Biogenic sulfide for azo dye decolorization from textile dyeing wastewater

Internal cycling of Fe3+/Fe2+ within Fe3O4 on cathode promotes green degradation of reactive brilliant red X-3B on anode

Reactive brilliant red X-3B (RBRX-3B) wastewater is difficult to decolourise, not readily biodegradable, and large in quantity. Therefore, the efficient removal of RBRX-3B is crucial. In this paper, a green and efficient electrochemical-electro-Fenton system with Fe3O4-modified carbon felt bag cathode (ECEF-Fe3O4) was set up to degrade RBRX-3B wastewater. Experiments confirmed that the removal of RBRX-3B by ·OH or H2O2 is quite low, and RBRX-3B can be completely oxidised and degraded directly on the anode. Long-cycle experimental data further shows that the degradation efficiency of RBRX-3B on the anode is 100% at 70 min at the reaction rate constants (k) of 0.071 min-1 in ECEF-Fe3O4 while that of RBRX-3B on the cathode is only 16.8 ± 0.9%. The generation of ·OH is mainly catalysed through the internal cycling of Fe3+/Fe2+ within Fe3O4 on the cathode, and the generation and annihilation of ·OH on the cathode enhance the oxidation efficiency of the anode, achieving the green and effective removal of RBRX-3B by the anode in ECEF-Fe3O4.

Mechanism of decolorization and degradation of direct brown D3G by a halo-thermophilic consortium

Azo dye wastewater has garnered significant attention from researchers because of its association with high-temperature, high-salt, and high-alkali conditions. In this study, consortium ZZ efficiently decolorized brown D3G under halophilic and thermophilic conditions. he results indicated that consortium ZZ, which was mainly dominated by Marinobacter, Bacillus, and Halomonas, was achieved decolorization rates ranging from 1 to 10% at temperatures between 40 °C and 50 °C, while maintaining a pH range of 7 to 10 for direct brown D3G degradation. Through the comprehensive utilization of UV-vis spectral analysis, Fourier transform infrared (FTIR), gas chromatography mass spectrometric (GC-MS) techniques, as well as metagenomic analysis, the decolorization and degradation pathway of direct brown by consortium ZZ was proposed. The azo dye reductase, lignin peroxidase, and laccase were also highly expressed in the decolorization process. Additionally, phytotoxicity tests using seeds of Cucumis sativus and Oryza sativa revealed that the intermediates generated showed no significant toxicity compared with distilled water. This investigation elucidated the pivotal contribution of consortium ZZ to azo dye degradation and provided novel theoretical insights along with practical guidance for azo dye treatment at halo-thermophilic conditions.

Role of perovskite non-stoichiometry on catalytic oxygen dark activation for the removal of azo dyes from wastewater

Effluents of the dying and printing industries are a significant contributor to water pollution. Since synthetic dyes are primarily resistant to natural degradation, they remain in water bodies for an exceptionally long time if discharged untreated. Oxygen dark activation is a promising candidate for the degradation of azo dyes as it does not require the use of additional reagents or even the presence of light. It is an advanced catalytic oxidation process that converts oxygen dissolved in wastewater into reactive oxygen species, which subsequently break down dye molecules. The role of the catalyst is to accelerate the process by acting as a bridge for the electron transfer between the dye molecules and adsorbed oxygen. It has been reported that the textural and structural properties of the catalyst play a key role in generating reactive oxygen species. In this work, we synthesized, characterized, and evaluated a series of strontium-based perovskite oxides for the catalytic degradation of azo dyes under dark conditions. The degradation of different dyes was studied in a batch reactor under various conditions, and the reaction progress was monitored by UV-vis absorption spectroscopy. The results showed that the degradation of azo dye was faster when the azo bond was weakened by either electron-withdrawing groups or due to the formation of a stable hydrazone structure. To evaluate the effect of structural defects on the oxygen dark activation process, cation non-stoichiometry was separately introduced in the parent perovskite SrFeO3 at both A and B sites. Under identical reaction conditions, the degradation efficiency of A-site deficient perovskite Sr0.90FeO3 (94 %) and B-site deficient SrFe0.80O3 (95 %) was higher than the stoichiometric perovskite SrFeO3 (46 %). These results demonstrate that cation deficiency in the SrFeO3 structure strongly favors the catalytic degradation of azo dyes via oxygen dark activation.

