Photocathode optimization and microbial community in the solar-illuminated bio-photoelectrochemical system for nitrofurazone degradation

Enhanced degradation of tetracycline under natural sunlight through the synergistic effect of Ag3PO4/MIL-101(Fe) photocatalysis and Fenton catalysis: Mechanism, pathway, and toxicity assessment

Here, we show that the adverse environmental and health effects of tetracycline (TC) can be efficiently reduced by encapsulating Ag₃PO₄ into MIL-101(Fe) to construct a Ag₃PO₄/MIL-101(Fe) heterojunction composite through advanced oxidation processes, such as Fenton catalysis, photocatalysis, and photo-Fenton catalysis. Notably, the reaction can be driven by natural sunlight and does not require any artificial energy source. Remarkably, the optimal degradation of TC can be achieved under different compositions of the composite system through photocatalysis and photo-Fenton catalysis. For photo-Fenton catalysis, the maximum degradation rate of TC (2.5730 min^-1) is achieved when the mass ratio of MIL-101(Fe) to Ag₃PO₄ in the composite is 5:1, which is 31.65- and 3.12-fold of that in the Ag₃PO₄ + PDS + Sunlight and MIL-101(Fe) + PDS+ Sunlight catalyst systems, respectively. Moreover, the internal conversion of matrix during photocatalysis and Fenton catalysis processes inhibits the photocorrosion of Ag₃PO₄ and improves the reusability of the composite. Furthermore, it is found that both radical and non-radical species participate in the TC degradation. Besides, the degradation products and catalytic mechanism of Ag₃PO₄ and Ag₃PO₄/MIL-101(Fe) systems are explored. The toxicity evaluation results suggest that the intermediates produced during Ag₃PO₄/MIL-101(Fe) catalysis have a lower biotoxicity than those produced during Ag₃PO₄ catalysis. Overall, this work provides an effective strategy to inhibit the inherent photocorrosion of Ag₃PO₄ and establishes an efficient catalytic system for the treatment of organic-contaminated wastewater under natural sunlight conditions.

Engineering microbes for enhancing the degradation of environmental pollutants: A detailed review on synthetic biology

Anthropogenic activities resulted in the deposition of huge quantities of contaminants such as heavy metals, dyes, hydrocarbons, etc into an ecosystem. The serious ill effects caused by these pollutants to all living organisms forced in advancement of technology for degrading or removing these pollutants. This degrading activity is mostly depending on microorganisms owing to their ability to survive in harsh adverse conditions. Though native strains possess the capability to degrade these pollutants the development of genetic engineering and molecular biology resulted in engineering approaches that enhanced the efficiency of microbes in degrading pollutants at faster rate. Many bioinformatics tools have been developed for altering/modifying genetic content in microbes to increase their degrading potency. This review provides a detailed note on engineered microbes - their significant importance in degrading environmental contaminants and the approaches utilized for modifying microbes. The genes responsible for degrading the pollutants have been identified and modified fir increasing the potential for quick degradation. The methods for increasing the tolerance in engineered microbes have also been discussed. Thus engineered microbes prove to be effective alternate compared to native strains for degrading pollutants.

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.

Chlortetracycline degradation performance and mechanism in the self-biased bio-photoelectrochemical system constructed with an oxygen-defect-rich BiVO4/Ni9S8 photoanode

Efficient photoelectrodes are highly desired in bio-photoelectrochemical systems (BPES). Herein, in this paper, the oxygen defect-rich BiVO₄/Ni₉S₈ photoanode was developed and coupled with a biocathode for enhanced chlortertracycline (CTC) degradation and current generation in the self-biased BPES. Characterization results showed that the optimized BiVO₄/Ni₉S₈-7 mg-150 °C NF exhibited the best photocatalytic activity, due to that the rich oxygen vacancies and Ni₉S₈ could significantly improve light absorption, enhance photo-generated carriers separation, and accelerate charges transfer. CTC (20 mg L^-1) removal efficiency from the BPES was about 1.3 times (82.3% vs 64.7%) of that from the unilluminated reactor, and current output (0.68 A m^-3) was about 7.6 times (0.09 A m^-3). The dominant species in genus level was Geobacter, which is capable of reducing nitroaromatics and in favor of reductive dehalogenation of CTC. Besides, Comamonas and Rhodopseudomonas that are capable of degrading antibiotics were also detected. Possible degradation pathways and mechanism of CTC degradation in the BPES were proposed. This research advances the development of photoelectrode materials for light-driven BPESs and enriches antibiotics degradation mechanism.

