Simultaneous adsorption of phosphate and tetracycline by calcium modified corn stover biochar: Performance and mechanism

Sustainable enhancement of biochar and biochar composite properties through temperature-controlled pyrolysis of agricultural biomass and marble waste

This study explores the utilization of cocoa pod husk, coconut shell, and marble waste as raw materials to prepare biochar and biochar/marble composites adsorbents. The influence of pyrolysis temperatures 500, 600, and 700 °C was evaluated to obtain more information about the thermal behavior of these adsorbents and to precisely engineer the physicochemical properties of biochar and its composites, facilitating the development of highly efficient and sustainable materials, while maximizing process efficiency and resource utilization. The adsorbent samples were analyzed using elemental analysis, surface area and porosity measurements, infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetry, and point of zero charge analysis. Results indicated that higher pyrolysis temperatures enhanced porosity, aromaticity, and surface functional groups. Increasing the temperature from 500 to 700 °C led to a decrease in biochar yields, with coconut biochar yields declining from 31.7 % to 28.5 % and cocoa biochar from 36.1 % to 31.2 %. In contrast, composite yields exceeded 50 % due to marble content. The addition of marble significantly improved the specific surface area (SSA) and porosity, with the SSA values of biochar ranging from 12.0 m2 g-1 to 29.1 m2 g-1 and the SSA of the biochar composite ranging from 47.3 m2 g-1 to 95.1 m2 g-1. Ca(OH)2 and MgO phases were identified on the surfaces of the biochar composites, demonstrating the capacity to facilitate cation exchange with adsorbates (e.g., herbicides), thereby enhancing the adsorption process. These properties contribute to the development of strategic, eco-friendly, and highly efficient adsorbent materials.

Structural engineering on keratin to tailor porous structure of biochar for high-efficiency tetracycline removal

The inherent complexity of biomass poses challenges in designing or controlling the porous structure of biochar after intense activation reactions. Here, structural engineering on keratin was developed to modulate the porous structure of bovine-horn-derived biochar via the controllable coupled oxidation and pyrolysis reactions. The possible chemical reaction pathways of the coupled oxidation and pyrolysis reactions were proposed. The structural transition involving β-sheets and random coils and the chemical changes in sulfur-containing functional groups regulate the rigidity of keratin molecules, impacting the pore formation of gas expansion. After the coupled oxidation and pyrolysis reactions at 180 °C, the resulting material contains approximately 35 % β-sheet content and 0.915 wt% oxidative sulfur. These characteristics contribute to production of micro-/meso-porous biochar, which has a mesopore content of 61 %, a specific surface area exceeding 2800 m2 g-1, and an average pore size of 2.68 nm. The obtained porous biochar shows a high adsorption capacity (1362.5 mg g-1) for tetracycline owing to the tailored micro-/meso-porous structures, as analyzed through model fitting and density functional theory calculations. This work provides a facile structural engineering strategy towards biomass for the sustainable and controllable production of high-performance porous carbon materials.

Chitosan hydrogel membrane embedded by metal-modified biochars for slow-release fertilizers

Slow-release fertilizers show great promise for advancing agricultural sustainability by enhancing nutrient efficiency and mitigating environmental impacts. Herein, we propose an approach that embeds chitosan hydrogel membranes with metal-modified biochars to encapsulate N-P-K compound fertilizers, referred to as CS-MBC-SRFs. Our results demonstrate that CS-MBC-SRFs exhibit superior slow-release performance for N, P, and K compared to others (commercial NPK compound fertilizers, chitosan-coated, and biochar-embedded chitosan-coated fertilizers). Over a 33-day soil column test, CS-MBC-SRFs showed cumulative leaching ratios of <8.93 % for N, 18.4 % for P, and 14.4 % for K. Incorporating metal-modified biochar into the chitosan hydrogel membrane significantly enhances its swelling and mechanical properties while maintaining biodegradability and water-retention capacity. Mechanistic investigations reveal that nutrient release from CS-MBC-SRFs primarily occurs via diffusion through the hydrogel membrane, with the metal-modified biochar surface enhancing nutrient adsorption and delaying release. Additionally, the metal-modified biochars improved swelling and mechanical properties of the chitosan hydrogel membrane, significantly reducing nutrient diffusion. Pot tests demonstrated that CS-MBC-SRFs effectively promoted chili plant growth, ensuring high N-P-K utilization and improving chili fruit nutritional indices. Economic analysis further highlights the promising application prospects of CS-MBC-SRFs.

Phosphorus recovery and reuse: Innovating with biochar in the circular economy

Global challenges of phosphorus pollution and scarcity underscore an urgent need for the efficient recycling of this critical resource. Biochar, a sustainable and economical material, has demonstrated significant potential as an adsorbent for phosphorus, offering a viable solution for its recovery from wastewater. Various techniques have been explored to improve the ability of biochar to adsorb inorganic phosphate. While numerous studies have reviewed methods of biochar modification, the underlying adsorption mechanisms, and the thermodynamics and kinetics involved, a thorough examination that addresses the practical challenges of real-world wastewater treatment is currently lacking. This review aims to fill this gap by quantitatively analyzing the impact of coexisting species in wastewater on the adsorption of phosphate and by exploring the potential for simultaneous removal of other contaminants, such as nutrients, heavy metals, and dissolved organic matter. The review also discusses factors that affect the desorption of phosphate from biochar and presents practical applications for biochars post-adsorption. These applications include their use as slow-release phosphorus fertilizers, additives in concrete, and as novel adsorbents for the removal of heavy metals. This comprehensive analysis serves to synthesize current research on phosphate recovery by biochars and to propose practical uses for the adsorbed phosphorus, thereby guiding the development of biochar adsorption technology towards more effective and practical phosphorus management strategies.

The fate of antibiotics during phosphate recovery processes - A critical review

The principles of circular economy encourage the recovery of phosphorus from nutrient-rich waste streams such as animal manure, domestic wastewater, and urine to supplement existing sources of raw phosphorus. However, these waste streams also contain a wide variety of contaminants of emerging concern including antibiotics, and the recovery of phosphorus from these waste streams results in the co-occurrence of antibiotics with the recovered phosphorus products. This paper provides a comprehensive overview of the fate of environmentally relevant antibiotics in three major existing and upcoming phosphorus recovery processes: precipitation-, membrane-, and adsorption-based treatment. In general, the co-occurrence of antibiotics in recovered phosphorus increases with the presence of dissolved organic matter (DOM) and cations due to π-π interaction and cationic bridge formation, respectively. Additionally, antibiotics display pH-based speciation resulting in electrostatic interactions with recovered phosphorus at pH > 7.0. Furthermore, this critical review establishes a new metric, the relative antibiotic-to‑phosphorus (RAP), defined as the ratio of the concentration of antibiotics to phosphorus in recovered phosphorus to that of the phosphorus-rich waste. Precipitation-based methods, particularly struvite, demonstrated the lowest RAP, while the RAP in carbon-based adsorbents was 1.8 × 108 times higher than in membrane-based processes. In reviewing literature on the fate of antibiotics in phosphorus recovery processes, several research needs are also highlighted: the fate of non-tetracycline antibiotics, simultaneous investigation of phosphorus and antibiotic fate in membrane- and adsorption-based methods, treatment methods to mitigate the co-occurrence of antibiotics in recovered phosphorus product, and the release of antibiotics from recovered phosphate products.

Polydopamine-modified sodium alginate hydrogel for microplastics removal: Adsorption performance, characteristics, and kinetics

The potential health hazards of micro/nanoplastics in food have become a significant concern. This study developed a Polydopamine-modified sodium alginate hydrogel (PMSAH) for removing microplastics in daily drinking water. The hydrogel's performance, characteristics, and kinetics for microplastic removal were systematically evaluated. Results demonstrated that the incorporation of polydopamine reduced the hydrogel's surface zeta potential and increased its adsorption capacity for microplastics. PMSAH5 exhibited the highest removal efficiency, reaching approximately 99.6 %. Additionally, polydopamine-modified sodium alginate hydrogel exhibited higher elasticity and thermal stability. The hydrogel successfully adsorbed microplastics, regardless of their size and surface charge. This adsorption was driven by the combined action of multiple forces, resulting in multilayer adsorption. The unique advantages of polydopamine-mediated multi-molecular interactions present a promising and environmentally friendly approach for effective removal of microplastics in daily drinking water.

