Valorisation of post-sorption materials: Opportunities, strategies, and challenges

Soil application potential of post-sorbents produced by co-sorption of humic substances and nutrients from sludge anaerobic digestion reject water

This study introduces a novel soil conditioning approach using humic substances (HSs) and nutrients co-recovered from reject water from sewage sludge anaerobic digestion. For the first time, HSs and nutrients were simultaneously recovered through sorption on low-cost, environmentally inert materials: natural rock opoka (OP) and waste autoclaved aerated concrete (WAAC). This innovative application of OP and WAAC as carriers and delivery agents for soil-relevant substances offers potential for resource recovery and soil conditioning. Results indicate that the post-sorption opoka (PS-OP) and post-sorption waste autoclaved aerated concrete (PS-WAAC) effectively release retained HSs at 350-480 μg g⁻1 d⁻1, respectively. These materials also show potential as NPK fertilizers, releasing 280-430 μg g⁻1 d⁻1 N-NH₄⁺, 80-150 μg g⁻1 d⁻1 P-PO₄³⁻, and 270-350 μg g⁻1 d⁻1 K⁺. Additionally, PS-OP demonstrated promising fungicide properties, reducing P. diachenii growth by 31% at a concentration of 1 g L⁻1. A two-way ANOVA indicated that the effects of PS-OP and PS-WAAC on soil physicochemical and biological parameters varied with plant species. Both post-sorbents improved the quality of soil collected from sand mining area, increasing cation exchange capacity by 7%-85% and organic matter content by 10%-58%. They also enhanced the functional potential of soil microbial communities, increasing their metabolic activities by 23%-36% in soils sown with clover and by 33%-39% in soils sown with rapeseed. An opposite effect was observed in soils sown with sorghum, suggesting these amendments may not universally act as plant biostimulants. The effectiveness of these post-sorbents in enhancing plant growth varied depending on plant species and the mineral base of the post-sorbent. PS-OP increased the total length of clover and sorghum by 41% and 36%, and their fresh biomass by 82% and 80%, respectively. In turn, PS-WAAC increased the total length of clover and sorghum by 76% and 17%, and their fresh biomass by 29% and 15%, respectively. It was notably more effective than PS-OP for rapeseed. This study proposes a strategy to decrease reliance on non-renewable resources and costly sorbents while minimizing environmental impact. It shows that PS-OP and PS-WAAC can enhance soil quality, microbial activity, and plant growth. Given their origins, these amendments are recommended for soil remediation, particularly in degraded areas. Future research should focus on optimizing their application across various plant species to maximize effectiveness.

Comparing Conventional and Advanced Approaches for Heavy Metal Removal in Wastewater Treatment: An In-Depth Review Emphasizing Filter-Based Strategies

Various industrial activities release heavy metal ions into the environment, which represent one of the major toxic pollutants owing to their severe effects on the environment, humans, and all living species. Despite several technological advances and breakthroughs, wastewater treatment remains a critical global issue. Traditional techniques are dedicated to extracting heavy metal ions from diverse wastewater origins, encompassing coagulation/flocculation, precipitation, flotation, and ion exchange. Their cost, side toxicity, or ineffectiveness often limit their large-scale use. Due to their adaptable design, simple operation, and reasonable cost, membrane filtration and adsorption have proven their efficiency in removing metals from wastewater. Recently, adsorption-based filters have appeared promising in treating water. Within this range, filters incorporating natural, synthetic, or hybrid adsorbents present an appealing alternative to conventional approaches. This review aims to list and describe the conventional and advanced wastewater treatment methods by comparing their efficiency, cost, and environmental impact. Adsorption-based filters were highlighted due to the significant advantages they can provide.

Renewing Interest in Zeolites as Adsorbents for Capture of Cationic Dyes from Aqueous and Ethanolic Solutions: A Simulation-Based Insight into the Efficiency of Dye Adsorption in View of Wastewater Treatment and Valorization of Post-Sorption Materials

The impact of solvents on the efficiency of cationic dye adsorption from a solution onto protonated Faujasite-type zeolite (FAU-Y) was investigated in the prospect of supporting potential applications in wastewater treatment or in the preparation of building blocks for optical devices. The adsorption isotherms were experimentally determined for methylene blue (MB) and auramine O (AO) from single-component solutions in water and in ethanol. The limiting dye uptake (saturation capacity) was evaluated for each adsorption system, and it decreased in the order of MB-water > AO-water > AO-ethanol > MB-ethanol. The mutual distances and orientations of the adsorbed dye species, and their interactions with the oxygen sites of the FAU-Y framework, with the solvent molecules, and among themselves were inferred from Monte Carlo simulations and subsequently utilized to rationalize the observed differences in the saturation capacity. The dye-solvent competition and the propensity of the dyes to form compact pi-stacked dimers were shown to play an important role in establishing a non-uniform distribution of the adsorbed species throughout the porous space. The two effects appeared particularly strong in the case of the MB-water system. The necessity of including solvent effects in modeling studies is emphasized.

