly growing due to increasing pollution levels. Vanadium is a hazardous heavy metal that poses health issues with an exposure concentration of about 2 ppm. It is regularly discharged by some industries and poses an environmental challenge. There are no sustainable green treatment methods for discharged effluents to mitigate vanadium threats to humans and the environment. In this study, the goal was to develop a green, sustainable method for removing vanadium and to utilize the produced biomass for biofuels, thus offsetting the treatment cost. Microalgae Chlorella sorokiniana SU1 and Picochlorum oklahomensis were employed for vanadium (III) treatment. The maximum removal was 25.5 mg L-1 with biomass and lipid yields of 3.0 g L-1 and 884.4 mg L-1 respectively after 14 days of treatment. The vanadium removal capacity by microalgae was further enhanced up to 2-2.7 folds while optimizing the key parameters, pH, and temperature before removing biomass from the liquid phase. FTIR is used to analyse the reactive groups in algal cell walls to confirm vanadium adsorption and to understand the dominant and quantitative interactions. Zeta potential analysis helps to find out the most suitable pH range to facilitate the ionic bonding of biomass and thus maximum vanadium adsorption. This study addresses regulating external factors for enhancing the removal performance during microalgal biomass harvesting, which significantly enhances the removal of vanadium (III) from the aqueous phase. This strategy aims to improve the removal efficiency of microalgal treatment at an industrial scale for the bioremediation of vanadium and other inorganic pollutants.

Synthesis of fatty acid-based ammonium ionic liquids and their application for extraction of Co(II) and Ni(II) metals ions from aqueous solution.

Leaching of cobalt and nickel into diverse water streams has become an environmental hazard and is continuously impacting human health through the food chain. Solvent extraction is the most widely accepted for separating these metals, but traditional extractants employed in conjunction with molecular diluents often lack selectivity and caused major environmental hurdles. Therefore, the development of cost-effective, environmentally friendly technologies for recovering these heavy metals has been strongly encouraged in recent years. Herein, two halogens free, low viscous, biocompatible fatty acid-based hydrophobic ionic liquids (ILs), i.e., methytrioctylammonium oleate, methytrioctylammonium linoleate were synthesized, analytically characterized and employed for recovery of cobalt, Co(II) and nickel, Ni(II) from their aqueous solutions. Extraction behaviour of Co(II) and Ni(II) was further evaluated by varying equilibrium time, ILs molar concentration, metal loading, and temperature. Thermodynamic parameters such as enthalpy change and Gibbs free energy change were also studied during extraction process. Slope analysis suggested that the extraction mechanism was an exothermic process that followed ion-transfer from the aqueous phase to the organic phase. Results showed that both fatty acid based-ILs were found to be capable of extracting >99% of Co(II) and Ni(II) from aqueous solutions at 298 K, in 15 min of shaking time using a 1:1 (org: aq.) ratio at low concentrations of 2.5-10 g L-1. Furthermore, for methyltrioctylammonium oleate IL, Co(II) extraction was selectively preferred over Ni(II) extraction when the metal concentration was increased to above to 10 g L-1. The stripping results showed that 2 M H2SO4, and 2 M HCl successfully stripped out >99% of Co(II) and Ni(II) from the organic phase, respectively compared to HNO3.

Critical challenges and technological breakthroughs in food waste hydrolysis and detoxification for fuels and chemicals production.

Organic waste has increased as the global population and economy have grown exponentially. Food waste (FW) is posing a severe environmental issue because of mismanaged disposal techniques, which frequently result in the squandering of carbohydrate-rich feedstocks. In an advanced valorization strategy, organic material in FW can be used as a viable carbon source for microbial digestion and hence for the generation of value-added compounds. In comparison to traditional feedstocks, a modest pretreatment of the FW stream utilizing chemical, biochemical, or thermochemical techniques can extract bulk of sugars for microbial digestion. Pretreatment produces a large number of toxins and inhibitors that affect bacterial fuel and chemical conversion processes. Thus, the current review scrutinizes the FW structure, pretreatment methods (e.g., physical, chemical, physicochemical, and biological), and various strategies for detoxification before microbial fermentation into renewable chemical production. Technological and commercial challenges and future perspectives for FW integrated biorefineries have also been outlined.

Recent updates in biohydrogen production strategies and life-cycle assessment for sustainable future.

