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

Recycling of TiO2-containing waste and utilization by photocatalytic degradation of a reactive dye solution

Recently, the utilization of wastes, recovery of high value-added products from waste, and their use as raw materials in other industries with the logic of industrial symbiosis has become an important issue. In this study, removal efficiency of Reactive Orange 16 (RO16) dye from aqueous solution was studied using TiO₂ catalyst recycled from an industrial waste effluent. The recycling of TiO₂ waste from a paints manufacturing industry was carried out by sintering the TiO₂-containing waste. The catalyst usability of TiO₂-containing powder was then investigated in the removal of RO16 dye by photocatalytic oxidation process. In photocatalytic oxidation studies, TiO₂/UV and TiO₂/UV/H₂O₂ processes were investigated, where the effect of annealing temperature, the effect of H₂O₂ concentration, and the adsorption and photocatalytic effects on RO16 dye removal were studied. The results showed that 100% RO16 removal was obtained for the 10 mg/L initial RO16 concentration using the TiO₂ (1 g/L)/UV process. At high initial RO16 concentration (50 mg/L), 100% RO16 removal was achieved by adding 10 mM H₂O₂.

Fate and effects of microplastics in wastewater treatment processes

Microplastics (MPs) have garnered growing attention of researchers, as they are proved to be hazardous to the environment and humans. Wastewater treatment plants (WWTPs) are deemed as an important releasing source of MPs to the environment, and thus it is of significance to study the behavior of MPs in WWTPs. In this review, the fate of MPs in WWTPs and their effects on different wastewater treatment processes have been comprehensively discussed. Studies have shown that the secondary treatment is the most efficient process to remove MPs from wastewaters with a removal rate around 98%. The presence of MPs can increase reagent addition dosage, inhibit nitrogen conversion rate, and cause membrane fouling in wastewater treatment processes. Besides, the influences of MPs on activated sludge mainly exert on nitrification and denitrification processes, sludge digestion, and microbial communities. However, it is worth noting that different methods have been employed to determine the concentrations of MPs in WWTPs. As a result, the removal performance on MPs in WWTPs is difficult to be accurately assessed. Moreover, complicated interaction among MPs and other environmental pollutants may expand the impacts of MPs on wastewater treatment processes, which still remains insufficiently investigated. Therefore, this review has also proposed some knowledge gaps existing in present MP studies in WWTPs, and would provide reference to alleviate the adverse effects of MPs for future research.

Solar Light-Irradiated Photocatalytic Degradation of Model Dyes and Industrial Dyes by a Magnetic CoFe2O4-gC3N4 S-Scheme Heterojunction Photocatalyst

Magnetic CoFe₂O₄-gC₃N₄ nanocomposites were successfully synthesized, and their photocatalytic activities toward the decomposition of model synthetic dyes (e.g., methylene blue, methyl orange, and Congo red) in the presence of H₂O₂ were evaluated under simulated solar light irradiation. The 50CoFe₂O₄-50gC₃N₄ nanocomposite exhibited the highest catalytic activity. The catalytic activity of 50CoFe₂O₄-50gC₃N₄ toward the photodegradation of some industrially used dyes (such as Drimaren Turquoise CL-B p, Drimaren Yellow CL-2R p, and Drimaren Red CL-5B p) was also examined, and the catalyst exhibited its capability to decompose the industrial dyes completely. An aqueous mixture of these dyes was prepared to mimic the dye-containing wastewater, which was fully photodegraded within 30 min. 50CoFe₂O₄-50gC₃N₄ also exhibited facile magnetic separability from the reaction mixture after the accomplishment of photocatalysis reaction and stable performance after five cycles. The high photocatalytic efficiency to degrade several dyes, including dyes used in textile industries, under solar light irradiation makes 50CoFe₂O₄-50gC₃N₄ a promising photocatalyst for the treatment of dye-containing wastewater discharged from industries.

