Bivalves and bivalve shells have been suggested as possible approaches for wastewater treatment, but comparison of the efficiency of both approaches under similar conditions is rarely reported. In this context, this study aims to assess the efficiency of clams and clam shells (fresh and dry) of the bivalve Corbicula fluminea in removing pharmaceutical contaminants from urban wastewater and in decreasing its environmental hazardous potential. Experiments were conducted under batch conditions using secondary effluent from an urban wastewater treatment plant (WWTP). To evaluate the efficacy of these processes in reducing the environmental hazardous potential of treated wastewater, an integrative approach was adopted, encompassing chemical removal, physicochemical alterations, and ecotoxicological effects. Both approaches increased pH and pronouncedly increased inorganic carbon, whereas decreased total suspended solids; fresh shells increased turbidity. The bulk removal of the quantified compounds varied as follows: fresh shells (34%) > clams 24 h and clams 48 h (30%) > dry shells (20%) > aeration (2%). The compounds removed to a larger extent were acetaminophen (> 77%) and atenolol acid (> 69%). Both approaches caused minor changes in the toxicity of the wastewater to daphnids, microalgae and lettuce. The results suggest that shell-based removal of contaminants might have better applicability in wastewater treatment than clams, especially considering the challenges of maintaining these organisms in real treatment settings.

Pharmaceutical residues are persistent contaminants that resist conventional wastewater treatment and can disrupt ecosystems; however, microorganisms provide a promising biobased solution to transform or mineralize these complex xenobiotics. Whether pollutant-adapted communities maintain their degradative capacity under realistic environmental conditions remains a long-standing debate in environmental biotechnology. Here, microbial consortia enriched in six membrane bioreactors under high pharmaceutical concentration (100 mg/L) retained full biodegradation capacity across a 5000-fold concentration range. After prolonged exposure to six model compounds (atenolol, caffeine, diclofenac, enalapril, ibuprofen, and paracetamol) complete removal occurred for all except diclofenac. Degradation remained efficient even at lower and environmentally relevant concentrations (1 mg/L-20 µg/L) and recovered rapidly upon re-exposure to higher loads (100 mg/L). Metagenomic profiling revealed enrichment of oxygenase-mediated catabolic pathways supporting this resilience. When transferred to a 7 liters bioreactor treating real wastewater, the adapted community removed targeted and untargeted pharmaceuticals, demonstrating robustness, scalability, and strong potential for sustainable micropollutant remediation.

This study developed an electrocoagulation (EC) system using recycled aluminum can tabs (AlCT) as sacrificial anodes and systematically evaluated its applicability for treating brewery wastewater (BWW) and the effluents from purple phototrophic bacteria (PPB) reactor. The results showed that the AlCT EC system achieved efficient removal of color, turbidity, total suspended solid (TSS), and phosphate under optimal conditions of 1.4 A and 60 min. Further optimization of pH, conductivity, and electrode spacing (respectively 5, 5.5 mS/cm, and 3 cm) improved energy efficiency. Three intensification strategies of the AlCT EC system markedly enhanced system performance: 1) Aluminum sludge powder (AlSP) seeding promoted heterogeneous nucleation of Al(OH)3 flocs and enhanced phosphorus fixation; 2) The Ti-AlCT composite anode improved current distribution and suppressed anodic passivation; and 3) The dual-anode/dual-cathode parallel configuration (DE Ti-AlCT EC) reduced ohmic loss, enabling maximum removal capacity at an energy consumption as low as 7.5 kWh/m3. The attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR) analyses helped the understanding of the coexistence of adsorption, bridging, and sweep-flocculation mechanisms. Overall, AlCT demonstrates strong potential as a waste-derived electrode material, providing key role in effective pollutant removal and improved energy efficiency in AlCT EC system. Accordingly, the AlCT EC system offers a practical engineering pathway for advanced industrial wastewater treatment via the concept of “Waste-to-Treat-Waste”.

