Resource recovery using enriched purple phototrophic bacteria in an outdoor flat plate photobioreactor: Suspended vs. attached growth.

Purple phototrophic bacteria (PPB) can produce single-cell protein from wastewater at high yields. Growing in a biofilm vs suspended can improve product quality and consistency. This study compares suspended and attached growths of enriched PPB cultures in an outdoor flat plate photobioreactor treating poultry-processing wastewater. Attached growth had lower VFA removal efficiencies (95 ± 2.7 vs 84 ± 6.4 %) due to light limitations and low substrate diffusion rates. Nevertheless, similar overall treatment performances and productivities were achieved (16 ± 2.2 and 18 ± 2.4 gCOD·m-2·d-1 for attached and suspended) at loading rates of 1.2-1.5 gCOD·L-1·d-1. Biofilms had higher quality than suspended biomass, with lower ash contents (6.9(0.6)% vs 57(16)%) and higher PPB abundances (0.45-0.67 vs 0.30-0.45). The biofilm (20-50 % of the total biomass) might be used as feed and the suspended fraction as fertiliser, improving the economics of the process. Semi-continuous PPB growth outdoors as biofilm is technically feasible, obtaining a superior product without jeopardising performance.

Urea hydrolysis and long-term storage of source-separated urine for reuse as fertiliser is insufficient for the removal of anthropogenic micropollutants.

Human and animal source-separated urine, stored and allowed to naturally hydrolyse (the bio-catalysed transformation of urea to ammonia and bicarbonate), has been used for millennia as a fertiliser in agriculture. In a context of growing water scarcity and climate uncertainty, source-separation of urine is facing a strong revival thanks to the emergence of cost-effective waterless collection systems. Concomitantly, urine source-separation can be used as a method for nutrient recovery and subsequent reuse. In its simplest form, such recovery consists of collection followed by urea hydrolysis and storage as sole treatment. Numerous guidelines, including by the World Health Organisation, consider that this is sufficient to stabilise the nutrients and inactivate any potential pathogens in the urine. However, it is still unclear whether said urine is effectively free from other compounds of concern, such as anthropogenic micropollutants with known toxicological effects. Moreover, it is also currently unknown if the metabolites produced by human consumption of these products behave in similar way during short- and long-term storage i.e. whether any changes in chemical structure mean that these could be sorbed and/or precipitated in a different way, or if they can potentially be degraded by the biomass inherently present in urine collection systems. Finally, there is currently no knowledge of whether the observed concentrations of micropollutants in stored hydrolysed urine could potentially have toxicological effects if/when applied to soils and edible crops. To fill these research gaps, 20 commonly consumed compounds were selected in this study and their concentrations in the liquid and solid phases studied in the short- and long-term (up to ≥ 2 years). During the initial process of urea hydrolysis (≤ 5 days), ethyl-glucuronide was the sole compound effectively removed (by deconjugation), while only two other compounds, erythromycin and its metabolite, saw a reduction in their concentration (likely due to biomass sorption). Subsequently, during early storage (≤ 15 days), only three additional compounds were removed: paracetamol (> 99%), acesulfame (11.5%) and carbamazepine-10,11 epoxide (40.7%). Finally, long-term storage of up to 24 months did not result in any further significant removal for any of the measured compounds, indicating that the procedure of hydrolysis + storage is not effective for the removal of anthropogenic micropollutants. The results of this investigation raise strong concerns about the direct reuse of hydrolysed/stored human source-separated urine, and evidence the need for post-processing before implementation as fertiliser into edible crops due to the inherent toxicological risk, particularly to infants.

Modelling and techno-economic assessment of (bio)electrochemical nitrogen removal and recovery from reject water at full WWTP scale.