Bioreduction (AuIII to Au0) and stabilization of gold nanocatalyst using Kappa carrageenan for degradation of azo dyes

Colloidal gold nanoparticles (AuNPs) have been used in high technology applications due to their optical and electronic properties. Unfortunately, these broader applications are severely hampered by their agglomeration tendency and instability. Therefore, in this study, highly stable and aggregation resistant AuNPs were synthesized using Kappa carrageenan (κ-car) media (as a reducing and stabilizing agent) by a green synthesis protocol. The effect of different factors of reaction such as the concentration of κ-car (C_κ-car %), reaction time (t), temperature (T), and solution pH (here after simply define to 'reaction parameters') was studied by one-variable-at-a-time technique to optimize the yield production of AuNPs. The characterization of AuNPs synthesized at optimum conditions revealed that the particles are spherical in shapes, smaller in size (13.5 ± 5.1 nm) with a narrow distribution, highly crystalline (d-spacing = 0.230 nm) in nature, well stabilized (zeta potential = -22.1 mV) by coating by a thin layer of κ-car carbohydrate. The synthesized AuNPs reveal excellent catalytic function in the degradation (up to 99%) of azo-dyes. The kinetics study in the degradation reaction revealed that the technique could be extended to real wastewater treatment applications.

Microbial degradation of Procion Red by Pseudomonas stutzeri

The bacterium Pseudomonas stutzeri SPM-1, obtained from textile wastewater dumping sites of Surat, Gujarat was studied for the degradation of the textile azo dye Procion Red-H3B. The optimization was carried on the phenanthrene enrichment medium followed by exposing it to variable environmental factors and nutritional sources. The complete decolorization of dye (50 mg/L) happened within 20 h of incubation at pH 8 and temperature 32 ± 0.2 °C under microaerophilic conditions. Decolourization was monitored with the shifting of absorbance peak in UV-Vis spectrophotometry and HPLC analysis. The physicochemical studies of effluent before and after the treatment revealed 85%, 90%, and 65% decline in BOD, COD, and TOC levels. The strain showed significant activities of azoreductase (95%), laccase (76%), and NADH-DCIP reductase (88%) at 12 h, 10 h, and 8 h of growth respectively indicating evidence for reductive cleavage of the dye. The changes in the functional groups were confirmed by the presence of new peaks in FT-IR data. GC-MS analysis helped in recognizing the degraded dye compounds thus elucidating the proposed pathway for degradation of Procion Red-H3B. The potential of the bioremediation process was concluded by a phytotoxicity test using two plants, Vigna radiata and Cicer arietinum. Our study demonstrates that the strain Pseudomonas stutzeri SPM-1 has rapid decolorization efficiency and holds a noteworthy perspective in industrial application for textile wastewater treatment.

Design and optimization of a hybrid process based on hollow-fiber membrane/coagulation for wastewater treatment

Treatment of textile wastewater using ultrafiltration membranes was carried out in this study. Since membrane fouling is a major operational problem that decreases the membrane separation efficiency, wastewater was treated with polyaluminum chloride (PACl) and alum (aluminum sulfate) as coagulant to decrease the fouling of ultrafiltration membranes. PACl was selected as the best coagulant in the experiments. Also, chitosan was used as coagulant aid upon developing the hybrid process. The obtained optimum dosage of PACl coagulant was 100 mg/L, and maximum turbidity and COD removal of 35% and 66% were attained, respectively. The pretreated wastewater by coagulation was sent to ultrafiltration process for further removal of turbidity and COD. Three ultrafiltration hollow-fiber membranes made of polypropylene (PP), polyvinylidene fluoride (PVDF), and polyethersulfone (PES) were applied in this study. In general, the filtration results were evaluated for two types of samples treated under coagulation and without treatment; the results were unfavorable for the second type. The effects of transmembrane pressure (TMP) and cross velocity on membranes performance were also investigated for process optimization. The obtained results showed that PVDF membrane had the highest flux and turbidity removal, whereas the PES membrane had the highest COD removal. Also, the results revealed that turbidity and COD removal by all membranes were decreased by increasing TMP and cross velocity.

