Review paper on current technologies for decolourisation of textile wastewaters: perspectives for anaerobic biotechnology

Synergistic efficiency of modified banana leaf derived cellulose-g-C3N4 hybrid composite: a sustainable approach for visible-light-driven photodegradation of dyes

The adverse effects on human health and water supplies due to widespread use of dyes including methylene blue (MB) and rhodamine B necessitate their removal. Photocatalytic decontamination offers an alternative method which is cost effective and ecofriendly compared to other costly dye removal processes. The combination of graphitic carbon nitride (g-C3N4) and cellulose from readily available modified banana leaves (MBLC) has not been explored for color degradation. The present work investigates the application of a promising g-C3N4-MBLC composite for the photocatalytic removal of methylene blue and rhodamine B dyes. The two-component hybrid composite was synthesized utilizing the one-pot in situ thermal polymerization techniques. Furthermore, multiple analytical methods were exploited to comprehensively assess the structural and morphological characteristics of the synthesized g-C3N4-cellulose hybrid composite. The composites exhibited photocatalytic activity, successfully degrading 93.35% of RhB and 92.06% (30 mg L-1) of MB dyes within 120 minutes under visible irradiation. Analysis of scavenging effects indicated that ˙O2 - and h+ radicals were the primary reactive oxygen species (ROS) responsible for the photodegradation of the dyes. Additionally, the synthesized composite showed excellent reusability, maintaining 81% efficiency after five consecutive cycles, highlighting its potential for practical applications, particularly in pollutant removal.

Simultaneous degradation of direct black BN dye wastewater and electricity generation by red soil microbial fuel cells

Azo dyes, widely used in industries, pose environmental challenges due to their recalcitrance and potential carcinogenicity. Microbial fuel cells (MFCs) offer a sustainable solution by coupling wastewater treatment with renewable energy production. However, research on polyazo dye treatment using MFCs remains limited. This study developed a novel MFC system using red soil as the anode substrate (RSMFC) to treat direct black BN wastewater, focusing on removal efficiency, power generation, and microbial community dynamics. The concentration of direct black BN influenced the RSMFC's performance, showing a "low promotion and high inhibition" effect on electricity generation. The system achieved a peak power density of 584.82 mW/m3. GC-MS analysis identified primary degradation products, including 13-Docosenamide, (Z)- and Bis(2-ethylhexyl) phthalate, revealing the degradation pathway of direct black BN. Microbial community analysis highlighted the roles of Bosea, Citrifermentans, Desulfosporosinus, and Pseudomonas in dye tolerance and degradation. Additionally, influent concentrations of 300 mgCOD/L, containing 99.7 mg/L direct black BN, significantly enriched electricigens such as Geobacter, Desulfovibrio, Pseudomonas, and Acinetobacter. Our findings provide essential groundwork for optimizing RSMFCs and advancing azo dye wastewater treatment technologies. The simultaneous removal of direct black BN and electricity generation in the RSMFC holds promise for sustainable environmental management.

Harnessing the rhizosphere sponge to smooth pH fluctuations and stabilize contaminant retention in biofiltration system

Fluctuating pH conditions can affect heavy metal mobility, thereby limiting the efficiency of biofiltration systems (BS). To address this, we developed an innovative rhizosphere sponge, biochar-based bioreactor (RBB), designed to stabilize Cd2+ removal across a pH range of 5 to 9. RBB consistently outperformed the control, achieving a notable 91.3 % Cd2+ removal at pH 5. By creating optimized oxygen and redox zoning, the rhizosphere sponge enhanced both biochar surface reactions and microbial activity. Under acidic conditions, biochar facilitated Fe2+/Mn2+ precipitation into stable (oxy)hydroxides, a process further driven by microbial oxidation. Consequently, RBB accumulated 1.54 times more Fe-Mn oxide-bound Cd than the control, effectively reducing Cd2+ mobility. Additionally, loosely bound extracellular polymeric substances claimed preferential Cd2+ sequestration after acidification. The stabilized microecology and increased ecological niches, allowing RBB to better buffer against pH fluctuations, presenting it as a robust solution for sustainable heavy metal remediation in variable environments.

Fungus mediated synthesis of biogenic palladium catalyst for degradation of azo dye

Dyes are the coloured substances that are applied on different substrates such as textiles, leather and paper products, etc. Azo dyes release from the industries are toxic and recalcitrant wastewater pollutants, therefore it is necessary to degrade these pollutants from water. In this study, the palladium (0) nanoparticles (PdNPs) were generated through the biological process and exhibited for the catalytic degradation of azo dye. The palladium nanoparticles (PdNPs) were synthesized by using the cell-free approach i.e. extract of fungal strain Rhizopus sp. (SG-01), which significantly degrade the azo dye (methyl orange). The amount of catalyst was optimized by varying the concentration of PdNPs (1 mg/mL to 4 mg/mL) for 10 mL of 50 ppm methyl orange (MO) dye separately. The time dependent study demonstrates the biogenic PdNPs could effectively degrade the methyl orange dye up to 98.7% with minimum concentration (3 mg/mL) of PdNPs within 24 h of reaction. The long-term stability and effective catalytic potential up to five repeated cycles of biogenic PdNPs have good significance for acceleration the degradation of azo dyes. Thus, the use of biogenic palladium nanoparticles for dye degradation as outlined in the present study can provide an alternative and economical method for the synthesis of PdNPs as well as degradation of azo dyes present in wastewater and is helpful to efficiently remediate textile effluent.

Recent Advances in Utilizing Lignocellulosic Biomass Materials as Adsorbents for Textile Dye Removal: A Comprehensive Review

This review embarks on a comprehensive journey, exploring the application of lignocellulosic biomass materials as highly effective adsorbents for the removal of textile dyes (cationic and anionic dyes) from wastewater. A literature review and analysis were conducted to identify existing gaps in previous research on the use of lignocellulosic biomass for dye removal. This study investigates the factors and challenges associated with dye removal methods and signifies their uses. The study delves into the pivotal role of several parameters influencing adsorption, such as contact time, pH, concentration, and temperature. It then critically examines the adsorption isotherms, unveiling the equilibrium relationship between adsorbent and dye and shedding light on the mechanisms of their interaction. The adsorption process kinetics are thoroughly investigated, and a detailed examination of the adsorbed rate of dye molecules onto lignocellulosic biomass materials is carried out. This includes a lively discussion of the pseudo-first, pseudo-second, and intra-particle diffusion models. The thermodynamic aspects of the adsorption process are also addressed, elucidating the feasibility and spontaneity of the removal process under various temperature conditions. The paper then dives into desorption studies, providing insights into the regeneration potential of lignocellulosic biomass materials for sustainable reusability. The environmental impact and cost-effectiveness of employing lignocellulosic biomass materials in textiles including Congo Red, Reactive Black 5, Direct Yellow 12, Crystal Violet, Malachite Green, Acid Yellow 99, and others dyes from wastewater treatment are discussed, emphasizing the significance of eco-friendly solutions. In summary, this review brings together a wealth of diverse studies and findings to present a comprehensive overview of lignocellulosic biomass materials as adsorbents for textile cationic and anionic dye removal, encompassing various aspects from influential parameters to kinetics, adsorption isotherms, desorption, and thermodynamics studies. Its scope and other considerations are also discussed along with its benefits. The collective knowledge synthesized in this paper is intended to contribute to the advancement of sustainable and efficient water treatment technologies in the textile industry.