Bioelectrochemical systems provide a platform for microbial CO2 reduction to organic compounds such as acetate or methane. However, their performance is limited by low CO2 solubility, mass transfer limitations, and significant pH gradients at electrode surfaces. Recently, Microbial Electrochemical Fluidized Bed Reactors (ME-FBRs) have emerged as an alternative configuration to mitigate these limitations. ME-FBR uses electroconductive particles as fluidized electrodes for enhancing surface area, mixing, mass transfer, and microbe–electrode interactions.This review covers current knowledge on CO2 fixation in ME-FBR, including similar concepts like moving electrodes, slurry electrodes, and capacitor granular beds. The conductive material is key, and activated carbon showed promise; however, chemical modifications of alternative materials (e.g. glassy carbon) are opening new opportunities to improve electron transfer and catalytic performance.Finally, the use of ME-FBR for growing autotrophic photosynthetic microorganisms like purple phototrophic bacteria expands the scope of biorefinery applications from CO2.

This study investigates whether bioelectrochemical stimulation can redirect electron flow in the purple phototrophic bacteria Rhodopseudomonas palustris 42OL to enhance the production of biomass, bio‑hydrogen (H₂), and polyhydroxybutyrate (PHB). R. palustris 42OL was cultivated in a single-chamber bioelectrochemical system (BES) fed with brewery wastewater under cathodic potentials of -0.3, -0.6, and - 0.8 V (vs Ag/AgCl). Metabolic shifts were evaluated by RT-qPCR targeting three key genes: nifH (responsible for H2 evolution via nitrogenase), phaC (which regulates PHB synthesis), and rbcL (which controls carbon fixation and biomass growth). Results demonstrate that polarization at -0.3 and - 0.6 V (vs Ag/AgCl) significantly enhances system performance. Biomass production peaked at -0.3 V (0.91 g/L), representing a 60% increase over the electrode-free control. Polarization at -0.6 V maximized byproduct generation, yielding 70.35 mL H2/L (a 511% increase compared to the control) and 115.3 mg PHB/g VSS (a 250% increase). Molecular expression supported these trends, revealing that applied potentials actively regulate intracellular electron partitioning. These findings demonstrate that controlled cathodic stimulation is a powerful tool for directing microbial metabolism toward targeted resource recovery. This proof of concept provides the essential foundation for future research and a possible scale-up, advancing the transition toward sustainable wastewater valorization.

Biorefineries offer a sustainable model that supports circular economy and nutrient recovery from waste feedstocks. Biorefineries were centered on microalgae for biomass and biofuel generation, but the concept has shifted toward inclusion of more versatile microorganisms to cope with diversity of waste substrates. Purple phototrophic bacteria (PPB) are particularly interesting, as they can treat wastewater while producing biomass, polyhydroxybutyrate (PHB), and carotenoids. Furthermore, PPB can utilize electrodes as extracellular electron donors, enhancing the synthesis of these products. Additionally, electrochemical moving bed reactors have been shown to improve PHB production by supporting electroactivity in planktonic cells. In this study, a photo microbial electrochemical moving bed reactor (photoME-MBR) was scaled up from 250 mL to 50 L, which constitutes the largest example for a bioelectrochemically-assisted PPB case study. The new configuration was operated under cathodic conditions to assess biomass, PHB, and carotenoid production; brewery wastewater treatment efficiency, and bioelectrochemical performance. Synthesis of value-added products at pilot scale was comparable to laboratory-scale productivity, while achieving organic pollutants removal at a rate of 136 gTOC/m3·d. Cathodic polarization significantly enhanced PHB production (100 mgPHB/gDryBiomass) by promoting extracellular electron uptake from the conductive bed. Microbial community analysis identified Rhodopseudomonas sp. and Bradyrhizobium sp. as dominant genera.

