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The need for sustainable technological solutions for wastewater management at different scales has led to the emergence of several promising integrated bioelectrochemical technologies in the past decade. A thorough assessment of these technologies is imperative to understand their practical implementation feasibility and to identify the key challenges to prioritise the research and development work. Our multicriteria-based assessment reveals that the integrated technologies are efficient for wastewater treatment in terms of normalised land footprint [(0.31-1.39 m

The discharge of emerging pollutants, such as beta-blockers (BB), has been recognized as one of the major threats to the environment due to the ecotoxicity associated with these emerging pollutants. The BB are prescribed to treat high blood pressure and cardiovascular diseases; however, even at lower concentration, these pollutants can pose eco-toxic impacts towards aquatic organisms. Additionally, owing to their recalcitrant nature, BB are not effectively removed through conventional technologies, such as activated sludge process, trickling filter and moving bed bioreactor; thus, it is essential to understand the degradation mechanism of BB in established as well as embryonic technologies, like adsorption, electro-oxidation, Fenton process, ultraviolet-based advance oxidation process, ozonation, membrane systems, wetlands and algal treatment. In this regard, this review articulates the recalcitrant nature of BB and their associated removal technologies. Moreover, the major advantages and limitations of these BB removal technologies along with the recent advancements with regard to the application of innovative materials and strategies have also been elucidated. Therefore, the present review intends to aid the researchers in improving the BB removal efficiency of these technologies, thus alleviating the problem of the release of BB into the environment.

Cytotoxic, mutagenic, and carcinogenic contaminants, such as heavy metals and radionuclides, have become an alarming environmental concern globally, especially for developed and developing nations. Moreover, inefficient prevalent wastewater treatment technologies combined with increased industrial activity and modernization has led to increase in the concentration of toxic metals and radioactive components in the natural water bodies. However, for the improvement of ecosystem of rivers, lakes, and other water sources different physicochemical methods such as membrane filtration, reverse osmosis, activated carbon adsorption, electrocoagulation, and other electrochemical treatment are employed, which are uneconomical and insufficient for the complete abatement of these emerging pollutants. Therefore, the application of bioremediation employing aquatic macrophytes and microphytes have gained considerable importance owing to the benefits of cost-effectiveness, eco-friendly, and higher energy efficiency. Thus, the present review aims to enlighten the readers on the potential application of algae, cyanobacteria, plant, and other aquatic micro- and macrophytes for the elimination of carcinogenic metals and radioactive isotopes from wastewater. Additionally, the use of transgenic plants, genetically modified species, algal-bacterial symbiosis for the enhancement of removal efficiency of mutagenic contaminants are also highlighted. Furthermore, species selection based on robustness, mechanism of different pathways for heavy metal and radionuclide detoxification are elucidated in this review article.

Possibility of pyrolyzing high-density polyethylene (HDPE) waste and activating the HDPE-derived carbon (HDC) to be utilized as an oxygen reduction reaction (ORR) catalyst in microbial fuel cell (MFC) was explored. The Fourier transform infra-red spectrum of synthesized HDC indicated the presence of key surface functional groups that aid in catalyzing ORR, while the X-ray diffractogram indicated carbonization of HDC that enhanced electrical conductivity. Cyclic voltammogram and electrochemical impedance spectroscopy of HDC demonstrated an ORR peak current density of − 2.46 mA cm‒2, which was found to be comparable with commercial activated carbon (AC, − 2.71 mA cm‒2). The MFC with HDC as cathode catalyst (MFC–HDC) rendered a power density (115 mW m‒2) that was only 25% lower than the MFC with commercial AC as a catalyst (MFC–AC). Organic matter removal efficiency of MFC–HDC was comparable to MFC–AC. Thus, the low-cost HDC electrocatalyst (0.025 $ g‒1) exhibited catalytic performance comparable with AC (12 $ g‒1) and difference between the performance of the two MFCs with HDC and AC as catalyst can be attributed to the lower specific surface area (232 m2 g‒1) of the HDC catalyst as compared to AC (1200 m2 g‒1). Thus, for future applications, the specific surface area of HDC catalyst need to be improved to make it competitive with commercial AC.

