Renewable sustainable biocatalyzed electricity production in a photosynthetic algal microbial fuel cell (PAMFC)

Whole-cell biophotovoltaic systems for renewable energy generation: A systematic analysis of existing knowledge

The development of carbon-neutral fuel sources is an essential step in addressing the global fossil energy crisis. Whole-cell biophotovoltaic systems (BPVs) are a renewable, non-polluting energy-generating device that utilizes oxygenic photosynthetic microbes (OPMs) to split water molecules and generate bioelectricity under the driving of light energy. Since 2006, BPVs have been widely studied, with the order magnitudes of power density increasing from 10-4 mW/m2 to 103 mW/m2. This review examines the extracellular electron transfer (EET) mechanisms and regulation techniques of BPVs from biofilm to external environment. It is found that the EET of OPMs is mainly mediated by membrane proteins, with terminal oxidase limiting the power output. Synechocystis sp. PCC6803 and Chlorella vulgaris are two species that produce high power density in BPVs. The use of metal nanoparticles mixing, 3D pillar array electrodes, microfluidic technology, and transient-state operation models can significantly enhance power density. Challenges and potential research directions are discussed, including a deeper analysis of EET mechanisms and dynamics, the development of modular devices, integration of multiple regulatory components, and the exploration of novel BPV technologies.

Microalgae-bacteria nexus for environmental remediation and renewable energy resources: Advances, mechanisms and biotechnological applications

Microalgae and bacteria, known for their resilience, rapid growth, and proximate ecological partnerships, play fundamental roles in environmental and biotechnological advancements. This comprehensive review explores the synergistic interactions between microalgae and bacteria as an innovative approach to address some of the most pressing environmental issues and the demands of clean and renewable freshwater and energy sources. Studies indicated that microalgae-bacteria consortia can considerably enhance the output of biotechnological applications; for instance, various reports showed during wastewater treatment the COD removal efficiency increased by 40%-90.5 % due to microalgae-bacteria consortia, suggesting its great potential amenability in biotechnology. This review critically synthesizes research works on the microalgae and bacteria nexus applied in the advancements of renewable energy generation, with a special focus on biohydrogen, reclamation of wastewater and desalination processes. The mechanisms of underlying interactions, the environmental factors influencing consortia performance, and the challenges and benefits of employing these bio-complexes over traditional methods are also discussed in detail. This paper also evaluates the biotechnological applications of these microorganism consortia for the augmentation of biomass production and the synthesis of valuable biochemicals. Furthermore, the review sheds light on the integration of microalgae-bacteria systems in microbial fuel cells for concurrent energy production, waste treatment, and resource recovery. This review postulates microalgae-bacteria consortia as a sustainable and efficient solution for clean water and energy, providing insights into future research directions and the potential for industrial-scale applications.

Photo-assisted microbial fuel cell systems: critical review of scientific rationale and recent advances in system development

Bioelectrochemical systems such as microbial fuel cells (MFCs) have gained extensive attention due to their abilities to simultaneously treat wastewater and generate renewable energy resources. Recently, to boost the system performance, the photoelectrode has been incorporated into MFCs for effectively exploiting the synergistic interaction between light and microorganisms, and the resultant device is known as photo-assisted microbial fuel cells (photo-MFCs). Combined with the metabolic reaction of organic compounds by microorganisms, photo-MFCs are capable of simultaneously converting both chemical energy and light energy into electricity. This article aims to systematically review the recent advances in photo-MFCs, including the introduction of specific photosynthetic microorganisms used in photo-MFCs followed by the discussion of the fundamentals and configurations of photo-MFCs. Moreover, the materials used for photoelectrodes and their fabrication approaches are also explored. This review has shown that the innovative strategy of utilizing photoelectrodes in photo-MFCs is promising and further studies are warranted to strengthen the system stability under long-term operation for advancing practical application.

The use of algae for environmental sustainability: trends and future prospects

Algae are photosynthetic prokaryotic or eukaryotic ubiquitously found group of organisms. Their enormous potentiality in coping up with various environmental crises has been well documented. Algae have proven to be ideal for biomonitoring of water pollution and help in removing the pollutants with their process of bioremediation apart from the production of eco-friendly sources of energy. Industries like food and pharmaceuticals are exploiting algae for producing several value-added products. The agricultural sector is also highly benefited from microalgae, as they are the good promoters of crop growth. The CO₂-removing potential of algae proves to be an asset in fighting climate change. Moreover, the relatively easy and inexpensive methods of sampling and culturing of algae make them more popular. In this paper, we review the sustainable application aspects of algae in various areas like pollution control, energy production, agriculture, and fighting climate change. Critical discussions have been made on the recent trends and advances of algal technologies indicating future prospects.