Tetracycline removal from aqueous media and hospital wastewater using a magnetic composite of mango lignocellulosic kernel biochar/MnFe2O4/Cu@Zn-BDC MOF

This study explored the use of mango lignocellulosic kernel biochar (MKB) modified with MnFe2O4 magnetic nanoparticles and a Cu@Zn-BDC metal-organic framework (MOF) (MKB/MnFe2O4/Cu@Zn-BDC MOF) for tetracycline (TC) removal from aqueous solutions and hospital wastewater. The modified biochar exhibited strong magnetic properties (19.803 emu/g) and a specific surface area of 30.456 m2/g, facilitating easy separation after adsorption. Using Response Surface Methodology-Central Composite Design (RSM-CCD), the adsorption model demonstrated high accuracy (F-value: 315.510, p < 0.0001, R2 = 0.9959). Thermodynamic analysis indicated that the process was endothermic and spontaneous, driven by physical interactions, with positive enthalpy and negative Gibbs free energy values. The pseudo-second-order kinetic model best described the adsorption, highlighting significant chemical interactions, while the Freundlich isotherm suggested adsorption on heterogeneous surfaces. The maximum TC adsorption capacities for MKB and its magnetic composite were 27.050 mg/g and 42.670 mg/g, respectively. The RL, n, and E parameters confirmed the desirability and physical nature of the interactions (0-1,〉1, and < 8 kJ/mol, respectively). The intraparticle diffusion model indicated multiple mechanisms were involved, and the biochar maintained excellent performance across reuse cycles, making it a highly effective and reusable adsorbent for water and wastewater treatment.

Phosphoric acid based geopolymer foam-activated carbon composite for methylene blue adsorption: isotherm, kinetics, thermodynamics, and machine learning studies

In this study, a binary composite adsorbent based on activated carbon and phosphoric acid geopolymer foam (ACP) was prepared by combining phosphoric acid geopolymer (PAGP) with activated carbon (AC) and applied for the removal of methylene blue (MB). Activated carbon was thoroughly mixed with a mixture of fly ash and metakaolin in varying ratios, followed by phosphoric acid activation and thermal curing. The ACP adsorbent was characterized using scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectrophotometer, X-ray diffractometer (XRD), surface area analyser (SAP), and thermogravimetric analyser (TGA). Batch analysis was performed to examine the effects of various adsorption parameters including pH (2, 4, 6, 7, 8, and 10), adsorbent dosage (0.06-0.2 g), MB concentration (50-250 mg L-1), contact duration (up to 240 minutes), and temperature (25-55 °C). The ACP with 70% PAGP and 30% AC was found to be the most suitable adsorbent as it maintained its structure and exhibited better MB adsorption. The ACP had a surface area of 47.36 m2 g-1 and a pore size of 5.6 nm and was found to be amorphous in nature. The adsorption equilibrium reached in 240 minutes at pH 7, indicating an efficient adsorption process. The adsorption increased with the initial dye concentration and decreased with the increase in temperature. The ideal parameters for adsorption of MB using ACP include 0.2 g of adsorbent, 25 °C, pH 10, and 240 minutes. The adsorption data fitted well with the Langmuir isotherm, pseudo-second-order (PSO) kinetics model, and three-step intraparticle diffusion (IPD) model. The adsorption capacity calculated using the Langmuir isotherm was 204.8 mg g-1 with an R 2 = 0.989. Thermodynamics parameters showed that the adsorption process was exothermic, energetically favourable, and associated with a decrease in entropy. According to the FTIR findings, pH effect, Langmuir isotherm, PSO kinetics, IPD model, and thermodynamics factors, chemisorption is identified as the predominant process. Different machine learning models, i.e., gaussian process regression (GPR), support vector regression (SVR and SVR-rbf), random forest regression (RFR), decision tree regression (DTR) and artificial neural network (ANN), were trained and tested using adsorption capacity and % removal data. The ANN model (random search) demonstrated better performance compared to other models, achieving an R 2 value of 0.873 for adsorption capacity and 0.799 for % removal on test data.

Magnetic nanoparticle modified moss Biochar: A novel solution for effective removal of enrofloxacin from aquaculture water

The presence of residual antibiotics in water constitutes a potential threat to aquatic environments. Therefore, designing environmentally friendly and efficient biochar adsorbents is crucial. Aquaculture by-product moss (bryophyte) was transformed into biochar, which can eliminate antibiotics from wastewater through adsorption. This study successfully fabricated moss biochar (BC) and magnetically modified moss biochar (MBC), and explored their adsorption performance for enrofloxacin (ENR). Characterization analyses revealed that the specific surface area, total pore volume, and the quantity of functional groups of the MBC were significantly larger than those of the BC. The Langmuir isotherm model suggests that the maximum adsorption capacities of BC and MBC for ENR are 7.24 mg g⁻1 and 11.62 mg g⁻1. The adsorption process conforms to a pseudo-second-order kinetic model. Studies carried out at different temperatures disclose the spontaneous and endothermic thermodynamic characteristics of the system. Under neutral conditions, the adsorption efficiency attains its peak. The existence of various coexisting ions in water exerts a negligible influence on the adsorption process; furthermore, when the concentration of humic acid (HA) ranges from 0 to 20 mg/L, the removal rate remains above 90%. In actual water samples, the antibiotic removal rate can be as high as 96.84%. After three cycles of reuse, the structure of MBC remains unchanged while maintaining a high removal efficiency. The primary mechanisms for antibiotic adsorption by MBC involve electrostatic interactions, hydrophobic interactions, pore-filling effects, hydrogen bonding, and π-π interactions. This reusable magnetic moss biochar provides a promising research direction for effectively eliminating antibiotics from water sources.

Preparation of calcium-based phosphate adsorbent and mineral-rich humic acid fertilizer from biomass ash and bamboo by hydrothermal-pyrolysis: Performance and mechanism

Biomass ash (BA) contains alkaline cations such as K, Ca, and Mg. Due to its high pH, direct application to the soil may result in soil salinization. Composting of BA with organic matter is an effective strategy, but the composting cycle is long and there is a large amount of insoluble residue in the product. Therefore, this research proposed for the first time using the hydrothermal method to rapidly convert BA and bamboo powder (BP) into water - soluble fertilizer (WSF) within 4 h. The insoluble hydrothermal residue was further converted into calcium - rich biochar phosphorus adsorption material by a simple pyrolysis process. WSF was neutral and contained humic acid and elements like K, Ca, Mg, and Si. A 14 - day wheat hydroponic experiment showed that the addition of 0.0125% WSF increased the fresh weight of wheat by 18.77% compared with deionized water. The calcium - based biochar adsorbent produced by pyrolysis had an ideal adsorption capacity of up to 113.6 mg P g-1 for phosphate in water, higher than many existing reports. The adsorption mechanisms mainly included surface precipitation, ion exchange, and electrostatic attraction. Moreover, the calcium - rich biochar sample slowly released phosphorus into water after adsorbing phosphate. When the pH was 3 or 4, the removal rate of Pb2+, Cd2+, and Cu2+ at 15 - 20 mg L-1 was as high as 99%. This indicated its potential as a slow - release fertilizer and heavy metal remediation agent. This research provided a new way of thinking for the treatment and disposal of BA.

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

Study on the adsorption of phosphate by composite biochar of phosphogypsum and rape straw

Wastewater containing phosphorus is often added by industrial activities, which is bad for the environment. In this study, composite biochar (PG-RS700) was prepared from phosphogypsum (PG) and rape straw (RS) for the treatment of phosphate in wastewater. SEM, FTIR, XRD and XPS characterization results showed that PG and RS were successfully combined. When PG-RS700 was dosed at 1.5 g/L and the phosphate solution concentration was 50 mg/L and pH = 8, the phosphate removal rate was 100% and the adsorption capacity was three times higher than the corresponding pure PG and RS. The quasi-secondary kinetic model indicated that the adsorption mechanism was chemisorption, and the maximum adsorption capacity for phosphate in the Langmuir isotherm model was 102.25 mg/g. Through pot experiment, the phosphorus adsorbed material obviously promoted the growth of plants. PG-RS700 can be used as a powerful adsorbent to treat phosphate in water and return it to soil as phosphate fertilizer.