The Microbial Desalination Cell (MDC) is an energy self-sufficient and sustainable technology that can simultaneously address wastewater treatment, bioenergy production, and water desalination in a single device. The technology has arisen from the combination of membrane-based technology, such as an electrodialysis cell, with a microbial fuel cell, in which a third chamber has been added to act as a desalination chamber. In this sense, MDCs are based on microbial electrochemical technology, in which biological wastewater treatment can be coupled to the desalination of a saline stream using ion exchange membranes without external energy input. The scaling-up of MDC technology is still a challenging process, and more pilot-scale studies are needed to ensure proper implementation for real applications (i.e. urban or industrial wastewater). This work discusses the main factors in MDC performance affecting the scaling-up and the outcomes from reported attempts for developing pilot-plants based on MDC technology.

The integration of microbial electrochemical technologies (MET) into treatment wetland (TW) led to a new generation of nature-based solution so-called METland (R). In this context, METland (R) concept was further expanded to modular METland (R) while a comprehensive evaluation of a demo scale is reported for the treatment of real domestic wastewater. The overall treatment system included the following METland biofilter configurations: i) a horizontal flow modular unit, ii) a downflow unit made of EC coke, and iii) a downflow unit made of EC biochar. This hybrid treatment system aims to enhance pollutant removal efficiency through MET, leveraging the conductive properties of substrates to optimize microbial metabolic processes. The system exhibited high COD removal efficiency (>90 %) regardless of high feeding rate (ca. 0.5m(3)/m(2)day) and significant nitrogen removal, with the EC biochar-based biofilter (ECBB) unit showing high ammonia removal efficiency (90 %). Standard treatment wetlands do not incorporate tools for monitoring the in situ performance of the systems. However, the electrochemical nature of the METland (R) allows continuous monitoring by measuring electrochemical parameters. In this context, electric potential (EP) measurements revealed spatial variations in electron utilization within the wetland, correlating with pollutant degradation. The electron current density (J = 43.99 mA/m(2)) within the system decreased along the flow path, indicating a consistent electrochemical activity aligned with the treatment process. High correlations between J values and COD concentrations suggest the potential use of electrochemical indicators as proxies for pollutant levels in wastewater treatment. This study gives insights into the electrochemical behavior of the system to provide a foundation for future optimization.

The decomposition of buried straw in rice fields during post-harvest generates volatile fatty acids (VFA), thus activating methanogenesis (1). In this study, bioelectrochemical biosensors were used to measure the in-situ electrical current produced by electroactive microorganisms, related to the biodegradation of buired straw, in outdoor mesocosms containing rice paddy soil from the Ebro Delta (Spain) .Three biosensors (BS1-BS3), based on bioelectrochemical cells buried in the water saturated soil (at a -10 cm), were used in 3 rice paddy soil mesocosms, with a poised working electrode (graphite) potential at +0.2V vs Ag/AgCl, by using a potentiostat. During 5 months (November 2022-March 2023), the production of electrical current (I) in the soil mesocosms was monitored using chronoamperometry. The presence of electroactive microbial biofilms on the electrodes was assessed by cyclic voltammetry (CV). Simultaneously, soil chemical parameters were monitored (total and soluble COD, VFA and CH4 emission), and microbial diversity (bacteria and archaea) in the soil and the electrodes biofilms was assessed by 16S rRNA-metabarcoding.Chronoamperometry data in BS1-BS3 showed a marked current production curve from the day 3 to 5 after straw addition, with an I max of 110-180µA (4.26-6.91 µA cm-2) at day 10, remaining higher than the baseline for 30-45 days, and concomitant with VFA accumulation (69-28 mg-eq Acetic kg-1 soil , 7-40 days) and a high emission rate of CH4 (198.1±101.0 mg C-CH4· m-2 soil · h-1 7 days after straw addition. The CV revealed electroactive profiles in the 3 biosensors, similar in BS1-BS2 (oxidation peak -0.16/-0.22 V vs Ag/AgCl, similar to Geobacter), and different in BS3 (oxidation peak +0.26 V vs Ag/AgCl), revealing different electroactive microbial communities. 16S-based metataxonomy revealed an enrichment of well known electroactive bacteria on the three anode biofilm but with different relative predominances, encompassing mainly Desulfobulbus in BS1-BS3, Geobacter mainly in BS1, but in less predominance in BS2 and BS3, Proteiniclasticum solely in BS3, and Clostridium in BS2 and BS3. Methanogenic archaea such as Methanosarcina and Methanobacterium were also depicted on the anode, but at lower relative abundance than observed in the soil, where ammonium oxidizing archaea (Nitrososphaera and candidatus Nitrosocaldus) were also predominant.The results showed the capacity of the bioelectrochemical-based biosensors for real time detection of microbial in-situ degradation processes of buried edible organic carbon (straw) in the soil of rice paddy fields, also linked to methane emissions.AknowledgementsThis research was funded by Agencia Estatal de Investigación (PID2019-111572RB-I00/AEI/10.13039/501100011033 ) from Spain. References1. Martínez-Eixarch, M., Alcaraz, C., Viñas, M., Noguerol, J., Aranda, X., Prenafeta-Boldú, F. X., Saldaña-De la Vega, J.A., Català, M.M. & Ibáñez, C. (2018). Neglecting the fallow season can significantly underestimate annual methane emissions in Mediterranean rice fields. PLoS One, 13(5), e0198081. DOI: 10.1371/journal.pone.0202159

