Sequential anaerobic-aerobic treatment using plant microbe integrated system for degradation of azo dyes and their aromatic amines by-products

Cellulosic ethanol stillage for methane production by integrating single-chamber anaerobic digestion and microbial electrolysis cell system

Anaerobic digestion provides a solution to the inefficient use of carbon resources caused by improper disposal of corn stover-based ethanol stillage (CES). In this regard, we developed a single-chamber anaerobic digestion integrated microbial electrolysis cells system (AD-MEC) to convert CES into biogas while simultaneously upgrading biogas in-situ by employing voltages ranging from 0 to 2.5 V. Our results demonstrated that applying 1.0 V increased the CH4 yield by 55 % and upgraded the CH4 content in-situ to 82 %. This voltage also promoted the well-formed biofilm on the electrodes, resulting in a 20-fold increase in current. However, inhibition was observed at high voltages (1.5-2.5 V), suppressing syntrophic organic acid-oxidizing bacteria (SOB). The dissociation between SOB and methanogens led to accumulation of propionic and butyric acid, which, in turn, inhibited methanogens. The degradation of CES was accelerated by unclassified_o_norank_c_Desulfuromonadia on the anode, likely leading to an increase in mixotrophic methanogenesis due to the synergistic interaction among Aminobacterium, Sedimentibacter, and Methanosarcina. Furthermore, the enrichment of electroactive bacteria (EB) such as Enterococcus and Desulfomicrobium likely facilitates direct interspecies electron transfer to Methanobacterium, thereby promoting the conversion of CO2 to CH4 through hydrogenotrophic methanogenesis. Rather than initially stimulating the EB in the bulk solution to accelerate the start-up process of AD, our study revealed that applying mild voltage up to 1.0 V tended to mitigate the negative impact on the original microorganisms, as it gradually enriched EB on the electrode, thereby enhancing biogas production.

Methyl Red degradation by a subseafloor fungus Schizophyllum commune 15R-5-F01: efficiency, pathway, and product toxicity

Synthetic dyes pose a significant environmental threat due to their complex structures and resistance to microbial degradation. S. commune 15R-5-F01 exhibited over 96% degradation efficiency of Methyl Red in a medium with 100 mg L-1 Methyl Red within 3 h. The fungus demonstrated adaptability to various environmental conditions, including different pH levels, temperatures, oxygen concentrations, salinity, and heavy metals. S. commune 15R-5-F01 is capable of achieving repeated cycles of Methyl Red reduction with sustained degradation duration minimum of 6 cycles. It showed a maximum Methyl Red biodegradation capacity of at least 558 mg g-1 dry mycelia and a bioadsorption capacity of 57 mg g-1. Gas chromatography-mass spectrometry analysis confirmed the azo reduction of Methyl Red into N,N-dimethyl-p-phenylenediamine and 2-aminobenzoic acid. Enzymatic activity assays indicated the involvement of lignin peroxidases, laccases, and manganese peroxidase in the biodegradation process. Phytotoxicity tests on Triticum eastivum, Oryza sativa, and Vigna umbellata seeds revealed reduced toxicity of the degradation products compared to Methyl Red. This study identifies S. commune 15R-5-F01 as a viable candidate for the sustainable degradation of synthetic dyes in industrial wastewater.

Purifying surface water contaminated with azo dyes using nanofiltration: Interactions between dyes and dissolved organic matter

In this research, the interactions of two azo dyes, Methyl Orange (MO) and Eriochrome Black T (EBT), with dissolved organic matter (DOM) in surface water were studied, emphasizing their removal using nano-filtration membranes (NF-270 and NF-90). High-Performance Size Exclusion Chromatography (HPSEC) findings indicated that the dyes' molecular weight in deionized (DI) water ranged from 500 to 15k Dalton (Da), adjusting peak intensities with Jingmi River (JM) water Beijing. Notably, when dyes were diluted in JM water, ultraviolet (UV533 & 466, and UV254), together with total organic carbon (TOC) parameters, revealed color removal rates of 99.49% (EBT), 94.2% (MO), 87.6% DOM removal, and 86% TOC removal for NF-90. The NF-90 membrane demonstrated a 75% flux decline for 50 mL permeate volume due to its finer pore structure and higher rejection effectiveness. In contrast, the NF-270 membrane showed a 60% decline in flux under the same conditions. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis of dye-treated membranes in JM water revealed that the NF-270 showed a CC bond peak at 1660 cm-1 across various samples, while analyzing NF-90, the peaks at 1400 cm-1, 1040 cm-1, 750 cm-1, and 620 cm-1 disappeared for composite sample removal. The hydrophobicity of each membrane is measured by the contact angle (CA), which identified that initial CAs for NF-270 and NF-90 were 460 and 700, respectively, that were rapidly declined but stabilized after a few seconds of processing. Overall, this investigation shows that azo dyes interact with DOM in surface waters and enhance the removal efficiency of NF membranes.