Highly efficient removal of aqueous phosphate via iron-manganese fabricated biochar: Performance and mechanism

Biochar (BC) has emerged as a potential solution to phosphate removal from wastewater primarily resulting from global overuse of fertilizers. Further modification by embedment of iron (Fe)-manganese (Mn) oxides on BC can enhance phosphate removal; however, the modification method serves as a vital factor underlying distinctive removal performances and mechanisms, which have yet been systematically examined. Herein, two Fe-Mn modified BC, Fe/MnBC (comprised of Fe3O4 and MnO2) and Fe-MnBC (comprised of MnFe2O4), were comprehensively investigated for gaining insights into the unsolved perspectives. The results indicated that Fe-MnBC exhibited a markedly greater maximum phosphate adsorption capacity of 135.88 mg g-1 than that of Fe/MnBC with 17.93 mg g-1. The comparative results based on microstructure and spectroscopic analyses suggested that different Fe and Mn oxides were successfully loaded, which played a distinctive role in phosphate removal. Further characterizations unveiled that the key mechanisms for phosphate removal by Fe/MnBC are inner-sphere complexation and precipitation, while electrostatic interaction and outer-sphere complexation are the dominant mechanisms underlying the notable performance of Fe-MnBC. The delicately designed Fe-MnBC with special structure and property also enabled a superior regeneration capacity, which presented a promisingly high phosphate removal efficacy of over 81.34% after five cycles. These results enhance comprehension regarding the impact of biochar modification techniques on phosphate removal, offering positive indications for the remediation of excessive phosphate and other pollutant-containing water through feasible design and green chemicals.

Novel Fe/Ca oxide co-embedded coconut shell biochar for phosphorus recovery from agricultural return flows

Efficient elimination and recovery of phosphorus from agricultural return flows are crucial for effective eutrophication management and phosphorus reuse. In this study, a neutral Fe/Ca oxide co-embedded biochar (FCBC) was synthesized using calcium peroxide and ferrous chloride as precursors for phosphate recovery from agricultural return flows. FCBC possesses a highly intricate pore structure and an abundance of surface-active groups. Fe/Ca oxides were loaded onto the biochar in the form of Ca2Fe2O5, Fe2O3, and CaCO3. FCBC demonstrated a broad pH tolerance range (pH = 6-12) in the aquatic environment. The maximum saturation adsorption capacity was 53.31 mg g-1. Phosphorus removal is influenced by Ca3(PO4)2 generation, intra-particle diffusion, and electrostatic attraction. The produced FCBC showed exceptional phosphorus removal efficiency in the presence of various anions, except for wastewater with high concentrations of SO4 2-, CO3 2-, HCO3 -, and F- (>500 mg L-1). FCBC can effectively remove phosphorus from agricultural return flows and reduce the risk of the water environment. Returning it to the field can also mitigate the depletion of phosphorus resources, effectively reduce carbon emissions from farmland, improve soil fertility, and realize multiple benefits.

Recycling and reuse of waste agricultural plastics with hydrothermal pretreatment and low-temperature pyrolysis method

Recycling and reuse of agricultural plastics is an urgent worldwide issue. In this work, it is shown that low-density polyethylene (PE) typically used in mulch films can be converted into high-capacity P and N adsorbents through a two-step method that uses hydrothermal pretreatment (180 °C, 24 h) followed by pyrolysis at 500 °C with Ca(OH)2 additive. CaPE@HC500 materials prepared with the proposed two-step method were found to have high adsorption capacities for phosphate (263.6 mg/g) and nitrogen (200.7 mg/g) over wide ranges of pH (3-11). Dynamic adsorption of phosphate by CaPE@HC500 material in a packed-bed had a half-time breakthrough of 210 min indicating the feasibility of continuous systems. Material stability, cost, environmental-friendliness, and recyclability of the CaPE@HC500 material were determined to be superior to literature-proposed Ca-containing adsorbents. The two-step method for converting waste agricultural plastic mulch films into adsorbents is robust and highly-applicable to industrial settings.

Synergistic adsorption of methylene blue using ternary composite of phosphoric acid geopolymer, calcium alginate, and sodium lauryl sulfate

The removal of dyes from the aquatic ecosystem is necessary being a major threat to life. For enhanced remediation of methylene blue (MB) dye, a new ternary biopolymer-geopolymer-surfactant composite adsorbent is synthesized by combining phosphoric acid geopolymer (PAGP), calcium alginate (Alg), and sodium lauryl sulfate (SLS). During the synthesis of the composites, PAGP and SLS were mixed with the alginate matrix, producing porous hybrid beads. The PAGP-SLS-alginate (PSA) beads prepared were characterized using different analytical tools, i.e., scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FTIR), X-ray diffractometry (XRD), surface area and porosimetery (SAP), and thermogravimetric analysis (TGA). To ascertain the ideal conditions for the adsorption process, a batch reactor procedure was used to investigate the effects of several parameters on MB adsorption, including pH (2, 4, 6, 8, 10), PSA adsorbent dosage (0.06-0.12 g), MB concentration (50-500 mg/L), contact time (15 to 300 min), and temperature (25, 35, and 45 °C). The SEM investigation indicated that ~ 1860 μm-sized PSA beads with 6-8 μm voids are generated. Based on XRD, FTIR, and SAP examinations, the material is amorphous, having numerous functional groups and an average pore size of 6.42 nm. Variation of pH has a little effect on the adsorption process, and the pH of 7.44 was found to be the pHpzc of the PSA beads. According to the findings of the batch study, equilibrium adsorption was obtained in 270-300 min, showing that the adsorption process was moderately slow-moving and effective. The dye adsorption linearly increased with initial dye concentration over concentration range of 50-500 mg/L and reciprocally decreased with rise in temperature. 0.06 g adsorbent dose, 25 °C, pH10, and 270 min were found to be the better conditions for adsorption experiments. Langmuir isotherm fitted well compared to Freundlich, Temkin, and Dubinin-Radushkevich (DR) isotherm models on the experimental data, and the maximum adsorption capacity(qmax) calculated was 1666.6 mg. g-1. Pseudo-second-order (PSO) kinetics model and multi steps (two) intra particle diffusion (IPD) model fitted well on the adsorption kinetics data. The system's entropy, Gibbs free energy, and change in enthalpy were measured and found to be -109.171 J. mol-1. K-1, - 8.198 to - 6.014 kJ. mol-1, and - 40.747 kJ. mol-1. Thermodynamics study revealed that adsorption process is exothermic, energetically favorable and resulting in the decrease in randomness. Chemisorption is found to be the dominant mechanism as confirmed by pH effect, Langmuir isotherm, PSO kinetics, IPD model, and thermodynamics parameters. PSA beads were successfully regenerated using ethanol in a course of 120 min and re-used for five times. To sum up, the PSA adsorbent's impressive adsorption capability of 1666.66 mg/g highlights its potential as a successful solution for methylene blue removal. The results of this study add to the expanding corpus of information on sophisticated adsorption materials and demonstrate PSA's potential for real-world uses in wastewater treatment and environmental clean-up.

Endogenous iron-enriched biochar derived from steel mill wastewater sludge for tetracycline removal: Heavy metals stabilization, adsorption performance and mechanism

Steel mill wastewater sludge, as an iron-enriched solid waste, was expected to be converted into iron-enriched biochar with acceptable environmental risk by pyrolysis. The purpose of our study was to evaluate the chemical speciation transformation of heavy metals in biochar under various pyrolysis temperatures and its reutilization for tetracycline (TC) removal. The experimental data indicated that pyrolysis temperature was a key factor affecting the heavy metals speciation and bioavailability in biochar, and biochar with pyrolysis temperature at 450 °C was the most feasible for reutilization without potential risk. The endogenous iron-enriched biochar (FSB450) showed highly efficient adsorption towards TC, and its maximum adsorption capacity could reach 240.38 mg g-1, which should be attributed to its excellent mesoporous structure, abundant functional groups and endogenous iron cycling. The endogenous iron was converted to a stable iron oxide crystalline phase (Fe3O4 and MgFe2O4) by pyrolysis, which underwent a valence transition to form a coordination complex with TC by electron shuttling in the FSB450 matrix. The study provides a win-win approach for resource utilization of steel wastewater sludge and treatment of antibiotic contamination in wastewater.