Advancements in application of modified biochar as a green and low-cost adsorbent for wastewater remediation from organic dyes

Synthetic organic dyes, which are resistant to biodegradation, pose a notable health risk, potentially leading to cancer and respiratory infections. Researchers have addressed this concern by exploring physicochemical methods to remove organic dyes from wastewater. A particularly promising solution involves modified biochar adsorbents, which demonstrate high efficiency in organic dye removal. Biochar, a charcoal-like material derived from biomass pyrolysis, offers advantages such as low cost, eco-friendliness, high efficiency and reusability. Beyond its role in sustainable soil remediation, biochar proves effective in removing organic dyes from wastewater after undergoing physical or chemical modification. Acid-base activation or metal-heteroatom impregnation enhances biochar's adsorption capacity. This comprehensive review examines the attributes of biochar, common methods for production and modification, and the impacts of raw materials, pyrolysis temperature, heating rate and residence time. It further elucidates the biochar adsorption mechanism in the removal of organic dyes, assessing factors influencing efficiency, including biochar feedstock, solution pH, adsorption temperature, particle size, initial dye concentration, biochar dosage and reaction time. It explores challenges, opportunities, reusability and regeneration methods of biochar in treating organic dye wastewater. It also discusses recent advances in organic dye removal using adsorption-based biochar. The review ultimately advocates for enhancing biochar's adsorption performance through post-modification.

Adsorbents for water decontamination: A recycling alternative for fiber precursors and textile fiber wastes

The exponential growth in textile fiber production and commensurate release of textile waste-based effluents into the environment has significant impacts on human wellbeing and the long-term planetary health. To abate these negative impacts and promote resource circularity, efforts are being made to recycle these waste materials via conversion into adsorbents for water decontamination. This review critically examines plant- and regenerated cellulose-based fibers for removing water pollutants such as heavy metals, dyes, pharmaceutical and petrochemical wastes. The review reveals that chemical modification reactions such as grafting, sulfonation, carboxymethylation, amination, amidoximation, xanthation, carbon activation, and surface coating are normally employed, and the adsorption mechanisms often involve Van der Waals attraction, electrostatic interaction, complexation, chelation, ion exchange, and precipitation. Furthermore, the adsorption processes and thus the adsorption mechanisms are influenced by factors such as surface properties of adsorbents, pollutant characteristics including composition, porosity/pore size distribution, specific surface area, hydrophobicity/hydrophobicity, and molecular interactions. Besides, feasibility of the approaches in terms of handling and reuse, environmental fate, and economic impact was evaluated, in addition to the performances of the adsorbents, the prospects, and challenges. As current cost analysis is non-exhaustive, it is recommended that researchers focus on extensive cost analysis to fully appreciate the true cost effectiveness of employing these waste materials. In addition, more attention must be paid to potential chemical leaching, post-adsorption handling, and disposal. Based on the review, fiber precursors and textile fiber wastes are viable alternative adsorbents for sustainable water treatment and environmental management, and government entities must leverage on these locally accessible materials to promote recyclability and circularity.

Acetamiprid's degradation products and mechanism: Part II - Inert atmosphere and charge storage

Reuse and/or recycling of spent adsorbents is taking a central role in modern thinking and catalyzed carbonization is the way forward. Herein we explore the carbonization of adsorbed acetamiprid, in an inert atmosphere, as a way of recycling and producing nitrogen-rich carbon material for potential use in supercapacitors. Added value material and the reuse of the adsorbent were achieved by carbonization at 700 °C under argon. The formation of a nitrogen-doped carbon layer as an active material on the adsorbent, bonded through a C-Si linkage, has been conclusively verified through elemental composition quantification using XPS and EDX measurements. Two-stage catalytic decomposition and condensation of the adsorbed pesticide is followed by TGA and TPD-MS. Attained carbon-based materials give stable Faradaic capacitance with a slight dependency on the number of adsorbing cycles. Capacitance calculated with respect to the adlayer carbon material reaches values as high as 610 F g-1. Galvanostatic Charge/Discharge measurement confirmed the stability of explored materials with a slight increase in capacitance over 1000 cycles. The presented results envisage electroactive materials preparation from environmental pollutants, adding value to spent adsorbents.

Triggering antibacterial activity of a common plant by biosorption of selected heavy metals

The presented study proposes an efficient utilization of a common Thymus serpyllum L. (wild thyme) plant as a highly potent biosorbent of Cu(II) and Pb(II) ions and the efficient interaction of the copper-laden plant with two opportunistic bacteria. Apart from biochars that are commonly used for adsorption, here we report the direct use of native plant, which is potentially interesting also for soil remediation. The highest adsorption capacity for Cu(II) and Pb(II) ions (qe = 12.66 and 53.13 mg g-1, respectively) was achieved after 10 and 30 min of adsorption, respectively. Moreover, the Cu-laden plant was shown to be an efficient antibacterial agent against the bacteria Escherichia coli and Staphylococcus aureus, the results being slightly better in the former case. Such an activity is enabled only via the interaction of the adsorbed ions effectively distributed within the biological matrix of the plant with bacterial cells. Thus, the sustainable resource can be used both for the treatment of wastewater and, after an effective embedment of metal ions, for the fight against microbes.