Biohydrogen (bio-H2) is regarded as a clean, non-toxic, energy carrier and has enormous potential for transforming fossil fuel-based economy. The development of a continuous high-rate H2 production with low-cost economics following an environmentally friendly approach should be admired for technology demonstration. Thus, the current review discusses the biotechnological and thermochemical pathways for H2 production. Thermochemical conversion involves pyrolysis and gasification routes, while biotechnological involves light-dependent processes (e.g., direct and indirect photolysis, photo/ dark fermentation strategies). Moreover, environmentally friendly technologies can be created while utilizing renewable energy sources including lignocellulosic, wastewater, sludge, microalgae, and others, which are still being developed. Lifecycle assessment (LCA) evaluates and integrates the economic, environmental, and social performance of H2 production from biomass, microalgae, and biochar. Moreover, system boundaries evaluation, i.e., global warming potential, acidification, eutrophication, and sensitivity analysis could lead in development of sustainable bioenergy transition with high economic and environmental benefits.

Regulation and augmentation of anaerobic digestion processes via the use of bioelectrochemical systems.

Anaerobic digestion (AD) is a biological process that can be used to treat a wide range of carbon-rich wastes and producerenewable, green energy. To maximize energy recovery from various resources while controlling inhibitory chemicals, notwithstanding AD's efficiency, many limitations must be addressed. As a result, bioelectrochemical systems (BESs) have emerged as a hybrid technology, extensively studied to remediate AD inhibitory chemicals, increase AD operating efficacy, and make the process economically viable via integration approaches. Biogas and residual intermediatory metabolites such as volatile fatty acids are upgraded to value-added chemicals and fuels with the help of the BES as a pre-treatment step, within AD or after the AD process. It may also be used directly to generate power. To overcome the constraints of AD in lab-scale applications, this article summarizes BES technology and operations and endorses ways to scale up BES-AD systems in the future.

Recycling of cathode material from spent lithium-ion batteries: Challenges and future perspectives.

The intrinsic advancement of lithium-ion batteries (LIBs) for application in electric vehicles (EVs), portable electronic devices, and energy-storage devices has led to an increase in the number of spent LIBs. Spent LIBs contain hazardous metals (such as Li, Co, Ni, and Mn), toxic and corrosive electrolytes, metal casting, and polymer binders that pose a serious threat to the environment and human health. Additionally, spent LIBs may serve as an economic source for transition metals, which could be applied to redesigning under a closed-circuit recycling process. Thus, the development of environmentally benign, low cost, and efficient processes for recycling of LIBs for a sustainable future has attracted worldwide attention. Therefore, herein, we introduce the concept of LIBs and review state-of-art technologies for metal recycling processes. Moreover, we emphasize on LIB pretreatment approaches, metal extraction, and pyrometallurgical, hydrometallurgical, and biometallurgical approaches. Direct recycling technologies combined with the profitable and sustainable cathode healing technology have significant potential for the recycling of LIBs without decomposition into substituent elements or precipitation; hence, these technologies can be industrially adopted for EV batteries. Finally, commercial technological developments, existing challenges, and suggestions are presented for the development of effective, environmentally friendly recycling technology for the future.

Algae biorefinery: A promising approach to promote microalgae industry and waste utilization.

Microalgae have a number of intriguing characteristics that make them a viable raw material aimed at usage in a variety of applications when refined using a bio-refining process. They offer unique capabilities that allow them to be used in biotechnology-related applications. As a result, this review explores how to increase the extent to which microalgae may be integrated with various additional biorefinery uses in order to improve their maintainability. In this study, the use of microalgae as potential animal feed, manure, medicinal, cosmeceutical, ecological, and other biotechnological uses is examined in its entirety. It also includes information on the boundaries, openings, and improvements of microalgae and the possibilities of increasing the range of microalgae through techno-economic analysis. According to the findings of this review, financing supported research and shifting the focus of microalgal investigations from biofuels production to biorefinery co-products can help guarantee that they remain a viable resource. Furthermore, innovation collaboration is unavoidable if one wishes to avoid the high cost of microalgae biomass handling. This review is expected to be useful in identifying the possible role of microalgae in biorefinery applications in the future.

Recent advances in black liquor valorization.

Lignocellulosic biomass is projected as a prospective renewable alternative to petroleum for the production of fuel and chemicals. Pretreatment is necessary to disrupt the lignocellulosic structure for extraction of cellulose. Biomass after pretreatment is segregated into cellulose rich solid fraction and black liquor (lignin and hemicelluloses) as a liquid stream. The plant polysaccharide-based industry primarily utilizes the cellulosic fraction as raw material, and carbon rich black liquor discarded as waste or burnt for energy recovery. This review highlights the recent advancements in the biological and chemical valorization of black liquor into fuels and chemicals. The recent research attempted for bioconversion of black liquor into Bioplastic, Biohydrogen, Biogas, and chemicals has been discussed. In addition, the efforts to replace the conventional energy recovery method with the advanced chemical process along with their modifications have been reviewed that will decide the sustainability of the lignocellulosic biomass-based industry.