At conventional wastewater treatment plants (WWTPs), reject waters originating from the dewatering of anaerobically digested sludge contain the highest nitrogen concentrations within the plant and thereby have potential for realising nitrogen recovery in a reusable form. At the same time, nitrogen removal from reject waters has potential to reduce the energetic and chemical demands of the WWTP due to a reduced nutrient load to the activated sludge process. In recent years, (bio)electrochemical methods have been extensively studied for nitrogen recovery from reject waters in laboratory-scale but not yet implemented in real WWTP environments, particularly due to concerns about the need for large capital investments. This study assessed the techno-economic feasibility of retrofitting a (bio)electrochemical nitrogen removal and recovery (NRR) unit into the reject water circulation line of a full-scale WWTP through modelling. Data from laboratory-scale (bio)electroconcentration ((B)EC) experiments was used to construct a simple, semi-empirical model block integrated into the Benchmark Simulation Model No. 2 (BSM2) simulating a generalised WWTP. The effects of nitrogen removal from the reject water on both the effluent quality and operational costs of the WWTP were assessed and compared to the BSM2 performance without an NRR unit. In all studied scenarios, the effluent quality index was improved by 4-11%, while both the aeration (7-19% decrease) and carbon (24-71%) requirements were reduced. The additional energy consumed by the NRR unit increased the total operational cost index by >18%, but the revenue assumed for the generated nutrient product (20 EUR kgN-1) was enough to make the BEC-NRR scenarios at realistically low current densities (1 and 5 A m-2) economically attractive compared to the control. A sensitivity analysis revealed that electricity price and nutrient product value had the most notable effects on the feasibility of the NRR unit. The results suggest a key factor in making (bio)electrochemical NRR economically viable is to reduce its electricity consumption further, while the anticipated increases in nitrogen fertiliser prices can help accelerate the adoption of these methods in larger scale.

Electrochemical oxidation processes for PFAS removal from contaminated water and wastewater: fundamentals, gaps and opportunities towards practical implementation.

Electrochemical oxidation (EO) is emerging as one of the most promising methods for the degradation of recalcitrant per- and poly-fluoroalkyl substances (PFASs) in water and wastewater, as these compounds cannot be effectively treated with conventional bio- or chemical approaches. This review examines the state of the art of EO for PFASs destruction, and comprehensively compares operating parameters and treatment performance indicators for both synthetic and real contaminated water and wastewater media. The evaluation shows the need to use environmentally-relevant media to properly quantify the effectiveness/efficiency of EO for PFASs treatment. Additionally, there is currently a lack of quantification of sorption losses, resulting in a likely over-estimation of process' efficiencies. Furthermore, the majority of experimental results to date indicate that short-chain PFASs are the most challenging and need to be prioritized as environmental regulations become more stringent. Finally, and with a perspective towards practical implementation, several operational strategies are proposed, including processes combining up-concentration followed by EO destruction.

Implementation of a Sulfide-Air Fuel Cell Coupled to a Sulfate-Reducing Biocathode for Elemental Sulfur Recovery.

Bio-electrochemical systems (BES) are a flexible biotechnological platform that can be employed to treat several types of wastewaters and recover valuable products concomitantly. Sulfate-rich wastewaters usually lack an electron donor; for this reason, implementing BES to treat the sulfate and the possibility of recovering the elemental sulfur (S0) offers a solution to this kind of wastewater. This study proposes a novel BES configuration that combines bio-electrochemical sulfate reduction in a biocathode with a sulfide-air fuel cell (FC) to recover S0. The proposed system achieved high elemental sulfur production rates (up to 386 mg S0-S L-1 d-1) with 65% of the sulfate removed recovered as S0 and a 12% lower energy consumption per kg of S0 produced (16.50 ± 0.19 kWh kg-1 S0-S) than a conventional electrochemical S0 recovery system.

Anodic electro-fermentation: Empowering anaerobic production processes via anodic respiration.

In nature as well as in industrial microbiology, all microorganisms need to achieve redox balance. Their redox state and energy conservation highly depend on the availability of a terminal electron acceptor, for example oxygen in aerobic production processes. Under anaerobic conditions in the absence of an electron acceptor, redox balance is achieved via the production of reduced carbon-compounds (fermentation). An alternative strategy to artificially stabilize microbial redox and energy state is the use of anodic electro-fermentation (AEF). This emerging biotechnology empowers respiration under anaerobic conditions using the anode of a bioelectrochemical system as an undepletable terminal electron acceptor. Electrochemical control of redox metabolism and energy conservation via AEF can steer the carbon metabolism towards a product of interest and avoid the need for continuous and cost-inefficient supply of oxygen as well as the production of mixed reduced by-products, as is the case in aerobic production and fermentation processes, respectively. The great challenge for AEF is to establish efficient extracellular electron transfer (EET) from the microbe to the anode and link it to central carbon metabolism to enhance the synthesis of a target product. This article reviews the advantages and challenges of AEF, EET mechanisms, microbial energy gain, and discusses the rational choice of substrate-product couple as well as the choice of microbial catalyst. Besides, it discusses the potential of the industrial model-organism Bacillus subtilis as a promising candidate for AEF, which has not been yet considered for such an application. This prospective review contributes to a better understanding of how industrial microbiology can benefit from AEF and analyses key-factors required to successfully implement AEF processes. Overall, this work aims to advance the young research field especially by critically revisiting the fundamental aspects of AEF.