Bioelectricity production and shortcut nitrogen removal by microalgal-bacterial consortia using membrane photosynthetic microbial fuel cell

Membrane photosynthetic microbial fuel cell (MPMFC) utilizes O₂, NO₃^- and NO₂^- as cathodic electron acceptors, enabling simultaneous treatment of nitrogen, CO₂ and organic carbon in the cathode compartment. In this work, development of a novel cathodic process with in situ nitritation via microalgal photosynthesis during the light period is reported for achieving shortcut nitrogen removal (SNR) from ammonium-rich wastewater. Moreover, a tubular low-cost ceramic membrane was used to separate and recycle the microalgal-bacterial biomass to the cathode compartment during the continuous operation. The influence of NH₄⁺ concentration and ratio of chemical oxygen demand to total nitrogen on the MPMFC performance was examined. Denitritation under dark and anoxic conditions occurred due to denitrifying bacteria (DNB) subsequent to nitritation under light and aerobic conditions by ammonia-oxidizing bacteria (AOB) in the consortia. Final concentrations of NH₄⁺ and NO₂^- in the effluent of 0.10 mg NH₄⁺-L^-1 and 0.02 mg NO₂^--L^-1, respectively, were obtained using MPMFC which resulted in a nitrogen removal efficiency of 99 ± 0.5%. The maximum electricity production achieved using the MPMFC was 56 ± 0.1 mA. This study demonstrated that combining microalgal photosynthesis, nitritation and denitritation in the cathode compartment of MPMFC is advantageous for avoiding the cost due to external aeration and organic carbon source necessary for ammonium removal as well as utilization of NO₂^- or NO₃^- as an electron acceptor.

Live diatoms as potential biocatalyst in a microbial fuel cell for harvesting continuous diafuel, carotenoids and bioelectricity

Microbial fuel cell (MFC) with live diatoms (Nitzschia palea) displacing bacteria in the anodic chamber generated electrical potential. Unlike other microalgae, diatoms fix 25% of atmospheric CO₂, thus releasing O₂. They perform photolysis of water by photosynthesis in the plastid during light photoperiod and cellular respiration in the mitochondria during dark, producing electrons and protons, respectively. The electrogenic property of diatom was explored and evaluated by comparing the potential changes with reference fuel cell without diatoms and that operated with diatoms in the anodic chamber. Such photosynthetic diatom microbial fuel cell (PDMFC) employed f/2 media rich in nitrates, phosphates, metasilicates, trace metals and vitamins as the anolyte and potassium permanganate as catholyte enhanced the output voltage by 3^rd day. The maximum power density for PDMFC was 12.62 mWm^-2 and coulombic efficiency of 22.95%. Besides this, the fixed diatom cells at anode showed about 64.28% increase in lipid production on 15th day compared to that on 1st day along with the increment in formation of complex fatty acid methyl esters and carotenoids during its operation. Hence, diatoms can be envisaged to substitute bacteria in the anodic chamber of MFC to simultaneously produce bioelectricity and other valuable compounds. Further their silica nanoporous architecture serve as good absorbents for heavy metal removal found in many wastewaters.

Management of Cattle Dung and Novel Bioelectricity Generation Using Microbial Fuel Cells: An Ingenious Experimental Approach

Microbial fuel cells (MFCs) are the rising modern equipment for the generation of bioelectricity from organic matters. In this study, MFCs in two formats are assembled and concurrently operated for a 30-day period in a batch mode manner. Natural biowaste cattle dung slurry with mediators is used as a substrate persistently for the enhancement of electron transfer rate and additionally for the augmentation of required electrical parameters. Under similar conditions, the MFC setups are experimented with a variety of anode-cathode material combinations, namely carbon-carbon, copper-carbon, and zinc-carbon. The performance of these MFCs during the testing period is evaluated independently and compared by plotting polarization data generated by them. It is revealed that maximum current and power densities are achieved from all these MFCs and the best attained values are 1858 mA/m2 and 1465 mW/m2, respectively, for the novel single-chamber zinc-carbon electrode MFC. The corresponding findings present that the MFC with zinc-carbon electrodes has the better power density than other MFCs. Being conductive and higher standard potential metal electrodes have improved the capability to act in place of carbon family electrodes for MFC-based power applications. Although the MFC power generation is low, but modifications in configurations, electrodes, microbe-rich biowaste, mediators, and power management may enhance the power output to a significant level for commercialization of this technology. The unique feature of this research is to explore the pertinent use of conductive metal electrodes to enhance the power generation capability of MFCs through biowaste as an alternative power source for small applications. The novelty of this research is presented through usage of conductive metal electrodes for the performance analysis of MFCs.

