Performance and microbial community structures of hydrolysis acidification process treating azo and anthraquinone dyes in different stages

Harnessing the potential of white rot fungi and ligninolytic enzymes for efficient textile dye degradation: A comprehensive review

The contamination of wastewater with textile dyes has emerged as a pressing environmental concern due to its persistent nature and harmful effects on ecosystems. Conventional dye treatment methods have proven inadequate in effectively breaking down complex dye molecules. However, a promising alternative for textile dye degradation lies in the utilization of white rot fungi, renowned for their remarkable lignin-degrading capabilities. This review provides a comprehensive analysis of the potential of white rot fungi in degrading textile dyes, with a particular focus on their ligninolytic enzymes, specifically examining the roles of lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase in the degradation of lignin and their applications in textile dye degradation. The primary objective of this paper is to elucidate the enzymatic mechanisms involved in dye degradation, with a spotlight on recent research advancements in this field. Additionally, the review explores factors influencing enzyme production, including culture conditions and genetic engineering approaches. The challenges associated with implementing white rot fungi and their ligninolytic enzymes in textile dye degradation processes are also thoroughly examined. Textile dye contamination poses a significant environmental threat due to its resistance to conventional treatment methods. White rot fungi, known for their ligninolytic capabilities, offer an innovative approach to address this issue. The review delves into the intricate mechanisms through which white rot fungi and their enzymes, including LiP, MnP, and laccase, break down complex dye molecules. These enzymes play a pivotal role in lignin degradation, a process that can be adapted for textile dye removal. The review also emphasizes recent developments in this field, shedding light on the latest findings and innovations. It discusses how culture conditions and genetic engineering techniques can influence the production of these crucial enzymes, potentially enhancing their efficiency in textile dye degradation. This highlights the potential for tailored enzyme production to address specific dye contaminants effectively. The paper also confronts the challenges associated with integrating white rot fungi and their ligninolytic enzymes into practical textile dye degradation processes. These challenges encompass issues like scalability, cost-effectiveness, and regulatory hurdles. By acknowledging these obstacles, the review aims to pave the way for practical and sustainable applications of white rot fungi in wastewater treatment. In conclusion, this comprehensive review offers valuable insights into how white rot fungi and their ligninolytic enzymes can provide a sustainable solution to the urgent problem of textile dye-contaminated wastewater. It underscores the enzymatic mechanisms at play, recent research breakthroughs, and the potential of genetic engineering to optimize enzyme production. By addressing the challenges of implementation, this review contributes to the ongoing efforts to mitigate the environmental impact of textile dye pollution. PRACTITIONER POINTS: Ligninolytic enzymes from white rot fungi, like LiP, MnP, and laccase, are crucial for degrading textile dyes. Different dyes and enzymatic mechanisms is vital for effective wastewater treatment. Combine white rot fungi-based strategies with mediator systems, co-culturing, or sequential treatment approaches to enhance overall degradation efficiency. Emphasize the broader environmental impact of textile dye pollution and position white rot fungi as a promising avenue for contributing to mitigation efforts. This aligns with the overarching goal of sustainable wastewater treatment practices and environmental conservation. Consider scalability, cost-effectiveness, and regulatory compliance to pave the way for sustainable applications that can effectively mitigate the environmental impact of textile dye pollution.

Electrically supported mediator Co(II)-activated peroxydisulfate synergistic process for organic contaminants elimination