Multifunctional self-assembled adsorption microspheres based on waste bamboo shoot shells for multi-pollutant water purification

In this study, multilayer self-assembled multifunctional bamboo shoot shell biochar microspheres (BSSBM) were prepared, in which bamboo shoot shell biochar was used as the carrier, titanium dioxide as the intermediate medium, and chitosan as the adhesion layer. The adsorption behavior of BSSBM on heavy metals Ag(I) and Pd(II), antibiotics, and dye wastewater was systematically analyzed. BSSBM shows a wide range of adsorption capacity. BSSBM is a promising candidate for the purification of real polluted water, not only for metal ions, but also for Tetracycline (TC) and Methylene Blue (MB). The maximum adsorption amounts of BSSBM on Pd(II), Ag(I), TC and MB were 417.3 mg/g, 222.5 mg/g, 97.2 mg/g and 42.9 mg/g, respectively.The adsorption of BSSBM on Pd(II), MB and TC conformed to the quasi-first kinetic model, and the adsorption on Ag(I) conformed to the quasi-second kinetic model. BSSBM showed remarkable selective adsorption capacity for Ag(I) and Pd(II) in a multi-ion coexistence system. BSSBM not only realized the high value-added utilization of waste, but also had the advantages of low cost, renewable and selective adsorption. BSSBM demonstrated its potential as a new generation of multifunctional adsorbent, contributing to the recovery of rare/precious metals and the treatment of multi-polluted water.

Development of calcium-modified biochar for enhanced phytoremediation of human-induced salt pollutants (HISPs)

Soil salinization is a major environmental hazard that limits land availability. Human-induced salt pollutants (HISPs) are regularly presented in large quantities on the contaminated site (such as brine leakages and salt-water spills), causing a devastating shock with high salt stress to the ecosystem. For instance, Saskatchewan resulted in a 48% drop in wheat production and a 0.3% decline in provincial GDP. As the calcium-modified biochar can potentially ameliorate the negative effects of HISPs on plants and improve the plant, phytoremediation with calcium-modified biochar can have increased detoxification of hazardous pollutants from sites. Therefore, the objective of our study was to develop a biochar-assisted phytoremediation employing diverse approaches to calcium modification for the sustainable removal of HISPs. The co-pyrolyzed calcium biochar achieved a remarkable removal rate of 18.06%, reducing salinity from 9.44 to 7.81 dS/m. During a 90-day long-term phytoremediation, the overall reduction rate of calcium-modified biochar stimulated the germination and growth of Thinopyrum ponticum. The result of post-treatment further indicated that co-pyrolyzed biochar with Ca transferred salt into the plant compared to Ca-coated biochar, which only immobilized HISPs on its surface. These results offer two different treatment approaches for diverse situations involving HISPs contamination, addressing current in-situ spills and providing a calcium-related biochar technology for further research in desalination.

Dual valorization of coastal biowastes for tetracycline remediation and biomethane production: A composite assisted anaerobic digestion

Harnessing coastal biowaste for dual valorization in water treatment and biofuel production holds paramount importance for sustainability and resource challenges. This study investigated the potential of engineered composite (CABC) derived from coastal biowaste-based materials for tetracycline (TC) removal and biomethane production. High-yield calcium carbonate (CaCO3; 95.65%; bivalve shells) and biochar (GA-BC; 41.50%; green macroalgae) were produced and used as precursors for CABC. The characterization results revealed presence of β-CaCO3 and ν2-CO3 aragonite in CaCO3, and composite homogeneity was achieved. The CABC exhibited a maximum TC sorption capacity of 342.26 mg/g via synergistic sorption mechanisms (i.e., surface/pore filling, electrostatic attraction, calcium ion exchange, and chelation). Supplementation of anaerobic digestion process with GA-BC, CaCO3, and CABC was investigated via three consecutive cycles. Biochemical methane potential of glucose as a sole substrate was increased from 157.50 to 217.00, 187.00, and 259.00 mL-CH4, while dual substrate (glucose+TC) treatment was increased from 94.5 to 146.5, 129.0, and 153.00 mL-CH4 for GA-BC, CaCO3, and CABC, respectively. Moreover, system stability and TC removal were increased with the addition of GA-BC (40.90%), CaCO3 (16.30%), and CABC (53.70%). Therefore, this study exemplifies the circular bioeconomy approach, demonstrating the sustainable use of biowaste-derived composite for water treatment and biofuel production.

Utilizing different types of biomass materials to modify steel slag for the preparation of composite materials used in the adsorption and solidification of Pb in solutions and soil

This study utilized discarded steel slag (SS) as raw material and prepared modified steel slag materials (SS-SBC, SS-NBC, SS-BHA) through modification with biomass materials such as straw biochar (SBC), nutshell biochar (NBC), and biochemical humic acid (BHA). These materials were then applied for the removal of Pb from both solution and soil. The physical and chemical properties of the materials were analyzed using characterization techniques such as SEM, EDS, XRD, and BET. The specific surface area of the modified materials increased from the original 3.8584 m2/g to 34.7133 m2/g, 181.7329 m2/g, and 7.7384 m2/g, respectively. The study then explored the influence of different adsorption conditions on the adsorption capacity of Pb in solution, determining the optimal conditions as follows: initial concentration of 200 mg/L, adsorbent mass of 0.04 g, temperature of 15 °C, and pH = 2. To further investigate the adsorption process, kinetic and isotherm models were established. The results indicated that the adsorption process for all three materials followed a pseudo-second-order kinetic model and Freundlich isotherm model, suggesting a multi-layer chemical adsorption. Thermodynamic analysis revealed that the adsorption process was an exothermic spontaneous reaction. Soil cultivation experiments were conducted to explore the effects of different material addition amounts and cultivation times on the passivation of Pb-polluted soil. Analysis of heavy metal forms in the soil revealed that the addition of modified materials reduced the acid-extractable form of Pb in the soil and increased the residual form, which is beneficial for reducing the migration of Pb in the soil. FT-IR and XPS analyses were employed to study the functional groups, element composition, and valence states before and after adsorption passivation of Pb by the three materials. The results confirmed that the adsorption mechanisms of SS-SBC, SS-NBC, and SS-BHA mainly involved electrostatic adsorption, ion and ligand exchange, and surface precipitation. This study not only provides a new material for adsorbing and immobilizing heavy metals in soil and water but also offers a new approach for the resource utilization of steel slag waste.

A sustainable and highly efficient fossil-free carbon from olive stones for emerging contaminants removal from different water matrices

The olive stone is a large waste product of the olive oil extraction industry. The present study investigates developing activated carbon from olive stone waste (OSAC) to remove pharmaceuticals from water. Different temperatures and olive stone: KOH ratios were studied. The OSAC produced at 750 °C and 1:3 ratio was found to have the highest porosity and surface area and was tested in the adsorption process. Diclofenac and ciprofloxacin were selected as model contaminants. The adsorption process was optimized with regards to OSAC dosage, pH, temperature, and initial concentration of adsorbate. The OSAC was found to be effective for a wide pH range (2-11) with an optimum dosage of 1 g/L at 25 °C. The pharmaceuticals were almost completely removed in 75 min. The adsorption was endothermic and followed first-order kinetics with physical mechanisms such as electrostatic possibly being the main driver. The optimum conditions were applied to test the removal of diclofenac and ciprofloxacin in synthetic water, lake water (Lake Balaton, Hungary) and secondary wastewater for seven cycles. There was little difference between the removal of the tested water matrices highlighting the potency of OSAC as an adsorbent for pharmaceutical removal in industrial applications. The removal dropped from >99% for the first cycle to 20-30% for the seventh cycle.

Efficient Adsorption of Nitrogen and Phosphorus in Wastewater by Biochar

Nitrogen and phosphorus play essential roles in ecosystems and organisms. However, with the development of industry and agriculture in recent years, excessive N and P have flowed into water bodies, leading to eutrophication, algal proliferation, and red tides, which are harmful to aquatic organisms. Biochar has a high specific surface area, abundant functional groups, and porous structure, which can effectively adsorb nitrogen and phosphorus in water, thus reducing environmental pollution, achieving the reusability of elements. This article provides an overview of the preparation of biochar, modification methods of biochar, advancements in the adsorption of nitrogen and phosphorus by biochar, factors influencing the adsorption of nitrogen and phosphorus in water by biochar, as well as reusability and adsorption mechanisms. Furthermore, the difficulties encountered and future research directions regarding the adsorption of nitrogen and phosphorus by biochar were proposed, providing references for the future application of biochar in nitrogen and phosphorus adsorption.