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.

Phyco-remediation of swine wastewater as a sustainable model based on circular economy

Pork production has expanded in the world in recent years. This growth has caused a significant increase in waste from this industry, especially of wastewater. Although there has been an increase in wastewater treatment, there is a lack of useful technologies for the treatment of wastewater from the pork industry. Swine farms generate high amounts of organic pollution, with large amounts of nitrogen and phosphorus with final destination into water bodies. Sadly, little attention has been devoted to animal wastes, which are currently treated in simple systems, such as stabilization ponds or just discharged to the environment without previous treatment. This uncontrolled release of swine wastewater is a major cause of eutrophication processes. Among the possible treatments, phyco-remediation seems to be a sustainable and environmentally friendly option of removing compounds from wastewater such as nitrogen, phosphorus, and some metal ions. Several studies have demonstrated the feasibility of treating swine wastewater using different microalgae species. Nevertheless, the practicability of applying this procedure at pilot-scale has not been explored before as an integrated process. This work presents an overview of the technological applications of microalgae for the treatment of wastewater from swine farms and the by-products (pigments, polysaccharides, lipids, proteins) and services of commercial interest (biodiesel, biohydrogen, bioelectricity, biogas) generated during this process. Furthermore, the environmental benefits while applying microalgae technologies are discussed.

Effect of graphene quantum dot size on plant growth

We found a straightforward dependence of plant growth on the sizes of graphene quantum dots. Enormous GQDs, such as graphene with dimensions of micrometers, neither promoted nor inhibited the growth. In contrast, synthesized GQDs with dimensions of about 10 nm best promoted the plant growth. Moreover GQDs synthesized using an "intelligent" chemistry robot yielded even better growth results than did GQDs synthesized conventionally by humans. In addition, a theoretical model was derived for the mechanism of the promotion of plant growth by GQDs.

Improved performance of carbon nanotubes embedded photomicrobial solar cell

Enhancing the energy efficiency of power out is a key issue of microorganisms based energy harvesting. Here, we introduced carbon nanotubes (CNTs) into a photomicrobial solar cell (PMSC) system in order to increase the harvesting energy power. Microcystis aeruginosa was used as a solar energy converter, microorganism. It revealed that when a small amount of CNTs (e.g. 0.001 wt%) were added in the cyanobacterium suspension, the photocurrents were enhanced dramatically. The optical and electrical properties of the CNT suspension were analyzed. The biochemical features of the PMSC were evaluated under dark and light conditions. This study is expected to offer a strategic way for harvesting living cell-based solar energy in a more efficient manner.

Powering the Environmental Internet of Things

The Internet of Things (IoT) is a constantly-evolving area of research and touches almost every aspect of life in the modern world. As technology moves forward, it is becoming increasingly important for these IoT devices for environmental sensing to become self-powered to enable long-term operation. This paper provides an outlook on the current state-of-the-art in terms of energy harvesting for these low-power devices. An analytical approach is taken, first defining types of environments in which energy-harvesters operate, before exploring both well-known and novel energy harvesting techniques and their uses in modern-day sensing.

Advances in algal-prokaryotic wastewater treatment: A review of nitrogen transformations, reactor configurations and molecular tools

The synergistic activity of algae and prokaryotic microorganisms can be used to improve the efficiency of biological wastewater treatment, particularly with regards to nitrogen removal. For example, algae can provide oxygen through photosynthesis needed for aerobic degradation of organic carbon and nitrification and harvested algal-prokaryotic biomass can be used to produce high value chemicals or biogas. Algal-prokaryotic consortia have been used to treat wastewater in different types of reactors, including waste stabilization ponds, high rate algal ponds and closed photobioreactors. This review addresses the current literature and identifies research gaps related to the following topics: 1) the complex interactions between algae and prokaryotes in wastewater treatment; 2) advances in bioreactor technologies that can achieve high nitrogen removal efficiencies in small reactor volumes, such as algal-prokaryotic biofilm reactors and enhanced algal-prokaryotic treatment systems (EAPS); 3) molecular tools that have expanded our understanding of the activities of algal and prokaryotic communities in wastewater treatment processes.

