Paradigm shift in Nutrient-Energy-Water centered sustainable wastewater treatment system through synergy of bioelectrochemical system and anaerobic digestion.

With advancements in research and the necessity of improving the performance of bioelectrochemical system (BES), coupling anaerobic digestion (AD) with BES is crucial for energy gain from wastewater and bioremediation. Hybridization of BES-AD concept opens new avenues for pollutant degradation, carbon capture and nutrient-resource recovery from wastewater. The strength of merging BES-AD lies in synergy, and this approach was employed to differentiate fads from strategies with the potential for full-scale implementation and making it an energy-positive system. The integration of BES and AD system increases the overall performance and complexity of combined system and the cost of operation. From a technical standpoint, the primary determinants of BES-AD feasibility for field applications are the scalability and economic viability. High potential market for such integrated system attract industrial partners for more industrial trials and investment before commercialization. However, BES-AD with high energy efficacy and negative economics demands performance boost.

Optimizing electrochemically active microorganisms as a key player in the bioelectrochemical system: Identification methods and pathways to large-scale implementation.

The rapid global economic growth driven by industrialization and population expansion has resulted in significant issues, including reliance on fossil fuels, energy scarcity, water crises, and environmental emissions. To address these issues, bioelectrochemical systems (BES) have emerged as a dual-purpose solution, harnessing electrochemical processes and the capabilities of electrochemically active microorganisms (EAM) to simultaneously recover energy and treat wastewater. This review examines critical performance factors in BES, including inoculum selection, pretreatment methods, electrodes, and operational conditions. Further, authors explore innovative approaches to suppress methanogens and simultaneously enhance the EAM in mixed cultures. Additionally, advanced techniques for detecting EAM are discussed. The rapid detection of EAM facilitates the selection of suitable inoculum sources and optimization of enrichment strategies in BESs. This optimization is essential for facilitating the successful scaling up of BES applications, contributing substantially to the realization of clean energy and sustainable wastewater treatment. This analysis introduces a novel viewpoint by amalgamating contemporary research on the selective enrichment of EAM in mixed cultures. It encompasses identification and detection techniques, along with methodologies tailored for the selective enrichment of EAM, geared explicitly toward upscaling applications in BES.

Bioremediation of hydrocarbon by co-culturing of biosurfactant-producing bacteria in microbial fuel cell with Fe2O3-modified anode.

The most common type of environmental contamination is petroleum hydrocarbons. Sustainable and environmentally friendly treatment strategies must be explored in light of the increasing challenges of toxic and critical wastewater contamination. This paper deals with the bacteria-producing biosurfactant and their employment in the bioremediation of hydrocarbon-containing waste through a microbial fuel cell (MFC) with Pseudomonas aeruginosa (exoelectrogen) as co-culture for simultaneous power generation. Staphylococcus aureus is isolated from hydrocarbon-contaminated soil and is effective in hydrocarbon degradation by utilizing hydrocarbon (engine oil) as the only carbon source. The biosurfactant was purified using silica-gel column chromatography and characterised through FTIR and GCMS, which showed its glycolipid nature. The isolated strains are later employed in the MFCs for the degradation of the hydrocarbon and power production simultaneously which has shown a power density of 6.4 W/m3 with a 93% engine oil degradation rate. A biogenic Fe2O3 nanoparticle (NP) was synthesized using Bambusa arundinacea shoot extract for anode modification. It increased the power output by 37% and gave the power density of 10.2 W/m3. Thus, simultaneous hydrocarbon bioremediation from oil-contamination and energy recovery can be achieved effectively in MFC with modified anode.

Astaxanthin as a King of Ketocarotenoids: Structure, Synthesis, Accumulation, Bioavailability and Antioxidant Properties.

