Constructed wetlands integrated with microbial fuel cells (MFC-CWs) have been recently developed and tested for removing antibiotics. However, the effects of carbon source availability, electron transfer flux and cathode conditions on antibiotics removal in MFC-CWs through co-metabolism remained unclear. In this study, four experiments were conducted in MFC-CW microcosms to investigate the influence of carbon source species and concentrations, external resistance and aeration duration on sulfamethoxazole (SMX) and tetracycline (TC) removal and bioelectricity generation performance. MFC-CWs supplied with glucose as carbon source outperformed other carbon sources, and moderate influent glucose concentration (200 mg L⁻¹) resulted in the best removal of both SMX and TC. Highest removal percentages of SMX (99.4%) and TC (97.8%) were obtained in MFC-CWs with the external resistance of 700 Ω compared to other external resistance treatments. SMX and TC removal percentages in MFC-CWs were improved by 4.98% and 4.34%, respectively, by increasing the aeration duration to 12 h compared to no aeration. For bioelectricity generation performance, glucose outperformed sodium acetate, sucrose and starch, with the highest voltages of 386 ± 20 mV, maximum power density (MPD) of 123.43 mW m⁻³, and coulombic efficiency (CE) of 0.273%. Increasing carbon source concentrations from 100 to 400 mg L⁻¹, significantly (p < 0.05) increased the voltage and MPD, but decreased the internal resistance and CE. The highest MPD was obtained when the external resistance (700 Ω) was close to the internal resistance (600.11 Ω). Aeration not only improved the voltage and MPD, but also reduced the internal resistance. This study demonstrates that carbon source species and concentrations, external resistances and aeration duration, all play vital roles in regulating SMX and TC removal in MFC-CWs.

The insufficient removal of pollutants and bioelectricity production have become a bottleneck for high-concentration saline wastewater treatment through microbial fuel cell (MFC) technology. Herein, a novel supercapacitor MFC (SC-MFC) was constructed with carbon nanofibers composite electrodes to investigate pollutant removal ability, power generation, and electrochemical properties using real landfill leachate. The possible extracellular electron transfer and nitrogen element conversion pathways in the bioanode were also analyzed. Results showed that the SC-MFC had higher pollutant removal rates (COD: 59.4 ± 1.2%; NH₄⁺-N: 78.2 ± 1.6%; and TN: 77.8 ± 1.2%), smaller internal impedance Rₜ (∼6 Ω), higher exchange current density i₀ (2.1 × 10⁻⁴ A cm⁻²), and a larger catalytic current j₀ (704 μA cm⁻²) with 60% leachate than those with 10% and 20% leachate, resulting in a power output of 298 ± 22 mW m⁻². Ammonium could be incorporated by chemoautotrophic bacteria to produce organic compounds that could be further utilized by heterotrophs to generate power when biodegradable organic matters are depleted. Three conversion pathways of nitrogen might be involved, including NH₄⁺ diffusion from anode to cathode chamber, nitrification, and the denitrification process. Additionally, cyclic voltammetry tests showed that both the direct electron transfer (DET) and the mediator electron transfer in bioanode were involved and dominated by DET. The microbial analysis revealed that the bioanode was dominated by salt-tolerant denitrifying bacteria (38.5%), which was deduced to be the key functional microorganism. The electrochemically active bacteria decreased significantly from 61.7% to 4% over three stages of leachate treatment. Overall, the SC-MFC has demonstrated the potential for wastewater treatment along with energy harvesting and provides a new avenue toward sustainable leachate management.

Bioelectrochemical systems (BESs) convert the energy present in wastewater to recover resources like bioelectricity, hydrogen, nutrients, heavy metals, minerals, and industrial chemicals. Various aspects of BES have been discussed here along with their applications and other advantages towards bioenergy recovery. More scientifically organized cross-discipline research efforts are required to scale-up these systems and to get benefit of recovering useful energy from waste materials. Full-scale implementation of bioelectrochemical wastewater treatment is complicated because certain microbiological, technological, and economic challenges need to be resolved that have not previously been encountered in any other wastewater treatment system. BES has higher prospects for in situ remediation of polluted water body or marshy soils and sediments. This technology is likely to evolve as a way of treating sewage, industrial, or agricultural wastewater, not only by lowering the amount of energy required, but at the same time producing electricity, hydrogen, or other chemicals of high value. Thus, after improving the performance of the BES, widening the scope for products recovery by developing better understanding of the process and with efforts to reduce its production cost, it can become a sustainable technology for treatment of wastewater with added advantage of recovery of resources and bioenergy.