Treatment of azo dye-containing wastewater in a combined UASB-EMBR system: Performance evaluation and membrane fouling study

This work investigated the treatment of azo dye-containing wastewater in an upflow anaerobic sludge blanket (UASB) reactor combined with an electro-membrane bioreactor (EMBR). Current densities of 20 A m-2 and electric current exposure mode of 6'ON/30'OFF were applied to compare the performance of the EMBR to a conventional membrane bioreactor (MBR). The results showed that dye (Drimaren Red CL-7B) removal occurred predominantly in the UASB reactor, which accounted for 57% of the total dye removal achieved by the combined system. When the MBR was assisted by electrocoagulation, the overall azo dye removal efficiency increased from 60.5 to 67.1%. Electrocoagulation batch tests revealed that higher decolorization rates could be obtained with a current density of 50 A m-2. Over the entire experimental period, the combined UASB-EMBR system exhibited excellent performance in terms of chemical oxygen demand (COD) and NH4+-N removal, with average efficiencies above 97%, while PO43--P was only consistently removed when the electrocoagulation was used. Likewise, a consistent reduction in the absorption spectrum of aromatic amines was observed when the MBR was electrochemically assisted. In addition to improving the pollutants removal, the use of electrocoagulation reduced the membrane fouling rate by 68% (0.25-0.08 kPa d-1), while requiring additional energy consumption and operational costs of 1.12 kWh m-3 and 0.32 USD m-3, respectively. Based on the results, it can be concluded that the combined UASB-EMBR system emerges as a promising technological approach for textile wastewater treatment.

An ecofriendly approach to bioremediate nickel oxide nanoparticles using a macrofungus, Pleurotus fossulatus

Nowadays, nickel oxide nanoparticles are in great demands owing to their use in many sectors. These nanoparticles may release into aquatic environment from different industries and cause negative effect on aquatic flora and fauna. Therefore, an effective and efficient method is required to remove these nanoparticles from contaminated water. Hence, the aim of this study was to bioremediate nickel oxide nanoparticles using a macrofungus, Pleurotus fossulatus, and to analyze its impact on fungal physiology. For this purpose, fungal spawns were inoculated in malt dextrose agar media containing different concentrations of nickel oxide nanoparticles (24 mg/l, 48 mg/l, and 100 mg/l) as well as control group (having no nickel oxide nanoparticles) and allowed to grow for a period of 20 days. Fungal mycelia as well as media were collected at different time intervals (5th day, 10th day, 15th day, and 20th day) for evaluation of Ni concentration and different biochemical parameters. Ni removal efficiency of P. fossulatus from media was found to be highest in 48 mg/l (66.98%) followed by 24 mg/l (60.83%) and 100 mg/l (18.03%), respectively. Increased level of metallothionein, lipid peroxidation, activity of different antioxidant enzymes (superoxide dismutase, catalase, glutathione s transferase, glutathione reductase), activity of ligninolytic enzymes (laccase, lignin peroxidase, manganese peroxidase), and shift in FTIR spectra were also reported in mycelia cultured in malt dextrose agar media containing nickel oxide nanoparticles. This study suggests that P. fossulatus has great efficiency to remediate nanoparticles from contaminated water and it can be utilized as potential agent in wastewater treatment plants by different industries.

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO-LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO-LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2 mmol doped CN sample that showed two times better photocatalytic activity than the pure one.

Recent advances in environmental and agricultural applications of hydrochars: A review

Hydrochar is a carbonaceous material that is generated through the process of hydrothermal carbonization (HTC) from biomass, which has garnered considerable attention in recent years owing to its potential applications in a diverse range of fields, such as environmental remediation and agriculture. Hydrochar is produced from a diverse range of biomass waste materials and retains exceptional properties, including high carbon content, stability, and surface area, making it an optimal candidate for various enviro-agricultural applications. Moreover, it delves into the production process of hydrochar, with explicit emphasis on the optimization of certain properties during the production of hydrochar from bio-waste. Furthermore, the potential of hydrochar as an adsorbent and catalyst support for heavy metals and dyes was extensively explored, along with a soil remediation potential that can improve the physical, chemical and biological properties of soil. This comprehensive review aims to provide a thorough overview of hydrochar with a particular focus on its production, properties, and prospective applications. The significance of hydrochar is accentuated and the growing need for alternative sources of energy and materials that are environmentally sustainable is highlighted in this paper. Besides, the consequence of hydrochar on soil properties such as water-holding capacity, nutrient retention, and total soil porosity, as well as its influence on soil chemical properties such as cation exchange capacity, electrical conductivity, and surface functionality is scrutinized.

Recovery of Ag(I) from Wastewater by Adsorption: Status and Challenges

Untreated or inadequately treated silver-containing wastewater may pose adverse effects on hu-man health and the ecological environment. Currently, significant progress has been made in the treatment of Ag(I) in wastewater using adsorption methods, with adsorbents playing a pivotal role in this process. This paper provides a systematic review of various adsorbents for the recovery and treatment of Ag(I) in wastewater, including MOFs, COFs, transition metal sulfides, metal oxides, biomass materials, and other polymeric materials. The adsorption mechanisms of these materials for Ag(I) are elaborated upon, along with the challenges currently faced. Furthermore, insights into optimizing adsorbents and developing novel adsorbents are proposed in this study.