Selective Extraction of Medium-Chain Carboxylic Acids by Electrodialysis and Phase Separation.

Carboxylic acids obtained via the microbial electrochemical conversion of waste gases containing carbon dioxide (i.e., microbial electrosynthesis) can be used in lieu of nonrenewable building-block chemicals in the manufacture of a variety of products. When targeting valuable medium-chain carboxylic acids such as caproic acid, electricity-driven fermentations can be limited by the accumulation of fermentation products in the culturing media, often resulting in low volumetric productivities and titers due to direct toxicity or inhibition of the biocatalyst. In this study, we tested the effectiveness of a simple electrodialysis system in upconcentrating carboxylic acids from a model solution mimicking the effluent of a microbial electrochemical system producing short- and medium-chain carboxylic acids. Under batch extraction conditions, the electrodialysis scheme enabled the recovery of 60% (mol mol-1) of the total carboxylic acids present in the model fermentation broth. The particular arrangement of conventional monopolar ion exchange membranes and hydraulic recirculation loops allowed the progressive acidification of the extraction solution, enabling phase separation of caproic acid as an immiscible oil with 76% purity.

Extracellular electron transfer by Microcystis aeruginosa is solely driven by high pH.

Extracellular electron transfer (EET) by the cyanobacterium Microcystis aeruginosa was investigated. Observations indicate that EET onto an electrode poised at + 0.6 vs. standard hydrogen electrode (SHE) is triggered by high pH, more evidently at pH levels above 9. Light intensity does not appear to affect electricity generation, indicating that this may not be a "biophotovoltaic" process. The generated current density was amplified with stepwise pH increases from approximately 5 mA m-2 at pH 7.8 to 30 mA m-2 at pH 10.5, for dense (0.4 mg mL-1 dry weight) Microcystis aeruginosa suspensions with dissolved CO2 and O2 approaching equilibrium with atmospheric concentrations. The upsurge in current density was more pronounced (from 5 mA m-2 at pH 7.8 to 40 mA m-2 at pH 10.2) in the absence of the cells' natural electron acceptors, dissolved CO2 and O2. However, the latter effect is more likely due to competition for electrons by oxygen than to reductive stress. EET in this species is therefore a light-independent process that is enhanced by increasing pH, with reasons that are still unknown, but either related to the involvement of protons in the last step of electron transfer, or to intracellular pH control.

Staged electrochemical treatment guided by modelling allows for targeted recovery of metals and rare earth elements from acid mine drainage.

Acid mine drainage (AMD) is a challenge for current and legacy mining operations worldwide given its potential to severely harm ecosystems and communities if inadequately managed. Treatment costs for AMD are amongst the highest in the industrial wastewater treatment sector, with limited sustainable options available to date. This work demonstrates a novel chemical-free approach to tackle AMD, whereby staged electrochemical neutralisation is employed to treat AMD and concomitantly recover metals as precipitates. This approach was guided by physico-chemical modelling and tested on real AMD from two different legacy mine sites in Australia, and compared against conventional chemical-dosing-based techniques using hydrated lime (Ca(OH)2) and sodium hydroxide (NaOH). The electrochemical treatment demonstrated the same capacity than Ca(OH)2 to neutralise AMD and remove sulfates, and both were significantly better than NaOH. However, the electrochemical approach produced less voluminous and more easily settleable sludge than Ca(OH)2. Moreover, the staged treatment approach demonstrated the potential to produce metal-rich powdered solids with a targeted composition, including rare earth elements and yttrium (REY). REY were recovered in concentrations up to 0.1% of the total solids composition, illustrating a new avenue for AMD remediation coupled with the recovery of critical metals.

Recovery of elemental sulfur with a novel integrated bioelectrochemical system with an electrochemical cell.