Aminated Rapeseed Husks (Brassica napus) as an Effective Sorbent for Removing Anionic Dyes from Aqueous Solutions

The study investigated the effect of modifying rapeseed husks with ammonia and epichlorohydrin on their sorption capacity against anionic reactive dyes: Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84). Its scope included sorbents characterization (FTIR, pHPZC), determination of pH influence on the sorption effectiveness of dyes, the adsorption kinetics of dyes, as well as the maximum sorption capacity. The study proved that the reaction of rapeseed husk biomass with ammonia can lead to its amination, namely to the introduction of amine functional groups into the material's structure. The sorption effectiveness of RB5 and RY84 on the tested sorbents was the highest in the pH range of 2-3. The dye sorption kinetics was well described by the pseudo-second-order model. The sorption equilibrium time ranged from 90 to 180 min, and depended on the initial concentration of dyes and the number of amino groups on the sorbent's surface. The most efficient of the sorbents tested were rapeseed husks pre-activated with epichlorohydrin and then aminated with ammonia. Their sorption capacity determined for RB5 and RY84 was 135.83 mg/g and 114.23 mg/g, respectively, which was 794% and 737% higher than that of the non-modified husks.

Biochar Derived from Post-Adsorbent for Immobilizing Cu and Cd in Sediment: The Effect on Heavy Metal Species and the Microbial Community Composition

Many biomass wastes or their modified forms have been investigated as heavy metal adsorbents. However, less emphasis has been placed on post-adsorbent management or possible further utilization. In this study, biochar (BC) derived from modified bamboo adsorbent after the adsorption of Cu from an aqueous solution was used for the in situ remediation of lake sediment contaminated with Cd and Cu. The results indicated that the Cu concentration was extremely low (≤0.015 mg/L), while Cd was not detected in the overlying water or the interstitial water after the 90-day BC treatment. The pH value (7.5-8.1) slightly increased, and the toxicity characteristic leaching procedure (TCLP) leachability of the Cu and Cd in the sediment decreased overall. Cu and Cd were preferentially transformed into more stable species. The findings highlighted the potential possibility of BC derived from post-adsorbent being used for sediment remediation. However, the BC addition produced significant effects on the sediment microbial activity and community structure. In general, with an increase in BC, the urease activity increased, while the alkaline phosphatase and invertase activity decreased, which could be attributed to the BC itself. In addition, significant changes in both bacterial and fungal genera were observed. Hence, a cautious approach should be taken in the practical application of BC.

Spectral evidence of acetamiprid's thermal degradation products and mechanism

Herein we unequivocally identify the mechanism of zeolite-catalysed thermal degradation of pesticide, employing Fourier-transform infrared spectroscopy (FTIR), Raman and mass spectrometry following temperature decomposition (TPDe/MS). We demonstrate that Y zeolite can effectively adsorb a significant amount of acetamiprid both in a single trial (168 mg/g) and in 10 cycles (1249 mg/g) with intermittent thermal regeneration at 300 °C. Sectional vibrational analysis of acetamiprid two-stage thermal degradation is performed for pristine and supported pesticide. The acetamiprid Raman spectral changes appear at 200 °C, while partial carbonization occurs at 250 °C. The gradual disappearance of the FTIR bands of acetamiprid is seen up to 270 °C when two Raman signature bands for carbonised material emerged. The TPDe/MS profiles reveal the evolution of mass fragments - in the first step, cleavage of the CC bond occurs between the aromatic core of the molecule and its tail-end, followed by cleavage of the CN bond. The mechanism of adsorbed acetamiprid degradation follows the same step, at significantly lower temperatures, as the process is catalysed by the interaction of acetamiprid nitrogens and zeolite support. Reduced temperature degradation allows for a quick recovery process that leaves 65% efficacy after 10 cycles. After numerous cycles of recovery, a subsequent one-time heat treatment at 700 °C completely restores initial efficacy. The efficient adsorption, novel details on degradation mechanism and ease of regeneration procedure place the Y zeolite at the forefront of future all-encompassing environmental solutions.

