A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters

Nanocomposite ZnO/g-C3N4 for Improved Degradation of Dyes under Visible Light: Facile Preparation, Characterization, and Performance Investigations

In this study, ZnO/g-C3N4 nanocomposites were prepared via a physical mixing-calcination process for improved degradation of dyes under visible light irradiation. The BET surface area, pore volume, crystal size, and pHpzc of the ZnO/g-C3N4 composite were 3.9 m2/g, 0.034 cm3/g, 18.1 nm, and 7.7, respectively. Although the morphology of the ZnO/g-C3N4 composite was very different from that of pure g-C3N4, their average pore sizes were similar. The Eg of the ZnO/g-C3N4 composite (3.195 eV) was slightly lower than that of ZnO (3.195) but much higher than that of g-C3N4 (2.875). The interface interaction of ZnO and g-C3N4, which was revealed by oscillations of Zn-C, benefited the transport of photoinduced charge carriers and reduced the recombination of electron-hole. As the result, the ZnO/g-C3N4 composite had higher photocatalytic activity than ZnO and g-C3N4. Its degradation efficiency (DE) value for methylene blue (MB) in 90 min and rate constant were 93.2 % and 0.025 min‑1, respectively. In addition, the effects of ZnO/urea molar ratio, catalyst dosage, solution pH, and concentration of dye on photocatalytic degradation of MB were completely investigated. The photocatalytic performance of the ZnO/g-C3N4 composite was evaluated by the degradation of other persistent organic compounds, also compared to other catalysts in the literatures. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Simultaneous Fractionation, Desalination, and Dye Removal of Dye/Salt Mixtures by Carbon Cloth-Modified Flow-electrode Capacitive Deionization

The critical challenges of using electromembrane processes [e.g., electrodialysis and flow-electrode capacitive deionization (FCDI)] to recycle resources (e.g., water, salts, and organic compounds) from wastewater are the fractionation of dissolved ionic matter, the removal/recovery of organic components during desalination, and membrane antifouling. This study realized the simultaneous fractionation, desalination, and dye removal/recovery (FDR) treatment of dye/salt mixtures through a simple but effective approach, that is, using a carbon cloth-modified FCDI (CC-FCDI) unit, in which the carbon cloth layer was attached to the surface of each ion-exchange membrane (IEM). The IEMs and carbon-based flow-electrodes were responsible for the fractionation and desalination of dye and salt ions, while the carbon cloth layers contributed to the active membrane antifouling and dye removal/recovery by the electrosorption mechanism. Attributed to such features, the CC-FCDI unit accomplished the effective FDR treatment of dye/salt mixtures with wide ranges of salt and dye concentrations (5-20 g L^-1 NaCl and 200-800 ppm methylene blue) and different dye components (cationic and anionic dyes) under various applied voltages (1.2-3.2 V). Moreover, the active membrane antifouling by virtue of the carbon cloth facilitated the excellent and sustainable FDR performance of CC-FCDI. The removal/recovery of dyes from the carbon cloth strongly depends on the characteristics of dye molecules, the surface properties of the carbon cloth, and the local pH at the IEM/CC interfaces. This study sheds light on the strategies of using multifunctional layer-modified FCDI units to reclaim resources from various high-salinity organic wastewater.

Low-cost novel nano-constructed granite composites for removal of hazardous Terasil dye from wastewater

The hazardous dyes on mixing with water resources are affecting many life forms. Granite stone is popular worldwide for decorating floors, making other forms of decorative materials and items. Granite stone powder waste can be obtained free of cost from marble factories as factories spend on the disposal of this waste. In the present study, novel granite stone powder waste composite has been prepared and utilized for the effective removal of Terasil dye. Two types of granite including gray granite and white granite were used in pure, calcinized, and chemically modified forms. Freundlich adsorption isotherm model best explained the adsorption mechanism of dye removal using granite composites as compared to other adsorption isothermal models. Characterization techniques like scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were used for the determination of morphological features and functional groups of granite composites. The obtained results were statistically analyzed using analysis of variance (ANOVA) along with the post hoc Tukey test. An extraordinarily high Terasil dye uptake capacity (more than 400 mg/g) was exhibited by granite composites prepared using sodium metasilicate. The synthesized novel nano-constructed composites provided a viable strategy as compared to the pure granite stone for dye removal from wastewater water.

Highly efficient and rapid purification of organic dye wastewater using lignin-derived hierarchical porous carbon

Coating manufacturing, textile processing, and plastic industry have led to dramatical release levels of hazardous organic dye pollutants threatening public health and the environment. To solve this problem, porous carbon materials are being developed following with the United Nations initiative on water purification. However, conventional porous carbon materials face many challenges, such as limited removal rates, low adsorption capacity, and high chemicals consumption, hampering their large-scale utilization in dye wastewater treatment. Herein, we demonstrate a high-performance lignin-derived hierarchical porous carbon (LHPC) material directly prepared from renewable lignin through a low-cost activation procedure. The large specific surface area (1824 m²/g) enables the rapid and effective adsorption of organic dyes. Therefore, the LHPC exhibits an ultrahigh adsorption ability (1980.63 mg/g) and removal rate (99.03% in 10 min) for Azure B, superior to that of other adsorbents. Additionally, the LHPC adsorbent, organic dyes, eluting agent, and water all can be recycled and reused in a designed close-looped system. Its high removal ability and rate, strong retrievability, low-cost and scalable production combined with high dyes adsorption universality, positions our LHPC as a promising commercial adsorbent candidate for the purification of harmful organic dye wastewater, especially for heavily polluted area with an insistent demand for clear water.