An overview on microalgal-bacterial granular consortia for resource recovery and wastewater treatment.

Excessive generation of wastewater is a matter of concern around the globe. Wastewater treatment utilizing a microalgae-mediated process is considered an eco-friendly and sustainable method of wastewater treatment. However, low biomass productivity, costly harvesting process, and energy extensive cultivation process are the major bottleneck. The use of the microalgal-bacteria granular consortia (MBGC) process is economic and requires less energy. For efficient utilization of MBGC, knowledge of its structure, composition and interaction are important. Various microscopic, molecular and metabolomics techniques play a significant role in understating consortia structure and interaction between partners. Microalgal-bacteria granular consortia structure is affected by various cultivation parameters like pH, temperature, light intensity, salinity, and the presence of other pollutants in wastewater. In this article, a critical evaluation of recent literature was carried out to develop an understanding related to interaction behavior that can help to engineer consortia having efficient nutrient removal capacity with reduced energy consumption.

Recent advances in commercial biorefineries for lignocellulosic ethanol production: Current status, challenges and future perspectives.

Cellulosic ethanol production has received global attention to use as transportation fuels with gasoline blending virtue of carbon benefits and decarbonization. However, due to changing feedstock composition, natural resistance, and a lack of cost-effective pretreatment and downstream processing, contemporary cellulosic ethanol biorefineries are facing major sustainability issues. As a result, we've outlined the global status of present cellulosic ethanol facilities, as well as main roadblocks and technical challenges for sustainable and commercial cellulosic ethanol production. Additionally, the article highlights the technical and non-technical barriers, various R&D advancements in biomass pretreatment, enzymatic hydrolysis, fermentation strategies that have been deliberated for low-cost sustainable fuel ethanol. Moreover, selection of a low-cost efficient pretreatment method, process simulation, unit integration, state-of-the-art in one pot saccharification and fermentation, system microbiology/ genetic engineering for robust strain development, and comprehensive techno-economic analysis are all major bottlenecks that must be considered for long-term ethanol production in the transportation sector.

Upgrading the value of anaerobic fermentation via renewable chemicals production: A sustainable integration for circular bioeconomy.

The single bioprocess approach has certain limitations in terms of process efficiency, product synthesis, and effective resource utilization. Integrated or combined bioprocessing maximizes resource recovery and creates a novel platform to establish sustainable biorefineries. Anaerobic fermentation (AF) is a well-established process for the transformation of organic waste into biogas; conversely, biogas CO2 separation is a challenging and expensive process. Biological fixation of CO2 for succinic acid (SA) mitigates CO2 separation issues and produces commercially important renewable chemicals. Additionally, utilizing digestate rich in volatile fatty acid (VFA) to produce medium-chain fatty acids (MCFAs) creates a novel integrated platform by utilizing residual organic metabolites. The present review encapsulates the advantages and limitations of AF along with biogas CO2 fixation for SA and digestate rich in VFA utilization for MCFA in a closed-loop approach. Biomethane and biohydrogen processes CO2 utilization for SA production is cohesively deliberated along with the role of biohydrogen as an alternative reducing agent to augment SA yields. Similarly, MCFA production using VFA as a substrate and functional role of electron donors namely ethanol, lactate, and hydrogen are comprehensively discussed. A road map to establish the fermentative biorefinery approach in the framework of AF integrated sustainable bioprocess development is deliberated along with limitations and factors influencing for techno-economic analysis. The discussed integrated approach significantly contributes to promote the circular bioeconomy by establishing carbon-neutral processes in accord with sustainable development goals.

2G waste lignin to fuel and high value-added chemicals: Approaches, challenges and future outlook for sustainable development.