Efficient Adsorbent Derived from Phytolith-Rich Ore for Removal of Tetracycline in Wastewater

In recent decades, the tetracycline (TC) concentration in aquatic ecosystems has gradually increased, leading to water pollution problems. Various mineral adsorbents for the removal of tetracyclines have garnered considerable attention. However, efficient adsorbents suitable for use in a wide pH range environment have rarely been reported. Herein, a phytolith-rich adsorbent (PRADS) was prepared by a simple one-step alkali-activated pyrolysis treatment using phytolith as a raw material for effectively removing TC. PRADS, benefiting from its porous structure, which consists of acid- and alkali-resistant, fast-adsorbing macroporous silica and mesoporous carbon, is highly desirable for efficient TC removal from wastewater. The results indicate that PRADS exhibited excellent adsorption performance and stability for TC over a wide pH range of 2.0-12.0 under the coexistence of competing ions, which could be attributed to the fact that PRADS has a porous structure and contains abundant oxygen-containing functional groups and a large number of bonding sites. The adsorption mechanisms of PRADS for TC were mainly attributed to pore filling, hydrogen bonding, π-π electron-donor-acceptor, and electrostatic interactions. This work could offer a novel preparation strategy for the effective adsorption of pollutants by new functionalized phytolith adsorbents.

Use of waste marble powder for the synthesis of novel calcium-rich biochar: Characterization and application for phosphorus recovery in continuous stirring tank reactors

This study investigates-for the first time-the synthesis of a novel Ca-rich biochar (N-Ca-B) and its potential use for phosphorus (P) recovery from both synthetic solutions (SS) and treated urban wastewater (TUW) in a continuous stirring tank reactor (CSTR) mode. The novel biochar was synthesized by pyrolysis at 900 °C of a mixture composed of three different materials: animal biomass (poultry manure; PM), lignocellulosic waste (date palm fronds; DPFs), and abundant mineral waste (waste marble powder; WMP). Characterization of N-Ca-B showed that it has good textural properties: well-developed porosity, and high specific surface area. Furthermore, high calcium hydroxide (Ca(OH)2) and calcium oxides (CaO) nanoparticle loads were observed on the biochar surface. The dynamic CSTR assays indicated that the P recovery efficiency mainly depended on the biochar mass, P influent concentration, and, especially, the Ca content of the feeding solution. Owing to its richness in Ca cations, TUW exhibited the highest adsorbed P amount (109.2 mg g-1), i.e., about 14% larger than the SS. P recovery occurs through precipitation as hydroxyapatite, surface complexation, and electrostatic interactions with positively charged biochar particles. In real-world scenarios, CSTR systems can be applied as a tertiary treatment step in existing wastewater treatment plants (WWTPs). Decanted P-loaded biochar can be used in agriculture as a slow-release fertilizer instead of commercial products.

Weathered Coal-Immobilized Microbial Materials as a Highly Efficient Adsorbent for the Removal of Lead

Most research on immobilized microorganisms employs biomass charcoal as a carrier, but limited studies explore coal-based resources for microbial immobilization. Herein, lead-resistant functional strains were immobilized using weathered coal as a carrier, resulting in the development of a weathered coal-immobilized microbial material (JK-BW) exhibiting high efficiency in lead removal from solutions. A quadratic polynomial model for the adsorption capacity and adsorption rate of JK-BW on Pb2+ was developed using the Box-Behnken method to determine the optimal adsorption conditions. The Pb2+ adsorption mechanism of JK-BW was studied through batch adsorption and desorption experiments along with SEM-EDS, BET, FT-IR, and XPS analyses. Findings indicated that optimal conditions were identified at 306 K temperature, 0.36 g/L adsorbent dosage, and 300 mg/L initial solution concentration, achieving a peak adsorption performance of 338.9 mg/g (308 K) for the immobilized material, surpassing free cell adsorption by 3.8 times. Even after four cycles of repeated use, the material maintained its high adsorption capacity. Pb2+ adsorption by JK-BW involved monolayer chemisorption with ion exchange, complexation, precipitation, physical adsorption, and microbial intracellular phagocytosis. Ion exchange accounted for 22-42% and complexation accounted for 39-57% of the total adsorption mechanisms, notably involving exchanges with K, Ca, Na, and Mg ions as well as complexation with -OH, -COOH, CO-OH, -COOH, CO-, NH2, and the β-ring of pyridine for Pb2+ adsorption.

Adsorption recovery of phosphorus in contaminated water by calcium modified biochar derived from spent coffee grounds

Phosphate recovery from water is essential for reducing water eutrophication and alleviating the phosphorus resource crisis. In this study, spent coffee grounds and CaCl2 were used as raw materials and a modifier, respectively, to create a novel calcium modified biochar (MBC) for removing phosphorus from water. The modified biochar (MBC) was the best at removing phosphorous when the modifier concentration was 1.5 M with theoretically maximum adsorption capacity of 70.26 mg/g. MBC also performed well in the wide pH range of 3-11 under different phosphorus concentration gradients, with phosphorus removal efficiency of more than 50 %. According to kinetic analysis, the adsorption process at low phosphorus concentrations (50-100 mg/L) can be more properly described by the pseudo-first-order model, while the pseudo-second-order model best describes the adsorption process at high concentrations (200-600 mg/L). The thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Characterization results revealed that surface precipitation, complexation, and ligand exchange were the dominant mechanisms of phosphorus adsorption. MBC has great potential to recover phosphorus from wastewater.

Enhancing efficient reclaim of phosphorus from simulated urine by magnesium-functionalized biochar: Adsorption behaviors, molecular-level mechanistic explanations and its potential application

Magnesium-functionalized Magnolia grandiflora Linn leaf-derived biochar (MBC) capable of efficiently reclaiming phosphorus from urine was synthesized by slow co-pyrolysis. Four adsorption kinetic and seven adsorption isotherm models were fitted to the batch adsorption and desorption experimental data, and it was found that pseudo-first-order kinetic model and multilayer model with saturation best described the phosphate-phosphorus (PO43--P) adsorption process by MBC. MBC and phosphorus-saturated MBC (P-MBC) were found to offer outstanding phosphorus adsorption and slow release properties, respectively. Based on material characterization, statistical physics, adsorption energy distribution and statistical thermodynamics, a multi-ionic, inclined orientation, entropy-driven spontaneous endothermic process of MBC on PO43--P was proposed, involving physicochemical interactions (porous filling, electrostatic attraction, ligand exchange and surface precipitation). Further, seed germination and early seedling growth experiments proved that P-MBC can be used as a slow-release fertilizer. Overall, MBC offers prospective applications as an efficient phosphorus adsorbent and then as a slow-release fertilizer.

Recent insights into mechanism of modified bio-adsorbents for the remediation of environmental pollutants

Rapid industrialization has exacerbated the hazard to health and the environment. Wide spectrums of contaminants pose numerous risks, necessitating their disposal and treatment. There is a need for further remediation methods since pollutant residues cannot be entirely eradicated by traditional treatment techniques. Bio-adsorbents are gaining popularity due to their eco-friendly approach, broad applicability, and improved functional and surface characteristics. Adsorbents that have been modified have improved qualities that aid in their adsorptive nature. Adsorption, ion exchange, chelation, surface precipitation, microbial uptake, physical entrapment, biodegradation, redox reactions, and electrostatic interactions are some of the processes that participate in the removal mechanism of biosorbents. These processes can vary depending on the particular biosorbent and the type of pollutants being targeted. The systematic review focuses on the many modification approaches used to remove environmental contaminants. Different modification or activation strategies can be used depending on the type of bio-adsorbent and pollutant to be remediated. Physical activation procedures such as ultrasonication and pyrolysis are more commonly used to modify bio-adsorbents. Ultrasonication process improves the adsorption efficiency by 15-25%. Acid and alkali modified procedures are the most effective chemical activation strategies for adsorbent modification for pollution removal. Chemical modification increases the removal to around 95-99%. The biological technique involving microbial culture is an emerging field that needs to be investigated further for pollutant removal. A short evaluation of modified adsorbents with multi-pollutant adsorption capability that have been better eliminated throughout the adsorption process has been provided.

