Dye Wastewater Treatment Research Articles

Advanced PPS/MOFs composite nanofiltration membranes derived from contra-diffusion synthesis for precise molecular separation

To meet the separation requirements of polyphenylene sulfide (PPS) membranes in extremely harsh environments and to enhance the separation performance of PPS membrane material, this study utilizes Zeolitic imidazolate framework (ZIF) material with a porous structure to modify the structure of the PPS membranes. Using the Contra-diffusion synthesis method, we successfully created PPS composite membranes that were modified by ZIF-8. At the end of the three-hour reaction time, a continuous and dense layer of ZIF-8 crystals with uniform crystal size and regular crystal shape was produced on the matrix membrane's surface. The permeance to rhodamine B aqueous solution is 42.54 L m−2 h−1 bar−1, and the retention rate is 99.5 %, which has high permeability and retention performance. In the anti-pollution performance test, the composite membrane's flux recovery rate is 72.9 %, which has good anti-pollution performance. After immersion in strong acids, strong alkalis, and a variety of organic solvents, the appearance shows no evident flaws, and the separation performance in strong alkalis and five different types of organic solvents stays steady, demonstrating excellent alkali and solvent resistance. This proves that composite membranes have great potential for application in dye wastewater treatment.

Biological treatment of methyl orange dye and textile wastewater using halo-alkaliphilic bacteria under highly alkaline conditions.

As the textile wastewater is highly saline and has high pH it is important to employ extremophilic microbes to survive in harsh conditions and provide effective bioremediation of textile dyes. This study aims to find a sustainable solution for dye removal by investigating the potential of an indigenously isolated bacterium, Nesterenkonia lacusekhoensis EMLA3 (halo-alkaliphilic) for treatment of an azo dye, methyl orange (MO) and textile effluent. MO dye decolorization studies were conducted using mineral salt media (MSM) by varying incubation time (0-120h), initial dye concentration (50-350mg/L), pH (7.0-12.0), inoculum dose (3-10%), agitation (stationary, 100rpm and 200rpm), and temperature (20-55°C). Dye removal by the bacterium for 50mg/L of dye was > 97.0% within 72h of incubation at pH 11.0 in stationary condition. Bacterium had excellent reusability i.e. > 97% dye removal for up to 5 cycles. Moreover, bacterium has the potential for co-removal of chromium (VI) (3.5-28mg/L), and also almost complete dye removal in presence of high amount of NaCl. Liquid chromatography-mass spectrometry showed degradation as the mechanism of dye removal. Application of the bacterium to MO dye spiked real textile wastewater showed excellent dye removal. Phyto-toxicity assessment conducted on Vigna radiata and Triticum aestivum seeds, showed 100% germination of biotreated textile wastewater indicating its reuse potential.

MOF incorporated Polyethersulfone/Polylactic Acid ultrafiltration membranes for the catalytic removal of dyes via persulfate activation

This study synthesized novel nanocellulose/zeolitic Imidazolate Framework nanocomposite blended Polyethersulfone/Polylactic Acid (PES/PLA-CNF@ZIF-8) membranes through a modified phase inversion process. This is the first time that a nanocellulose-MOF composite catalytic nanomaterial has been synthesized and used as an additive in polymeric membranes. The morphology and chemical structure of the membranes and nanoparticles were characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) respectively. Membrane wettability and crystalline structure were characterised by contact angle, and X-ray diffraction (XRD) analysis respectively. CNF@ZIF-8 modified membranes showed improved contact angle which decreased from 76° in the pristine membranes to 40° in 2 wt% membranes, bulk porosity increased from 74.3.3 % to 81.06 % while the pure water flux increased from 208.30 Lm-2h−1 to 348.73 Lm-2h−1. Further, the modified membranes showed an increase in surface roughness reaching 84.14 nm in 2 wt% membranes. The synthesized membranes have been used as catalysts in the activation of persulfate to degrade Rhodamine B dye. The modified membranes displayed a high catalytic effect (>90 %) in activating persulfate to degrade RhB dye when compared to pristine membranes which showed a degradation efficiency of < 35 %. The study found that the optimum parameters for pH, membrane (catalyst) dosage, oxidant and initial dye concentration were 5, 0.3 g, 0.4 mM and 10 ppm respectively. Quenching experiments showed that •SO4- and •OH radicals were responsible for the dye degradation, with •SO4- radicals playing a major role in the oxidative degradation of the RhB dye. The synthesized membranes showed good stability when tested within five cycles, with the membranes showing degradation efficiency ranging from 92.1 % in the 1st cycle to 91.9 % in the 3rd cycle, before decreasing to 75.3 % in the 5th cycle. This study has therefore shown that the synthesized PES/PLA-CNF@ZIF-8 membranes have potential for use as catalysts in the degradation of cationic dyes in wastewater treatment through persulfate activation.