Among homogeneous catalysts, cobalt ions exhibit ultra-high persulfate activation performance. In this work, an electrically supported medium Co(II) activated peroxydisulfate synergistic process was established to eliminate organic contaminants in water. The synergistic catalytic effect was verified by comparing the oxidative degradation performance and reaction rate constant of different coupling systems. The decolorization ability of E-Co(II)-PDS on reactive black 5 (RB5) was explored, and the results showed that the removal rate of RB5 can reach 93.21% under the optimized conditions of current density of 5.71 mA/cm², initial pH of 4, Co(II) concentration of 0.2 mM and PDS concentration of 5 mM. The effect of water matrix on the removal of RB5 was studied, and it was found that HCO₃^- and humic acid significantly inhibited the degradation of RB5, while Cl^- and H₂PO₄^- could effectively promote it at a certain concentration. Notably, the degradation of RB5 in E-Co(II)-PDS system achieved lower energy consumption, with an energy consumption per unit volume (EE/O) value of 0.4304 kWh·m^-3. EPR test, quenching experiments and contribution rate analysis showed that the oxidation active species in E-Co(II)-PDS process were Co(III), sulfate radicals and hydroxyl radicals, and their oxidation contribution rates were 15.72%, 12.69% and 53.25%, respectively. Finally, the decomposition process of RB5 was proposed by the mass spectrometry results. The electric current promotes cobalt ion cycling and PDS activation through electron transfer, and induces Co(II) to promote the activation of PDS, which is the main mechanism of E-Co(II)-PDS system to achieve the robust degradation ability of RB5.

Nanoscale zerovalent copper (nZVC) catalyzed environmental remediation of organic and inorganic contaminants: A review

Over the past decade, the nano zerovalent copper has emerged as an effective nano-catalyst for the environment remediation processes due to its ease of synthesis, low cost, controllable particle size and high reactivity despite its release during the remediation process and related concentration dependent toxicities. However, the improvised techniques involving the use of supports or immobilizer for the synthesis of Cu⁰ has significantly increased its stability and motivated the researchers to explore the applicability of Cu⁰ for the environment remediation processes, which is evident from access to numerous reports on nano zerovalent copper mediated remediation of contaminants. Initially, this review allows the understanding of the various resources used to synthesize zerovalent copper nanomaterial and the structure of Cu⁰ nanoparticles, followed by focus on the reaction mechanism and the species involved in the contaminant remediation process. The studies comprehensively presented the application of nano zerovalent copper for remediation of organic/inorganic contaminants in combination with various oxidizing and reducing agents under oxic and anoxic conditions. Further, it was evaluated that the immobilizers or support combined with various irradiation sources originates a synergistic effect and have a significant effect on the stability and the redox properties of nZVC in the remediation process. Therefore, the review proposed that the future scope of research should include rigorous focus on deriving an exact mechanism for synergistic effect for the removal of contaminants by supported nZVC.

Synthetic azo dye bio-decolorization by Priestia sp. RA1: process optimization and phytotoxicity assessment

Azo compounds represent the most diverse group of colorants widely employed in industrial sectors. Being highly toxic and recalcitrant compound, azo dyes pose a threat to plants, animals, and humans. In the present report, bio-decolorization of azo dye, reactive black 5, was evaluated by newly isolated Priestia sp. RA1. Strain RA1 was able to decolorize 97% of 100 ppm reactive black 5 in 60 h. Specific activity of dye decolorization was found to be 0.233 μmol min^-1 g^-1 dry cells. Successful decolorization over a broad range of pH, salinity, temperature, and initial dye concentration was observed. Phytotoxicity assay on agriculturally important crops showed considerable difference in percentage seed germination and growth when treated with original and bio-decolorized dye samples. Bio-decolorization at high dye concentrations, promising decolorization rate, and non-toxic nature of treated products suggest the potential of strain RA1 for bioremediation of dye-contaminated water and its re-use in the industries.

Comprehensive insights into core microbial assemblages in activated sludge exposed to textile-dyeing wastewater stress