Exploration of Reactive Black 5 Dye Desorption from Composite Hydrogel Beads—Adsorbent Reusability, Kinetic and Equilibrium Isotherms

A low-cost adsorbent was prepared by using cherry stones powder and chitosan and used to retain Reactive Black 5 dye from aqueous solution. Then, the spent material was submitted to a regeneration process. Five different eluents (water, sodium hydroxide, hydrochloric acid, sodium chloride and ethanol) were tested. Among them, sodium hydroxide was selected for an advanced investigation. Values of three working conditions, namely the eluent volume, its concentration and the desorption temperature, were optimized by Response Surface Methodology-Box–Behnken Design. In the established settings (NaOH volume: 30 mL, NaOH concentration: 1.5 M, working temperature: 40 °C), three successive cycles of adsorption/desorption were conducted. The analysis performed by Scanning Electron Microscopy and by Fourier Transform Infrared Spectroscopy revealed the evolution of the adsorbent throughout the dye elution from the material. Pseudo-second-order kinetic model and Freundlich equilibrium isotherm were able to accurately describe the desorption process. Based on the acquired results, our outcomes sustain the suitability of the synthesized material as dye adsorbent and the possibility of efficaciously recycling and reusing it.

Hydrothermal recycling of carbon absorbents loaded with emerging wastewater contaminants

Adsorption using carbon materials is one of the most efficient techniques for removal of emerging contaminants such as pharmaceuticals from wastewater. However, high costs are a major hurdle for their large-scale application in areas currently under economic constraints. While most research focuses on decreasing the adsorbent price by increasing its capacity, treatment costs for exhausted adsorbents and their respective end-of-life scenarios are often neglected. Here, we assessed a novel technique for recycling of exhausted activated biochars based on hydrothermal treatment at temperatures of 160-320 °C. While a treatment temperature of 280 °C was sufficient to fully degrade all 10 evaluated pharmaceuticals in solution, when adsorbed on activated biochars certain compounds were shielded and could not be fully decomposed even at the highest treatment temperature tested. However, the use of engineered biochar doped with Fe-species successfully increased the treatment efficiency, resulting in full degradation of all 10 parent compounds at 320 °C. The proposed recycling technique showed a high carbon retention in biochar with only minor losses, making the treatment a viable candidate for environmentally sound recycling of biochars. Recycled biochars displayed potentially beneficial structural changes ranging from an increased mesoporosity to additional oxygen bearing functional groups, providing synergies for subsequent applications as part of a sequential biochar system.

Nutrient Recovery from Digestate of Agricultural Biogas Plants: A Comparative Study of Innovative Biocoal-Based Additives in Laboratory and Full-Scale Experiments

Nutrients can be recovered from the digestate of an agricultural biogas plant in the form of solid fraction and serve as crop fertilizers. Removal of suspended solids with screw press separators is the most commonly used technique for treating digestate from biogas plants. To increase separation efficiency and nutrient transfer to the solid phase during separation, eight biocoal-based additives were investigated, which were based on beech wood and produced by pyrolysis at temperatures of 350 °C and 600 °C. Four of the biocoals were impregnated with CaCl₂ or MgCl₂ before pyrolysis. The reaction time between the additives and the digestate varied from 5 min to 2 weeks. The application of MgCl₂-impregnated biocoal synthesized at 600 °C for 20 h increased the nutrient removal efficiency by 76.33% for ammonium and 47.15% for phosphorus, compared to the control (the untreated digestate).

Potential applications of spent adsorbents and catalysts: Re-valorization of waste

Water pollution has increased with the growth of human population and its industrial activities. Textile effluents constitute a particular threat due to the presence of heavy metals and dyes. Adsorption is one of the most applied technologies in contaminant removal owing to its high efficiency, low cost, practical implementation and possibility to operate in several experimental conditions. However, this process implies the generation of spent materials, representing a limitation to scale-up. Although the applications of exhausted solids in effluent treatments have not been extensively reviewed before, their reutilization appears to be an environmentally and economically attainable alternative. This work summarizes the potential value of solids post-use. The open literature reports that spent adsorbents based on polysaccharides with iron oxides may adsorb up to 1 g g^-1 of organic pollutants and up to near 100% of metallic ions from wastewater (Cu²⁺, Cd²⁺, Zn²⁺, Pb²⁺). The studied conditions vary from 30 to 60 °C, 0,05 to 6 g L^-1 of adsorbent, 10 mg L^-1 to 250 mg L^-1 of organic pollutants (dyes) and pH between 2 and 8. Spent adsorbents in dye removal have proven to have near 95% efficiency in metallic ion adsorption. Otherwise, the spent solids could be applied to remove Ca²⁺ and Mg²⁺ to decrease the hardness of water. Furthermore, at the end-of-life, these materials could be used in cement and ceramic production. To achieve these aims, it is necessary to design the bioadsorbents and biocatalysts considering not only their primary uses (as adsorbent of organic pollutants), but also secondary applications (as toxic metal or hardness removal) and even their final destination (as additive in ceramic or cement production). Finally, further studies are required on the composition, properties, stability at long-term and the life-cycle cost of these materials when they are applied in the construction industry.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