Treatment of synthetic dye containing textile raw wastewater effluent using UV/Chlorine/Br photolysis process followed by activated carbon adsorption

This study investigated the efficiency and feasibility of ultraviolet (UV)-assisted photolysis of synthetic dye containing textile raw wastewater effluent. For a said purpose, in-house developed UV/Chlorine/Br process was followed in the presence of activated carbon (AC) which additionally facilitate the dye adsorption. In UV/Chlorine process Cl^•, Cl₂^•-, and HO^• are generated in the solution and destroyed compounds that cannot be oxidized by the conventional oxidant. In this process, free bromine is formed and photolyzed by UV radiation and generate Br^• and Br₂^•- that can enhance the rate of pollutant degradation. In the present study, the dye removal efficiency was contributed by dark bromide (7.18%), UV irradiation (26.8%), dark chlorination (78.67%), and UV/Chlorine/Br (87.01%), respectively. With increasing pH from 3.0 to 8.30, the dye removal efficiency was enhanced but decreased by further increasing pH values. In addition, magnetized activated carbon from pomegranate husk using dual-stage chemical activation was used for post-adsorption of the residual dye and its degradation byproducts. The adsorption of the dye residues by AC followed the second-order kinetics with the rate constant of 1.7 × 10^-3. The phytotoxicity of the treated textile wastewater by UV irradiation, dark chlorination, and UV/Chlorine/Br was assessed by seed germination of Lepidium sativum seeds. The highest inhibition effect on seed germination was related to treated wastewater by UV irradiation (more than 90% inhibition) that alleviated to less than 10% when this effluent diluted to 5% v/v. The highest germination was observed when the seeds were irrigated by the effluent of the UV/Chlorine/Br process. The significant reduction in the toxicity of the treated wastewater revealed that the UV/Chlorine/Br process has a considerable potential to effectively detoxify textile wastewater. Graphical abstract.

A new approach to study the degradation of the organic pollutants by A-doped MxOy/B photocatalysts

This work presents a new approach and a comprehensive mechanism to study the kinetics of the photodegradation of the organic pollutants. The vital role of various operational factors on the degradation of the organic pollutants is explained using this method. The proposed approach is based on the simple strategies and a powerful computational method. Two new variables "the effective concentration of photon" (I_eff) and "the effective concentration of the reactive centers" (RC) are defined to better understand the effect of operational parameters on the organic pollutant photodegradation. The optimum conditions of the photocatalytic degradation can be determined with the help of this method. This approach was used to study the kinetics of photodegradation of the organic pollutants on the [Formula: see text] photocatalysts. The provided mechanism has been examined with the some experimental data. The high correlations between the experimental data and the fitting results under different conditions prove this mechanism could be reliable.

A review of plant-based coagulants for turbidity and cyanobacteria blooms removal

In recent years, the proliferation of Harmful Cyanobacterial Blooms (CyanoHABs) has increased with water eutrophication and climate change, impairing human health and the environment in relation to water supply. In drinking water treatment plants (DWTPs), the bio-coagulation based on natural coagulants has been studied as an eco-friendly alternative technology to conventional coagulants for both turbidity and CyanoHABs removal. Plant-based coagulants have demonstrated their coagulation efficiency in turbidity removal, as reported in several papers but its ability in cyanobacterial removal is still limited. This paper mainly reviewed the application of plant-based coagulants in DWTPs, with focus on turbidity removal, including cyanobacterial cells. The future potential uses of these green coagulants to reduce noxious effects of cyanobacterial proliferation are presented. Green coagulants advantages and limitations in DWTPs are reviewed and discussed summarizing more than 10 years of knowledge.

Highly Efficient Organic Dyes Capture Using Thiol-Functionalized Porous Organic Polymer

It is of great significance to develop new materials for efficient capture cationic dyes methylene blue (MB) and malachite green (MG). In this work, a novel triptycene-based porous organic polymer with abundant thiol groups (TPP-SH) was prepared successfully by postmodification with a high surface area and robust triptycene-based porous organic polymer (TPP). The obtained TPP-SH exhibited a high surface area, good porosity, and good thermal stability. In addition, TPP-SH was highly effective at capturing MB and MG from aqueous solution because of the abundant thiols in its hierarchical structure. Under optimal adsorption conditions, the maximum adsorption capacities of MB and MG calculated by the Langmuir model at room temperature were 1146.3 and 689.6 mg g-1, respectively. These values are higher than those of many reported materials. The MB and MG adsorption rates were 0.0154 and 6.69 × 10-4 mg g-1 min-1, respectively. Furthermore, the polymer TPP-SH had a good recycling performance after adsorption-desorption at least five times. Therefore, the TPP-SH exhibited a high adsorption capacity, fast adsorption kinetics, and easy-recycling behavior, providing a new avenue for the preparation of green functionalized adsorbents with good performance for water decontamination.

Performance Evaluation of a Hybrid Enhanced Membrane Bioreactor (eMBR) System Treating Synthetic Textile Effluent

The textile industry produces a high volume of wastewater rich in toxic and harmful chemicals. Therefore, it is necessary to apply wastewater treatment methods such as membrane bioreactor (MBR) to achieve high efficiency, process stability, small footprint, and low maintenance costs. This work performed a study on a synthetic textile wastewater treatment using an enhanced membrane bioreactor (eMBR) equipped with two anoxic and one aerobic reactor and a UV disinfection unit. The results showed 100% removal of total suspended solids, 81.8% removal of chemical oxygen demand, and 96% removal of color. The SEM analysis indicated that the pores of the membrane were blocked by a compact and dense gel layer, as observed by the presence of the fouling layer. According to these results, an eMBR hybrid system is a suitable option for treating synthetic textile wastewater. Opportunities to increase the efficiencies in the removal of some pollutants, as well as stabilizing and standardizing the process are the improvements which require further investigations.

Potential risks and approaches to reduce the toxicity of disinfection by-product - A review

Water contamination through anthropogenic and industrial activities has led to the emergence and necessity of disinfection methods. Chlorine and bromine gases, often used to disinfect water, resulted in the by-product formation by reacting with organic matter. The Disinfectant by-products (DBP) led to the formation of Trihaloaceticacid (TAA), Trihalomethane (THM), and other minor components. The release of chemicals has also led to the outbreak of diseases like infertility, asthma, stillbirth, and types of cancer. There are new approaches that are found to be useful to compensate for the generation of toxic by-products and involve membrane technologies, namely reverse osmosis, ultrafiltration, and nanofiltration. This review mainly focuses on the toxicology effects of DBPs and various approaches to mitigate the same. The health hazards caused by different DBPs and the various treatment techniques available for the removal are discussed. In addition, a critical comparison of the different removal techniques was discussed.