One-step electrospun ZnFe₂O₄/ZnO/CuO composite photo-Fenton nanofibers for efficient degradation of organic dyes

The ZnFe₂O₄/ZnO/CuO composite photo-Fenton nanofibers were successfully synthesized via the parallel electrospinning technique, exhibiting a morphology composed of nanofibers intertwined with nanospheres, with a diameter predominantly ranging from 150.5±39.98 nm. During the photo-Fenton reaction, Fe³⁺ ions in ZnFe₂O₄ served as electron traps, facilitating their reduction to Fe²⁺ upon capturing electrons from the conduction band, and Fe²⁺ interacted with H₂O₂ to generate additional ·OH radicals, which were then reoxidized to Fe³⁺, sustaining the catalytic cycle. When illuminated for 150 min, the degradation efficiencies of Rhodamine B (RhB) in the ZnFe₂O₄/ZnO/CuO composite photo-Fenton nanofiber systems, with varying volumes of H₂O₂ (0.05 mL, 0.1 mL and 0.2 mL) added, were 83.02 %, 93.33 %, and 90.34 %, respectively. The optimal photocatalytic degradation efficiency of 93.33 % was achieved with the addition of 0.1 mL of H₂O₂. In this photo-Fenton process, both photogenerated holes (h⁺) and ·OH radicals played pivotal roles under light irradiation. The findings of this study offer valuable insights into the application of photocatalysis for the treatment of industrial dye wastewater. The ZnFe₂O₄/ZnO/CuO composite photo-Fenton nanofibers present a promising alternative to traditional treatment methods, demonstrating high efficiency, environmental friendliness, and significant potential for industrial-scale application. This research significantly contributes to the fields of environmental protection and sustainable development.

Development of Monolithic Hyper-Cross-Linked Polystyrene-Supported Ultrasmall Nano-Ag Catalysts for Enhanced NaBH4-Mediated Dye Degradation.

Synthesizing catalyst supports with appropriate compositions and structures is crucial for reducing the sizes of metal nanoparticles and enhancing their catalytic activities. In this work, a series of monolithic hyper-cross-linked supports (HCP-CC) with hierarchical pores were synthesized. The monolithic structure facilitated easy operation in catalytic reactions, while the composition and structure of HCP-CC could be tailored simultaneously by utilizing the functional cross-linking agent cyanogen chloride. Furthermore, in situ loading of nano-Ag into HCP-CC resulted in the hybrid catalyst HCP-CC-Ag. The synergy of confinement and coordination effect controlled and limited the size of nano-Ag to approximately 3 nm, classifying them as ultrasmall nanoparticles, which ensured outstanding catalytic activity. This hybrid catalyst could improve the reaction rate constant to 0.423 min-1; it efficiently promoted the degradation of organic dye and exhibited great universality and recyclability, making it a potential heterogeneous catalyst for dye wastewater treatment.

Efficient Removal of Cationic Dye by Biomimetic Amorphous Calcium Carbonate: Behavior and Mechanisms.

The search for efficient, environmentally friendly adsorbents is critical for purifying dye wastewater. In this study, we produced a first-of-its-kind effective biomimetic amorphous calcium carbonate (BACC) using bacterial processes and evaluated its capacity to adsorb a hazardous organic cationic dye-methylene blue (MB). BACC can adsorb a maximum of 494.86 mg/g of MB, and this excellent adsorption performance was maintained during different solution temperature (10-55 °C) and broad pH (3-12) conditions. The favorable adsorption characteristics of BACC can be attributable to its hydrophobic property, porosity, electronegativity, and perfect dispersity in aqueous solution. During adsorption, MB can form Cl-Ca, S-O, N-Ca, and H-bonds on the surface of BACC. Since BACC has excellent resistance to adsorption interference in different water bodies and in real dye wastewater, and can also be effectively recycled six times, our study is an important step forward in dye wastewater treatment applications.