Astaxanthin (3,3-dihydroxy-ß, ß-carotene-4,4-dione) is a ketocarotenoid synthesized by Haematococcus pluvialis/lacustris, Chromochloris zofingiensis, Chlorococcum, Bracteacoccus aggregatus, Coelastrella rubescence, Phaffia rhodozyma, some bacteria (Paracoccus carotinifaciens), yeasts, and lobsters, among others However, it is majorly synthesized by Haematococcus lacustris alone (about 4%). The richness of natural astaxanthin over synthetic astaxanthin has drawn the attention of industrialists to cultivate and extract it via two stage cultivation process. However, the cultivation in photobioreactors is expensive, and converting it in soluble form so that it can be easily assimilated by our digestive system requires downstream processing techniques which are not cost-effective. This has made the cost of astaxanthin expensive, prompting pharmaceutical and nutraceutical companies to switch over to synthetic astaxanthin. This review discusses the chemical character of astaxanthin, more inexpensive cultivating techniques, and its bioavailability. Additionally, the antioxidant character of this microalgal product against many diseases is discussed, which can make this natural compound an excellent drug to minimize inflammation and its consequences.

Scalable architecture of low-cost household microbial fuel cell for domestic wastewater treatment and simultaneous energy recovery.

Researchers are still trying to achieve desirable results while treating actual wastewater at the field size when scaling up a microbial fuel cell (MFC). This pilot-scale project aimed to create a decentralised system for treating domestic wastewater and concurrent energy generation that may be used as a model for the decentralisation process. In this investigation, a cylindrical-shaped earthen membrane was utilized. The arrangement was deployed on-site at a residence for the treatment of domestic wastewater as well as simultaneous generation of power. From August until November 2021, the 36 L pilot-scale setup was operational for a period of 92 days. The setup's performance was affected by seasonal temperature variations during the operation period. The system's performance was measured in terms of COD, nitrate, and NH3-N removal, with the highest results being 93.52 %, 84.93 %, and 74.78 %, respectively. The pilot-scale setup achieved the highest current of 43.7 mA, and the output voltage of the setup was boosted to 4.1 V using a power management system. The sustainable operation of pilot household MFC showed a positive indication for field application with a low-cost solution.

Tailoring a highly conductive and super-hydrophilic electrode for biocatalytic performance of microbial electrolysis cells.

Bioelectrochemical hydrogen production via microbial electrolysis cells (MECs) has attracted attention as the next generation of technology for the hydrogen economy. MECs work by electrochemically active bacteria reducing organic compounds at the anode. However, the hydrophobic nature of carbon-based anodes suppresses the release of the produced gas and water penetration, which significantly reduces the possibility of microbial attachment. Consequently, a limited surface area of the anode is used, which decreases hydrogen production efficiency. In this study, the bifunctional material poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was applied to the surface of a three-dimensional carbon felt anode to enhance the hydrogen production efficiency of an MEC owing to the high conductivity of PEDOT and super-hydrophilicity of PSS. In experiments, the PEDOT:PSS-modified anode almost doubled the hydrogen production efficiency of the MEC compared with the control anode owing to the increased capacitance current (239.3 %) and biofilm formation (220.7 %). The modified anode reduced the time required for the MEC to reach a steady state of hydrogen production by 14 days compared to the control anode. Microbial community profiles demonstrated that the modified anode had a greater abundance of electrochemically active bacteria than the control anode. This simple method could be widely applied to various bioelectrochemical systems (e.g., microbial fuel cells and solar cells) and to scaling up MECs.

Scale-up of the bioelectrochemical system: Strategic perspectives and normalization of performance indices.