Enhanced Adsorption of Methylene Blue Dye on Functionalized Multi-Walled Carbon Nanotubes

Carbon nanomaterials are promising adsorbents for dye removal from wastewater also due to their possible surface functionalization that, in principle, can increase the adsorption rate and provide regeneration. To investigate the real advantages of functionalization, we synthesized and characterized through IR, TGA, TEM, XPS and DLS measurements a multi-walled carbon nanotube (MWCNT) derivative bearing benzenesulfonate groups (MWCNT-S). The obtained material demonstrated to have good dispersibility in water and better capability to adsorb methylene blue (MB) compared to the pristine MWCNT adsorbent. Adsorption kinetic studies showed a very fast process, with a constant significantly higher with respect not only to that of the unfunctionalized MWCNT adsorbent but also to those of widely used activated carbons. Moreover, the adsorption capacity of MWCNT-S is more than doubled with respect to that of the insoluble pristine MWCNT adsorbent, thanks to the dispersibility of the derivatives, providing a larger available surface, and to the possible electrostatic interactions between the cationic MB and the anionic sulfonate groups. Additionally, the reversibility of ionic interactions disclosed the possibility to release the adsorbed cationic pollutant through competition with salts, not only regenerating the adsorbent, but also recovering the dye. Indeed, by treating the adsorbed material for 1 h with 1 M NaCl, a regeneration capacity of 75% was obtained, demonstrating the validity of this strategy.

Advancing sustainable water treatment strategies: harnessing magnetite-based photocatalysts and techno-economic analysis for enhanced wastewater management in the context of SDGs

Herein, we explore the holistic integration of magnetite-based photocatalysts and techno-economic analysis (TEA) as a sustainable approach in wastewater treatment aligned with the Sustainable Development Goals (SDGs). While considerable attention has been devoted to photocatalytic dye degradation, the nexus between these processes and techno-economic considerations remains relatively unexplored. The review comprehensively examines the fundamental characteristics of magnetite-based photocatalysts, encompassing synthesis methods, composition, and unique properties. It investigates their efficacy in photocatalytic degradation, addressing homogeneous and heterogeneous aspects while discussing strategies to optimize photodegradation efficiency, including curbing electron-hole recombination and mitigating scavenging effects and interference by ions and humic acid. Moreover, the management aspects of magnetite-based photocatalysts are examined, focusing on their reusability and regeneration post-dye removal, along with the potential for reusing treated wastewater in relevant industrial applications. From a techno-economic perspective, the study evaluates the financial feasibility of deploying magnetite-based photocatalysts in wastewater treatment, correlating reduced pollution and the marketing of treated water with social, economic, and environmental objectives. By advocating the integration of magnetite-based photocatalysts and TEA, this paper contributes insights into scalable and profitable sustainable wastewater treatment practices. It underscores the alignment of these practices with SDGs, emphasizing a comprehensive and holistic approach to managing wastewater in ways that meet environmental, economic, and societal objectives.

Green Organo-Photooxidative Method for the Degradation of Methylene Blue Dye

This study used an organophoto-oxidative material to degrade the toxic azo dye, methylene blue (MB), due to its hazardous effects on aquatic life and humans. MB is traditionally degraded using metal-based catalysts, resulting in high costs. Several organic acids were screened for organo-photooxidative applications against various azo dyes, and ascorbic acid (AA), also known as vitamin C, was found to be best for degradation due to its high photooxidative activity. It is an eco-friendly, edible, and efficient photooxidative material. A photocatalytic box has been developed for the study of organo-photooxidative activity. It was found that when AA was added, degradation efficiency increased from 42 to 95% within 240 min. Different characterization techniques, such as HPLC and GC-MS, were used after degradation for the structural elucidation of degraded products. DFT study was done for the investigation of the mechanistic study behind the degradation process. A statistical tool, RSM, was used for the optimization of parameters (concentration of dye, catalyst, and time). This study develops sustainable and effective solutions for wastewater treatment.

Using structural equation modeling to assess the genotoxic and mutagenic effects of heavy metal contamination in the freshwater ecosystems: A study involving Oreochromis niloticus in an urban river

Chemical pollutants represent a leading problem for aquatic ecosystems, as they can induce genetic, biochemical, and physiological changes in the species of these ecosystems, thus compromising their adaptability and survival. The Capibaribe River runs through the state of Pernambuco, located in Northeastern Brazil, and passes through areas of agricultural cultivation, densely populated cities, and industrial centers, primarily textiles. Despite its importance, few ecotoxicological studies have been conducted on its environment, and knowledge about pollution patterns and their effects on its biota is still being determined. The objective of this study was to evaluate the water quality and the damage supposed to be caused by pollutants on the DNA specimens of Nile tilapia (Oreochromis niloticus) obtained from seven strategic points of Capibaribe. Tilapia specimens and water were collected during the rainy and dry seasons from 2015 to 2017. The following characteristics were analyzed: physicochemical (six), metal concentration (seven), local pluviosity, micronuclei, and comet assay. The physicochemical and heavy metal analyses were exploratory, whereas the ecotoxicological analyses were hypothetical. To verify this hypothesis, we compared the groups of fish collected to the results of the micronuclei test and comet assay. We created a Structural Equation Model (SEM) to determine how each metal's micronuclei variables, damage index, pluviosity, and concentration were related. Our results demonstrated that the highest values for markers of genetic damage were detected at points with the highest heavy metal concentrations, especially iron, zinc, manganese, chromium, and cadmium. The SEM demonstrated that metals could explain the findings of the genotoxicity markers. Moreover, other pollutants, such as pesticides, should be considered, mainly where the river passes through rural areas. The results presented here demonstrate that the Capibaribe River has different degrees of contamination and confirm our hypothesis.

Tuning disorder in structurally colored bioinspired photonic glasses

Colloidal crystals, such as opals, display bright and iridescent colors when assembled from submicron particles. While the brightness and purity of iridescent colors are well suited for ornaments, signaling, and anticounterfeiting, their angle dependence limits the range of their applications. In contrast, colloidal glasses display angle-independent structural color that is tunable by the size and local arrangement of particles. However, the angle-independent color of colloidal photonic glasses usually yields pastel colors that are not vivid due to the disorder in the particle assembly. Here, we report an electrophoretic assembly platform for tuning the level of disorder in the particle system from a colloidal crystal to a colloidal glass. Altering the electric field in our electrophoretic platform allows for deliberate control of the assembly kinetics and thus the level of order in the particle assembly. With the help of microscopy, X-ray scattering, and optical characterization, we show that the photonic properties of the assembled films can be tuned with the applied electric field. Our analyses reveal that angle-independent color with optimum color brightness can be achieved in typical colloidal suspensions when the range of order is at ∼3.2 particle diameters, which is expected at a moderate electric field of ∼15 V mm-1.