Establishing robust ZnO-sodium alginate nanocomposite for dye wastewater treatment: characterization, RSM methodology, and mechanism evaluation.

In today's world, water is a highly valued resource, and enhancing the quality of this natural endowment is a significant concern and a worldwide endeavor. This study sought to purify real wastewater and water tainted with methylene blue (MB) by immobilizing ZnO nanoparticles onto an alginate matrix using a straightforward approach and a three-dimensional structure. After analyzing the impact of , it was determined that 93.84% of MB was successfully removed (time = 120 min, dye concentration = 15 mg/L, catalyst amount = 2.5 g). The effects of inorganic ions and water types were investigated to simulate real wastewater conditions, and the catalyst performed satisfactorily. Alginate played a significant role in selectively removing dye, and the catalyst effectively removed 80.36% of MB and, in contrast, 20% of methyl orange (MO). The practical application of the catalyst was evaluated in textile wastewater treatment, and the catalyst showed satisfactory performance. An average 2.49% reduction in dye removal was observed after five stages of using the catalyst, demonstrating the beads' excellent stability. The composites were subjected to free radical trapping experiments to ascertain the active species. According to the results, and acted as the main reaction species in the degradation of MB. At the end, the synergistic mechanism of adsorption and degradation in MB removal was presented.

Nanocomposite of cellulose nanofibers/alumina for effective adsorption of brilliant blue and ethyl orange dyes: Equilibrium, kinetic and mechanism studies

Our study investigated the performance of a nanocomposite prepared from TEMPO- oxidized cellulose nanofibers (CNF) and alumina (Al2O3) on two models of anionic dyes namely Brilliant blue FCF (B.B) and Ethyl orange (E.O) dyes. Here the Al2O3 was prepared using the solution combustion (SC) method. Cellulose nanofibers were prepared from local agriculture waste (bagasse) and mixed with Al2O3 nanoparticles for preparing composite films through the casting technique. Various analytical tools have been used to characterize cellulose nanofibers and cellulose nanofibers/ Al2O3 nanocomposite, including, FTIR, FE- SEM, TEM, and XRD. In the conducted batch experiments aimed at optimizing various operational factors, the study of adsorption isotherms revealed that the data closely align with the freundlich adsorption isotherm model, demonstrating multilayer adsorption. Furthermore, it was found that, the pseudo-second-order model fit the data effectively. Thus, CNF/ Al2O3 nanocomposite was found to be an active adsorbent for handling solutions containing the anionic dyes, which shows its hopeful tolerable of being a highly reusable, cost-effective sustainable and adsorbent for dyeing wastewater treatment.

PVA/AMPS hydrogels: Promising adsorbents for wastewater treatment with high efficiency and reusability

AbstractA PVAMPS hydrogel was synthesized through chemical cross‐linking and semi‐interpenetration of Poly (vinyl Alcohol) (PVA) and 2‐Acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) with glutaraldehyde in distilled water. Various ratios of PVA/AMPS, namely PVAMPS‐1 (2:1), PVAMPS‐2 (1:1), and PVAMPS‐3 (1:2), were examined to understand their individual impacts on gel formation. The synthesis of hydrogels was confirmed using FT‐IR and solid‐state 13C NMR spectroscopy. The PVAMPS hydrogels demonstrated high efficiency as a selective adsorbent for removing cationic dyes, such as Methylene Blue, Safranine‐O, and Thionine, from aqueous solutions, with over 90% removal of cationic dyes observed within 18 hours. Regeneration and reusability studies revealed that even after four cycles, the adsorption capacity of the PVAMPS hydrogels remained exceptionally high, with removal rates exceeding 90% for Methylene Blue. However, for Safranine‐O and Thionine, the removal rates dropped to 20% and 23%, respectively, after four cycles. These findings underscore the promising potential of PVAMPS hydrogels for the removal of cationic dyes in wastewater treatment.

