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

Coagulation promotes the spread of antibiotic resistance genes in secondary effluents

Wastewater treatment plants (WWTPs) are biological hotspots receiving the residual antibiotics and antibiotic resistant bacteria/genes (ARB/ARGs) that greatly influence the spread of antibiotic resistance in the environment. A common method used in WWTPs for the purification of secondary effluent is coagulation. Notwithstanding the increasing health concern of antibiotic resistance in WWTPs, the impact of coagulation on the emergence and spread of antibiotic resistance remains unclear. To shed light on this, our study investigated the behavior of four representative ARB types (tetracycline, sulfamethoxazole, clindamycin, and ciprofloxacin resistance) during the coagulation process in a model wastewater treatment plant. Our search showed a significant reduction in the presence of ARBs after either PAC or FeCl3 coagulation, with removal efficiencies of 95% and 90%, respectively. However, after 4 days of storage, ARB levels in the coagulated effluent increased by 6-138 times higher than the original secondary effluent. It suggests a potential resurgence and spread of antibiotic resistance after coagulation. Detailed studies suggest that coagulants, particularly PAC, may facilitate the transfer of ARGs among different bacterial species by the enhanced cell-cell contact during coagulation-induced bacterial aggregation. This transfer is further enhanced by the factors such as auxiliary mixing, longer incubation time and ideal operating temperatures. In addition, both PAC and FeCl3 affected gene expression associated with bacterial conjugation, leading to an increase in conjugation efficiency. In conclusion, while coagulation serves as a purification method, it might inadvertently boost the spread of ARGs during tertiary wastewater treatment. This underscores the importance of implementing subsequent measures to mitigate this effect. Our findings provide a deeper understanding of the challenges posed by bacterial antibiotic resistance in wastewater and pave the way for devising more effective ARB and ARG management strategies.

Natural marmatite photocatalyst for treatment of mineral processing wastewater to help zero wastewater discharge

Mineral processing wastewater (MPW) with large discharge and high toxicity affects environmental safety, and the realizing zero discharge of MPW is of great significance for reducing environmental pollution, saving water resources, and promoting the sustainable development of the mining industry. In this study, we reported natural marmatite (NM) as a low-cost and efficient photocatalyst for the treatment of MPW to help zero wastewater discharge. The photocatalytic activity of NM was evaluated by the removal of total organic carbon (TOC) from MPW under visible-light illumination, and the optimal degradation conditions were discussed. Results showed that superoxide free radicals (·O2-) were the dominant active species responsible for organic pollutants degradation, and 74.25% TOC removal was obtained after 120 min reaction under the optimum treatment conditions. Meanwhile, the wastewater treated by NM photocatalysis can be reused in the flotation system without adverse impact on the product index. Based on these findings, a model of zero wastewater discharge for flotation with the help of photocatalytic treatment was established, it indicated that the water of the whole system can be balanced without affecting the ore dressing index, which showed that visible light-driven photocatalyst has a promising application prospect in the treatment and recycling of industrial wastewater.

Feasibility of sludge deep dewaterability improvement for incineration disposal by combined conditioning of freeze-thaw and sawdust

Sludge incineration is the main strategy for sludge reduction in China. The combined conditioning of lime and chemical agents has been proven to achieve sludge dewatering by disrupting the extracellular polymeric substances (EPS) of sludge and reducing its compressibility. However, when incineration is the intended disposal purpose, this method poses challenges such as incomplete combustion, equipment corrosion, secondary pollution, and decreased calorific value of sludge cake. In contrast, freeze-thaw conditioning, coupled with sawdust as a high-calorific-value bio-waste, emerges as an efficient and clean alternative. The research investigates the synergistic effects of freeze-thaw and sawdust co-conditioning on various sludge properties, including dewaterability, compressibility, consolidation, permeability, microscopicity, and calorific value. The study reveals that the combined conditioning significantly reduces water content and compressibility while increasing void ratio, consolidation, permeability, and enhancing the calorific value of the sludge cake. Specifically, sludge cake conditioned with 60% dried solids (DS) sawdust and freeze-thaw achieved a water content (Wc) of 49.07% and a calorific value of 1422.3 kcal/kg, meeting standards for self-sustained incineration. With heat recovery, the combined conditioning generates an economic revenue of 25.1 $/t DS after deducting costs, thereby reducing the overall cost of sludge reduction treatment. This research offers a clean and practical solution for sludge incineration and reduction, demonstrating great economic value and application potential.

Purification of aqueous orange II solution through adsorption and visible-light-induced photodegradation using ZnO-modified g-C3N4 composites

Semiconductor-based remediation enables environmentally friendly methods of removing aqueous pollutants. Simply fabricated ZnO modified g-C3N4 composites were utilized as bifunctional adsorptive photocatalysts for orange II removal from aqueous solution through adsorption and photocatalysis processes. The adsorption isotherm data of the g-C3N4 (g-CN) and ZnO modified g-C3N4 (ZCN) composites on orange II solution were better fitted with the Langmuir isotherm compared to the Freundlich isotherm. The maximum adsorption capacity for ZCN-2.5 was slightly higher than that of bare g-CN. According to the adsorption thermodynamics investigation of ZCN-2.5 in orange II solution, the positive values of Gibb's free energy change (ΔG0) suggested a non-spontaneous adsorption process. Furthermore, the negative values of entropy change (ΔS) and enthalpy change (ΔH) indicated the decrement of randomness and exothermic nature during the adsorption process, respectively. The photocatalytic degradation kinetics of g-CN and ZCN composites indicated that the degradation process follows the pseudo-first-order reaction kinetic. The degradation rate of orange II with the ZCN-2.5 composite was 6.67 times higher than that obtained with bare g-CN. Possible adsorption and photocatalytic mechanisms have been proposed.

Neem biomass derived carbon quantum dots synthesized via one step ultrasonification method for ecofriendly methylene blue dye removal

This article presents a one-step ultrasonication technique for generating biomass carbon dots (BCDs) from neem bark (Azadirachta indica) powder. The BCDs were characterized using modern techniques such as UV-Vis, FTIR, Raman, XRD, HRTEM, FESEM, EDAX, and Zeta potential analyses. Unlike traditional nanocomposite bed systems, this study utilized BCDs as a liquid-phase adsorbent for the regenerative adsorption of the environmentally harmful dye, methylene blue (MB), through an in-situ precipitation reaction. This involved the formation of BCDs-MB adduct via an electrostatic mechanism. The adsorption capacity and percentage of removal were remarkable at 605 mg g-1 and 64.7% respectively, exceeding various solid-based adsorption methods in the literature. The Langmuir isotherm and pseudo-second-order kinetics model provided an excellent fit for this system. The calculated thermodynamic parameter, Gibbs free energy change (ΔG) was negative, indicating a spontaneous, exothermic, and physisorption-based mechanism. The regenerative capacity of our system was further demonstrated by successfully extracting and recovering the MB dye (64%) using ethyl alcohol as the solvent. This method provides an efficient means of recovering valuable cationic organic dye compounds from contaminated environments.