Carbon dots as potential candidate for photocatalytic treatment of dye wastewater

Water is the utmost important element for the existence of life. In recent decades, water resources have become highly contaminated by a variety of pollutants, especially toxic dyes that are harmful to both living beings and environment. Hence, there is an urgent need to develop more effective methods than traditional wastewater treatment approaches for treatment of hazardous dyes. Herein, we have addressed the various aspects related to the effective and economically feasible method for photocatalytic degradation of these dyes employing carbon dots. The photocatalysts based on carbon dots including those mediated from biomass have many superiorities over conventional methods such as utilization of economically affordable, non-toxic, rapid reactions, and simple post-processing steps. The current study will also facilitate better insight into the understanding of photocatalytic treatment of dye-polluted wastewater for future wastewater treatment studies. Additionally, the possible mechanistic pathways of photocatalytic dye decontamination, several challenges, and future perspectives have also been summarized.

Optimising Wastewater Treatment: Acinetobacter sp. IrC1 as a potential multi-resistant bacterium for copper accumulation and dyes decolourisation

Improper disposal of waste containing copper and dye is an environmental issue that must be resolved immediately due to its harmful, non-degradable and toxic properties. Bioremediation efficiency can improve by cultivating copper and dye multi-resistant bacteria to remove various pollutant types simultaneously. This study aims at establishing the multi-resistance of Acinetobacter sp. IrC1 to copper and dyes. The effects of copper concentration on growth were determined using a spectrophotometer, while accumulation was analysed using an atomic absorption spectrophotometer. Bacteria-mediated dye decolourisation dyes were observed based on clear zone formation around bacterial colonies, while decolourisation percentage was calculated using a spectrophotometer. Results demonstrate that Acinetobacter sp. IrC1 resisted up to 8 mM CuSO4 and accumulated up to 292.93 mg/g dry weight of copper cells. Acinetobacter sp. IrC1 isolates were also resistant to 500 ppm Methylene Blue, Malachite Green, Congo Red, Mordant Orange, Reactive Black, Direct Yellow, Reactive Orange, Remazol, Wantex Red and Wantex Yellow dye, successfully removing up to 68.35% and 79.50% Methylene Blue and Basic Fuchsine in a medium containing 3 mM CuSO4, respectively. Further investigations are required to analyse the genetic composition of multi-resistant bacteria to optimise the effectiveness of indigenous bacterial isolates as bioremediation agents.

Dyeing wastewater treatment in horizontal-vertical constructed wetland using organic waste media

A hybrid constructed wetland (CW) system with horizontal and vertical flow combination was evaluated for treating carbon-deficient synthetic dyeing wastewater containing 100 mg/L Reactive Yellow 145 dye. Organic waste products such as cow manure and wood chips were added as media in horizontal CW, and gravel as vertical CW media. Horizontal and vertical CWs were planted with Typha angustifolia. Horizontal CW was operated in continuous mode at hydraulic retention time (HRT) of 3 d and vertical CW in batch mode at 1 d HRT. The results suggested the potential application of a cost-effective horizontal-vertical hybrid CW to remove azo dyes from low-carbon dyeing wastewater. In horizontal CW, organic media was used as the carbon source for microbial dye degradation, resulting in 90% colour removal in the absence of available carbon in dyeing wastewater. Proteobacteria, Firmicutes and Bacteroidetes played a dominant role in dye degradation in horizontal CW. Vertical CW removed dye degradation organics, 69% ammonium-nitrogen and 39% organic-nitrogen. Phytotoxicity assays indicated toxicity reduction along the CW treatment path.

Application of Salvinia sps. in remediation of reactive mixed azo dyes and Cr (VI) - Its pathway elucidation

The emerging industrialization has resulted in the rapid growth of textile industries across the globe. The presence of xenobiotic pollutants in textile wastewater threatens the ecosystem. Applying different microbes (bacteria, fungi & algae) has paved the way for phytoremediation - the eco-friendly, cost-effective method. The present study focuses on the phytoremediation of reactive dyes - Reactive red, Reactive Brown & Reactive Black and Cr (VI) in synthetic textile wastewater using Salvinia sps. The mixed azo dyes of each 100 mg/L showed decolourization of 75 ± 0.5% and 82 ± 0.5% of removal of 20 mg/L of Cr (VI) after eight days of incubation in a phytoreactor setup. Chlorophyll analysis revealed the gradual decrease in the photosynthetic pigments during the remediation. The degraded metabolites were analyzed using FT-IR and showed the presence of aromatic amines on day zero, which were converted to aliphatic amines on day four. The GC-MS analysis revealed the disruption of -NN- bond, rupture of -CN- bond, scission of -N-N-bond, and loss of -SO₃H from the Reactive Black dye leading to the formation of an intermediate p-Hydroxy phenylhydrazinyl. The rupture of Reactive red dye resulted in the formation of p-Hydrazinyl toluene sulphonic acid, Naphthyl amine -3,6-disulphonic acid and 8-Hydroxy Naphthyl amine -3,6-disulphonic acid. Decarboxylation, desulphonation, deoxygenation and deamination of Reactive Brown dye showed the presence of different metabolites and metabolic pathways were proposed for the reactive azo dyes which were phytoremediated.

