Potential of using kaolin as a natural adsorbent for the removal of pollutants from tannery wastewater

NB. Insecticidal formulation based on essential oil from Ocimum basilicum Linn. Herb supported onto modified kaolinite for stored maize protection

In this study, essential oil was obtained by hydrodistillation from the leaves of Ocimum basilicum and it was analyzed by GC-MS. Eucalyptol (11.19 %), trans-iso eugenol (13.12 %), hexadecanoic acid methyl ester (19.26 %) and 9-octadecenoic acid (z)-methyl ester (25.12 %) had been the leading four main components of the plant leaves of the essential oil. The unmodified and modified kaolin was characterized and analyzed by XRD, FT-IR, TGA and SEM/EDX and thus the principal mineral of the nanoclay was proved to be kaolinite. The hydrodistiled essential oil in the absence of the clay support was evaluated within 24 h of exposure time and the outcome revealed that it was insecticidally active against the maize weevil, S. zeamais adults. Moreover, the exposure time effect, the formulation efficiency, the effect of remnant and stability of the prepared formulations were investigated and the results indicated an enhancement of bioinsecticides for a long period with upgraded persistence against the S. zeamais. Finally, the results recommend that O. basilicum essential oil - modified kaolinite formulations should be used as best options to chemical insecticides in pest control of stored products like stored maize grain insects, S. Zeamais.

Adsorption of Bichromate and Arsenate Anions by a Sorbent Based on Bentonite Clay Modified with Polyhydroxocations of Iron and Aluminum by the "Co-Precipitation" Method

The physicochemical properties of natural bentonite and its sorbents were studied. It has been established the modification of natural bentonites using polyhydroxoxides of iron (III) (mod.1_Fe_5-c) and aluminum (III) (mod.1_Al_5-c) by the "co-precipitation" method led to changes in their chemical composition, structure, and sorption properties. It was shown that modified sorbents based on natural bentonite are finely porous (nanostructured) objects with a predominance of pores of 1.5-8.0 nm in size. The modification of bentonite with iron (III) and aluminum compounds by the "co-precipitation" method also leads to an increase in the sorption capacity of the obtained sorbents with respect to bichromate and arsenate anions. A kinetic analysis showed that, at the initial stage, the sorption process was controlled by an external diffusion factor, that is, the diffusion of the sorbent from the solution to the liquid film on the surface of the sorbent. The sorption process then began to proceed in a mixed diffusion mode when it limited both the external diffusion factor and the intra-diffusion factor (diffusion of the sorbent to the active centers through the system of pores and capillaries). To clarify the contribution of the chemical stage to the rate of adsorption of bichromate and arsenate anions by the sorbents under study, kinetic curves were processed using equations of chemical kinetics (pseudo-first-order, pseudo-second-order, and Elovich models). It was found that the adsorption of the studied anions by the modified sorbents based on natural bentonite was best described by a pseudo-second-order kinetic model. The high value of the correlation coefficient for the Elovich model (R2 > 0.9) allows us to conclude that there are structural disorders in the porous system of the studied sorbents, and their surfaces can be considered heterogeneous. Considering that heterogeneous processes occur on the surface of the sorbent, it is natural that all surface properties (structure, chemical composition of the surface layer, etc.) play an important role in anion adsorption.

Exploring the Efficiency of Algerian Kaolinite Clay in the Adsorption of Cr(III) from Aqueous Solutions: Experimental and Computational Insights

The current study comprehensively investigates the adsorption behavior of chromium (Cr(III)) in wastewater using Algerian kaolinite clay. The structural and textural properties of the kaolinite clay are extensively characterized through a range of analytical methods, including XRD, FTIR, SEM-EDS, XPS, laser granulometry, N2 adsorption isotherm, and TGA-DTA. The point of zero charge and zeta potential are also assessed. Chromium adsorption reached equilibrium within five minutes, achieving a maximum removal rate of 99% at pH 5. Adsorption equilibrium is modeled using the Langmuir, Freundlich, Temkin, Elovich, and Dubinin-Radushkevitch equations, with the Langmuir isotherm accurately describing the adsorption process and yielding a maximum adsorption capacity of 8.422 mg/g for Cr(III). Thermodynamic parameters suggest the spontaneous and endothermic nature of Cr(III) sorption, with an activation energy of 26.665 kJ/mol, indicating the importance of diffusion in the sorption process. Furthermore, advanced DFT computations, including COSMO-RS, molecular orbitals, IGM, RDG, and QTAIM analyses, are conducted to elucidate the nature of adsorption, revealing strong binding interactions between Cr(III) ions and the kaolinite surface. The integration of theoretical and experimental data not only enhances the understanding of Cr(III) removal using kaolinite but also demonstrates the effectiveness of this clay adsorbent for wastewater treatment. Furthermore, this study highlights the synergistic application of empirical research and computational modeling in elucidating complex adsorption processes.