Optimization and modelling of magnesium oxide (MgO) photocatalytic degradation of binary dyes using response surface methodology

Textile industry dye effluent contains a mixture of different kinds of dyes. Many times, photocatalysis is targeted as a solution for the treatment of dye effluent from the textile industry. Many researches have been published related to the photocatalysis of single textile dyes but in the real-world scenario, effluent is a mixture of dyes. Magnesium oxide (MgO) is used as a photocatalyst to treat a mixture (binary solution) of Methylene blue (MB) and Methylene violet (MV) along with individual MB and MV dyes in this article. MgO shows remarkable photocatalytic activity at about 93 and 88% for MB and MV dye in binary solution within 135 min. Furthermore, to study the influence of process parameters, experiments are designed with the help of the central composite design (CCD), and Response surface methodology (RSM) is used to study the interactions between parameters. For this study, five parameters are selected i.e., Photocatalyst dosage, initial concentration of both dyes, time of exposure to the light source, and pH of the binary solution. The photocatalytic process is also optimized and finally optimization of process parameters is validated with an experiment. The result of the validation experiment is very close to the predicted photocatalytic activity.

One-Step Synthesis of Polyethyleneimine-Grafted Styrene-Maleic Anhydride Copolymer Adsorbents for Effective Adsorption of Anionic Dyes

Wastewater containing organic dyes has become one of the important challenges in water treatment due to its high salt content and resistance to natural degradation. In this work, a novelty adsorbent, PEI-SMA, was prepared by grafting polyethyleneimine (PEI) onto styrene-maleic anhydride copolymer (SMA) through an amidation reaction. The various factors, such as pH, adsorbent dosage, contact time, dye concentration, and temperature, which may affect the adsorption of PEI-SMA for Reactive Black 5 (RB5), were systematically investigated by static adsorption experiments. The adsorption process of PEI-SMA for RB5 was more consistent with the Langmuir isotherm model and the pseudo-second-order model, suggesting a single-layer chemisorption. PEI-SMA exhibits excellent adsorption performance for RB5 dye, with a maximum adsorption capacity of 1749.19 mg g-1 at pH = 2. Additionally, PEI-SMA exhibited highly efficient RB5 competitive adsorption against coexisting Cl- and SO42- ions and cationic dyes. The adsorption mechanism was explored, and it can be explained as the synergistic effect of electrostatic interaction, hydrogen bonding and π-π interaction. This study demonstrates that PEI-SMA could act as a high performance and promising candidate for the effective adsorption of anionic dyes from aqueous solutions.

One-step carbonization/activation synthesis of chitosan-based porous sheet-like carbon and studies of adsorptive removal for Rhodamine B

In this work, new N, O-codoped chitosan-derived carbon adsorbents (CKC-x, x refer to the calcination temperature) were synthesized over a simple process of chitosan-KOH aerogel production and simultaneous carbonization/activation of the aerogel. CKC-700 was characterized by sheet-like morphology (even containing a portion of carbon nano-sheet of 3 nm thickness), high porosity and specific surface area (1702.1 m2/g), and pyridinic/pyrrolic/graphitic N groups. The simultaneous carbonization/activation of chitosan-KOH aerogel prepared by top-down coagulation of chitosan aqueous solution by KOH aqueous solution rendered these beneficial characteristics. CKC-700 exhibited a superior adsorption capacity for Rhodamine B (RhB) to other chitosan-derived carbon adsorbents, and the maximum adsorption capacity for RhB of 594 mg/g was achieved at 55 °C. CKC-700 also possessed reasonable reusability for the removal of RhB, and the removal efficiency was still above 95 % in the fifth cycle. The effects of adsorption temperature and time, adsorbent dose, organic dye concentration, and solution pH on the adsorption capacity of CKC-700 were studied. Moreover, the adsorption isotherm, kinetics, thermodynamics, and the adsorption mechanism of RhB on CKC-700 were discussed. In addition, CKC-700 also showed favorable adsorption performance for methylene blue (441 mg/g), methyl orange (457 mg/g), and congo red (500 mg/g) at around 25 °C.

Sequential Approach for Water Purification Using Seashell-Derived Calcium Oxide through Disinfection and Flocculation with Polyphosphate for Chemical Pollutant Removal

Safe water supply is usually inadequate in areas without water treatment plants and even in a city under emergency conditions due to a disaster, even though safe water is essential for drinking and other various purposes. The purification of surface water from a river, lake, or pond requires disinfection and removal of chemical pollutants. In this study, we report a water purification strategy using seashell-derived calcium oxide (CaO) via disinfection and subsequent flocculation with polyphosphate for chemical pollutant removal. Seashell-derived CaO at a concentration (2 g L-1) higher than its saturation concentration caused the >99.999% inactivation of bacteria, mainly due to the alkalinity of calcium hydroxide (Ca(OH)2) produced by hydration. After the disinfection, the addition of sodium polyphosphate at 2 g L-1 allowed for the flocculation of CaO/Ca(OH)2 particles with adsorbing chemical pollutants, such as Congo red, dichlorodiphenyltrichloroethane, di(2-ethylhexyl)phthalate, and polychlorinated biphenyls, for removing these pollutants; purified water was obtained through filtration. Although this purified water was initially highly alkaline (pH ∼ 12.5), its pH decreased into a weak alkaline region (pH ∼ 9) during exposure to ambient air by absorbing carbon dioxide from the air with the precipitating calcium carbonate. The advantages of this water purification strategy include the fact that the saturation of CaO/Ca(OH)2 potentially serves as a visual indicator of disinfection, that the flocculation by polyphosphate removes excessive CaO/Ca(OH)2 as well as chemical pollutants, and that the high pH and Ca2+ concentrations in the resulting purified water are readily decreased. Our findings suggest the usability of seashell-derived material-polymer assemblies for water purification, especially under emergency conditions due to disasters.

Green synthesis of carbon quantum dots from teak leaves biomass for in situ precipitation and regenerative-removal of methylene blue-dye

The objective of this study was to completely eliminate environmentally harmful cationic organic dye from aqueous solutions using the one-step ultrasonication method, renowned for its energy efficiency, user-friendliness, and minimal requirement for chemical resources, making it particularly suitable for large-scale applications. To achieve effective environmental remediation, we employed carbon dots derived from teak leaf biomass (TBCDs) layered with graphene oxide. We conducted a thorough characterization of the TBCDs using UV-vis spectroscopy (with absorption peaks at λmax = 208 and 276 nm), FTIR spectroscopy (confirming the presence of various functional groups including -OH, -CH, C = O, COO-, C-O-C, and = C-H), Raman spectroscopy (with bands at 1369 cm-1 (D-Band) and 1550 cm-1 (G-Band), and an intensity ratio (ID/IG) = 0.88, indicating structural defects correlated with the sp3 hybridization sites on the TBCDs), XRD analysis (indicating an amorphous nature of particles), HRTEM imaging (showing homogeneous dispersal of TBCDs with typical sizes ranging from 2 to 10 nm), FESEM analysis (showing a flat surface and minuscule particles), and Zeta potential analysis (revealing a surface charge peak at -51.0 mV). Our adsorption experiments yielded significant results, with a substantial 50.1 % removal rate and an impressive adsorption capacity of 735.2 mg g-1. Theoretical adsorption parameters were rigorously analyzed to understand the adsorption behavior, surface interactions, and mechanisms. Among these models, the Langmuir isotherm in conjunction with pseudo-second-order kinetics provided an exceptional fit (with R2 values closer to 1) for our system. The Gibbs free energy (ΔG) was found to be negative at all temperatures, indicating the spontaneity of the reaction. Regarding mechanism, electrostatic attraction ((+ve) MB dye + (- ve) TBCDs), π-π stacking adsorption facilitated by the graphitic structure, formation of multiple hydrogen bonds due to polar functional groups, and a pore-filling mechanism wherein the cationic MB dye fills the pores of TBCDs with graphene oxide layers, forming an adduct were identified. Furthermore, we demonstrated the regenerative capacity of our system by effectively extracting and recovering the MB dye (with a regeneration rate of 77.1%), utilizing ethyl alcohol as the solvent. These findings not only provide valuable insights into the adsorption capabilities of TBCDs but also highlight the potential of our approach in the recovery of expensive cationic organic dye compounds from polluted environments.