Azo dyes degradation by microorganisms - An efficient and sustainable approach

Synthetic aromatic compounds consisting of various functional groups are known as dyes. These colored compounds are often discharged in effluents, and they are very dangerous to aquatic life. Basically, the dye industry started by using natural plant and insect sources, and then suddenly turned into artificial manufacturing. Natural equilibrium of our environment gets changed by the reduction in photosynthetic activity due to the dyes. In China 900,000 tons of all kinds of dyes are usually produced, which are used in many industries like food, textile, food, paper and leather. Untreated wastewater contaminates aquatic bodies by causing eutrophication, change in water color, oxygen depletion which affect aquatic organisms to a great extent. Dye wastewater is now the key environmental pollution form. In recent eras an extensive study line has been developed to explore the dye decolorization and biodegradation under both aerobic as well as anaerobic conditions. In this review, the chemistry, toxicity and microbial biodegradation/decolorization are presented. Some recent studies along with the new techniques and methodologies of remediating the dye pollution are also discussed to provide the bases of their handling. Overall, efficient and high biodegradation potential make microbes an impending foundation for green chemistry to eradicate toxic dyes from industrial wastewater.

Valorization of phenol contaminated wastewater for lipid production by Rhodosporidium toruloides 9564T

Phenol is one of the most common hazardous organic compound presents in several industrial effluents which directly affects the aquatic environment. The present study envisaged the phenol biodegradation and simultaneous lipid production along with its underlying mechanism by oleaginous yeast Rhodosporidium toruloides 9564^T. Experiments were designed using simulated wastewater by varying phenol concentration in the range of 0.25-1.5 g/L and inoculum size of 1, 5, and 10% with and without glucose. The oleaginous yeast was found to completely degrade up to 0.75 g/L phenol with lipid accumulation of 26.3%. Phenol at > 0.5 g/L severely inhibited the growth of R. toruloides 9564^T at 1% and 5% inoculum size. Phenol toxicity up to 0.75 g/L can be overcome by increasing inoculum size to 10%. The maximum specific growth rate (μ_max) and phenol degradation rate (q_max) were found to be 0.0717 h^-1 and 0.01523 h^-1, respectively. The enzymatic pathway study suggested that R. toruloides 9564^T follows an ortho cleavage pathway for phenol degradation and lipid accumulation. Phytotoxicty and cytotoxicity tests for treated and untreated samples clearly demonstrated a decline in toxicity of the treated wastewater. R. toruloides brought about an important paradigm shift toward a circular economy in which industrial wastewater is considered a valuable resource for bioenergy production.

Molecular response of Anoxybacillus sp. PDR2 under azo dye stress: An integrated analysis of proteomics and metabolomics

Treating azo dye wastewater using thermophilic bacteria is considered a more efficient bioremediation strategy. In this study, a thermophilic bacterial strain, Anoxybacillus sp. PDR2, was regarded as the research target. This strain was characterized at different stages of azo dye degradation by using TMT quantitative proteomic and non-targeted metabolome technology. A total of 165 differentially expressed proteins (DEPs) and 439 differentially metabolites (DMs) were detected in comparisons between bacteria with and without azo dye. It was found that Anoxybacillus sp. PDR2 can degrade azo dye Direct Black G (DBG) through extracellular electron transfer with glucose serving as electron donors. Most proteins related to carbohydrate metabolism, including acetoacetate synthase, and malate synthase G, were overexpressed to provide energy. The bacterium can also self-synthesize riboflavin as a redox mediator of in vitro electron transport. These results lay a theoretical basis for industrial bioremediation of azo dye wastewater.

Demonstration of a plant-microbe integrated system for treatment of real-time textile industry wastewater

The real-time textile dyes wastewater contains hazardous and recalcitrant chemicals that are difficult to degrade by conventional methods. Such pollutants, when released without proper treatment into the environment, impact water quality and usage. Hence, the textile dye effluent is considered a severe environmental pollutant. It contains mixed contaminants like dyes, sodium bicarbonate, acetic acid. The physico-chemical treatment of these wastewaters produces a large amount of sludge and costly. Acceptance of technology by the industry mandates that it should be efficient, cost-effective and the treated water is safe for reuse. A sequential anaerobic-aerobic plant-microbe system with acclimatized microorganisms and vetiver plants, was evaluated at a pilot-scale on-site. At the end of the sequential process, decolorization and total aromatic amine (TAA) removal were 78.8% and 69.2% respectively. Analysis of the treated water at various stages using Fourier Transform Infrared (FTIR), High Performance Liquid Chromatography (HPLC)) Gas Chromatography-Mass Spectrometry (GC-MS) Liquid Chromatography-Mass Spectrometry (LC-MS) indicated that the dyes were decolourized and the aromatic amine intermediates formed were degraded to give aliphatic compounds. Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM) analysis showed interaction of microbe with the roots of vetiver plants. Toxicity analysis with zebrafish indicated the removal of toxins and teratogens.