The Diversity and Community Composition of Three Plants' Rhizosphere Fungi in Kaolin Mining Areas

Mining activities in the kaolin mining area have led to the disruption of the ecological health of the mining area and nearby soils, but the effects on the fungal communities in the rhizosphere soils of the plants are not clear. Three common plants (Conyza bonariensis, Artemisia annua, and Dodonaea viscosa) in kaolin mining areas were selected and analyzed their rhizosphere soil fungal communities using ITS sequencing. The alpha diversity indices (Chao1, Shannon, Simpson, observed-species, pielou-e) of the fungal communities decreased to different extents in different plants compared to the non-kauri mining area. The β-diversity (PCoA, NMDS) analysis showed that the rhizosphere soil fungal communities of the three plants in the kaolin mine area were significantly differentiated from those of the control plants grown in the non-kaolin mine area, and the extent of this differentiation varied among the plants. The analysis of fungal community composition showed that the dominant fungi in the rhizosphere fungi of C. bonariensis and A. annua changed, with an increase in the proportion of Mycosphaerella (genus) by about 20% in C. bonariensis and A. annua. An increase in the proportion of Didymella (genus) by 40% in D. viscosa was observed. At the same time, three plant rhizosphere soils were affected by kaolin mining activities with the appearance of new fungal genera Ochrocladosporium and Plenodomus. Predictive functional potential analysis of the samples revealed that a significant decrease in the potential of functions such as biosynthesis and glycolysis occurred in the rhizosphere fungal communities of kaolin-mined plants compared to non-kaolin-mined areas. The results show that heavy metals and plant species are the key factors influencing these changes, which suggests that selecting plants that can bring more abundant fungi can adapt to heavy metal contamination to restore soil ecology in the kaolin mining area.

Influence of conditioner and straw on the herbaceous plant-based phytoremediation copper tailings: a field trial at Liujiagou tailings pond, China

A field trial was performed to carry out an enhanced phytoremediation technique for multi-metal contaminated copper tailings by Sudan grass (Sorghum Sudanese), ryegrass (Lolium perenne L.), and Bermuda grass (Cynodon dactylon), using conditioner (TH-LZ01) and straw combination into composite amendments as soil amendments, aimed to obtain the maximum of phytoremediation effect. The results showed that compared with untreated herbaceous plants, the application of conditioner and straw planted with herbaceous plants reduced the pH and conductivity and increased the organic matter and water content of the copper tailings to different degrees. With the addition of conditioner and straw, the DTPA-Cd, DTPA-Cu, DTPA-Pb, and DTPA-Zn contents in the copper tailings showed a decreasing trend compared with the untreated group. The herbaceous plants were promoted to reduce the percentage contents of acid soluble fractions Cd, Cu, Pb, and Zn and to increase the percentage contents of reducible, oxidizable, and residual fractions heavy metals (Cd, Cu, Pb, and Zn) in the copper tailings to different degrees. The contents of Cd, Cu, Pb, and Zn in the underground part of herbaceous plants were higher than those in the aboveground part, and the contents of Cd, Cu, Pb, and Zn in the aboveground part and underground part decreased after adding conditioner and straw, which indicated that the conditioner and straw inhibited the transport of heavy metals in the plant. Furthermore, the principal component analysis showed that the application of conditioner and straw with planting ryegrass had more potential for improving the physicochemical properties of copper tailings and reducing heavy metal toxicity, followed by Bermuda grass and Sudan grass.