Coagulation as an effective method for cyanobacterial bloom control: A review

Eutrophication, the over-enrichment with nutrients, for example, nitrogen and phosphorus, of ponds, reservoirs and lakes, is an urgent water quality issue. The most notorious symptom of eutrophication is a massive proliferation of cyanobacteria, which cause aquatic organism death, impair ecosystem and harm human health. The method considered to be most effective to counteract eutrophication is to reduce external nutrient inputs. However, merely controlling external nutrient load is insufficient to mitigate eutrophication. Consequently, a rapid diminishing of cyanobacterial blooms is relied on in-lake intervention, which may encompass a great variety of different approaches. Coagulation/flocculation is the most used and important water purification unit. Since cyanobacterial cells generally carry negative charges, coagulants are added to water to neutralize the negative charges on the surface of cyanobacteria, causing them to destabilize and precipitate. Most of cyanobacteria and their metabolites can be removed simultaneously. However, when cyanobacterial density is high, sticky secretions distribute outside cells because of the small size of cyanobacteria. The sticky secretions are easily to form complex colloids with coagulants, making it difficult for cyanobacteria to destabilize and resulting in unsatisfactory treatment effects of coagulation on cyanobacteria. Therefore, various coagulants and coagulation methods were developed. In this paper, the focus is on the coagulation of cyanobacteria as a promising tool to manage eutrophication. Basic principles, applications, pros and cons of chemical, physical and biological coagulation are reviewed. In addition, the application of coagulation in water treatment is discussed. It is the aim of this review article to provide a significant reference for large-scale governance of cyanobacterial blooms. PRACTITIONER POINTS: Flocculation was a promising tool for controlling cyanobacteria blooms. Basic principles of four kinds of flocculation methods were elucidated. Flocculant was important in the flocculation process.

Green industry work: production of FeCl3 from iron and steel industry waste (mill scale) and its use in wastewater treatment

Mill scale (MS) is considered to be a significant metallurgical waste, but there is no economical method yet to utilize its metal content. In this study, which covers various processes in several stages, the solution of iron in MS, which is the Iron and Steel Industry (I&SI) waste, as FeCl3 (MS-FeCl3) in the thermoreactor in the presence of HCl, was investigated. In the next step, the conditions for using this solution as a coagulant in the treatment of I&SI wastewater were investigated using the jar test. The results of the treated water sample were compared by chemical oxygen demand (COD), total suspended solids (TSS), color, and turbidity analyses using commercial aluminum sulfate (Al2(SO4)3) and FeCl3 (C-FeCl3). Additionally, heavy metal analyses were conducted, and the treatment performance of three coagulants was presented. Accordingly, while 2.0 mg/L anionic polyelectrolyte was consumed at a dosage of 4.05 mg/L Al2(SO4)3 at pH 7.0, 0.25 mg/L anionic polyelectrolyte was consumed at a dosage of 1.29 mg/L at pH 5.0 in the C-FeCl3 and MS-FeCl3 studies. Also, Fe, Cr, Mn, Ni, Zn, Cd, Hg, and Pb removal efficiencies were over 93.56% for all three coagulant usage cases. The results showed that the wastewater treatment performance of MS-FeCl3 by the recycling of MS, which is an I&SI waste, was at the same level as C-FeCl3. Thus, thanks to recycling, waste scale can be used as an alternative to commercial products for green production.

Current trends in textile wastewater treatment-bibliometric review

A bibliometric study using 1992 to 2021 database of the Science Citation Index Expanded was carried out to identify which are the current trends in textile wastewater treatment research. The study aimed to analyze the performance of scholarly scientific communications in terms of yearly publications/citations, total citations, scientific journals, and their categories in the Web of Sciences, top institutions/countries and research trends. The annual publication of scientific articles fluctuated in the first ten years, with a steady decrease for the last twenty years. An analysis of the most common terms used in the authors' keywords, publications' titles, and KeyWords Plus was carried out to predict future trends and current research priorities. Adsorbent nanomaterials would be the future of wastewater treatment for decoloration of the residual dyes in the wastewater. Membranes and electrolysis are important to demineralize textile effluent for reusing wastewater. Modern filtration techniques such as ultrafiltration and nanofiltration are advanced membrane filtration applications.

Innovations in textile wastewater management: a review of zero liquid discharge technology

Zero liquid discharge (ZLD) technology emerges as a transformative solution for sustainable wastewater management in the textile industry, emphasizing water recycling and discharge minimization. This review comprehensively explores ZLD's pivotal role in reshaping wastewater management practices within the textile sector. With a primary focus on water recycling and minimized discharge, the review thoroughly examines the economic and environmental dimensions of ZLD. Additionally, it includes a comparative cost analysis against conventional wastewater treatment methods and offers a comprehensive outlook on the global ZLD market. Presently valued at US $0.71 billion, the market is anticipated to reach US $1.76 billion by 2026, reflecting a robust annual growth rate of 12.6%. Despite ZLD's efficiency in wastewater recovery, environmental challenges, such as heightened greenhouse gas emissions, increased carbon footprint, elevated energy consumption, and chemical usage, are discussed. Methodologies employed in this review involve an extensive analysis of existing literature, empirical data, and case studies on ZLD implementation in the textile industry worldwide. While acknowledging existing adoption barriers, the review underscores ZLD's potential to guide the textile industry toward a more sustainable and environmentally responsible future.

Intermolecular interactions in mixed dye systems and the effects on dye wastewater treatment processes

Dye wastewater discharge is a critical concern across textiles, paper, cosmetics, and other industries. This study explores the impact of dye-dye interactions on chemical coagulation and ultrafiltration process. Using basic and reactive dyes, representing cationic and anionic compounds, the intricate interplay between these dyes was examined through spectroscopic analysis. Remarkably, interactions between dyes of opposite charges exhibited significant effects on both techniques. Electrostatic attractions played a key role. Positive coagulant hydrolysates selectively attracted negative dyes, while negatively charged membranes effectively captured positive dyes. Combining dyes with opposite charges resulted in enhanced removal efficiency, addressing challenging dyes collectively. This discovery offers a novel approach to improving dye removal, utilizing opposite-charged dye mixtures can tackle stubborn dyes unmanageable by conventional methods.

