Chitin biomass powered microbial fuel cell for electricity production using halophilic Bacillus circulans BBL03 isolated from sea salt harvesting area

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants' load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Extracellular electrons transferred from honey probiotic Bacillus circulans inhibits inflammatory acne vulgaris

Bacillus circulans (B. circulans) is widely used as an electrogenic bacterium in microbial fuel cell (MFC) technology. This study evaluated whether B. circulans can ferment glucose to generate electricity and mitigate the effects of human skin pathogens. The electricity production of B. circulans was examined by measuring the voltage difference and verified using a ferrozine assay in vitro. To investigate the fermentation effects of B. circulans on inhibition of human skin pathogens, Cutibacterium acnes (C. acnes) was injected intradermally into mice ears to induce an inflammatory response. The results revealed that the glucose-B. circulans co-culture enhanced electricity production and significantly supressed C. acnes growth. The addition of roseoflavin to inhibit flavin production considerably reduced the electrical energy generated by B. circulans through metabolism and, in vivo test, recovered C. acnes count and macrophage inflammatory protein 2 (MIP-2) levels. This suggests that B. circulans can generate electrons that affect the growth of C. acnes through flavin-mediated electron transfer and alleviate the resultant inflammatory response. Our findings demonstrate that probiotics separated from natural substances and antimicrobial methods of generating electrical energy through carbon source fermentation can help in the treatment of bacterial infections.

Microbial electro deionization for waste water treatment - A critical review on methods, applications and mechanism

Electro deionization using microbial communities has been proven as a competent method for desalination and abatement of water pollution by removing ionic chemicals from the target waters. Microbial Desalination Cell (MDC) facilitates microbial deionization which can either support or be a substitute for the conventional desalination methods. Generation of electricity is accomplished by the bio electrochemical oxidation of organic compounds present as contaminants in wastewater which in turn attribute to the migration of ions in MDC system. The present review aims to elucidate the theory, principles and the application of microbial desalination cell and microbial fuel cell (MFC) in treatment of saline and wastewaters. Air cathode MDC and stacked MDC for purification of saline water are found to give promising results. Air pump assisted microbial desalination cell reported 150.39 ppm h^-1 of salt removal with an operational time period of 80 h and showed consistent results. Hence the air cathode assisted MDC showed dominant capacity of salt removal compared to stacked MDC. Also, three major types of microbial fuel cell, namely photosynthetic biofilm MFC, constructive wetland MFC and ceramic membrane supported MFC are reviewed for their potentials in wastewater treatment by deionization method and electricity generation. Complete (100%) removal of chemical oxygen demand was reported by photosynthetic microbial fuel cell operated for 16 days having 435.8 Ω of external resistance. When constructive wetland microbial fuel cell was operated for 10 days with 1000 ohms of external resistance, it exhibited complete (100%) removal of chemical oxygen demand from the wastewater. About 92% of chemical oxygen demand removal was demonstrated by ceramic membrane supported microbial fuel. Compared to ceramic membrane microbial fuel cell, photosynthetic and constructive wetland microbial fuel cell displayed better performance in terms of pollutant removal capacity and economical factor. Ability of the electrogenic species, namely Geobacter, Shewanella, Clostridium and Bacillus and the photosynthetic species, namely Chorella Vulgaris Rhodopsuedomonas, and Scenedesmus abundans in microbial deionization methods and their performance levels reported by several researchers are presented.

Lignocellulosic hydrolysate based biorefinery for marine exopolysaccharide production and application of the produced biopolymer in environmental clean-up

The present study deals with the utilization of lignocellulosic hydrolysate-based carbon source for exopolysaccharide (EPS) production using newly reported marine Echinicola sediminis BBL-M-12. This bacterium produced 7.56 g L^-1 and 5.32 g L^-1 of EPS on supplementing 30 g L^-1 glucose and 10 g L^-1 xylose as the sole carbon source, respectively. Whereas on feeding Miscanthus hydrolysate (MCH) with glucose content adjusting to 20 g L^-1, E. sediminis BBL-M-12 produced 6.18 g L^-1 of EPS. The inhibitors study showed bacterium could tolerate higher concentrations of fermentation inhibitors include furfural (0.05%), 5-hydroxymethylfurfural (0.1%), vanillin (0.1%) and acetate (0.5%). Moreover, the EPS composition was greatly altered with the type and concentration of carbon source supplied, although β-D-Glucopyranose, β-D-Galactopyranose, and β-D-Xylopyranose were the dominant monomers detected. Interestingly, E. sediminis BBL-M-12 EPS revealed excellent environmental applications like clay flocculation, oil emulsification, and removal of humic acid, textile dye, and heavy metal from the aqueous phase.