Sulfide as an alternative electron donor to glucose for power generation in mediator-less microbial fuel cell

The objective of this study was to investigate the power generation in a dual-chamber microbial fuel cell (MFC). As one of the effective parameters, glucose concentration was studied in the range of 100-1000 mg/L. At the optimum concentration of 500 mg/L of glucose, maximum power generation was 186 mW/m². As an alternative, sulfide was used as an electron donor and maximum power output was 401 mW/m² at the concentration of 100 mg/L; which was more than twice of power produced using glucose. Moreover, sulfide removal efficiencies of 70%, 66%, 60%, and 64% were obtained when initial sulfide concentrations of 10, 20, 80, and 100 mg/L were used, respectively.

Microbial Fuels Cell-Based Biosensor for Toxicity Detection: A Review

With the unprecedented deterioration of environmental quality, rapid recognition of toxic compounds is paramount for performing in situ real-time monitoring. Although several analytical techniques based on electrochemistry or biosensors have been developed for the detection of toxic compounds, most of them are time-consuming, inaccurate, or cumbersome for practical applications. More recently, microbial fuel cell (MFC)-based biosensors have drawn increasing interest due to their sustainability and cost-effectiveness, with applications ranging from the monitoring of anaerobic digestion process parameters (VFA) to water quality detection (e.g., COD, BOD). When a MFC runs under correct conditions, the voltage generated is correlated with the amount of a given substrate. Based on this linear relationship, several studies have demonstrated that MFC-based biosensors could detect heavy metals such as copper, chromium, or zinc, as well as organic compounds, including p-nitrophenol (PNP), formaldehyde and levofloxacin. Both bacterial consortia and single strains can be used to develop MFC-based biosensors. Biosensors with single strains show several advantages over systems integrating bacterial consortia, such as selectivity and stability. One of the limitations of such sensors is that the detection range usually exceeds the actual pollution level. Therefore, improving their sensitivity is the most important for widespread application. Nonetheless, MFC-based biosensors represent a promising approach towards single pollutant detection.

Assisting cultivation of photosynthetic microorganisms by microbial fuel cells to enhance nutrients recovery from wastewater

Spirulina was cultivated in cathodic compartments of photo-microbial fuel cells (P-MFC). Anodic compartments were fed with swine-farming wastewater, enriched with sodium acetate (2.34g_CODL^-1). Photosynthetic oxygen generation rates were sufficient to sustain cathodic oxygen reduction, significantly improving P-MFC electrochemical performances, as compared to water-cathode control experiments. Power densities (0.8-1Wm^-2) approached those of air-cathode MFCs, run as control. COD was efficiently removed and only negligible fractions leaked to the cathodic chamber. Spirulina growth rates were comparable to those of control (MFC-free) cultures, while pH was significantly (0.5-1unit) higher in P-MFCs, due to cathodic reactions. Alkaliphilic photosynthetic microorganisms like Spirulina might take advantage of these selective conditions. Electro-migration along with diffusion to the cathodic compartment concurred for the recovery of most nutrients. Only P and Mg were retained in the anodic chamber. A deeper look into electro-osmotic mechanisms should be addressed in future studies.

Enhanced Extracellular Polysaccharide Production and Self-Sustainable Electricity Generation for PAMFCs by Scenedesmus sp. SB1

In this study, a freshwater microalga, Scenedesmus sp. SB1, was isolated, purified, and identified by its internal transcribed spacer region (ITS1-5.8S-ITS2). Media optimization through the Plackett-Burman Design and response surface methodology (RSM) showed a maximum exopolysaccharide (EPS) production of 48 mg/L (1.8-fold higher than that for unoptimized media). Characterization using gas chromatography-mass spectrometry, Fourier transform infrared, X-ray diffraction, and thermogravimetric analysis reveals that the EPS is a sulfated pectin polysaccharide with a crystallinity index of 15.2% and prompt thermal stability. Furthermore, the photoelectrogenic activity of Scenedesmus sp. SB1 inoculated in BG-11 and RSM-optimized BG-11 (ROBG-11) media was tested by cyclic voltammogram studies, revealing the potential of the inoculated strain in ROBG-11 toward photosynthetic algal microbial fuel cells over normal BG-11. To the best of our knowledge, functional group characterization, physical and thermal property and media optimization for EPS production by RSM and electrogenic activity studies are reported for the first time in Scenedesmus sp. SB1.