Simultaneous removal of phosphate and tetracycline using LaFeO3 functionalised magnetic biochar by obtained ultrasound-assisted sol-gel pyrolysis: Mechanisms and characterisation

Excessive phosphate and tetracycline (TC) contaminants pose a serious risk to human health and the ecological environment. As such exploring the simultaneous adsorption of phosphate and TC is garnering increasing attention. In this study, an efficient lanthanum ferrate magnetic biochar (FLBC) was synthesised from crab shells using an ultrasound-assisted sol-gel method to study its performance and mechanisms for phosphate and TC adsorption in aqueous solutions in mono/bis systems. According to the Langmuir model, the developed exhibited a maximum adsorption capacity of 65.62 mg/g for phosphate and 234.1 mg/g for TC (pH:7.0 ± 0.1, and 25 °C). Further, it exhibited high resistance to interference and pH suitability. In practical swine wastewater applications, whereby the concentrations of phosphate and TC are 37 and 19.97 mg/L, respectively, the proposed material demonstrated excellent performance. In addition, electrostatic adsorption, chemical precipitation and ligand exchange were noted to be the main mechanisms for phosphate adsorption by FLBC, whereas hydrogen bonding and π-π interaction were the main adsorption mechanisms for TC adsorption. Therefore, this study successfully prepared a novel and efficient adsorbent for phosphate and TC.

Enhanced soil P immobilization and microbial biomass P by application of biochar modified with eggshell

Phosphate fertilizers have been excessively applied in agricultural production, bringing the risk of phosphorus (P) loss to nearby river systems and low utilization efficiency. In this study, eggshell-modified biochars prepared by pyrolysis of eggshell and corn straw or pomelo peel were applied to soil for enhancing P immobilization and utilization. The structure and properties of modified biochars before and after P adsorption were analyzed using the Brunauer-Emmett-Teller (BET) nitrogen adsorption method, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The eggshell-modified biochar performed an excellent adsorption performance for P (up to 200 mg/g), which was well described by the Langmuir model (R2 > 0.969), showing monolayer chemical adsorption with homogenous surface. The Ca(OH)2 appeared on the surface of eggshell modified biochars and changed to Ca5(PO4)3(OH) and CaHPO4(H2O)2 after P adsorption. The release of immobilized P by modified biochar increased with decreased pH. In addition, pot experiments of soybean indicated that the combined application of modified biochar and P fertilizer significantly increased the content of microbial biomass P in soil, raising from 4.18 mg/kg (control group) to 51.6-61.8 mg/kg (treatment group), and plants height increased by 13.8-26.7%. Column leaching experiments showed that P concentration in the leachate decreased by 97.9% with the modified biochar application. This research provides a new perspective that the eggshell-modified biochar could serve as a potential soil amendment for enhancing P immobilization and utilization.

Biochar facilitates methanogens evolution by enhancing extracellular electron transfer to boost anaerobic digestion of swine manure under ammonia stress

This study explored the mechanisms by which biochar mitigates ammonia inhibition in anaerobic digestion (AD) of swine manure. Findings show 2-8 g/L exogenous ammonia dosages gradually inhibited AD, leading to decreases in the efficiencies of hydrolysis, acidogenesis and methanogenesis by 3.4-70.8%, 6.0-82.0%, and 4.9-93.8%, respectively. However, biochar addition mitigated this inhibition and facilitated methane production. Biochar enhanced microbial activities related to electron transport and extracellular electron transfer. Moreover, biochar primarily enriched Methanosarcina, which, consequently, upregulated the genes encoding formylmethanofuran dehydrogenase and methenyltetrahydromethanopterin cyclohydrolase for the CO2-reducing methanogenesis pathway by 26.9-40.8%. It is believed that biochar mediated direct interspecies electron transfer between syntrophic partners, thereby enhancing methane production under ammonia stress. Interestingly, biochar removal did not significantly impact the AD performance of the acclimated microbial community. This indicated the pivotal role of biochar in triggering methanogen evolution to mitigate ammonia stress rather than the indispensable function after the enrichment of ammonia-resistance methanogen.

Enhanced adsorption of Congo red from urea/calcium chloride co-modified biochar: Performance, mechanisms and toxicity assessment

Adsorbents with excellent physicochemical properties and green synthetic routes are desired for efficient removal of Congo red (CR) wastewater. Hence, a novel approach was proposed within this work. Biochar NCBC obtained from Medulla Tetrapanacis was synthesized through co-modification with urea/calcium chloride. NCBC exhibited an enormous surface area (750.09 m2/g) and a micro-mesoporous composite structure. Higher nitrogen content was detected on the surface of NCBC (8.17%) compared to that of urea directly modified biochar (4.63%). Nitrogen observed on the surface of NCBC was presented as graphitic N, pyrrolic N, amine N as well as pyridinic N. Kinetic and isothermal investigations revealed the active sites on NCBC to be homogeneous and bind to CR mainly by chemisorption. Calculated maximum sorption of CR on NCBC was 2512.82 mg/g basing on Langmuir model. Moreover, the practicality of NCBC was further proved by the cultivation of Nelumbo nucifera Gaertn. and Penicillium.

Tetracycline Adsorption Performance and Mechanism Using Calcium Hydroxide-Modified Biochars

Tetracycline is frequently found in various environments and poses significant ecological risks. Calcium hydroxide-modified biochar has shown potential as a material for removing multiple classes of pollutants from wastewater streams. The tetracycline-adsorption performance and mechanism of alkali-modified biochars derived from nine wastes (corn straw, rice straw, swine manure, cypress powder, wheat straw, peanut shell, walnut shell powder, soybean straw, and corncobs) were investigated in the study. Among the four alkalis tested, calcium hydroxide exhibited the most effective modification effects at a pyrolysis temperature of 500 °C. Straw biomass was most suitable to be modified by calcium hydroxide, and calcium hydroxide-modified biochar showed the highest adsorption performance for tetracycline. The maximum adsorption capacities were 8.22 mg g-1 for pristine corn straw biochar and 93.46 mg g-1 for calcium hydroxide-modified corn straw biochar. The tetracycline adsorption mechanism by calcium hydroxide-modified corn straw biochar involved hydrogen bonding, oxygen-containing functional groups, Ca2+ metal complexation, and electrostatic attraction. Consequently, calcium hydroxide-modified corn straw biochar emerges as an environment-friendly, cost-effective, and efficient tetracycline adsorbent.

Efficient Adsorption Removal of Phosphate from Rural Domestic Sewage by Waste Eggshell-Modified Peanut Shell Biochar Adsorbent Materials

In order to promote the improvement of the rural living environment, the treatment of rural domestic sewage has attracted much attention in China. Meanwhile, the rural regions' sewage discharge standards are becoming increasingly stringent. However, the standard compliance rate of total phosphorus (TP) is very low, and TP has become the main limiting pollutant for the water pollutants discharge standards of rural domestic sewage treatment facilities. In this study, waste eggshell (E) was employed as a calcium source, and waste peanut shell (C) was employed as a carbon source to prepare calcium-modified biochar adsorbent materials (E-C). The resulting E-C adsorbent materials demonstrated efficient phosphate (P) adsorption from aqueous solutions over the initial pH range of 6-9 and had adsorption selectivity. At an eggshell and peanut shell mass ratio of 1:1 and a pyrolysis temperature of 800 °C, the experimental maximum adsorption capacity was 191.1 mg/g. The pseudo second-order model and Langmuir model were best at describing the adsorption process. The dominant sorption mechanism for P is that Ca(OH)2 is loaded on biochar with P to form Ca5(PO4)3OH precipitate. E-C was found to be very effective for the treatment of rural domestic sewage. The removal rate of TP in rural domestic sewage was 91-95.9%. After adsorption treatment, the discharge of TP in rural sewage met the second-grade (TP < 3 mg/L) and even first-grade (TP < 2 mg/L). This study provides an experimental basis for efficient P removal by E-C adsorbent materials and suggests possible applications in rural domestic sewage.