Insights into the azo dye decolourisation and denitrogenation in micro-electrolysis enhanced counter-diffusion biofilm system

In this study, electron transport pathways were activated and diversified by coupling counter-diffusion biofilms with micro-electrolysis for Alizarin yellow R (AYR) denitrogenation. Due to the binding of AYR to two residues of EC 4.1.3.36 with higher binding energy, the expression of EC 4.1.3.36 was down-regulated, causing the EC 3.1.2.28 and EC 2.5.1.74 for menaquinone synthesis (redox mediator) undetectable in Membrane aerated biofilm reactors (MABR). Spontaneous electron generation in the micro electrolysis-coupled MABR (ME-MABR) significantly activated two enzymes. Activated menaquinone up-regulated decolourisation related genes expression in ME-MABR, including azoR (2.12 log2), NQO1 (2.97 log2), wrbA (0.45 log2), and ndh (0.47 log2). The diversified electron flow pathways also promoted the nitrogen metabolism coding genes up-regulation, accelerating further inorganic nitrogen denitrogenation after AYR mineralisation. Compared to MABR, the decolourisation, mineralisation, and denitrogenation in ME-MABR increased by 25.80 %, 16.53 %, and 13.32 %, respectively. This study provides new insights into micro-electrolysis enhanced removal of AYR.

The enhancement effect of n-Fe3O4 on methyl orange reduction by nitrogen-fixing bacteria consortium

Although the anaerobic reduction of azo dyes is ecofriendly, high ammonia consumption remains a significant challenge. This work enriched a mixed nitrogen-fixing bacteria consortium (NFBC) using n-Fe3O4 to promote the anaerobic reduction of methyl orange (MO) without exogenous nitrogen. The enriched NFBC was dominated by Klebsiella (80.77 %) and Clostridium (17.16 %), and achieved a 92.7 % reduction of MO with an initial concentration of 25 mg·L-1. Compared with the control, the consortium increased the reduction efficiency of MO, cytochrome c content, and electron transport system (ETS) activity by 11.86 %, 89.86 %, and 58.49 %, respectively. When using 2.5 g·L-1 n-Fe3O4, the extracellular polymeric substances (EPS) of NFBC were present in a concentration of 85.35 mg·g-1. The specific reduction rates of MO by NFBC were 2.26 and 3.30 times faster than those of Fe(II) and Fe(III), respectively, while the enrichment factor of the ribosome pathway in NFBC exceeded 0.75. Transcriptome, carbon consumption, and EPS analyses suggested that n-Fe3O4 stimulated carbon metabolism and secreted protein synthesized by the mixed culture. The latter occurred due to the increased activity of consortium and the content of redox substances. These findings demonstrate that n-Fe3O4 promoted the efficiency of mixed nitrogen-fixing bacteria for removing azo dyes from wastewater. This innovative approach highlights the potential of integrating nanomaterials with biological systems to effectively address complex pollution challenges.

Bioaugmented biological contact oxidation reactor for treating simulated textile dyeing wastewater

In this study, modified polyamide fibers were used as biocarriers to enrich dense biofilms in a multi-stage biological contact oxidation reactor (MBCOR) in which partitioned wastewater treatment zone (WTZ) and bioaugmentation zone (BAZ) were established to enhance the removal of methyl orange (MO) and its metabolites while minimizing sludge yields. WTZ exhibited high biomass loading capacity (5.75 ± 0.31 g/g filler), achieving MO removal rate ranging from 68 % to 86 % under different aeration condition within 8 h in which the most dominant genus Chlorobium played an important role. In the BAZ, Pseudoxanthomonas was the dominant genus while carbon starvation stimulated the enrichment of chemoheterotrophy and aerobic_chemoheterotrophy genes thereby enhanced the microbial utilization of cell-released substrates, MO as well as its metabolic intermediates. These results revealed the mechanism bioaugmentation on MBCOR in effectively eliminating both MO and its metabolites.