Synthesis and characterization of SnO2 NPs for photodegradation of eriochrome black-T using response surface methodology

The domestic and industrial sewage contains an extensive range of various organic compounds. Due to the toxicity of these materials, their degradation is considered one of the great environmental challenges. To address this problem, SnO₂ nanoparticles (NPs) were synthesized via a green route, and they were used as an efficient catalyst for the degradation of an organic dye. In the stage of synthesis of nanoparticles, Thymus vulgaris L. extract acted as an efficient capping agent and renewable reducing agent, and SnO₂ NPs were synthesized without addition of any hazardous surfactants. The successful synthesis of SnO₂ NPs was confirmed by XRD, FT-IR, SEM, EDX, and TEM. The photocatalytic performance of SnO₂ NPs was examined for the degradation of eriochrome black-T (ECBT) as a toxic organic dye in aqueous medium under ultraviolet irradiation. Furthermore, the response surface methodology (RSM) with central composite design (CCD) model was carried out to study of the effects of three different operational parameters on degradation of ECBT. In this design, initial pH of solution (3-11), reaction time (0.5-4 h), and the catalyst loading (0.05-0.12 g) were selected as three factors, whereas the degradation efficiency was chosen as the response. The results of the experimental design indicated that initial pH and catalyst loading were highly significant factors, whereas the reaction time was less important than other factors. Also, recyclability of catalyst was investigated, and the obtained results showed that SnO₂ NPs could be easily recovered and reused for at least 4 cycles without any significant decrease in their activity.

Green synthesis of Quercus coccifera hydrochar in subcritical water medium and evaluation of its adsorption performance for BR18 dye

In this study, we investigated the production conditions of Quercus coccifera hydrochar, which is an inexpensive and easy available adsorbent, for the adsorption of Basic Red 18 (BR18) azo dye. The hydrochar was produced in the eco-friendly subcritical water medium (SWM). The effects of the pH (2-10), adsorbent size (45-106 μm), adsorbent dose (0.5-1.5 g/L), dye concentration (40-455 mg/L), and contact time (5-120 min) were studied via optimization experiments. The optimum conditions were pH 10, particle size of 45 μm, particle amount of 1.5 g/L, dye concentration of 455 mg/L, and 60 min. The removal efficiency increased sharply for the first 5 min; after that the removal efficiency reached a steady state at 60 min, with a maximum removal of 88.7%. The kinetic studies for the adsorption of BR18 dye in aqueous solution using hydrochar showed pseudo-second-order kinetics. The Langmuir and Freundlich isotherm models were used to explain the relationship between adsorbent and adsorbate, and Freundlich isotherm was the most suitable model because of its high regression coefficient (R²) value. The intraparticle diffusion model was used to determine the adsorption mechanism of BR18 onto Q. coccifera acorn hydrochar. Desorption studies were also carried out using different types of acid and different molarities.

Development of photochemical integrated submerged membrane bioreactor for textile dyeing wastewater treatment

A pilot-scale photocatalytic membrane bioreactor (PMBR) was developed for the treatment of textile dyeing wastewater. The PMBR is made of mild steel rectangular reactor of photocatalytic unit and polyethersulphone submerged hollow fibre membrane bioreactor unit with the working volume of about 20 L. For easy recovery, the tungsten oxide (WO₃) and WO₃/1% graphene oxide (GO)-powdered photocatalyst were made into bead and immersed in photocatalytic reactor. Graphene oxide incorporation has shown better results in decolourisation and degradation when compared with WO₃ alginate alone. The incorporation of GO into WO₃ minimises the recombination of photogenerated electron-hole pairs. The operating conditions such as 3 h of contact time for photocatalysis reaction (WO₃/1% GO), 10 h hydraulic retention time for MBR and 100 kPa of transmembrane pressure were optimised. Chemical oxygen demand removal efficiency of 48% was attained with photocatalysis, and the removal efficiency was further increased up to 76% when integrated with MBR. The colour removal efficiency after photocatalysis was 25% further increased up to 70% with MBR. Complete total suspended solid removal has been achieved with this hybrid system.

