Zero-valent iron effectively enhances valuable products generated from wastewater containing 2-bromo-4,6-dinitroaniline during hydrolysis acidification process: Performance and mechanisms

Elucidating distinct roles of chemical reduction and autotrophic denitrification driven by three iron-based materials in nitrate removal from low carbon-to-nitrogen ratio wastewater

Effective nitrate removal is a key challenge when treating low carbon-to-nitrogen ratio wastewater. How to select an effective inorganic electron donor to improve the autotrophic denitrification of nitrate nitrogen has become an area of intense research. In this study, the nitrate removal mechanism of three iron-based materials in the presence and absence of microorganisms was investigated with Fe2+/Fe0 as an electron donor and nitrate as an electron acceptor, and the relationship between the iron materials and denitrifying microorganisms was explored. The results indicated that the nitrogen removal efficiency of each iron-based material coupled sludge systems was higher than that of iron-based material. Furthermore, compared with the sponge iron coupled sludge system (60.6%-70.4%) and magnetite coupled sludge (56.1%-65.3%), the pyrite coupled sludge system had the highest removal efficiency of TN, and the removal efficiency increased from 62.5% to 82.1% with time. The test results of scanning electron microscope, X-ray photoelectron spectroscopy and X-ray diffraction indicated that iron-based materials promoted the attachment of microorganisms and the chemical reduction of nitrate in three iron-based material coupled sludge systems. Furthermore, the pyrite coupled sludge system had the highest nitrite reductase activity and can induce microorganisms to secrete more extracellular polymer substances. Combined with high-throughput sequencing and PICRUSt2 functional predictive analysis software, the total relative abundance of the dominant bacterial in pyrite coupled sludge system was the highest (72.06%) compared with the other iron-based material systems, and the abundance of Blastocatellaceae was relatively high. Overall, these results suggest that the pyrite coupled sludge system was more conducive to long-term stable nitrate removal.

Metatranscriptome analysis unveils the mechanisms of zero-valent iron enhancing reactivation of starvation hydrolysis acidification sludge by inducing high-level gene expression

Hydrolysis acidification (HA) is a promising method for wastewater treatment and resource recovery. However, the extended time required for bacterial reactivation after starvation or a change in living conditions often poses a challenge to the efficient operation of the system. Although the addition of zero-valent iron (ZVI) could enhance HA performance, its effects on sludge reactivation in the HA process are not fully understood. In this study, ZVI was employed to accelerate sludge reactivation and its involved genetic mechanisms were unveiled. The results demonstrated that ZVI addition activated the sludge within 35 days with stable HA performance. Sludge characteristics revealed that ZVI improved active biomass, enzyme activity (by 11.4 % ∼ 26.7 %), ETS activity (by 566 %), and cell viability, with a higher concentration of MLVSS, live cells, more microbial byproducts in EPS, and relative abundance of HA bacteria (63.41 %). Moreover, metatranscriptome analysis showed that ZVI upregulated the expression of genes related to key enzymes in carbohydrate degradation metabolism, biosynthesis of electron transfer media such as heme and ubiquinone, and biosynthesis of vital cofactors like vitamin B12 and folate during microbial growth and metabolism. These findings suggest that ZVI enhanced electron transfer, bacterial growth, and metabolism, resulting in effective starch conversion and VFAs generation. Overall, these results deepen our understanding of the mechanism by which ZVI enhanced HA sludge reactivation, providing valuable information for addressing sludge starvation issues in HA systems.

In situ reductive dehalogenation of groundwater driven by innovative organic carbon source materials: Insights into the organohalide-respiratory electron transport chain

In situ bioremediation using organohalide-respiring bacteria (OHRB) is a prospective method for the removal of persistent halogenated organic pollutants from groundwater, as OHRB can utilize H₂ or organic compounds produced by carbon source materials as electron donors for cell growth through organohalide respiration. However, few previous studies have determined the suitability of different carbon source materials to the metabolic mechanism of reductive dehalogenation from the perspective of electron transfer. The focus of this critical review was to reveal the interactions and relationships between carbon source materials and functional microbes, in terms of the electron transfer mechanism. Furthermore, this review illustrates some innovative strategies that have used the physiological characteristics of OHRB to guide the optimization of carbon source materials, improving the abundance of indigenous dehalogenated bacteria and enhancing electron transfer efficiency. Finally, it is proposed that future research should combine multi-omics analysis with machine learning (ML) to guide the design of effective carbon source materials and optimize current dehalogenation bioremediation strategies to reduce the cost and footprint of practical groundwater bioremediation applications.

Multi-omics reveals 2-bromo-4,6-dinitroaniline (BDNA)-induced hepatotoxicity and the role of the gut-liver axis in rats

2-Bromo-4, 6-dinitroaniline (BDNA) is a widespread azo-dye-related hazardous pollutant. However, its reported adverse effects are limited to mutagenicity, genotoxicity, endocrine disruption, and reproductive toxicity. We systematically assessed the hepatotoxicity of BDNA exposure via pathological and biochemical examinations and explored the underlying mechanisms via integrative multi-omics analyses of the transcriptome, metabolome, and microbiome in rats. After 28 days of oral administration, compared with the control group, 100 mg/kg BDNA significantly triggered hepatotoxicity, upregulated toxicity indicators (e.g., HSI, ALT, and ARG1), and induced systemic inflammation (e.g., G-CSF, MIP-2, RANTES, and VEGF), dyslipidemia (e.g., TC and TG), and bile acid (BA) synthesis (e.g., CA, GCA, and GDCA). Transcriptomic and metabolomic analyses revealed broad perturbations in gene transcripts and metabolites involved in the representative pathways of liver inflammation (e.g., Hmox1, Spi1, L-methionine, valproic acid, and choline), steatosis (e.g., Nr0b2, Cyp1a1, Cyp1a2, Dusp1, Plin3, arachidonic acid, linoleic acid, and palmitic acid), and cholestasis (e.g., FXR/Nr1h4, Cdkn1a, Cyp7a1, and bilirubin). Microbiome analysis revealed reduced relative abundances of beneficial gut microbial taxa (e.g., Ruminococcaceae and Akkermansia muciniphila), which further contributed to the inflammatory response, lipid accumulation, and BA synthesis in the enterohepatic circulation. The observed effect concentrations here were comparable to the highly contaminated wastewaters, showcasing BDNA's hepatotoxic effects at environmentally relevant concentrations. These results shed light on the biomolecular mechanism and important role of the gut-liver axis underpinning BDNA-induced cholestatic liver disorders in vivo.