Indigenous Bacillus paramycoides spp. and Alcaligenes faecalis: sustainable solution for bioremediation of hospital wastewater

Farmers near towns and cities are using a wide range of highly polluted wastewaters for crop irrigation in Pakistan due to severe freshwater shortage. The present study aimed to promote indigenous bacterial strains isolated from domestic, hospital, textile, pharmaceutical and mixed wastewaters to remove contaminants and colour and render these wastewaters safer for irrigation. Thirty seven bacterial strains were isolated from five wastewater samples collected from different sites in Lahore, Pakistan. Under optimal growth conditions, three isolates (D6, D7 and P1) showed >93% decolourisation potential in the treatment of hospital wastewater. 16S rDNA sequencing identified two of these isolates (D6 and D7) as showing 100% and 99.86% homology to Bacillus paramycoides spp. - novel strains from B. cereus group. Isolate P1 showed 97.47% homology to Alcaligenes faecalis. GCMS analysis of the untreated hospital wastewater revealed the presence of pharmaceutic pollutants, i.e. Phenol (876 µg/L), Salicylic acid (48 µg/L), Caffeine (7 µg/L), Naproxen (23 µg/L), Octadecene (185 µg/L) and Diazepam (14 µg/L). The analysis of treated hospital wastewaters showed percentage degradation of pharmaceutic pollutants (100%-43%) and significant reduction in the BOD₅ (91%-68%), COD (89%-52%) and heavy metals concentrations. These strains therefore can represent a low-cost and low-tech alternative to bioremediate complex matrices of hospital wastewater prior to crop irrigation to support the achievement of clean re-usable water in developing countries like Pakistan.

Effect of nano bentonite on direct yellow 50 dye removal; Adsorption isotherm, kinetic analysis, and thermodynamic behavior

Developing countries suffering from the toxicity of different industrial effluents especially dyes. This study successfully prepared and characterized nano-bentonite for anionic dye removal (DY 50). The prepared nanoparticles were characterized by X-Ray Diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscope (SEM), EDAX analysis, FT-IR, and TGA and the obtained results indicated the formation of nanoparticles with an average size of 15 nm. The effect of different operating conditions was studied using different pH, dose, contact time, temperature, and initial DY 50 concentrations. The obtained results indicated that nano bentonite was able to adsorb about 78.3 and 100% for initial concentrations of 100±8.1 and 20 ±1.62 mg/L, respectively. The optimum removal conditions were observed at acidic media (pH 3) using sorbent material dosage 1 g/L for 45 min and 30°C. The adsorption isotherm, kinetic analysis, and thermodynamic behavior were studied by using linear equation form, and the adjusted R2 was compared to detect the preferred models. The adsorption isotherm indicated that heterogeneous, as well as multilayer adsorption, plays an important role in the removal of dye. Kinetic studies indicated the chemisorption interaction between sorbed and adsorbed molecules. Thermodynamic behavior indicated the reaction is exothermic with ∆H equal to −5.24 KJ/mol and ∆S equal −74.2 J/K.mol. Finally, this study strongly recommended using nano bentonite for DY 50 removal from an aqueous solution. The RSM relations show significant relations in all removal models with p-value <0.001. The ANN results indicated that the most effective operating conditions are the effect of nano bentonite dose followed by the pH effect.

Adsorptive removal of organic dyes via porous materials for wastewater treatment in recent decades: A review on species, mechanisms and perspectives

Organic dyes, a type of high toxic and carcinogenic chemicals that present severe threats to human and aquatic life, are the most commonly seen organic pollutants in wastewater of industries such as textile, rubber, cosmetic industry etc. Various techniques for the removal of dyes are compared in this review. Adsorption has proven to be a facile and promising approach for the removal of dyes in wastewater. This work focuses on the latest development of various porous materials for the adsorption of organic dyes. The characteristics, functionalization and modification of different porous materials are also presented. Furthermore, adsorption behaviors and mechanism of these adsorbents in the adsorption of organic dyes are critically reviewed. Finally, challenges and opportunities for future research in the development of novel materials for the highly efficient removal of dyes are proposed.

Carrier-Free Cross-linked Laccase Crystals for Biocatalytic Degradation of Textile Industrial Effluents

Herein, laccase from Trametes versicolor was used to fabricate carrier-free cross-linked laccase crystals (CLLCs) and deployed as a robust catalyst for waste effluent treatment. The surface morphology and involvement of functional group attributes of CLLCs were scrutinized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). As fabricated CLLCs were subjected to kinetic characterization by assessing the effects of pH environment, thermal profile, and substrate (determination of K_m and V_max) on the activity. A fully characterized CLLCs fraction was used to treat synthetic dyes containing waste effluents taken from various industries, i.e., Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills. Degradation profile revealed 36.8%, 27.6%, 39.9%, and 26.4% degradation of Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills, respectively, by the free form of laccase, whereas the biocatalytic activity of CCLCs led to 78.6%, 75.6%, 85.5%, and 63.3% degradation of those effluents. The decrease in peak and mass region alongside the presence of new peaks in GC-MS affirms the effective decolorization of contaminated waste effluents. CLLCs retained over 70% and 50% of their degradation activity after 3 and 5 cycles, respectively. In conclusion, CLLCs might represent a robust bioprocess to improve the usability of laccase for various synthetic dyes containing waste effluents to diminish environmental pollution from the dye-based industries.

Biomass production of carbohydrate-rich filamentous microalgae coupled with treatment and nutrients recovery from acrylonitrile butadiene styrene based wastewater: Synergistic enhancement with low carbon dioxide supply strategy

This study attempted to remove acrylonitrile and acetophenone from simulated acrylonitrile butadiene styrene (ABS) based wastewater while recovering nitrogen and phosphorus using the carbohydrate-rich filamentous microalgae Tribonema sp.. Results showed that typical acetophenone and acrylonitrile presented significant inhibitory effect on Tribonema sp. growth and co-metabolism of CO₂ improved the tolerance of Tribonema sp. to toxic pollutants. The microalgae biomass increased by 34.47% (3.16 g/L) and 58.17% (3.97 g/L) via supplementing 2% CO₂ in the 100 mg/L acrylonitrile and acetophenone groups, respectively. The filamentous microalga was rich in carbohydrates and its productivity was further enhanced by 32.52% and 70.34%, respectively, in 100 mg/L acrylonitrile and acetophenone groups with 2% CO₂ supplement. The synergistic CO₂ supply strategy effectively enhanced the biomass production of filamentous microalgae, and moreover, improved the treatment efficiency of ABS based wastewater simulated by acetophenone or acrylonitrile addition, while at same time enhanced the recovery of nitrogen and phosphorus nutrients.