Quantum dot synthesis from waste biomass and its applications in energy and bioremediation

Quantum dots (QDs) are getting special attention due to their commendable optical properties and applications. Conventional metal-based QDs have toxicity and non-biodegradability issues, thus it becomes necessary to search for renewable precursor molecules for QDs synthesis. In recent years, biomass-based carbon rich QDs (CQDs) have been introduced which are mainly synthesised via carbonization (pyrolysis and hydrothermal treatment). These CQDs offered higher photostability, biocompatibility, low-toxicity, and easy tunability for physicochemical properties. Exceptional optical properties become a point of attraction for its multifaceted applications in various sectors like fabrication of electrodes and solar cells, conversion of solar energy to electricity, detection of pollutants, designing biosensors, etc. In recent years, a lot of work has been done in this field. This article will summarize these advancements along in a special context to biomass-based QDs and their applications in energy and the environment.

Impact of light on microalgal photosynthetic microbial fuel cells and removal of pollutants by nanoadsorbent biopolymers: Updates, challenges and innovations

Photosynthetic microbial fuel cells (PMFCs) with microalgae have huge potential for treating wastewater while simultaneously converting light energy into electrical energy. The efficiency of such cells directly depends on algal growth, which depends on light intensity. Higher light intensity results in increased potential as well as enhancement in generation of biomass rich in biopolymers. Such biopolymers are produced either by microbes at anode and algae at cathode or vice versa. The biopolymers recovered from these biological sources can be added in wastewater alone or in combination with nanomaterials to act as nanoadsorbents. These nanoadsorbents further increase the efficiency of PMFC by removing the pollutants like metals and dyes. In this review firstly the effect of different light intensities on the growth of microalgae, importance of diatoms in a PMFC and their impact on PMFCs efficiencies have been narrated. Secondly recovery of biopolymers from different biological sources and their role in removal of metals, dyes along with their impact on circular bioeconomy have been discussed. Thereafter bottlenecks and future perspectives in this field of research have been narrated.

Novel Polyhydroxybutyrate-Degrading Activity of the Microbulbifer Genus as Confirmed by Microbulbifer sp. SOL03 from the Marine Environment

Ever since bioplastics were globally introduced to a wide range of industries, the disposal of used products made with bioplastics has become an issue inseparable from their application. Unlike petroleum-based plastics, bioplastics can be completely decomposed into water and carbon dioxide by microorganisms in a relatively short time, which is an advantage. However, there is little information on the specific degraders and accelerating factors for biodegradation. To elucidate a new strain for biodegrading poly-3-hydroxybutyrate (PHB), we screened out one PHB-degrading bacterium, Microbulbifer sp. SOL03, which is the first reported strain from the Microbulbifer genus to show PHB degradation activity, although Microbulbifer species are known to be complex carbohydrate degraders found in high-salt environments. In this study, we evaluated its biodegradability using solid- and liquid-based methods in addition to examining the changes in physical properties throughout the biodegradation process. Furthermore, we established the optimal conditions for biodegradation with respect to temperature, salt concentration, and additional carbon and nitrogen sources; accordingly, a temperature of 37°C with the addition of 3% NaCl without additional carbon sources, was determined to be optimal. In summary, we found that Microbulbifer sp. SOL03 showed a PHB degradation yield of almost 97% after 10 days. To the best of our knowledge, this is the first study to investigate the potent bioplastic degradation activity of Microbulbifer sp., and we believe that it can contribute to the development of bioplastics from application to disposal.