Electrochemists and ecological engineers find environmental bioelectrochemistry appealing; however, there is a big gap between expectations and actual progress in bioelectrochemical system (BES). Implementing such technology opens new opportunities for novel electrochemical reactions for resource recovery and effective wastewater treatment. Loopholes of BES exist in its scaling-up applications, and numerous attempts toward practical applications (200, 1000, and 1500 L) are key successive indicators toward its commercialization. This review emphasized the critical rethinking of standardization of performance indices i.e. current generation (A/m2), net energy recovery (kWh/kg·COD), product/resource yield (mM), and economic feasibility ($/kWh) to make fair comparison with the existing treatment system. Therefore, directional perspectives, including modularity, energy-cost balance, energy and resource recovery, have been proposed for the sustainable market of BES. The current state of the art and up-gradation in resource recovery and contaminant removal warrants a systematic rethinking of functional worth and niches of BES for practical applications.

Scalability of microbial electrochemical technologies: Applications and challenges.

During wastewater treatment, microbial electrochemical technologies (METs) are a promising means for in situ energy harvesting and resource recovery. The primary constraint for such systems is scaling them up from the laboratory to practical applications. Currently, most research (∼90%) has been limited to benchtop models because of bioelectrochemical, economic, and engineering design limitations. Field trials, i.e., 1.5 m3 bioelectric toilet, 1000 L microbial electrolysis cell and industrial applications of METs have been conducted, and their results serve as positive indicators of their readiness for practical applications. Multiple startup companies have invested in the pilot-scale demonstrations of METs for industrial effluent treatment. Recently, advances in membrane/electrode modification, understanding of microbe-electrode interaction, and feasibility of electrochemical redox reactions have provided new directions for realizing the practical application. This study reviews the scaling-up challenges, success stories for onsite use, and readiness level of METs for commercialization that is inexpensive and sustainable.

Effectiveness of constructed wetland integrated with microbial fuel cell for domestic wastewater treatment and to facilitate power generation.

Constructed wetlands (CWs) have gained a lot of attention for wastewater treatment due to robustness and natural pollutant mitigation characteristics. This widely acknowledged technology possesses enough merits to derive direct electricity in collaboration with microbial fuel cell (MFC), thus taking advantage of microbial metabolic activities in the anoxic zone of CWs. In the present study, two identical lab-scale CWs were selected, each having 56 L capacity. One of the CW integrated with MFC (CW-MFC) contains two pairs of electrodes, i.e., carbon felt and graphite plate. The first pair of CW-MFC consists of a carbon felt cathode with a graphite plate anode, and the second pair contains a graphite plate cathode with a carbon felt anode. The other CW was not integrated with MFC and operated as a traditional CW for evaluating the performance. CW-MFC and CW were operated in continuous up-flow mode with a hydraulic retention time of 3 days and at different organic loading rates (OLRs) per unit surface area, such as 1.45 g m-2 day-1 (OLR-1), 2.43 g m-2 day-1 (OLR-2), and 7.25 g m-2 day-1 (OLR-3). The CW-MFC was able to reduce the organic matter, phosphate, and total nitrogen by 92%, 93%, and 70%, respectively, at OLR of 1.45 g m-2 day-1, which was found to be higher than that obtained in conventional CW. With increase in electrochemical redox activities, the second pair of electrodes made way for 3 times higher power density of 16.33 mW m-2 as compared to the first pair of electrodes in CW-MFC (5.35 mW m-2), asserting carbon felt as a good anode material to be used in CW-MFC. The CW-MFC with carbon felt as an anode material is proposed to improve the electro-kinetic activities for scalable applications to achieve efficient domestic wastewater treatment and electricity production.

Fungal-mediated electrochemical system: Prospects, applications and challenges.

Microbial fuel cells (MFCs) that generate bioelectricity from biodegradable waste have received considerable attention from biologists. Fungi play a significant role as both anodic and cathodic catalysts in MFCs. Saccharomyces cerevisiae is a fungus with an ability to transfer electrons through mediators such as methylene blue (MB), neutral red (NR) or even without a mediator. This unique role of fungal cells in exocellular electron transfer (EET) and their interactions with electrodes hold a lot of promise in areas such as wastewater treatment where yeast cell-based MFCs can be used. The present article highlights the physico-chemical factors affecting the performance of fungal-mediated MFCs in terms of power output and degradation of organic pollutants, along with the challenges associated with fungal MFCs. In addition, to this comparative assessment of fungal-mediated bio-electrochemical systems, their development, possible applications and potential challenges are also discussed.