Microbial fuel cell (MFC) is a sustainable technology to treat cattle manure slurry (CMS) for converting chemical energy to bioelectricity. In this work, two types of allochthonous inoculum including activated sludge (AS) and domestic sewage (DS) were added into the MFC systems to enhance anode biofilm formation and electricity generation. Results indicated that MFCs (AS + CMS) obtained the maximum electricity output with voltage approaching 577 ± 7 mV (~ 196 h), followed by MFCs (DS + CMS) (520 ± 21 mV, ~ 236 h) and then MFCs with autochthonous inoculum (429 ± 62 mV, ~ 263.5 h). Though the raw cattle manure slurry (RCMS) could facilitate electricity production in MFCs, the addition of allochthonous inoculum (AS/DS) significantly reduced the startup time and enhanced the output voltage. Moreover, the maximum power (1.259 ± 0.015 W/m²) and the highest COD removal (84.72 ± 0.48%) were obtained in MFCs (AS + CMS). With regard to microbial community, Illumina HiSeq of the 16S rRNA gene was employed in this work and the exoelectrogens (Geobacter and Shewanella) were identified as the dominant members on all anode biofilms in MFCs. For anode microbial diversity, the MFCs (AS + CMS) outperformed MFCs (DS + CMS) and MFCs (RCMS), allowing the occurrence of the fermentative (e.g., Bacteroides) and nitrogen fixation bacteria (e.g., Azoarcus and Sterolibacterium) which enabled the efficient degradation of the slurry. This study provided a feasible strategy to analyze the anode biofilm formation by adding allochthonous inoculum and some implications for quick startup of MFC reactors for CMS treatment.

Petrochemical industry is one of the major and rapidly growing industry that generates a variety of toxic and recalcitrant organic pollutants as by-products, which are not only harmful to the aquatic animals but also affects human health. The majority of the components of petrochemical wastewater (PW) are carcinogenic, genotoxic and phytotoxic in nature; hence, this complex wastewater generated from different petrochemical processes should be efficiently treated prior to its disposal in natural water bodies. The established technologies like advanced oxidation, membrane bioreactor, electrocoagulation and activated sludge process employed for the treatment of PW are highly energy intensive and incurs high capital and operation cost. Moreover, these technologies are not effective in completely eliminating petroleum hydrocarbons present in PW. Thus, to reduce the energy requirement and also to transform the chemical energy trapped in these organic matters present in this wastewater into bioelectricity and other value-added products, microbial electrochemical technologies (METs) can be efficaciously used, which would also compensate the treatment cost by transforming these pollutants into bioenergy and valuables. In this regard, this review elucidates the feasibility and application of different METs as an appropriate alternative for the treatment of PW. Furthermore, the numerous bottlenecks towards the real-life application and commercialization of pioneering METs have also been articulated.

Microbial fuel cell (MFC) is a recommended treatment to remediate hexavalent chromium (Cr(VI)) in wastewater. In this study, a wood carbon (WC) electrode was introduced in MFC to enhance the Cr(VI) removal efficiency. WC electrode in MFC completely removed Cr(VI) as compared to the carbon cloth (31.12%) and carbon felt (34.83) within 48 h of operation at 20 mg L⁻¹ of Cr(VI) concentration. The maximum power density of WC electrode was 62.59 mW m⁻² higher than 0.115 and 3.154 mW m⁻² of carbon cloth and felt respectively. The specific surface area of WC increased to 158.47 m⁻² g⁻¹ after high-temperature carbonization, and electrochemical tests indicate it has higher electrocatalytic ability. Therefore, WC might be a good electrode material to effectively remove Cr(VI) and generate bioelectricity simultaneously.