Kinetic study on the degradation of Acid Red 88 azo dye in a constructed wetland-microbial fuel cell inoculated with Shewanella oneidensis MR-1.

Removal of Acid Red 88 (AR88) as an azo dye from the synthetic type of wastewater was studied in a laboratory-made constructed wetland microbial fuel cell (CW-MFC) inoculated with Shewanella oneidensis MR-1 (SOMR-1). Plant cultivation was implemented using a typical CW plant known as Cyperus alternifolius. The complexity of the SOMR-1 cell membrane having different carriers of electrons and H+ ions gives the microbe special enzymatic ability to participate in the AR88 oxidation link to the O2 reduction. Nernst equation developed based on analyzing the involved redox potential values in these electron exchanges is describable quantitatively in terms of the spontaneity of the catalyzed reaction. Power density (PD) at 100mg/L of the AR88 under closed-circuit conditions in the presence of the plant was 11.83 mW/m2. Reduction of internal resistance positively affected the PD value. In determining degradation kinetics, two approaches were undertaken: chemically in terms of first- and second-order reactions and biochemically in terms of the mathematical equations for rate determination developed on the basis of substrate inhibitory concept. The first-order rate constant was 0.263h-1 without plant cultivation and 0.324h-1 with plant cultivation. The Haldane kinetic model revealed low ks and ki values indicating effective degradation of the AR88. Moreover, the importance of acclimatization in terms of the crucial role of lactate was discussed. These findings suggest that integrating the SOMR-1 electrochemical role with CW-MFC could be a promising approach for the efficient degradation of azo dyes in wastewater treatment.

Novel carboxymethyl cellulose-based hydrogel embedded with metal organic framework for efficient cationic dye removal from water

The rGO/CMC/β-CD (RCβ) hydrogel was synthesized from reduced graphene oxide (rGO), β-cyclodextrin (β-CD) and sodium carboxymethyl cellulose (CMC) by radical polymerization. A novel hydrogel adsorbent was created by growing the metal-organic framework (Cu-BTC) in-situ on RCβ hydrogel, which has excellent adsorption capacities for cationic dyes in wastewater. The adsorption parameters such as the amount of adsorbent, pH of solution and adsorption time were optimized through batch adsorption experiments. Under the optimal conditions of pH 6.0, adsorbent dosage of 0.01 g and experimental temperature of 25 °C, Langmuir isothermal model was used to fit the maximum adsorption capacities of methylene blue (MB), crystal violet (CV) and malachite green (MG), which were 892.66, 842.75 and 633.77 mg g−1, respectively. The fitting results of adsorption kinetics revealed that the pseudo-second-order model can describe the adsorption process better. Based on proposed studies, the dye molecules were adsorbed onto RCβ@Cu-BTC hydrogel mainly through electrostatic interaction, hydrogen bonding and π–π interactions. After five cycles, the adsorption efficiency of the RCβ@Cu-BTC hydrogel for MB, CV and MG can still reach 80 %, 77 % and 72 %, which shows that the adsorbent has good adsorption performance. Various adsorption experiments show that RCβ@Cu-BTC hydrogel has great potential in treating dye wastewater.

Insights into mixed dye pollutant degradation by oxygen and air plasma bubbling array