Bacteria Associated with Echinodorus cordifolius and Lepironia articulata Enhance Nitrogen and Phosphorus Removal from Wastewater

Phytoremediation and bioremediation are eco-friendly methods of wastewater treatment that are widely used throughout the world to reduce anthropogenic water contamination. This study was conducted to assess the effectiveness of symbiotic bacteria in phytoremediation using two aquatic plants, Echinodorus cordifolius and Lepironia articulata, that were tested in sterilized and unsterilized groups. The results showed that unsterilized plants removed more phosphate, ammonium, nitrate and nitrite than the sterilized plants. In untreated and unsterilized E. cordifolius groups, the dominant bacterium was Calothrix (46.90 and 49.69%, respectively), which was higher than in the sterilized E. cordifolius group (38.88%). In untreated and unsterilized groups of L. articulata, Clostridium was a dominant bacterium. The proportion of Clostridium was much lower in the sterilized L. articulata group (1.31%) than in the untreated (13.71%) and unsterilized (49.02%) groups. Our results suggested that root-associated bacteria in E. cordifolius and L. articulata were effective in the removal of phosphorus and nitrogen from domestic wastewater.

Synthesis and Characterization of Magnetic Fe3O4/Zeolite NaA Nanocomposite for the Adsorption Removal of Methylene Blue Potential in Wastewater Treatment

In this research, the magnetic Fe3O4/zeolite NaA nanocomposite (Fe3O4/ZA), Fe3O4 nanoparticles, and zeolite NaA have been synthesized by facile hydrothermal methods for adsorption removal of methylene blue from aqueous solution. The as-synthesized Fe3O4/ZA nanocomposite was characterized by X-ray diffraction (XRD), MicroRaman analysis, Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray fluorescence (XRF), N2 adsorption isotherms (BET), and UV-VIS analysis. The results show that with a small weight loading of Fe3O4, the ∼3.3% Fe3O4/ZA sample exhibits a high adsorption capacity (∼40.36 mg·g−1) and removal efficiency (∼96.8%) compared to that of the zeolite NaA (∼32.99 mg·g−1 and 79.11%, respectively). Interestingly, the removal efficiency and the adsorption capacity increase rapidly with the increase of adsorption time (10–60 minutes) and Fe3O4 loading (∼3.3–9.3% wt.) in the Fe3O4/ZA composition. The adsorption mechanism of MB molecules of the Fe3O4/ZA can be addressed at the combination of the interaction between active sites on the surfaces and edges of the invert spinel ferrite Fe3O4 nanoparticles and zeolite NaA with MB molecules. Our approach provides a simple, efficient, and scalable synthesis process that render practical applications of the magnetic Fe3O4/ZA nanocomposite as a lower-cost adsorbent for wastewater treatment.

Impact of long-term storage of various redox-sensitive supported nanocomposites on their application in removal of dyes from wastewater: Mechanisms delineation through spectroscopic investigations

For the prevention of freshwater reservoirs from contamination through industrial effluents, eco-friendly adsorbents with minimal aging impact are required. Here, redox-sensitive nanoscale zero-valent iron(nZVI) particles were supported on four different surfaces with varying bentonite(B)/charcoal(C) ratio to mimic layered and porous surfaces. Different dyes, i.e. rhodamine-B(RB) and methylene blue(MB) were reacted with redox-sensitive supported nZVI composites, and degradation mechanisms were delineated using FT-IR spectroscopic analysis of reaction precipitates. A 300-day exposure to open-air was provided to the composites to comparatively evaluate the impact of aging on their reactivity for dyes in wastewater. Results interpret that dyes removal was a combination of different interfacial chemical processes, i.e., reduction or organic degradation probably through Fenton like processes, along with sorption. These mechanisms were found to be surface dependent, i.e., nZVI on charcoal enriched porous surfaces, degrade dyes through organic degradation while on layered clay surfaces, MB gets removed through reduction with limited and slower RB removal. Nanocomposites show a minimal impact of aging with removal capacities >100 mg/g for BC-1/3-nZVI and C-nZVI for MB and 50-75 mg/g for RB with significant removal in wastewater. Overall, the study concludes C-nZVI and novel BC-1/3-nZVI as two efficient dye adsorbents with minimal aging impact.