Simultaneous adsorption of ciprofloxacin and Cu2+ using Fe and N co-doped biochar: Competition and selective separation

The treatment of combined antibiotics and heavy metals pollution is a critical challenge. Herein, iron and nitrogen co-doped biochar (Fe/N-BC) was synthesized using rape straw as precursor, and applied for the adsorption of ciprofloxacin (CIP) and Cu2+ in single and binary systems. The qmax for CIP and Cu2+ were 46.45 mg g-1 and 30.77 mg g-1, respectively. Adsorption decreased in a binary matrix, indicating that there was a competitive effect between CIP and Cu2+, which might be due to CIP and Cu2+ sharing similar active adsorption sites on Fe/N-BC. Interestingly, CIP and Cu2+ co-adsorption was a pH-dependent process. Fe/N-BC has potential to highly selectively separate CIP/Cu2+ from mixed solutions through adjusting pH values. Furthermore, adsorption mechanisms were systematically investigated in this research. This research could help to provide a deeper understanding of the synchronously removing specific antibiotics and heavy metals by biochar adsorbents.

Recent developments in metallic-nanoparticles-loaded biochars synthesis and use for phosphorus recovery from aqueous solutions. A critical review

Phosphorus (P) represents a major pollutant of water resources and at the same time a vital element for human and plants. P recovery from wastewaters and its reuse is a necessity in order to compensate the current important depletion of P natural reserves. The use of biochars for P recovery from wastewaters and their subsequent valorization in agriculture, instead of synthetic industrial fertilizers, promotes circular economy and sustainability concepts. However, P retention by pristine biochars is usually low and a modification step is always required to improve their P recovery efficiency. The pre- or post-treatment of biochars with metal salts seems to be one of the most efficient approaches. This review aims to summarize and discuss the most recent developments (from 2020- up to now) in: i) the role of the feedstock nature, the metal salt type, the pyrolysis conditions, and the experimental adsorption parameters on metallic-nanoparticles-loaded biochars properties and effectiveness in recovering P from aqueous solutions, as well as the dominant involved mechanisms, ii) the effect of the eluent solutions nature on the regeneration ability of P-loaded biochars, and iii) the practical challenges facing the upscaling of P-loaded biochars production and valorization in agriculture. This review shows that the synthesized biochars through slow pyrolysis at relatively high temperatures (up to 700-800 °C) of mixed biomasses with Ca- Mg-rich materials or impregnated biomasses with specific metals in order to from layered double hydroxides (LDHs) biochars composites exhibit interesting structural, textural and surface chemistry properties allowing high P recovery efficiency. Depending on the pyrolysis's and adsorption's experimental conditions, these modified biochars may recover P through combined mechanisms including mainly electrostatic attraction, ligand exchange, surface complexation, hydrogen bonding, and precipitation. Moreover, the P-loaded biochars can be used directly in agriculture or efficiently regenerated with alkaline solutions. Finally, this review emphasizes the challenges concerning the production and use of P-loaded biochars in a context of circular economy. They concern the optimization of P recovery process from wastewater in real-time scenarios, the reduction of energy-related biochars production costs and the intensification of communication/dissemination campaigns to all the concerned actors (i.e., farmers, consumers, stakeholders, and policymakers) on the benefits of P-loaded biochars reuse. We believe that this review is beneficial for new breakthroughs on the synthesis and green application of metallic-nanoparticles-loaded biochars.

Hydrochloric acid-modified fungi-microalgae biochar for adsorption of tetracycline hydrochloride: Performance and mechanism

Novel biochar (BC) was prepared by pyrolysis using Aspergillus oryzae-Microcystis aeruginosa (AOMA) flocs as raw materials. It has been used for tetracycline hydrochloride (TC) adsorption along with acid (HBC) and alkali modification (OHBC). Compared with BC (114.5 m² g^-1) and OHBC (283.9 m² g^-1), HBC had a larger specific surface area (S_BET=338.6 m² g^-1). Meanwhile, the Elovich kinetic and Sip isotherm models adequately fit the adsorption data, and intraparticle diffusion is the controlling factor for TC adsorption diffusion on HBC. Furthermore, the thermodynamic data indicated that this adsorption was endothermic and spontaneous. The experimental results demonstrated that there are multiple interactions during the adsorption reaction process, including pore filling, H-bonds, π-π interaction, hydrophobic affinity, and van der Waals forces. In general, biochar prepared from flocs of AOMA can be used to remediate tetracycline-contaminated water, and it is of great significance in improving resource utilization.

Novel Y2O3 based calcium-alginate beads for highly selective adsorption of phosphate from aqueous solution

Recently, selective phosphorus removal from aqueous solution has been a highly desirable strategy to combat eutrophication due to the increasingly stringent phosphorous emission standards. However, conventional adsorbents pose the limitations in phosphate removal suffering from lack of selectivity and stability under complicated condition and poor separation. In this study, novel Y₂O₃ based calcium-alginate (Y₂O₃/SA) beads of feasible stability and highly selectivity towards phosphate by encapsulating Y₂O₃ nanoparticles inside calcium-alginate beads via Ca²⁺ controlled gelation process was synthesized and characterized. The phosphate adsorption performance and mechanism were investigated. In general, a high selectivity among co-existing anions was found with co-existing anion concentration up to 62.5 times of the phosphate concentration. Additionally, phosphate adsorption by Y₂O₃/SA beads exhibited stable performance over a wide pH range between 2 and 10, while reaching the maximum adsorption capacity at pH 3 (48.54 mg-P/g). The value of point of zero charge (pH_pzc) of Y₂O₃/SA beads was approximately 3.45. Pseudo-second-order and Freundlich isotherm models can well accord with kinetics and isotherms data. The FTIR and XPS characterizations analyzed that inner-sphere complexes were proposed to be the major contributor of Y₂O₃/SA beads for phosphate removal. In conclusion, Y₂O₃/SA beads as the mesoporous material exhibited excellent stability and selectivity towards phosphate removal.

One-pot preparation of layered double oxides-engineered biochar for the sustained removal of tetracycline in water

Tetracycline (TC) and sugarcane bagasse had both exerted enormous strain on environmental security. In this work, new composite adsorbent designed by impregnating bio-waste bagasse with magnesium-aluminum layered double oxides (BC-MA) was innovatively brought forward for TC removal. Benefiting from the abundant adsorption sites supplied by developed pores structure (0.308 cm³·g^-1), enlarged surface area (256.8 m²·g^-1) and reinforced functional groups, the maximum adsorption amount of BC-MA for TC reached 250.6 mg g^-1. Moreover, BC-MA displayed desirable adsorption capacity in diverse water environments coupled with excellent sustainable regeneration ability. The absorption process of TC by BC-MA was spontaneous and endothermic, and the pivotal rate-limiting stage pertained to intraparticle diffusion. The mechanisms proposed here mainly concerned π-π interactions, pore filling, complexation and hydrogen bonding. These findings suggested that the synthesis of modified biochar from bagasse would offer new opportunities for simultaneous waste resource reuse and water pollution control.

Efficient Adsorption of Tebuconazole in Aqueous Solution by Calcium Modified Water Hyacinth-Based Biochar: Adsorption Kinetics, Mechanism, and Feasibility

The application of fungicides (such as tebuconazole) can impose harmful impacts on the ecosystem and humans. In this study, a new calcium modified water hyacinth-based biochar (WHCBC) was prepared and its effectiveness for removing tebuconazole (TE) via adsorption from water was tested. The results showed that Ca was loaded chemically (CaC₂O₄) onto the surface of WHCBC. The adsorption capacity of the modified biochar increased by 2.5 times in comparison to that of the unmodified water hyacinth biochar. The enhanced adsorption was attributed to the improved chemical adsorption capacity of the biochar through calcium modification. The adsorption data were better fitted to the pseudo-second-order kinetics and the Langmuir isotherm model, indicating that the adsorption process was dominated by monolayer adsorption. It was found that liquid film diffusion was the main rate-limiting step in the adsorption process. The maximum adsorption capacity of WHCBC was 40.5 mg/g for TE. The results indicate that the absorption mechanisms involved surface complexation, hydrogen bonding, and π-π interactions. The inhibitory rate of Cu²⁺ and Ca²⁺ on the adsorption of TE by WHCBC were at 4.05-22.8%. In contrast, the presence of other coexisting cations (Cr⁶⁺, K⁺, Mg²⁺, Pb²⁺), as well as natural organic matter (humic acid), could promote the adsorption of TE by 4.45-20.9%. In addition, the regeneration rate of WHCBC was able to reach up to 83.3% after five regeneration cycles by desorption stirring with 0.2 mol/L HCl (t = 360 min). The results suggest that WHCBC has a potential in application for removing TE from water.

