Long-term biological hydrogen production by agar immobilized Rhodobacter capsulatus in a sequential batch photobioreactor

Sodium alginate based artificial biofilms polymerized by electrophoretic deposition for microbial hydrogen generation

This study developed an artificial biofilm of Rhodospirillum rubrum bacteria immobilized within an alginate matrix using electrophoretic deposition (EPD) on an electrode. The resulting biofilm immobilized bacteria effectively and maintained a high survival rate, facilitating stable and high-efficiency hydrogen generation for longer periods compared to biofilms produced using free bacteria. Hydrogen production efficiency remained constant when the substrate was periodically replaced, indicating that the bacteria could survive within the biofilm for long-term hydrogen production. EPD produced mechanically stable large-scale biofilms economically and rapidly, which effectively overcame operational limitations such as culture medium temperature, pH, and flow rate. Therefore, this proposed method has the potential to accelerate the commercialization of biohydrogen production systems through large-scale biofilm production to facilitate continuous hydrogen generation. The technique can be utilized in various hydrogel-based applications, providing a cost-effective and efficient manufacturing process with customized biological and mechanical properties. The developed biofilms have implications beyond biohydrogen production and could be applied to hydrogel-based medical, cosmetic, and food applications. This study highlights the importance of immobilizing bacteria for stable and efficient hydrogen generation and demonstrates the potential of EPD in fabricating mechanically stable biofilms for large-scale production.

Development of stable agar/carrageenan-Fe3O4-Klebsiella pneumoniae composite beads for efficient phenol degradation

It's of practical importance but highly challenging for cell immobilization supports to maintain mechanical strength and reduce microbial leakage in environmental and industrial applications. Herein, we developed an agar/κ-carrageenan composite hydrogel to entrap Klebsiella pneumoniae with the combination of nano-Fe₃O₄ for processing phenol wastes. The agar/carrageenan-K. pneumoniae composite bead showed good pelletizing properties, superior material strength and high cell loading. Introduction of nano-Fe₃O₄ to the composite gel further enhanced phenol degradation rate by >10% owing to strengthened phenol oxidation by Fe₃O₄-induced hydroxyl radicals (·OH) and improved mass and electron transfers. 50 successive cycles of degradation and recycling using the agar/carrageenan-K. pneumoniae composite bead showed that 1500 mg/L phenol was fully degraded for all cycles with the highest rate of 55.12 mg L^-1·h^-1 obtained at the 15th cycles. The improved stability and recyclability render the as-prepared immobilized phenol-degrading bacteria with great potential for industrial applications.

Waste-to-energy nexus: A sustainable development

An upsurge in global population due to speedy urbanization and industrialization is facing significant challenges such as rising energy-demand, enormous waste-generation and environmental deterioration. The waste-to-energy nexus based on the 5R principle (Reduce, Reuse, Recycle, Recovery, and Restore) is of paramount importance in solving these Gordian knots. This review essentially concentrates on latest advancements in the field of 'simultaneous waste reduction and energy production' technologies. The waste-to-energy approaches (thermal and biochemical) for energy production from the agricultural residues are comprehensively discussed in terms environmental, techno-economic, and policy analysis. The review will assess the loopholes in order to come up with more sophisticated technologies that are not only eco-friendly and cost-effective, but also socially viable. The waste-to-energy nexus as a paradigm for sustainable development of restoring waste is critically discussed considering future advancement plans and agendas of the policy-makers.

Molecular Characterization of a Novel 1,3-α-3,6-Anhydro-L-Galactosidase, Ahg943, with Cold- and High-Salt-Tolerance from Gayadomonas joobiniege G7

1,3-α-3,6-anhydro-L-galactosidase (α-neoagarooligosaccharide hydrolase) catalyzes the last step of agar degradation by hydrolyzing neoagarobiose into monomers, D-galactose, and 3,6-anhydro-Lgalactose, which is important for the bioindustrial application of algal biomass. Ahg943, from the agarolytic marine bacterium Gayadomonas joobiniege G7, is composed of 423 amino acids (47.96 kDa), including a 22-amino acid signal peptide. It was found to have 67% identity with the α-neoagarooligosaccharide hydrolase ZgAhgA, from Zobellia galactanivorans, but low identity (< 40%) with the other α-neoagarooligosaccharide hydrolases reported. The recombinant Ahg943 (rAhg943, 47.89 kDa), purified from Escherichia coli, was estimated to be a monomer upon gel filtration chromatography, making it quite distinct from other α-neoagarooligosaccharide hydrolases. The rAhg943 hydrolyzed neoagarobiose, neoagarotetraose, and neoagarohexaose into D-galactose, neoagarotriose, and neoagaropentaose, respectively, with a common product, 3,6- anhydro-L-galactose, indicating that it is an exo-acting α-neoagarooligosaccharide hydrolase that releases 3,6-anhydro-L-galactose by hydrolyzing α-1,3 glycosidic bonds from the nonreducing ends of neoagarooligosaccharides. The optimum pH and temperature of Ahg943 activity were 6.0 and 20°C, respectively. In particular, rAhg943 could maintain enzyme activity at 10°C (71% of the maximum). Complete inhibition of rAhg943 activity by 0.5 mM EDTA was restored and even, remarkably, enhanced by Ca²⁺ ions. rAhg943 activity was at maximum at 0.5 M NaCl and maintained above 73% of the maximum at 3M NaCl. K_m and V_max of rAhg943 toward neoagarobiose were 9.7 mg/ml and 250 μM/min (3 U/mg), respectively. Therefore, Ahg943 is a unique α-neoagarooligosaccharide hydrolase that has cold- and high-salt-adapted features, and possibly exists as a monomer.