Microbial Electrochemical Fluidized Reactors (ME-FBR) changed the paradigm for growing electroactive bacteria from a biofilm strategy to a planktonic mode, while still performing direct extracellular electron transfer from oxidative metabolism in absence of redox mediators. Glassy carbon was the material selected for growing planktonic Geobacter sulfurreducens in ME-FBR. However, the material was unable to retain cells so applications implying continuous operation have been compromised. In this context, a tailor-made chemical strategy was followed considering the large amount of cytochromes C present on the outermost membrane of bacteria form of the Geobacter genus. In this work, a commercial glassy carbon (GC) was chemically modified with surface oxygen groups (SOGs) mainly carboxylic type with high affinity for heme group of cytochrome C. The functionalized material did conserve the structural and textural features and i) promoted the biofilm formation of Geobacter using acetate as sole carbon and electron donor source, and ii) increased the current density and acetate removal rate in comparison with pristine carbon. Thus, the new material enriched in carboxylic-type SOGs facilitates a-la-carte anchorage of electroactive bacteria to move on from a planktonic-based to a biofilm-based strategy, so ME-FBR operation could be expanded from batch to continuous mode, while electrical current was still possible.

Due to its metabolic versatility, mixed communities of purple phototrophic bacteria could be exploited for production of added value products using an electrode as electron donor. Indeed, microbial electrosynthesis has already been proved as a suitable strategy for polyhydroxybutyrate production under photoautotrophic conditions. In contrast with classical biofilm-based electromicrobiology studies, fluid-like electrodes can tune planktonic microbial metabolism to enhance biodegradation rates in brewery wastewater. In this work we have explored polyhydroxybutyrate production in a mixed community enriched from brewery wastewater using a photo-microbial electrochemical moving bed reactor (photoME-MBR). The bioelectrochemical reactor was operated under cathodic conditions (-0.8 V vs Ag/AgCl) with acetate as carbon source as a mean to evaluate i) PHB production and ii) bioelectrochemical performance. We observed how a cathodic polarization of the moving electrode played a key role on PHB production stimulating both direct microbial electron uptake from the conductive bed and electrochemically produced hydrogen in the vicinity of the current collector. Overall, the polarized reactor outperformed the non-polarized reactor by four-fold regarding PHB production rate. In addition, microbial communities analysis revealed Rhodopseudomonas sp. and Bradyrhizobium sp. as main genera in combination with other electroactive genera like Geosporobacter sp. This work revealed that cathodic moving beds could present a feasible platform for biorefineries and added value products production.