Preparation and dye adsorption properties of activated carbon/clay/sodium alginate composite hydrogel membranes

A hydrogel membrane was prepared using activated carbon and sodium dodecyl sulphate modified montmorillonite clay incorporated into sodium alginate polymer. The activated carbon was prepared from a locally available susbine plant. The physiochemical characteristics of the synthesized hydrogel membrane were investigated using FTIR, SEM, EDX, and TGA techniques. The performance of the membrane was evaluated as an adsorbent by methyl red adsorption from water. The adsorption behavior of the hydrogel membrane was investigated under varying conditions of pH (2-10), membrane dose (0.0025-0.015 mg g-1), equilibrium adsorption time (30-360 minutes), solution temperature (25-45 °C) and dye concentration (100-500 mg L-1). The maximum adsorption capacity of the hydrogel membrane was 248.13 mg g-1. The kinetics of methyl red adsorption on hydrogel membrane best followed the pseudo-second order (PSO). The equilibrium adsorption results suggested that it obeyed the Freundlich isotherm very closely (R2 = 0.994). The thermodynamics of methyl red adsorption on the hydrogel membrane revealed that the adsorption was spontaneous (ΔS° = 16.15 kJ K-1 mol-1), favorable (ΔG° = -3.51 kJ mol-1), and endothermic (ΔH° = -1.48 kJ mol-1) in nature. These investigations suggested that the fabricated hydrogel membrane could be suitably used for methyl red adsorption from the solution.

Unveiling the Microfiber Release Footprint: Guiding Control Strategies in the Textile Production Industry

Microplastic fibers from textiles have been known to significantly contribute to marine microplastic pollution. However, little is known about the microfiber formation and discharge during textile production. In this study, we have quantified microfiber emissions from one large and representative textile factory during different stages, spanning seven different materials, including cotton, polyester, and blended fabrics, to further guide control strategies. Wet-processing steps released up to 25 times more microfibers than home laundering, with dyeing contributing to 95.0% of the total emissions. Microfiber release could be reduced by using white coloring, a lower dyeing temperature, and a shorter dyeing duration. Thinner, denser yarns increased microfiber pollution, whereas using tightly twisted fibers mitigated release. Globally, wet textile processing potentially produced 6.4 kt of microfibers in 2020, with China, India, and the US as significant contributors. The study underlined the environmental impact of textile production and the need for mitigation strategies, particularly in dyeing processes and fiber choice. In addition, no significant difference was observed between the virgin polyesters and the used ones. Replacing virgin fibers with recycled fibers in polyester fabrics, due to their increasing consumption, might offer another potential solution. The findings highlighted the substantial impact of textile production on microfiber released into the environment, and optimization of material selection, knitting technologies, production processing, and recycled materials could be effective mitigation strategies.

Rice mill wastewater management in the era of circular economy

Several nations around the world use rice as their primary food staple because of its tremendous nutritional value. India's expanding population has sparked a proliferation of rice mills as a result of the country's growing rice demand. However, small and medium-scale industries lack adequate facilities for processing effluents and other waste generated. Paddy is typically processed by parboiling, which involves soaking it in water, boiling it with steam, and then drying and milling. Around 1-1.5 L of water is necessary to partially cook 1 kg of unhusked rice, with approximately half of this water being discharged as effluent. Disposal of rice mill effluent (RME) in water bodies or on the land causes severe damage to soil and water. An inclusive examination of diverse approaches for the treatment and stabilization of partially cooked rice milling effluents is provided. Moreover, the document provides a concise overview of contemporary and environmentally friendly technologies for treating RME. Adsorption, electrocoagulation, chemical coagulation, and bioremediation using microbes, plants, and microalgae are all included in these methods. This manuscript discusses the concept of a circular economy, which is focused on enhancing environmental sustainability through the recycling and repurposing of generated waste into raw materials for the creation of new products. In addition, this review aims to focus on the impact of RME on soils and water species and the status of sustainable management at the point of circular economy with RME bioenergy production (bioelectricity, biomethane, and bio-hydrogen).

Spherical Polyelectrolyte Brushes as Flocculants and Retention Aids in Wet-End Papermaking

As the criteria of energy conservation, emission reduction, and environmental protection become more important, and with the development of wet-end papermaking, developing excellent retention aids is of great significance. Spherical polyelectrolyte brushes (SPBs) bearing polyelectrolyte chains grafted densely to the surface of core particle have the potential to be novel retention aids in wet-end papermaking not only because of their spherical structure, but also due to controllable grafting density and molecular weight. Such characteristics are crucial in order to design multi-functional retention aids in sophisticated papermaking systems. This review presents some important recent advances with respect to retention aids, including single-component system and dual-component systems. Then, basic theory in papermaking is also briefly reviewed. Based on these advances, it emphatically describes spherical polyelectrolyte brushes, focused on their preparation methods, characterization, conformation, and applications in papermaking. This work is expected to contribute to improve a comprehensive understanding on the composition, properties, and function mechanisms of retention aids, which helps in the further investigation on the design of novel retention aids with excellent performance.

A new solvent-free pathway for inducing quaternized lignin-derived high molecular weight polymer

In this work, kraft lignin (KL) was polymerized with vinylbenzyl chloride (VBC) in a molar ratio of 1.8:1 (KL: VBC) using sodium persulfate (Na2S2O8) as an initiator at pH 9-10 and temperature of 80-90 °C for 3 h to produce polymer kraft lignin-g-poly(4-vinylbenzyl chloride) KL-poly(VBC) 1. Then, the grafting reaction was conducted with two different imidazole-based monomers of different side-chain lengths (methyl and n-butyl), namely, 1-methylimidazole (MIM), 1-n-butylimidazole (BIM), which led to the formation of novel polymers, kraft lignin-g-poly(4-vinylbenzyl-1-methylimidazolium chloride) KL-poly(VBC-MIM) 2a and kraft lignin-g-poly(4-vinylbenzyl-1-n-butyl imidazolium chloride) KL-poly(VBC-BIM) 2b. The polymer 2a generated a larger molecular weight polymer with a higher charge density and solubility than polymer 2b since the n-butyl group would cause steric hindrance and weaker monomer to react with intermediate polymer 1 in the second stage. The contact angle analysis confirmed more hydrophilicity of polymer 2a, and elemental analysis confirmed the more successful polymerization of polymer 2a. Applying the generated polymers as flocculants for a kaolin suspension confirmed that polymer 2a had similar performance with commercial cationic polyacrylamide (CPAM) flocculants, even though polymer 2a had a smaller molecular weight. This polymerization offers a promising pathway for generating cationic polymers with excellent performance as a flocculant for suspensions.

Treatment of textile wastewater using the Co(II)/NaHCO3/H2O2 oxidation system

Textile wastewater (TWW) is one of the most hazardous wastewaters for ecosystems when it is discharged directly into water streams without adequate treatment. Some organic pollutants, such as dyes in TWW, are considered refractory compounds that are difficult to degrade using conventional chemical and biological methods. The bicarbonate-activated peroxide (BAP) system is an advanced oxidation process (AOP) based on applying H2O2, which has been demonstrated to be a clean and efficient technology for dye degradation, with the advantage of operating under slightly alkaline pH conditions. In this study, response surface methodology (RSM) based on a central composite design (CCD) was used to optimize the degradation of TWW contaminated with the azo dye Acid Black 194 using the BAP system catalyzed with cobalt ions in solution (Co2+). The analysis of variance (ANOVA) technique was applied to identify significant variables and their individual and interactive effects on the degradation of TWW. The optimum reagent concentrations for degrading TWW at 25 °C and with 45 μM Co2+ were 787.61 and 183.34 mM for H2O2 and NaHCO3, respectively. Under these conditions, complete decolorization (≥99.40), 32.20 % mineralization, and 52.02 % chemical oxygen demand removal were achieved. Additionally, the acute toxicity of textile wastewater before and after oxidation was evaluated with guppy fish (Poecilia reticulata), showing a total reduction in mortality after treatment with the Co2+-BAP system. The Co2+-BAP oxidation system is a potential method for textile wastewater treatment, which, in addition to achieving complete decolorization and partial mineralization, improves biodegradability and reduces the toxicity of the treated water.