Seafood Processing Chitin Waste for Electricity Generation in a Microbial Fuel Cell Using Halotolerant Catalyst Oceanisphaera arctica YHY1

In this study, a newly isolated halotolerant strain Oceanisphaera arctica YHY1, capable of hydrolyzing seafood processing waste chitin biomass, is reported. Microbial fuel cells fed with 1% chitin and 40 g L−1 as the optimum salt concentration demonstrated stable electricity generation until 216 h (0.228 mA/cm2). N-acetyl-D-glucosamine (GlcNAc) was the main by-product in the chitin degradation, reaching a maximum concentration of 192.01 mg g−1 chitin at 120 h, whereas lactate, acetate, propionate, and butyrate were the major metabolites detected in the chitin degradation. O. arctica YHY1 utilized the produced GlcNAc, lactate, acetate, and propionate as the electron donors to generate the electric current. Cyclic voltammetry (CV) investigation revealed the participation of outer membrane-bound cytochromes, with extracellular redox mediators partly involved in the electron transfer mechanism. Furthermore, the changes in structural and functional groups in chitin after degradation were analyzed using FTIR and XRD. Therefore, the ability of O. arctica YHY1 to utilize waste chitin biomass under high salinities can be explored to treat seafood processing brine or high salt wastewater containing chitin with concurrent electricity generation.

Engineering of Shewanella marisflavi BBL25 for biomass-based polyhydroxybutyrate production and evaluation of its performance in electricity production

Polyhydroxybutyrate (PHB) is a biodegradable plastic with physical properties similar to petrochemically derived plastics. Here, Shewanella marisflavi BBL25 was engineered by inserting the pLW487 vector containing polyhydroxyalkanoates synthesis genes from Ralstonia eutropha H16. Under optimal conditions, the engineered S. marisflavi BBL25 produced 1.99 ± 0.05 g/L PHB from galactose. The strain showed high tolerance to various inhibitors and could utilize lignocellulosic biomass for PHB production. When barley straw hydrolysates were used as a carbon source, PHB production was 3.27 ± 0.19 g/L. In addition, PHB production under the microbial fuel cell system was performed to confirm electricity coproduction. The maximum electricity current output density was 1.71 mA/cm², and dry cell weight (DCW) and PHB production were 11.4 g/L and 6.31 g/L, respectively. Our results demonstrated PHB production using various lignocellulosic biomass and the feasibility of PHB and electricity production, simultaneously, and it is the first example of PHB production in engineered Shewanella.

Substrate salinity: A critical factor regulating the performance of microbial fuel cells, a review

Substrate salinity is a critical factor influencing microbial fuel cells (MFCs) performance and various studies have suggested that increasing substrate salinity first improves MFC performance. However, a further increase in salinity that exceeds the salinity tolerance of exoelectrogens shows negative effects because of inhibited bacterial activity and increased activation losses. In this review, electricity generation and contaminant removal from saline substrates using MFCs are summarized, and results show different optimal salinities for obtaining maximum performance. Then, electroactive bacteria capable of tolerating saline environments and strategies for improving salinity tolerance are discussed. In addition to ohmic resistance and bacterial activity, membrane resistance and catalyst performance will also be affected by substrate salinity, all of which jointly contribute the final overall MFC performance. Therefore, the combined effect of salinity is analyzed to illustrate how the MFC performance changes with increasing salinity. Finally, the challenges and perspectives of MFCs operated in saline environments are discussed.

Improvement of polyhydroxybutyrate (PHB) plate-based screening method for PHB degrading bacteria using cell-grown amorphous PHB and recovered by sodium dodecyl sulfate (SDS)

Poly(3-hydroxybutyrate) (PHB) is a biobased and biodegradable plastic. Considering the environmental issues of petroleum-based plastics, PHB is promising as it can be degraded in a relatively short time by bacteria to water and carbon dioxide. Substantial efforts have been made to identify PHB-degrading bacteria. To identify PHB-degrading bacteria, solid-based growth or clear zone assays using PHB as the sole carbon source are the easiest methods; however, PHB is difficult to dissolve and distribute evenly, and bacteria grow slowly on PHB plates. Here, we suggest an improved PHB plate assay using cell-grown PHB produced by Halomonas sp. and recovered by sodium dodecyl sulfate (SDS). Preparation using SDS resulted in evenly distributed PHB plates that could be used for sensitive depolymerase activity screening in less time compared with solvent-melted pellet or cell-grown PHB. With this method, we identified 15 new strains. One strain, Cutibacterium sp. SOL05 (98.4% 16S rRNA similarity to Cutibacterium acne), showed high PHB depolymerase activity in solid and liquid conditions. PHB degradation was confirmed by clear zone size, liquid culture, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results indicate this method can be used to easily identify PHB-degrading bacteria from various sources to strengthen the benefits of bioplastics.