Impact of untreated and microbially treated equalization tank effluent of textile industry on freshwater fish Channa punctata using haematological, biochemical, histopathological and ultrastructural analysis

The unregulated expulsion of untreated or partially treated industrial effluents poses serious threat to the aquatic ecosystem. Therefore, in the present study fish Channa punctata were exposed to untreated and microbially treated equalization tank effluent of textile industry and toxicity studies were carried out for 45 days. The study was planned to analyze the toxicity proffered by textile effluents through haematological, biochemical, histopathological and ultrastructural analysis in blood, liver and gill tissues of fish. While comparing untreated and microbially treated effluent exposed groups haematological parameters were significantly (P ≤ 0.05) less in the untreated effluent exposed group whereas White blood cell count was highly escalated. However, in the microbially treated groups, the alterations were less severe. Increased malondialdehyde content indicating oxidative stress, reduced Catalase (CAT) and Superoxide dismutase (SOD) activity showing a weakened antioxidant defence system and increased glutathione activity was also perceived in untreated effluent exposed groups in comparison to microbially treated groups. Histopathological alterations in gill (telangiectasia, lamellae fusion, breakage, vacuolization and bending of lamellae) and liver (sinusoid dilations, fusion, necrosis and congestion) were more pronounced and severe in the untreated effluent exposed group as compared to microbially treated group. The results observed in histopathology were further reaffirmed by scanning electron microscopy. The study clearly highlights less alterations and deformities in microbially treated effluent groups in comparison to untreated effluent groups. These findings, therefore, necessitate the search for more effective microbial inocula for the better treatment of effluents in order to protect the aquatic life as well as human beings.

Highlights

Channa punctata exposed for 15, 30 and 45 days to untreated and microbially treated equalization tank effluent of textile industry.Untreated and microbially treated effluent exposed fish elicited alterations in blood, liver and gill tissuesHaematology, biochemical, histopathology and ultrastructural analysis resulted in massive pathologies in groups subjected to untreated effluent inducing maximum damage after 45 days of exposure.Less pronounced toxicity in fish C. punctata was observed in fish exposed to microbially treated effluent indicating its efficacy in toxicity reduction.

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.

Biodegradation of furfuryl alcohol by indigenous Bacillus species of industrial effluent-contaminated sites: estimation, biokinetics and toxicity assessment of bio-transformed metabolites

Furfuryl alcohol (FA) and other furanic compounds have garnered considerable attention in the quest for sustainable alternatives. FA-based resins have been used in various sectors that entail the release of FA into the environment. Hence, to ensure sustainability in this scenario, devising a dependable approach to its degradation is imperative. Given the crucial role of bacterial strains in the biodegradation of various organic pollutants, this study investigates the microbial degradation of FA, using bacterial strains isolated from sites that are constantly exposed to industrial waste. Three potential isolates were identified as B. paramycoides, B. cereus, and B. tequilensis by 16S rRNA gene sequencing. At a concentration of 300 µg/ml, these isolates demonstrated efficient FA degradation; 60-70% (at 300 µg/ml FA) and 50-60%, (at 500 µg/ml FA). Fourier-transform infrared (FTIR) spectroscopy and High-Performance Liquid Chromatography (HPLC) analysis further supported the result that the bacterial isolates consumed FA as the carbon source. Liquid chromatography-mass spectrometry (LC-MS) facilitates the detection of the major metabolic intermediate product in which FA gets transformed. The prominent peaks at 113 and 119 m/z obtained in the MS spectra of the degraded FA samples indicated the possibility of the conversion of FA into furoic acid or levulinic acid. The phytotoxicity bioassay findings revealed the non-toxic nature of the bio-transformed products as compared to pure FA. This investigation presents the initial documentation of the FA degradative potential of Bacillus strains, thereby augmenting the understanding of the prospective implementation of Bacillus species in industrial waste treatment projects.

Preparation of pH-sensitive composite polyethersulfone membranes embedded by Ag(I) coordination polymer for the removal of cationic and anionic dyes

A pH-sensitive polyethersulfone (PES) membrane was prepared with the aid of newly synthesized Ag(I) coordination polymer (Ag(I)-CP) particles. Indicating obvious adsorptive property toward dyes, the Ag(I)-based metalorganic framework (MOF) was selected to be used as an additive to improve the dye selectivity of PES membranes for both cationic and anionic dyes. The performance examination and characterization of prepared membranes indicated the influence of Ag(I)-CP in PES membrane improvement. The effect of feed pH approved the membrane response to pH changes in dye removal results. By adjusting feed pH based on pHpzc of Ag(I)-CP, it is possible to remove both anionic and cationic dyes (97% of acid orange 7 (AO) & and 100% of methylene blue (MB)) from the effluent along with an enhanced permeated flux. The results offered a synergism in embedding Ag(I)-CP in PES membrane in dye removal efficiency. The additive particles can be applied with their natural size (200-300 nm) without severe influence on the uniformity of the membrane morphology if the optimum Ag(I)-CP content is considered.

Dye removal with emulsion liquid membrane: experimental design and response surface methodology

This work aims to removing anionic food dyes, Acid Red18 (E124) and Quinoline Yellow WS (E104), from their aqueous solutions. The Emulsion Liquid Membrane (ELM) technique was used. ELM consists of diluent (kerosene), nonionic surfactant (0.5 wt. % Triton X-45), Aliquat 336 as an extractant. Sulfuric acid (H2SO4) solution was used as an internal aqueous phase. The key parameters impacting the stability of liquid membrane and the efficiency of dye removal were investigated; Almost 98% of E124 at 50 mg/L are successfully extracted under optimum conditions. The extraction of a mixture of the two dyes at equal concentrations (25 mg/L) was conducted and their extraction showed more than 95% of efficiency. The experimental results of dye mixture (E124, E104) extraction were expressed by the following three quantities: The concentration of Triton X-45, the concentration of Aliquat 336, and the internal phase concentration of H2SO4, represented on three dimensional plots using the Box-Behnken design and the response surface methodology. For each of the parameters, the values of which were determined by experimental design, these results were subjected to empirical smoothing. The values, thus calculated, are consistent with the measurements.

Decolorization of various dyes by microorganisms and green-synthesized nanoparticles: current and future perspective

Various types of colored pigments have been recovered naturally from biological sources including shells, flowers, insects, and so on in the past. At present, such natural colored substances (dyes) are replaced by manmade dyes. On the other hand, due to their continuous usage in various purpose, these artificial dyes or colored substances persist in the environmental surroundings. For example, industrial wastewater contains diverse pollutant substances including dyes. Several of these (artificial dyes) were found to be toxic to living organisms. In recent times, microbial-based removal of dye(s) has gained more attention. These methods were relatively inexpensive for eliminating such contaminants in the environmental system. Hence, various researchers were isolated microbes from environmental samples having the capability of decolorizing synthetic dyes from industrial wastewater. Furthermore, the microorganisms which are genetically engineered found higher degradative/decolorize capacity to target compounds in the natural environs. Very few reviews are available on specific dye treatment either by chemical treatments or by bacteria and/or fungal treatments. Here, we have enlightened literature reports on the removal of different dyes in microbes like bacteria (including anaerobic and aerobic), fungi, GEM, and microbial enzymes and also green-synthesized nanoparticles. This up-to-date literature survey will help environmental managements to co-up such contaminates in nature and will help in the decolorization of dyes.