Several industrial activities produce wastewater with high sulfate content that can cause significant environmental issues. Although bioelectrochemical systems (BESs) have recently been studied for the treatment of sulfate contained in this wastewater, the recovery of elemental sulfur with BESs is still in its beginnings. This work proposes a new reactor configuration named BES-EC, consisting of the coupling of a BES with an electrochemical cell (EC), to treat this type of wastewater and recover elemental sulfur. The reactor consisted of four electrodes: i) an abiotic anode, ii) a biocathode for the autotrophic sulfate reduction, iii) an anode of an electrochemical cell (EC) for the partial oxidation of sulfide to elemental sulfur (the biocathode and the EC anode were placed in the same chamber) and iv) an abiotic EC cathode. Several cathode potentials and sulfate loads were tested, obtaining high sulfate removal rates (up to 888 mg SO42--S L-1 d-1 at -0.9 V vs. SHE with a specific energy consumption of 9.18 ±â€¯0.80 kWh kg-1 SO42--S). Exceptionally high theoretical elemental sulfur production rates (up to 498 mg S0-S L-1 d-1) were achieved with the EC controlled at a current density of 2.5 A m-2. Electron recovery around 80% was observed throughout most of the operation of the integrated system. In addition, short experiments were performed at different current densities, observing that sulfate removal did not increase proportionally to the higher applied current density. However, when the BES was controlled at 30 A m-2 and the EC at 7.5 A m-2, the proportion of elemental sulfur produced corresponded to 92.9 ±â€¯1.9% of all sulfate removed.

Microbial electrosynthesis system with dual biocathode arrangement for simultaneous acetogenesis, solventogenesis and carbon chain elongation.

A microbial electrosynthesis cell comprising two biological cathode chambers sharing the same anode compartment is used to promote the production of C2-C4 carboxylic acids and alcohols from carbon dioxide. Each cathode chamber provides ideal pH conditions to favor acetogenesis/carbon chain elongation (pH = 6.9), and solventogenesis (pH = 4.9), respectively, without the requirement of external acid/base dosing.

Electroactive haloalkaliphiles exhibit exceptional tolerance to free ammonia.

Electrochemical activity in bacteria has been observed in numerous environments and conditions. However, enrichments in circumneutral freshwater media where acetate is the main electron donor seem to invariably lead to the dominance of Geobacter spp. Here we report on an electroactive bacterial consortium which was enriched on acetate as electron donor, but in a medium which reproduces hydrolysed urine (high pH, high salinity and high free ammonia). The consortium was found to be free of Geobacter species, whereas a previously undescribed community dominated by species closely related to Pseudomonas and Desulfuromonas was established. The salient features of this community were as follows: (i) high electroactivity, with anodic current densities up to 47.4 ± 2.0 A m-2; (ii) haloalkaliphilicity, with top performance at a medium pH of 10 and 19.5 ± 0.5 mS cm-1; and (iii) a remarkably high tolerance to free ammonia toxicity at over 2200 mgNH3-N L-1. This community is likely to find applications in microbial electrochemical technology for nutrient recovery from source-separated urine.

A modelling approach to assess the long-term stability of a novel microbial/electrochemical system for the treatment of acid mine drainage.

Microbial electrochemical processes have potential to remediate acid mine drainage (AMD) wastewaters which are highly acidic and rich in sulfate and heavy metals, without the need for extensive chemical dosing. In this manuscript, a novel hybrid microbial/electrochemical remediation process which uses a 3-reactor system - a precipitation vessel, an electrochemical reactor and a microbial electrochemical reactor with a sulfate-reducing biocathode - was modelled. To evaluate the long-term operability of this system, a dynamic model for the fluxes of 140 different ionic species was developed and calibrated using laboratory-scale experimental data. The model identified that when the reactors are operating in the desired state, the coulombic efficiency of sulfate removal from AMD is high (91%). Modelling also identified that a periodic electrolyte purge is required to prevent the build-up of Cl- ions in the microbial electrochemical reactor. The model furthermore studied the fate of sulfate and carbon in the system. For sulfate, it was found that only 29% can be converted into elemental sulfur, with the rest complexating with metals in the precipitation vessel. Finally, the model shows that the flux of inorganic carbon under the current operational strategy is insufficient to maintain the autotrophic sulfate-reducing biomass. The modelling approach demonstrates that a change in system operational strategies plus close monitoring of overlooked ionic species (such as Cl- and HCO3 -) are key towards the scaling-up of this technology.