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.

A bio-anodic filter facilitated entrapment, decomposition and in situ oxidation of algal biomass in wastewater effluent

This study examined for the first time the use of bioelectrochemical systems (BES) to entrap, decompose and oxidise fresh algal biomass from an algae-laden effluent. The experimental process consisted of a photobioreactor for a continuous production of the algal-laden effluent, and a two-chamber BES equipped with anodic graphite granules and carbon-felt to physically remove and oxidise algal biomass from the influent. Results showed that the BES filter could retain ca. 90% of the suspended solids (SS) loaded. A coulombic efficiency (CE) of 36.6% (based on particulate chemical oxygen demand (PCOD) removed) was achieved, which was consistent with the highest CEs of BES studies (operated in microbial fuel cell mode (MFC)) that included additional pre-treatment steps for algae hydrolysis. Overall, this study suggests that a filter type BES anode can effectively entrap, decompose and in situ oxidise algae without the need for a separate pre-treatment step.

An investigation of anode and cathode materials in photomicrobial fuel cells

Photomicrobial fuel cells (p-MFCs) are devices that use photosynthetic organisms (such as cyanobacteria or algae) to turn light energy into electrical energy. In a p-MFC, the anode accepts electrons from microorganisms that are either growing directly on the anode surface (biofilm) or are free floating in solution (planktonic). The nature of both the anode and cathode material is critical for device efficiency. An ideal anode is biocompatible and facilitates direct electron transfer from the microorganisms, with no need for an electron mediator. For a p-MFC, there is the additional requirement that the anode should not prevent light from perfusing through the photosynthetic cells. The cathode should facilitate the rapid reaction of protons and oxygen to form water so as not to rate limit the device. In this paper, we first review the range of anode and cathode materials currently used in p-MFCs. We then present our own data comparing cathode materials in a p-MFC and our first results using porous ceramic anodes in a mediator-free p-MFC.

Polyaniline-Supported Bacterial Biofilms as Active Matrices for Platinum Nanoparticles: Enhancement of Electroreduction of Carbon Dioxide

A hybrid matrix composed of a porous polyaniline underlayer, a robust bacterial biofilm and a multiwalled carbon nanotube overlayer has been demonstrated to function as highly active support for dispersed Pt catalytic nanoparticles during the electroreduction of carbon dioxide in neutral medium (phosphate buffer at pH 6.1). In contrast with bare Pt nanoparticles (deposited at a glassy carbon substrate), application of the hybrid system produces sizeable CO2-reduction currents in comparison to those originating from hydrogen evolution. The result is consistent with an enhancement in the reduction of carbon dioxide. However, the biofilm-based matrix tends to inhibit the catalytic properties of platinum towards proton discharge (competitive reaction) or even oxygen reduction. The hydrated structure permits easy unimpeded flow of aqueous electrolyte at the electrocatalytic interface. Although application of the polyaniline underlayer can be interpreted in terms of stabilization and improvement of the biofilm adherence, the use of carbon nanotubes facilitates electron transfer to Pt catalytic sites. It is apparent from the voltammetric stripping-type analytical experiments that, although formation of some methanol and methanoic acid cannot be excluded, carbon monoxide seems to be the main CO2-reduction product.

In-Situ Remediation Approaches for the Management of Contaminated Sites: A Comprehensive Overview

Though several in-situ treatment methods exist to remediate polluted sites, selecting an appropriate site-specific remediation technology is challenging and is critical for successful clean up of polluted sites. Hence, a comprehensive overview of all the available remediation technologies to date is necessary to choose the right technology for an anticipated pollutant. This review has critically evaluated the (i) technological profile of existing in-situ remediation approaches for priority and emerging pollutants, (ii) recent innovative technologies for on-site pollutant remediation, and (iii) current challenges as well as future prospects for developing innovative approaches to enhance the efficacy of remediation at contaminated sites.