Comprehensive technological assessment for different treatment methods of leather tannery wastewater

The leather-making process necessitates large amounts of water and consequently generates tons of liquid waste as leather tannery wastewater (TWW) is disposed of directly in the open environment. Open disposal of untreated TWW into the natural environment causes an accumulation of various polluting compounds, including heavy metals, dyes, suspended solids inorganic matter, biocides, oils, tannins, and other toxic chemicals. It thus poses potential hazards to the environment and human health. This study primarily focuses on providing in-depth insight into the characteristics, treatment strategies, and regulatory frameworks for managing TWW in leather processing industries. Different technologies of conventional physico-chemical (equalization, coagulation, and adsorption), advanced approaches (Fenton oxidation, ozonation, cavitation), thermo-catalytic and biological treatments available to treat TWW, and their integrative approaches were also highlighted. This review also sheds light on the most frequently applied technologies to reduce contaminant load from TWW though there are several limitations associated with it such as being ineffective for large quantities of TWW, waste generation during treatment, and high operational and maintenance (O&M) costs. It is concluded that the sustainable alternatives applied in the current TWW technologies can minimize O&M costs and recirculate the treated water in the environment. The exhaustive observations and recommendations presented in this article are helpful in the industry to manage TWW and recirculate the water in a sustainable manner.

Stabilizing Cr(Ⅲ) deriving from tannery sludge with kaolin and organic matter

Stabilizing Cr(III) in tannery sludge (TS) via harmless method has always been the goal of environmental pollution treatment. In this study, a simple method to stabilize Cr(III) in TS is proposed via adding kaolin, based on the fact a large amount of organic matter contained in TS. Comprehensive characterizations confirm that kaolin can stabilize Cr(Ⅲ) via its abundant -OH and lamellar structure. Moreover, there are hydrogen bond interactions and ligand exchange-surface complexation between organic matter and kaolin, which is more conducive to form a stable ternary complex with Cr(III), in a state of organic matter-Cr(III)-kaolin. Simultaneously, the BCR sequential extraction experiment shows that the unstable water and acid soluble state of Cr(III) are reduced (from 0.61% to 0.35%), which further indicates that the stabilization of Cr(III) is successful.

Field site soil aquifer treatment shows enhanced wastewater quality: Evidence from vadose zone hydro-geophysical observations

Soil aquifer treatment (SAT) is an emerging, nature-based, economically viable wastewater treatment solution. Currently, most SAT experiments are done at the laboratory scale, which cannot generate the same conditions as natural field sites and limits the understanding of treatment efficiency. The current study carried out in situ SAT experiments in the Musi River basin in India, where wastewater irrigation is a common practice. SAT efficiency was determined using an integrated approach, including electrical resistivity tomography (ERT) surveys, soil investigations (grain size, permeability, and moisture measurements), and biochemical characterization of raw and SAT treated wastewater. The ERT scans of SAT column show lower order electrical resistivity 10-30 Ω-m with enhanced chargeability >5-6 mV/V attributed to the vadose zone, characterized by clay-rich soil and sandy soil up to 5-6 m depth. The increase in sand percentage (>70%) below 140-160 cm depth corroborates with the high moisture content (23.5%). The vadose zone permeability (K) 1.58 m/day and discharge (Q) 38.19 m3/day is used to determine the pollutants reduction efficiency of SAT column. Hydrogeological and biogeochemical observations reveal that the improved dissolved oxygen from <1.0 to 5-6 mg/L in the vadose zone catalyzes the oxidation of organic matter resulting in the reduction of BOD and COD up to 92% and 97%, respectively, and denitrification reducing NO3-- (0.55 kg/day). In addition, the precipitation and adsorption by kaolinite clay prompted the reduction of PO42- (0.26 kg/day). Furthermore, the oxic-vadose zone could not support the growth of coliforms and faecal coliforms, and the reduction observed was up to 99.99% in the SAT production well. Overall, the results indicated a positive outcome with SAT efficiency and framed the SAT sitting criteria for different geological environments.