Assessing the effects of textile leachates in fish using multiple testing methods: From gene expression to behavior

The textile industry, while of major importance in the world economy, is a toxic industry utilizing and emitting thousands of chemical substances into the aquatic environment. The aim of this project was to study the potentially harmful effects associated with the leaching of chemical residues from three different types of textiles: sportswear, children's bath towels, and denim using different fish models (cell lines, fish larvae and juvenile fish). A combination of in vitro and in vivo test systems was used. Numerous biomarkers, ranging from gene expression, cytotoxicity and biochemical analysis to behavior, were measured to detect effects of leached chemicals. Principle findings indicate that leachates from all three types of textiles induced cytotoxicity on fish cell lines (RTgill-W1). Leachates from sportswear and towels induced mortality in zebrafish embryos, and chemical residues from sportswear reduced locomotion responses in developing larval fish. Sportswear leachate increased Cyp1a mRNA expression and EROD activity in liver of exposed brown trout. Leachates from towels induced EROD activity and VTG in rainbow trout, and these effects were mitigated by the temperature of the extraction process. All indicators of toxicity tested showed that exposure to textile leachate can cause adverse reactions in fish. These findings suggested that chemical leaching from textiles from domestic households could pose an ecotoxicological threat to the health of the aquatic environment.

Removal of methylene blue and lead(ii) via PVA/SA double-cross-linked network gel beads loaded with Fe3O4@KHA nanoparticles

The adsorption of MB and Pb(ii) onto and regeneration of PVA/SA/Fe₃O₄@KHA magnetic gel beads.

Allochthonous and Autochthonous Halothermotolerant Bioanodes From Hypersaline Sediment and Textile Wastewater: A Promising Microbial Electrochemical Process for Energy Recovery Coupled With Real Textile Wastewater Treatment

The textile and clothing industry is the first manufacture sector in Tunisia in terms of employment and number of enterprises. It generates large volumes of textile dyeing wastewater (TDWW) containing high concentrations of saline, alkaline, and recalcitrant pollutants that could fuel tenacious and resilient electrochemically active microorganisms in bioanodes of bioelectrochemical systems. In this study, a designed hybrid bacterial halothermotolerant bioanode incorporating indigenous and exogenous bacteria from both hypersaline sediment of Chott El Djerid (HSCE) and TDWW is proposed for simultaneous treatment of real TDWW and anodic current generation under high salinity. For the proposed halothermotolerant bioanodes, electrical current production, chemical oxygen demand (COD) removal efficiency, and bacterial community dynamics were monitored. All the experiments of halothermotolerant bioanode formation have been conducted on 6 cm² carbon felt electrodes polarized at -0.1 V/SCE and inoculated with 80% of TDWW and 20% of HSCE for 17 days at 45°C. A reproducible current production of about 12.5 ± 0.2 A/m² and a total of 91 ± 3% of COD removal efficiency were experimentally validated. Metagenomic analysis demonstrated significant differences in bacterial diversity mainly at species level between anodic biofilms incorporating allochthonous and autochthonous bacteria and anodic biofilm containing only autochthonous bacteria as a control. Therefore, we concluded that these results provide for the first time a new noteworthy alternative for achieving treatment and recover energy, in the form of a high electric current, from real saline TDWW.

Removal of Different Dye Solutions: A Comparison Study Using a Polyamide NF Membrane

The removal of organic dyes in aquatic media is, nowadays, a very pressing environmental problem. These dyes usually come from industries, such as textiles, food, and pharmaceuticals, among others, and their harm is produced by preventing the penetration of solar radiation in the aquatic medium, which leads to a great reduction in the process of photosynthesis, therefore damaging the aquatic ecosystems. The feasibility of implementing a process of nanofiltration in the purification treatment of an aqueous stream with small size dyes has been studied. Six dyes were chosen: Acid Brown-83, Allura Red, Basic Fuchsin, Crystal Violet, Methyl Orange and Sunset Yellow, with similar molecular volume (from 250 to 380 Å). The nanofiltration membrane NF99 was selected. Five of these molecules with different sizes, shapes and charges were employed in order to study the behavior of the membrane for two system characteristic parameters: permeate flux and rejection coefficient. Furthermore, a microscopy study and a behavior analysis of the membrane were carried out after using the largest molecule. Finally, the Spiegler-Kedem-Katchalsky model was applied to simulate the behavior of the membrane on the elimination of this group of dyes.