Bioelectrochemical systems (BESs) are a unique group of wastewater remediating technology that possesses the added advantage of valuable recovery with concomitant wastewater treatment. Moreover, due to the application of robust microbial biocatalysts in BESs, effective removal of emerging contaminants (ECs) can be accomplished in these BESs. Thus, this review emphasizes the recent demonstrations pertaining to the removal of complex organic pollutants of emerging concern present in wastewater through BES. Owing to the recalcitrant nature of these pollutants, they are not effectively removed through conventional wastewater treatment systems and thereby are discharged into the environment without proper treatment. Application of BES in terms of ECs removal and degradation mechanism along with valuables that can be recovered are discussed. Moreover, the factors affecting the performance of BES, like biocatalyst, substrate, salinity, and applied potential are also summarized. In addition, the present review also elucidates the occurrence and toxic nature of ECs as well as future recommendations pertaining to the commercialization of this BES technology for the removal of ECs from wastewater. Therefore, the present review intends to aid the researchers in developing more efficient BESs for the removal of ECs from wastewater.

The presence of emerging pollutants in the environment can pose potential risks to the natural ecosystem. Hence, the efficacious removal of emerging pollutants, like pharmaceuticals, including anti...

Microbial fuel cell (MFC) is a type of bio-electrochemical system, which harvests bioelectricity by oxidizing the organic material present in the wastewater. Performance of a MFC relies on the both anodic and cathodic reaction kinetics. The oxygen reduction reaction (ORR) occurring on the cathode is a sluggish reaction, which majorly diminishes the power generation of a MFC. In this context, the use of metal organic frameworks (MOFs) is appropriate as a cathode catalyst to boost the ORR kinetics, thus enhancing the power generation of MFCs. The higher specific surface area, excellent catalytic activity and precise permeable structure of MOFs render them suitable for the application as cathode catalysts to enhance ORR in MFCs. Hence, there is a wide scope of implementation of different low-cost MOF-based cathode catalysts in MFCs, which would not only enhance its performance but also would diminish the fabrication cost of field-scale MFCs. This review therefore provides the detailed understanding on both the synthesis methods and structural characteristics of MOFs and also explains the mechanism of ORR, role of cathode catalysts and application of MOFs as cathode catalysts in MFCs.

Solvent-free algal cell lysis using fungal enzyme for enhanced lipid recovery diminishes per unit production cost of algal biodiesel. In this investigation, a triple chamber photosynthetic microbial fuel cell (PMFC) was fabricated, where positive potential was imposed in the extraction chamber to draw the negatively charged lipid ions from the cathodic chamber. Under optimum imposed potential of + 3.0 V (vs standard hydrogen electrode) and with 3.5% (v/v) dosage of fungal enzyme in to the algal consortium of cathodic chamber, a maximum of 79.0% of lipid was recovered. Additionally, enzyme-assisted de-oiled algal biomass was applied in the anodic chamber to function as substrate and mediator for exo-electrogens, and the maximum power density of 10.0 W/m

The emission of CO

Microbial electrosynthesis (MES) is a budding technology, where the principles of bioelectrochemical systems are employed to sequester CO2 and concomitantly produce value-added organic chemicals. The inferior production rate of organic chemicals in MES is a major roadblock in the real field application of this novel technology, which needs to be overcome by applying biocompatible metal-based cathode catalysts. Therefore in the present investigation, Rh and TiO2 microparticles were applied as cathode catalyst in MES and performance was compared based on production rate of organic chemicals and electrochemical parameters. The electrochemical properties of Rh and TiO2 were illustrated by employing cyclic voltammetry and electrochemical impedance spectroscopy, and reduction in overpotential associated with hydrogen evolution reaction was noticed for TiO2 coated electrode. Moreover, the production rate of acetate was also enhanced by 2.14 and 1.3 times due to the application of TiO2 (MES-Ti) and Rh (MES-Rh), respectively, as cathode catalyst in comparison to the MES operated without any cathode catalyst. Better bacterial attachment and more production of hydrogen were also observed for MES-Ti, which was fundamental to the improved performance of MES-Ti. Therefore, TiO2 can be deliberated as an effective cathode catalyst in MES to escalate its production rate.