Investigating the effectiveness of rice husk-derived low-cost activated carbon in removing environmental pollutants: a study of its characterization

The chemically activated biochar was produced through the pyrolysis of rice husk. Thermal gravimetric and elemental analysis were conducted to characterize the raw rice husk. The activated biochar product underwent evaluation through SEM, BET and, FT-IR analysis. This cost-effective activated carbon was utilized as an adsorbent for the elimination of environmental pollutants. At a temperature of 25 °C, the activated biochar product exhibited an impressive maximum CO2 adsorption capacity of 152 mg/g. This exceptional performance can be attributed to its notable surface area and porosity, measuring at 2,298 m2/g and 0.812 cm3/g, respectively. This product was also utilized to remove methyl red (MR) dye from an aqueous solution. The optimal parameters for the removal of MR were determined as follows: a pH of 6.0, a temperature of 25 °C, an initial MR concentration of 50 mg/L, and an adsorbent dosage of 0.4 g/L. At a duration of 140 min, the system attained its maximum equilibrium adsorption capacity, reaching a value of 62.06 mg/g. Furthermore, the calculated maximum MR removal efficiency stood at an impressive 99.31%. The thermodynamic studies demonstrated that the MR removal process was spontaneous, exothermic, and increased randomness. Kinetic studies suggested that the pseudo-second-order model can fit well.

Multi-factorial investigation of the effect of biochar of the secondary medicinal residue of snow lotus on the adsorption of two azo dyes, methyl red and methyl orange

Azo dye residues pollute water, which are difficult to decompose, and posing a major threat to the ecological environment. The residues of Chinese medicine still have many possibilities for use after its medicinal value has been brought into play. In this study, secondary residue biochar activation (Na2 CO3 -modified, SBA) and secondary residue biochar (unmodified, SBC) were prepared from the secondary residue of snow lotus at 200-600°C. Surface features were obtained by Brunauer-Emmett-Teller N2 method and combined with scanning electron microscopy, and their structures were analyzed by x-ray diffraction spectroscopy, Fourier infrared and near-infrared spectroscopy. The effects of five factors, including initial concentration, contact time and adsorption temperature and so forth, on the adsorption of methyl red (MR) and methyl orange (MO) solutions were investigated. Results showed that the biochar yield, specific surface area, and pore size increased after modification. modification promoted the formation of the internal structure aromatization and oxygen-containing functional groups. Adsorption experiments showed that the surroundings pH = 8, the dyes adsorption concentration of 8 mg/L, adsorption temperature of 20-40°C and time of about 1 h were more stable. Under the condition, the removal of MO by SBA could reach approximately 60%-80% (480-640 mg/g), while the removal of MR could reach more than 90% (>720 mg/g).The charcoal prepared and modified under high temperature conditions was more effective for MO adsorption, while MR relied on low temperature effectively. This study provides a new choice of adsorbent for MR and MO and finds a new direction for the utilization of snow lotus residues.

Removal of Methylene Blue from Aqueous Solutions by Surface Modified Talc

In this study, raw talc powder surface modification was conducted, and the powder was modified in two different methods using acid washing and ball milling. Modified talc was characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). In order to investigate the adsorption capacity of modified talc on dyes, adsorption experiments were carried out with methylene blue (MB) in aqueous solutions as the target contaminant. The findings of the characterization revealed that both modifications increased the adsorption capacity of talc, which was attributed to changes in specific surface area and active groups. The influence of process parameters such as contact time, pH, dye concentration, and adsorbent dosage on the adsorption performance was systematically investigated. Modified talc was able to adsorb MB rapidly, reaching equilibrium within 60 min. Additionally, the adsorption performance was improved as the pH of the dye solution increased. The isotherms for MB adsorption by modified talc fitted well with the Langmuir model. The pseudo-second-order model in the adsorption kinetic model properly described the adsorption behavior. The results show that the modified talc can be used as an inexpensive and abundant candidate material for the adsorption of dyes in industrial wastewater.

Effect of Enhanced Hydrolytic Acidification Process on the Treatment of Azo Dye Wastewater

The hydrolysis acidification process is an economical and effective method, but its efficiency is still low in treating azo dye wastewater. It is therefore crucial to find more suitable and efficient means or techniques to further strengthen the process of treating azo dye wastewater by a hydrolytic acidification process. In this study, a hydrolytic acidification aerobic reactor was used to simulate the azo dye wastewater process. The change of wastewater quality during the reaction process was monitored, and the deep enhancement effect of single or composite biological intensification technology on the treatment of azo dye wastewater by the hydrolytic acidification process was also explored. Co-substrate strengthening and the addition of fructose co-substrate can significantly improve the efficiency of hydrolytic acidification. Compared with the experimental group without the addition of fructose, the decolorization ratio of wastewater was higher (93%) after adding fructose co-substrate. The immobilization technology was strengthened, and the immobilized functional bacteria DDMZ1 pellet was used to treat the simulated azo dye wastewater. The results showed that the composite technology experimental group with the additional fructose co-matrix had a better decolorization efficiency than the single immobilized bio-enhancement technology, with the highest decolorization ratio of 97%. As a composite biological intensification method, the fructose co-matrix composite with immobilized functional bacteria DDMZ1 technology can be applied to the treatment of azo dye wastewater.