Microorganisms in activated sludge are widely recognized for their roles in wastewater treatment. However, previous studies were mainly concerned with the diversity and driving factors of microbial communities within domestic wastewater treatment, and those of domestic wastewater treatment systems mixed with industrial wastewater are poorly understood. In this research, three different full-scale aerobic activated sludge (AS) wastewater treatment systems fed with municipal, textile-dyeing, and mixed wastewater, respectively, were monitored over the operation course of three months. 16S rRNA amplicon sequencing analysis revealed that the microbial communities in textile-dyeing wastewater activated sludge (AS) exhibited significantly lower richness and diversity (p < 0.01, Adonis) compared to those fed with municipal wastewater. In contrast, textile-dyeing derived AS selectively enriched microbial taxa with aromatic degradation and denitrification potentials. Further, FARPROTAX and metabolomics indicated the inhibition of 72.5% metabolic functions (p < 0.01) in AS from the system fed with textile-dyeing wastewater, including the pathways of pentose phosphate metabolism, purine metabolism, and glycerophospholipid metabolism. Overall, this study corroborates textile-dyeing wastewater is a novel microbial niche and could suppress sludge performance by inhibiting microbial activity and metabolism, raising concerns on AS-based systems for industrial wastewater treatment.

Long-Term Exposure to Azo Dyes from Textile Wastewater Causes the Abundance of Saccharibacteria Population

Discharge of untreated wastewater is one of the major problems in various countries. The use of azo dyes in textile industries are one of the key xenobiotic compounds which effect both soil and water ecosystems and result in drastic effect on the microbial communities. Orathupalayam dam, which is constructed over Noyyal river in Tamil Nadu, India has become a sink of wastewater from the nearby textile industries. The present study had aimed to characterize the bacterial diversity and community profiles of soil collected from the vicinity of the dam (DS) and allied agricultural field (ALS) nearby the catchment area. The soil dehydrogenase and cellulase activities were significantly lower in DS compared to ALS. Additionally, the long-term exposure to azo dye compounds resulted in higher relative abundance of Saccharibacteria (36.4%) which are important for degradation of azo dyes. On the other hand, the relative abundance of Proteobacteria (25.4%) were higher in ALS. Interestingly, the abundance of Saccharibacteria (15.2%) were also prominent in ALS suggesting that the azo compounds might have deposited in the agricultural field through irrigation. Hence, this study revealed the potential bacterial phyla which can be key drivers for designing viable technologies for degradation of xenobiotic dyes.

Microbial degradation of dyes: An overview

Industrialization increases use of dyes due to its high demand in paper, cosmetic, textile, leather and food industries. This in turn would increase wastewater generation from dye industrial activities. Various dyes and its structural compounds present in dye industrial wastewater have harmful effects on plants, animals and humans. Synthetic dyes are more resistant than natural dyes to physical and chemical methods for remediation which makes them more difficult to get decolorize. Microbial degradation has been researched and reviewed largely for quicker dye degradation. Genetically engineered microorganisms (GEMs) play important role in achieving complete dye degradation. This paper provides scientific and technical information about dyes & dye intermediates and biodegradation of azo dye. It also compiles information about factors affecting dye(s) biodegradation, role of genetically modified organisms (GMOs) in process of dye(s) degradation and perspectives in this field of research.

Bacterial degradation of anthraquinone dyes

Anthraquinone dyes, which contain anthraquinone chromophore groups, are the second largest class of dyes after azo dyes and are used extensively in textile industries. The majority of these dyes are resistant to degradation because of their complex and stable structures; consequently, a large number of anthraquinone dyes find their way into the environment causing serious pollution. At present, the microbiological approach to treating printing and dyeing wastewater is considered to be an economical and feasible method, and reports regarding the bacterial degradation of anthraquinone dyes are increasing. This paper reviews the classification and structures of anthraquinone dyes, summarizes the types of degradative bacteria, and explores the possible mechanisms and influencing factors of bacterial anthraquinone dye degradation. Present research progress and existing problems are further discussed. Finally, future research directions and key points are presented.

