Efficient photocatalytic reduction of nitrate byproducts during anammox process by novel extracellular polymeric substances-embedded NH2-MIL-101(Fe) photocatalysts

Metatranscriptomics sheds light on electron transfer in anammox bacteria enhanced by the redox mediator neutral red

Enhancing the activity of key enzymes has been recognized as an effective strategy to improve anammox performance. Neutral red (NR), a potent redox-active electron carrier, has been shown to boost various enzyme activities and microbial reaction rates. However, its potential to enhance anammox performance remains underexplored. This study aimed to investigate the effects of different NR concentrations on anammox nitrogen removal efficiency and gene transcription levels. The results revealed that anammox activity increased with NR doses in the lower concentration range (0.05-0.3 g L-1). The optimal dosage at 0.1 g L-1 significantly increased specific anammox activity (SAA) by 16.73 ± 2.68% (p ≤ 0.001), compared to the control without NR addition. Moreover, the total EPS concentration increased by 16.87 ± 1.20% (p ≤ 0.01). Conversely, NR concentrations exceeding the optimal range inhibited anammox activity. Metatranscriptomic analysis showed that appropriate NR supplementation upregulated the expression of cofactor modules related to electron transfer and functional genes (hdh and hzsB) involved in anammox nitrogen removal, thereby enhancing overall performance. Moreover, the mild oxidative stress induced by low NR doses was mitigated through the upregulation of antioxidant genes. In contrast, excessive NR (0.5-1.0 g L-1) led to an accumulation of reactive oxygen species (ROS) that overwhelmed the antioxidant defense system, resulting in impaired electron transfer and reduced metabolic activity. Specifically, when the NR concentration was increased to 1.0 g L-1, SAA decreased significantly by 26.45 ± 2.55% (p ≤ 0.001). These findings indicate that appropriately controlled NR supplementation can improve anammox activity, providing a promising strategy for rapid start-up and improved nitrogen removal in practical anammox systems.

The design and preparation of PDI modified NH2-MIL-101(Fe) for high efficiency removal of dimethoate in peroxymonosulfate system: Performance, mechanism, pathway and toxicity assessment

The widespread use of organophosphorus pesticide dimethoate (DMT) in agriculture poses a threat to human health. In this work, the perylene tetracarboxylic diimide (PDI) modified NH2-MIL-101(Fe) (PDI/MIL) with strong covalent bond C(=O)-N were designed and prepared by a step solvothermal method. The synergistic effect between photocatalytic and peroxymonosulfate (PMS) activation for the DMT elimination over PDI/MIL was gained. Interestingly, PDI/MIL(1:10)/PMS showed boosting degradation efficiency (95.6%) for DMT under 18 min simulated sunlight irradiation. Its apparent reaction rate constant was 24.7 times higher than that of NH2-MIL-101(Fe)/PMS. Moreover, its reusability, stability and mineralization ability were evaluated, and a remarkable mineralization rate of 95.3% with 90 min was achieved. The enhanced activity were attributed to the formation of amide bond that exhibited superior charger transport ability and amount of produced active species. Combined the results obtained from the HPLC-MS and molecular structure characteristics of DMT analyzed by Fukui index, the degradation pathways were proposed. The toxicity of intermediates were predicted by Ecological Structure Activity Relationship (ECOSAR), Toxicity Estimation Software Tool (T.E.S.T.), and Vibrio fischeri experiments. Our work provided deep insights into the mechanisms of DMT degradation via photocatalysis-activated PMS over organic semiconductor modified metal organic frameworks.

Amorphous Cu/Fe nanoparticles with tandem intracellular and extracellular electron capacity for enhancing denitrification performance and recovery of co-contaminant suppressed denitrification

In this study, a functionally stable insoluble Cu/Fe nanoparticles (Cu/Fe NPs) were synthesized and applied denitrification with different contaminants. The results showed that 50 mg/L Cu/Fe NPs increased NO3--N reduction rate up to 14.3 mg/(L·h) about 3 folds compared with the control system (4.7 mg/(L·h)), and Cu/Fe NPs exhibited excellent restorative effects on NO3--N reduction under the stress of Cd2+, Nitrovin and Methyl Orange. Meanwhile, electrochemical analyses, enzyme activities, and related genes abundance together showed that pilus, cytochrome c and flavin mononucleotide were electron carriers to tandem extracellular and intracellular, increasing electron flux acting on NO3--N in the respiratory chain. Metagenomic sequencing showed that microbial metabolic activity, electroactive bacteria (EAB) abundance with bi-directional electron transfer and Cu/Fe-compatible bacterial abundance were increased. Furthermore, denitrification performance was maintained by establishing C-EAB-Cu/Fe NPs cycling network. This study provided insights and applications for expanding the use of insoluble mediators in denitrification systems.

Interspecies cooperation-driven photogenerated electron transfer processes and efficient multi-pathway nitrogen removal in the g-C3N4-anammox consortia biohybrid system

Photocatalytic materials-microbial biohybrid systems pave the way for solar-driven wastewater nitrogen removal. In this study, interspecies cooperation in photogenerated electron transfer and efficient nitrogen removal mechanism in the g-C3N4-anammox consortia biohybrid system were first deciphered. The results indicated that the essential extracellular electron carriers (cytochrome c and flavin) for anammox genomes were provided by associated bacteria (BACT3 and CHLO2). This cooperation, regulated by the ArcAB system and electron transfer flavoprotein, made anammox bacteria the primary photogenerated electron sink. Furthermore, an efficient photogenerated electron harness was used to construct a reductive glycine pathway (rGlyP) in anammox bacteria inventively, which coexisted with the Wood-Ljungdahl pathway (WLP), constituting a dual-pathway carbon fixation model, rGlyP-WLP. Carbon fixation products efficiently contributed to the tricarboxylic acid cycle, while inhibiting electron diversion in anabolism. Photogenerated electrons were targeted channeled into nitrogen metabolism-available electron carriers, enhancing anammox and dissimilatory nitrate reduction to ammonium (DNRA) processes. Moreover, ammonia assimilation by the glycine cleavage system in rGlyP established an alternative ammonia removal route. Ultimately, multi-pathway nitrogen removal involving anammox, DNRA, and rGlyP achieved 100 % ammonia removal and 94.25 % total nitrogen removal efficiency. This study has expanded understanding of anammox metabolic diversity, enhancing its potential application in carbon-neutral wastewater treatment.