Investigating the role of anodic potential in the biodegradation of carbamazepine in bioelectrochemical systems

Unravelling the mechanisms of organic micropollutant removal in bio-electrochemical systems: Insights into sorption, electrochemical degradation, and biodegradation processes

Bio-electrochemical systems (BESs) have recently been proposed as an efficient treatment technology to remove organic micropollutants from water treatment plants. In this study, we aimed to differentiate between sorption, electrochemical transport/degradation, and biodegradation. Using electro-active microorganisms and electrodes, we investigated organic micropollutant removal at environmentally relevant concentrations, clarifying the roles of sorption and electrochemical and biological degradation. The role of anodic biofilms on the removal of 10 relevant organic micropollutants was studied by performing separate sorption experiments on carbon-based electrodes (graphite felt, graphite rod, graphite granules, and granular activated carbon) and electrochemical degradation experiments at two different electrode potentials (-0.3 and 0 V). Granular activated carbon showed the highest sorption of micropollutants; applying a potential to graphite felt electrodes increased organic micropollutant removal. Removal efficiencies >80 % were obtained for all micropollutants at high anode potentials (+0.955 V), indicating that the studied compounds were more susceptible to oxidation than to reduction. All organic micropollutants showed removal when under bio-electrochemical conditions, ranging from low (e.g. metformin, 9.3 %) to exceptionally high removal efficiencies (e.g. sulfamethoxazole, 99.5 %). The lower removal observed under bio-electrochemical conditions when compared to only electrochemical conditions indicated that sorption to the electrode is key to guarantee high electrochemical degradation. The detection of transformation products of chloridazon and metformin indicated that (bio)-electrochemical degradation occurred. This study confirms that BES can treat some organic micropollutants through several mechanisms, which merits further investigation.

Bio-electrochemical degradation of carbamazepine (CBZ): A comprehensive study on effectiveness, degradation pathway, and toxicological assessment

Recent attention on the detrimental effects of pharmaceutically active compounds (PhACs) in natural water has spurred researchers to develop advanced wastewater treatment methods. Carbamazepine (CBZ), a widely recognized anticonvulsant, has often been a primary focus in numerous studies due to its prevalence and resistance to breaking down. This study aims to explore the effectiveness of a bio-electrochemical system in breaking down CBZ in polluted water and to assess the potential harmful effects of the treated wastewater. The results revealed bio-electro degradation process demonstrated a collaborative effect, achieving the highest CBZ degradation compared to electrodegradation and biodegradation techniques. Notably, a maximum CBZ degradation efficiency of 92.01% was attained using the bio-electrochemical system under specific conditions: Initial CBZ concentration of 60 mg/L, pH level at 7, 0.5% (v/v) inoculum dose, and an applied potential of 10 mV. The degradation pathway established by identifying intermediate products via High-Performance Liquid Chromatography-Mass Spectrometry, revealed the complete breakdown of CBZ without any toxic intermediates or end products. This finding was further validated through in vitro and in vivo toxicity assays, confirming the absence of harmful remnants after the degradation process.

Enhanced biodegradation of perfluorooctanoic acid in a dual biocatalyzed microbial electrosynthesis system

The toxic perfluorooctanoic acid (PFOA) is widely spread in terrestrial and aquatic habitats owing to its resistance to conventional degradation processes. Advanced techniques to degrade PFOA requires drastic conditions with high energy cost. In this study, we investigated PFOA biodegradation in a simple dual biocatalyzed microbial electrosynthesis system (MES). Different PFOA loadings (1, 5, and 10 ppm) were tested and a biodegradation of 91% was observed within 120 h. Propionate production improved and short-carbon-chain PFOA intermediates were detected, which confirmed PFOA biodegradation. However, the current density decreased, indicating an inhibitory effect of PFOA. High-throughput biofilm analysis revealed that PFOA regulated the microbial flora. Microbial community analysis showed enrichment of the more resilient and PFOA adaptive microbes, including Methanosarcina and Petrimonas. Our study promotes the potential use of dual biocatalyzed MES system as an environment-friendly and inexpensive method to remediate PFOA and provides a new direction for bioremediation research.