Comparative Study of Cationic Dye Adsorption Using Industrial Latex Sludge with Sulfonate and Pyrolysis Treatment

Industrial latex sludge as raw material was made into sulfonated latex sludge (SLS) and latex sludge active carbon (LSC) adsorbents by sulfonate and pyrolysis treatment to remove textile dye cationic blue X-GRRL from aqueous solution. The adsorption properties of SLS and LSC for X-GRRL were studied and compared by investigating the experimental parameters such as adsorbents dosage, pH, contact time and initial concentration. The kinetics of adsorption on SLS and LSC followed the pseudo-second-order kinetic model well. The adsorption isotherm and thermodynamic studies were further used to evaluate and compare the adsorption process of X-GRRL on SLS and LSC. The maximum adsorption capacities were 1219.6 mg/g for SLS and 476.2 mg/g for LSC according to the Langmuir model, respectively. These findings not only provide a sustainable strategy to turn industrial solid waste latex sludge into useful material for environment remediation, but also develop an efficient adsorbent for the treatment of dye wastewater.

Biodegradation and decolorization of textile dyes by bacterial strains: a biological approach for wastewater treatment

Textile industry releases large quantities of toxic dyes, which is a threat to public health and needs proper management before their release into environment. Out of the different approaches used these days, biodegradation and bio-decolorization is considered an eco-friendly and effective technique as this involves the use of microbes. This technique has the potential to be used effectively for a wide variety of dyes. In biological methods, mainly bacteria, fungi, and some algae are usually employed to remove or decolorize dyes present in textiles effluents and wastewaters. A number of researchers have used bacterial strains and relevant isolated enzymes successfully to decolorize a number of dyes. In this review article, various biological methods that have been used for the biodegradation and decolorization of textile dyes have been described. The review will also revive the significance of biological methods over other physical and chemical treatment methods that would be helpful in ensuring clean environment if used on large scale. Out of these methods, biodegradation through bacterial strains is considered as the best alternative to control water pollution as the growth rate of bacteria is considerably high as compared to other microorganisms. Thus if used the required biomass needed for biodegradation can be obtained in comparatively short interval of time.

Mesoporous silica synthesized from natural local kaolin as an effective adsorbent for removing of Acid Red 337 and its application in the treatment of real industrial textile effluent

This paper presents a synthesis of mesoporous silica (MS) from natural clay as a silica source using Pluronic L35 (EO11PO16EO11) as a structure-directing agent. The prepared material was characterized by XRD, X-ray fluorescence, thermogravimetric analysis, SEM, TEM, and N2 adsorption-desorption analyses. Then, mesoporous material was used for the removal of Acid Red 337 (AR337) from aqueous solution, and the treatment of real textile effluent. The effect of pH, contact time, weight of adsorbent, and initial concentration was studied in batch adsorption. The synthesized mesoporous material showed good discoloration efficiency with a 62% percentage. Experiment with real textile wastewater showed that 39%, 40%, and 31.5% of the color, TOC, and chemical oxygen demand respectively were eliminated by using 1 g of MS per liter of wastewater.

Assessment of natural coagulants to remediate Tunisian textile wastewater by combining physicochemical, analytical, and toxicological data

Due to the complexity and variability of textile wastewater composition, a constant search for new treatment strategies that are efficient, eco-friendly, and cost-effective is mandatory. In the present study, the efficiency of coagulation-flocculation using biocoagulants derived from cactus Opuntia ficus indica and eggplant Solanum melongena to remove toxic compounds from Tunisian textile wastewater samples was evaluated by combining assays to investigate physicochemical properties and in vitro (geno)toxicity with analytical chemistry. Both natural coagulants could significantly improve the physicochemical properties of the textile wastewater samples compared to the traditionally used chemical coagulant. The highest rate of decolorization was achieved after treatment with the cactus-derived coagulant. The analytical study revealed the presence of only crystal violet dye (CV) in only one sample. Both natural coagulants were able to remove CV, which may (partially) explain the decolorization of the treated samples. Only one untreated textile effluent induced a genotoxic response in the VITOTOX^® assay. The genotoxic effect was not linked to the presence of CV and was no longer observed after treatment with each of the natural coagulants, suggesting the effectiveness of the remediation treatments to remove potentially genotoxic compound(s). However, in the other genotoxicity tests, no biologically relevant effects were observed for any of the tested samples. In conclusion, although the physicochemical data indicate that the use of natural coagulants (cactus and eggplant) could be an interesting alternative treatment process to the chemical coagulant for detoxifying textile effluents, these results were only partially supported by the toxicological and analytical data.

