Comparison of electrogenic capabilities of microbial fuel cell with different light power on algae grown cathode

Microbial electrosynthesis of valuable chemicals from the reduction of CO2: a review

The present energy demand of the world is increasing but the fossil fuels are gradually depleting. As a result, the need for alternative fuels and energy sources is growing. Fuel cells could be one alternative to address the challenge. The fuel cell can convert CO2 to value-added chemicals. The potential of bio-fuel cells, specifically enzymatic fuel cells and microbial fuel cells, and the importance of immobilization technology in bio-fuel cells are highlighted. The review paper also includes a detailed explanation of the microbial electrosynthesis system to reduce CO2 and the value-added products during microbial electrosynthesis. Future research in bio-electrochemical synthesis for CO2 conversion is expected to prioritize enhancing biocatalyst efficiency, refining reactor design, exploring novel electrode materials, understanding microbial interactions, integrating renewable energy sources, and investigating electrochemical processes for carbon capture and selective CO2 reduction. The challenges and perspectives of bio-electrochemical systems in the application of CO2 conversion are also discussed. Overall, this review paper provides valuable insights into the latest developments and criteria for effective research and implementation in bio-fuel cells, immobilization technology, and microbial electro-synthesis systems.

Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235 MJ/Kg, indicating the cell's high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.

Evaluating application of photosynthetic microbial fuel cell to exhibit efficient carbon sequestration with concomitant value-added product recovery from wastewater: A review

The emission of CO2 from industrial (24%) and different anthropogenic activities, like transportation (27%), electricity production (25%), and agriculture (11%), can lead to global warming, which in the long term can trigger substantial climate changes. In this regard, CO2 sequestration and wastewater treatment in tandem with bioenergy production through photosynthetic microbial fuel cell (PMFC) is an economical and sustainable intervention to address the problem of global warming and elevating energy demands. Therefore, this review focuses on the application of different PMFC as a bio-refinery approach to produce biofuels and power generation accompanied with the holistic treatment of wastewater. Moreover, CO2 bio-fixation and electron transfer mechanism of different photosynthetic microbiota, and factors affecting the performance of PMFC with technical feasibility and drawbacks are also elucidated in this review. Also, low-cost approaches such as utilization of bio-membrane like coconut shell, microbial growth enhancement by extracellular cell signalling mechanisms, and exploitation of genetically engineered strain towards the commercialization of PMFC are highlighted. Thus, the present review intends to guide the budding researchers in developing more cost-effective and sustainable PMFCs, which could lead towards the commercialization of this inventive technology.

Employing algal biomass for fabrication of biofuels subsequent to phytoremediation

An alga belongs to the multi-pertinent group which can add to a significant sector of environment. They show a prevailing gathering of microorganisms for bioremediation due to their significant capacity to inactivate toxic heavy metals. It can easily absorb or neutralize the toxicity of heavy metals from water and soil through phytoremediation. Biosorption is a promising innovation that focuses on novel, modest, and exceptionally successful materials to apply in phytoremediation technology. Furthermore, algal biomass can be used for biofuel generation after phytoremediation using thermochemical or biological transformation processes. The algal components get affected by heavy metals during phytoremediation, but with the help of different techniques, these are yield efficient. The extreme lipid and mineral substances of microalgae have been proven helpful for biofuel manufacturing and worth extra products. Biofuels produced are bio-oil, biodiesel, bioethanol, biogas, etc. The reuse capability of algae can be utilized toward ecological manageability and economic facility. In this review article, the reuse and recycling of algal biomass for biofuel production have been represented. This novel technique has numerous benefits and produces eco-friendly and economically beneficial products.