Empowering Adsorption and Photocatalytic Degradation of Ciprofloxacin on BiOI Composites: A Material-by-Design Investigation

Binary and ternary composites of BiOI with NH2-MIL-101(Fe) and a functionalized biochar were synthesized through an in situ approach, aimed at spurring the activity of the semiconductor as a photocatalyst for the removal of ciprofloxacin (CIP) from water. Experimental outcomes showed a drastic enhancement of the adsorption and the equilibrium (which increased from 39.31 mg g-1 of bare BiOI to 76.39 mg g-1 of the best ternary composite in 2 h time), while the kinetics of the process was not significantly changed. The photocatalytic performance was also significantly enhanced, and the complete removal of 10 ppm of CIP in 3 h reaction time was recorded under simulated solar light irradiation for the best catalyst of the investigated batch. Catalytic reactions supported by different materials obeyed different reaction orders, indicating the existence of different mechanisms. The use of scavengers for superoxide anion radicals, holes, and hydroxyl radicals showed that although all these species are involved in CIP photodegradation, the latter play the most crucial role, as also confirmed by carrying out the reaction at increasing pH conditions. A clear correlation between the reduction of BiOI crystallite sizes in the composites, as compared to the bare material, and the material performance as both adsorbers and photocatalyst was identified.

Poly (Vinyl Alcohol) Hydrogels Boosted with Cross-Linked Chitosan and Silver Nanoparticles for Efficient Adsorption of Congo Red and Crystal Violet Dyes

In our previous work, three different weight ratios of chitosan/PVA (1:3, 1:1, and 3:1) were blended and then cross-linked with trimellitic anhydride isothiocyanate (TAI) at a concentration depending on their chitosan content, obtaining three hydrogels symbolized by H13, H11, and H31. Pure chitosan was cross-linked with TAI, producing a hydrogel symbolized by H10. Further, three H31-based silver nanoparticles composites (H31/AgNPs1%, H31/AgNPs3%, and H31/AgNPs5%) were also synthesized. They were investigated, for the first time in this study, as adsorbents for Congo Red (CR) and Crystal Violet (CV) dyes. The removal efficiency of CR dye increased with increasing H10 content in the hydrogels, and with increasing AgNP content in the composites, reaching 99.91% for H31/AgNPs5%. For CV dye, the removal efficiency increased with the increase in the PVA content. Furthermore, the removal efficiency of CV dye increased with an increasing AgNP content, reaching 94.7% for H31/AgNPs5%. The adsorption capacity increased with the increase in both the initial dye concentration and temperature, while with an increasing pH it increased in the case of CV dye and decreased in the case of CR dye. The adsorption of CV dye demonstrated that the Freundlich isotherm model is better suited for the experimental results. Moreover, the results were best fitted with pseudo-second-order kinetic model.

Light-Based 3D Printing of Complex-Shaped Photonic Colloidal Glasses

Colloidal glasses display angle-independent structural color that is tunable by the size and local arrangement of sub-micrometer particles. While films, droplets, and microcapsules with isotropic structural color have been demonstrated, the shaping of colloidal glasses in three dimensions remains an open manufacturing challenge. Here, a light-based printing platform for the shaping of colloidal glasses into 3D objects featuring complex geometries and vivid structural color after thermal treatment is reported. Rheology, photopolymerization, and calcination experiments are performed to design the photoreactive resins leading to printable colloidal glasses. With the help of microscopy, scattering, and optical characterization, it is shown that the photonic properties of the printed objects reflect the locally ordered microstructure of the glass. The capability of the platform in creating 3D objects with isotropic structural color is illustrated by printing lattices and miniaturized sculpture replicas with unique shapes and multimaterial designs.

Identifying pollution dynamics using discrete Fourier transform: From an urban-rural river, Central Mexico

The quality of life and human survival is dependent on sustainable development and sanitation of water bodies in an environment. The present research focuses on cyclicity data of more than 750,000 records of parameters associated with the water quality from a rural-urban river monitoring stations in real-time from River Atoyac in Central Mexico. The events detected in the instrumental records correlated with 2528 laboratory and instrumental determinations. The 64 polluting compounds were grouped into inorganic compounds (metals and metalloids) and organic compounds (pesticides, herbicides, hydrocarbons). Metal associated compounds were grouped along mechanical, pharmaceutical and textile industries which associates itself with the entry of polluting components. The cyclicity of the events was detected through Discrete Fourier Transformation time series analysis identifying the predominant events in each station. These highlight the events at 23-26 h corresponding to a circadian pattern of the metabolism of the city. Likewise, pollution signals were detected at 3.3, 5.5, and 12-14 h, associated with discharges from economic activities. Multivariate statistical techniques were used to identify the circadian extremes of a regionalized cycle of polluting compounds in each of the stations. The results of this research allow pollution prevention using a mathematical analysis of time series of different quality parameters collected at monitoring stations in real-time as a tool for predicting polluting events. The DFT analysis makes it possible to prevent polluting events in different bodies of water, allowing to support the development of public policies based on the supervision and control of pollution.

Life cycle assessment of sequential microbial-based anaerobic-aerobic reactor technology developed onsite for treating textile effluent

Although biological treatment of textile effluent is a preferred option for industries avoiding toxic chemical sludge production and disposal, requirement of several extra pre-treatment units like neutralization, cooling systems or additives, results in higher operational cost. In the present study, a pilot scale sequential microbial-based anaerobic-aerobic reactor technology (SMAART) was developed and operated for the treatment of real textile effluent in the industrial premises in continuous mode for 180 d. The results showed an average ∼95% decolourization along with ∼92% reduction in the chemical oxygen demand establishing the resilience against fluctuations in the inlet parameters and climate conditions. Moreover, the pH of treated effluent was also reduced from alkaline range (∼11.05) to neutral range (∼7.76) along with turbidity reduction from ∼44.16 NTU to ∼0.14 NTU. A comparative life cycle assessment (LCA) of SMAART with the conventional activated sludge process (ASP) showed that ASP caused 41.5% more negative impacts on environment than SMAART. Besides, ASP had 46.15% more negative impact on human health, followed by 42.85% more negative impact on ecosystem quality as compared to SMAART. This was attributed to less electricity consumption, absence of pre-treatment units (cooling and neutralization) and less volume of sludge generation (∼50%) while using SMAART. Hence, integration of SMAART within the industrial effluent treatment plant is recommended to achieve a minimum waste discharge system in pursuit of sustainability.

