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We developed an innovative strategy to address the inhibition of anode-respiring bacteria due to voltage reversal in serially stacked microbial fuel cells by inducing cathodic voltage reversal and H 2 O 2 production. When platinum-coated carbon (Pt/C) cathodes were employed (stacked MFC Pt/C) and the MFC was operated with acetate medium, the last unit (MFC 4) caused a voltage reversal of −0.8 V with a substantial anode overpotential of 1.22 V. After replacing the Pt/C cathode with a Pt-free carbon gas diffusion electrode in MFC 4, an electrode overpotential, approximately 0.5 V, was shifted from the anode to the cathode, inducing cathodic voltage reversal. Under cathodic voltage reversal, MFC 4 generated H 2 O 2 at a production rate of 117 mg H 2 O 2 /m2-h. Hence, under cathodic voltage reversal induced by Pt-free cathodes, due to less anode polarization, the anode-respiring activity can largely be sustained in a stacked MFC that treats organic wastewater consistently and the quality of treated wastewater may be improved with energy-efficient and on-site generated H 2 O 2. • A sluggish MFC caused voltage reversal with significant anode overpotential. • Replacing Pt-coated cathode with carbon gas diffusion electrode induced cathodic voltage reversal. • Cathodic voltage reversal shifted 0.5 V of anode overpotential to the cathode. • H 2 O 2 was produced in the stacked MFC at cathodic voltage reversal. [ABSTRACT FROM AUTHOR]

Thauera is a genus of denitrifying and phosphorus-accumulating bacteria used for removing nitrogen and phosphorus from wastewater. Dissolved oxygen is one of the main factors affecting denitrification and phosphorus accumulation, and there is currently little research on the oxygen sensing regulation mechanism of Thauera bacteria. We studied denitrifying phosphorus accumulation and gene transcription expression of Thauera sp. RT1901 in anaerobic, microaerobic, and aerobic environments and analyzed the protein structure and regulation mode of two oxygen-sensing systems. The results showed that the strain could achieve the similar denitrification and phosphorus accumulation effect in microaerobic environment as in anaerobic environment. Transcriptome analysis showed that as the oxygen concentration continued to rise, the core carbon and phosphorus metabolism pathways of the strain remained unchanged, and the respiratory system shifted from nitrate respiration to aerobic respiration, thereby inhibiting the denitrification pathway. The fumarate nitrate reduction (FNR) protein and FixLJ two-component system performed oxygen sensing to jointly regulate the expression of respiratory genes. The FNR protein formed a dimer in an anaerobic environment, activating denitrification-related genes and inhibiting cytochrome oxidase-related genes. The FixLJ system conducted signal transduction through phosphorylation in a low oxygen environment and activated the transcription of the fixK gene. The FixK protein has a similar structure and function as the FNR protein but is not directly affected by oxygen. These results reveal the oxygen sensing regulation mechanism of Thauera sp. RT1901 in the denitrification and phosphorus accumulation process, providing new insights for further studying the functions of this genus of bacteria in wastewater treatment systems. [Display omitted] • The N and P removal mechanisms of Thauera are evaluated in different oxygen environments. • Thauera regulates the respiratory chain and transport to adapt to oxygen changes. • The FNR protein performs oxygen sensing and regulates in anaerobic and aerobic environments. • The FixLJ system performs oxygen sensing and regulates in microaerobic and aerobic environments. [ABSTRACT FROM AUTHOR]

Petrochemical wastewater contains inhibitory compounds such as aromatics that are toxic to microorganisms during biological treatment. The compact and layered structure and the high amount of extracellular polymeric substances (EPS) in aerobic granular sludge (AGS) can contribute to protecting microorganisms from the harsh environment. This study evaluated the changes in the granule properties, pollutants removal, microbial metabolic potential and molecular microbial characteristics of the AGS process for petrochemical wastewater treatment. Granules treating petrochemical wastewater had a higher SVI 30 /SVI 5 value (0.94) than that treating synthetic wastewater. An increase in bioactivity and EPS secretion with higher bio-polymer composition, specifically the functional groups such as hydroxyl, alkoxy and amino in protein, was observed, which promoted biomass aggregation. The granules also had more than 2-fold higher specific oxygen utilization rate. The AGS-SBR process obtained an average COD removal of 93% during petrochemical wastewater treatment and an effluent bCOD of below 1 mg L−1. No obvious inhibition of nitrification and denitrification activity was observed in the processes attributed to the layered structure of AGS. The average effluent NH 4 +-N of 5.0 mg L−1 was obtained and TN removal efficiencies of over 80.0% was achieved. Molecular microbial analysis showed that abundant functional genera Stenotrophomonas and Pseudoxanthomonas contributed to the degradation of aromatics and other petroleum organic pollutants. They were enriched with the variation of group behavior while metabolisms of amino acids and carboxylic acids by the relevant functional genera (e.g., Cytophagia) were significantly inhibited. The enrichment of Flavobacterium and Thermomonas promoted nitrification and denitrification, respectively. This research revealed the rapid start-up, enhanced granule structural strength, high inhibition resistance and considerable performance of AGS-SBR for petrochemical wastewater treatment. [Display omitted] • AGS kept stability and high efficiency in petrochemical wastewater treatment. • Average COD removal of 93% and TN removal of over 80% were achieved. • High SVI 30 /SVI 5 and bioactivity with increased EPS secretion were observed. • Stenotrophomonas and Pseudoxanthomonas contributed to petroleum organic degradation. • AGS process showed significant potential for petrochemical wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel heterogeneous Fenton-like process driven by visible light is proposed. • Reactivity is strongly enhanced without the use of reducing agents and TiO 2 modification. • Fe(III) reduction for PS activation can be accomplished via LMCT in organic-TiO 2 -Fe(III). • It can be operated at low iron dosage and neutral conditions against Fenton system. • The excellent and long-lasting catalytic performance is mediated via synergistic effect. Efficient transformation of Fe(III) to Fe(II) enhances the efficiency of persulfate-based Fenton-like process (e.g., Fe(II)-PS system). Here, we developed a novel heterogeneous Fenton-like system driven by visible light (organic-Fe(III)-PS-TiO 2 -Vis) for effective reduction of Fe(III), activation of PS and degradation of organic pollutants without the need for external reducing agents or modifications in TiO 2. The visible light-induced ligand-to-metal (organic-to-TiO 2) charge transfer (LMCT) remarkably boosting Fe(III) reduction to increase reactive oxygen species (ROS) via PS activation, and further enhanced the self-degradation and mineralization of various organics, including phenolics (bisphenol A and phenol), antibiotics (ibuprofen and tetracycline), and dyes (methylene bule and rhodamine B). Compared with traditional Fe(II)-PS and Fe(II)–H 2 O 2 systems, the organic-Fe(III)-PS-TiO 2 -Vis process requires a lower dosage of iron salt. The effective pH range has been broadened to neutral conditions due to effective prevention of Fe(III) precipitation and rapid circulation of Fe(III)/Fe(II). The comprehensive mechanistic study indicated that a synergistic effect was generated via Fe(III) reduction, PS activation, ROS generation and organic decomposition, resulting in sustainable and excellent catalytic performance of this novel Fenton-like process. Further, the results of cycling experiments and tests involving real industrial wastewater highlight the enormous potential of the proposed LMCT-mediated heterogeneous Fenton-like process in environmental remediation. [ABSTRACT FROM AUTHOR]