Management of tannery waste effluents towards the reclamation of clean water using an integrated membrane system: A state-of-the-art review

Tanning and other leather processing methods utilize a large amount of freshwater, dyes, chemicals, and salts and produce toxic waste, raising questions regarding their environmental sensitivity and eco-friendly nature. Total suspended solids, total dissolved solids, chemical oxygen demand, and ions such as chromium, sulfate, and chloride turn tannery wastewater exceedingly toxic for any living species. Therefore, it is imperative to treat tannery effluent, and existing plants must be examined and upgraded to keep up with recent technological developments. Different conventional techniques to treat tannery wastewater have been reported based on their pollutant removal efficiencies, advantages, and disadvantages. Research on photo-assisted catalyst-enhanced deterioration has inferred that both homogeneous and heterogeneous catalysis can be established as green initiatives, the latter being more efficient at degrading organic pollutants. However, the scientific community experiences significant problems developing a feasible treatment technique owing to the long degradation times and low removal efficiency. Hence, there is a chance for an improved solution to the problem of treating tannery wastewater through the development of a hybrid technology that uses flocculation as the primary treatment, a unique integrated photo-catalyst in a precision-designed reactor as the secondary method, and finally, membrane-based tertiary treatment to recover the spent catalyst and reclaimable water. This review gives an understanding of the progressive advancement of a cutting-edge membrane-based system for the management of tanning industrial waste effluents towards the reclamation of clean water. Adaptable routes toward sludge disposal and the reviews on techno-economic assessments have been shown in detail, strengthening the scale-up confidence for implementing such innovative hybrid systems.

Treatment of tannery effluent by adsorption onto fly ash released from thermal power stations: Characterisation, optimization, kinetics, and isotherms

Fly ash is a significant pollutant in thermal power stations. Although this waste harms the environment and humans, it is badly removed and managed, and only a few studies are interested in this waste. For that, this study aims to valorise fly ash into potential adsorbents to treat tannery effluents for the first time. The physicochemical characterisation showed that fly ash has a pHpzc of 9.78, a very porous structure, a high specific surface area of 3127.2 m²/g with a total pore volume of 3.27 cm³/g, and a high silica and aluminium percentage. SEM showed that the fly ash studied has a small particle size ranging between 32 nm and 100 μm. Batch adsorption experiments were done, and the effects of adsorption parameters were investigated. The kinetics and isotherms models indicate that the equilibriums were achieved in 30 min, where the maximum uptake capacity was 2496, 223.7 and 106.8 mg/g for Chemical Oxygen Demand (COD), chromium (VI) and sulfide ions, respectively. The kinetic data were well fitted to the pseudo-second-order model and showed that adsorption onto fly ash may be chemical and physical simultaneously. Freundlich's model gave a better fit for the experimental adsorption equilibrium data and displayed multilayer adsorption. The thermodynamic isotherm showed that the adsorption onto fly ash is thermodynamically spontaneous (ΔG° < 0) and endothermic (ΔH° > 0). In conclusion, fly ash, which is a free material, has a more robust adsorption capacity than other expensive materials. Thus, it can be a promising, eco-friendly, attractive adsorbent for industrial wastewater treatment.

Modified kaolin hydrogel for Cu2+ adsorption

Removal of Cu2+ ions from contaminated water is an important but challenging task. This study reports the synthesis of a composite hydrogel from two natural polysaccharides, namely, sodium alginate and chitosan, using inexpensive kaolin as a raw material and polyacrylamide as a modifier. The hydrogel had a high adsorption capacity and selectivity for Cu2+. The composite hydrogel was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The pseudo-second-order kinetic model was the most suitable model for the kinetic results, and the Langmuir isotherm model was the most representative of the sorption system. The results revealed that the adsorption process was mainly controlled by chemisorption. The maximum adsorption capacity of the adsorbent was 106.4 mg·g−1. Therefore, this study presents a new perspective on the application of composite hydrogels as Cu2+ adsorbents.

Natural Clay Minerals as Potential Arsenic Sorbents from Contaminated Groundwater: Equilibrium and Kinetic Studies