Microfiber from textile dyeing and printing wastewater of a typical industrial park in China: Occurrence, removal and release

Microfibers (MFs) are fibrous micro particles of longitude <5 mm, including natural fibers and fibrous microplastics. Microplastic pollution has become a world issue. As the major section of fiber production and processing, textile industry is an important potential source of microfibers, while receiving limited attention. To better understand the source and fate of textile microfibers, in this study, a typical textile industrial park in China is selected as the studying site. Microfibers in textile wastewater from typical textile mills and centralized wastewater treatments plants (WWTPs) of the park, and microfibers in nearby surface water were identified and characterized. The main results showed that the microfiber concentration in textile printing and dyeing wastewater could reach as high as 54,100 MFs/L. Although the removal efficiencies of microfibers by existing wastewater treatment processes can be over 85%, the average microfiber concentration in the effluents from the centralized WWTPs of the industrial park still reached 537.5 MFs/L, releasing 430 billion microfiber items per day. Microfiber release from textile wastewater is considerably higher than that from municipal sewage treatment plants, making it a significant contributor to microfibers in natural water bodies. Small-sized and colored microfibers increased in proportion in the treated effluents. Given the complex textile wastewater constituents, the potential negative environmental impacts of textile microfibers may be intensified by the enhanced adsorption and transfer of textile pollutants through these microfibers.

Magnesium Silicate Polymer as a Coagulant for Reactive Dye Removal from Wastewater: Considering the Intrinsic pH in Magnesium Silicate Polymer and Coagulation Behavior

A magnesium silicate polymeric coagulant (MgSiPC), which is an inorganic polymer for dye removal from wastewater, was prepared with different pH by copolymerization. The acidity was a key factor in the preparation of the MgSiPC. In the present research, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to analyze the characterization of optimum coagulants. Additionally, the response surface method (RSM) was applied to optimize the process of coagulation-flocculation. The results of FT-IR and XRD implied that the main components of the MgSiPC with pH 1.50-2.50 were almost the same. SEM images showed that MgSiPCs with pH 1.50-2.50 exhibited different structures including cluster and lamellar shape structure, compact rod-like and network structure, and a kind of irregular geometry shape structure. In the process of coagulation-flocculation, MgSiPCs with pH 1.50-2.50 showed highly efficient coagulation performance. The removal rate of reactive yellow 2(RY2) could reach above 90% at a dosage of 50-70 mg/L and initial pH 12.00, while the removal rate of reactive blue 2 (RB2) could attain above 93% at a dosage of 50-80 mg/L and initial pH 12.00. Moreover, MgSiPCs with pH 2.00 had the highest efficiency. The results of RSM showed that the optimum combination of the MgSiPC's dosage and initial pH was 62 mg/L and 12.08 for RY2 and 78 mg/L and 12.00 for RB2, respectively. Under optimum experimental conditions, the predicted data from this model were 96% for RY2 and 100% for RB2, which was consistent with the actual experimental data. Therefore, a pH of 2.00 is considered to be the optimal acidity for preparing MgSiPCs.

Elucidation of electrocoagulation mechanism in the removal of Blue SI dye from aqueous solution using Al-Al, Cu-Cu electrodes - A comparative study

This work presents the research on the treatment of an anthraquinone derivatives of disperse dye Blue SI from aqueous solution using aluminium for the optimization of operational parameters like pH, current density, addition of electrolyte, contact time for the color removal efficiency (CRE) and the results are compared with the performance of copper electrodes in electrocoagulation (EC). The parameters for maximum CRE was found with Al at current density 40 Am^-2, time 10 min at pH 7, and for Cu at 60 Am^-2 15 min, at pH 6 were optimized. The characterization of the treated water using HPLC, MS studies revealed intermediate compounds. From the XPS analysis of the sludge obtained, the mechanism of EC was deduced. Treated aqueous solution was studied for its phytotoxicity with Vigna radiata and ecotoxicity studies were conducted on Artemia salina to study the toxicity effect of the intermediatory products in the treated dye solution. Blue SI dye aqueous solution treated with aluminium electrodes shows no or lesser toxicity in plants as well as in ecotoxic study compared with copper electrodes.