Enhanced bio-electrochemical performance of microbially catalysed anode and cathode in a microbial electrosynthesis system

Most bio-electrochemical systems (BESs) use biotic/abiotic electrode combinations, with platinum-based abiotic electrodes being the most common. However, the non-renewability, cost, and poisonous nature of such electrode systems based on noble metals are major bottlenecks in BES commercialisation. Microbial electrosynthesis (MES), which is a sustainable energy platform that simultaneously treats wastewater and produces chemical commodities, also faces the same problem. In this study, a dual bio-catalysed MES system with a biotic anode and cathode (MES-D) was tested and compared with a biotic cathode/abiotic anode system (MES-S). Different bio-electrochemical tests revealed improved BES performance in MES-D, with a 3.9-fold improvement in current density compared to that of MES-S. Volatile fatty acid (VFA) generation also increased 3.2-, 4.1-, and 1.8-fold in MES-D compared with that in MES-S for acetate, propionate, and butyrate, respectively. The improved performance of MES-D could be attributed to the microbial metabolism at the bioanode, which generated additional electrons, as well as accumulative VFA production by both the bioanode and biocathode chambers. Microbial community analysis revealed the enrichment of electroactive bacteria such as Proteobacteria (60%), Bacteroidetes (67%), and Firmicutes + Proteobacteria + Bacteroidetes (75%) on the MES-S cathode and MES-D cathode and anode, respectively. These results signify the potential of combined bioanode/biocathode BESs such as MES for application in improving energy and chemical commodity production.

Carbamazepine degradation and genome sequencing of a novel exoelectrogen isolated from microbial fuel cells

Extracellular electron transfer and pharmaceutical products degradation mechanisms of electrochemical active microbial are helpful in optimizing electricity generation and biotoxic contaminants removal for microbial fuel cells (MFCs). An exoelectrogenic bacterial strain (designated as LYK-6) capable of degrading carbamazepine was first isolated from MFCs operated with carbamazepine as unique fuel. The strain LYK-6 was identified as the member of Pseudomonas genus according to morphological characteristics and 16S rRNA gene sequence analysis. Carbamazepine degradation rate of the strain LYK-6 was determined as 56.28% in inorganic salt medium using carbamazepine as sole carbon source. There were two oxidation peaks located at -0.044 V and 0.288 V revealed with differential pulse voltammetry analysis of the strain LQK-6. The maximum voltage of MFCs inoculated the strain LYK-6 reached to 187 mV when the MFCs fed with carbamazepine. The complete genome of the strain LYK-6 was of 4,454,672 bp in length and encoding 4209 protein genes. Genome annotation and functional gene analysis showed that the strain LYK-6 had significant genes encoding proteins responsible for the degradation of carbamazepine. The results demonstrated that the strain LYK-6 was promising application for the treatment of carbamazepine contaminant water by MFCs. This finding increases the known diversity of exoelectrogens.

Integration of microbial electrochemical systems and photocatalysis for sustainable treatment of organic recalcitrant wastewaters: Main mechanisms, recent advances, and present prospects

In recent years, microbial electrochemical systems (MESs) have demonstrated to be an environmentally friendly technology for wastewater treatment and simultaneous production of value-added products or energy. However, practical applications of MESs for the treatment of recalcitrant wastewater are limited by their low power output and slow rates of pollutant biodegradation. As a novel technology, hybrid MESs integrating biodegradation and photocatalysis have shown great potential to accelerate the degradation of bio-recalcitrant pollutants and increase the system output. In this review, we summarize recent advances of photo-assisted MESs for enhanced removal of recalcitrant pollutants, and present further discussion about the synergistic effect of biodegradation and photocatalysis. In addition, we analyse in detail different set-up configurations, discuss mechanisms of photo-enhanced extracellular electron transfer, and briefly present ongoing research cases. Finally, we highlight the current limitations and corresponding research gaps, and propose insights for future research.

Enhanced metronidazole removal by binary-species photoelectrogenic biofilm of microaglae and anoxygenic phototrophic bacteria

High efficient removal of antibiotics during nutriments recovery for biomass production poses a major technical challenge for photosynthetic microbial biofilm-based wastewater treatment since antibiotics are always co-exist with nutriments in wastewater and resist biodegradation due to their strong biotoxicity and recalcitrance. In this study, we make a first attempt to enhance metronidazole (MNZ) removal from wastewater using electrochemistry-activated binary-species photosynthetic biofilm of Rhodopseudomonas Palustris (R. Palustris) and Chlorella vulgaris (C. vulgaris) by cultivating them under different applied potentials. The results showed that application of external potentials of -0.3, 0 and 0.2 V led to 11, 33 and 26-fold acceleration in MNZ removal, respectively, as compared to that of potential free. The extent of enhancement in MNZ removal was positively correlated to the intensities of photosynthetic current produced under different externally applied potentials. The binary-species photoelectrogenic biofilm exhibited 18 and 6-fold higher MNZ removal rate than that of single-species of C. vulgaris and R. Palustris, respectively, due to the enhanced metabolic interaction between them. Application of an external potential of 0V significantly promoted the accumulation of tryptophan and tyrosine-like compounds as well as humic acid in extracellular polymeric substance, whose concentrations were 7.4, 7.1 and 2.0-fold higher than those produced at potential free, contributing to accelerated adsorption and reductive and photosensitive degradation of MNZ.

