With the growing use of fossil fuels and industrial activity, the amount of carbon dioxide (CO2) emission is continuously increasing and is considered a primary contributor to climate change. CO2 ...emissions from stationary resources (coal fire, cement plants, and other industry) can be reduced by using various carbon capture and sequestration (CCS) technologies. In this article, recent advancements in various biological methods (i.e., carbonic anhydrase (CA), hydrogenation of CO2 to formate, reduction of CO2 to methane, CO2 conversion into methanol by enzyme cascade, and the role of RuBisCo enzyme) that have been reported for CO2 capture are discussed, along with their advantages and limitations. A brief overview of other physicochemical (absorption, adsorption, cryogenic, and membrane) technologies is also provided. Although biological methods are ecofriendly and can be performed under ambient conditions, these approaches are still not cost effective, as the reactions require cofactors, and the enzymes lose activity when exposed to hot flue gas and ionic liquids. Most captured CO2 is stored by mineralization using a geological and ocean storage method without providing any economic benefit. It is a question of interest as to how we can utilize CO2 and generate revenue. Utilization of CO2 as a feedstock to produce bioenergy is a possible approach. Various microbes capable of utilizing CO2 as feedstock and producing biofuels (biodiesel and bioalcohol) have been reported. These two technologies, i.e., CO2 capture and bioconversion of CO2 into bioenergy, can be integrated to develop a process that not only mitigates CO2 effects on the environment but also solves energy problems while generating revenue.
•Carbon dioxide (CO2) is contributing in global warming.•CO2 can be used as a resource for bioenergy production.•Electro-biological and integrated system are efficient methods for CO2 to bioenergy conversion.
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•Biodiesel is a renewable and ecofriendly biofuel.•It can be produced using transesterification, emulsification and pyrolysis process etc.•Enzyme catalyzed and biomass derived ...catalysts reactions are economic and ecofriendly.•Process intensification technology results in higher yield with lower wastes.
Biodiesel is a non-toxic renewable energy source that is gaining attention globally owing to its direct applicability in preexisting engines without any modification. Various technologies from laboratory scale to industrial scale have been developed, and many plants have been established for biodiesel production using various feedstocks. Using biobased technology in biodiesel production is advantageous as these methods generate less waste and are considered ecofriendly. This article mainly discusses the availability of various oil resources (edible, non-edible, waste cooking oils (WCO)) and the advancements in technology related to oil extraction. Specifically, biobased methods, such as immobilized enzymes (matrix) and heterogeneous catalysts (derived from biomass), reported to catalyze the transesterification reaction for biodiesel production are discussed in detail. Biodiesel production using conventional technologies results in low yield and purity and is time-consuming. Newly introduced process intensification technologies (microreactor, membrane reactor, microwave, reactive distillation, and centrifugal contractor) to overcome these issues are also discussed. The need to develop integrated process technologies for biodiesel production to make the process more economical is emphasized.
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•PHA production from biowaste is an economic and ecofriendly approach.•Microbes are able to recover resource from waste and produce PHA.•C, N, P and dissolved oxygen are the main ...factors that affect PHA production.•The downstream process has a big impact on whole cost of PHA production.•Functionalization of PHA has potential to improve their applications.
Biowaste management is a challenging job as it is high in nutrient content and its disposal in open may cause a serious environmental and health risk. Traditional technologies such as landfill, bio-composting, and incineration are used for biowaste management. To gain revenue from biowaste researchers around the world focusing on the integration of biowaste management with other commercial products such as volatile fatty acids (VFA), biohydrogen, and bioplastic (polyhydroxyalkanoates (PHA)), etc. PHA production from various biowastes such as lignocellulosic biomass, municipal waste, waste cooking oils, biodiesel industry waste, and syngas has been reported successfully. Various nutrient factors i.e., carbon and nitrogen source concentration and availability of dissolved oxygen are crucial factors for PHA production. This review is an attempt to summarize the recent advancements in PHA production from various biowaste, its downstream processing, and other challenges that need to overcome making bioplastic an alternate for synthetic plastic.