Anthropogenic contamination with petroleum hydrocarbons is a serious environmental problem. Especially dramatic is the case of environments limited in electron acceptors because, natural attenuation is not sufficient to cope with contamination that remains persistent. Groundwater pollution by oil spills has attracted an ever-growing interest in a water scarcity scenario due to global warming. The surveillance of risk sites through monitoring tools is the most suitable strategy for prevention. In this work we have investigated the detection of contaminants derived from oil industry, BTEX and ETBE, in groundwater by means of a microbial electrochemical sensor. For this purpose, we use a biosensor (polarized at 0.6 V) immersed in artificial groundwater: i) at microcosm scale and ii) at mesocosm scale. Detection of BTEX was tested separately in biosensors at microcosm scale, showing a clear response in electrical current after exposure to contaminants. The response observed in presence of BTEX and ETBE was significant and fast (<2 h) by this biosensor. Additionally, microbial community analysis was performed on the anodic biofilm after BTEX exposure. The results show two main groups of microorganisms: electroactive and hydrocarbon-degrading bacteria. This suggests that the microbial community could play an important role in the biosensor performance.

The shift towards sustainable wastewater treatment focuses on nutrient recovery through biorefineries, highlighting the importance of microalgae, cyanobacteria, and, more recently, purple phototrophic bacteria for their metabolic flexibility and adaptability. Activated sludge has been the primary strategy for wastewater treatment worldwide for the last century. The efficiency of this process has improved the quality of life and reduced the impact of wastewater on the ecosystem by preventing eutrophication processes. However, given the energetic demand for wastewater treatment, the strategy is now shifting towards nutrient recovery from wastewater instead of pollutant removal (Verstraete et al., 2009).

Abstract Microbial electrosynthesis (MES) constitutes a bioelectrochemical process where bacteria uptake electrons extracellularly from a polarized electrode to incorporate them into their anabolic metabolism. However, the efficiency of current MES reactor designs can be lower than expected due to limitations regarding electron transfer and mass transport. One of the most promising bioreactor configurations to overcome these bottlenecks is the Microbial Electrochemical Fluidized Bed Reactor (ME‐FBR). In this study, microbial CO2 fixation is investigated for the first time in a ME‐FBR operated as a 3‐phase reactor (solid–liquid–gas). An electroconductive carbon bed, acting as a working electrode, was fluidized with gas and polarized at different potentials (−0.6, −0.8 and −1 V vs. Ag/AgCl) so it could act as an electron donor (biocathode). Under these potentials, CO2 fixation and electron transfer were evaluated. Autotrophic electroactive microorganisms from anaerobic wastewater were enriched in a ME‐FBR in the presence of 2‐bromoethanosulfonic acid (BES) to inhibit the growth of methanogens. Cyclic voltammetry analysis revealed interaction between the microorganisms and the cathode. Furthermore, volatile fatty acids like propionate, formate and acetate were detected in the culture supernatant. Acetate production had a maximum rate of ca. 1 g L−1 day−1. Planktonic cell biomass was produced under continuous culture at values as high as ca. 0.7 g L−1 dry weight. Overall, this study demonstrates the feasibility of employing a fluidized electrode with gaseous substrates and electricity as the energy source for generating biomass and carboxylic acids.

Expanded graphite (EG) electrodes gather several advantages for their utilization in microbial electrochemical technologies (MET). Unfortunately, the low microbial electroactivity makes them non-practical for implementing them as electrodes. The objective of this work is to explore the enhancement of microbial electroactivity of expanded graphite (commercial PV15) through the generation of nanopores by CO2 treatment. The changes in properties were thoroughly analysed by TG, XRD, Raman, XPS, gas adsorption, SEM and AFM, as well as microbial electroactivity in the presence of Geobacter sulfurreducens. Nanopores remarkably enhance the microbially derived electrical current (60-fold increase). Given the inaccessibility of micron-sized bacteria to these nanopores, it is suggested that the electric charge exchanged by electroactive microorganisms might be greatly affected by the capability of the electrode to compensate these charges through ion adsorption. The increased microbial current density produced on activated PV15 opens the possibility of using such materials as promising electrodes in MET.