Microbial Fuel Cell-Based Biological Oxygen Demand Sensors for Monitoring Wastewater: State-of-the-Art and Practical Applications

Environmental pollution has been a continuous threat to sustainable development and global well-being. It has become a significant concern worldwide to combat the ecological crisis using low-cost innovative technologies. Biological oxygen demand (BOD) is a key indicator to comprehend the quality of water to guarantee environmental safety and human health; however, none of the present technologies are capable of online monitoring of the water at the source. Microbial fuel cells (MFC) are a promising technology for simultaneous power generation and wastewater treatment. MFCs have also been shown in fascinating applications to measure and detect the toxic pollutants present in wastewater. These are the bioreactors where exoelectrogenic microorganisms catalyze the conversion of the inherent chemical energy stored in organic compounds to electrical energy. Sensors employ energy conversion to measure BOD, which is considered an international index for the detection of organic material load present in wastewater. The MFC-based BOD sensors have gone through a wide range of advancement from mediator to mediator-less, double chamber to single-chamber, and large size to miniature. There have been detailed studies to improve the accuracy and reproducibility of the sensors for commercial applications. Additionally, multistage MFC-based BOD biosensors and miniature MFC-BOD sensors have also been ubiquitous in recent years. A considerable amount of work has been carried out to improve the performance of these devices by fabricating the proton exchange membranes and altering catalysts at the cathode. However, there remains a dearth for the fabrication of the devices in aspects like suitable microbes, proton exchange membranes, and cheaper catalysts for cathodes for effective real-time monitoring of wastewater. In this review, an extensive study has been carried out on various MFC-based BOD sensors. The efficiency and drawbacks associated with the different MFC-based BOD sensors have been critically evaluated, and future perspectives for their development have been investigated. The breadth of work compiled in this review will accelerate further research in MFC-based BOD biosensors. It will be of great importance to broad ranges of scientific research and industry.

Implications of agar and agarase in industrial applications of sustainable marine biomass

Agar, a major component of the cell wall of red algae, is an interesting heteropolysaccharide containing an unusual sugar, 3,6-anhydro-L-galactose. It is widely used as a valuable material in various industrial and experimental applications due to its characteristic gelling and stabilizing properties. Agar-derived oligosaccharides or mono-sugars produced by various agarases have become a promising subject for research owing to their unique biological activities, including anti-obesity, anti-diabetic, immunomodulatory, anti-tumor, antioxidant, skin-whitening, skin-moisturizing, anti-fatigue, and anti-cariogenic activities. Agar is also considered as an alternative sustainable source of biomass for chemical feedstock and biofuel production to substitute for the fossil resource. In this review, we summarize various biochemically characterized agarases, which are useful for industrial applications, such as neoagarooligosaccharide or agarooligosaccharide production and saccharification of agar. Additionally, we succinctly discuss various recent studies that have been conducted to investigate the versatile biological activities of agar-derived saccharides and biofuel production from agar biomass. This review provides a basic framework for understanding the importance of agarases and agar-derived saccharides with broad applications in pharmaceutical, cosmetic, food, and bioenergy industries.

A Mediated BOD Biosensor Based on Immobilized B. Subtilis on Three-Dimensional Porous Graphene-Polypyrrole Composite

We have developed a novel mediated biochemical oxygen demand (BOD) biosensor based on immobilized Bacillus subtilis (B. subtilis) on three-dimensional (3D) porous graphene-polypyrrole (rGO-PPy) composite. The 3D porous rGO-PPy composite was prepared using hydrothermal method following with electropolymerization. Then the 3D porous rGO-PPy composite was used as a support for immobilizing negatively charged B. subtilis denoted as rGO-PPy-B through coordination and electrostatic interaction. Further, the prepared rGO-PPy-B was used as a microbial biofilm for establishing a mediated BOD biosensor with ferricyanide as an electronic acceptor. The indirect determination of BOD was performed by electrochemical measuring ferrocyanide generated from a reduced ferricyanide mediator using interdigited ultramicroelectrode array (IUDA) as the working electrode. The experimental results suggested a good linear relationship between the amperometric responses and BOD standard concentrations from 4 to 60 mg/L, with a limit detection of 1.8 mg/L (S/N ≥ 3). The electrochemical measurement of real water samples showed a good agreement with the conventional BOD₅ method, and the good anti-interference as well as the long-term stability were well demonstrated, indicating that the proposed mediated BOD biosensor in this study holds a potential practical application of real water monitoring.