Cytochrome P450s (CYPs) are heme-thiolated enzymes that catalyze the oxidation of CH bonds in a regio and stereoselective manner. Activation of the non-activated carbon atom can be further enhanced ...by multistep chemo-enzymatic reactions; moreover, several useful chemicals can be synthesized to provide alternative organic synthesis routes. Given their versatile functionality, CYPs show promise in a number of biotechnological fields. Recently, various CYPs, along with their sequences and functionalities, have been identified owing to rapid developments in sequencing technology and molecular biotechnology. In addition to these discoveries, attempts have been made to utilize CYPs to industrially produce biochemicals from available and sustainable bioresources such as oil, amino acids, carbohydrates, and lignin. Here, these accomplishments, particularly those involving the use of CYP enzymes as whole-cell biocatalysts for bioresource biotransformation, will be reviewed. Further, recently developed biotransformation pathways that result in gram-scale yields of fatty acids and fatty alkanes as well as aromatic amino acids, which depend on the hosts used for CYP expression, and the nature of the multistep reactions will be discussed. These pathways are similar regardless of whether the hosts are CYP-producing or non-CYP-producing; the limitations of these methods and the ways to overcome them are reviewed here.
•The recent progresses of CYP-dependent multi step cascade reaction•Whole cell biotransformation of fatty acids and fatty alkanes•Whole cell biotransformation of aromatic amino acids•Promising host and limitations for CYP-dependent whole cell biotransformation•Space-time yields of CYP-dependent whole cell biotransformation
Carbon constraints, as well as the growing hazard of greenhouse gas emissions, have accelerated research into all possible renewable energy and fuel sources. Microbial electrolysis cells (MECs), a ...novel technology able to convert soluble organic matter into energy such as hydrogen gas, represent the most recent breakthrough. While research into energy recovery from wastewater using microbial electrolysis cells is fascinating and a carbon-neutral technology that is still mostly limited to lab-scale applications, much more work on improving the function of microbial electrolysis cells would be required to expand their use in many of these applications. The present limiting issues for effective scaling up of the manufacturing process include the high manufacturing costs of microbial electrolysis cells, their high internal resistance and methanogenesis, and membrane/cathode biofouling. This paper examines the evolution of microbial electrolysis cell technology in terms of hydrogen yield, operational aspects that impact total hydrogen output in optimization studies, and important information on the efficiency of the processes. Moreover, life-cycle assessment of MEC technology in comparison to other technologies has been discussed. According to the results, MEC is at technology readiness level (TRL) 5, which means that it is ready for industrial development, and, according to the techno-economics, it may be commercialized soon due to its carbon-neutral qualities.
6‐Bromoindirubin (6BrIR), found in Murex sea snails, is a precursor of indirubin‐derivatives anticancer drugs. However, its synthesis remains limited due to uncharacterized biosynthetic pathways and ...difficulties in site‐specific bromination and oxidation at the indole ring. Here, we present an efficient 6BrIR production strategy in Escherichia coli by using four enzymes, that is, tryptophan 6‐halogenase fused with flavin reductase Fre (Fre‐L3‐SttH), tryptophanase (TnaA), toluene 4‐monooxygenase (PmT4MO), and flavin‐containing monooxygenase (MaFMO). Although most indole oxygenases preferentially oxygenate the electronically active C3 position of indole, PmT4MO was newly characterized to perform C2 oxygenation of 6‐bromoindole with 45% yield to produce 6‐bromo‐2‐oxindole. In addition, 6BrIR was selectively generated without indigo and indirubin byproducts by controlling the reducing power of cysteine and oxygen supply during the MaFMO reaction. These approaches led to 34.1 mg/L 6BrIR productions, making it possible to produce the critical precursor of the anticancer drugs only from natural ingredients such as tryptophan, NaBr, and oxygen.
Regulating the biosynthesis of indigo and indirubin has been continuously attempted. However, there is still no definitive way to control the production of each molecule due to the difficulties of regiospecific oxygenation and bromination at the indole ring. Here, we present an efficient 6‐bromoindirubin production strategy in Escherichia coli using an enzymatic system, that is, tryptophan 6‐halogenase SttH, toluene 4‐monooxygenase PmT4MO, and flavin‐containing monooxygenase MaFMO. Through the process, the critical precursor of indigoid drugs can be regiospecifically produced from tryptophan.
Biomass gasification produces syngas, mainly comprised of CO and H2 along with H2S, CO2, N2, and tar compounds. Inorganic carbon present in syngas as CO and CO2 can be utilized for the production of ...several value-added chemicals including ethanol, higher alcohols, fuels, and hydrogen. However, chemical sequestration operates at a high temperature of 300–500 °C and pressure of 3–5 MPa in the presence of heavy metal catalysts. Catalyst regeneration and the maintenance of high temperature and pressure increased the cost of operation. Microorganisms like algae and bacteria including Acetobacterium and Clostridium also have the potential to sequester carbon from the gas phase. Research has emphasized the production of microbial metabolites with a high market value from syngas. However, scale-up and commercialization of technology have some obstacles like inefficient mass transfer, microbial contamination, inconsistency in syngas composition, and requirement for a clean-up process. The current review summarizes the recent advances in syngas production and utilization with special consideration of alcohol and energy-related products along with challenges for scale-up.