Physico-chemical and biological treatment strategies for converting municipal wastewater and its residue to resources.

An increase in urbanization and industrialization has not only contributed to an improvement in the lifestyle of people, but it has also contributed to a surge in the generation of wastewater. To date, conventional physico-chemical and biological treatment methods are widely used for the treatment of wastewater. However, the efficient operation of these systems require substantial operation and maintenance costs, and the application of novel technologies for the treatment and disposal of sludge/residues. This review paper focuses on the application of different treatment options such as chemical, catalyst-based, thermochemical and biological processes for wastewater or sludge treatment and membrane-based technologies (i.e. pressure-driven and non-pressure driven) for the separation of the recovered products from wastewater and its residues. As evident from the literature, a wide variety of treatment and resource recovery options are possible, both from wastewater and its residues; however, the lack of planning and selecting the most appropriate design (treatment train) to scale up from pilot to the field scale has limited its practical application. The economic feasibility of the selected technologies was critically analyzed and the future research prospects of resource recovery from wastewater have been outlined in this review.

Blending of microbial inocula: An effective strategy for performance enhancement of clayware Biophotovoltaics microbial fuel cells.

Performance of clayware Biophotovoltaics (BPVs) with three variants of inocula namely anoxygenic photosynthetic bacteria (APB) rich Effective microbes (EM), Up-flow anaerobic sludge blanket reactor (UASB) sludge, SUPER-MIX the blend of EM and UASB inoculum were evaluated on the basis of electrical output and pollutant removal. SUPER-MIX inocula with microbial community comprising of 28.42% APB and 71.58% of other microbes resulted in peak power density of 275 mW/m2, 69.3 ± 1.74% Coulombic efficiency and 91 ± 3.96% organic matter removal. The higher performance of the SUPER-MIX than EM and UASB inocula was due to the syntrophic associations of the various APBs and other heterogenous microorganisms in perfect blend which improved biocatalytic electron transfer, electro-kinetic activities with higher redox current and bio-capacitance. The promising performance of clayware BPVs with SUPER-MIX inocula indicate the possibility of BPVs to move towards the scale-up process to minimize the investment towards pure culture by effective blending strategies of inocula.

Modeling and optimization strategies towards performance enhancement of microbial fuel cells.

Considering the complexity associated with bioelectrochemical processes, the performance of a microbial fuel cell (MFC) is governed by input operating parameters. For scaled-up applications, a MFC system needs to be modeled from engineering perspectives in terms of optimum operating conditions to get higher performance and energy recovery. Several conceptual numerical models to advanced computational simulation approaches have been developed to represent simple-form of a complex MFC system. Application of mathematical and computation models are explored to establish the relationship between operating input-variables and power output. The present review discusses about the complexity of system, modeling strategies used and reality of such modeling for scaling-up applications of MFCs. Additionally, the selection of an appropriate mathematical model reduces the computational duration and provides better understanding of the system process. It also explores the possibility and progress towards commercialization of MFCs and thus the need of development of model-based optimization and process-control approaches.

Suppressing methanogens and enriching electrogens in bioelectrochemical systems.

Suppression of methanogens is considered as one of the main challenges in achieving the practical application of several types of bioelectrochemical system (BES). Feasibility of mixed culture as an inoculum in BES is mainly restricted by methanogenic population. Methanogens compete with electrogens (in bioanodes) or acetogens (in biocathodes) for substrate which results in diminishing Coulombic efficiency. Selection of particular inoculum pretreatment method affects the microbial diversity in anodic/cathodic microenvironments and hence the performance of BES. This review discusses various physical, chemical and biological pretreatment methods for suppressing the growth of methanogens. Selective microbial enrichment in anodic/cathodic biofilm can be promoted with bioaugmentation and/or applied external potential approach to harvest maximum Coulombs from the substrate. For field application of BES, physical pretreatment methods can be proposed with intermittent addition of chemical inhibitors and conversion of methane to electricity in order to make the process inexpensive along with recovering the maximum energy.