Improved decolorization and mineralization of azo dye in an integrated system of anaerobic bioelectrochemical modules and aerobic moving bed biofilm reactor

In this study, a stacked integrated system with anaerobic bioelectrochemical system (BES) and aerobic moving bed biofilm reactor (MBBR) was developed to improve the decolorization and mineralization of azo dye. This stacked BES-MBBR exhibited better performance with acid orange (AO7) decolorization of 96.4 ± 0.6% and chemical oxygen demand (COD) removal of 87.7 ± 4.4%. Contribution of each module in the BES and MBBR stages indicated that BES modules enhanced the pretreatment process in AO7 decolorization, and MBBR played an important role in further removal of COD. The mechanism analysis indicated that the azo bond was cleaved with reductive decolorization at biocathode in the anaerobic BES stages, and then the intermediate products can be further oxidized with COD removal in the aerobic MBBR stage. This work demonstrated that the integrated system with stacked anaerobic BES and aerobic MBBR could provide a promising way for the pretreatment and post-treatment of refractory wastewater.

Visible Light-Based Ag3PO4/g-C3N4@MoS2 for Highly Efficient Degradation of 2-Amino-4-acetylaminoanisole (AMA) from Printing and Dyeing Wastewater

In this research, the preparation of a Ag₃PO₄/g-C₃N₄@MoS₂ photocatalyst and the performance and mechanism of degradation of 2-amino-4-acetaminoanisole (AMA) were studied. The phase composition and morphology of the synthesized samples were comprehensively characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), ultraviolet–visible diffuse reflectance (UV–Vis), and photoelectron spectroscopy (XPS). The catalytic performance of the photocatalyst was evaluated by the visible-light catalytic degradation of the AMA. The experimental results show that the Ag₃PO₄/g-C₃N₄@MoS₂ composite photocatalyst has stronger photocatalytic oxidation and reduction capabilities than Ag₃PO₄ and Ag₃PO₄/g-C₃N₄. The material only decreases by 31.3% after five cycles of use, indicating that the material has good light stability. Free radical capture experiments prove that photo-generated holes (h⁺) and superoxide radicals (·O₂⁻) are the main active substances in the photocatalytic process. The fundamental studies in the present research provide a new perspective for constructing an innovative type of visible-light photocatalyst and a new way to promote the photocatalytic degradation of organic pollutants.

Plant microbe based remediation approaches in dye removal: A review

Increased industrialization demand using synthetic dyes in the newspaper, cosmetics, textiles, food, and leather industries. As a consequence, harmful chemicals from dye industries are released into water reservoirs with numerous structural components of synthetic dyes, which are hazardous to the ecosystem, plants and humans. The discharge of synthetic dye into various aquatic environments has a detrimental effect on the balance and integrity of ecological systems. Moreover, numerous inorganic dyes exhibit tolerance to degradation and repair by natural and conventional processes. So, the present condition requires the development of efficient and effective waste management systems that do not exacerbate environmental stress or endanger other living forms. Numerous biological systems, including microbes and plants, have been studied for their ability to metabolize dyestuffs. To minimize environmental impact, bioremediation uses endophytic bacteria, which are plant beneficial bacteria that dwell within plants and may improve plant development in both normal and stressful environments. Moreover, Phytoremediation is suitable for treating dye contaminants produced from a wide range of sources. This review article proves a comprehensive evaluation of the most frequently utilized plant and microbes as dye removal technologies from dye-containing industrial effluents. Furthermore, this study examines current existing technologies and proposes a more efficient, cost-effective method for dye removal and decolorization on a big scale. This study also aims to focus on advanced degradation techniques combined with biological approaches, well regarded as extremely effective treatments for recalcitrant wastewater, with the greatest industrial potential.

Biogenic sulfide for azo dye decolorization from textile dyeing wastewater

Azo dye is the most versatile class of dyes used in the textile industry. Although the sulfidogenic process shows superiority in the removal of azo dye, the role of biogenic sulfide produced by sulfate-reducing bacteria (SRB) in the decolorization of azo dye is unclear. This study explored the mechanism of biogenic sulfide for removal of a model azo dye (Direct Red 81 (DR 81)) through biotic and abiotic batch tests with analysis of intermediates of the azo dye degradation. The results showed that biogenic sulfide produced from sulfate reduction directly cleaved two groups of azo bond (-NN-), thereby achieving decolorization. Moreover, the decolorization rate was enhanced by nearly 3-fold (up to 42 ± 1 mg/L-hr; removal efficiency > 99%) by adding an external carbon source or elevating the initial azo dye concentration. This study showed that biogenic sulfide plays an essential role in azo dye decolorization and provides a new avenue for the potential application of biogenic sulfide from the sulfidogenic system for the treatment of azo dye-laden wastewater.