Accelerated Reinforcement of Calcareous sand via Biomineralization with Aluminum Ion Flocculant

Microbially induced calcium carbonate precipitation (MICP) is an immensely growing technique that utilizes the metabolic pathways of bacteria to form calcite precipitation throughout the soil matrix, leading to improve geotechnical engineering properties. However, the excessive number of treatments limited the application of MICP for strengthening calcareous sand. To reduce the number of treatments and develop efficiencies, this paper investigates the optimized treatment protocol of adding aluminum ion flocculants to the cementing solution to accelerate the curing rate of the MICP and its effect. The results show that adding a certain concentration of AlCl3 to the cementing solution can resulted in a rapid increase in strength of the calcareous sand column. When 0.02 M aluminum chloride was added to the cementing solution, the unconfined compressive strength of the sand column reached 827 kPa after three treatments, and it reached 2 MPa after five treatments, while the control group needed to be treated 10 and 15 times, respectively, to reach equivalent strengths. In this paper, the unconfined compressive strength of the sand column formed using the proposed method was 27-40 times that of the control group at the same calcium carbonate content. The presented experimental approach can be used as a tool to design the treatment protocol for the engineering application of MICP-reinforced calcareous sand in practice.

A quaternary ammonium salt grafted tannin-based flocculant boosts the conjugative transfer of plasmid-born antibiotic resistance genes: The nonnegligible side of their flocculation-sterilization properties

This study developed dual-function tannin-based flocculants, namely tannin-graft-acrylamide-diallyl dimethyl ammonium chloride (TGCC-A/TGCC-C), endowed with enhanced flocculation-sterilization properties. The impacts of these flocculants on proliferation and transformation of antibiotic resistance genes (ARGs) among bacteria during the flocculation-deposition process were examined. TGCC-A/TGCC-C exhibited remarkable flocculation capacities towards both Escherichia coli and Staphylococcus aureus, encompassing a logarithmic range of initial cell density (108-109 CFU/mL) and a broad pH spectrum (pH 2-11). The grafted quaternary ammonium salt groups played pivotal parts in flocculation through charge neutralization and bridging mechanisms, concurrently contributing to sterilization by disrupting cellular membranes. The correlation between flocculation and sterilization entails a sequential progression, where an excess of TGCC, initially employed for flocculation, is subsequently consumed for sterilization purposes. The frequencies of ARGs conjugative transfer were enhanced in bacterial flocs across all TGCC treatments, stemming from augmented bacterial aggregation and cell membrane permeability, elicited stress response, and up-regulated genes encoding plasmid transfer. These findings underscore the indispensable role of flocculation-sterilization effects in mediating the propagation of ARGs, consequently providing substantial support for the scientific evaluation of the environmental risks associated with flocculants in the context of ARGs dissemination during the treatment of raw water featuring high bacterial density.

Electrochemical treatment of textile wastewater using copper electrodes

The conventional electrode aluminum used in electrocoagulation (EC) for the textile wastewater undergoes pitting type of corrosion, so dissolution of the same is very high during electrolysis. This research focuses on the treatment of real-time textile effluent with copper electrodes that corrode uniformly during electrolysis, with optimizing operating parameters for high color removal efficiency (CRE%). The sludge acquired was analyzed by XPS and XRD to study the mechanism of dye removal. The treated effluent was subjected to phytotoxicity analysis using Vigna radiata to study the toxicity effect of the intermediary products. 98.6% of CRE was attained in treating the effluent with copper electrodes. XPS and XRD results showed that both Cu(OH)2 and CuO served as coagulants in the dye removal. The phytotoxicity results showed that the percentage of germination, shoot and root lengths of Vigna radiata in the treated effluent were similar to the results obtained for the control.

Facile Synthesis of gC3N4-Exfoliated BiFeO3 Nanocomposite: A Versatile and Efficient S-Scheme Photocatalyst for the Degradation of Various Textile Dyes and Antibiotics in Water

Water pollution engendered from textile dyes and antibiotics is a globally identified precarious concern that is causing dreadful risks to human health as well as aquatic lives. This predicament is escalating the quest to develop competent photocatalysts that can degrade these water pollutants under solar light irradiation. Herein, we report an efficient photocatalyst comprising a hierarchical structure by integrating the layered graphitic carbon nitride (gC3N4) with nanoflakes of exfoliated BiFeO3. The coexistence of these two semiconducting nanomaterials leads to the formation of an S-scheme heterojunction. This nanocomposite demonstrated its excellent photocatalytic activity toward the degradation of several textile dyes (Yel CL2R, Levasol Yellow-CE, Levasol Red-GN, Navy Sol-R, Terq-CL5B) and various antibiotics (such as tetracycline hydrochloride (TCH), ciprofloxacin (CPX), sulfamethoxazole (SMX), and amoxicillin (AMX)) under the simulated solar light irradiation. As this photocatalyst exhibits its versatile activity toward the degradation of several commercial dyes as well as antibiotics, this work paves the path to develop a reasonable, eco-benign, and highly efficient photocatalyst that can be used in the practical approach to remediate environmental pollution.

Ecotoxicological response surface analysis of salt and pH in textile effluent on Bacillus subtilis and Lactuca sativa

Textile effluents, although their composition can vary considerably, typically contain high levels of dissolved salts and exhibit wide variations in pH. Ecotoxicological studies regarding the effects of these parameters, however, have been limited owing to the need for sensitive and easy-to-handle bioindicators that require low amounts of sampling, are cost-effective, time-efficient, and ethically endorsed. This kind of study, additionally, demands robust multi-factorial statistical designs that can accurately characterize the individual and combined relationship between variables. In this research, Response Surface Methodology (RSM) was used to calculate the individual and interaction effects of NaCl concentration and pH value of a Simulated Textile Effluent (STE) on the development rate (DR) of the bioindicators: Bacillus subtilis bacteria and Lactuca sativa lettuce. The results demonstrated that the bioindicators were sensitive to both NaCl and pH factors, where the relative sensitivity relationship was B. subtilis > L. sativa. The quadratic equations generated in the experiments indicated that increased concentrations of 50-250 mg L-1 of NaCl caused a perturbance of 1.40%-34.40% on the DR of B. subtilis and 0.50%-12.30% on L. sativa. The pH factor at values of 3-11 caused an alteration of 27.00%-64.78% on the DR of the B. subtilis and 51.37%-37.37% on the L. sativa. These findings suggest that the selected bioindicators could serve as effective tools to assess the ecotoxicological effects of textile effluents on different ecological systems, and the RSM was an excellent tool to consider the ecotoxicological effects of the parameters and to describe the behavior of the results. In conclusion, the NaCl and pH factors may be responsible for disrupting different ecosystems, causing imbalances in their biodiversity and biomass. Before discharge or reuse, it is suggested to remove salts and neutralize pH from textile effluents and, mostly, develop novel, eco-friendlier textile processing techniques.