Architectural adaptations of microbial fuel cells.

Conventional wastewater treatment consumes a large amount of money worldwide for removal of pollutants prior to its discharge into water body or facilitating reuse. Decreasing energy expenditure during wastewater treatment and rather recovering some value-added products while treating wastewater is an important goal for researchers. Microbial fuel cells (MFCs) are representative bioelectrochemical systems, which offer energy-efficient wastewater treatment. MFCs convert chemical energy of organic matter into electrical energy by using biocatalytic activities. Although MFCs are not truly commercialized, they have potential to make energy-gaining wastewater treatment technologies and represent their capabilities successfully. Over the last decade, MFCs have developed remarkably in almost every dimension including wastewater treatment capabilities, power output, and cost optimization; however, its architectural design is an important consideration for scaling up. Here, we review various architectural advancements and technology up-gradation MFCs have experienced during its journey, to take this technology step forward for commercialization.

Simultaneous Wastewater Treatment, Algal Biomass Production and Electricity Generation in Clayware Microbial Carbon Capture Cells.

Performance of microbial carbon capture cells (MCCs), having a low-cost clayware separator, was evaluated in terms of wastewater treatment and electricity generation using algae Chlorella pyrenoidosa in MCC-1 and Anabaena ambigua in MCC-2 and without algae in a cathodic chamber of MCC-3. Higher power production was achieved in MCC-1 (6.4 W/m3) compared to MCC-2 (4.29 W/m3) and MCC-3 (3.29 W/m3). Higher coulombic efficiency (15.23 ± 1.30%) and biomass production (66.4 ± 4.7 mg/(L*day)) in MCC-1 indicated the superiority of Chlorella over Anabaena algae for carbon capture and oxygen production to facilitate the cathodic reduction. Algal biofilm formation on the cathode surface of MCC-1 increased dissolved oxygen in the catholyte and decreased the cathodic charge transfer resistance with increase in reduction current. Electrochemical analyses revealed slow cathodic reactions and increase in internal resistance in MCC-2 (55 Ω) than MCC-1 (30 Ω), due to lower oxygen produced by Anabaena algae. Thus, biomass production in conjunction with wastewater treatment, CO2 sequestration and electricity generation can be achieved using Chlorella algal biocathode in MCC.

Enhancing the performance of single-chambered microbial fuel cell using manganese/palladium and zirconium/palladium composite cathode catalysts.

Application of ZrO2, MnO2, palladium, palladium-substituted-zirconium oxide (Zr0.98Pd0.02O2) and palladium-substituted-manganese oxide (Mn0.98Pd0.02O2) cathode catalysts in a single-chambered microbial fuel cell (MFC) was explored. The highest power generation (1.28W/m3) was achieved in MFC with Mn0.98Pd0.02O2 catalyst, which was higher than that with MnO2 (0.58W/m3) alone; whereas, MFC having Zr0.98Pd0.02O2 catalyzed cathode and non-catalyzed cathode produced powers of 1.02 and 0.23W/m3, respectively. Also, low-cost zirconium-palladium-composite showed better catalytic activity and capacitance over ZrO2 with 20A/m3 current production and demonstrated its suitability for MFC applications. Cyclic voltammetry analyses showed higher well-defined redox peaks in composite catalysts (Mn/Zr-Pd-C) over other catalyzed MFCs containing MnO2 or ZrO2. Electrochemical behaviour of composite catalysts on cathode showed higher availability of adsorption sites for oxygen reduction and, hence, enhanced the rate of cathodic reactions. Thus, Mn/Zr-Pd-C-based composite catalysts exhibited superior cathodic performance and could be proposed as alternatives to costly Pd-catalyst for field applications.