Biosorption capacity of Mucor circinelloides bioaugmented with Solanum nigrum L. for the cleanup of lead, cadmium and arsenic

The biosorption and bioaugmentation performances of Mucor circinelloides were investigated under different contact time, initial metal(loid) concentration and species. The microbe-plant interaction appeared synergistic with enhancing plant growth and alleviating oxidative damages induced by lead, cadmium and arsenic. The bioaugmentation with M. circinelloides led to significant immobilization on lead, cadmium and arsenic as indicated by the decreases of metal(loid) transfer and bioavailability in plant-microbe aqueous system. Lead, cadmium and arsenic were mainly allocated on cell wall and a few parts entered into intercellular system, suggesting cell wall adsorption and intracellular bioaccumulation served as the main mechanisms of M. circinelloides. The adsorption kinetics and isotherms on lead, cadmium and arsenic were fitted well with the pseudo-second-order and Langmuir models, with the maximum adsorption capacities of 500, 15.4 and 29.4 mg·g^-1 fungal biomass at pH 6.0 and 25 ℃. The optimum initial concentration and contact time were 300-10-20 mg·L^-1 and 2 h. This study provides a basis for M. circinelloides as a promising adsorbent and bioaugmented agent for the cleanup of soil/aqueous environment contaminated with lead, cadmium and arsenic.

Magnetic nanocomposites for sustainable water purification-a comprehensive review

Numerous contaminants in huge amounts are discharged to the environment from various anthropogenic activities. Waterbodies are one of the major receivers of these contaminants. The contaminated water can pose serious threats to humans and animals, by distrubing the ecosystem. In treating the contaminated water, adsorption processes have attained significant maturity due to lower cost, easy operation and environmental friendliness. The adsorption process uses various adsorbent materials and some of emerging adsorbent materials include carbon- and polymer-based magnetic nanocomposites. These hybrid magnetic nanocomposites have attained extensive applications in water treatment technologies due to their magnetic properties as well as combination of unique characteristics of organic and inorganic elements. Carbon- and polymer-related magnetic nanocomposites are more adapted materials for the removal of various kinds of contaminants from waterbodies. These nanocomposites can be produced via different approaches such as filling, pulse-laser irradiation, ball milling, and electro-spinning. This comprehensive review is compiled by reviewing published work of last the latest recent 3 years. The review article extensively focuses on different approaches for producing various carbon- and polymer-based magnetic nanocomposites, their merits and demerits and applications for sustainable water purification. More specifically, use of carbon- and polymer-based magnetic nanocomposites for removal of heavy metal ions and dyes is discussed in detail, critically analyzed and compared with other technologies. In addition, commercial viability in terms of regeneration of adsorbents is also reviewed. Furthermore, the future challenges and prospects in employing magnetic nanocomposites for contaminant removal from various water sources are presented.

A Performance Comparison of Anaerobic and an Integrated Anaerobic-Aerobic Biological Reactor System for the Effective Treatment of Textile Wastewater

The accumulation of recalcitrant azo dyes from untreated textile effluents has adversely impacted the ecosystem. The immense stability in their nature is conferred by the presence of azo bonds (N=N) in their structure. The reduction of this azo bond occurs exclusively under anaerobic conditions giving rise to colorless aromatic amines, which are carcinogenic. In the present study, a synthetic textile effluent containing mixed azo dyes such as Reactive Red, Reactive Black, and Reactive Brown, was treated using activated sludge under anaerobic conditions in a lab-scale anaerobic sequential batch reactor (An-SBR). At a concentration of 100 mg/L of mixed azo dyes, the An-SBR gave a maximum of 88% decolorization detected through UV-visible spectroscopy. Physicochemical analyses revealed 73% removal of BOD, 90% TDS removal, 69% COD removal, 4.05% TKN removal, 66% chloride removal, and 73% hardness removal. When the concentration of dyes was increased to 500 mg/L, the treatment showed a decrease in decolorization efficiency. This was then compared to a sequential anaerobic-aerobic treatment process performed in An-SBR and a laboratory-scale aerobic moving bed biofilm reactor (MBBR). The study revealed that the sequential process held more potential for commercial application than exclusively an anaerobic process. The metabolites formed during the treatment phase were extracted and analyzed by FT-IR and HPLC and identified through GC-MS analyses and were compared to those found in the untreated effluent. A phytotoxicity test was conducted on the remainder (secondary) sludge using Vigna unguiculata, and it was found to show a 50% reduction in germination and retardation in root and shoot length.