High biosorption of cationic dye onto a novel material based on paper mill sludge

The valorization of paper mill sludge (PMS) is the main goal of this study. The emissions of PMS continue to increase at global scale, especially from packaging paper and board sectors. The raw sludge was used to prepare an adsorbent to remove toxic pollutants from wastewater, the methylene blue (MB), an organic dye. Firstly, the physico-chemical characterization of PMS was done determining the crystalline phases of PMS fibers, the content of main elements, and the pH zero point charge, which was determined at around pH 7. The adsorption of MB on PMS powder was studied at 18 °C with an agitation of 200 rpm, being the best operating conditions 30 min of contact time, 250 mg L-1 of initial MB concentration and 0.05 g in 25 mL of adsorbent dose. Experimental data of MB adsorption was fitted to Langmuir and Freundlich isotherm equations. The Langmuir model was more accurate for the equilibrium data of MB adsorption at pH 5.1. The PFOM and PSOM were adjusted to experimental adsorption kinetics data, being PSOM, which describes better the MB adsorption by PMS powder. This was confirmed by calculating the maximum adsorption capacity with PSOM, which was 42.7 mg g-1, being nearly similar of the experimental value of 43.5 mg g-1. The analysis of adsorption thermodynamics showed that the MB was adsorbed exothermically with a ΔH0 = - 20.78 kJ mol-1, and spontaneously with ΔG0 from - 0.99 to - 6.38 kJ mol-1 in the range of temperature from 291 to 363 K, respectively. These results confirm that the sludge from paper industry can be used as biosorbent with remarkable adsorption capacity and low cost for the treatment of wastewater. PMS can be applied in the future for the depollution of the effluents from the textile industry, which are highly charged with dyes.

Porous polymer magnetic adsorbents for dye wastewater treatment

Dye wastewater discharged from industries has caused serious environmental problems. The recent decade has witnessed adsorption technology emerging as an advanced dye wastewater treatment method with great potential Therefore, we fabricated two kinds of magnetic porous adsorbents (HSF and HSVF) with different specific surface areas and activity sites. Both of which exhibit excellent performance with remarkable dye adsorption capacities, especially HSVF. We further investigated their adsorption kinetic and isotherm in detail. Therein, HSVF showed a nice desorption capacity, and it could be recycled rapidly by magnetism, which exhibited the advantages of effective, easy operation, and low cost. In addition, their adsorption kinetic and isotherm were further studied and compared in detail. The results revealed that introducing strong active sites could improve both the adsorption capacity and rate effectively even though sacrificing part of specific surface areas, indicating that active sites might play a dominant role during the dye adsorption process.

Integrating reverse osmosis and forward osmosis (RO-FO) for printing and dyeing wastewater treatment: impact of FO on water recovery

Reverse osmosis (RO) alone has low water recovery efficiency because of membrane fouling and limited operating pressure. In this study, a combined reverse osmosis-forward osmosis (RO-FO) process was used for the first time to improve the water recovery efficiency of secondary effluent in printing and dyeing wastewater. The effects of operating pressure and pH on water recovery and removal efficiency of RO-FO were investigated. The results showed that the optimum conditions were an operating pressure of 1.5 MPa and a feed solution pH of 9.0. Under optimal operating conditions, most of the organic and inorganic substances in the wastewater can be removed, and the rejection of total organic carbon (TOC), Sb, Ca, and K were 98.7, 99.3, 97.0, and 92.7%, respectively. Fluorescence excitation-emission matrices coupled with parallel factor (EEM-PARAFAC) analysis indicated that two components (tryptophan and tyrosine) in the influent were effectively rejected by the hybrid process. The maximum water recovery (Rw, max) could reach 95%, which was higher than the current single RO process (75%). This research provided a feasible strategy to effectively recover water from printing and dyeing wastewater.

Natural-based coagulants/flocculants as sustainable market-valued products for industrial wastewater treatment: a review of recent developments

Industrial wastewater is categorized as a voracious consumer of fresh water and a high-strength source of pollution. Coagulation-flocculation is a simple and cost-effective technique for removing organic/inorganic compounds and colloidal particles from industrial effluents. Despite the outstanding natural properties, biodegradability, and efficacy of natural coagulants/flocculants (NC/Fs) in industrial wastewater treatment, their significant potential to remediate such effluents is underappreciated, particularly in commercial scale applications. Most reviews on NC/Fs focused on the possible application of plant-based sources such as plant seeds, tannin, certain vegetables/fruit peels, and their lab-scale potential. Our review expands the scope by examining the feasibility of using natural materials from other sources for industrial effluent decontamination. By analyzing the latest data on NC/Fs, we identify the most promising preparation techniques for making these materials stable enough to compete with traditional options in the marketplace. An interesting presentation of the results of various recent studies has also been highlighted and discussed. Additionally, we highlight the recent success of using magnetic-natural coagulants/flocculants (M-NC/Fs) in treating diverse industrial effluents, and discuss the potential for reprocessing spent materials as a renewable resource. The review also offers different concepts for suggested large-scale treatment systems used by MN-CFs.

A comparative study on polyaluminum chloride (PACl) and Moringa oleifera (MO) chemically enhanced primary treatment (CEPT) in enhanced biogas production: anaerobic digestion performance and the Gompertz model

A comparative study was performed to estimate biogas production from sludge produced by organic and inorganic chemically enhanced primary treatments (CEPTs). To this end, the effects of two coagulants, polyaluminum chloride (PACl) and Moringa oleifera (MO), on CEPT and biogas production in anaerobic digestion were surveyed within an incubation period of 24 days. The optimal dosage and pH of PACl and MO were optimized in terms of sCOD, TSS and VS parameters in the CEPT process. Next, the digestion performance of anaerobic digestion reactors fed with sludge obtained from PACl and MO coagulants at a batch mesophilic reactor (37 ± 1 °C) was surveyed from the biogas production, volatile solid reduction (VSR) and Gompertz model. At the optimal conditions (pH = 7 and dosage = 5 mg L^-1), the removal efficiency of COD, TSS and VS in CEPT assisted with PACL was 63, 81 and 56%, respectively. Moreover, CEPT assisted with MO led to the removal efficiency of COD, TSS and VS until 55, 68 and 25%, respectively. The highest methane yield (0.598 L g_{VS removed}^-1) was obtained in an anaerobic digestion reactor with sludge from the MO coagulant. The anaerobic digestion of CEPT sludge instead of primary sludge resulted in higher sCOD removal efficiency, and 43-50% of sCOD was observed compared with the removal of 32% for the primary sludge. Furthermore, the high coefficient of determination (R²) demonstrated the trustworthy predictive precision of the modified Gompertz model with actual data. The combination of CEPT and anaerobic digestion, especially using natural coagulants, provides a cost-effective and practical way to increase BMP from primary sludge.

A novel recycling way of blast furnace dust from steelworks: Electrocoagulation coupled micro-electrolysis system in indigo wastewater treatment

In this study, a novel electrocoagulation electrode, based on blast furnace dust (BFD) from steelworks waste, was prepared for indigo wastewater treatment, and the performance was compared with different ratios of Fe-C composite electrodes. The BFD electrode exhibited great electrochemical performance and removal effect. The presence of Fe-C micro-electrolysis in the electrocoagulation system of the BFD electrode was demonstrated by FT-IR, Raman, ESR, and quenching experiments. Density Functional Theory (DFT) calculations further demonstrated that the iron-carbon ratio could influence the degree of O-O breaking and enhance ·OH generation. Finally, the BFD electrode's operating parameters were perfected, and the COD removal and decolorization could reach 75.7% and 95.8% within 60 min, respectively. Fe-C composite electrodes reduce energy consumption compared with the traditional Fe/Al electrode and have a lower production cost, which provides a potential way to recycle and reuse the resources of solid waste in steelworks, the concept of "waste controlled by waste" is realized.