Enhancing the power generation in microbial fuel cells with effective utilization of goethite recovered from mining mud as anodic catalyst.

Catalytic effect of goethite recovered from iron-ore mining mud was studied in microbial fuel cells (MFCs). Characterization of material recovered from mining mud confirms the recovery of iron oxide as goethite. Heat treated goethite (550 °C) and untreated raw goethite were coated on stainless-steel anode of MFC-1 and MFC-2, respectively; whereas, unmodified stainless-steel anode was used in MFC-3 (control). Fivefold increment in power was obtained in MFC-1 (17.1 W/m(3) at 20 Ω) than MFC-3 (3.5 W/m(3)). MFC with raw goethite coated anode also showed enhanced power (11 W/m(3)). Higher Coulombic efficiency (34%) was achieved in MFC-1 than control MFC-3 (13%). Decrease in mass-transport losses and higher redox current during electrochemical analyses support improved electron transfer with the use of goethite on anode. Cheaper goethite coating kinetically accelerates the electron transfer between bacteria and anode, proving to be a novel approach for enhancing the electricity generation along with organic matter removal in MFC.

Enhancing waste activated sludge digestion and power production using hypochlorite as catholyte in clayware microbial fuel cell.

Waste activated sludge was digested in anodic compartment of dual chambered clayware microbial fuel cell (MFC). Performance of MFC was evaluated using oxygen (MFC-1) and hypochlorite (MFC-2) as cathodic electron acceptors. Power production of 8.7 W/m(3) was achieved using hypochlorite as catholyte, which was two times higher than using oxygen (4.2 W/m(3)). Total chemical oxygen demand of sludge was reduced by 65.4% and 84.7% in MFC-1 and MFC-2, respectively. Total and volatile suspended solids reductions were higher in MFC-2 (75.8% and 80.2%, respectively) as compared to MFC-1 (66.7% and 76.4%, respectively). Use of hypochlorite demonstrated 3.8 times higher Coulombic efficiency (13.8%) than oxygen. Voltammetric and impedance analysis revealed increase in reduction peak (from 8 to 24 mA) and decreased polarization resistance (from 42.6 to 26.5 Ω). Hypochlorite proved to be better cathodic electron acceptor, supporting rapid sludge digestion within 8 days of retention time and improved power production in MFC.

Effective ammonium removal by anaerobic oxidation in microbial fuel cells.

Dual-chamber microbial fuel cells (MFCs), made of clayware cylinder, were operated at different chemical oxygen demands: ammonium-nitrogen (COD:NH4+) ratio (1:1, 10:1 and 5:1) under batch mode for simultaneous removal of ammonia and organic matter from wastewater. Ammonium-N removal efficiencies of 63-32.66% were obtained for COD:NH4+ ratio of 1:10, respectively. Average COD removal efficiencies demonstrated by these MFCs were about 88%; indicating effective use of MFCs for treatment of wastewater containing organic matter and high ammonia concentration. MFCs operated with COD:NH4+ ratio of 10:1 produced highest volumetric power density of 752.88 mW/m3. The ammonium-N removal slightly increased when microbes were exposed to only ammonium as a source of electron when organic source was not supplemented. When this MFC was operated with imposed potential on cathode and without aeration in the cathode chamber, oxidation of ammonium ions at a faster rate confirmed anaerobic oxidation. During the non-turnover condition of cyclic voltammetry, MFC operated with COD:NH4+ ratio of 10:1 gave higher oxidative and reductive currents than MFC operated with COD:NH4+ ratio of 1:1 due to higher redox species. Successful application of such an anammox process for ammonium oxidation in MFCs will be useful for treatment of wastewater containing higher ammonium concentration and harvesting energy in the form of electricity.