How to Obtain Maximum Environmental Applicability from Natural Silicates

Unmodified natural silicates (bentonite, kaolin, clinoptilolite and diatomites) were tested as adsorbents for the organic pollutants in water tables using Methylene Blue (MB) as the model adsorbate. Among the selected materials, bentonite adsorbed as much as 237 mg/g, confirming its excellent suitability for pollutant removal. Spectral evidence confirmed successful MB immobilization at the bentonite surface. Furthermore, the thermal treatment of MB-saturated adsorbent in an inert atmosphere at 700 °C produced a carbon/silicate composite. EDX confirmed the formation of the nitrogen-doped carbon overlay on the silica scaffold and the obtained composite material was probed as an electrode material for oxygen reduction in an alkaline solution. Reduction proceeded via a two-electron mechanism with the main product being HO2−, a known nucleophile, which was subsequently used to degrade/demethylate MB. The composite showed a considerable 70% MB removal rate after an hour of electrochemical treatment. The synergy between the processes of adsorption of MB and the surface-generated HO2− dictates the efficiency of the method and points to a possible route for spent adsorbent reuse in the form of a durable product for environmental protection.

Nanocellulose for Sustainable Water Purification

Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure-property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.

Valorization of agro-industrial biowaste to green nanomaterials for wastewater treatment: Approaching green chemistry and circular economy principles

Water pollution is one of the most critical issues worldwide and is a priority in all scientific agendas. Green nanotechnology presents a plethora of promising avenues for wastewater treatment. This review discusses the current trends in the valorization of zero-cost, biodegradable, and readily available agro-industrial biowaste to produce green bio-nanocatalysts and bio-nanosorbents for wastewater treatment. The promising roles of green bio-nanocatalysts and bio-nanosorbents in removing organic and inorganic water contaminants are discussed. The potent antimicrobial activity of bio-derived nanodisinfectants against water-borne pathogenic microbes is reviewed. The bioactive molecules involved in the chelation and tailoring of green synthesized nanomaterials are highlighted along with the mechanisms involved. Furthermore, this review emphasizes how the valorization of agro-industrial biowaste to green nanomaterials for wastewater treatment adheres to the fundamental principles of green chemistry, circular economy, nexus thinking, and zero-waste manufacturing. The potential economic, environmental, and health impacts of valorizing agro-industrial biowaste to green nanomaterials are highlighted. The challenges and future outlooks for the management of agro-industrial biowaste and safe application of green nanomaterials for wastewater treatment are summarized.

Recent Developments in the Application of Bio-Waste-Derived Adsorbents for the Removal of Methylene Blue from Wastewater: A Review

Over the last few years, various industries have released wastewater containing high concentrations of dyes straight into the ecological system, which has become a major environmental problem (i.e., soil, groundwater, surface water pollution, etc.). The rapid growth of textile industries has created an alarming situation in which further deterioration to the environment has been caused due to substances being left in treated wastewater, including dyes. The application of activated carbon has recently been demonstrated to be a highly efficient technology in terms of removing methylene blue (MB) from wastewater. Agricultural waste, as well as animal-based and wood products, are excellent sources of bio-waste for MB remediation since they are extremely efficient, have high sorption capacities, and are renewable sources. Despite the fact that commercial activated carbon is a favored adsorbent for dye elimination, its extensive application is restricted because of its comparatively high cost, which has prompted researchers to investigate alternative sources of adsorbents that are non-conventional and more economical. The goal of this review article was to critically evaluate the accessible information on the characteristics of bio-waste-derived adsorbents for MB's removal, as well as related parameters influencing the performance of this process. The review also highlighted the processing methods developed in previous studies. Regeneration processes, economic challenges, and the valorization of post-sorption materials were also discussed. This review is beneficial in terms of understanding recent advances in the status of biowaste-derived adsorbents, highlighting the accelerating need for the development of low-cost adsorbents and functioning as a precursor for large-scale system optimization.

Efficient Removal of Organic Contaminants from Aqueous Solution by Highly Compressible Reusable Three-Dimensional Printing Sponges

Adsorption is considered to be one of the most effective and economically viable technologies for removing contaminants from the environment. However, the disadvantages of its high-cost complicated process and difficulty in efficient recycling limit its practical application. Herein, a thermoplastic elastomer-polyvinyl alcohol composite (LAY-FOMM 60) sponge three-dimensional structure (3D printing sponge) was fabricated by the fused filament fabrication combined with water erosion technique. The size and shape of the resultant sponge were tailored, and the batch of adsorption/desorption experiments of Rhodamine B (RhB) onto the sponge was performed. The results show that the adsorption of RhB on the 3D printing sponge was mainly via physical adsorption, and pseudo-second-order and Langmuir models exhibited good correlation with the adsorption kinetic and isotherm data, respectively. Thermodynamic parameters suggest that the adsorption is an endothermic and spontaneous process. It is worth to note that the adsorption/desorption efficiency can be raised by compression. This results in high efficiency and low cost for adsorption/desorption process and benefit for regeneration of the adsorbent. The adsorption capacity was maintained over 85% of the initial capacity after being used for five cycles. The approach provides a simple strategy for manufacturing customizable porous adsorbent materials that meet various water treatment requirements.