Abstract Synthetic organic dye pollutants pose a serious threat to the aquatic ecological environment due to their difficulty in complete degradation. This study employed a plasma bubble array reactor to degrade individual and mixed dye pollutant solutions of Sunset Yellow (SY), Methyl Orange (MO), and Methyl Violet (MV). The degradation efficiencies and mechanisms of the plasma were investigated under different working gas atmospheres. It was found that oxygen plasma degraded the target dyes and their mixtures more significantly than air plasma. Specifically, compared with air plasma, the removal of single dyes SY, MO and MV by oxygen plasma was increased by 76.6%, 13.8% and 3%, respectively, after 20 min of treatment. As for mixed dyes, after 25 min treatment, oxygen plasma removed 99.1%, which was 31.6% higher than air plasma. However, the degradation kinetic order in oxygen plasma was SY &gt; MO &gt; MV, while that in air plasma was MV &gt; MO &gt; SY. Combined with the detection of reactive oxygen-nitrogen species (RONS), the results showed that the reactive oxygen species (ROS) played an important role in the degradation of SY, and it was also important for the degradation of MO, whereas both the ROS and reactive nitrogen species (RNS) were important for the degradation of MV. Scavenger experiments revealed that hydroxyl (·OH) and superoxide anion (·O2-) played the most important roles in the degradation process. The three dyes were basically completely degraded within 14-20 minutes of treatment, with corresponding yields of 1.94-2.79 g/kWh. Possible degradation pathways for each dye were deduced based on LC-MS and the toxicities of solutions were evaluated by phytotoxicity tests and ion chromatography. The results showed that the biotoxicity of the intermediates was significantly reduced. This study may provide a feasible option for effective application of plasma technology in organic dye wastewater treatment.

A novel cross-flow Ag/wood composite filter for high-concentration organic dye wastewater treatment

A novel cross-flow Ag/wood composite filter for high-concentration organic dye wastewater treatment

Synthesizing high performance robust PSf loose nanofiltration membranes through nanobubble-assisted pore-forming

Loose nanofiltration (LNF) membranes have extensive applications in precision separation processes, however, synthesizing highly permselective LNF membranes is still a considerable obstacle. Nanobubble-assisted pore-forming method was adapted to prepare a highly perm-selective LNF membrane for the first time in this work, using polysulfone (PSf) as the membrane-forming material, azodicarbonamide (AC) as the reactive pore-forming agents, and NaOH solution as the coagulation and immersion baths. By leveraging nano-bubbles produced through the reaction between AC and NaOH without adding other pore-forming agents, the membrane-forming process of PSf was regulated. It was found that the PSf LNF membranes prepared in NaOH-solution coagulation and immersion baths exhibited significantly enhanced permeation performance without compromising the rejection. These results suggested that the coagulation and immersion post-treatment processes under NaOH solution had a great effect upon the structure and the property of the membranes. The LNF membrane prepared from 20 wt% PSf casting solution with 8 wt% AC achieved a permeation flux of 188.7 L m−2 h−1, and a Congo red (CR, Mw =696 Da) rejection of over 99 %, while a rejection of NaCl below 7 %, showing a good separation for the CR/NaCl mixed solution. Additionally, the membrane exhibited favorable mechanical properties, with a tensile strength as high as 6.5 MPa and a fracture elongation reaching as much as 32.3 %. This work provided a novel approach for producing high-performance LNF membranes in treating dye wastewater.

Mechanical force-induced oxygen vacancies facilitate enhanced piezo-photocatalytic activity in AgNbO3

Piezo-photocatalysis has emerged as a promising strategy for addressing environmental pollution and the rapidly escalating energy crisis. However, it is still challenging to improve its degradation rate constant. To address this issue, herein, we proposed an innovative strategy of combining both hydrothermal synthesis and high energy mechanical ball milling process in AgNbO3 (AN) photo-catalyst. It is interesting that the hydrothermally synthesized and ball-milled AN demonstrated a record degradation rate constant (k) of 0.213 min−1 for Rhodamine B (RhB), with an 11-fold improvement compared to the un-ball-milled samples. Furthermore, the degradation rate remained high level at 97.3 % after four cycles. The distinguished performance is attributed to the production of large amount of OVs (oxygen vacancies) in hydrothermally synthesized and ball-milled AN, which narrows the bandgap, reduces the recombination of photo-generated carriers, and enhances the absorption of O₂ and OH⁻, thereby efficiently generating superoxide radicals (•O₂⁻) and hydroxyl radicals (•OH). This work presents a novel approach for enhancing the piezo-photocatalytic activity of lead-free piezoelectric materials, which holds broad application prospects in the catalytic treatment of dye wastewater.