The role of microbiome in carbon sequestration and environment security during wastewater treatment

Wastewater treatment is an essential aspect of the earth's sustainable future. However, different wastewater treatment methods are responsible for carbon discharge into the environment, raising environmental risks. Hence, such wastewater treatment methods are required that can minimize carbon release without compromising the treatment quality. Microbiome-based carbon sequestration is a potential method for achieving this goal. Limited studies have been carried out to investigate how microbes can capture and utilize CO₂. This review summarizes the approaches including microbial electrolytic carbon capture, microbial electrosynthesis, microbial fuel cell, microalgae cultivation, and constructed wetlands that employ microbes to capture and utilize CO₂. Electroactive Bacteria (EAB) convert carbon dioxide to carbonates and bicarbonates in subsequent steps after organic matter decomposition. Similarly, microbial electrosynthesis (MES) not only helps capture carbon but also produces secondary products (production of polyhydroxyalkanoates by Gram-negative rod Aeromonas hydrophila bacteria) of commercial importance during wastewater treatment. In addition to this, microbial carbon capture cells (MCCs) have been now utilized for energy generation and carbon sequestration at the same time during wastewater treatment. Moreover, microalgae cultivation has also been found to capture CO₂ at a rapid pace while releasing O₂ as a consequence of photosynthesis. Hence, microbe-based wastewater treatment has quite a potential due to two-fold benefits like carbon sequestration and by-product formation.

Circulation of anodic effluent to the cathode chamber for subsequent treatment of wastewater in photosynthetic microbial fuel cell with generation of bioelectricity and algal biomass

Synthetic wastewater containing 1500 mg L^-1 of COD was treated in the anode chamber for 5, 10, and 20 d. An anode chamber was conducted under anaerobic conditions with mixed culture bacteria inoculum attached to the anode. Anodic effluent was transferred to the cathode chamber for further treatment for 5, 10, and 20 d as the growth medium of Chlorella vulgaris. The microalgal photosynthesis process provided oxygen for the cathodic reaction. In 5 d of anodic hydraulic retention time (HRT), the effluent contained high COD, resulting in low power generation in the P-MFC due to the heterotrophic metabolism carried out by microalgae diminishing photosynthesis. However, high biomass productivity up to 0.649 g L^-1 d^-1 was obtained in the subsequent treatment of 5 d in the cathode chamber. An anodic HRT of 10 d resulted in higher power generation (0.0254 kWh kg^-1 COD), and higher COD removal efficiency up to 60%. A further 10 d treatment in the cathode chamber increased the COD removal efficiency up to 74%. Anode and cathode chambers combined removed 79% of NH₄⁺-N concentration from the original synthetic wastewater within 20 d. This study demonstrated that the anodic effluent of the P-MFC can be utilized in the cathode chamber as a growth medium for microalgae if conducted with appropriate HRT in the anode. P-MFC provides a promising sustainable solution for wastewater treatment while generating electricity and algal biomass as by-products.

Integrated Approach for Wastewater Treatment and Biofuel Production in Microalgae Biorefineries

The increasing world population generates huge amounts of wastewater as well as large energy demand. Additionally, fossil fuel’s combustion for energy production causes the emission of greenhouse gases (GHG) and other pollutants. Therefore, there is a strong need to find alternative green approaches for wastewater treatment and energy production. Microalgae biorefineries could represent an effective strategy to mitigate the above problems. Microalgae biorefineries are a sustainable alternative to conventional wastewater treatment processes, as they potentially allow wastewater to be treated at lower costs and with lower energy consumption. Furthermore, they provide an effective means to recover valuable compounds for biofuel production or other applications. This review focuses on the current scenario and future prospects of microalgae biorefineries aimed at combining wastewater treatment with biofuel production. First, the different microalgal cultivation systems are examined, and their main characteristics and limitations are discussed. Then, the technologies available for converting the biomass produced during wastewater treatment into biofuel are critically analyzed. Finally, current challenges and research directions for biofuel production and wastewater treatment through this approach are outlined.