Bioelectricity Generation in a Microbial Fuel Cell with a Self-Sustainable Photocathode

This study aims to construct an MFC with a photosynthetic algae cathode, which is maintained by self-capturing CO2 released from the anode and utilizing solar energy as energy input. With this system, a maximum power density of 187 mW/m(2) is generated when the anode off gas is piped into the catholyte under light illumination, which is higher than that of 21 mW/m(2) in the dark, demonstrating the vital contribution of the algal photosynthesis. However, an unexpected maximum power density of 146 mW/m(2) is achieved when the anode off gas is not piped into the catholyte. Measurements of cathodic microenvironments reveal that algal photosynthesis still takes place for oxygen production under this condition, suggesting the occurrence of CO2 crossover from anode to cathode through the Nafion membrane. The results of this study provide further understanding of the algae-based microbial carbon capture cell (MCC) and are helpful in improving MCC performance.

Photosynthetic solar cell using nanostructured proton exchange membrane for microbial biofilm prevention

Unwanted biofilm formation has a detrimental effect on bioelectrical energy harvesting in microbial cells. This issue still needs to be solved for higher power and longer durability and could be resolved with the help of nanoengineering in designing and manufacturing. Here, we demonstrate a photosynthetic solar cell (PSC) that contains a nanostructure to prevent the formation of biofilm by micro-organisms. Nanostructures were fabricated using nanoimprint lithography, where a film heater array system was introduced to precisely control the local wall temperature. To understand the heat and mass transfer phenomena behind the manufacturing and energy harvesting processes of PSC, we carried out a numerical simulation and experimental measurements. It revealed that the nanostructures developed on the proton exchange membrane enable PSC to produce enhanced output power due to the retarded microbial attachment on the Nafion membrane. We anticipate that this strategy can provide a pathway where PSC can ensure more renewable, sustainable, and efficient energy harvesting performance.

Effect of light on the production of bioelectricity and added-value microalgae biomass in a Photosynthetic Alga Microbial Fuel Cell

This study demonstrates the simultaneous production of bioelectricity and added-value pigments in a Photosynthetic Alga Microbial Fuel Cell (PAMFC). A PAMFC was operated using Chlorella vulgaris in the cathode compartment and a bacterial consortium in the anode. The system was studied at two different light intensities and the maximum power produced was 62.7 mW/m(2) with a light intensity of 96 μE/(m(2)s). The results showed that increasing light intensity from 26 to 96 μE/(m(2)s) leads to an increase of about 6-folds in the power produced. Additionally, the pigments produced by the microalga were analysed and the results showed that the light intensity and PAMFC operation potentiated the carotenogenesis in the cathode compartment. The demonstrated possibility of producing added-value microalgae biomass in microbial fuel cell cathodes will increase the economic feasibility of these bioelectrochemical systems, allowing the development of energy efficient systems for wastewater treatment and carbon fixation.

Merging metabolism and power: development of a novel photobioelectric device driven by photosynthesis and respiration

Generation of renewable energy is one of the grand challenges facing our society. We present a new bio-electric technology driven by chemical gradients generated by photosynthesis and respiration. The system does not require pure cultures nor particular species as it works with the core metabolic principles that define phototrophs and heterotrophs. The biology is interfaced with electrochemistry with an alkaline aluminum oxide cell design. In field trials we show the system is robust and can work with an undefined natural microbial community. Power generated is light and photosynthesis dependent. It achieved a peak power output of 33 watts/m² electrode. The design is simple, low cost and works with the biological processes driving the system by removing waste products that can impede growth. This system is a new class of bio-electric device and may have practical implications for algal biofuel production and powering remote sensing devices.

Operation of a horizontal subsurface flow constructed wetland--microbial fuel cell treating wastewater under different organic loading rates

The aim of the present work is to determine whether a horizontal subsurface flow constructed wetland treating wastewater could act simultaneously as a microbial fuel cell (MFC). Specifically, and as the main variable under study, different organic loading rates were used, and the response of the system was monitored. The installation consisted of a synthetic domestic wastewater-feeding system and a pilot-scale constructed wetland for wastewater treatment, which also included coupled devices necessary to function as an MFC. The wetland worked under continuous operation for 180 d, treating three types of synthetic wastewater with increasing organic loading rates: 13.9 g COD m(-2) d(-1), 31.1 g COD m(-2) d(-1), and 61.1 g COD m(-2) d(-1). The COD removal efficiencies and the cell voltage generation were continuously monitored. The wetland worked simultaneously as an MFC generating electric power. Under low organic loading rates, the wastewater organic matter was completely oxidised in the lower anaerobic compartment, and there were slight aerobic conditions in the upper cathodic compartment, thus causing an electrical current. Under high organic loading rates, the organic matter could not be completely oxidised in the anodic compartment and flowed to the cathodic one, which entered into anaerobic conditions and caused the MFC to stop working. The system developed in this work offered similar cell voltage, power density, and current density values compared with the ones obtained in previous studies using photosynthetic MFCs, sediment-type MFCs, and plant-type MFCs. The light/darkness changes caused voltage fluctuations due to the photosynthetic activity of the macrophytes used (Phragmites australis), which affected the conditions in the cathodic compartment.

