Dyestuffs from textile industry wastewaters: Trends and gaps in the use of bioflocculants

Green synthesis of ZnO nanoparticles using Justicia adhatoda for photocatalytic degradation of malachite green and reduction of 4-nitrophenol

Achieving the smallest crystallite/particle size of zinc oxide nanoparticles (ZnO NPs) reported to date, measuring 5.2/12.41 nm with Justicia adhatoda (J. adhatoda) leaf extract, this study introduces a facile green synthesis. Utilizing aqueous J. adhatoda leaf extract as both a reducing and stabilizing agent, the method leverages the plant's rich phytochemical composition to produce highly crystalline and morphologically controlled ZnO NPs. This precise particle size control highlights the effectiveness of the synthesis process in morphological tuning. The synthesized NPs were thoroughly characterized using XRD, UV-vis spectroscopy, FTIR, FESEM, and HRTEM, which collectively revealed superior crystallinity, controlled morphology, and unique surface properties conferred by phytochemical bio-capping. The photocatalytic performance of these biogenic ZnO NPs was evaluated for the degradation of two model pollutants: malachite green (MG), a synthetic dye, and 4-nitrophenol (4-NP), a toxic organic compound. The NPs exhibited exceptional photocatalytic efficiency, achieving 99.8% MG degradation within 180 minutes and demonstrating a rapid photocatalytic reduction of 4-NP to 4-aminophenol with a reaction rate constant of 0.245 min-1 under UV and sunlight irradiation. Mechanistic studies attributed this high performance to reactive oxygen species (ROS) generation and electron-hole pair interactions, supported by improved charge separation and high surface area. This work not only establishes the potential of J. adhatoda-mediated ZnO NPs in addressing persistent organic pollutants but also sets a benchmark for size-controlled NPs synthesis. By delivering scalable and eco-friendly water remediation technologies, this study advances green nanotechnology.

Environmentally Benign Freeze-dried Biopolymer-Based Cryogels for Textile Wastewater Treatments: A review

Motivated by sustainability and environmental protection, great efforts have been paid towards water purification and attaining complete decolorization and detoxification of polluted water effluent. Textile effluent, the main participant in water pollution, is a complicated mixture of toxic pollutants which seriously impact human health and the entire ecosystem. Developing effective materials for potential removal of the water contaminants is urgent. Recently, cryogels have been applied in wastewater sectors due to their unique physiochemical attributes(e.g. high surface area, lightweight, porosity, swelling-deswelling, and high permeability). These features robustly affected the cryogel's performance, as adsorbent material, particularly in wastewater sectors. This review serves as a detailed reference to the cryogels derived from biopolymers and applied as adsorbents for the purification of textile drainage. We displayed an overview of: the existing contaminants in textile effluents (dyes and heavy metals), their sources, and toxicity; advantages and disadvantages of the most common treatment techniques (biodegradation, advanced chemical oxidation, membrane filtration, coagulation/flocculation, adsorption). A simple background about cryogels (definition, cryogelation technique, significant features as adsorbents, and the adsorption mechanisms) is also discussed. Finally, the bio-based cryogels dependent on biopolymers such as chitosan, xanthan, cellulose, PVA, and PVP, are fully discussed with evaluating their maximum adsorption capacity.

Efficacy of exopolysaccharide in dye-laden wastewater treatment: A comprehensive review

The discharge of dye-laden wastewater into the water streams causes severe water and soil pollution, which poses a global threat to aquatic ecosystems and humans. A diverse array of microorganisms such as bacteria, fungi, and algae produce exopolysaccharides (EPS) of different compositions and exhibit great bioflocculation potency to sustainably eradicate dyes from water bodies. Nanomodified chemical composites of EPS enable their recyclability during dye-laden wastewater treatment. Nevertheless, the selection of potent EPS-producing strains and physiological parameters of microbial growth and the remediation process could influence the removal efficiency of EPS. This review will intrinsically discuss the fundamental importance of EPS from diverse microbial origins and their nanomodified chemical composites, the mechanisms in EPS-mediated bioremediation of dyes, and the parametric influences on EPS-mediated dye removal through sorption/bioflocculation. This review will pave the way for designing and adopting futuristic green and sustainable EPS-based bioremediation strategies for dye-laden wastewater in situ and ex situ.

Reshaping environmental sustainability: Poultry by-products digestate valorization for enhanced biochar performance in methylene blue removal