Adsorption of Methyl Red and Methylene Blue on Carbon Bioadsorbents Obtained from Biogas Plant Waste Materials

In this study, biocarbon was obtained from the waste material corn digest. Carbon adsorbents were obtained by physical activation of the precursor with CO2. Detailed physicochemical characterization of the biocarbon was carried out using low-temperature nitrogen adsorption/desorption, Boehm titration, zero-charge point (pHpzc) and iodine number. In addition, the sorption capacity of the biocarbon agents towards an aqueous solution of methylene blue and methyl red was determined, and the kinetics of the adsorption process were determined. The biocarbon adsorbents were characterized by an average developed specific surface area covering the range from 320 to 616 m2/g. The sorption capacity of the biocarbon adsorbents against methylene blue ranged from 40 mg/g to 146 mg/g, and for methyl red it covered the range from 31 mg/g to 113 mg/g. It was shown that the efficiency of organic dye removal by the obtained biocarbons depends on the initial concentration of the adsorbate solution, its mass, shaking rate, adsorbent-adsorbate contact time and temperature. The results obtained from the Langmuir and Freundlich kinetic models showed that the Langmuir model is the most suitable model for describing the adsorption of the studied pollutants on biocarbon. In turn, the adsorption kinetics of dyes is described according to the pseudo-second-order model. Adsorption studies also showed that as the process temperature increases, the removal efficiency of methylene blue and methyl red increases.

Electrospun nanofibrous membranes for membrane distillation application-A dynamic life cycle assessment (dLCA) approach

Membrane distillation (MD) for water desalination and purification has been gaining prominence to address the issues relating to water security and the destruction of aquatic ecosystems globally. Recent advances in electrospun membranes for MD application have improved antifouling and anti-wetting performance. However, the environmental impacts associated with producing novel electrospun membranes still need to be clarified. It is imperative to quantify and analyze the tradeoffs between membrane performance and impacts at the early stages of research on these novel membranes. Life Cycle Assessment (LCA) is an appropriate tool to systematically account for environmental performance, all the way from raw material extraction to the disposal of any product, process, or technology. The inherent lack of detailed datasets for emerging technologies contributes to significant uncertainties, making the adoption of traditional LCA challenging. A dynamic LCA (dLCA) is performed to guide the sustainable design and selection of emerging electrospun poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrospun membrane (E-PH) and hybridizing polydimethylsiloxane (PDMS) on E-PH membrane (E-PDMS) for dyeing wastewater treatment technologies. The associated environmental impacts are related to the high energy demands required for fabricating electrospun nanofibrous membranes. After LCA analysis, the E-PDMS membrane emerges as a promising membrane, due to the relatively low impact/benefit ratio and the high performance achieved in treating dyeing wastewater.

Enhanced photocatalytic and antibacterial activities of novel Ag-HA bioceramic nanocatalyst for waste-water treatment

Hydroxyapatite (HA), the most common bioceramic material, offers attractive properties as a catalyst support. Highly crystalline mono-dispersed silver doped hydroxyapatite (Ag-HA) nanorods of 60 nm length was developed via hydrothermal processing. Silver dopant offered enhanced chemisorption for crystal violet (CV) contaminant. Silver was found to intensify negative charge on the catalyst surface; in this regard enhanced chemisorption of positively charged contaminants was accomplished. Silver dopant experienced decrease in the binding energy of valence electron for oxygen, calcium, and phosphorous using X-ray photoelectron spectroscopy XPS/ESCA; this finding could promote electron-hole generation and light absorption. Removal efficiency of Ag-HA nanocomposite for CV reached 88% after the synergistic effect with 1.0 mM H2O2; silver dopant could initiate H2O2 cleavage and intensify the release of active ȮH radicals. Whereas HA suffers from lack of microbial resistance; Ag-HA nanocomposite demonstrated high activity against Gram-positive (S. aureus) bacteria with zone of inhibition (ZOI) mm value of 18.0 mm, and high biofilm inhibition of 91.1%. Ag-HA nanocompsite experienced distinctive characerisitcs for utilization as green bioceramic photocatalyst for wastewater treatment.

Evaluating the efficacy of wood decay fungi and synthetic fungal consortia for simultaneous decolorization of multiple textile dyes

Wastewater from the textile industry dyeing process containing high loads of synthetic dyes leads to pollution of water with these toxic and genotoxic dyes. Much effort has been put towards developing biological systems to resolve this issue. Mycoremediation is a well-known approach using fungi to remove, degrade, or remediate pollutants and can be applied to decolorize textile dyes in industrial effluent. Fungal strains from four genera of Polyporales, namely Coriolopsis sp. TBRC 2756, Fomitopsis pinicola TBRC-BCC 30881, Rigidoporus vinctus TBRC 6770, and Trametes pocas TBRC-BCC 18705, were studied for decolorization efficiency, and R. vinctus was found to exhibit the greatest activity in removing all seven tested reactive dyes and one acid dye with a decolorization efficiency of 80% or more within 7 days under limited oxygen. This fungus simultaneously degraded multiple dyes in synthetic wastewater as well as industrial effluent from the dyeing process. To enhance the decolorization rate, various fungal consortia were formulated for testing. However, these consortia only trivially improved efficiency compared with using R. vinctus TBRC 6770 alone. Evaluation of R. vinctus TBRC 6770 decolorization ability was further performed in a 15-L bioreactor to test its ability to eliminate multiple dyes from industrial effluent. The fungus took 45 days to adapt to growth in the bioreactor and subsequently reduced dye concentration to less than 10% of the initial concentration. The following six cycles required only 4-7 days to reduce dye concentrations to less than 25%, demonstrating that the system can run efficiently for multiple cycles without the need for extra medium or other carbon sources.