Degradation of diclofenac via sequential reduction-oxidation by Ru/Fe modified biocathode dual-chamber bioelectrochemical system: Performance, pathways and degradation mechanisms

A sequential reduction-oxidation for DCF degradation was proposed by alternating anaerobic/aerobic conditions at Ru/Fe-biocathode in a dual-chamber bioelectrochemical system (BES). Results showed that Ru/Fe-electrode was successfully fabricated by in-situ electro-deposition, which was rough and uniformly distributed with Ru⁰ and Fe⁰ particles. The morphologic changing and biocompatibility were favorable to increase the surface area and enhance microbial adhesion on Ru/Fe-electrode. At an applied voltage of 0.6 V, the potential and impedance of Ru/Fe-biocathode were -0.80 V and 26 Ω, respectively, lower than that of carbon-felt-biocathode. It led to a higher DCF degradation efficiency of 93.2% under anaerobic conditions, which was superior to that of 88.0% under aerobic conditions. Using NaHCO₃ as carbon source, DCF removal efficiency increased with increasing applied voltage, but decreased with increasing initial DCF concentration. Thirteen intermediates were measured, and two degradation pathways were proposed, among which sequential reduction-oxidation of DCF was the main pathway, dechlorination intermediates were first generated by [H] attacked under anaerobic conditions, further oxidized by microbes and OH attacked under aerobic conditions, achieving 69.6% of mineralization. After 4 d of reaction, microcystis aeruginosa growth inhibition rate decreased from 22.9 to 8.0%, signifying a significant reduction in biotoxicity. Bacteria (e.g. Nitrobacter, Nitrosomonas, Pseudofulvimonas, Aquamicrobium, Sulfurvermis, Lentimicrobiaceae, Anaerobineaceae, Bacteroidales, Hydrogenedensaceae, Dethiosulfatibacter and Azoarcus) for DCF degradation were enriched in Ru/Fe-biocathode. Microbes in Ru/Fe-biocathode had established defense mechanisms to acclimate to the unfriendly environment, while Ru/Fe-biocathode possessed higher nitrification and denitrification activities than carbon-felt-biocathode, and Ru/Fe-biocathode might be of aerobic and anaerobic biodegradation activities. DCF could be mineralized by the synergistic reaction between Ru/Fe and bacteria under sequential anaerobic/aerobic conditions.

Visible-light-driven Z-scheme Zn3In2S6/AgBr photocatalyst for boosting simultaneous Cr (VI) reduction and metronidazole oxidation: Kinetics, degradation pathways and mechanism

It is urgently needed to develop high-performance materials that can synchronously remove heavy metals and organic pollutants. Herein, the visible-light responsive Zn₃In₂S₆/AgBr composites were prepared for concurrent removals of metronidazole (MNZ) and Cr (VI). In the Cr (VI)-MNZ coexisting system, the removals of MNZ and Cr (VI) using the optimized Zn₃In₂S₆/AgBr-15 photocatalyst reached 98.2% and 94.8% within 2 h, respectively; higher than those using counterparts. The radical species trapping and electron spin resonance (ESR) results demonstrated that ·OH was the most dominated species for MNZ oxidation, and photo-generated electrons were responsible for Cr (VI) reduction. Besides, slight competition for ·O₂- during the simultaneous MNZ degradation and Cr (VI) reduction occurred. Energy band structure analysis, ESR and the outstanding photocatalytic performance for MNZ and Cr (VI) removals demonstrated that the Zn₃In₂S₆/AgBr-15 was a Z-scheme photocatalyst, which promoted photo-induced carrier's separation. Possible MNZ degradation pathways and mechanism over the Z-scheme Zn₃In₂S₆/AgBr were also proposed based on the identified intermediates. This study could inspire new ideas for design of efficient Z-scheme photocatalysts for wastewater treatment.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Nitrofurazone Removal from Water Enhanced by Coupling Photocatalysis and Biodegradation