A Stable Fe-Zn Modified Sludge-Derived Biochar for Diuron Removal: Kinetics, Isotherms, Mechanism, and Practical Research

To remove typical herbicide diuron effectively, a novel sludge-derived modified biochar (SDMBC600) was prepared using sludge-derived biochar (SDBC600) as raw material and Fe-Zn as an activator and modifier in this study. The physico-chemical properties of SDMBC600 and the adsorption behavior of diuron on the SDMBC600 were studied systematically. The adsorption mechanisms as well as practical applications of SDMBC600 were also investigated and examined. The results showed that the SDMBC600 was chemically loaded with Fe-Zn and SDMBC600 had a larger specific surface area (204 m²/g) and pore volume (0.0985 cm³/g). The adsorption of diuron on SDMBC600 followed pseudo-second-order kinetics and the Langmuir isotherm model, with a maximum diuron adsorption capacity of 17.7 mg/g. The biochar could maintain a good adsorption performance (8.88-12.9 mg/g) under wide water quality conditions, in the pH of 2-10 and with the presence of humic acid and six typical metallic ions of 0-20 mg/L. The adsorption mechanisms of SDMBC600 for diuron were found to include surface complexation, π-π binding, hydrogen bonding, as well as pore filling. Additionally, the SDMBC600 was tested to be very stable with very low Fe and Zn leaching concentration ≤0.203 mg/L in the wide pH range. In addition, the SDMBC600 could maintain a high adsorption capacity (99.6%) after four times of regeneration and therefore, SDMBC600 could have a promising application for diuron removal in water treatment.

Pyrolysis temperature affects the physiochemical characteristics of lanthanum-modified biochar derived from orange peels: Insights into the mechanisms of tetracycline adsorption by spectroscopic analysis and theoretical calculations

Biochar (BC) derived from orange peels was modified using LaCl₃ to enhance its tetracycline (TC) adsorption capacity. SEM-EDS, FT-IR, XRD, and BET were used to characterize the physiochemical characteristics of La-modified biochar (La-BC). Batch experiments were conducted to investigate the effects of several variables like pyrolysis temperature, adsorbent dosage, initial pH, and coexisting ions on the adsorption of TC by La-BC. XPS and density functional theory (DFT) were used to elucidate the TC adsorption mechanism of La-BC. The results demonstrated that La was uniformly coated on the surface of the La-BC. The physiochemical characteristics of La-BC highly depended on pyrolysis temperature. Higher temperature increased the specific surface area and functional groups of La-BC, thus enhancing its TC adsorption capacity. La-BC prepared at 700 °C (BC@La-700) achieved the maximum adsorption capacity of 143.20 mg/g, which was 6.8 and 4.6 times higher than that of BC@La-500 and BC@La-600, respectively. The mechanisms of TC adsorption by La-BC were most accurately described by the pseudo-second-order kinetic model. Furthermore, the adsorption isotherm of La-BC was consistent with the Freundlich model. BC@La-700 achieved good TC adsorption efficiencies even at a wide pH range (pH 4-10). Humic acid significantly inhibited TC adsorption by La-BC. The presence of coexisting ions (NH₄⁺, Ca²⁺, NO₃^-) did not significantly affect the adsorption capacity of La-BC, particularly BC@La-700. Moreover, BC@La-700 also exhibited the best recycling performance, which achieved relative high adsorption capacity even after 5 cycles. The XPS results showed that π-π bonds, oxygen-containing functional groups, and La played a major role in the adsorption of TC on La-BC. The result of DFT showed that the adsorption energy of La-BC was the greatest than that of other functional groups on biochar. Collectively, our findings provide a theoretical basis for the development of La-BC based materials to remove TC from wastewater.

Phosphorus recovery and reuse in water bodies with simple ball-milled Ca-loaded biochar

The demand to control eutrophication in water bodies and the risk of phosphorus scarcity have prompted the search for treatment technologies for phosphorus recovery. In this study, ball-milled Ca-loaded biochar (BMCa@BC) composites were prepared with CaO and corn stover biochar as raw materials by a new ball-milling method to recover phosphorus from water bodies. Experimental results demonstrated that BMCa@BC could efficiently adsorb phosphorus in water bodies with an excellent sorption capacity of 329 mg P/g. Hydrogen bonding, electrostatic attraction, complexation, and surface precipitation were involved in adsorption process. In addition, phosphorus recovered by BMCa@BC had high bioavailability (86.7 % of TP) and low loss (3.3 % of TP) and was a potential slow-release fertilizer. P-laden BMCa@BC significantly enhanced seed germination and growth in planting experiments, proving that it could be used as a substitute for P-based fertilizer. After five cycles of regeneration, BMCa@BC still showed good adsorption recovery and the P-enriched desorption solution could be recovered as Ca-P products with the fertilizer value. Overall, BMCa@BC has good cost-effectiveness and practical applicability in phosphorus recovery. This provides a new way to recover and reuse phosphorus effectively.

Effect of water-washing pretreatment on the enhancement of tetracycline adsorption by biogas residue biochar

Biochar preparation was a feasible strategy for realizing the reduction, harmlessness, and resource utilization of biogas residue (BR) simultaneously. How to enhance the adsorption performance of biogas residue biochar through simple, friendly, and effective way still needs to be investigated. In this study, water-washing pretreatment of BR was adopted before biochar preparation (BRBC-W), and pristine biochar (BRBC) was also produced to serve as control. The adsorption behavior and possible adsorption mechanisms of tetracycline (TC) onto biochars were comprehensively studied. The results showed that water-washing pretreatment could increase the surface area and mesoporous volume of biochar from 358.63 to 391.98 cm³∙g^-1, and 0.459 to 0.488 cm³∙g^-1, respectively. More graphitic structure was observed in BRBC-W. In addition, the surface morphology, element content, minerals composition, and surface functional groups also changed in biochar after water-washing pretreatment. The pseudo-second-order and Redlich-Peterson models better descried the adsorption behavior of TC on BCRBC-W. The maximum adsorption capacity of BRBC and BRBC-W for TC based on Langmuir isotherm was 224.93 and 306.94 mg·g^-1, respectively. The adsorption affinity of BRBC-W toward TC was greater than that of BRBC. BRBC and BRBC-W can effectively remove TC in water within a wide pH range and under the interference of co-existing ions. The adsorption mechanism of TC onto BRBC and BRBC-W included ore filling, π-π interaction, and hydrogen bonding. The enhancement of TC on BRBC-W by water-washing pretreatment was attributable to the strengthening of pore diffusion and π-π interaction. Therefore, water-washing pretreatment effectively enhanced the adsorption performance of BRB, and BRBC-W was an effective eco-friendly adsorbent for the removal of TC from aquatic environment.

Rethinking of the intraparticle diffusion adsorption kinetics model: Interpretation, solving methods and applications

Adsorption is a widely used unit process in various fields, such as chemical, environmental and pharmaceutical, etc. The intraparticle diffusion adsorption kinetics model is one of the most widely used adsorption kinetics models. However, the application and solving method of this model have yet to be discussed. This model has two forms (q_t = kt^1/2 and q_t = kt^1/2 + constant, where q_t is the adsorption capacity at time t, k and constant are the model parameters), which have not been unified yet. Moreover, the interpretation of this kinetics model lacks a theoretical basis (if the line passes through the origin point (0, 0), the adsorption is dominated by the intraparticle diffusion; if not, it is a multiple adsorption process). In this study, we analyzed the proper equations of the intraparticle diffusion model and their applications, discussed the interpretation of the mass transfer steps revealed by this model, and provided the solving methods. The result indicated that the piecewise function q_t = k₁t^1/2 (0 ≤ t ≤ t₁); q_t - q_t = t1 = k₂(t - t₁)^1/2 (t₁ < t ≤ t₂) is the proper form of this model. The adsorbate diffusion in the pores inside the adsorbent is the mass transfer step revealed by this model. The statistical parameters should be used to evaluate the fitting results instead of judging whether the model lines pass through the origin point (0, 0). We provide the solving methods to use the Origin and Microsoft EXCEL software to solve the model. Our study established the method for application of the intraparticle diffusion model.