Lignin is produced as a byproduct in cellulosic biorefinery as well in pulp and paper industries and has the potential for the synthesis of a variety of phenolics chemicals, biodegradable polymers, and high value-added chemicals surrogate to conventional petro-based fuels. Therefore, in this critical review, we emphasize the possible scenario for lignin isolation, transformation into value addition chemicals/materials for the economic viability of current biorefineries. Additionally, this review covers the chemical structure of lignocellulosic biomass/lignin, worldwide availability of lignin and describe various thermochemical (homogeneous/heterogeneous base/acid-catalyzed depolymerization, oxidative, hydrogenolysis etc.) and biotechnological developments for the production of bio-based low molecular weight phenolics, i.e. polyhydroxyalkanoates, vanillin, adipic acid, lipids etc. Besides, some functional chemicals applications, lignin-formaldehyde ion exchange resin, electrochemical and production of few targeted chemicals are also elaborated. Finally, we examine the challenges, opportunities and prospects way forward related to lignin valorization.

Characterization of ionic liquid pretreated plant cell wall for improved enzymatic digestibility.

An insight into the properties of cell wall of mustard stalk (MS) pretreated by five ionic liquids (ILs) revealed ILs interaction with cellulose, hemicellulose and lignin components. Differential Scanning Calorimetry (DSC) showed increased pore size coupled with increased population of pores evoked by certain ILs in better facilitating enzymatic accessibility. Interestingly, all the five ILs predominantly increased the propensity of two pore sizes formation; 19 and 198 nm, but remarkable difference in the pore volumes of pretreated MS suggested the supremacy of [OAc]- based ILs, resulting in higher glucose yields. Cellulose I to II transition in pretreated MS was supported by the reduced total crystallinity index (TCI), lateral order index (LOI) values. Strong inverse correlation existed between the said parameters and residual acetyl content with enzymatic hydrolysis (R2 > 0.8). An inverse relationship between hydrogen bond basicity, LOI and TCI suggested it to be a good indicator of IL pretreatment efficiency.

Intensification of steam explosion and structural intricacies impacting sugar recovery.

Dilute acid (DA) pretreatment at pilot level failed for cotton stalk (CS) due to the technical issues posed by its inherent nature. Reasonable glucan conversion has been reported via two-stage pretreatment but adds on to the process cost. Proposed herewith is a single-stage steam explosion (SE) process preceded by water extraction resulting in high sugar recovery from CS. Raising the extraction temperature to 80°C increased the glucan conversion from 37.9 to 52.4%. Further improvement up to 68.4% was achieved when DA was incorporated during the room temperature extraction. LC-MS revealed the formation of xylo-oligomers limiting the glucan conversion in proportion to the length of xylo-oligomers. Varying extraction conditions induced structural alterations in biomass after SE evident by compositional analysis, Infrared Spectroscopy, X-Ray Diffraction and Scanning Electron Microscopy. Overall glucose recovery, i.e. 75.8-76.7% with and without DA extraction respectively was achieved.

Ionic liquid pretreatment of biomass for sugars production: Driving factors with a plausible mechanism for higher enzymatic digestibility.

In this study, five ionic liquids (ILs) have been explored for biomass pretreatment for the production of fermentable sugar. We also investigated the driving factors responsible for improved enzymatic digestibility of various ILs treated biomass along with postulating the plausible mechanism thereof. Post pretreatment, mainly two factors impacted the enzymatic digestibility (i) structural deformation (cellulose I to II) along with xylan/lignin removal and (ii) properties of ILs; wherein, K-T parameters, viscosity and surface tension had a direct influence on pretreatment. A systematic investigation of these parameters and their impact on enzymatic digestibility is drawn. [C2mim][OAc] with ß-value 1.32 resulted 97.7% of glucose yield using 10 FPU/g of biomass. A closer insight into the cellulose structural transformation has prompted a plausible mechanism explaining the better digestibility. The impact of these parameters on the digestibility can pave the way to customize the process to make biomass vulnerable to enzymatic attack.

Structural features of dilute acid, steam exploded, and alkali pretreated mustard stalk and their impact on enzymatic hydrolysis.

To overcome the recalcitrant nature of biomass several pretreatment methodologies have been explored to make it amenable to enzymatic hydrolysis. These methodologies alter cell wall structure primarily by removing/altering hemicelluloses and lignin. In this work, alkali, dilute acid, steam explosion pretreatment are systematically studied for mustard stalk. To assess the structural variability after pretreatment, chemical analysis, surface area, crystallinity index, accessibility of cellulose, FT-IR and thermal analysis are conducted. Although the extent of enzymatic hydrolysis varies upon the methodologies used, nevertheless, cellulose conversion increases from <10% to 81% after pretreatment. Glucose yield at 2 and 72h are well correlated with surface area and maximum adsorption capacity. However, no such relationship is observed for xylose yield. Mass balance of the process is also studied. Dilute acid pretreatment is the best methodology in terms of maximum sugar yield at lower enzyme loading.