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Abstract This review investigates the pervasive issue of dye effluent pollution in African surface waters, focusing on its significant adverse effects on both human health and environmental quality. Drawing from 63 articles published between 2004 and 2022, the review includes studies from Northern, Western, Eastern, Central, and Southern Africa, illustrating the widespread nature of dye contamination across the continent. Five primary sources of dye effluents are identified: textiles, food industries, dye producers, artisan dyes, and tannery-paint industries, all of which contribute substantially to the degradation of water quality. The physicochemical properties of dye effluents show high toxicity levels in surface waters, with significant regional variations. These variations highlight the importance of considering the specific characteristics of dye types and processing chemicals to fully understand the contamination levels. In evaluating treatment methods, the review finds that adsorption, coagulation/flocculation, filtration, and advanced oxidation processes (AOPs) such as photocatalysis, photo-Fenton oxidation, and plasma-chemical treatment are effective in mitigating dye pollution. The application of these methods varies across different African regions, indicating the need for region-specific approaches based on local conditions and available resources. The review also examines the impact of dye effluents on aquatic ecosystems and human health, with risk assessments revealing effects ranging from acute to chronic. This demonstrates the urgent need for targeted interventions to address dye effluent pollution in African surface waters, thereby protecting both environmental and public health. Graphical Abstract

This review investigates the pervasive issue of dye effluent pollution in African surface waters, focusing on its significant adverse effects on both human health and environmental quality. Drawing from 63 articles published between 2004 and 2022, the review includes studies from Northern, Western, Eastern, Central, and Southern Africa, illustrating the widespread nature of dye contamination across the continent. Five primary sources of dye effluents are identified: textiles, food industries, dye producers, artisan dyes, and tannery-paint industries, all of which contribute substantially to the degradation of water quality. The physicochemical properties of dye effluents show high toxicity levels in surface waters, with significant regional variations. These variations highlight the importance of considering the specific characteristics of dye types and processing chemicals to fully understand the contamination levels. In evaluating treatment methods, the review finds that adsorption, coagulation/flocculation, filtration, and advanced oxidation processes (AOPs) such as photocatalysis, photo-Fenton oxidation, and plasma-chemical treatment are effective in mitigating dye pollution. The application of these methods varies across different African regions, indicating the need for region-specific approaches based on local conditions and available resources. The review also examines the impact of dye effluents on aquatic ecosystems and human health, with risk assessments revealing effects ranging from acute to chronic. This demonstrates the urgent need for targeted interventions to address dye effluent pollution in African surface waters, thereby protecting both environmental and public health. Highlights: Dye effluent pollution severely impacts human health and the environment, particularly in African surface waters. Six key industries contribute to dye pollution in Africa: textile, food, pharmaceutical, tannery, paint, and artisanal. Effective treatment methods like adsorption, filtration, and AOPs show promise but require larger-scale implementation [ABSTRACT FROM AUTHOR]

The present study evaluates the Decolorization and pollutant removal efficiency of chemically impregnated coconut shell-activated carbon using textile dye effluent in the filtration system. The coconut shell zinc chloride activated carbon (CSZAC) was used as a filtering media in wastewater treatment due to its wider pore space with better surface area (590.80 m2 g−1) and higher adsorption capacity. The SEM micrograph revealed that the activated carbon had networks of parallel running pores with internal microstructure and more active sites. The designed activated carbon filter system has dimensions of 90 x 60 x 30 cm; the sections included are the holding tank (50 liters capacity), filtration tank and storage tank with the optimized flow rate of 5 x 10−4 m3 min−1. The Color, pH, EC, TDS, TSS, BOD and COD of textile dyeing wastewater were significantly reduced, after the treatment through the CSZAC filtration system. The initial color concentration of textile dye effluent was 7021 HU and after treatment, the color was fully reduced and became colorless. CSZAC treatment reduced the BOD from 600 mg L−1 to 89.7 mg L−1 (80.6 per cent) and COD from 2500 mg L−1 to 205 mg L−1 (90.5 per cent). Therefore, CSZAC can be used as an effective adsorbent material to remove different dye compounds and pollutants from textile wastewater. [ABSTRACT FROM AUTHOR]