A mini review on bio-electrochemical systems for the treatment of azo dye wastewater: State-of-the-art and future prospects

Azo dyes are typical toxic and refractory organic pollutants widely used in the textile industry. Bio-electrochemical systems (BESs) have great potential for the treatment of azo dyes with the help of microorganisms as biocatalysts and have advanced significantly in recent years. However, the latest and significant advancement and achievements of BESs treating azo dyes have not been reviewed since 8 years ago. This review thus focuses on the recent investigations of BESs treating azo dyes from the year of 2013-2020 in order to broaden the knowledge and deepen the understanding in this field. In this review, azo dyes degradation mechanisms of BESs are first elaborated, followed by the introduction of BES configurations with the emphasis on the novelties. The azo dye degradation performance of BESs is then presented to demonstrate their effectiveness in azo dye removal. Effects of various operating parameters on the overall performance of BESs are comprehensively elucidated, including electrode materials, external resistances and applied potentials, initial concentrations of azo dyes, and co-substrates. Predominant microorganisms responsible for degradation of azo dyes in BESs are highlighted in details. Furthermore, the combination of BESs with other processes to further improve the azo dye removal are discussed. Finally, an outlook on the future research directions and challenges is provided from the viewpoint of realistic applications of the technology.

Microbial Electrochemical Fluidized Bed Reactor: A Promising Solution for Removing Pollutants From Pharmaceutical Industrial Wastewater

The capacity of electroactive bacteria to exchange electrons with electroconductive materials has been explored during the last two decades as part of a new field called electromicrobiology. Such microbial metabolism has been validated to enhance the bioremediation of wastewater pollutants. In contrast with standard materials like rods, plates, or felts made of graphite, we have explored the use of an alternative strategy using a fluid-like electrode as part of a microbial electrochemical fluidized bed reactor (ME-FBR). After verifying the low adsorption capacity of the pharmaceutical pollutants on the fluid-bed electrode [7.92 ± 0.05% carbamazepine (CBZ) and 9.42 ± 0.09% sulfamethoxazole (SMX)], our system showed a remarkable capacity to outperform classical solutions for removing pollutants (more than 80%) from the pharmaceutical industry like CBZ and SMX. Moreover, the ME-FBR performance revealed the impact of selecting an anode potential by efficiently removing both pollutants at + 200 mV. The high TOC removal efficiency also demonstrated that electrostimulation of electroactive bacteria in ME-FBR could overcome the expected microbial inhibition due to the presence of CBZ and SMX. Cyclic voltammograms revealed the successful electron transfer between microbial biofilm and the fluid-like electrode bed throughout the polarization tests. Finally, Vibrio fischeri-based ecotoxicity showed a 70% reduction after treating wastewater with a fluid-like anode (+ 400 mV), revealing the promising performance of this bioelectrochemical approach.

Enhanced product selectivity in the microbial electrosynthesis of butyrate using a nickel ferrite-coated biocathode

Microbial electrosynthesis (MES) is a potential sustainable biotechnology for the efficient conversion of carbon dioxide/bicarbonate into useful chemical commodities. To date, acetate has been the main MES product; selective electrosynthesis to produce other multi-carbon molecules, which have a higher commercial value, remains a major challenge. In this study, the conventional carbon felt (CF) was modified with inexpensive nickel ferrite (NiFe₂O₄@CF) to realize enhanced butyrate production owing to the advantages of improved electrical conductivity, charge transfer efficiency, and microbial-electrode interactions with the selective microbial enrichment. Experimental results show that the modified electrode yielded 1.2 times the butyrate production and 2.7 times the cathodic current production of the CF cathode; product selectivity was greatly improved (from 37% to 95%) in comparison with CF. Microbial community analyses suggest that selective microbial enrichment was promoted as Proteobacteria and Thermotogae (butyrate-producing phyla) were dominant in the NiFe₂O₄@CF biofilm (~78%). These results demonstrate that electrode modification with NiFe₂O₄ can help realize greater selective carboxylate production with improved MES performance. Hence, this technology is expected to be greatly useful in future reactor designs for scaled-up technologies.