Template-assisted synthesis of molecularly imprinted polymers for the removal of methyl red from aqueous media

This study entails the synthesis of molecularly imprinted polymers (MIPs) with good selectivity coefficients for azo dye as a potential sorbent material to extract azo dye from polluted aqueous media. A series of MIPs for methyl red (MR) as a template, were synthesized by changing the molar ratio of functional monomers, via precipitation polymerization format of non-covalent approach. Water-soluble functional monomer; acrylic acid (AA) was used to weave the frame work of polymers while ethylene glycol dimethacrylate (EGDMA) was utilized as crosslinking monomer. The impact of different experimental parameters, such as mole ratio of monomer (functional) to crosslinking monomer on the molecular recognition was investigated. The highly efficient and selective MR-MIP was used for the removal of spiked MR dye from different water samples. The selected imprinted polymer, MR1-MIP was able to selectively remove the MR molecules from aqueous media. A significant amount of dye was removed by MR1-MIP from the river water samples with a high degree of removal efficiency i.e. 92.25%. The imprinting factor of 3.75 for MR1-MIP indicated that the high selectivity in terms of adsorption for MR. A minimum loss of only ~ 3.35% in the removal efficiency within ten sequential cycles of adsorption-desorption study evidenced that MR-MIPs could be used as the most cost effective and best sorbent for the removal of MR from polluted water. Furthermore, the structural properties of MR-MIPs were characterized by FTIR and EDX, whereas TGA, SEM and BET were used to describe the thermal, morphological and surface structures of the particles, respectively.

Sequential photo electro oxidation and biodegradation of textile effluent: Elucidation of degradation mechanism and bacterial diversity

Textile effluent contains a highly toxic and refractory azo dyes. Eco-friendly method for efficient decolorization and degradation of textile effluent is essential. In the present study, treatment of textile effluent was carried through sequential electro oxidation (EO) and photo electro oxidation (PEO) using RuO₂-IrO₂ coated titanium electrode as an anode and cathode followed by biodegradation. The pre-treatment of textile effluent by photo electro oxidation for 14 h exhibited 92% of decolorization. Subsequent biodegradation of the pre-treated textile effluent enhanced the reduction of chemical oxygen demand to 90%. Metagenomics results exhibited that Flavobacterium, Dietzia, Curtobacterium, Mesorhizobium, Sphingobium, Streptococcus, Enterococcus, Prevotellaand Stenotrophomonas bacterial communities majorly involved in the biodegradation of textile effluent. Hence, integrating sequential photo electro oxidation and biodegradation proposed an efficient and eco-friendly approach for treating textile effluent.

Enhanced Visible-Photocatalytic Activities in Strong Acids and Strong Alkalis of Flexible Iron-SrTiO3 Nanofibrous Membranes

Traditional SrTiO₃ (STO) materials have high brittleness and poor deformation resistance. In this work, macroscopically flexible iron-doped SrTiO₃ (SFTO) nanofibrous membranes were prepared by electrospinning and calcination, which can be easily isolated and can maintain integrity to recycle as photocatalysts. Moreover, the SFTO nanofibrous membranes showed enhanced photocatalytic performance under strong acids (pH = 2) and strong alkalis (pH = 12). The SFTO nanofibrous membranes increased the catalytic rate of Congo red (CR) dye by about 10 times in visible light. The mechanism of photocatalytic activity enhancement was discussed by the combined effects of hydroxyl radicals and superoxide radicals. The successful preparation of SFTO nanofibrous membranes has offered a simple and economical approach to photocatalysis as well as environmental remediation.

Transformation from biofiltration unit to hybrid constructed wetland-microbial fuel cell: Improvement of wastewater treatment performance and energy recovery

This study aimed to compare the performance of biofiltration, constructed wetland, and constructed wetland microbial fuel cell (CW-MFC). The transformation from a biofiltration unit to a hybrid CW-MFC was demonstrated with the advantages of improvement of wastewater treatment while generating electricity simultaneously. The introduction of plants to the upper region of the bioreactor enhanced the DO level by 0.8 mg/L, ammonium removal by 5 %, and COD removal by 1 %. The integration of electrodes and external circuits stimulated the degradation rate of organic matter in the anodic region (1 % without aeration and 3 % with aeration) and produced 5.13 mW/m³ of maximum power density. Artificial aeration improved the nitrification efficiency by 38 % and further removed the residual COD to an efficiency of 99 %. The maximum power density was also increased by 3.2 times (16.71 mW/m³) with the aid of aeration. In treating higher organic loading wastewater (3M), the maximum power density showed a significant increment to 78.01 mW/m³ (4.6-fold) and the COD removal efficiency was 98 %. The ohmic overpotential dominated the proportion of total loss (67-91 %), which could be ascribed to the low ionic conductivity. The reduction in activation and concentration loss contributed to the lower internal resistance with the additional aeration and higher organic loading. Overall, the transformation from biofiltration to a hybrid CW-MFC system is worthwhile since the systems quite resemble while CW-MFC could improve the wastewater treatment as well as recover energy from the treated wastewater.

Optimization Study on Synergistic System of Photocatalytic Degradation of AR 26 and UV-LED Heat Dissipation

In this work, a novel UV-LED/TiO2 photocatalytic system, having a single layer with ten LED beads, was designed to simultaneously achieve UV-LED cooling and wastewater degradation, to deal with heat dissipation problems of high-power UV-LEDs. To gain more insight into this system, the parameters affecting both cooling and photocatalytic performance were first optimized using AR 26 as a basis. With respect to sewage, sewage with a flow rate of 80 mL/min and a temperature of 20 °C helped to keep a lower temperature of UV-LED, which benefits the long-term operation stability of LED beads. For parameters affecting the photocatalytic performance only, the experiments showed that TiO2 with moderate dosing (0.75 g/L) under strong acid conditions (pH = 2) helped to further improve photocatalytic activity when the initial concentration of AR 26 was 45 mg/L. Lastly, to illustrate the advantages of this novel system, the performance of the synergistic system was compared with a conventional photocatalytic reactor with respect to degradation performance, optical quantum efficiency, and energy consumption. The results showed that the degradation efficiency and light source utilization ratio of this coupled system were, respectively, 2.1 times and 1.5 times as much as those of a conventional reactor. As the unit power consumption of the synergistic system was only 0.18-fold more than that of a conventional reactor, our work suggests that this synergistic system with the advantage of LED lamp beads has a bright future in dealing with refractory organic pollutants of sewage.

Mixed-valence molybdenum oxide as a recyclable sorbent for silver removal and recovery from wastewater

Silver ions in wastewater streams are a major pollutant and a threat to human health. Given the increasing demand and relative scarcity of silver, these streams could be a lucrative source to extract metallic silver. Wastewater is a complex mixture of many different metal salts, and developing recyclable sorbents with high specificity towards silver ions remains a major challenge. Here we report that molybdenum oxide (MoO_x) adsorbent with mixed-valence (Mo(V) and Mo(VI)) demonstrates high selectivity (distribution coefficient of 6437.40 mL g^-1) for Ag⁺ and an uptake capacity of 2605.91 mg g^-1. Our experimental results and density functional theory calculations illustrate the mechanism behind Ag⁺ adsorption and reduction. Our results show that Mo(V) species reduce Ag⁺ to metallic Ag, which decreases the energy barrier for subsequent Ag⁺ reductions, accounting for the high uptake of Ag⁺ from wastewater. Due to its high selectivity, MoO_x favorably adsorbs Ag⁺ even in the presence of interfering ions. High selective recovery of Ag⁺ from wastewater (recovery efficiency = 97.9%) further supports the practical applications of the sorbent. Finally, MoO_x can be recycled following silver recovery while maintaining a recovery efficiency of 97.1% after five cycles. The method is expected to provide a viable strategy to recover silver from wastewater.