Carbon Based Polymeric Nanocomposites for Dye Adsorption: Synthesis, Characterization, and Application

Agglomeration and restacking can reduce graphene oxide (GO) activity in a wide range of applications. Herein, GO was synthesized by a modified Hummer's method. To minimize restacking and agglomeration, in situ chemical oxidation polymerization was carried out to embed polyaniline (PANI) chains at the edges of GO sheets, to obtain GO-PANI nanocomposite. The GO-PANI was tested for the adsorptive removal of brilliant green (BG) from an aqueous solution through batch mode studies. Infrared (FT-IR) analysis revealed the dominance of hydroxyl and carboxylic functionalities over the GO-PANI surface. Solution pH-dependent BG uptake was observed, with maximum adsorption at pH 7, and attaining equilibrium in 30 min. The adsorption of BG onto GO-PANI was fit to the Langmuir isotherm, and pseudo-second-order kinetic models, with a maximum monolayer adsorption capacity (q_m) of 142.8 mg/g. An endothermic adsorption process was observed. Mechanistically, π-π stacking interaction and electrostatic interaction played a critical role during BG adsorption on GO-PANI.

Degradation and Toxicity Analysis of a Reactive Textile Diazo Dye-Direct Red 81 by Newly Isolated Bacillus sp. DMS2

An efficient diazo dye degrading bacterial strain, Bacillus sp. DMS2 was isolated from a long-term textile dye polluted environment. The strain was assessed for its innate ability to completely degrade and detoxify Direct Red 81 (DR81) textile dye under microaerophilic conditions. The degradation ability of strain showed significant results on optimizing the nutritional and environmental parameters. Based on statistical models, maximum efficiency of decolorization achieved within 24 h for 100 mg/l of dye supplemented with glucose (0.02%), MgSO₄ (0.002%) and urea (0.5%) at 30°C and pH (7.0). Moreover, a significant catabolic induction of a laccase and azoreductase suggested its vital role in degrading DR81 into three distinct metabolites (intermediates) as by-products. Further, toxicity analysis of intermediates were performed using seeds of common edible plants, aquatic plant (phytotoxicity) and the nematode model (animal toxicity), which confirmed the non-toxic nature of intermediates. Thus, the inclusive study of DMS2 showed promising efficiency in bioremediation approach for treating industrial effluents.

Using Electrolytic Manganese Residue to prepare novel nanocomposite catalysts for efficient degradation of Azo Dyes in Fenton-like processes

In this study, Electrolytic Manganese Residue (EMR) was treated by EDTA-2Na/NaOH, ultrasonic etching, and hydrothermal reaction to obtain a novel nanocomposite catalyst (called N-EMR), which then was used, together with H₂O₂, to treat synthetic textile wastewater containing Reactive Red X-3B, Methyl Orange, Methylene blue and Acid Orange 7. Results indicated that the N-EMR had a nano-sheet structure in sizes of 100-200 nm; new iron and manganese oxides with high activity were produced. The mixture of a small amount of N-EMR (40 mg/L) and H₂O₂ (0.4 × 10^-3 M) could removal about 99% of azo dyes (at 100 mg/L in 100 mL) within 6-15 min, much faster than many advanced oxidation processes (AOPs) reported in the literature. The elucidation of the associated mechanism for azo dyes degradation indicates that azo dyes were attacked by superoxide radicals, hydroxyl radicals, and electron holes generated within system. N-EMR was found to be reusable and showed limited inhibition by co-existing anions and cations. Moreover, high removal efficiency of azo dyes could happen in the system with a wide range of pH (1-8.5) and temperatures (25-45 °C), indicating that the process developed in this study may have broad application potential in treatment of azo dyes contaminated wastewater.

Decoding social behaviors in a glycerol dependent bacterial consortium during Reactive Blue 28 degradation

Biodegradation of reactive azo dyes has been an arduous problem for decades. Several efficient biosystems have been proposed for dye degradation, but most of them are dependent on the availability of costly co-substrates such as peptone, yeast extract, and/or glucose. The present study describes the azo dye degradation by a bacterial consortium using glycerol as a sole co-substrate. The consortium was developed from a mixed bacterial culture obtained upon enrichment of soil sediment for Reactive Blue 28 (RB28) decolorization in the presence of glycerol (0.1%; v/v). The consortium with three bacterial species, i.e., Stenotrophomonas acidaminiphila APG1, Cellulomonas sp. APG4, and Pseudomonas stutzeri APG2, designated as "SCP," decolorized 92% of 100 ppm dye in 96 h. The intricacies of the interactions existing within the members of the consortium were resolved by a simple and unique analysis called "BSocial." Among all the members, Cellulomonas sp. APG4 exerted a net-positive impact for decolorization (%) on the consortium. The net fitness of the community increased when all the three species were present, and thus, all of them were selected for further analysis. Moreover, APG4 seemed to be central in the reductive decolorization as it possessed the highest reductase activity. The dye degradation by the consortium was demonstrated by UV-Visible spectroscopy, HPTLC, and FTIR spectroscopy of control and decolorized cell-free supernatant. The LC-ESI-MS analysis of metabolites extracted from decolorized cell-free medium led to the identification of degradation products, thus leading us to propose the plausible pathway for degradation of RB28 by bacterial consortium.