Sargassum natans I Algae: An Alternative for a Greener Approach for the Synthesis of ZnO Nanostructures with Biological and Environmental Applications

In this work, the influence of the Sargassum natans I alga extract on the morphological characteristics of synthesized ZnO nanostructures, with potential biological and environmental applications, was evaluated. For this purpose, different ZnO geometries were synthesized by the co-precipitation method, using Sargassum natans I alga extract as stabilizing agent. Four extract volumes (5, 10, 20, and 50 mL) were evaluated to obtain the different nanostructures. Moreover, a sample by chemical synthesis, without the addition of extract, was prepared. The characterization of the ZnO samples was carried out by UV-Vis spectroscopy, FT-IR spectroscopy, X-ray diffraction, and scanning electron microscopy. The results showed that the Sargassum alga extract has a fundamental role in the stabilization process of the ZnO nanoparticles. In addition, it was shown that the increase in the Sargassum alga extract leads to preferential growth and arrangement, obtaining well-defined shaped particles. ZnO nanostructures demonstrated significant anti-inflammatory response by the in vitro egg albumin protein denaturation for biological purposes. Additionally, quantitative antibacterial analysis (AA) showed that the ZnO nanostructures synthesized with 10 and 20 mL of extract demonstrated high AA against Gram (+) S. aureus and moderate AA behavior against Gram (-) P. aeruginosa, depending on the ZnO arrangement induced by the Sargassum natans I alga extract and the nanoparticles' concentration (ca. 3200 µg/mL). Additionally, ZnO samples were evaluated as photocatalytic materials through the degradation of organic dyes. Complete degradation of both methyl violet and malachite green were achieved using the ZnO sample synthesized with 50 mL of extract. In all cases, the well-defined morphology of ZnO induced by the Sargassum natans I alga extract played a key role in the combined biological/environmental performance.

Construction of Cu-N coordination into natural biopolymer lignin backbone for highly efficient and selective removal of cationic dyes

Here, a Cu²⁺-doped lignin-based adsorbent (Cu-AL) was fabricated via the amination and Cu²⁺-doping of industrial alkali lignin for massive and selective adsorption of cationic dyes azure B (AB) and saffron T (ST). The Cu-N coordination structures endowed Cu-AL with stronger electronegativity and higher dispersity. Through the electrostatic attraction, π-π interaction, H-bonding, and Cu²⁺ coordination, the adsorption capacities of AB and ST reached up to 1168 and 1420 mg g^-1, respectively. The pseudo-second-order model and Langmuir isotherm model were more relevant to the AB and ST adsorption on Cu-AL. Based on the thermodynamic study, the adsorption progresses were endothermic, spontaneous, and feasible. The Cu-AL maintained high removal efficiency to dyes after 4 reuses (>80%). Importantly, the Cu-AL could efficiently remove and separate AB and ST from dye mixtures even in real time. All the above characteristics demonstrated that Cu-AL was an excellent adsorbent for fast wastewater treatment.

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

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

Interfacial Polymerization on Polyethersulfone Ultrafiltration Membrane to Prepare Nanofiltration Layers for Dye Separation

Nanofiltration membranes are of great significance to the treatment of dye wastewater. Interfacial polymerization is a widely used method to fabricate nanofiltration membranes. In this study, the interaction of tannic acid-assisted polyethylene polyamine (PEPA) with terephthalaldehyde (TPAL) was performed on PES ultrafiltration membranes using novel nitrogen-rich amine monomers and relatively less reactive aldehyde-based monomers. A new nanofiltration membrane ((T-P-T)/PES) was prepared by interfacial polymerization. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were used to analyze the elemental composition, bonding state, and surface morphology of the membrane surface. The effects of the PEPA deposition time, TPAL concentration, interfacial reaction time, and curing time on the nanofiltration layer were investigated. The modified membrane, prepared under optimal conditions, showed strong dye separation ability. The permeation of the modified membrane could reach 68.68 L·m^-2·h^-1·bar^-1, and the rejection of various dyes was above 99%. In addition, the (T-P-T)/PES membrane showed good stability during long-term dye separation.

Application of xanthan gum as coagulant-aid for decolorization of synthetic Congo red wastewater

In recent years, utilization of polysaccharides as natural coagulant and coagulant-aid has become a topic of interest, due to the nature of biopolymers that are renewable, biodegradable, and non-toxic. In this study, Congo red, as a model dye substance, was treated using polyaluminium chloride (PAC) as the main coagulant and xanthan gum as the coagulant aid. For this purpose, the effect of pH (3-9), xanthan gum dose (0.5-4 mg/L), and the initial concentration of Congo red dye (50-100 mg/L) to the dye removal and sludge volume were investigated. The outcome of this investigation indicates that the best pH for Congo red coagulation occurred at pH 3, due to the charge neutralization mechanism. The addition of coagulant-aid dose increases the %-removal and sludge volume until reaching the best coagulant-aid dose of 2 mg/L that results in a %-removal value of 93.81% and a sludge volume of 23.5 mL/L. Further addition of xanthan gum reduced the %-removal and sludge volume due to the inter-polymer force causing more difficult floc formation. The best initial concentration of dye occurred at a Congo red concentration of 50 mg/L, with a %-removal value of 93.81% with PAC (15 mg/L) and xanthan gum (2 mg/L) coagulants. This value is considerably higher than PAC and xanthan gum only which amounts to 81.16 and 7.18%, respectively. Based on these results, it is apparent that xanthan gum can positively contribute to dye coagulation while reducing the use of harmful inorganic coagulant.

Intermolecular degradation of aromatic compound and its derivatives via combined sequential and hybridized process

The under-treated wastewater, especially remaining carcinogenic aromatic compounds in wastewater discharge has been expansively reported, wherein the efficiency of conventional wastewater treatment is identified as the primary contributor source. Herein, the advancement of wastewater treatments has drawn much attention in recent years. In the current study, combined sequential and hybridized treatment of thermolysis and coagulation-flocculation provides a novel advancement for environmental emerging pollutant (EP) prescription. This research is mainly demonstrating the mitigation efficiency and degradation pathway of pararosaniline (PRA) hybridized and combined sequential wastewater treatment. Notably, PRA degradation dominantly via a linkage of reaction: thermal cleavage, deamination, silication and diazene reduction. Thermolysis acts as an initiator for the PRA decomposition through thermally induced bond dissociation energy (BDE) for molecular fragmentation whilst coagulation-flocculation facilitates the formation of organo-bridged silsesquioxane as the final degradation product. Different from conventional treatment, the hybridized treatment showed excellent synergistic degradability by removing 99% PRA and its EPs, followed by combined sequential treatment method with 86% reduction. Comprehensive degradation pathway breakdown of carcinogenic and hardly degradable aromatic compounds provides a new insight for wastewater treatment whereby aniline and benzene are entirely undetectable in effluent. The degradation intermediates, reaction derivatives and end products were affirmed by gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy and ultraviolet-visible spectrophotometry (GC-MS, FTIR and UV-Vis). This finding provides valuable guidance in establishing efficient integrated multiple-step wastewater treatments.