Broken into pieces: The challenges of determining sulfonated azo dyes in biological reactor effluents using LC-ESI-MS/MS analysis

Most studies on the biodegradation of textile azo dyes use color as parameter for measuring the efficiency of degradation. Although widely employed, spectrophotometric methods are susceptible to the interference of metabolites or degradation products from the biological treatment. We propose a method for determination of a model sulfonated azo dye (Direct Black 22, DB22) in wastewater using solid-phase extraction (SPE) and liquid chromatography - electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). MS analysis in negative electrospray ionization mode showed DB22 as the most abundant precursor ion, corresponding to [M-3Na + H]^2-, which yields two radical anions of m/z 370.1 and m/z 645 after MS/MS fragmentation by collision-induced dissociation (CID). Calibration curve presented adequate linearity and precision in the range of 120-1500 ng mL^-1, and recovery and detection limit were appropriate to the typically employed working concentrations. Nevertheless, we observed that standard heating of DB22 under alkaline conditions to simulate the production of wastewater during dye-baths resulted in loss of MS/MS signal, without affecting color. Further analysis showed that DB22 undergoes hydrolysis and does not remain unaltered in solution. Alternative methods of hydrolysis evaluated resulted in no MS/MS signal as well. SPE-LC-ESI-MS/MS analysis evidenced the structural change of DB22 in aqueous solution while the dyeing-capacity was preserved. This technique has also the potential of being tailored to consider the detection of the hydrolyzed fragments of azo dyes in wastewater for appropriate quantification, but it was not the scope of the current step of this research. Color remains as a more reliable parameter for monitoring azo compounds which are unstable in aqueous solution, while a more robust and holistic method needs to be developed for the speciation of the DB22 products of thermal hydrolysis.

WITHDRAWN: Heavy metal ions and dyes removal from aqueous solution using Aloevera-based biosorbent: A systematic review

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the authors, editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. The publisher apologizes to the readers for this unfortunate erro

Development and operation of immobilized cell plug flow bioreactor (PFR) for treatment of textile industry effluent and evaluation of its working efficiency

The release of untreated/partially treated effluent and solid waste from textile dyeing industries, having un-reacted dyes, their hydrolysed products and high total dissolved solids (TDS) over the period of time had led to the deterioration of ecological niches. In an endeavour to develop a sustainable and effective alternative to conventional approaches, a plug flow reactor (PFR) having immobilized cells of consortium of three indigenous bacterial isolates was developed. The reactor was fed with effluent collected from the equalization tank of a textile processing unit located near city of Amritsar, Punjab (India). The PFR over a period of 3 months achieved 97.98 %, 82.22 %, 87.36%, 77.71% and 68.75% lowering of colour, chemical oxygen demand (COD), biological oxygen demand (BOD), total dissolved solids (TDS) and total suspended solids (TSS) respectively. The comparison of the phytotoxicity and genotoxicity of untreated and PFR-treated output samples using plant and animal models indicated significant lowering of respective toxicity potential. This is a first report, as per best of our knowledge, regarding direct treatment of textile industry effluent without any pre-treatment and with minimal nutritional inputs, which can be easily integrated into already existing treatment plant. The successful implementation of this system will lower the cost of coagulants/flocculants and also lowering the sludge generation.

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.

Bacterial oxidoreductive enzymes as molecular weapons for the degradation and metabolism of the toxic azo dyes in wastewater: a review

Azo dyes are extremely toxic and pose significant environmental and health risks. Consequently, mineralization and conversion to simple compounds are required to avoid their hazardous effects. A variety of enzymes from the bacterial system are thought to be involved in the degradation and metabolism of azo dyes. Bioremediation, a cost effective and eco-friendly biotechnology, involving bacteria is powered by bacterial enzymes. As mentioned, several enzymes from the bacterial system serve as molecular weapons in the degradation of these dyes. Among these enzymes, azoreductase, oxidoreductase, and laccase are of great interest for the degradation and decolorization of azo dyes. Combination of the oxidative and reductive enzymes is used for the removal of azo dyes from water. The aim of this review article is to provide information on the importance of bacterial enzymes. The review also discusses the genetically modified microorganisms in the biodegradation of azo dyes in polluted water.

Simultaneous bioremediation of Disperse orange-2RL Azo dye and fatty acids production by Scenedesmus obliquus cultured under mixotrophic and heterotrophic conditions

Several types of green photosynthetic microalgae can grow through the process of heterotrophic growth in the dark with the help of a carbon source instead of the usual light energy. Heterotrophic growth overcomes important limitations in the production of valuable products from microalgae, such as the reliance on light, which complicates the process, raises costs, and lowers the yield of potentially useful products. The present study was conducted to explore the potential growth of green microalga Scenedesmus obliquus under mixotrophic and heterotrophic conditions utilizing Disperse orange 2RL Azo dye as a carbon source to produce a high lipid content and the maximum dye removal percentage. After 7 days of algal growth with dye under mixotrophic and heterotrophic conditions with varying pH levels (5, 7, 9, and 11), KNO₃ concentrations (1, 1.5, 2, and 3 g/L), and dye concentrations (20, 40, and 60 ppm); dye removal percentage, algal dry weight, and lipid content were determined. The results showed that the highest decolorization of Disperse orange 2RL Azo dye (98.14%) was attained by S. obliquus in heterotrophic medium supplemented with glucose at the optimal pH 11 when the nitrogen concentration was 1 g/L and the dye concentration was 20 ppm. FT-IR spectroscopy of the dye revealed differences in peaks position and intensity before and after algal treatment. S. obliquus has a high concentration of oleic acid, which is enhanced when it is grown with Disperse orange 2RL Azo dye, making it ideal for production of high-quality biodiesel. In general, and in the vast majority of instances, heterotrophic cultivation is substantially less expensive, easier to set up, and requires less maintenance than mixotrophic cultivation. Heterotrophic cultivation allows for large-scale applications such as separate or mixed wastewater treatment along with biofuel production.