Entangled ZnO on Ultrathin Hollow Fibers for UV-Aided Pollutant Decomposition

Zinc oxide (ZnO), a widely used ultraviolet (UV) degrading substance, offers high selectivity for wastewater treatment, but the leaching of ZnO into water could cause secondary contamination. Using porous substrates to fix and load ZnO is a promising technical method to improve the water purification efficiency and recycling durability of ZnO. However, limited by the slow kinetics and shielding effects, it is challenging to use traditional techniques to introduce ZnO into the interior of a hollow structure. Here, inspired by an ancient dyeing procedure, we formed a unique single-molecule bio-interfacial entanglement as an absorption layer to capture the catalyst for ZnO electroless deposition (ELD) on the surface of natural ultrathin hollow-structured Kapok fibers. With curcumin serving as a linking bridge, ELD allowed the spontaneous formation of intensive ZnO nanocrystals on both the outer and inner walls. ZnO-kapok as the catalyst for ultraviolet photodecomposition of organic pollutants (methylene blue (MB) and phenol as model pollutants) delivered a decomposition efficiency of 80% and outstanding durability. Further modification of the ZnO-kapok catalyst by doping with reduced graphene oxide (rGO) showed an improvement in photodegradation performance of 90% degradation under 2-h irradiation with 21.85 W/dm² light power. Moreover, to the best of our knowledge, this is the first report featuring ZnO loading on both the outer and inner walls of a fiber-structured hollow kapok material, which provides inspiration for immobilization of metallic oxides on hollow-structured materials for further applications in renewable catalysis, chemical engineering, and energy storage fields.

Review on effect of different type of dyes on advanced oxidation processes (AOPs) for textile color removal

The textile industry is one of the most valuable industries, especially in developing countries, because it employs a large portion of the workforce. However, the development of the textile industry has led to increasing concern about environmental issues. Wastewater from the textile industry has a high COD and an undesirable color. Color is one of the problems with the wastewater due to its toxicity and low biodegradability. Color in textile wastewater mainly originates from the dyestuff used during the dyeing or printing process. Amongst all of available technology for color removal, advanced oxidation processes (AOPs) are considered one of the best and the most potential technology. However, the understanding of AOPs reaction mechanism to degrade dyestuff is still limited. In general, dyes degradation mechanism will vary and mainly depend on the chemical structure of the dyes itself. Some reaction pathway that seems less favorable thermodynamically can still happen during the process. Understanding the mechanism will be beneficial for future dyes improvement, especially on developing the moiety of the aromatic compound in order to produce easily degraded dyes while maintaining the fastness quality.

Knowledge extraction of sonophotocatalytic treatment for acid blue 113 dye removal by artificial neural networks

Removing decolorizing acid blue 113 (AB113) dye from textile wastewater is challenging due to its high stability and resistance to removal. In this study, we used an artificial neural network (ANN) model to estimate the effect of five different variables on AB113 dye removal in the sonophotocatalytic process. The five variables considered were reaction time (5-25 min), pH (3-11), ZnO dosage (0.2-1.0 g/L), ultrasonic power (100-300 W/L), and persulphate dosage (0.2-3 mmol/L). The most effective model had a 5-7-1 architecture, with an average deviation of 0.44 and R² of 0.99. A sensitivity analysis was used to analyze the impact of different process variables on removal efficiency and to identify the most effective variable settings for maximum dye removal. Then, an imaginary sonophotocatalytic system was created to measure the quantitative impact of other process parameters on AB113 dye removal. The optimum process parameters for maximum AB 113 removal were identified as 6.2 pH, 25 min reaction time, 300 W/L ultrasonic power, 1.0 g/L ZnO dosage, and 2.54 mmol/L persulfate dosage. The model created was able to identify trends in dye removal and can contribute to future experiments.

Influence of Initial pH Value on the Adsorption of Reactive Black 5 Dye on Powdered Activated Carbon: Kinetics, Mechanisms, and Thermodynamics

The aim of this work was to investigate the influence of initial pH value (pH₀) on the isothermal adsorption of Reactive Black 5 (RB5) dye on commercial powdered activated carbon. Four initial pH values were chosen for this experiment: pH₀ = 2.00, 4.00, 8.00, and 10.00. In order to investigate the mechanism of adsorption kinetic, studies have been performed using pseudo-first-order and pseudo-second-order kinetic models as well as an intraparticle diffusion model. In addition, thermodynamic parameters of adsorption were determined for pH₀ = 4.00. Results of this research showed that the initial pH value significantly influences the adsorption of RB5 dye onto activated carbon. The highest adsorption capacities (q_e) and efficiencies of decolouration were observed for initial pH values of pH₀ = 2.00 (q_e = 246.0 mg g⁻¹) and 10.00 (q_e = 239.1 mg g⁻¹) due to strong electrostatic interactions and attractive π···π interactions, respectively. It was also shown that the adsorption of RB5 dye on activated carbon at all initial pH values is kinetically controlled, assuming a pseudo-second-order model, and that intraparticle diffusion is not the only process that influences on the adsorption rate.

Application of a phosphonium-based ionic liquid for reactive textile dye removal: Extraction study and toxicological evaluation

Textile dyeing processes are known for their negative environmental impacts due to the production of aqueous effluents containing toxic dyes. Therefore, new wastewater treatment processes need to be developed to treat such effluents, including Liquid-Liquid Extraction (LLE) process using Ionic Liquids (IL). This work aimed to evaluate the application of the hydrophobic IL trihexyltetradecylphosphonium decanoate to extract black, navy, and royal reactive dyes from water and evaluate the toxicological aspects of the resulting water stream. We investigated the effect of selected parameters, such as pH (2-12), temperature (20-50 °C), salt effects, dye concentration (0.5-50 mg/L), and phase volume ratio (900-9000) on the dye extraction. The results showed extraction yields as high as 97% for the three dyes and an extraction capacity of approximately 300 mg/g for black and navy dyes and 400 mg/g for royal. The toxicity tests involved Lactuca sativa, Triticum aestivium L, and Daphnia magna as bioindicators. The difference between the toxicity of the dye solutions before and after extraction was not statistically significant when L. sativa and Triticum aestivum L were used as bioindicators. However, the extracted solution showed increased toxicity towards D. magna due to traces of IL. Overall, the IL has a high extraction capacity for the black, navy, and royal dyes. Nevertheless, further studies on LLE associated with other processes must be carried out to reduce the risk linked to the toxicity of IL transferred to the water.