Characterization of Two Cactus Formulation-Based Flocculants and Investigation on Their Flocculating Ability for Cationic and Anionic Dyes Removal

Dye invasion in wastewaters is undeniably one of the crucial environmental concerns in addition to the supplement of toxic synthetic chemical flocculants used for color removal using the conventional coagulation-flocculation process. With the aim to improve the flocculation stage in terms of reagents safety and ensure dyes removal, the present study explores the flocculating effectiveness of two natural, stable, and eco-friendly cactus formulations, namely 60 °C oven-dried (DP) and lyophilized (LP) cladodes. Both formulations were assessed to treat cationic (Methylene blue; MB) and anionic (Methyl Orange; MO) dye solutions as a substitution attempt for the currently questioned employed synthetic chemical flocculants. Obtained results demonstrate that, in conjunction with alum as coagulant, the lyophilized powder (LP) bio-based flocculant appears to be the most efficient cactus formulation, showing a significant color (83%) and a turbidity (69%) abatement for the cationic dye (MB) and, respectively, 63% and 62% for the anionic one (MO). Additionally, the flocculation activity of the LP formula remained high over an eight-month period of storage. Moreover, based on the Fourier transform infrared (FTIR) spectroscopic analysis and the chemical characterization of cactus formulations, the occurring flocculation mechanisms of the dye removal are presumed to be based on both adsorption and bridging phenomena. Further, the significant color and turbidity decline achieved upon the addition of the lyophilized cactus cladodes powder (LP), enhancing thus the coagulation performance of the alum-based coagulant, proved the effectiveness of this bio-flocculant compared to the commonly used chemical flocculant (polyacrylamide). Hence, it was suggested that lyophilized cactus cladodes as a natural flocculant could be one of the effective surrogates to chemical flocculants conventionally used in wastewater treatment for the sake of a safer and sustainable environment.

Chromosomal Abnormalities in Allium cepa Induced by Treated Textile Effluents: Spatial and Temporal Variations

Appropriate effluent treatment processes are expected to significantly reduce the toxicity of effluents before they are released to the natural environment. The present study was aimed to assess the spatial and temporal variations of the physical and chemical water quality parameters of a natural water body receiving treated textile effluents and to assess the chromosomal abnormalities induced by the treated textile effluents. Four sampling sites (A: effluent discharge point; B: 100 m downstream from site A along the tributary; C: 200 m downstream from site A along the tributary; D: 100 m upstream from site A along the tributary) were selected associated to a tributary that received treated textile effluent. The physical and chemical water quality parameters were measured in the composite water samples collected from the study sites, and Allium cepa bioassay was conducted using aged tap water as the control. Sampling was conducted in both rainy and dry seasons. The conductivity, TDS, COD, and colour intensity of the water samples collected from the study sites were significantly higher during the dry season compared to those in the rainy season. Allium cepa root meristematic cells exposed to water samples from sites A, B, and C showed a significantly high interphase and prophase indices compared to those exposed to aged tap water and upstream site during both rainy and dry seasons. The mitotic index of the root tip cells of Allium cepa bulbs exposed to the water samples collected from the effluent discharge point (site A) and from the 100 m downstream site from site A (site B) was significantly lower than that of the other sites in both rainy and dry seasons. However, the mitotic index of the root tip cells of Allium cepa bulbs exposed to the water samples from the upstream site was not significantly different from that of the control treatment during both sampling seasons. The bioassay indicated that the mitotic index and phase index of the root meristematic cells of Allium cepa can be affected by the treated textile effluents released to the water body and the occurrence of C metaphase, chromosomal adherence, bridges, disturbed anaphase, vagrant chromosomes, and chromosomal breaks indicated that the treated textile effluent receiving tributary can possibly contain genotoxic and mutagenic compounds which can induce chromosomal abnormalities.