Production of zeolitic materials in pilot scale based on coal ash for phosphate and potassium adsorption in order to obtain fertilizer

The use of different types of zeolites (X, Na-P1, and 4A) synthesized by different methods and scales were tested in this work to adsorb nutrients present in synthetic solutions and industrial effluents for later application as fertilizer. Modifications with calcium chloride were performed on the zeolite with the best performance to increase its adsorption capacity. The best performing zeolite was type X (ZXH) produced on a pilot scale by the hydrothermal process. Its adsorption capacity without modification was 149 mg P-PO₄/g zeolite and 349 mg K/g zeolite. With the change, there was a fourfold increase in these results, which were up to threefold higher than reported in the literature. The kinetic model that best characterized the adsorption process was the intraparticle diffusion model, and the equilibrium isotherm was that of Freundlich. The adsorption tests performed with industrial effluent showed high removal of the nutrients of interest (> 90% for PO₄^3- and > 95% for K⁺). The desorption tests with zeolites nutrient-loaded from synthetic solutions showed 13 to 24% PO₄^3- and 14 to 47% K⁺ release within 24 h, while for zeolite nutrient-loaded from effluent the release were 7 and 100% for PO₄^3- and K⁺, respectively. The results we obtained in this work indicated the potential use of zeolites in the treatment of effluent and its application as a fertilizer.

Study of the removal of ciprofloxacin by Zn–GO@SA aerogel microspheres

Zn–GO@SA aerogel microspheres were prepared via a simple ionic–gel method, showing excellent adsorption performance toward ciprofloxacin and easy separation from solution.

Electrochemical energy storage electrodes from fruit biochar

This review investigates the electrochemical energy storage electrode (EESE) as the most important part of the electrochemical energy storage devices (EES) prepared from fruit-derived carbon. The EES devices include batteries, supercapacitors, and hybrid devices that have various regular and advanced applications. The preparation of EESE from fruit wastes not only reduce the price of the electrode but also lead to enhance the electrochemical properties of the electrode. The astonishing results of fruits biochar at electrochemical analyses guarantee the performance of these electrodes as EESE. Also, using fruit waste as the precursor of the EESE due to protect the environment and reduce environmental pollutions.

Activated biochar derived from Opuntia ficus-indica for the efficient adsorption of malachite green dye, Cu+2 and Ni+2 from water

Applicability of biochar in water treatment is gaining interest due to its sustainability and low production cost. Herein, the biochar (BC) and activated biochar (ABC) synthesized from the cladodes of Opuntia ficus-indica (OFI) cactus were evaluated as a renewable adsorbent for adsorption of organic as well as inorganic pollutants including malachite green (MG) dye, Cu⁺² and Ni⁺² heavy metals. The modification of biochar with NaOH resulted higher surface basicity regarding more oxygen containing functional groups on the surface. The maximum uptake of 1341 mg g^-1, 49 mg g^-1 and 44 mg g^-1 onto activated biochar for malachite green dye, Cu⁺² and Ni⁺² was acquired through the best fitted Langmuir isotherm model. Pseudo-second-order and Elovich models were found to provide a suitable fit indicating towards the chemisorption of all three components. Film diffusion and chemisorption are the main steps in adsorption of MG dye and heavy metals on activated biochar. The adsorption mechanisms were also hypothesized for adsorption of MG dye, Cu⁺² and Ni⁺². The remarkable adsorption capacities with higher reusability characteristics for adsorption of organic pollutants as well as inorganic heavy metals entrusts this activated biochar as a potential cost-effective adsorbent to mitigate water pollution issue.

Critical review of magnetic biosorbents: Their preparation, application, and regeneration for wastewater treatment

The utilisation of magnetic biosorbents (metal or metal nanoparticles impregnated onto biosorbents) has attracted increasing research attention due to their manipulable active sites, specific surface area, pore volume, pore size distribution, easy separation, and reusability that are suitable for remediation of heavy metal(loid)s and organic contaminants. The properties of magnetic biosorbents (MB) depend on the raw biomass, properties of metal nanoparticles, modification/synthesis methods, and process parameters which influence the performance of removal efficiency of organic and inorganic contaminants. There is a lack of information regarding the development of tailored materials for particular contaminants and the influence of specific characteristics. This review focuses on the synthesis/modification methods, application, and recycling of magnetic biosorbents. In particular, the mechanisms and the effect of sorbents properties on the adsorption capacity. Ion exchanges, electrostatic interaction, precipitation, and complexation are the dominant sorption mechanisms for ionic contaminants whereas hydrophobic interaction, interparticle diffusion, partition, and hydrogen bonding are the dominant adsorption mechanisms for removal of organic contaminants by magnetic biosorbents. In generally, low pyrolysis temperatures are suitable for ionic contaminants separation, whereas high pyrolysis temperatures are suitable for organic contaminants removal. Additionally, magnetic properties of the biosorbents are positively correlated with the pyrolysis temperatures. Metal-based functional groups of MB can contribute to an ion exchange reaction which influences the adsorption capacity of ionic contaminants and catalytic degradation of non-persistent organic contaminants. Metal modified biosorbents can enhance adsorption capacity of anionic contaminants significantly as metal nanoparticles are not occupying positively charged active sites of the biosorbents. Magnetic biosorbents are promising adsorbents in comparison with other adsorbents including commercially available activated carbon, and thermally and chemically modified biochar in terms of their removal capacity, rapid and easy magnetic separation which allow multiple reuse to minimize remediation cost of organic and inorganic contaminants from wastewater.