Chlorobenzene levels, component distribution, and ambient severity in wastewater from five textile dyeing wastewater treatment plants

Chlorobenzenes (CBs) present in synthetic dyes are discharged into natural waters during the treatment of textile dyeing wastewater, which may have adverse effects on human and environment. In this study, the existence and removal of 12 CBs in different units of five treatment plants were examined. The ecological risk of CBs in textile dyeing wastewater was assessed by ambient severity (AS) and risk quotients (RQs). The results showed that trichlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene were ubiquitous in textile dyeing wastewater, and their distribution was similar. In one of the plants, the content of hexachlorobenzene was found to be as high as 9.277 μg/L in the raw water, which was an oil-water mixture. In other plants, there was no significant difference in the content and composition of CBs among influent and effluent suggesting that the conventional wastewater treatment plants cannot improve the existence of them. Monochlorobenzene and dichlorobenzene were not detected, which may have been related to strong volatility, biochemical properties, and weak instrument sensitivity. In the treatment process and effluent, trichlorobenzene is the main pollutant and accounted for 39.51% of all CB. CB removal was found only in the anaerobic system, while the aerobic system did not have the corresponding removal effect on CB and total organic carbon. According to ecological risk assessment, CBs in effluent has not been found the significant potential harm to human health (AS < 1), but posed moderate ecological risk to aquatic ecosystem (RQs > 0.1).

Intermittent aeration strategy for azo dye biodegradation: A suitable alternative to conventional biological treatments?

Most solutions for biological treatment of azo dyes are based on conventional anaerobic-aerobic processes, but transition to full scale demands technology simplification and cost reductions. We suggest a new approach, in which aeration is intermittently supplied for simultaneous removal of color and toxic metabolites in a single compartment. Effects of aeration strategy and glucose concentration on decolorization and organic matter removal were assessed using factorial design (32) and response surface analysis. Bioreactors were inoculated with microorganisms previously acclimated to Direct Black 22 (DB22), which was the azo compound used in this study. Assays performed with synthetic textile wastewater showed that long-term decolorization was not impaired at a moderate level of aeration (4 hourly-cycles per day). Aerated batches presented lower color removal velocities, but these negative impacts were offset by increasing initial glucose concentration. Higher degrees of mineralization of the azo compound and higher organic matter removals were achieved in intermittently aerated experiments, which led to lower toxicity to Daphnia magna. Biomolecular analysis revealed that the microbial community structure was strongly associated with operational efficiency parameters. These findings suggest intermittent aeration can be implemented to accomplish enhanced azo dye biodegradation.

Silver nanoparticles in dye effluent treatment: A review on synthesis, treatment methods, mechanisms, photocatalytic degradation, toxic effects and mitigation of toxicity

The current scenario of water resources shows the dominance of pollution caused by the draining of industrial effluents. The polluted waters have resulted in severe health and environmental hazards urging for a suitable alternative to resolve the implications. Various physical and chemical treatment steps currently in use for dye effluent treatment are more time consuming, cost-intensive, and less effective. Alternatively, nanoparticles due to their excellent surface properties and chemical reactivity have emerged as a better solution for dye removal and degradation. In this regard, the potential of silver nanoparticles in dye effluent treatment was greatly explored. Efforts were taken to unravel the kinetics and statistical optimization of the treatment conditions for the efficient removal of dyes. In addition, the role of silver nanocomposites has also experimented with colossal success. On the contrary, studies have also recognized the mechanisms of silver nanoparticle-mediated toxicity even at deficient concentrations and their deleterious biological effects when present in treated water. Hence, the fate of the silver nanoparticles released into the treated water and sludge, contaminating the soil, aquatic environment, and underground water is of significant concern. This review summarizes the current state of knowledge regarding the use of silver nanoparticles and silver-based nanocomposites in effluent treatment and comprehends the recent research on mitigation of silver nanoparticle-induced toxicity.

Design and Preparation of Chitosan-Crosslinked Bismuth Ferrite/Biochar Coupled Magnetic Material for Methylene Blue Removal

Biochar obtained by pyrolysis of the fiber plant kenaf was mixed with bismuth ferrite (BiFeO₃) in a chitosan-containing acetic acid solution, magnetized, and modified to prepare a chitosan-crosslinked BiFeO₃/biochar coupled magnetic material. The adsorption properties of the composite were investigated using methylene blue dissolved in water, and the effects of external conditions, such as pH, methylene blue concentration, reaction time, and temperature, on the adsorption performance were studied. The adsorption data were fitted and analyzed with kinetic and isotherm models, and the results showed that the BiFeO₃/biochar coupled magnetic material effectively adsorbed methylene blue. The amounts adsorbed onto this magnetic material increased with increasing initial methylene blue concentration, reaction time, and temperature, and the adsorption performance improved under neutral and alkaline conditions. The pseudo-first-order kinetic and Langmuir isotherm models satisfactorily fitted the adsorption data, showing that the adsorption of methylene blue involved both chemical and physical adsorption. The maximum adsorption capacity of methylene blue onto the BiFeO₃/biochar coupled magnetic material reached 18.942 mg·g⁻¹ at 25 °C, confirming the excellent dye binding activity of this material.