Arsenic (As) contaminated groundwater is a worldwide concern due to its chronic effects on human health. The objectives of the study were to evaluate natural inexpensive raw laterite (RL) and kaolinite (RK) for their potential use as As sorbents and to understand the As sorption on laterite and kaolinite by employing sorption and kinetic models. Raw laterite and RK were tested for EC, pH, XRF and CEC as basic parameters. Batch sorption and kinetic experiments data were fitted in the sorption (Langmuir and Freundlich) model and kinetic (pseudo-first and pseudo-second order) reaction equations, respectively. Morphological and structural changes were observed in RL and RK samples before and after As saturation by employing FTIR and SEM. The major constituent in RL was Fe and Al oxides while in RK major oxides were silica and Al. The Freundlich sorption model well explained the experimental data, indicating a greater sorption capacity of RL on a hetero-layered surface compared to RK. The kinetic reaction equations showed that equilibrium was achieved after a contact time of 240 min and the adsorption was chemisorption in nature. The RL and RK were found to be effective sorbents for As removal, however, RL showed maximum As adsorption and thus superior in comparison with RK. Structural and morphological characterization reveals the role of Fe and Al oxides in the case of RL, and Al oxides in the case of RK, in the adsorption of As. Hence this study concludes that these naturally occurring inexpensive resources can be used as sorbent agents for As-contaminated drinking water treatment.

Polymer Nanocomposite Membrane for Wastewater Treatment: A Critical Review

With regard to global concerns, such as water scarcity and aquatic pollution from industries and domestic activities, membrane-based filtration for wastewater treatment has shown promising results in terms of water purification. Filtration by polymeric membranes is highly efficient in separating contaminants; however, such membranes have limited applications. Nanocomposite membranes, which are formed by adding nanofillers to polymeric membrane matrices, can enhance the filtration process. Considerable attention has been given to nanofillers, which include carbon-based nanoparticles and metal/metal oxide nanoparticles. In this review, we first examined the current status of membrane technologies for water filtration, polymeric nanocomposite membranes, and their applications. Additionally, we highlight the challenges faced in water treatment in developing countries.

Adsorption of Chromate Ions by Layered Double Hydroxide-Bentonite Nanocomposite for Groundwater Remediation

Herein, magnesium/aluminum-layered double hydroxide (MgAl-LDH) and bentonite (BT) nanocomposites (LDH–BT) were prepared by co-precipitation (CP), exfoliation–reassembly (ER), and simple solid-phase hybridization (SP). The prepared LDH–BT nanocomposites were preliminarily characterized by using powder X-ray diffractometry, scanning electron microscopy, and zeta-potentiometry. The chromate adsorption efficacies of the pristine materials (LDH and bentonite) and the as-prepared nanocomposites were investigated. Among the composites, the LDH–BT_SP was found to exhibit the highest chromate removal efficiency of 65.7%. The effect of varying the LDH amount in the LDH–BT composite was further investigated, and a positive relationship between the LDH ratio and chromate removal efficiency was identified. The chromate adsorption by the LDH–BT_SP was performed under various concentrations (isotherm) and contact times (kinetic). The results of the isotherm experiments were well fitted with the Langmuir and Freundlich isotherm model and demonstrate multilayer chromate adsorption by the heterogeneous LDH–BT_SP, with a homogenous distribution of LDH nanoparticles. The mobility of the as-prepared LDH–BT_SP was investigated on a silica sand-filled column to demonstrate that the mobility of the bentonite is dramatically decreased after hybridization with LDH. Furthermore, when the LDH–BT_SP was injected into a box container filled with silica sand to simulate subsurface soil conditions, the chromate removal efficacy was around 43% in 170 min. Thus, it was confirmed that the LDH–BT prepared by solid-phase hybridization is a practical clay-based nanocomposite for in situ soil and groundwater remediation.

An Overview of Antibiotic Resistance and Abiotic Stresses Affecting Antimicrobial Resistance in Agricultural Soils

Excessive use of antibiotics in the healthcare sector and livestock farming has amplified antimicrobial resistance (AMR) as a major environmental threat in recent years. Abiotic stresses, including soil salinity and water pollutants, can affect AMR in soils, which in turn reduces the yield and quality of agricultural products. The objective of this study was to investigate the effects of antibiotic resistance and abiotic stresses on antimicrobial resistance in agricultural soils. A systematic review of the peer-reviewed published literature showed that soil contaminants derived from organic and chemical fertilizers, heavy metals, hydrocarbons, and untreated sewage sludge can significantly develop AMR through increasing the abundance of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARBs) in agricultural soils. Among effective technologies developed to minimize AMR's negative effects, salinity and heat were found to be more influential in lowering ARGs and subsequently AMR. Several strategies to mitigate AMR in agricultural soils and future directions for research on AMR have been discussed, including integrated control of antibiotic usage and primary sources of ARGs. Knowledge of the factors affecting AMR has the potential to develop effective policies and technologies to minimize its adverse impacts.