A Review of Non-Soil Biochar Applications

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Shape-tunable CuO-Nd(OH)3 nanocomposites with excellent adsorption capacity in organic dye removal and regeneration of spent adsorbent to reduce secondary waste

Herein, we report for the first time, the synthesis of CuO-Nd(OH)₃ nanocomposites via a co-precipitation method coupled with the hydrothermal aging process. Varying the pH of the reaction medium, the shape of the nanocomposites could be controlled which determines their surface areas. These CuO-Nd(OH)₃ nanocomposites exhibit very high adsorption capacity with successful removal of ∼ 97% of brilliant blue G (BBG) from water in 180 min under ambient condition. The adsorption process primarily follows Lagergren pseudo-first-order kinetics. The Langmuir isotherm model fits well with a very high monolayer adsorption capacity of 394.1 mg g^-1 at 30 °C. The mechanistic study supports chemisorption-type adsorption between the dye molecule and the adsorbent. Regeneration of the spent adsorbent makes the whole process cyclic and eco-friendly.

Insights into the mechanism of methylene blue removed by novel and classic biochars

The adsorption behavior and the underlying mechanism of methylene blue (MB) sorption on biochars prepared from different feedstocks at 500 °C were evaluated. The biochar feedstocks included Magnolia grandiflora Linn. leaves biochar (MBC), pomelo (Citrus grandis) peel biochar (PBC) and badam shell biochar (BBC). The results of characterizing and analyzing the samples showed that different biochars had different effects on the adsorption of MB. It could be found that MBC had the best adsorption effect on MB due to its largest average pore diameter of 5.55 nm determined by Brunauer-Emmett-Teller analysis. Under the optimal conditions, the maximum adsorption capacities of BBC, PBC and MBC were 29.7, 85.15 and 99.3 mg/g, respectively. The results showed that the amount of adsorption was affected by the pH value. The maximum adsorption capacity of MBC was 46.99 mg/g when it was at pH of 3, whereas for the same experimental conditions the maximum adsorption capacity of BBC and PBC was 25.29 mg/g at pH of 11 and 36.08 mg/g at pH of 7, respectively. Therefore, MBC was found to be a most efficient low-cost adsorbentl for dye wastewater treatment compared with BBC and PBC, and it had the best removal effect under acidic conditions.

Continuous dye adsorption and desorption on an invasive macrophyte (Salvinia minima)

The continuous adsorption-desorption of methylene blue (MB) on an invasive macrophyte, Salvinia minima, was investigated in fixed-bed columns. The effects of bed depth (h) (9.30, 18.70, and 28 cm), inlet dye concentration (C₀) (51 ± 1.20, 154 ± 2.00, and 250 ± 1.50 mg L^-1), and flow rate (Q) (7 and 14 mL min^-1) on dye removal and breakthrough curves were assessed. Thomas, modified dose-response (MDR) and bed depth service time (BDST) models were fitted to the experimental data. Desorption and regeneration studies were also performed. The breakthrough time was affected by h, C₀, and Q. The dynamic bed capacity at the breakthrough point (q_b) increased with increasing h but decreased with increasing C₀ and Q. Dynamic bed capacities (q_e) from 318 to 322 mg g^-1 were achieved at h = 28 cm, C₀ = 154 ± 2.0, or 250 ± 1.50 mg L^-1, independently of the Q value. High MB removals were also observed (75-78%). FTIR analysis revealed that hydroxyl and carboxyl groups could be involved in dye adsorption. MDR and BDST models were both successfully used to predict the breakthrough curves of MB adsorption onto S. minima. A high regeneration efficiency (> 87%) was obtained after three adsorption-desorption cycles. These results confirm that the use of S. minima biomass could be a very efficient and eco-friendly alternative for MB adsorption in continuous mode.

Dynamics and Kinetics of Cupric Ion Removal from Wastewaters by Tunisian Solid Crude Olive-Oil Waste

The present paper aims to develop a low cost, efficient, and environmentally-friendly process to purify (industrial) waters contaminated by copper by the use of oil mill wastes, through kinetic, thermodynamic, and equilibrium investigations. To do so, the raw adsorbent was characterized using different analytical techniques including X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Then, the interaction between copper and olive residues were examined during batch adsorption tests at various operating parameters, such as pH, initial concentration, contact time, and particle size. Kinetic data were best fitted with Broeurs-Sotolongo kinetic model. Additionally, it was found that film and intraparticle diffusion steps controlled simultaneously the mass transfer of copper onto olive mill solid waste. Among the eight tested models, Broeurs-Sotolongo isotherm suited the most the sorption, with regards to the function errors analysis. It was deduced that the adsorption of copper does not involve chemical bonds with high energy which allows easier regeneration steps and higher number of biosorbent regeneration cycles without any need for applying high temperature in the desorption reaction systems. The adsorption capacity (18.93 mg/g) calculated on the basis of this model was close to the experimental value (18.4 mg/g) but more interestingly it brought up that 50% of the generated amounts of olive wastes in Tunisia could eliminate 1.84 kTons of copper from industrial waters.