Azo dyes degradation and mutagenicity evaluation with a combination of microbiological and oxidative discoloration treatments

This work evaluated the degradation of the Acid Blue 161 and Procion Red MX-5B dyes in a binary solution by the filamentous fungus Aspergillus terreus and the yeast Saccharomyces cerevisiae in systems with and without electrochemical oxidation as the pretreatment process. UV-Vis spectrophotometry, high-performance liquid chromatography with (HPLC), Fourier transform infrared (FT-IR) spectroscopy and Salmonella/microsome assay (Ames test) were applied towards the degradation analysis of the dyes. Adsorption tests with white clay immobilized on alginate were also conducted after the discoloration treatments to remove intermediate metabolites formed during the degradation of the dye molecules. The discoloration treatments led to the complete color removal of the solutions in all the systems tested. The clay demonstrated affinity for the metabolites formed after discoloration treatments, the removal rates were variable, but the all systems has proved efficient. The Salmonella/microsome assay (Ames test) with strains TA98 and TA100 in the absence and presence of exogenous metabolism (S9 microsomal system, Moltox) revealed that the initial molecules and by-products of the metabolism of the dyes were direct mutagens. The electrochemical/A. terreus/clay system was able to discolor the solutions and transform the direct mutagens into non-mutagenic compounds in addition to reducing the mutagenic potency of the pro-mutagens to the Salmonella strain TA100/S9, which demonstrates the high efficiency of this system with regard to discoloring and degrading azo dye molecules and their by-products. Therefore, this study showed that although not having standard treatment system for this type of pollutant, the combination of treatments can be considered promising. The use of electrochemical oxidation along with microbiological treatment may lead to the degradation and mineralization of these compounds, reducing or eliminating the environmental impact caused by the improper disposal of these dyes in aquatic environments.

Kinetics study of dinitrodiazophenol industrial wastewater treatment by a microwave-coupled ferrous-activated persulfate process

In this study, a ferrous-activated persulfate (PS) process induced by microwave (MW) energy was used to treat an industrial wastewater containing dinitrodiazophenol (DDNP). The effect of different operational parameters, such as PS dose, initial pH, MW power, and the mass ratio of ferrous to PS [i.e., n(Fe²⁺/PS)], on chemical oxygen demand (COD) removal and the pseudo first-order constant k was systematically studied. Results showed that the constant k and COD removal increased considerably with increasing PS dose, MW power, and n(Fe²⁺/PS); however, the constant k and COD removal decreased proportionally as the initial pH increased from 3 to 11. A base-activated PS system was formed when the initial pH further increased to 13, which resulted in a dramatic increase of k and COD removal. Controlled experiments demonstrated that the synergetic effect of MW, Fe²⁺, and PS were significant. The value of k was 0.2425 min^-1, COD removal was 71.42%, and biodegradability remarkably increased from 0.056 to 0.6712 during treatment by MW-Fe²⁺/PS at a PS dose of 8 g/L, MW power of 600 W, initial pH of 3, n(Fe²⁺/PS) of 0.04, and reaction time of 14 min. Spectral analyses showed that the chromophores (including the diazo group and nitro group compounds) and benzene rings were greatly decomposed. Identification tests for reactive oxygen species showed that the predominant oxidizing species in the MW-Fe²⁺/PS process was the sulfate radical, and that the hydroxyl radical played a lesser role for color number elimination. From the perspective of both treatment efficiency energy consumption, the MW-Fe²⁺/PS process was confirmed to be an economical and promising pretreatment process for DDNP industrial wastewater.

Mechanism of adsorption of humic acid by modified aged refuse

In the present study, aged refuse (AR) was modified to be applied as an adsorbent to remove humic acid from water. The efficiency of humic acid removal by modified aged refuse (MAR) under different preparation conditions (calcination temperature, dose of aged refuse for calcination and holding time) was systematically investigated. Results showed that the optimum preparation conditions are calcination temperature = 700 °C, AR dose for calcination = 25 g, and holding time = 2.0 h. The characteristics of the modified aged refuse obtained under different calcination conditions were determined by Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy analysis. In addition, the effects of modified aged refuse dose and initial solution pH on adsorption performance were studied. The removal of humic acid increased with higher doses of modified aged refuse, and weak alkaline (initial pH = 8.0) conditions were favorable for humic acid removal. A pseudo-second order model fitted the experimental data well. Moreover, the adsorption isotherms were well described by the Langmuir isotherm model, in which the monolayer surface loading was calculated to be approximately 37 mg g⁻¹. During the adsorption process, the molecular weight, degree of condensation and aromaticity of humic acid were considerably decreased, according to 3D-EEM analysis. MAR as a new type of adsorbent thus provides a potential adsorption method for humic acid.

In the present study, aged refuse (AR) was modified to be applied as an adsorbent to remove humic acid from water.