The present study aimed to develop a pilot-scale integrated system composed of anaerobic biofilter (AF), a floating treatment wetland (FTW) unit, and a vertical flow constructed wetland coupled with a microbial fuel cell (CW-MFC) and a reactive bed filter (RBF) for simultaneously decentralized urban wastewater treatment and bioelectricity generation. The first treatment stage (AF) had 1450 L and two compartments: a settler and a second one filled with plastic conduits. The two CWs (1000 L each) were vegetated with mixed plant species, the first supported in a buoyant expanded polyethylene foam and the second (CW-MFC) filled with pebbles and gravel, whereas the RBF unit was filled with P adsorbent material (light expanded clay aggregate, or LECA) and sand. In the CW-MFC units, 4 pairs of electrode chambers were placed in different spacing. First, both cathode and anode electrodes were composed of graphite sticks and monitored as open circuit. Later, the cathode electrodes were replaced by granular activated carbon (GAC) and monitored as open and closed circuits. The combined system efficiently reduced COD (> 64.65%), BOD₅ (81.95%), N-NH₃ (93.17%), TP (86.93%), turbidity (94.3%), and total coliforms (removal of three log units). Concerning bioenergy, highest voltage values were obtained with GAC electrodes, reaching up to 557 mV (open circuit) and considerably lower voltage outputs with closed circuit (23.1 mV). Maximum power densities were obtained with 20 cm (0.325 mW/m²) and 30 cm (0.251 mW/m²). Besides the electrode superficial areas, the HRT and the water level may have influenced the voltage values, impacting DO and COD concentrations in the wastewater.

In this study, a new ecological dam based on the microbial fuel cell principle (MFCED) was designed to remove pollutants from river sediments and water bodies. Sediment organics were better removed in the MFCED mode in comparison with the other two modes (ecological dam with open circuit (OCED) and ecological dam filled with gravel in cathode chamber (GMFCED)). The difference of nitrogen source in water had little effect on the removal of chemical oxygen demand (COD) (70–80%), while nitrate was more readily removed in the MFCED. The voltage curve and power curve were measured to understand the bioelectricity generation of MFCED. During the stable operation phase of MFCED, the voltage was stabilized between 0.09–0.15 V. The results of high-throughput sequencing indicated that the anode and cathode diversities of MFCED were more than the other systems, and the species diversity of the anode was more than that of the cathode in the MFCED. Graphical abstract

The present work focused on the utilization of three local wastes, i.e., rambutan (Nephelium lappaceum), langsat (Lansium parasiticum), and mango (Mangifera indica) wastes, as organic substrates in a benthic microbial fuel cell (BMFC) to reduce the cadmium and lead concentrations from synthetic water. Out of the three wastes, the mango waste promoted a maximum current density (87.71 mA/m²) along with 78% and 80% removal efficiencies for Cd²⁺ and Pb²⁺, respectively. The bacterial identification proved that Klebsiella pneumoniae, Enterobacter, and Citrobacter were responsible for metal removal and energy generation. In the present work, the BMFC mechanism, current challenges, and future recommendations are also enclosed.

Strategic valorization of readily available sugarcane bagasse (SB) is very important for waste management and sustainable biorefinery. Conventional SB pretreatment methods are ineffective to meet the requirement for industrial adaptation. Several past studies have highlighted different pretreatment procedures which are lacking environmentally benign characteristics and effective SB bioconversion. This article provides an in-depth review of a variety of environmentally acceptable thermochemical and biological pretreatment techniques for SB. Advancements in the conversion processes such as pyrolysis, liquefaction, gasification, cogeneration, lignin conversion, and cellulose conversion via fermentation processes are critically reviewed for the formation of an extensive array of industrially relevant products such as biofuels, bioelectricity, bioplastics, bio adsorbents, and organic acids. This article would provide comprehensive insights into several crucial aspects of thermochemical and biological conversion processes, including systematic perceptions and scientific developments for value-added products from SB valorization. Moreover, it would lead to determining efficient pretreatment and/or conversion processes for sustainable development of industrial-scale sugarcane-based biorefinery.