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•Macroalgal biomass is a sustainable and renewable feedstock for PHA production.•Halomonas sp. have the capability to utilize galactose and glucose and produce PHA.•Eucheuma spinosum ...derived biochar is used to detoxify its biomass hydrolysate.•Detoxified and unsterilized hydrolysate valorized into PHA by Halomonas sp.
Macroalgae (seaweed) is considered a favorable feedstock for polyhydroxyalkanoates (PHAs) production owing to its high productivity, low land and freshwater requirement, and renewable nature. Among different microbes Halomonas sp. YLGW01 can utilize algal biomass-derived sugars (galactose and glucose) for growth and PHAs production. Biomass-derived byproducts furfural, hydroxymethylfurfural (HMF), and acetate affects Halomonas sp. YLGW01 growth and poly(3-hydroxybutyrate) (PHB) production i.e., furfural > HMF > acetate. Eucheuma spinosum biomass-derived biochar was able to remove 87.9 % of phenolic compounds from its hydrolysate without affecting sugar concentration. Halomonas sp. YLGW01 grows and accumulates a high amount of PHB at 4 % NaCl. The use of detoxified unsterilized media resulted in high biomass (6.32 ± 0.16 g cdm/L) and PHB production (3.88 ± 0.04 g/L) compared to undetoxified media (3.97 ± 0.24 g cdm/L, 2.58 ± 0.1 g/L). The finding suggests that Halomonas sp. YLGW01 has the potential to valorize macroalgal biomass into PHAs and open a new avenue for renewable bioplastic production.
Polyhydroxybutyrates (PHB) are biodegradable polymers that are produced by various microbes, including
Ralstonia, Pseudomonas
, and
Bacillus
species. In this study, a
Vibrio proteolyticus
strain, ...which produces a high level of polyhydroxyalkanoate (PHA), was isolated from the Korean marine environment. To determine optimal growth and production conditions, environments with different salinity, carbon sources, and nitrogen sources were evaluated. We found that the use of a medium containing 2% (w/v) fructose, 0.3% (w/v) yeast extract, and 5% (w/v) sodium chloride (NaCl) in M9 minimal medium resulted in high PHA content (54.7%) and biomass (4.94 g/L) over 48 h. Addition of propionate resulted in the production of poly(3-hydroxybutyrate-
co
-3-hydroxyvalerate) (P(HB-co-HV)) copolymer as propionate acts as a precursor for the HV unit. In these conditions, the bacteria produced poly(3-hydroxybutyrate-
co
-3-hydroxyvalerate) containing a 15.8% 3HV fraction with 0.3% propionate added as the substrate. To examine the possibility of using unsterilized media with high NaCl content for PHB production,
V. proteolyticus
was cultured in sterilized and unsterilized conditions. Our results indicated a higher growth, leading to a dominant population in unsterilized conditions and higher PHB production. This study showed the conditions for halophilic PHA producers to be later implemented at a larger scale.
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•Lignocellulosic biomass pretreatment leads to the production of various side products.•Eucheuma spinosum biochar (EB-BC 600) is specific to phenolics removal.•Furfural and HMF ...adsorption follow the pseudo-first-order of kinetics.•Furfural and HMF adsorption follow the Langmuir isotherm model.•The use of detoxified hydrolysates leads to high biomass and PHA production.
In this study, fourteen types of biochar produced using seven biomasses at temperatures 300 °C and 600 °C were screened for phenolics (furfural and hydroxymethylfurfural (HMF)) removal. Eucheuma spinosum biochar (EB-BC 600) showed higher adsorption capacity to furfural (258.94 ± 3.2 mg/g) and HMF (222.81 ± 2.3 mg/g). Adsorption kinetics and isotherm experiments interpreted that EB-BC 600 biochar followed the pseudo-first-order kinetic and Langmuir isotherm model for both furfural and HMF adsorption. Different hydrolysates were detoxified using EB-BC 600 biochar and used as feedstock for engineered Escherichia coli. An increased polyhydroxyalkanoates (PHA) production with detoxified barley biomass hydrolysate (DBBH: 1.71 ± 0.07 g PHA/L), detoxified miscanthus biomass hydrolysate (DMBH: 0.87 ± 0.03 g PHA/L) and detoxified pine biomass hydrolysate (DPBH: 1.28 ± 0.03 g PHA/L) was recorded, which was 2.8, 6.4 and 3.4 folds high as compared to undetoxified hydrolysates. This study reports the mechanism involved in furfural and HMF removal using biochar and valorization of hydrolysate into PHA.
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