Treatment of real industrial wastewater with high sulfate concentrations using modified Jordanian kaolin sorbent: batch and modelling studies

In the present study, BaCl₂ modified Jordanian kaolin sorbent (obtained from Mahis, Jordan) was used to remove sulfate-contaminated industrial wastewater. The kaolin sample was pretreated to enhance its adsorption capacity and then characterized using X-Ray fluorescence (XRF) and Fourier Transform Infrared Spectroscopy (FTIR). Equilibrium isotherms for the adsorption parameters were carried out experimentally, and the adsorption data correlated very well with Freundlich and Temkin and Dubinin-Radushkevich models. Furthermore, the adsorption kinetics followed the pseudo-first-order and intraparticle diffusion models perfectly. The estimated value of the maximum adsorption capacity qm = 85.08 mg/g indicates that kaolin has a very high capacity to adsorb sulfate ions at studied parameters. The estimated value of the mean free energy (4.87 kJ/mol) is very low, confirming physical type adsorption. The study results established that modified Jordanian kaolin could serve as a safe and effective natural adsorbent for sulfate-contaminated industrial wastewater.

Pollutant removal from dairy wastewater using live Azolla filiculoides in batch and continuous bioreactors

Fast and proper treatment of dairy wastewater is necessary before discharging it to the environment. In this study, healthy Azolla filiculoides was used to remove pollutants, including phosphorus (P), sodium (Na), chemical oxygen demand (COD), biological oxygen demand (BOD), and total dissolved solids (TDS) of dairy effluent in batch, continuous system, as well as continuous with the slow stirring system. These systems were handmade. The maximum removal efficiency was related to the P, which obtained 66.25% after 12 h in the batch bioreactor system. The highest removal of 13.69% after 21 h was obtained for Na using continuous with a slow stirring method. The highest removal related to the COD and BOD was 33.53% and 29.93% after 18 h, respectively, in continuous with the slow stirring system. TDS removal was achieved 31.44% after 24 h using the batch system. The results of these three systems were compared with each other using a one-way analysis of variance (ANOVA). There was no significant difference between them. Azolla filiculoides is an abundant plant in northern nature that a biosystem was used for optimum usage. It can be used as an efficient, inexpensive, and affordable bioadsorbent for dairy wastewater treatment. PRACTITIONER POINTS: Live Azolla filiculoides was used to remove pollutants. P, Na, BOD, COD, and TDS were removed from dairy wastewater. Batch, continuous, and continuous with the slow stirring systems were used. Live Azolla was an efficient, inexpensive, and affordable bio-adsorbent for dairy wastewater treatment.

Natural zeolite as a chromium VI removal agent in tannery effluents

This study concerns Cr(VI) removal using zeolites in a batch system for tannery effluent. In the initial stage, natural zeolite (ZN) and synthetic zeolite (ZS) were characterized, obtaining a Si/Al ratio of 4.64 and 1.60, and with predominant clinoptilolite and faujasite phases, the surface area of 9.34 and 25.82 m²/g and cation exchange capacity of 84.05 and 188.72 meq/100 g, respectively. Subsequently, ZN and ZS were activated with HCl and NaOH. Through preliminary tests, with a solution of K₂Cr₂O₇, it was determined that the highest Cr(VI) removal for both, ZN and ZS, was with NaOH activation, obtaining 82 and 56% removal, respectively. According to Ecuadorian regulations, the Cr(VI) concentration exceeds the maximum permissible limits on the tannery effluent. For this effluent, it was determined that the highest Cr(VI) removal, 45%, is obtained with 1 g of ZN activated with NaOH and 100 mL of effluent. With ZN-NaOH, removal tests were carried out in a fixed bed with 5, 10, and 20 g of natural zeolite. The natural zeolite also has chromium removal capacity in the bed system, achieving similar removals to those obtained in the batch experiments, but decreasing the treatment time. Thus, both natural and synthetic zeolites can remove Cr(VI) in tannery effluents, achieving this effluent with permissible limits.