Sugar sources as Co-substrates promoting the degradation of refractory dye: A comparative study

Four sugar sources were used as co-substrates to promote the degradation of a selected refractory dye reactive black 5 (RB5) by the natural bacterial flora DDMZ1. The boosting performance of the four sugar sources on RB5 decolorization ranked as: fructose > sucrose > glucose > glucose + fructose. Kinetic results of these four co-metabolism systems agreed well with a first-order kinetic model. Four sugar sources stimulated the extracellular azoreductase secretion causing enhanced enzyme activity. An increased formation of low molecular weight intermediates was caused by the addition of sugar sources. The toxicity of RB5 degradation products was significantly reduced in the presence of sugar sources. The bacterial community structure differed remarkably as a result of sugar sources addition. For a fructose addition, a considerably enriched population of the functional species Burkholderia-Paraburkholderia and Klebsiella was noted. The results enlarge our knowledge of the microkinetic and microbiological mechanisms of co-metabolic degradation of refractory pollutants.

Unveiling the activating mechanism of tea residue for boosting the biological decolorization performance of refractory dye

Conventional microbial treatments are challenged by new synthetic refractory dyes. In this work, tea residue was found serving as an effective activator to boost the decolorization performance of anthraquinone dye (reactive blue 19, RB19) by a new bacterial flora DDMY2. The unfermented West Lake Longjing tea residue showed the best enhancement performance. Seventeen main kinds of components in tea residue had been selected to take separate and orthogonal experiments on decolorization of RB19 by DDMY2. Results suggested epigallocatechin gallate (EGCG) in tea residue played important roles in boosting the treatment performance. Illumina MiSeq sequencing results confirmed that EGCG and tea residue pose similar impact on the change of DDMY2 community structure. Some functional bacterial genera unclassified_o_Pseudomonadales, Stenotrophomonas and Bordetella were enriched during the treatment of RB19 by EGCG and tea residue. These evidences suggested EGCG might be the key active component in tea residue that responsible for the enhancement effect on decolorization performance. These results revealed the activating mechanism of tea residue from the perspective of composition.

Fructose as an additional co-metabolite promotes refractory dye degradation: Performance and mechanism

In this work, the performance and mechanism for the boosting effects of fructose as an additional co-metabolite towards the biological treatment of reactive black 5 were systematically investigated. A decolorization efficiency of 98% was obtained in sample FRU200 (with 3 g/L fructose added based on 3 g/L yeast extract), which was 21% higher than that without fructose. Several intermediates with low molecular weight generated in sample FRU200 and different metabolic pathways were deduced. The bacterial community structure significantly changed due to fructose addition. Label-free quantitative proteomic approach suggested that several up-regulated proteins in sample FRU200 might play essential roles during the degradation. Furthermore, the mechanisms of RB5 degradation by proteins/enzymes of the dominant species in flora DDMZ1 were proposed. This work deepens our understanding of the molecular and ecological mechanism of fructose as co-metabolite enhancing the biodegradation of refractory organic pollutants by a natural bacterial flora.

Highly efficient biodegradation of reactive blue 19 under the activation of tea residue by a newly screened mixed bacterial flora DDMY2

In this study, a newly screened mixed bacterial flora DDMY2 had high decolorization capacity for anthraquinone dye reactive blue 19 (RB19) and the decolorization efficiency of 300 mg L⁻¹ RB19 could reach up to 98% within 48 h in the presence of tea residue. Results indicated that RB19 could be efficiently decolorized by flora DDMY2 in wide ranges of pH values (5.0–9.0), temperatures (30–40 °C) and initial dye concentrations (50–500 mg L⁻¹) under the activation of tea residue. Concentration of tea residue had been proved to significantly impact the decolorization performance. UV-vis spectrophotometry, Fourier transform infrared spectrometry and liquid chromatography/time-of-flight/mass spectrometry analysis showed three identified degradation products and the possible degradation pathway of RB19 was speculated. High-throughput sequencing analysis revealed the community structures of bacterial flora before and after domestication by tea residue. Based on the result, it was inferred that unclassified_o_Pseudomonadales, Brevibacillus, Stenotrophomonas and Bordetella activated by tea residue were responsible for the excellent decolorization performance. Results of this research deepen our understanding of the biodegradation process of anthraquinone dyes by bacterial flora and broaden the knowledge of utilizing tea residue as a bioactivator in biological treatment.

Tea residue promoted the decolorization of RB19 by activating flora DDMY2, revealing corresponding degradation pathways and functional genera in DDMY2.