Constructed Wetlands (CWs) were widely used as nature-based solution to effectively remove contaminants from wastewater, while offering benefits for ecological value and landscape services. However, one limited factor for practical applications of CW technology is the conventional construction style, which is a laborious and complex civil engineering. As such, an idea of modular CW (MCW) was proposed and embodiment was made for different scales of treatment wetland projects. This paper introduces the MCW concept and the efforts made to realize it. MCW is a revolutionary approach in wastewater treatment that combines efficiency, adaptability, and environmental sustainability. MCW represents a paradigm shift from traditional CWs, offering a pre-fabricated, modular solution that simplifies the complexities of civil engineering in wastewater management. These prefabricated modular structures, assembled off-site and installed on-site, provide a streamlined, flexible, and user-friendly alternative to conventional CWs. The innovative design of MCWs incorporates advanced substrates and technologies, integrating enhanced processes such as intermittent aeration, tidal flow, and circulating reflux. This novel approach significantly improves pollutant removal efficiency, reduces land usage, and addresses clogging issues through rapid module replacement. The paper comprehensively delved into the structural, substrate, plant, and operational aspects of MCWs. It highlights the environmental and economic benefits of MCWs, emphasizing their role as a cost-effective, environmentally-friendly solution for wastewater treatment. The study concludes by underscoring the potential of MCWs in spearheading new research and development in sustainable wastewater management, marking a new generation in CW systems.

The cost-effective and environmentally friendly substrates play an important role in functioning constructed wetlands (CWs). This study innovatively composes aluminum sludge and polyurethane under the action of a catalyst to develop a novel lightweight substrate (Al-NLS), which is expected to be used as a main substrate in CWs. The driving force of it lies in reducing construction costs of CWs in practice, while offering a flexible and considerably efficient substrate in CW. The bulk density of the resultant Al-NLS was apparently reduced by about 80 % compared with common substrate of gravel. The static adsorption experiments showed that the adsorption behavior of Al-NLS on phosphorus (P) was in accordance with Langmuir isotherm (with maximum P adsorption capacity of 1.12 mg/g,) and quasi-second-order kinetic models. The use of Al-NLS as a single stage wetland substrate to treat real domestic wastewater has favorable removal efficiencies of COD (65.9-74.3 %), TP (86.9-98.6 %), NH4+-N (61.1-52.2 %) and TN (35.4-45.6 %). The mechanisms of P removal onto Al-NLS were examined by various physiochemical characterizations of Al-NLS and raw alum sludge, which revealed that P adsorption was via forming Hydroxy-Al by ion exchange. In addition, high throughput sequencing analysis revealed that Al-NLS had positive impact on the richness and diversity of microbial community for pollutants removal, while the abundance of key functional bacteria such as proteobacteria and bacteroidota was higher in the longer retention time of CW (HRT = 2 days). These results indicated that Al-NLS could be used as a new alternative substrate in CWs technology.

Electrobioremediation is one of the most innovative disciplines for treating organic pollutants and it is based on the ability of electroactive bacteria to exchange electrons with electroconductive materials. Electroactive biofilters have been demonstrated to be efficient for treating urban wastewater with a low footprint; however, their application can be expanded for treating industrial wastewater containing significant concentrations (2.4 %vol) of commercial surfactants (containing lauryl sulfate, lauryl ether sulfate, cocamydopropyl betaine, and dodecylbenzene sulfonate, among others). Our electroactive biofilter outperformed a conventional inert biofilter made of gravel for all tested conditions, reaching removal rates as high as 4.5 kg COD/m3bed·day and withstood Organic Loading Rates as high as 9 Kg COD/m3·d without significantly affecting removal efficiency. The biomass accumulation reduced available bed volume in the electroactive biofilter just by 39 %, while the gravel biofilter decreased by 80 %. Regarding microbial communities, anaerobic and electroactive bacteria represented a substantial proportion of the total population in the electroactive biofilter. Pseudomonas was the dominant genus, while Cupriavidus, Shewanella, Citrobacter, Desulfovibrio, and Arcobacter were potential electroactive strains found in relevant proportions. The microbial community’s composition might be the key to understanding how high removal rates can coexist with limited biomass production, making electroactive biofilters a promising strategy to overcome classical biofilter limitations.