Recent Progress in Solar-Induced Direct Biomass-to-Electricity Hybrid Fuel Cell Using Microalgae as Feedstocks

Microalgae, as potential biodiesel feedstocks, have been widely reported to accumulate oil via genetic engineering techniques, or environmental stress regulation. Recently, the utilization of fuel cell technology to convert biomass into electricity has attracted much more attention due to its high efficiency, low pollution, low noise by microalgae as feedstocks. Normally, platinum and analogous noble metals as catalysts have been already demonstrated although they still exist lots of shortcomings. This mini review presents an overview of various fuel cell technologies with phosphomolybdic acid as catalysts for sustainable energy by using microalgae. Trends from literatures demonstrate that algal-based fuel cells could efficiently generate electricity, and concurrently produce high value-added products. This critical review can provide guiding suggestions for future study of algal-based energy conversion by fuel cell techniques.

A strategy for power generation from bilgewater using a photosynthetic microalgal fuel cell (MAFC)

Microbial fuel cells (MFCs) have recently been applied to generate electricity from oily wastewater. Although MFCs that utilize microalgae to provide a self-supporting oxygen (O₂) supply at the cathode have been well discussed, those with microalgae at the anode as an active biomass for treating wastewater and producing electrons are still poorly studied and understood. Here, we demonstrated a bilgewater treatment using single- and double-chamber microalgal fuel cells (SMAFC and DMAFC) capable of generating energy with a novel microalgal strain (Chlorella sorokiniana) that was initially isolated from oily wastewater. Compared to previous MFC studies using green algae, relatively high voltage output (151.3-160.1 mV, 71.3-83.4 mV m^-2 of power density) was observed in the SMAFC under O₂ controlled systems (i.e., acetate addition or light/dark cycle). It was assumed that, under the O₂ depletion, alternative electron acceptors such as bicarbonate may be utilized for power generation. A DMAFC showed better power density (up to 23.9%) compared to the SMAFC due to the separated cathode chamber which fully utilizes O₂ as an electron acceptor. Both SMAFC and DMAFC removed 67.2-77.4% of soluble chemical oxygen demands (SCOD) from the synthetic bilgewater. This study demonstrates that the application of algae-based MFCs is a feasible strategy to treat oil-in-water emulsion while generating electricity.

Synergistic effects in a microbial fuel cell between co-cultures and a photosynthetic alga Chlorella vulgaris improve performance

Microbial communities are catalysts that drive the operation of microbial fuel cells (MFCs). In this study, the use of a defined co-culture of Escherichia coli and Pseudomonas aeruginosa towards improved power generation in MFCs is described. The co-culture has been initially evaluated for substrate consumption, biofilm formation and microbial electron transfer activity. The co-culture gave an enhanced power density of 190.44 mW m⁻², while E. coli and P. aeruginosa as pure cultures generated lesser power densities of 139.24 and 158.76 mW m⁻² respectively. The photosynthetic alga Chlorella vulgaris was then inoculated in the cathode chamber. Co-cultures in the presence of C. vulgaris improved the mean power density from 175 mW m⁻² to 248 mW m⁻², a 41.7% rise. A synergistic effect was observed when the co-cultures were coupled with C. vulgaris. Combining co-cultures with photosynthetic MFCs offers a lot of promise in studying mechanisms and expanding the nature of applications.

Wastewater based microalgal biorefinery for bioenergy production: Progress and challenges

Treatment of industrial and domestic wastewater is very important to protect downstream users from health risks and meet the freshwater demand of the ever-increasing world population. Different types of wastewater (textile, dairy, pharmaceutical, swine, municipal, etc.) vary in composition and require different treatment strategies. Wastewater management and treatment is an expensive process; hence, it is important to integrate relevant technology into this process to make it more feasible and cost-effective. Wastewater treatment using microalgae-based technology could be a global solution for resource recovery from wastewater and to provide affordable feedstock for bioenergy (biodiesel, biohydrogen, bio-alcohol, methane, and bioelectricity) production. Various microalgal cultivation systems (open or closed photobioreactors), turf scrubber, and hybrid systems have been developed. Although many algal biomass harvesting methods (physical, chemical, biological, and electromagnetic) have been reported, it is still an expensive process. In this review article, resource recovery from wastewater using algal cultivation, biomass harvesting, and various technologies applied in converting algal biomass into bioenergy, along with the various challenges that are encountered are discussed in brief.