Microbial electrosynthesis (MES) is an innovative technology, which can yield valuable organic chemicals with concomitant CO2 sequestration by employing microbes as biocatalysts. The mode of operation has an imperative role in the performance of MES, thus, affecting the yield of synthesized organic chemicals from the MES. However, to the best of our knowledge, the optimal mode of operation for MES has not been determined till date. Hence, in the present investigation, two MES were operated: one in batch mode (MES-B) and another in continuous mode (MES-C), and their performance was monitored. The MES-B exhibited 31%, 33.5% and 44% higher production rate of acetate, propionate and butyrate, respectively, in comparison to MES-C. Moreover, the performance of MES-B also stabilized faster, and microbiome in the cathodic chamber of MES-B was able to accept 26% more electrons supplied to it externally, which were employed as reducing equivalents to reduce CO2. The enactment of MES-B was superior to that of MES-C due to the higher retention of CO2 and hydrogen in cathodic chamber of MES-B. Therefore, operating MES in batch mode would aid in yielding more organic chemicals through CO2 sequestration.

Polytriazoles are considered as an excellent high-performance polymer due to their outstanding set of properties. The current investigation reports the synthesis of a phosphorus-containing fluorina...

Clayware membrane amalgamated with 20% montmorillonite (M-20), acts as an excellent cost effective proton exchange membrane (PEM) for the application in field-scale microbial fuel cells (MFCs). In this investigation, M-20 membrane was pre-treated by acid (M-A), neutral water (M-N) and alkali (M-B), followed by the determination of the membrane properties to access their applicability in MFCs. With alkali treatment of M-20 membrane, maximum proton mass transfer coefficient of 6 × 10−6 cm s−1 was obtained, which was nearly five times higher than M-A (1.15 × 10−6 cm s−1) and four times higher than the control membrane, M-N. Proton conductivity was also found to be maximum for M-B (17.9 × 10−3 S cm−1), which was four times higher than both M-N (4.4 × 10−3 S cm−1) and M-A (4.6 × 10−3 S cm−1). Oxygen mass transfer coefficient was found to be minimum for M-B (4.02 × 10−5 cm s−1), which was considerably lesser than that observed for M-N (16.2 × 10−5 cm s−1) and M-A (13.8 × 10−5 cm s−1). Cation transport number of M-B (0.15 ± 0.01) was found to be two folds lower than M-N, demonstrating M-B is more selective towards proton transport compared to other cations. The MFC-B with M-B as PEM performed superior as compared with other MFCs, demonstrating coulombic efficiency (CE) of 10.2%, chemical oxygen demand (COD) removal efficiency of 88% and power density of 83.5 mW m−2. On the other hand, MFCs using M-A and M-N as PEM, demonstrated mediocre performance with CE of 6% and 7.6%, COD removal efficiency of 80% and 83% and power density of 40.4 ± 6.2 mW m−2 and 64.0 ± 5.8 mW m−2, respectively. Hence, alkali treatment of clayware ceramic membrane elucidated its appropriateness for proliferating the efficacy of MFCs and these are recommended for scaling up of MFCs.

Microbial fuel cell (MFC) is a bioelectrochemical system, which treats wastewater with simultaneous recovery of bioelectricity. Costly proton exchange membrane, like Nafion-117, brings a serious bottleneck towards the sustainable scaled-up application of this technology. For an appropriate field-scale demonstration of MFC, the fabrication cost needs to be reduced drastically. This can be achieved by using low-cost proton exchange membrane (PEM) in MFCs, which would demonstrate equivalent performance as commercially available expensive PEMs. Such a novel PEM constituting 5% goethite and natural clay as a base material was synthesized, named as G-5, and it was used in MFC as a separator. This G-5 membrane was estimated to be five folds cheaper than the commercially available Nafion-117 membrane, which is popularly used in MFC. Membrane properties, like water and acetate uptake, and proton conductivity of the G-5 membrane, were evaluated and compared with Nafion-117. A power density obtained from the MFC using G-5 as PEM (112.81 ± 8.74 mW/m2) was slightly higher than the MFC with Nafion-117 as PEM (106.95 ± 5.52 mW/m2). Chemical oxygen demand removal and Coulombic efficiency for MFC with G-5 membrane were found to be 22% and 8.6% higher, respectively, in comparison with that of the MFC with Nafion-117 as PEM. Thus, low-cost G-5 membrane demonstrated the potential to be used for scaling-up of MFCs to reduce fabrication cost for successful field-scale implementation of MFCs.