Recent advances in the polyurethane-based adsorbents for the decontamination of hazardous wastewater pollutants

The pollution of aquatic systems with noxious organic and inorganic contaminants is a challenging problem faced by most countries. Water bodies are contaminated with diverse inorganic and organic pollutants originating from various diffuse and point sources, including industrial sectors, agricultural practices, and domestic wastes. Such hazardous water pollutants tend to accumulate in the environmental media including living organisms, thereby posing significant environmental health risks. Therefore, the remediation of wastewater pollutants is a priority. Adsorption is considered as the most efficient technique for the removal of pollutants in aqueous systems, and the deployment of suitable adsorbents plays a vital role for the sustainable application of the technique. The present review gives an overview of polyurethane foam (PUF) as an adsorbent, the synthesis approaches of polyurethane, and characterization aspects. Further emphasis is on the preparation of the various forms of polyurethane adsorbents, and their potential application in the removal of various challenging water pollutants. The removal mechanisms, including adsorption kinetics, isotherms, thermodynamics, and electrostatic and hydrophobic interactions between polyurethane adsorbents and pollutants are discussed. In addition, regeneration, recycling and disposal of spent polyurethane adsorbents are reported. Finally, key knowledge gaps on synthesis, characterization, industrial applications, life cycle analysis, and potential health risks of polyurethane adsorbents are discussed.

Advanced Oxidation Processes and Biotechnological Alternatives for the Treatment of Tannery Wastewater

The tannery industry is one of the economic sectors that contributes to the development of different countries. Globally, Europe and Asia are the main producers of this industry, although Latin America and Africa have been growing considerably in recent years. With this growth, the negative environmental impacts towards different ecosystem resources as a result of the discharges of recalcitrated pollutants, have led to different investigations to generate alternative solutions. Worldwide, different technologies have been studied to address this problem, biological and physicochemical processes have been widely studied, presenting drawbacks with some recalcitrant compounds. This review provides a context on the different existing technologies for the treatment of tannery wastewater, analyzing the physicochemical composition of this liquid waste, the impact it generates on human health and ecosystems and the advances in the different existing technologies, focusing on advanced oxidation processes and the use of microalgae. The coupling of advanced oxidation processes with biological processes, mainly microalgae, is seen as a viable biotechnological strategy, not only for the removal of pollutants, but also to obtain value-added products with potential use in the biorefining of the biomass.

Investigation of water treatment sludge from drinking water treated with Zetafloc 553I coagulant for phosphorus removal from wastewater

Water treatment sludge have shown promising results as adsorbent for phosphorus and sulphate removal from real wastewater. The study was conducted through batch kinetics and equilibrium isotherm modes. The chemical composition reveal that aluminium compounds were dominant in the fresh sludge and aluminium phosphates were also observed in the used sludge. The results reveal that Manganese was leached from the material at all pH values investigated with the highest level observed at pH 2 and all concentrations higher than the national standard of discharge into the relevant environment. The point of zero charge of the adsorbent was pH 8.04 and high adsorption capacities for both sulphate and phosphate ions were observed at pH values lower than this point. Batch kinetic results revealed 96.0 ± 3.0% sulphates removal in the first 30 min whereas the highest phosphates removal was 88.0 ± 4.0% attained at 300 min of the experiment. Pseudo - second order reaction fitted the data better than Pseudo-first order reaction. The percentage removal of sulphates was observed decreasing with increasing adsorbent dose after 2.4 g dose but removal increased with increasing media dosage for phosphorus. The equilibrium data was better described by Freundlich isotherm with constants relating to adsorption capacities being 6.76 and 6.2 L g^-1 respectively, for sulphates and phosphates adsorption. The adsorption capacity of phosphates was observed decreasing with increasing temperature, but the results were not conclusive in the case of sulphates. The results reveal that copper, nickel, and zinc have affinity for sulphates. The water treatment sludge can be used for phosphate and sulphate removal from wastewater though the leachability of manganese is a concern. Further investigations through fixed bed columns will need to be investigated before field trials. In conclusion, the sludge can be used as adsorbent for phosphorus and sulphates removal from wastewater through filtration and onsite treatment methods such as vertical or horizontal flow wetland systems. The success of the adsorbent will reduce the costs associated with its disposal which can also lead to leachability of metals into the environment with time.