Valorization of food waste as adsorbents for toxic dye removal from contaminated waters: A review

Industrial contaminants such as dyes and intermediates are released into water bodies, making the water unfit for human use. At the same time large amounts of food wastes accumulate near the work places, residential complexes etc. polluting the air due to putrefaction. The need of the hour lies in finding innovative solutions for dye removal from wastewater streams. In this context, the article emphasizes adoption or conversion of food waste materials, an ecological nuisance, as adsorbents for the removal of dyes from wastewaters. Adsorption, being a well-established technique, the review critically examines the specific potential of food waste constituents as dye adsorbents. The efficacy of food waste-based adsorbents is examined, besides addressing the possible adsorption mechanisms and the factors affecting phenomenon such as pH, temperature, contact time, adsorbent dosage, particle size, and ionic strength. Integration of information and communication technology approaches with adsorption isotherms and kinetic models are emphasized to bring out their role in improving overall modeling performance. Additionally, the reusability of adsorbents has been highlighted for effective substrate utilization. The review makes an attempt to stress the valorization of food waste materials to remove dyes from contaminated waters thereby ensuring long-term sustainability.

Recent Applications of the Electrocoagulation Process on Agro-Based Industrial Wastewater: A Review

Agro-based final discharge is one of the major contributors to wastewater in the world. It creates high demand for efficient treatment. The electrocoagulation process can be used for agro-based wastewater treatment. The performance of the electrocoagulation process is based on several parameters, including the electrode materials, electrolysis time, current density, and electrolyte support. Agro-based industrial wastewater (AIW) treatment processes depend on the characteristics of the wastewater. The removal of organic content from various sources of AIW can reach up to more than 80%. Some studies show that the performance of the electrochemical process can be increased using a combination with other methods. Those other methods include biological and physical treatment. The results of previous research show that organic content and color can be degraded completely. The relationship between the energy consumption and operating cost was analyzed in order to show the efficiency of electrocoagulation treatment.

Engineered macroalgal and microalgal adsorbents: Synthesis routes and adsorptive performance on hazardous water contaminants

Colourants, micropollutants and heavy metals are regarded as the most notorious hazardous contaminants found in rivers, oceans and sewage treatment plants, with detrimental impacts on human health and environment. In recent development, algal biomass showed great potential for the synthesis of engineered algal adsorbents suitable for the adsorptive management of various pollutants. This review presents comprehensive investigations on the engineered synthesis routes focusing mainly on mechanical, thermochemical and activation processes to produce algal adsorbents. The adsorptive performances of engineered algal adsorbents are assessed in accordance with different categories of hazardous pollutants as well as in terms of their experimental and modelled adsorption capacities. Due to the unique physicochemical properties of macroalgae and microalgae in their adsorbent forms, the adsorption of hazardous pollutants was found to be highly effective, which involved different mechanisms such as physisorption, chemisorption, ion-exchange, complexation and others depending on the types of pollutants. Overall, both macroalgae and microalgae not only can be tailored into different forms of adsorbents based on the applications, their adsorption capacities are also far more superior compared to the conventional adsorbents.

A critical review in electrocoagulation technology applied for oil removal in industrial wastewater

EC process, which stands for Electrocoagulation, is considered a widespread wastewater remediation method that is investigated widely for an extensive variety of wastewater resources, based on its flexibility, easy setup, eco-friendly nature, and low footprint. The critical operative factors in the EC process and the crucial relation between EC and the typical chemical coagulation approach had been thoroughly evaluated because they are the main variables that govern the process of contaminant elimination. As a result, the EC process requires further investigations for scale-up simulations in the manufacturing scopes and optimization of operational parameters. Furthermore, the current paper studies the novel integrated separation methods with the combined EC process and also their limitations for improved wastewater remediation process for cleaner wastes, recycling processes, and water recovery. In this paper, the EC enhancement processes toward oil removal from wastewater have been reviewed which includes a concise representation of the source and features of oily wastewater. Additionally, the advanced remediation methods for oil-contained wastewater and the electrocoagulation process are presented. This review summarized the present utilization of electrocoagulation to eliminate oil from wastewater. Besides the process optimization and modeling investigations, the parameters that significantly affect the electrocoagulation remediation effectiveness are evaluated. Finally, the cutting-edge and sophisticated methods of electrocoagulation process for oil removal are presented.

Photocatalytic membranes: a new perspective for persistent organic pollutants removal

The presence of conventional and emerging pollutants infiltrating into our water bodies is a course of concern as they have seriously threatened water security. Established techniques such as photocatalysis and membrane technology have proven to be promising in removing various persistent organic pollutants (POP) from wastewaters. The emergence of hybrid photocatalytic membrane which incorporates both photocatalysis and membrane technology has shown greater potential in treating POP laden wastewater based on their synergistic effects. This article provides an in-depth review on the roles of both photocatalysis and membrane technology in hybrid photocatalytic membranes for the treatment of POP containing wastewaters. A concise introduction on POP's in terms of examples, their origins and their effect on a multitude of organisms are critically reviewed. The fundamentals of photocatalytic mechanism, current directions in photocatalyst design and their employment to treat POP's are also discussed. Finally, the challenges and future direction in this field are presented.

Treatment technologies for bakers' yeast production wastewater

Researchers in recent years have utilized a broad spectrum of treatment technologies in treating bakers' yeast production wastewater. This paper aims to review the treatment technologies for the wastewater, compare the process technologies, discuss recent innovations, and propose future perspectives in the research area. The review observed that nanofiltration was the most effective membrane process for the treatment of the effluent (at >95% pollutant rejection). Other separation processes like adsorption and distillation had technical challenges of desorption, a poor fit for high pollutant load and cost limitations. Chemical treatment processes have varying levels of success but they are expensive and produce toxic sludge. Sludge production would be a hurdle when product recovery and reuse are targeted. It is difficult to make an outright choice of the best process for treating the effluent because each has its merits and demerits and an appropriate choice can be made when all factors are duly considered. The process intensification of the industrial-scale production of the bakers' yeast process will be a very direct approach, where the process optimisation, zero effluent discharge, and enhanced recovery of value-added product from the waste streams are important approaches that need to be taken into account.