This study aimed to analyze the feasibility of removing Alizarin red S (ARS) used as model pollutant from aqueous solutions using the preparative porous silica composites (PSCs) as adsorbents which were prepared via hydrothermal approach. The physicochemical properties of materials were characterized by means of Transmission electron microscope (TEM), Scanning electron microscope (SEM), Energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller (BET) method, Barret-Joyner-Halenda (BJH) method, Fourier Transform Infrared Spectrometer (FTIR) and X-Ray Diffractometer (XRD). PSCs possessed the specific surface area were 731.6 m2/g, 420.9 m2/g, 294.6 m2/g, respectively. The presence of silica structures was confirmed by FTIR spectra. In order to confirm efficiency of composites as adsorbents and reveal adsorption mechanism, the impacts of pH, contact time, initial ARS concentration, temperature on adsorption were conducted. The adsorption experiment results showed that the adsorption efficiency of ARS onto PSC-3 was better than that of PSC-1 and PSC-2 at pH = 11. Furthermore, the adsorption kinetic models, isotherm models and thermodynamic model were analyzed for comprehensive adsorption process. The maximum adsorption capacity of PSC-3 for ARS was 43.1 mg/g. The pseudo-second-order kinetic model and Sips isotherm model were more suitable for experimental results. The adsorption process was endothermic according to the adsorption thermodynamic model. The free energy of adsorption required for ARS onto PSCs was less than 8 kJ/mol, indicating physical adsorption. What's more, PSC-3 possessed advantages of higher adsorption capacity and shorter equilibration time. Overall, these results made it potentially applicable as an effective adsorbent for ARS dye from effluent. [ABSTRACT FROM AUTHOR]

Organic dyes are extensively used in textile and batik industry. Dispose of untreated dye effluent into water system is hazardous to human and environment. Advanced oxidation process (AOPs) based on heterogeneous TiO2 photocatalyst is proven for effluent treatment. Immobilization of TiO2 photocatalyst on supporting substrate is one of the research focuses to realize its application in industry to minimize the loss of TiO2 photocatalyst over time during effluent treatment. Many synthesis techniques have been used to grow TiO2 photocatalyst on supporting substrates. However, these synthesis techniques are either timeor cost-consuming. In this work, a novel direct heating (DH) technique has been developed for the first time to deposit TiO2 particles on kanthal coils. The optimum deposition of TiO2 particles was achieved in 15 min using 60 W. The TiO2 particles contained mixture of anatase (82.7%) and brookite (17.3%), with an average particle size of 167.36±15.37 nm. The surface coverage of TiO2 particles on kanthal wire was good, with minimum agglomeration. The TiO2 particles deposited on kanthal coils recorded 43.7% of photodegradation efficiency in methylene blue removal under UV light. [ABSTRACT FROM AUTHOR]

Textile and cosmetic industries generate large amounts of dye effluents requiring treatment before discharge. This wastewater contains high levels of reactive dyes, low to none-biodegradable materials and chemical residues. Technically, dye wastewater is characterised by high chemical and biological oxygen demand. Biological, physical and pressure-driven membrane processes have been extensively used in textile wastewater treatment plants. However, these technologies are characterised by process complexity and are often costly. Also, process efficiency is not achieved in cost-effective biochemical and physical treatment processes. Membrane distillation (MD) emerged as a promising technology harnessing challenges faced by pressure-driven membrane processes. To ensure high cost-effectiveness, the MD can be operated by solar energy or low-grade waste heat. Herein, the MD purification of dye wastewater is comprehensively and yet concisely discussed. This involved research advancement in MD processes towards removal of dyes from industrial effluents. Also, challenges faced by this process with a specific focus on fouling are reviewed. Current literature mainly tested MD setups in the laboratory scale suggesting a deep need of further optimization of membrane and module designs in near future, especially for textile wastewater treatment. There is a need to deliver customized high-porosity hydrophobic membrane design with the appropriate thickness and module configuration to reduce concentration and temperature polarization (CP and TP). Also, energy loss should be minimized while increasing dye rejection and permeate flux. Although laboratory experiments remain pivotal in optimizing the MD process for treating dye wastewater, the nature of their time intensity poses a challenge. Given the multitude of parameters involved in MD process optimization, artificial intelligence (AI) methodologies present a promising avenue for assistance. Thus, AI-driven algorithms have the potential to enhance overall process efficiency, cutting down on time, fine-tuning parameters, and driving cost reductions. However, achieving an optimal balance between efficiency enhancements and financial outlays is a complex process. Finally, this paper suggests a research direction for the development of effective synthetic and natural dye removal from industrially discharged wastewater. [Display omitted] • Discharge of dye effluent requires robust and cost-effective treatment processes. • Membrane distillation emerged as a promising tool towards dye remediation. • The current study reviewed research advancement towards environmental dye remediation. • However, fouling and thermal efficiency of MD remain a major challenge. • The reviewed study suggested optimization of membrane and module designs for effective dye remediation. [ABSTRACT FROM AUTHOR]