High-Performance PBA12F@CS/PVA@ZIF-8 composite membranes for dye wastewater treatment

The effective filtration and treatment of dye wastewater through membrane technology can reduce environmental pollution and contribute to the realization of sustainability. In this study, a composite membrane for dye separation with antimicrobial properties is proposed which combines a support layer of PBA12F manufactured through electrospinning and a functional layer of CS/PVA@X-ZIF-8, resulting in the fabrication of PBA12F@CS/PVA@X-ZIF-8 nanofiber composite membrane. Compared to homogeneous PBA12F membranes, PBA12F@CS/PVA@X-ZIF-8 nanofiber composite membrane exhibits higher flux. As for the composite membrane with a ZIF-8 content of 0.1 wt%, the pure water flux reaches 65.04 L/m2·h, and a 50 % increase over the homogeneous membrane. Furthermore, an increase in ZIF-8 content leads to enhanced dye rejection and antimicrobial properties of the composite membrane, with inhibition rates exceeding 70 % for Escherichia coli and Staphylococcus aureus. The retention rates for pollutants BSA and HA exceed 90 %. These findings demonstrate the potential of PBA12F@CS/PVA@ZIF-8 composite membranes in pollution treatment.

Simultaneous optimization of electric production, azo dye, and yeast wastewater treatment in microbial fuel cell: Selection of the most suitable optimal conditions by PROMETHEE

Microbial fuel cell is a clean technology in which waste treatment and energy production continue simultaneously. Process performance depends on the independent variables and their interaction with each other specific to the waste to be treated. In this study, Microbial Fuel Cell (MFC), in which yeast production process wastewater is oxidized in the anolyte, and azo dye is reduced in the catholyte under abiotic conditions, was optimized using the Response Surface Methodology for maximum waste treatment and energy production. The independent variables were wastewater type, electrode array, and amount of sulfate-reducing inhibitor, while the dependent variables were azo dye removal, maximum power density, chemical oxygen demand (COD) removal, and coulomb efficiency. The effect of variables on all responses was determined using Analysis of Variance (ANOVA) and 3-dimensional (3D) graphs. The suitability of the models was tested by verification experiments under the determined optimum conditions (OPT 1, 2 and 3). Optimum experiments were ranked with the PROMETHEE approach according to azo dye removal (mg/L), maximum power density (mW/m2), COD removal (g/L), coulombic efficiency (%), and electrode cost (€/m2) criteria. The preference order of the optimum experiments was determined as OPT 1>OPT 2>OPT 3. With OPT 1, azo dye removal of 16.8 mg/L, maximum power density of 95.34 mW/m2, COD removal of 5.8 g/L and coulombic efficiency of 0.23 % were achieved. With a 1000 Ω external resistor, the maximum power density and coulombic efficiency increased to 147 mW/m2 and 1.5 %, respectively. In addition, the determined optimum experiments were examined using polarization curve and Electrochemical Impedance Spectroscopy.

Preparation of Composites Derived from Modified Loess/Chitosan and Its Adsorption Performance for Methyl Orange.

A modified loess/chitosan composite (ML@CS) was prepared via solution. The microstructure and physicochemical properties of ML@CS were characterised via scanning electron microscope (SEM), Zeta potential, X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), and thermogravimetric analysis (TGA). An aqueous solution of methyl orange (MO) was used as simulated wastewater from which the influence of the initial concentration and pH of MO, the dosage amount and regeneration performance of ML@CS, adsorption temperature, and time on the adsorption effect of MO were systematically investigated. The adsorption kinetics, isothermal adsorption, and adsorption mechanism were also analysed. The results indicate that ML@CS had a good adsorption effect on MO. When the initial concentration of MO was 200 mg/L, pH was 5.0, and ML@CS dosage was 1.0 g/L, the adsorption equilibrium could be reached within 180 min at room temperature, and the equilibrium adsorption capacity and removal rate reached 199.52 mg/g and 99.75%, respectively. After five adsorption-desorption cycles, the MO removal rate remained above 82%. The adsorption behaviour of ML@CS for MO conforms to the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model. The spontaneous exothermic process was mainly controlled by monolayer chemical adsorption and the physical adsorption only played an auxiliary role. ML@CS efficiently adsorbed MO in water and can be used as a high-efficiency, low-cost adsorbent for printing and dyeing wastewater treatment.