The rise in global atmospheric temperature due to increase in the atmospheric carbon dioxide concentration needs to be tackled immediately before it reaches the point of no return. The application of innovative technologies based on the concepts of bioelectrochemical systems (BESs) can contribute in this direction by simultaneously sequestrating CO2 and producing value-added products in the process. Wastewater treatment with simultaneous bioenergy and biofuel recovery is also one of the added advantage of employing BESs for CO2 fixation. This review focuses on the potential of employing BES-based technologies like microbial carbon capture, plant-microbial fuel cell and microbial electrosynthesis cell for the concomitant production of valuables and CO2 sequestration. Also, various parameters affecting performance of BES that need to be optimized for the proper field-scale demonstration of these technologies are discussed. Keywords: Bioelectrochemical systems, Carbon sequestration, Microbial carbon capture cell, Microbial fuel cells, Microbial electrosynthesis

Caffeine is one of the most widely detected and reported emerging contaminant in wastewater, groundwater as well as fresh and marine water bodies owing to its massive consumption, which has led to the bioaccumulation of caffeine in different aquatic environment. Hazardous effects of caffeine have been reported on aquatic biota, coral reefs, soil and microorganisms along with the detrimental health impact on humans. Conventional wastewater treatment plants have shown fairly high removal of caffeine ranging from 64% to 100%. However, caffeine is only partially biodegraded in biological units and is often reported in primary and secondary sludge. The present review article elucidates different electrochemical advanced oxidation processes (EAOPs), namely anodic oxidation (AO) and electro-Fenton (EF) process as alternative techniques for caffeine removal from wastewater and highlights their major findings. Additionally, information regarding performance of integrated systems comprising EAOPs and conventional technologies as well as state-of-art hybrid technologies, such as bioelectro-Fenton (BEF), photoelectron Fenton (PEF) have also been discussed to incorporate a broader perspective of EAOPs as a promising wastewater treatment technique. The review also intends to assist the readers in understanding the key challenges encountered during the operation of EAOPs and the critical parameters affecting removal efficiency along with the potential areas for future investigations for overcoming the drawbacks of EAOPs to make it sustainable technology for field-scale applications.

Microbial electrochemical technologies (METs) are a set of inventive tools that generate value-added by-products with concomitant wastewater remediation. However, due to the bottlenecks, like higher fabrication cost and inferior yield of resources, these inventive METs are still devoid of successful field-scale implementation. In this regard, application of quorum sensing (QS) mechanism to improve the power generation of the METs has gained adequate attention. The QS is an intercellular signalling mechanism that controls the bacterial social network in its vicinity via the synthesis of diffusible signal molecules labelled as auto inducers, thus ameliorating yield of valuables produced through METs. This state-of-the-art review elucidates different types of QS molecules and their working mechanism with the special focus on the widespread application of QS in the field of METs for their performance enhancement. Thus, this review intends to guide the researchers in rendering scalability to METs by integrating innovative QS mechanisms into them.

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 3rd 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.

Xenobiotics are newly identified contaminants, recently discovered to be present in the environment and possessing potential threat to different components of the ecosystems due to their i...

A two-stage continuous process was developed for treating medium-strength wastewater combining microbial fuel cell (MFC) using activated carbon (AC)/TiO2 composite as cathode catalyst and submerged membrane bioreactor (MBR). Synthetic wastewater, having total chemical oxygen demand (COD) of around 3 g/L, was introduced first in the anodic chamber of MFC in a continuous mode of operation followed by aerobic MBR. Submerged hollow-fibre ultra-filtration membrane assembly was attached to draw permeate from MBR. The electrical performance of MFC was evaluated by polarisation, which showed a maximum volumetric power density of 1.02 W/m3 with much lower whole-cell internal resistance of 10 Ω. The coulombic efficiency of MFC was estimated to be 0.31%, demonstrating AC/TiO2 composite as a promising cathode catalyst for applications in MFC. The permeate of MFC–MBR system showed 98.3 ± 0.3% and 81.9 ± 1.8% of COD and total Kjeldahl nitrogen removal efficiency, respectively, producing permeate with total suspended solids concentration of less than 5 mg/L. Thus, a two-stage reliable process for treatment of wastewater is demonstrated using integrated MFC–MBR for generating high-quality recyclable effluent and facilitating recovery of bio-electricity.