A novel bioelectrochemical system for chemical-free permanent treatment of acid mine drainage.

The mining sector is currently under unprecedented pressure due to stringent environmental regulations. As a consequence, a permanent acid mine drainage (AMD) treatment is increasingly being regarded as a desirable target with direct benefits for the environment and the operational and economic viability of the resources sector. In this study we demonstrate that a novel bioelectrochemical system (BES) can deliver permanent treatment of acid mine drainage without chemical dosing. The technology consists of a two-cell bioelectrochemical setup to enable the removal of sulfate from the ongoing reduction-oxidation sulfur cycle to less than 550 mg L-1 (85 ± 2% removal from a real AMD of an abandoned silver mine), thereby also reducing salinity at an electrical energy requirement of 10 ± 0.3 kWh kg-1 of SO42--S removed. In addition, the BES operation drove the removal and recovery of the main cations Al, Fe, Mg, Zn at rates of 151 ± 0 g Al m-3 d-1, 179 ± 1 g Fe m-3 d-1, 172 ± 1 g Mg m-3 d-1 and 46 ± 0 g Zn m-3 d-1 into a concentrate stream containing 263 ± 2 mg Al, 279 ± 2 mg Fe, 152 ± 0 mg Mg and 90 ± 0 mg Zn per gram of solid precipitated after BES fed-rate control treatment. The solid metal-sludge was twice less voluminous and 9 times more readily settleable than metal-sludge precipitated using NaOH. The continuous BES treatment also demonstrated the concomitant precipitation of rare earth elements together with yttrium (REY), with up to 498 ± 70 µg Y, 166 ± 27 µg Nd, 155 ± 14 µg Gd per gram of solid, among other high-value metals. The high-REY precipitates could be used to offset the treatment costs.

Selective cathodic microbial biofilm retention allows a high current-to-sulfide efficiency in sulfate-reducing microbial electrolysis cells.

Selective microbial retention is of paramount importance for the long-term performance of cathodic sulfate reduction in microbial electrolysis cells (MECs) due to the slow growth rate of autotrophic sulfate-reducing bacteria. In this work, we investigate the biofilm retention and current-to-sulfide conversion efficiency using carbon granules (CG) or multi-wall carbon nanotubes deposited on reticulated vitreous carbon (MWCNT-RVC) as electrode materials. For ~2months, the MECs were operated at sulfate loading rates of 21 to 309gSO4 -S/m2/d. Although MWCNT-RVC achieved a current density of 57±11A/m2, greater than the 32±9A/m2 observed using CG, both materials exhibited similar sulfate reduction rates (SRR), with MWCNT-RVC reaching 104±16gSO4 -S/m2/d while 110±13gSO4 -S/m2/d were achieved with CG. Pyrosequencing analysis of the 16S rRNA at the end of experimentation revealed a core community dominated by Desulfovibrio (28%), Methanobacterium (19%) and Desulfomicrobium (14%), on the MWCNT-RVC electrodes. While a similar Desulfovibrio relative abundance of 29% was found in CG-biofilms, Desulfomicrobium was found to be significantly less abundant (4%) and Methanobacterium practically absent (0.2%) on CG electrodes. Surprisingly, our results show that CG can achieve higher current-to-sulfide efficiencies at lower power consumption than the nano-modified three-dimensional MWCNT-RVC.

An iTRAQ characterisation of the role of TolC during electron transfer from Shewanella oneidensis MR-1.

Anodophilic bacteria have the ability to generate electricity in microbial fuel cells (MFCs) by extracellular electron transfer to the anode. We investigated the anode-specific responses of Shewanella oneidensis MR-1, an exoelectroactive Gammaproteobacterium, using for the first time iTRAQ and 2D-LC MS/MS driven membrane proteomics to compare protein abundances in S. oneidensis when generating power in MFCs, and growing in a continuous culture. The regulated dataset produced was enriched in membrane proteins. Proteins shown to be more abundant in anaerobic electroactive anodic cells included efflux pump TolC and an uncharacterised tetratricopeptide repeat (TPR) protein, whilst the TonB2 system and associated uncharacterised proteins such as TtpC2 and DUF3450 were more abundant in microaerobic planktonic cells. In order to validate the iTRAQ data, the functional role for TolC was examined using a δTolC knockout mutant of S. oneidensis. Possible roles for the uncharacterised proteins were identified using comparative bioinformatics. We demonstrate that employing an insoluble extracellular electron acceptor requires multiple proteins involved in cell surface properties. All MS and processed data are available via ProteomeXchange with identifier PXD004090.