Valorisation possibilities of exhausted biosorbents loaded with metal ions - A review

Biosorption is considered one of the most promising methods for removal of metal ions from aqueous effluents, due to its low-cost and eco-friendly characteristics. However, the exhausted biosorbents loaded with metal ions, obtained at the end of biosorption processes, are still a problem which should be solved to increase the applicability of biosorption on an industrial scale. In this study are examined three possibilities for the valorisation of exhausted biosorbents loaded with metal ions, namely: (i) regeneration and reuse of biosorbents in multiple biosorption cycles, (ii) the use of exhausted biosorbents as fertilizers for soils poor in essential microelements, and (iii) the pyrolysis of exhausted biosorbents, under well defined conditions. The main advantages and disadvantages of each valorisation possibility are reviewed in order to find the best way to use these cheap materials in accordance with the principles of the circular economy and thereby contributing to the development of sustainable biosorption technology.

Silver removal from aqueous solution by biochar produced from biosolids via microwave pyrolysis

The contamination of water with silver has increased due to the widespread applications of products with silver employed as antimicrobial agent. Adsorption is a cost-effective method for silver removal from aqueous solution. In this study biochar, produced from the microwave assisted pyrolysis of biosolids, was used for silver removal from an aqueous solution. The adsorption kinetics, isotherms and thermodynamics were investigated to better understand the silver removal process by biochar. X-ray diffraction results demonstrated that silver removal was a combination two consecutive mechanisms, reduction and physical adsorption. The Langmuir model fitted the experimental data well, showing that silver removal was predominantly a surface mechanism. The thermodynamic investigation demonstrated that silver removal by biochar was an exothermic process. The final nanocomposite Ag-biochar (biochar plus silver) was used for methylene blue adsorption and photodegradation. This study showed the potential of using biochar produced from biosolids for silver removal as a promising solution to mitigate water pollution and an environmentally sustainable approach for biosolids management and re-use.

Biosorption of Zn(II) from industrial effluents using sugar beet pulp and F. vesiculosus: From laboratory tests to a pilot approach

The aim of this work was to demonstrate the feasibility of the application of biosorption in the treatment of metal polluted wastewaters through the development of several pilot plants to be implemented by the industry. The use as biosorbents of both the brown seaweed Fucus vesiculosus and a sugar beet pulp was investigated to remove heavy metal ions from a wastewater generated in an electroplating industry: Industrial Goñabe (Valladolid, Spain). Batch experiments were performed to study the effects of pH, contact time and initial metal concentration on metal biosorption. It was observed that the adsorption capacity of the biosorbents strongly depended on the pH, increasing as the pH rises from 2 to 5. The adsorption kinetic was studied using three models: pseudo first order, pseudo second order and Elovich models. The experimental data were fitted to Langmuir and Freundlich isotherm models and the brown alga F. vesiculosus showed higher metal uptake than the sugar beet pulp. The biomasses were also used for zinc removal in fixed-bed columns. The performance of the system was evaluated in different experimental conditions. The mixture of the two biomasses, the use of serial columns and the inverse flow can be interesting attempts to improve the biosorption process for large-scale applications.

Fabrication of Stable and Regenerable Amine Functionalized Magnetic Nanoparticles as a Potential Material for Pt(IV) Recovery from Acidic Solutions

MnFe₂O₄@SiO₂-NH₂ magnetic nanocomposite (AFMNC) adsorbent with a particle size of ∼50 nm was successfully synthesized using a facile approach. The as-prepared composite particles showed a fast binding of Pt(IV) with easy magnetic solid-liquid separation. The kinetic data were fitted to both pseudo-first and second-order rate models, indicating that AFMNC exhibited a much higher rate of Pt(IV) binding (0.125 g mg^-1 min^-1) compared to that of commercial ion-exchange resin Amberjet 4200 (0.0002 g mg^-1 min^-1). The equilibrium adsorption data were fitted to the Langmuir isotherm model with a relatively high sorption capacity of 380 mg/g. Scanning transmission electron microscopy analysis demonstrated the presence of platinum chloride after sorption on AFMNC, suggesting an adsorbate-adsorbent anion-exchange interaction. In addition, due to its magnetic characteristics, AFMNC can be easily separated from the aqueous medium after the sorption process. The novel nanocomposite may facilitate recovery of Pt(IV) from waste solutions.