Rhodium with activated carbon as carbon base layer (Rh/AC) was exploited as an oxygen reduction reaction (ORR) catalyst to explore its applicability in microbial fuel cell (MFC). Four MFCs were fabricated using the Rh/AC catalyst, adopting varying Rh loadings of 0.5, 1.0 and 2.0 mg cm−2 and without Rh on carbon felt cathode in order to understand the optimum loading of this catalyst to enhance the performance of MFC. The participation of Rh/AC in ORR was confirmed by cyclic voltammetry and electron impedance spectroscopy analysis, which supported the enhanced charge transfer capacity of the cathode modified with the prepared catalysts. Volumetric power density of MFC was found to be improved by 2.6 times when Rh/AC was used as cathode catalyst (9.36 W m−3) at a loading of 2.0 mg cm−2 in comparison to the control MFC (3.65 W m−3) without Rh on the cathode. It was thus inferred that the increase in the Rh loading up to 2 mg cm−2 can improve the performance of MFC significantly.

Microbial fuel cell (MFC) technology has been widely experimented nowadays, as it is a promising clean energy technology, which can harvest bioelectricity while simultaneously treating wastewater. Platinum (Pt), a precious transition metal, has long been regarded as a superior catalyst material for oxygen reduction reaction (ORR) at the cathode of the MFCs, however the high cost associated with it clutch it back for field scale applications. In this study, Co3O4 or Fe3O4 was blended with synthetically prepared conductive ink to act as microporous layer to explore its efficacy as an ORR catalyst. Applicability of these catalysts on cathode was investigated in dual chambered aqueous cathode MFCs and the performance was compared with MFC without any cathode catalyst, MFC with only conductive ink and another MFC with Pt as benchmark ORR catalyst. X-Ray diffraction, Fourier transform infrared spectra, Raman and field emission scanning electron microscope analysis were done to characterize the prepared catalysts. Cathode containing Co3O4 with conductive ink demonstrated higher reduction current (- 30 mA) than cathode having Pt and conductive ink with Fe3O4 (- 9 mA each) during cyclic voltammetry analysis. MFCs having cathodes printed with conductive ink containing Co3O4 and Fe3O4 exhibited a maximum volumetric power density of 6.62 W m−3 and 5.06 W m−3, respectively, which were much higher than the one without any catalyst (2.95 W m−3). Similarly, coulombic efficiency (CE) of 22.3%, 17.1% and 11.2% was observed in MFCs having cathode with conductive ink containing Co3O4 or Fe3O4 and without any catalysts, respectively. Moreover, more than 90% chemical oxygen demand removal efficiency was observed for MFCs having cathode with conductive ink containing Co3O4 or Fe3O4. Importantly, the performance obtained from MFC with conductive ink blended Co3O4 was found superior compared to MFC having Pt as cathode catalyst, where later produced power density of 6.13 W m−3 and CE of 21.1%. Hence, it can be concluded that Co3O4 can be used as an alternative to expensive platinum for efficient ORR in MFCs to make this technology effective for field scale application.

Ruthenium (Ru) was impregnated with bismuth (Bi) to reduce the spectrum demand for the excitation of Ru to employ it as photocathode catalyst (Bi-Ru) in a microbial fuel cell (MFC) to amel...

The concentration of atmospheric CO2 is increasing at a frightening rate, which warrants the use of sustainable mitigation techniques to counter global warming, a repercussion of elevated atmospheric CO2 concentration. In this regard, microbial electrochemical technologies (METs) can be employed to sequester atmospheric CO2 and concomitantly produce valuables like bioelectricity and biofuels. Production of bioenergy in the form of bioelectricity and other value-added products through the degradation of organic matter present in wastewater with concomitant CO2 sequestration is the need of the hour to achieve environmental sustainability and promote circular bioeconomy, which mainly deals with the use of waste material as a resource for the production of valuables through biological means. The waste gas, CO2, emitted by various industries can be used as a feedstock by METs to produce biofuels and other value-added chemicals, thus achieving circular bioeconomy. Therefore, this chapter elucidates the scope of the application of MET as a sustainable technology to sequester atmospheric CO2 and simultaneously produce value-added by-products at an efficient engineering level and discusses the bottlenecks associated with these technologies.

Catalysts play an essential role in various electrochemical reactions followed during the synthesis of hydrogen peroxide (H2O2). Plenty of investigations on the role of catalysts in the sy...

A microbial fuel cell (MFC) is a bioelectrochemical system that can recover bioelectricity from wastewater, with simultaneous organic matter removal from the wastewater. However, due to th...