Effects of ferroferric oxide on azo dye degradation in a sulfate-containing anaerobic reactor: From electron transfer capacity and microbial community

Harnessing Iron Materials for Enhanced Decolorization of Azo Dye Wastewater: A Comprehensive Review

Highly colored azo dye-contaminated wastewater poses significant environmental threats and requires effective treatment before discharge. The anaerobic treatment method is a cost-effective solution, while its time-consuming and inefficient processes present substantial challenges for industrial scaling. Thus, the use of iron materials presents a promising alternative. Laboratory studies have demonstrated that systems coupled with iron materials enhance the decolorization efficiency and reduce the processing time. To fully realize the potential of iron materials for anaerobic azo dye treatment, a comprehensive synthesis and evaluation based on individual-related research studies, which have not been conducted to date, are necessary. This review provides, for the first time, an extensive and detailed overview of the utilization of iron materials for azo dye treatment, with a focus on decolorization. This review assesses the treatment potential, analyzed the influencing factors and their impacts, and proposed metabolic pathways to enhance anaerobic dye treatment using iron materials. Additionally, the physicochemical characteristics of iron materials are discussed to elucidate the mechanisms behind the enhanced bioreduction of azo dyes. This study further addresses the current obstacles and outlines future prospects for industrial-scale application of iron-coupled treatment systems.

Purification mechanism of microbial metabolism in kitchen-oil wastewater enhanced by cationic vacancies on γ-Al2O3

The use of catalyst materials to mediate the enhancement of microbial degradation in wastewater is a new economic and energy saving breakthrough in water treatment technology. In this study, γ-Al2O3, which is commonly used as catalyst/carrier, is used as biological filler to treat kitchen-oil wastewater with low biodegradability, and the COD removal rate is about 50 %. It is found that the complexation of cationic vacancies on Al2O3 surface with extracellular polymeric substance (EPS) secreted by microorganisms in wastewater lead to the polarization of electron distribution on biofilm. The efficient degrading bacteria are enriched on reaction interface and obtain electrons to maintain electron dynamic balance by enhancing the transmembrane metabolism of pollutants. The aluminum vacancies on Al2O3 surface accelerate the microbial degradation of pollutants. The cationic vacancies in the structure of catalyst accelerate the acquisition of exogenous electrons by microorganisms without the addition of external energy, which provides a new idea for catalytic fillers to enhance wastewater degradation.

Stimulating anaerobic digestion to degrade recalcitrant organic pollutants: Potential role of conductive materials-led direct interspecies electron transfer

This review aims to provide a comprehensive understanding of the potential of CMs-dominated DIET in the degradation of recalcitrant organic pollutants in AD. The review covers the mechanisms and efficiencies of recalcitrant organic pollutant degradation by CMs-dominated DIET, the comparison of degradation pathways between DIET and chemical treatment, recent insights on DIET-enhanced degradation, and the evaluation of the potential and future development of CMs-dominated DIET. The review emphasizes the importance of coupled syntrophic microorganisms, electron flux, and physicochemical properties of CMs in enhancing the degradation performance of AD. Additionally, it highlights the advantages of DIET-led syntrophic metabolism over traditional oxidation technologies in terms of environmental friendliness and efficiency. Finally, the review acknowledges the potential risks associated with introducing CMs into AD systems and provides guidance for waste treatment and energy recovery.

Enhanced purification of kitchen-oil wastewater driven synergistically by surface microelectric fields and microorganisms

The stable structure and toxic effect of refractory organic pollutants in wastewater lead to the problem of high energy consumption in water treatment technology. Herein, we propose a synergistic purification of refractory wastewater driven by microorganisms and surface microelectric fields (SMEF) over a dual-reaction-center (DRC) catalyst HCLL-S8-M prepared by an in situ growth method of carbon nitride on the Cu-Al₂O₃ surface. Characterization techniques demonstrate the successful construction of SMEF with strong electrostatic force over HCLL-S8-M based on cation-π interactions between metal copper ions and carbon nitride rings. With the catalyst as the core filler, an innovative fixed bed bioreactor is constructed to purify the actual kitchen-oil wastewater. The removal efficiency of the wastewater even with a very low biodegradability (BOD₅/COD = 0.33) can reach 60% after passing through this bioreactor. An innovative reaction mechanism is revealed for the first time that under the condition of a small amount of biodegradable organic matter, the SMEF induces the enrichment of electric active microorganisms (Desulfobulbus and Geobacter) in the wastewater, accelerates the interspecies electron transfer of intertrophic metabolism with the biodegradable bacteria through the extracellular electron transfer mechanism such as cytochrome C and self-secreted electron shuttle. The electrons of the refractory organic pollutants adsorbed on the surface of the catalyst are delocalized by the SMEF, which can be directly utilized by microorganisms through EPS conduction. The SMEF generated by electron polarization can maximize the utilization of pollutants and microorganisms in wastewater and further enhance degradation without adding any external energy, which is of great significance to the development of water self-purification technology.

Enhancement of methane production in anaerobic digestion of high salinity organic wastewater: The synergistic effect of nano-magnetite and potassium ions

During high salinity organic wastewater (HSOW) anaerobic digestion treatment, the process of methanogenesis can be severely inhibited in the high salinity environment, and the accumulation of volatile organic acids (VFAs) leads to failure of the anaerobic reaction. In this study, nano-magnetite and KCl were adopted to alleviate the inhibitory effect of high salinity and enhance the HSOW anaerobic digestion performance. The result showed that, under the optimal dosage of 200 mg/L, nano-magnetite addition promoted the anaerobic digestion performance, and the methane production increased by 11.06%. When KCl was added with a dosage of 0.174%, the methane production increased by 98.37%. The simultaneous addition of nano-magnetite (200 mg/L) and KCl showed a synergistic effect on enhancing HSOW anaerobic digestion performance, and the methane production increased by 124.85%. The addition of nano-magnetite and KCl promoted the conversion of VFAs, especially accelerated the degradation of propionic acid and butyric acid, also it promoted the activity of acetate kinase, dehydrogenase and F₄₂₀, and thereby enhanced the methanogenesis process. This study could provide a new method for enhancing the anaerobic digestion of HSOW.