Nickel ferrite/MXene-coated carbon felt anodes for enhanced microbial fuel cell performance

In recent years, the modification of electrode materials for enhancing the power generation of microbial fuel cells (MFCs) has attracted considerable attention. In this study, a conventional carbon felt (CF) electrode was modified by NiFe₂O₄ (NiFe₂O₄@CF), MXene (MXene@CF), and NiFe₂O₄-MXene (NiFe₂O₄-MXene@CF) using facile dip-and-dry and hydrothermal methods. In these modified CF electrodes, the electrochemical performance considerably improved, while the highest power density (1385 mW/m²), which was 5.6, 2.8, and 1.4 times higher than those of CF, NiFe₂O₄@CF, and MXene@CF anodes, respectively, was achieved using NiFe₂O₄-MXene@CF. Furthermore, electrochemical impedance spectroscopy and cyclic voltammetry results confirmed the superior bioelectrochemical activity of a NiFe₂O₄-MXene@CF anode in a MFC. The improved performance could be attributed to the low charge transfer resistance, high conductivity and number of catalytically active sites of the NiFe₂O₄-MXene@CF anode. Microbial community analysis demonstrated the relative abundance of electroactive bacteria on a NiFe₂O₄-MXene@CF anodic biofilm rather than CF, MXene@CF, and NiFe₂O₄@CF anodes. Therefore, these results suggest that combining the favorable properties of composite materials such as NiFe₂O₄-MXene@CF anodes can open up new directions for fabricating novel electrodes for renewable energy-related applications.

Biodegradation of Emerging Pharmaceuticals from Domestic Wastewater by Membrane Bioreactor: The Effect of Solid Retention Time

Although conventional biological treatment plants can remove basic pollutants, they are ineffective at removing recalcitrant pollutants. Membrane bioreactors contain promising technology and have the advantages of better effluent quality and lower sludge production compared to those of conventional biological treatment processes. In this study, the removal of pharmaceutical compounds by membrane bioreactors under different solid retention times (SRTs) was investigated. To study the effect of SRT on the removal of emerging pharmaceuticals, the levels of pharmaceuticals were measured over 96 days for the following retention times: 20, 30, and 40-day SRT. It was found that the 40-day SRT had the optimum performance in terms of the pharmaceuticals’ elimination. The removal efficiencies of the chemical oxygen demand (COD) for each selected SRT were higher than 96% at steady-state conditions. The highest degradation efficiency was observed for paracetamol. Paracetamol was the most removed compound followed by ranitidine, atenolol, bezafibrate, diclofenac, and carbamazepine. The microbial community at the phylum level was also analyzed to understand the biodegradability of pharmaceuticals. It was noticed that the Proteobacteria phylum increased from 46.8% to 60.0% after 96 days with the pharmaceuticals. The Actinobacteria class, which can metabolize paracetamol, carbamazepine, and atenolol, was also increased from 9.1% to 17.9% after adding pharmaceuticals. The by-products of diclofenac, bezafibrate, and carbamazepine were observed in the effluent samples.

MnCo2O4 coated carbon felt anode for enhanced microbial fuel cell performance

A highly efficient anode is very crucial for an improved microbial fuel cell (MFC) performance. In this study, a binder-free manganese cobalt oxide (MnCo₂O₄@CF) anode was synthesized using a conventional carbon felt (CF) by a facile hydrothermal method. A large electrochemically active and rough electrode surface area of MnCo₂O₄@CF anode improved the substrate fluxes and microbial adhesion/growth. Furthermore, the electrochemical tests on the synthesized anode confirmed the superior bioelectrochemical activity, reduced ion transfer resistance, and excellent capacitance. This resulted in an improved power density (945 mW/m²), which was 3.8 times higher than that of CF anode. The variable valence state, high stability and biocompatibility of MnCo₂O₄@CF resulted in continuous current density performance for five MFC cycles. High-throughput biofilm analysis revealed the enrichment of electricity producing phylum of Proteobacteria and Bacteroidetes (∼90.0%), which signified that the modified MnCo₂O₄ anode accelerated the enrichment of electro-active microbes.

Carbamazepine removal from wastewater and the degradation mechanism in a submerged forward osmotic membrane bioreactor

A submerged forward osmotic membrane bioreactor (FOMBR) was used to reveal the removal and degradation mechanism of carbamazepine (CBZ) from wastewater. The results showed that the removal mechanism consisted of the rejection of the forward osmotic (FO) membrane and biodegradation of the activated sludge. The removal efficiencies of COD, NH₄⁺-N, and CBZ by the FOMBR were approximately 94.77%-97.45%, 93.56%-99.28%, and 88.20%-94.45%, respectively. Moreover, the COD and NH₄⁺-N removal efficiencies were positively correlated with the increased CBZ concentrations. The results of the soluble microbial products (SMP) and extracellular polymeric substances (EPS) tests illustrated that the membrane fouling potential of EPS may be higher than that of SMP. According to the identified 14 degradation products, oxidation, hydroxylation, and decarboxylation were defined as the primary CBZ degradation mechanism. In addition, the RNA results showed that Delftia could be the characteristic bacteria in the CBZ degradation process.