Realizable wastewater treatment process for carbon neutrality and energy sustainability: A review

Despite a quick shift of global goals toward carbon-neutral infrastructure, activated sludge based conventional systems inhibit the Green New Deal. Here, a municipal wastewater treatment plant (MWWTP) for carbon neutrality and energy sustainability is suggested and discussed based on realizable technical aspects. Organics have been recovered using variously enhanced primary treatment techniques, thereby reducing oxygen demand for the oxidation of organics and maximizing biogas production in biological processes. Meanwhile, ammonium in organic-separated wastewater is bio-electrochemically oxidized to N₂ and reduced to H₂ under completely anaerobic conditions, resulting in the minimization of energy requirements and waste sludge production, which are the main problems in activated sludge based conventional processes. The anaerobic digestion process converts concentrated primary sludge to biomethane, and H₂ gas recovered from nitrogen upgrades the biomethane quality by reducing carbon dioxide in biogas. Based on these results, MWWTPs can be simplified and improved with high process and energy efficiencies.

Highly efficient degradation of reactive black KN-B dye by ultraviolet light responsive ZIF-8 photocatalysts with different morphologies

Zeolitic imidazolate framework ZIF-8, a type of metal-organic framework, has diverse applications in multiple catalytic fields due to its outstanding properties. Herein, ZIF-8 photocatalysts with three different morphologies (dodecahedral, pitaya-like, and leaf-like) are successfully synthesized under ambient conditions from zinc salts by altering the volume ratio of methanol and water used as a solvent. The as-synthesized ZIFs have high crystallinity with distinct BET surface areas. The experiments indicate that the ZIFs have high photocatalytic efficiency, in which the leaf-like structure (ZIF-8-F3) is the most efficient in the degradation of reactive black KN-B dye (RB5) under 365 nm UV irradiation. This is due to the efficient inhibition of electron-hole recombination or the higher migration of charge carriers in ZIF-8-F3, thus producing more reactive oxygen species, resulting in greater photocatalytic efficiency. At pH = 11, more than 95% of RB5 is degraded within 2 hours when using 1.0 g L^-1 of ZIF-8-F3. Besides, the photocatalytic and kinetic performances of ZIF-8-F3 are also investigated by optimizing the pH, initial RB5 concentration, and dosage of the used catalyst. These ZIF-8-F3 plates have been shown to be a promising material with high photostability and effective reusability, beneficial to various potential applications in environmental remediation issues.

A study on the efficiency of the sequential batch reactor on the reduction of wastewater pollution from oil washing

Industrial pollution discharges from washing fuel oils pose severe problems for the environment, particularly for the marine environment receiving these discharges. This work evaluates the biological treatment performance of wastewater (90 m³/h) rich in organic matter with low biodegradability using a sequential batch reactor (SBR) on a laboratory scale. The test using SBR was carried out for 25 days on a continuous cycle of 24 h (30 min of filling, 17 h of aeration, 4 h of anoxia, 2 h of settling, and 30 min of emptying). The feasibility of alternative sources of microorganisms from urban wastewater. The performance of the batch sequencing reactor was evaluated using turbidity, total suspended solids, chemical oxygen demand (COD), biological oxygen demand (BOD), ammonium, nitrate, and phenol as indicators. The results obtained showed that the COD/BOD ratio and the pollutant load vary from one campaign to another. The removal efficiency of COD, BOD, TSS (Total suspended solids), ammonium, nitrate, and phenol varies from 81%, 91%, 72%, 100%, 52%, and 63%. Thus, SBR-type treatment could be an interesting way to reduce pollution due to its simplicity, less space occupation, low energy consumption, and not requiring highly qualified personnel.

Insights into the decolorization of mono and diazo dyes in single and binary dyes containing wastewater and electricity generation in up-flow constructed wetland coupled microbial fuel cell

The treatment of single and binary azo dyes, as well as the effect of the circuit connection, aeration, and plant on the performance of UFCW-MFC, were explored in this study. The decolorization efficiency of Remazol Yellow FG (RY) (single dye: 98.2 %; binary dye: 92.3 %) was higher than Reactive Black 5 (RB5) (single: 92.3 %; binary: 86.7 %), which could be due to monoazo dye (RY) requiring fewer electrons to break the azo bond compared to the diazo dye (RB5). In contrast, the higher decolorization rate of RB5 in binary dye indicated the removal rate was affected by the electron-withdrawing groups in the dye structure. The closed circuit enhanced about 2% of color and 4% of COD removal. Aeration improved the COD removal by 6%, which could be contributed by the mineralization of intermediates. The toxicity of azo dyes was reduced by 11-26% and the degradation pathways were proposed. The dye removal by the plants was increased with a higher contact time. RB5 was more favorable to be uptook by the plant as RB5 holds a higher partial positive charge. 127.39 (RY), 125.82 (RB5), and 58.66 mW/m³ (binary) of maximum power density were generated. The lower power production in treating the binary dye could be due to more electrons being utilized for the degradation of higher dye concentration. Overall, the UFCW-MFC operated in a closed circuit, aerated, and planted conditions achieved the optimum performance in treating binary azo dyes containing wastewater (dye: 87-92%; COD: 91%) compared to the other conditions (dye: 83-92%; COD: 78-87%).

Investigation of functional performance of treatment systems for textile wastewater in selected textile industries in Tanzania

Textile industrialization is an integral part of the economic growth in Tanzania. However, the corresponding wastewater from textile treatment processes consists of dyes and auxiliaries associated with acute toxicological impacts. This necessitates an investigation of the functional performance of the industrial treatment systems used before effluent discharge. The study primarily accesses the catalog of industrial dyes and the functionality of the treatment system at Arusha, Morogoro and Dar es Salaam vis-à-vis the effluent physicochemical properties. The analytical study reveals disperse (42%), vat (34%) and reactive (26%) as the most used industrial dyes. The physicochemical properties of the quantified wastewater reveal a significant amount of and phosphorus which was consequent to the high turbidity, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) apart from the color at the different sampling points. Although the treatability of the wastewater was 90% efficient using an activated carbon system (237.33 ± 0.67 mg/L). Similarly, the use of aerated constructed wetlands shows efficiency in the remediation of the recalcitrant having a value of 12.13 ± 0.89^b mg/L (90%) and 13.22 ± 0.15^a mg/L (94%). Thereafter, needful recommendations were suggested based on the physicochemical properties of the textile wastewater and to improve the functionality of the treatment systems in the respective industries.

Efficient and recyclable degradation of organic dye pollutants by CeO2@ZIF-8 nanozyme-based non-photocatalytic system

Advanced oxidation processes-based catalysis system as the most typical pollutant degradation technology always suffer from poor durability and photo-dependent. Inspired by the fact that some nanomaterials exhibit catalytic properties closer to natural enzymes, a high peroxidase-like activity and stability CeO₂@ZIF-8 nanozyme was synthesized in this study for non-photodegradation of dyes pollution. Multiple characterization techniques were applied to prove the successful synthesis of the nanozyme. The influence of different parameters on the catalytic degradation of organic dye by nanozyme was investigated. This nanozyme achieved a maximum degradation efficiency of 99.81% for methyl orange and maintained its catalytic performance in repeated experiments. Possible degradation intermediates and pathways for methyl orange were then proposed. In addition, the CeO₂@ZIF-8 loaded starch/agarose films were prepared for the portable and recyclable remediation of real dye wastewater, which maintained more than 80% degradation efficiency after 5 successive cycles. These results suggested that nanozyme based non-photocatalytic system is a potential catalyst for dye degradation and it opens a new avenue to develop high-performance and recyclable catalysts for pollutant remediation.