Introducing a bio sorbent for removal of methylene blue dye based on flexible poly(glycerol sebacate)/chitosan/graphene oxide ecofriendly nanocomposites

As a consequence of industrial activities, one of the most prevalent components in wastewater is Water-soluble dyes needed to be removed. In this research, eco-friendly adsorbents based on poly(glycerol sebacate) (PGS), including PGS-graphene oxide nanoparticles (GO), PGS-graft-chitosan(CS), and PGS-CS-GO nanocomposites, have been proposed as efficient dye adsorbents for the wastewater treatment procedure. FESEM images showed that a smooth and uniform structure was created over incorporating CS into PGS. Besides, the presence of CS within PGS/GO nanocomposites had a positive impact on the exfoliation of GO. Moreover, it was found that the incorporation of both CS and GO into PGS reduced the glass transition of PGS. Besides, their coexistence can probably increase the chain regularity in the polymer matrix and cause a relatively larger crystal size of PGS. In this regard, the ternary nanocomposite saw a Tg value of -29.4 °C. A high adsorption capacity of 178 mg g^-1, as well as 99 removal% efficiency, were observed in the case of the PGS-CS-GO sample after 300 min at a dye concentration of 100 mg L^-1 and pH 7. Additionally, the adsorption capacity value of the adsorbent was preserved around 129 mg g^-1 after 7 cycles of adsorption-desorption. The findings revealed that innovatively synthesized PGS-g-CS/GO nanocomposites could efficiently remove methylene blue from water solutions. Hence, they can be used as a powerful and influential dye adsorbent to purify water solutions.

Sono-degradation of Reactive Blue 19 in aqueous solution and synthetic textile industry wastewater by nanoscale zero-valent aluminum

Reactive dyes, which are commonly used in the textile industry, are toxic and carcinogenic for the ecosystem and human health. The objective of this study was to investigate the removal of Reactive Blue 19 (RB19) from aqueous solution and synthetic textile industry wastewater using nanoscale zero-valent aluminum (nZVAl), ultrasonic bath (US-40 kHz), and combined US/nZVAl through the consideration of varying experimental parameters such as pH, nZVAl dosage, contact time, and initial RB19 dye concentration. The acidic pH value was an effective parameter to degrade RB19. As the nZVAl dosage and contact time increased, the degradation of RB19 dye from aqueous solution and synthetic textile industry wastewater increased using combined US/nZVAl process. A similar result was obtained for RB19 removal with combined US/nZVAl using 0.10 g dosage at 30 min, whereas it was obtained with nZVAl alone using 0.20 g dosage at 60 min. The sono-degradation process activated the nZVAl surface depending on US cavitation effect and shock waves, and increased RB19 dye uptake capacity with a shorter contact time and lower nZVAl dosage. Increasing the initial dye concentration decreased the removal efficiency for RB19. According to the obtained reusability results, nZVAl particles could be reused for four and two consecutive cycles of combined US/nZVAl and nZVAl alone, respectively.

Degradation of Reactive Brilliant Red X-3B by Photo-Fenton-like Process: Effects of Water Chemistry Factors and Degradation Mechanism

Azo dye wastewater belongs to the highly concentrated organic wastewater, which is difficult to be treated by traditional biological processes. The oxidation efficiency of a single physicochemical method is not considerable. Recent research indicated that the advanced oxidation processes (AOPs) based on the highly reactive hydroxyl radical (∙OH) became one of the preferred methods in dealing with such dye wastewater. In this paper, the typical azo dye, reactive brilliant red X-3B, was employed as the target pollutant, and the transition metal Mn and hydrogen peroxide as the catalysts. A photo-Fenton-like process, UV/Mn2+-H2O2 system, was established, which enables a combination of various technologies to improve azo dye degradation efficiency while reducing disposal costs. The results indicated that the UV/Mn2+-H2O2 system had the synergism of Mn2+/H2O2 and UV/H2O2, which was 2.6 times greater than the sum of the two individual effects. And the degradation of X-3B reached the optimum under the conditions of 0.59 mmol/L of the Mn2+, 10 mmol/L of the H2O2, pH = 6 and a high level of DO. The ∙OH, generated from chem-catalytic and photocatalytic decomposition of H2O2, played the predominant role in the decolorization of X-3B and mineralization of its intermediates. The ∙OH tended to attack and break the chromophore group, resulting in the rapid decolorization of X-3B. The azo bond in X-3B was easy to be decomposed in the form of N2, while the triazinyl group was recalcitrant for ring opening. The degradation process of the UV/Mn2+-H2O2 system preferred to be conducted at an acidic condition and appropriate concentrations of Mn2+ and H2O2. The alkaline condition would decrease the utilization of H2O2, and excessive H2O2 would also quench the ∙OH.

Evaluation of Amine Functionalized Thermal Power Plant Solid Waste for Industrial Wastewater Remediation

Micro/nanoparticles generated after the combustion of coal/lignite in the thermal power plants were modified with amino groups of (3-aminopropyl) triethoxysilane (APTES). These silane-based functional particles were applied in textile dye (xylenol orange, XO and methyl orange, MO) removal process to deal with an industrial wastewater problem. The maximum adsorption efficiencies of APTES coated micro/nanoparticles for MO and XO dye molecules were calculated to be around 98% and 75%, respectively. The adsorption behavior of the LCFA against dyes is also assessed by investigating the effect of adsorbent dosage, contact time, pH, and temperature. The optimum dye removal was observed at a pH of 4.0, and the equilibrium was achieved within 5 min. The maximum uptake capacities of LCFA-APTES for MO and XO dye molecules were calculated to be around 17.91 and 14.72 mg g−1, respectively. This value is approximately 3 − 5 times higher than the similar adsorbent in the literature. The uptake mechanism of MO and XO dyes onto LCFA-APTES is governed by electrostatic interaction and hydrogen bonding between dye molecules and APTES. The surface chemical modifications and the nature of functional groups were ascertained by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS). The application of recovered micro/nanoparticles from solid wastes and their utilization for wastewater treatment is important not only for economy of developing countries but also for protecting the environment.