The role of kaolin and kaolin/ZnO nanoadsorbents in adsorption studies for tannery wastewater treatment

In the present study, comparative studies of kaolin and kaolin/ZnO nanocomposites for the adsorption of Cr(VI), Fe(III), COD, BOD, and chloride from tannery wastewater were investigated. ZnO nanoparticles and kaolin/ZnO nanocomposites were prepared by sol-gel followed by wet-impregnation methods. The prepared adsorbents were characterized using different analytical tools such as X-ray diffraction, Fourier transforms infrared, high-resolution transmission electron microscopy, energy dispersive spectroscopy, selective area electron diffraction and Brunauer Emmett-Teller (BET) and X-ray Photoelectron Spectroscopy (XPS). The HRSEM/EDS/XPS analysis confirmed successful immobilization of clay structural network on the lattice layers of zincite hexagonal structure of ZnO nanoparticles. BET measurement showed an increase in the surface area of kaolin/ZnO nanocomposites (31.8 m²/g) when compared to kaolin (17 m²/g). Batch adsorption studies were carried out by varying the parameters such as contact time, adsorbent dosage and temperature. The maximum removal of Cr(VI) (100%), Fe(III) (98%), COD (95%), BOD (94%) and Chloride (78%) was obtained at 15 min by kaolin/ZnO composites. While 78% Cr(VI), 91% Fe(III), 91% COD, 89% BOD and 73% Chloride were removed by kaolin under the same conditions. The kaolin/ZnO nanocomposites exhibited better adsorption performance than kaolin due to higher surface area of the former than the latter. It was found that the Jovanovic isotherm model fitted the adsorption experimental data most with the highest correlation (R² > 0.99) for both nanoadsorbents and indicate the occurrence of adsorption on monolayer and heterogeneous surfaces. The mechanism for the adsorption of metal ions in tannery wastewater onto the nano-adsorbents was examined using Weber Morris intra-particle diffusion model and Boyd plot which showed that the adsorption process was both intra-particle and film diffusion controlled. The thermodynamic parameters such as enthalpy change showed that that adsorption of metal ions and other parameters was feasible, spontaneous and endothermic. The ZnO/clay nanocomposites exhibited excellent recyclable and re-useable properties even after six repeated applications and can, therefore, be applied in wastewater treatment for removal of heavy metals and other physicochemical parameters.

Removal of Ciprofloxacin with Aluminum-Pillared Kaolin Sodium Alginate Beads (CA-Al-KABs): Kinetics, Isotherms, and BBD Model

In recent years, the problem of water pollution caused by antibiotics has attracted wide attention. The common use of antibiotics represents a threat to both human health and environmental safety. The modification of kaolin clay is promising due to its high efficiency, easy operation, and low cost. In this study, a novel material, aluminum-pillared kaolin sodium alginate beads (CA-Al-KABs), was synthesized by gelling and solidification processes. The structure and chemical properties were characterized by various analytical methods. The influencing factors (such as adsorbent dosage, contacting time, pH, ion strength, temperature, and initial concentration) and adsorption mechanism of ciprofloxacin (CIP) were studied. Furthermore, adsorption kinetics, adsorption isotherms, and a Box–Behnken design (BBD) model were conducted. Moreover, CA-Al-KABs’ adsorption efficiency towards other antibiotics were also evaluated. The adsorption experiments showed that the acidic environment (pH = 4) was more favorable for the adsorption of ciprofloxacin. The adsorption kinetics of ciprofloxacin by CA-Al-KABs microspheres were confirmed to be more suitable with the pseudo-first-order kinetics model. The Langmuir isotherm model showed that the maximum adsorption capacity of CA-Al-KABs microspheres to ciprofloxacin was 68.36 mg/g at 308.15 K. The adsorption driving force of CIP near CA-Al-KABs may be the electrostatic attraction. Further, CIP could also form complexes with Ca2+ and Al—Al—OH on CA-Al-KABs, and thus CIP was attracted to the adsorbent. Adsorption thermodynamics showed that the adsorption process was exothermic, feasible, and spontaneous. In addition, the adsorption performance on other antibiotics indicated CA-Al-KABs’ broad application in the treatment of antibiotic wastewater.