Comparative treatment of textile dye wastewater with chemical coagulants and bacterial exopolysaccharides

Traces of chemical coagulants, such as alum, commonly used in wastewater treatment, remain in the water effluent and also result in secondary sludge that is difficult to treat. On the other hand, Extracellular Polymeric Substances (EPS) are safer and can be used as alternative bio flocculants. A study was hence done to compare the effectiveness of the treatment of Reactive Black 5 (RB5) textile wastewater with chemical coagulants and bacterial EPS. The jar test method was used to treat the wastewater with Alum and Polyferrous Sulphate (PFS) at varied pH (2–10) and respective dose concentrations. EPS was produced by bacteria isolated from cotton gin trash soil collected from Kitui ginnery in Kenya. EPS treatment was done at 30 °C for 72 h. EPS-producing bacteria isolates were identified by molecular analysis. The chemically and EPS-treated wastewater was analyzed for color, Total Dissolved Solids (TDS), and Chemical Oxygen Demand (COD). Respective color and TDS removal capacity by PFS and alum were (86.1% and 42.18%) and (85.1% and 69%) at their optimal conditions of (pH 7 and 100 mg/L) and (pH 7 and 140 mg/L). Similarly, PFS and alum reduced COD by 27.25% and 26.65%. Respective dye removal by YEAK2 −5 and YEPD K2 −2 EPS was 69.1% and 85.7%. However, YEPD K2 −2 and YEAK2 −5 EPS caused a respective rise of TDS by 40.14% and 67.17%. The respective reduction of COD by YEPD K2 −2 and YEAK2 −5 EPS was 56.25% and 54.24%. The chemically and EPS-treated wastewater met the National Environment Management Authority (NEMA) limits. The YEPD K2 −2 and YEAK2 −5 isolates were both identified as Bacillus sp. GC–MS and FTIR analysis results indicated that the two EPS were heteropolysaccharides composed of different sugar derivatives and hydroxyl as the main functional group. The results for treatment of the dye wastewater by Alum, PFS, and EPS were therefore comparable. The bacterial EPS bio flocculants can therefore serve as effective and cleaner substitutes to the alum and PFS chemical coagulants.

Bi2MoO6/MgIn2S4 S-scheme heterojunction with rich oxygen vacancies for effective organic pollutants degradation: Degradation pathways, biological toxicity assessment, and mechanism research

Designing and constructing novel photocatalysts for organic pollutant degradation is of critical significance for water environment treatment. Constructing a Bi2MoO6/MgIn2S4 (BMO/MIS) S-scheme heterojunction with oxygen vacancies, which efficiently removed RhB within visible light irradiation. Oxygen vacancies regulated the band structure of Bi2MoO6 (BMO) and enhanced the adsorption of RhB on the catalyst's surface. The S-scheme heterojunctions contributed to the separation and transfer of photo-generated charge, retained the optimal redox ability of Bi2MoO6-Vo (BMO-Vo) and MgIn2S4 (MIS) at the same time. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) further confirmed the S-scheme charge transfer mechanism and the presence of oxygen vacancies. Within 30 min of visible light irradiation, RhB was completely degraded by BMO/MIS-8%, while the degradation efficiency of RhB by BMO-Vo and MIS were only 39.93 % and 80.87 %, respectively. The kinetics constant is 0.1035 min−1 of BMO/MIS-8%, which was 20.29 and 1.95 times that of BMO-Vo and MIS, respectively. At the same time, BMO/MIS-8% achieved removal efficiency of 24.28 %, 56.53 %, 59.15 % and 100 % for MO, TC,H-TC and MB, respectively. Compared to the previously synthesized Bi-ZFO/BMO-Vo photocatalyst, BMO/MIS-8% demonstrated superior degradation efficiency, exhibiting a degradation kinetic constant that was 2.12 times greater than that of Bi-ZFO/BMO-Vo under visible light irradiation. To improve the practical application of BMO/MIS, the effects of pH, co-existing ions and types of pollutants on degradation efficiency were evaluated. In addition, the biological toxicity assessment showed a significant decrease in the toxicity of RhB degradation products. This work provides a feasible avenue for constructing Bi2MoO6-based heterojunctions to treat dye wastewater.