Application of macroalgal biomass derived biochar and bioelectrochemical system with Shewanella for the adsorptive removal and biodegradation of toxic azo dye

The present study aimed towards adsorptive removal of the toxic azo dye onto biochar derived from Eucheuma spinosum biomass. Characterization of the produced biochar was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). Eucheuma spinosum biochar (ES-BC) produced at 600 °C revealed a maximum adsorption capacity of 331.97 mg/g towards reactive red 120 dye. The adsorption data fitted best to the pseudo-second order kinetics (R² > 0.99) and Langmuir isotherm (R² > 0.98) models. These adsorption models signified the chemisorption mechanism with monolayer coverage of the adsorbent surface with dye molecules. Furthermore, the adsorption process was mainly governed by electrostatic interaction, ion exchange, metal complexation, and hydrogen bonding as supported by the solution pH, FTIR, XPS, and XRD investigation. Nevertheless, alone adsorption technology could not offer a complete solution for eliminating the noxious dyes. Therefore, the bioelectrochemical system (BES) equipped with previously isolated marine Shewanella marisflavi BBL25 was intended for the complete remediation of azo dye. The BES II demonstrated highest dye decolorization (97.06%) within 48 h at biocathode where the reductive cleavage of the azo bond occurred. Cyclic voltammetry (CV) studies of the BES revealed perfect redox reactions taking place where the redox mediators shuttled the electrons to the dye molecule to accelerate the dye decolorization. Besides, the GC-MS analysis revealed biotransformation of the dye into less toxic metabolites as tested using a phyto and cytogenotoxicity.

Insights into Advancements and Electrons Transfer Mechanisms of Electrogens in Benthic Microbial Fuel Cells

Benthic microbial fuel cells (BMFCs) are a kind of microbial fuel cell (MFC), distinguished by the absence of a membrane. BMFCs are an ecofriendly technology with a prominent role in renewable energy harvesting and the bioremediation of organic pollutants through electrogens. Electrogens act as catalysts to increase the rate of reaction in the anodic chamber, acting in electrons transfer to the cathode. This electron transfer towards the anode can either be direct or indirect using exoelectrogens by oxidizing organic matter. The performance of a BMFC also varies with the types of substrates used, which may be sugar molasses, sucrose, rice paddy, etc. This review presents insights into the use of BMFCs for the bioremediation of pollutants and for renewable energy production via different electron pathways.

Vibrio campbellii chitoporin: Thermostability study and implications for the development of therapeutic agents against Vibrio infections

Vibrio campbellii (formerly Vibrio harveyi) is a bacterial pathogen that causes vibriosis, which devastates fisheries and aquaculture worldwide. V. campbellii expresses chitinolytic enzymes and chitin binding/transport proteins, which serve as excellent targets for antimicrobial agent development. We previously characterized VhChiP, a chitooligosaccharide-specific porin from the outer membrane of V. campbellii BAA-1116. This study employed far-UV circular dichroism and tryptophan fluorescence spectroscopy, together with single channel electrophysiology to demonstrate that the strong binding of chitoligosaccharides enhanced thermal stability of VhChiP. The alanine substitution of Trp¹³⁶ at the center of the affinity sites caused a marked decrease in the binding affinity and decreased the thermal stability of VhChiP. Tryptophan fluorescence titrations over a range of temperatures showed greater free-energy changes on ligand binding (ΔG°_binding) with increasing chain length of the chitooligosaccharides. Our findings suggest the possibility of designing stable channel-blockers, using sugar-based analogs that serve as antimicrobial agents, active against Vibrio infection.

Chitin derived biochar for efficient capacitive deionization performance

The selection and preparation of an electrode material is the core of capacitive deionization. In order to obtain a material with a good deionization properties, we have designed an environmentally-friendly and simple way of preparing biochar. In this work, biochar was prepared by a thermal-deposition method and after chemical modification it was characterized with a scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The specific surface area of biochar modified by KOH is as high as 833.76 m² g⁻¹, but the specific surface area of the unmodified electrode material is only 126.43 m² g⁻¹. The electrochemical analysis (CV and EIS) of the biochar indicates that HC-800 has a lower charge transfer resistance and a higher specific capacitance, where the specific capacity of HC-800 reaches 120 F g⁻¹. A CDI property analysis of HC-800 shows a better electrosorption capacity of 11.52 mg g⁻¹ and better regeneration and cycling stability than CS-800. The desalination amount remains 87.23% after several cycles.

Schematic illustration of the fabrication of chitin derived biochar and KOH-activated chitin derived biochar electrodes for capacitive deionization.