Anaerobic digestion is a highly effective and innovative method for treating organic waste while simultaneously generating energy. However, the treatment of the resulting digestate remains a challenging endeavor. To address this issue, poultry by-products digestate is used in this study to prepare biochars at two different pyrolysis temperatures (500/600 °C). Despite their potential, the utilization of untreated biochar is restricted due to its inadequate adsorption capacity. Therefore, each biochar was chemically activated using either HNO3 or KOH to synthesize four activated biochars (BC5@KOH, BC6@HNO3, BC5@HNO3, and BC6@HNO3). The aim is to investigate how the nature of chemical activation and pyrolysis temperature influence the adsorption of methylene blue dye. Characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), Raman analysis, and pHpzc determination, were exploited to comprehensively elucidate the structure and composition of both unprocessed and chemically activated biochars. Among the activated biochars, the adsorbent BC5@HNO3 exhibits the highest methylene blue (MB) adsorption capacity, reaching 101.72 mg.g-1 at 298 K under (pH = 2, ads dose = 0.6 g.L-1, shaking time of 20 min, as optimal conditions for MB adsorption. Adsorption data for each adsorbent strongly aligns with both the Langmuir isotherm model and the pseudo-second-order kinetic model. Moreover, the thermodynamic study reveals that the adsorption process was endothermic and spontaneous. The adsorption mechanism of MB dye was explored using various analytical techniques, including FTIR, SEM, PZC, and pH impact assessment. The findings suggest correlations with electrostatic interactions, hydrogen bonding, pore filling, as well as n-π and π-π interactions. Apparently, activated biochars play a crucial role in efficiently removing methylene blue dye, showcasing their potential as environmentally friendly and effective adsorbents.

Anaerobic Membrane Bioreactor (AnMBR) for the Removal of Dyes from Water and Wastewater: Progress, Challenges, and Future Perspectives

The presence of dyes in aquatic environments can have harmful effects on aquatic life, including inhibiting photosynthesis, decreasing dissolved oxygen levels, and altering the behavior and reproductive patterns of aquatic organisms. In the initial phase of this review study, our aim was to examine the categories and properties of dyes as well as the impact of their toxicity on aquatic environments. Azo, phthalocyanine, and xanthene are among the most frequently utilized dyes, almost 70–80% of used dyes, in industrial processes and have been identified as some of the most commonly occurring dyes in water bodies. Apart from that, the toxicity effects of dyes on aquatic ecosystems were discussed. Toxicity testing relies heavily on two key measures: the LC50 (half-lethal concentration) and EC50 (half-maximal effective concentration). In a recent study, microalgae exposed to Congo Red displayed a minimum EC50 of 4.8 mg/L, while fish exposed to Disperse Yellow 7 exhibited a minimum LC50 of 0.01 mg/L. Anaerobic membrane bioreactors (AnMBRs) are a promising method for removing dyes from water bodies. In the second stage of the study, the effectiveness of different AnMBRs in removing dyes was evaluated. Hybrid AnMBRs and AnMBRs with innovative designs have shown the capacity to eliminate dyes completely, reaching up to 100%. Proteobacteria, Firmicutes, and Bacteroidetes were found to be the dominant bacterial phyla in AnMBRs applied for dye treatment. However, fouling has been identified as a significant drawback of AnMBRs, and innovative designs and techniques are required to address this issue in the future.

Could termites be hiding a goldmine of obscure yet promising yeasts for energy crisis solutions based on aromatic wastes? A critical state-of-the-art review

Biodiesel is a renewable fuel that can be produced from a range of organic and renewable feedstock including fresh or vegetable oils, animal fats, and oilseed plants. In recent years, the lignin-based aromatic wastes, such as various aromatic waste polymers from agriculture, or organic dye wastewater from textile industry, have attracted much attention in academia, which can be uniquely selected as a potential renewable feedstock for biodiesel product converted by yeast cell factory technology. This current investigation indicated that the highest percentage of lipid accumulation can be achieved as high as 47.25% by an oleaginous yeast strain, Meyerozyma caribbica SSA1654, isolated from a wood-feeding termite gut system, where its synthetic oil conversion ability can reach up to 0.08 (g/l/h) and the fatty acid composition in yeast cells represents over 95% of total fatty acids that are similar to that of vegetable oils. Clearly, the use of oleaginous yeasts, isolated from wood-feeding termites, for synthesizing lipids from aromatics is a clean, efficient, and competitive path to achieve "a sustainable development" towards biodiesel production. However, the lacking of potent oleaginous yeasts to transform lipids from various aromatics, and an unknown metabolic regulation mechanism presented in the natural oleaginous yeast cells are the fundamental challenge we have to face for a potential cell factory development. Under this scope, this review has proposed a novel concept and approach strategy in utilization of oleaginous yeasts as the cell factory to convert aromatic wastes to lipids as the substrate for biodiesel transformation. Therefore, screening robust oleaginous yeast strain(s) from wood-feeding termite gut system with a set of the desirable specific tolerance characteristics is essential. In addition, to reconstruct a desirable metabolic pathway/network to maximize the lipid transformation and accumulation rate from the aromatic wastes with the applications of various "omics" technologies or a synthetic biology approach, where the work agenda will also include to analyze the genome characteristics, to develop a new base mutation gene editing technology, as well as to clarify the influence of the insertion position of aromatic compounds and other biosynthetic pathways in the industrial chassis genome on the expressional level and genome stability. With these unique designs running with a set of the advanced biotech approaches, a novel metabolic pathway using robust oleaginous yeast developed as a cell factory concept can be potentially constructed, integrated and optimized, suggesting that the hypothesis we proposed in utilizing aromatic wastes as a feedstock towards biodiesel product is technically promising and potentially applicable in the near future.