Comparative study of antiestrogenic activity of two dyes after Fenton oxidation and biological degradation

In present study, two methods (Fenton oxidation and biological degradation) were used to degrade azo dye (Reactive Black 5, RB5) and anthraquinone dye (Remazol Brilliant Blue R, RBBR). The changes of antiestrogenic activities of these two dyes through two degradation methods were detected using the yeast two-hybrid assay method. Fluorescence spectroscopy together with gas chromatography-mass spectrometry (GC-MS) method was performed to analyze the metabolites of RB5 and RBBR after Fenton oxidation and biological degradation. Results indicated that by Fenton oxidation, the decolorization of RB5 and RBBR were 99.31% and 96.62%, respectively, which were much higher than that by biological degradation. Dissolved organic carbon (DOC) reduction rates of RB5 and RBBR after Fenton oxidation were also much higher than that after biological degradation. By Fenton oxidation, the antiestrogenic activities of RB5 and RBBR all decreased below detection limit after degradation, while by biological degradation all of them increased significantly after degradation. Fluorescence spectroscopy analysis and GC-MS analysis confirmed the degradation effects of RB5 and RBBR by these two degradation methods. In addition, fluorescence spectroscopy analysis revealed that the metabolites humic acid-like substances might contribute to the increasing of antiestrogenic activity of RB5 and RBBR after biological degradation.

Facile approach for synthesis of stable, efficient, and recyclable ZnO through pulsed sonication and its application for degradation of recalcitrant azo dyes in wastewater

In the present study, the ultrasound in pulsed mode was used as a part of an advanced oxidation method. The influence of the pulsed ultrasound mode for the preparation of the zinc oxide (ZnO) wurtzite nanoparticle was investigated. The catalysts synthesized were analysed using SEM, TEM, EDAX, BET surface area, XRD, and DRS to study their morphological and structural characterizations. The ZnO nanoparticles exhibited a highly hexagonal structure from pulsed sonication synthesis route. The efficiency of the decolourization of the reactive red 4 (RR4) dye was studied under different operation parameters such as dye concentration, initial solution pH, oxidant (e.g., H2O2) concentration, and catalyst loading. The hybrid combined process of pulsed sonolysis, pH (4.0), H2O2 (17.64 mmol), and catalyst (0.35 g/L) achieved 97% degradation and 87.5% chemical oxygen demand removal in about 20 min of reaction time. The cyclic degradation studies of RR4 removal with 0.35 g/L of ZnO showed the reusability of catalyst up to the fifth removal cycle with negligible loss in the catalytic performance. GC–MS study, used for the detection of the RR4 intermediates, revealed the oxidation–reduction reaction by the reactive radicals proceeded via the reductive cleavage of the azo bonds. The studied process, based on the pulsed ultrasound, is found to be effective for the degradation of RR4 dye.

Effect of combining adsorption-stripping treatment with acidification on the growth of Chlorella vulgaris and nutrient removal from swine wastewater

After swine wastewater (SW) was treated with adsorption-stripping stage, the concentration of NH₄⁺-N and Total phosphorus (TP) in SW significantly decreased from 598.04, 42.95 to 338.02, 8.36 mg L^-1, respectively. The concentration of heavy metals, especially Zn²⁺ (96.78%), decreased by the ion exchange of artificial zeolite (AZ). The acidification of SW could significantly improve the nutrient utilization efficiency and promote the growth rate of C. vulgaris due to the hydrolysis of macromolecular substances into smaller molecules usable for algae. By combining adsorption (Part I), stripping (Part II) and cultivation (Part III), the highest removal rates of NH₄⁺-N, TP, chemical oxygen demand (COD) and total organic carbon (TOC) from SW were 80.50, 96.90, 72.91, and 84.17%, respectively, and the OD₆₈₀ value was 1.129 (1.48 times of control) at pH 6.0. The combined system (Part I-III) can significantly enhance the removal efficiency of nutrient and biomass production by acidification.