Biochar dye adsorbents are touted as "green" and low-cost compared to metals/oxides and polymers. However, the most active of them require some form of multi-step chemical activation with toxic chemicals which tarnish their credentials. Going forward, there is a need to develop low-toxic chemical activators or discover new biomass sources that can generate high-value biochar adsorbents via physical activation. Herein, we demonstrate that unlike other biomass waste almond skin (WA-s) contains a unique network of lignocellulosic capillary-like structures (CN) buried inside a dense lignocellulosic shell. Via one-step carbonization at 900 °C under N 2 , the shell is removed exposing CN which transforms into defect-rich carbon macrostructures (AS-C-T). Data from spectroscopy analysis indicate that AS-C-T has the special ability to undergo carbonylation, at high temperatures, creating moderate acidic carbonyl (C O) interfaces that form selective hydrogen bonds with the acidic hydrogen of zwitterion methyl blue (MB), at pH 6.2 to 7.2. Such interactions induce high MB adsorption capacity (>3000 mgg−1) and selectivity comparable to the state-of-the-art. The hydrogen bonding is strong and irreversible; however, it creates secondary interfaces which ensure high recyclability. The adsorption reaction is endothermic and modeled by the pseudo-second-order kinetic, Langmuir, and Intra-particle diffusion. Practically, AS-C-T can be retrofitted to commercial filters to produce pathogen- and dye-free water. These properties make AS-C-T a potential "green" and low-cost adsorbent for dye effluents. Our results hint at the fact that biomass sources with intricate capillary structures might have unique interfacial properties which are useful for preparing high-value biochar adsorbents without chemical activation. [Display omitted] [ABSTRACT FROM AUTHOR]

Polyelectrolyte complexes (PECs) have received considerable attention in resource recovery from wastewater and enhanced separation technologies because they are multicomponent polymeric materials with unique wettability properties. From this perspective, we focused on new opportunities to develop photothermally effective PECs to separate oil/water emulsion and purify dye-contaminated wastewater. The PEC was also utilized for solar steam generation. Chondroitin sulfate (CS), a weak anionic polyelectrolyte material, was treated with a cationic copolymer of poly (acrylamide-co-diallyldimethylammonium chloride) (PAAm-DADMAc). This material is used as a membrane by modifying cellulose acetate filter paper. The formation of PECs was confirmed using various analytical techniques, and a cauliflower-like assembled microparticle morphology was achieved. The surfaces of the fabricated PEC self-assembled microparticles exhibited good emulsion separation efficiency (99.4%) and emulsion permeation flux of 2316 L m−2 h−1 bar−1 after eight filtration cycles. The versatile functional groups were recognized for their superhydrophilicity and underwater superoleophobic nature (approximately 150° of contact angle) for low-and high-viscosity oils. The abundance of functional groups in the PECs treated anionic Congo red dye, cationic methylene blue dye, and textile dyeing industrial effluent with 99% separation efficiency. In addition, PEC-modified membrane materials were successfully utilized as an effective solar steam generation to purify 3.5% NaCl contaminated water under 1 kW m−2. The evaporation rate was retained with 2.31 kg m−2 h−1 for five cycles. Overall, the proposed CS/PAAm-DADMAc/GO-modified membranes can offer a new route to treat oil-in-water emulsions and remove dye from wastewater at an industrial level along with solar desalination. Thus, the proposed materials will provide essential insights into scientific and practical accessibility for developing multifunctional membrane materials for wastewater treatment. • Polyelectrolyte materials derived from Chondroitin sulfate and PAAm-DADMAc. • Polyelectrolytes with GO exhibited 99.4% separation efficiency with emulsion. • Efficient membrane separation for oil-in-water and dye mixed emulsions. • Bio-inspired membrane is utilized for industrial effluent removal. • Modified membrane material is exploited as effective solar steam generator. [ABSTRACT FROM AUTHOR]

Graphene oxide can be used to store energy, as electrodes and purify industrial and domestic wastewater as photocatalysts and adsorbents because of its remarkable thermal, electrical, and chemical capabilities. Toward understanding graphene oxide (GO) based nanomaterials considering the background factors, the present review study investigated their characteristics, preparation methods, and characterization processes. The removal of contaminants from wastewater has recently been a focus of attention for materials based on GO. Progress in GO synthesis and surface modification has shown that they can be used to immobilize enzymes. It is possible to immobilize enzymes with varying characteristics on graphene-oxide-based substrates without sacrificing their functioning, thus developing a new environmental remediation platform utilizing nano biocatalysts. GO doping and co-doping with a variety of heterogeneous semiconductor-based metal oxides were included in a brief strategy for boosting GO efficiency. A high band-gap material was also explored as a possibility for immobilization, which shifts the absorption threshold to the visible range and increases photoactivity. For water treatment applications, graphene-based nanomaterials were used in Fenton reactions, photocatalysis, ozonation, photo electrocatalysis, photo-Fenton, and a combination of photon-Fenton and photocatalysis. Nanoparticles made from GO improved the efficiency of composite materials when used for their intended applications. As a result of the analysis, prospects and improvements are clear, especially when it comes to scaling up GO-based wastewater treatment technologies. [Display omitted] • Nano-based graphene oxide (GO) is useful in effective wastewater treatment. • To develop GO to treat wastewater, bottom-up and top-down approaches can be used. • Electro-chemical, mechanical, and surface properties of GO are pollutant traps. • GO plays an important role in adsorption-based water treatment systems. [ABSTRACT FROM AUTHOR]