Potential applications of algae in the cathode of microbial fuel cells for enhanced electricity generation with simultaneous nutrient removal and algae biorefinery: Current status and future perspectives

Production of biofuels and other value-added products from wastewater along with quality treatment is an uttermost necessity to achieve environmental sustainability and promote bio-circular economy. Algae-Microbial fuel cell (A-MFC) with algae in cathode chamber offers several advantages e.g. photosynthetic oxygenation for electricity recovery, CO₂-fixation, wastewater treatment, etc. However, performance of A-MFC depends on several operational parameters and also on electrode materials types; therefore, enormous collective efforts have been made by researchers for finding optimal conditions in order to enhance A-MFC performance. The present review is a comprehensive snapshot of the recent advances in A-MFCs, dealing two major parts: 1) the power generation, which exclusively outlines the effect of different parameters and development of cutting edge cathode materials and 2) wastewater treatment at cathode of A-MFC. This review provides fundamental knowledge, critical constraints, current status and some insights for making A-MFC technology a reality at commercial scale operation.

The effect of different light intensities and light/dark regimes on the performance of photosynthetic microalgae microbial fuel cell

This study develops a photosynthetic microalgae microbial fuel cell (PMMFC) engaged Chlorella vulgaris microalgae to investigate effect of light intensities and illumination regimes on simultaneous production of bioelectricity, biomass and wastewater treatment. The performance of the system under different light intensity (3500, 5000, 7000 and 10,000 lx) and light/dark regimes (24/00, 12/12, 16/8 h) was investigated. The optimum light intensity and light/dark regimes for achieving maximum yield of PMMFC were obtained. The maximum power density of 126 mW m^-3, the coulombic efficiency of 78% and COD removal of 5.47% were achieved. The maximum biomass concentration of 4 g l^-1 (or biomass yield of 0.44 g l^-1 day^-1) was obtained in continuous light intensity of 10,000 lx. The comparison of the PMMFC performance with air-cathode and abiotic-cathode MFCs shows that the maximum power density of air-cathode MFC was only 13% higher than PMMFC.

Bioelectrochemical systems using microalgae - A concise research update

Excess consumption of energy by humans is compounded by environmental pollution, the greenhouse effect and climate change impacts. Current developments in the use of algae for bioenergy production offer several advantages. Algal biomass is hence considered a new bio-material which holds the promise to fulfil the rising demand for energy. Microalgae are used in effluents treatment, bioenergy production, high value added products synthesis and CO₂ capture. This review summarizes the potential applications of algae in bioelectrochemically mediated oxidation reactions in fully biotic microbial fuel cells for power generation and removal of unwanted nutrients. In addition, this review highlights the recent developments directed towards developing different types of microalgae MFCs. The different process factors affecting the performance of microalgae MFC system and some technological bottlenecks are also addressed.

Enhanced bioelectricity generation and azo dye treatment in a reversible photo-bioelectrochemical cell by using novel anthraquinone-2,6-disulfonate (AQDS)/MnOx-doped polypyrrole film electrodes

A novel anthraquinone-2,6-disulfonate/MnO_x-doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation.

Microalgae-microbial fuel cell: A mini review

Microalgae-microbial fuel cells (mMFCs) are a device that can convert solar energy to electrical energy via biological pathways. This mini-review lists new research and development works on microalgae processes, microbial fuel cell (MFC) processes, and their combined version, mMFC. The substantial improvement and technological advancement are highlighted, with a discussion on the challenges and prospects for possible commercialization of mMFC technologies.