Rice Straw Biochar and Magnetic Rice Straw Biochar for Safranin O Adsorption from Aqueous Solution

This study investigates the adsorption of Safranin O (SO) from aqueous solution by both biochar and magnetic biochar derived from rice straw. Rice straw biochar (RSB) was made by pyrolysis in a furnace at 500 °C, using a heating rate of 10 °C·min−1 for 2 h in an oxygen-limited environment, whilst the magnetic rice straw biochar (MRSB) was produced via the chemical precipitation of Fe2+ and Fe3+. The physicochemical properties of the synthesized biochars were characterized using SEM, SEM- EDX, XRD, FTIR techniques, and N2 adsorption (77 K) and pHpzc measurements. Batch adsorption experiments were used to explore the effect of pH, biochar dosage, kinetics, and isotherms on the adsorption of SO. Experimental data of RSB and MRSB fit well into both Langmuir and Freundlich isotherm models, and were also well-explained by the Lagergren pseudo-second-order kinetic model. The maximum SO adsorption capacity of MRSB was found to be 41.59 mg/g, while for RSB the figure was 31.06 mg/g. The intra-particle diffusion model indicated that the intra-particle diffusion may not be the only rate-limiting step. The collective physical and chemical forces account for the adsorption mechanism of SO molecules by both RSB and MRSB adsorbents. The obtained results demonstrated that the magnetic biochar can partially enhance the SO adsorption capacity of its precursor biochar and also be easily separated from the solution by using an external magnet.

Kinetics and Performance of Biological Activated Carbon Reactor for Advanced Treatment of Textile Dye Wastewater

The kinetics and performance of a biological activated carbon (BAC) reactor were evaluated to validate the proposed kinetic model. The Freundlich adsorption capacity (Ka) and adsorption intensity constants (n) obtained from the batch experiments were 1.023 ± 0.134 (mg/g) (L/mg)1/n and 2.036 ± 0.785, respectively. The effective diffusivity (Ds) of the substrate within the activated carbon was determined by comparing the adsorption model value with the experimental data to find the best fit value (4.3 × 10–4 cm2/d). The batch tests revealed that the yield coefficient (Y) was 0.18 mg VSS/mg COD. Monod and Haldane kinetics were applied to fit the experimental data and determine the biokinetic constants, such as the maximum specific utilization rate (k), half-saturation constant (KS), inhibition constant (Ki), and biomass death rate coefficient (kd). The results revealed that the Haldane kinetics fit the experimental data better than the Monod kinetics. The values of k, KS, Ki, and kd were 3.52 mg COD/mg VSS-d, 71.7 mg COD/L, 81.63 mg COD/L, and 4.9 × 10−3 1/d, respectively. The BAC reactor had a high COD removal efficiency of 94.45% at a steady state. The average influent color was found to be 62 ± 22 ADMI color units, and the color removal efficiency was 73–100% (average 92.3 ± 10.2%). The removal efficiency for ammonium was 73.9 ± 24.4%, while the residual concentration of ammonium in the effluent was 1.91 ± 2.04 mg/L. The effluent quality from the BAC reactor could meet the discharge standard and satisfy the reuse requirements of textile dye wastewater.

Low-pressure highly permeable polyester loose nanofiltration membranes tailored by natural carbohydrates for effective dye/salt fractionation

With the continuous pressure of water contamination caused by textile industry, loose nanofiltration (LNF) membranes prepared by green materials with an extraordinary water permeability are highly desirable for the recovery and purification of dyes and salts. In this work, low-pressure LNF membranes with ultrahigh permeability were fabricated via one-step interfacial polymerization (IP), in which inexpensive natural carbohydrate-derived sugars with large size and low reactivity were utilized as aqueous monomers to design selective layer. A systematic characterization by chemical analysis and optical microscopy demonstrated that the formed polyester film features not only loosen the structure, but also results in a hydrophilic and negatively charged surface. The optimized sucrose-based membrane (Su0.6/TMC0.1) with an excellent water permeability of 52.4 LMH bar^-1 was found to have a high rejection of dyes and a high transmission of salts. In addition, the sugar-based membrane manifested an excellent anti-fouling performance and long-term stability. Furthermore, the non-optimized Gl0.6/TMC0.1 and Ra0.6/TMC0.1 membranes also shown a high water permeability, while maintaining a competitive dye/salt separation performance, which confirmed the universal applicability of the membrane design principle. Therefore, the proposed new strategy for preparing next-generation LNF membranes can contribute towards the textile wastewater treatment.

Floc formation and growth mechanism during magnesium hydroxide and polyacrylamide coagulation process for reactive orange removal

Magnesium hydroxide is commonly used as a coagulant for treating reactive dyes wastewater. However, the flocs are relatively small and coagulation process needs longer sedimentation time. Large flocs and short operation time are important for good coagulation performance. Coagulation floc formation and growth processes using magnesium hydroxide and polyacrylamide (PAM) dual-coagulant were investigated with controlled experiments through flocculation index (FI), floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. The final average floc size reached 58.5 and 4.96 μm with and absence of PAM addition during slow mixing periods. PAM feeding time and magnesium hydroxide formation time can affect the floc formation and growth processes. The results showed that floc formed rapidly during magnesium hydroxide generation within 90 s and flocs aggregated together by PAM bridging function. Reactive orange removal efficiency reached 99.3% with rapid mixing 250 rpm at 90 s during 100 mg/L magnesium ion addition, then adding 6 mg/L PAM at the beginning of slow mixing period in dual-coagulant system.

Effect of Cone-Plate Clarifier Structure Parameters on Flocculation Efficiency

In this study, a coal mine water flocculation system was established. A series of flocculation tests were carried out at different structural parameters (cylinder height, cone-plate insertion depth and cone-plate spacing) to better investigate the effect of the cone-plate clarifier on coal mine water treatment performance. Sixteen sampling points were set up in the system for data monitoring to generate the required data. The cone-plate clarifier was divided into five zones for flocculation analysis. The increased cylinder height facilitated the flocculation of particles in the micro flocculation zone and the settling of particles in the settlement zone. The chemicals used are polyaluminum chloride (PACl), Fe3O4 and polyacrylamide (PAM), corresponding to doses of 60 mg/L, 40 mg/L and 6 mg/L, respectively. Insufficient insertion depth of the cone-plate will cause the small flocs that have not been fully flocculated to enter the exit pipe zone directly through the cone-plate, while too much insertion depth will cause the large floc in the settlement zone to re-enter the exit pipe zone. The flocculation effect of small flocs increased as the cone-plate spacing decreased, which is consistent with the shallow pool theory. When the cone plate spacing was too narrow, the amount of fluid was reduced and the increase in fluid velocity reduced the flocculation effect. Curve fitting was conducted for Suspended solids(SS) and turbidity removal efficiency under each structural parameter to derive the variation of SS and turbidity removal efficiency under different structural parameters. The regression models of SS and turbidity removal efficiency on the cylinder height, cone-plate insertion depth and cone-plate spacing were established based on the curve fitting results, and the regression models were verified to be well fitted based on the comparison of experimental results. Finally, the optimal values of SS and turbidity removal efficiency were found based on the regression model. The flow rate of the cone-plate clarifier is 0.6 m3/h. The SS removal efficiency reached 96.82% when the cylinder height was 708 mm, the cone-plate insertion depth was 367 mm and the cone-plate spacing was 26 mm. The turbidity removal efficiency reached 86.75% when the cylinder height was 709 mm, the cone-plate insertion depth was 369 mm and the cone-plate spacing was 26 mm.