Marine phototrophic consortia transfer electrons to electrodes in response to reductive stress.

This work studies how extracellular electron transfer (EET) from cyanobacteria-dominated marine microbial biofilms to solid electrodes is affected by the availability of inorganic carbon (Ci). The EET was recorded chronoamperometrically in the form of electrical current by a potentiostat in two identical photo-electrochemical cells using carbon electrodes poised at a potential of +0.6 V versus standard hydrogen electrode under 12/12 h illumination/dark cycles. The Ci was supplied by the addition of NaHCO3 to the medium and/or by sparging CO2 gas. At high Ci conditions, EET from the microbial biofilm to the electrodes was observed only during the dark phase, indicating the occurrence of a form of night-time respiration that can use insoluble electrodes as the terminal electron acceptor. At low or no Ci conditions, however, EET also occurred during illumination suggesting that, in the absence of their natural electron acceptor, some cyanobacteria are able to utilise solid electrodes as an electron sink. This may be a natural survival mechanism for cyanobacteria to maintain redox balance in environments with limiting CO2 and/or high light intensity.

Fully reversible current driven by a dual marine photosynthetic microbial community.

The electrochemical activity of two seawater microbial consortia were investigated in three-electrode bioelectrochemical cells. Two seawater inocula - from the Sunshine Coast (SC) and Gold Coast (GC) shores of Australia - were enriched at +0.6 V vs. SHE using 12/12 h day/night cycles. After re-inoculation, the SC consortium developed a fully-reversible cathodic/anodic current, with a max. of -62 mA m(-2) during the day and +110 mA m(-2) at night, while the GC exhibited negligible daytime output but +98 mA m(-2) at night. Community analysis revealed that both enrichments were dominated by cyanobacteria, indicating their potential as biocatalysts for indirect light conversion to electricity. Moreover, the presence of γ-proteobacterium Congregibacter in SC biofilm was likely related to the cathodic reductive current, indicating its effectiveness at catalysing cathodic oxygen reduction at a surprisingly high potential. For the first time a correlation between a dual microbial community and fully reversible current is reported.

Source-separated urine opens golden opportunities for microbial electrochemical technologies.

The food security of a booming global population demands a continuous and sustainable supply of fertilisers. Their current once-through use [especially of the macronutrients nitrogen (N), phosphorus (P), and potassium (K)] requires a paradigm shift towards recovery and reuse. In the case of source-separated urine, efficient recovery could supply 20% of current macronutrient usage and remove 50-80% of nutrients present in wastewater. However, suitable technology options are needed to allow nutrients to be separated from urine close to the source. Thus far none of the proposed solutions has been widely implemented due to intrinsic limitations. Microbial electrochemical technologies (METs) have proved to be technically and economically viable for N recovery from urine, opening the path for novel decentralised systems focused on nutrient recovery and reuse.

Oxygen suppresses light-driven anodic current generation by a mixed phototrophic culture.

This paper describes the detrimental effect of photosynthetically evolved oxygen on anodic current generation in the presence of riboflavin upon illumination of a mixed phototrophic culture enriched from a freshwater pond at +0.6 V vs standard hydrogen electrode. In the presence of riboflavin, the phototrophic biomass in the anodic compartment produced an electrical current in response to light/dark cycles (12 h/12 h) over 12 months of operation, generating a maximum current density of 17.5 mA x m(-2) during the dark phase, whereas a much lower current of approximately 2 mA x m(-2) was generated during illumination. We found that the low current generation under light exposure was caused by high rates of reoxidation of reduced riboflavin by oxygen produced during photosynthesis. Quantification of biomass by fluorescence in situ hybridization images suggested that green algae were predominant in both the anode-based biofilm (55.1%) and the anolyte suspension (87.9%) with the remaining biovolume accounted for by bacteria. Genus-level sequencing analysis revealed that bacteria were dominated by cyanobacterium Leptolyngbia (∼35%), while the prevailing algae were Dictyosphaerium, Coelastrum, and Auxenochlorella. This study offers a key comprehension of mediator sensitivity to reoxidation by dissolved oxygen for improvement of microbial solar cell performance.