Microbial Transformation of Dissolved Organic Sulfur during the Oxic Process in 47 Full-Scale Municipal Wastewater Treatment Plants

Dissolved organic sulfur (DOS) is a significant part of effluent organic matter of wastewater treatment plants (WWTPs) and poses a potential ecological risk for receiving waters. However, the oxic process is a critical unit of biological wastewater treatment for microorganisms performing organic matter removal, wherein DOS transformation and its mechanism are poorly understood. This study investigated the transformation of DOS during the oxic process in 47 full-scale municipal WWTPs across China from molecular and microbial aspects. Surprisingly, evident differences in DOS variations (ΔDOS) separated sampled WWTPs into two groups: 28 WWTPs with decreased DOS concentrations in effluents (ΔDOS < 0) and 19 WWTPs with increased DOS (ΔDOS > 0). These two groups also presented differences in DOS molecular characteristics: higher nitrogen/carbon (N/C) ratios (0.030) and more peptide-like DOS (8.2%) occurred in WWTPs with ΔDOS > 0, implying that peptide-like DOS generated from microbes contributed to increased DOS in effluents. Specific microbe-DOS correlations (Spearman correlation, p < 0.05) indicated that increased effluent DOS might be explained by peptide-like DOS preferentially being produced during copiotrophic bacterial growth and accumulating due to less active cofactor metabolisms. Considering the potential environmental issues accompanying DOS discharge from WWTPs with ΔDOS > 0, our study highlights the importance of focusing on the transformation and control of DOS in the oxic process.

Microbial communities and metabolic pathways involved in reductive decolorization of an azo dye in a two-stage AD system

Multiple stage anaerobic system was found to be an effective strategy for reductive decolorization of azo dyes in the presence of sulfate. Bulk color removal (56-90%) was achieved concomitant with acidogenic activity in the 1st-stage reactor (R1), while organic matter removal (≤100%) and sulfate reduction (≤100%) occurred predominantly in the 2nd-stage reactor (R2). However, azo dye reduction mechanism and metabolic routes involved remain unclear. The involved microbial communities and conditions affecting the azo dye removal in a two-stage anaerobic digestion (AD) system were elucidated using amplicon sequencing (16S rRNA, fhs, dsrB and mcrA) and correlation analysis. Reductive decolorization was found to be co-metabolic and mainly associated with hydrogen-producing pathways. We also found evidence of the involvement of an azoreductase from Lactococcus lactis. Bacterial community in R1 was sensitive and shifted in the presence of the azo dye, while microorganisms in R2 were more protected. Higher diversity of syntrophic-acetate oxidizers, sulfate reducers and methanogens in R2 highlights the role of the 2nd-stage in organic matter and sulfate removals, and these communities might be involved in further transformations of the azo dye reduction products. The results improve our understanding on the role of different microbial communities in anaerobic treatment of azo dyes and can help in the design of better solutions for the treatment of textile effluents.

Adsorption of Methylene Blue on Azo Dye Wastewater by Molybdenum Disulfide Nanomaterials

In this study, flower-like MoS2 nanomaterials were synthesized by hydrothermal method with excess thiourea. The adsorption performance of MoS2 adsorbent for methylene blue (MB) in azo dye wastewater was studied. The morphology, crystal phase, and microstructure of nano MoS2 samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The effects of adsorption isotherm, kinetics, different hydrothermal time, and pH on the adsorption experiment were studied. The results showed that the MoS2 adsorbent with a hydrothermal time of 1 h had good adsorption properties for MB. The adsorption data accord with the Langmuir isotherm model, and the maximum adsorption capacity of MoS2 adsorbent is 200 mg/g, and the adsorption kinetics agrees well with the pseudo two-level model. The removal rate of MB is not significantly affected by the pH values. The large pH range can still maintain the removal rate above 93.47%, and the regeneration and recovery properties of MoS2 were also explored. Finally, the adsorption mechanism of MoS2 on MB is discussed.