Advanced treatment of dye manufacturing wastewater by electrocoagulation and electro-Fenton processes: Effect on COD fractions, energy consumption, and sludge analysis

This study investigated chemical oxygen demand (COD), color number (CN), and UV₂₅₄ removal from dye manufacturing wastewater via electrocoagulation (EC) and electro-Fenton (EF) processes. The effects of current density, initial pH, reaction time, and H₂O₂/COD ratio on the EC and EF processes were evaluated and optimum operating conditions were determined. The effects of EC and EF processes on COD fractions and the specific energy consumption of both processes were evaluated. Sludge analyses were conducted by organic removal to sludge ratio (ORSR) and Fourier Transform Infrared Spectroscopy spectra were assessed for characterization of generated sludge. Optimum operation conditions for the EC process were 21 mA/cm² current density, 7.3 initial pH, and 25 min reaction time while they were 21 mA/cm² current density, 3.5 initial pH, 1.25 H₂O₂/COD ratio, and 35 min reaction time for EF process. Under optimum conditions COD, CN, and UV₂₅₄ removal efficiencies were 38.5%, 90.1%, and 52.5%, respectively in EC process and 54.8%, 94.2%, and 88.1%, respectively in EF process. Both processes have a positive effect on the increase of biodegradable and soluble COD fractions. Higher ORSR and lower specific energy consumption were provided by the EF process under optimum conditions. The EF process is more effective when pollutant removal efficiencies, ORSR, and specific energy consumption are considered.

Treatment of Textile Wastewater Using Advanced Oxidation Processes—A Critical Review

Textile manufacturing is a multi-stage operation process that produces significant amounts of highly toxic wastewater. Given the size of the global textile market and its environmental impact, the development of effective, economical, and easy-to handle alternative treatment technologies for textile wastewater is of significant interest. Based on the analysis of peer-reviewed publications over the last two decades, this paper provides a comprehensive review of advanced oxidation processes (AOPs) on textile wastewater treatment, including their performances, mechanisms, advantages, disadvantages, influencing factors, and electrical energy per order (EEO) requirements. Fenton-based AOPs show the lowest median EEO value of 0.98 kWh m−3 order−1, followed by photochemical (3.20 kWh m−3 order−1), ozonation (3.34 kWh m−3 order−1), electrochemical (29.5 kWh m−3 order−1), photocatalysis (91 kWh m−3 order−1), and ultrasound (971.45 kWh m−3 order−1). The Fenton process can treat textile effluent at the lowest possible cost due to the minimal energy input and low reagent cost, while Ultrasound-based AOPs show the lowest electrical efficiency due to the high energy consumption. Further, to explore the applicability of these methods, available results from a full-scale implementation of the enhanced Fenton technology at a textile mill wastewater treatment plant (WWTP) are discussed. The WWTP operates at an estimated cost of CNY ¥1.62 m−3 (USD $0.23 m−3) with effluent meeting the China Grade I-A pollutant discharge standard for municipal WWTPs, indicating that the enhanced Fenton technology is efficient and cost-effective in industrial treatment for textile effluent.

Biodegradation of Reactive Red 198 by textile effluent adapted microbial strains

A sustainable technology to eliminate the persistent reactive dyes from the textile effluents discharged indiscriminately in the environment is highly desirous given the explosive growth of textile industries. The present study investigated the potential of two different bacterial strains, Bacillus cereus SKB12 and Enterobacter hormaechei SKB16 isolated from the dye house effluent sludge in the biotransformation of Reactive Red 198 (RR 198). Process variables such as temperature, pH, shaking conditions and contact time were optimized for the successful decolourization of RR 198. Maximum decolourization of 80% and 85% of RR 198 was achieved at pH 6 and 7, and 40 °C in microaerophilic conditions on treatment with B. cereus and E. hormaechei, respectively. High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS) analyses conducted further affirmed that the decolourization of RR 198 was rather due to biodegradation than biosorption through shift in wavenumbers, retention time variations and the appearance of lesser molecular weight peaks. Degradative pathway for RR 198 predicted based on the enzyme assay data and dye degraded metabolite peaks acquired through GC-MS analysis highlighted the significance of azoreductase and laccase in the degradation of RR 198 into smaller non-toxic compounds. In addition, toxicity assessment through zootoxicological and phytotoxicological experiments using brine shrimp and Vigna radiata validated the detoxified status of the metabolites thus proving the promising potentials of the bacterial strains in the remediation of azo dyes.

Ultrasound-assisted electrodeposition synthesis of nZVI-Pd/AC toward reductive degradation of methylene blue

A novel composite (nZVI/Pd-AC) was prepared by loading nanoscale zero-valent iron (nZVI) and Pd on activated carbon (AC) electrode under electrodeposition with ultrasound, which was used to reductive degradation of methylene blue (MB). The loading contents of Fe and Pd in composite materials were 15.84% and 2.06%, respectively. XPS results further confirmed that the as-prepared material contained Fe0 and Pd0. Without external conditions, MB could be degraded in the presence of nZVI/Pd-AC and reached equilibrium within 180 min. To investigate the reusability, the re-electrodeposition strategy was effective to refresh the active sites of nZVI/Pd-AC, and the removal efficiency only reduced by 4.51% in five circles indicating the good reusability of nZVI/Pd-AC composites. GC-MS was used to identify possible degradation pathways of MB; the results showed that the degradation products were mainly N, N-dimethylaniline and 2-amino-5-dimethylamino-benzenesulfonic acid. And the S-C, C-N bonds are the sites easier to be attacked.