A comprehensive review of microbial electrochemical systems as a platform technology

Microbial electrochemical systems (MESs) use microorganisms to covert the chemical energy stored in biodegradable materials to direct electric current and chemicals. Compared to traditional treatment-focused, energy-intensive environmental technologies, this emerging technology offers a new and transformative solution for integrated waste treatment and energy and resource recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. All MESs share one common principle in the anode chamber, in which biodegradable substrates, such as waste materials, are oxidized and generate electrical current. In contrast, a great variety of applications have been developed by utilizing this in situ current, such as direct power generation (microbial fuel cells, MFCs), chemical production (microbial electrolysis cells, MECs; microbial electrosynthesis, MES), or water desalination (microbial desalination cells, MDCs). Different from previous reviews that either focus on one function or a specific application aspect, this article provides a comprehensive and quantitative review of all the different functions or system constructions with different acronyms developed so far from the MES platform and summarizes nearly 50 corresponding systems to date. It also provides discussions on the future development of this promising yet early-stage technology.

Biological photovoltaics: intra- and extra-cellular electron transport by cyanobacteria

A large variety of new energy-generating technologies are being developed in an effort to reduce global dependence on fossil fuels, and to reduce the carbon footprint of energy generation. The term 'biological photovoltaic system' encompasses a broad range of technologies which all employ biological material that can harness light energy to split water, and then transfer the resulting electrons to an anode for power generation or electrosynthesis. The use of whole cyanobacterial cells is a good compromise between the requirements of the biological material to be simply organized and transfer electrons efficiently to the anode, and also to be robust and able to self-assemble and self-repair. The principle that photosynthetic bacteria can generate and transfer electrons directly or indirectly to an anode has been demonstrated by a number of groups, although the power output obtained from these devices is too low for biological photovoltaic devices to be useful outside the laboratory. Understanding how photosynthetically generated electrons are transferred through and out of the organism is key to improving power output, and investigations on this aspect of the technology are the main focus of the present review.

Anaerobic conversion of microalgal biomass to sustainable energy carriers--a review

This review discusses anaerobic production of methane, hydrogen, ethanol, butanol and electricity from microalgal biomass. The amenability of microalgal biomass to these bioenergy conversion processes is compared with other aquatic and terrestrial biomass sources. The highest energy yields (kJ g(-1) dry wt. microalgal biomass) reported in the literature have been 14.8 as ethanol, 14.4 as methane, 6.6 as butanol and 1.2 as hydrogen. The highest power density reported from microalgal biomass in microbial fuel cells has been 980 mW m(-2). Sequential production of different energy carriers increases attainable energy yields, but also increases investment and maintenance costs. Microalgal biomass is a promising feedstock for anaerobic energy conversion processes, especially for methanogenic digestion and ethanol fermentation. The reviewed studies have mainly been based on laboratory scale experiments and thus scale-up of anaerobic utilization of microalgal biomass for production of energy carriers is now timely and required for cost-effectiveness comparisons.

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

Electricity generation capabilities of microbial fuel cell with different light power on algae grown cathode were compared. Results showed that microbial fuel cell with 6 and 12W power of light always produced higher voltage and power density than with 18 and 26W. Similarly, microbial fuel cell with 6 and 12W of light power always displayed higher Coulombic efficiency and specific power than the one with 18 and 26W. The results also showed that microbial fuel cell with covered anodic chamber always displayed higher voltage, power density, Coulombic efficiency and specific power than the one without covered anodic chamber. Binary quadratic equations can be used to express the relationships between the light power and the voltage, power density, Coulombic efficiency and specific power. Although lower power of light on algae grown cathode and covering anodic chamber will increase system's electricity production, they will not significantly reduce its internal resistance.