(1) Background: Environmental contamination with antibiotics is particularly serious because the usual methods used in wastewater treatment plants turn out to be insufficient or ineffective. An interesting idea is to support natural biodegradation processes with physicochemical methods as well as with bioaugmentation with efficient microbial degraders. Hence, the aim of our study is evaluation of the effectiveness of different methods of nitrofurazone (NFZ) degradation: photolysis and photodegradation in the presence of two photocatalysts, the commercial TiO₂-P25 and a self-obtained Fe₃O₄@SiO₂/TiO₂ magnetic photocatalyst. (2) Methods: The chemical nature of the photocatalysis products was investigated using a spectrometric method, and then, they were subjected to biodegradation using the strain Achromobacter xylosoxidans NFZ2. Additionally, the effects of the photodegradation products on bacterial cell surface properties and membranes were studied. (3) Results: Photocatalysis with TiO₂-P25 allowed reduction of NFZ by over 90%, demonstrating that this method is twice as effective as photolysis alone. Moreover, the bacterial strain used proved to be effective in the removal of NFZ, as well as its intermediates. (4) Conclusions: The results indicated that photocatalysis alone or coupled with biodegradation with the strain A. xylosoxidans NFZ2 leads to efficient degradation and almost complete mineralization of NFZ.

A review on self-sustainable microbial electrolysis cells for electro-biohydrogen production via coupling with carbon-neutral renewable energy technologies

Microbial electrolysis cell (MEC) technology is a promising bioelectrochemical hydrogen production technology that utilizes anodic bio-catalytic oxidation and cathodic reduction processes. MECs require a lower external energy input than water electrolysis; however, as they also require the application of external power sources, this inevitably renders MEC systems a less sustainable option. This issue is the main obstacle hindering the practical application of MECs. Therefore, this review aims to introduce a self-sustainable MEC technology by combining conventional MECs with advanced carbon-neutral technologies, such as solar-, microbial-, osmotic-, and thermoelectric-powers (and their combinations). Moreover, new approaches to overcome the thermodynamic barriers and attain self-sustaining MECs are discussed in detail, thereby providing a working principle, current challenges, and future perspective in the field. This review provides comprehensive insights into reliable hydrogen production as well as the latest trends towards self-sustainable MECs for practical application.

Different refractory organic substances degradation and microbial community shift in the single-chamber bio-photoelectrochemical system

The single-chamber bio-photoelectrochemical system (BPES) with a BiOBr photocathode was developed for acid orange 7 (AO7), 2,4 dichlorophenol (2,4-DCP) and chloramphenicol (CAP) degradation under solar irradiation. Photoelectrochemical characterizations showed that the optimized BiOBr-photocathode exhibited great light-response property and excellent electrochemcial performance. Moreover, desired TOC removals were achieved for various organic pollutants, with the values of 90.97% (AO7), 81.41% (2,4-DCP) and 78.47% (CAP). Besides, the lower cathode potentials in the illuminated BPESs were favorable to efficient pollutants degradation. Significant microbial community shifts were observed among the inoculation and anodic biofilms from the BPES, and the most dominated species in anodic biofilms acclimated to various pollutants were Geobacter and Pseudomonas, which have the abilities of extracellular electrons transfer and organics degradation. Some other species that different from the inoculation were also identified from the BPES biofilms. This study suggested that BPES had great potential for refractory organics degradation.