Enhanced adsorption of phosphate on orange peel-based biochar activated by Ca/Zn composite: Adsorption efficiency and mechanisms

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

Machine learning-driven prediction of phosphorus removal performance of metal-modified biochar and optimization of preparation processes considering water quality management objectives

Developing an optimized and targeted design approach for metal-modified biochar based on water quality conditions and management is achievable through machine learning. This study leveraged machine learning to analyze experimental data on phosphate adsorption by metal-modified biochar from literature published in Web of Science. Using six machine learning models, the phosphate adsorption capacity of biochar and residual phosphate concentration were predicted. After hyperparameter optimization, the gradient boosting model exhibited superior training performance (R2 > 0.96). Metal load quantity, solid-liquid ratio, and pH were key factors influencing adsorption performance. Optimal preparation parameters indicated that Mg-modified biochar achieved the highest adsorption capacity (387-396 mg/g), while La-modified biochar displayed the lowest residual phosphate concentration (0 mg/L). The results of verification experiments based on optimized process parameters closely aligned with model predictions. This study introduces a new machine learning-based approach for tailoring biochar preparation processes considering different water quality management objectives.

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.

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

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

Efficiency and mechanism of phosphate adsorption and desorption of a novel Mg-loaded biochar material

Phosphate removal is complicated by the need for resource recovery. Biochar shows promise for efficient phosphate adsorption, but it must be modified to enhance its adsorption capacity. In this work, magnesium (Mg)-loaded biochar was synthesized through a two-step dipping and calcination process, and the MgBC600 product was used to adsorb phosphate from simulated water and biogas slurry wastewater. The phosphate adsorption capacity of Mg-loaded biochar was 109.35 mg/g, which was 12 times higher than that of unmodified biochar. The R2 of the Langmuir and pseudo-second-order kinetic models were 0.988 and 0.990, respectively, which fitted the phosphate adsorption process of MgBC600. Phosphate adsorption by MgBC600 was a spontaneous and endothermic process. The adsorption mechanism study showed that phosphate adsorption was controlled by the formation and electrostatic attraction of MgHPO4. In addition, 98% of chemically adsorbed phosphate was released after regeneration. Using phosphate-adsorbed MgBC600 as a soil amendment, Arabidopsis thaliana was 1.47 times higher than that in the biochar-only group, demonstrating that this is a promising strategy for enhancing phosphate adsorption efficiency and adsorbent recycling.

Effect of Modified Biochar Prepared by Co-pyrolysis of MgO on Phosphate Adsorption Performance and Seed Germination

Biochar is currently used as a phosphate adsorbent in water and subsequently as a soil amendment. In this study, modified biochar was prepared directly by co-pyrolysis of MgO and rice straw, and a preliminary ecotoxicological assessment was performed before the application of modified biochar to soil. The effects of single factors, such as pyrolysis temperature, dosage, pH, and coexisting ions, on phosphate adsorption performance were investigated. In addition, after phosphate adsorption, the effects of modified biochar leachate on the germination of corn and rice seeds were examined. The results showed that phosphate adsorption by the modified biochar first increased and then decreased as the pyrolysis temperature increased, with modified biochar prepared at 800 °C showing the greatest adsorption. In addition, a comprehensive cost analysis showed that the best phosphate adsorption effect of modified biochar was achieved at a dosage of 0.10 g and a solution pH of 3. In contrast, the presence of competitive coexisting ions, Cl- , NO3 - , CO3 2- , and SO4 2- , reduced the phosphate adsorption capacity of the modified biochar. The adsorption kinetics results revealed that the process of phosphate adsorption by the modified biochar was more in line with the pseudo-second-order model and dominated by chemisorption. Moreover, the adsorption isotherm results indicated that the process was more in line with the Langmuir model and dominated by monomolecular layer adsorption, with a maximum adsorption of 217.54 mg/g. Subsequent seed germination tests showed that phosphate-adsorbed modified biochar leachate had no significant effect on the germination rate of corn seeds, whereas it improved the germination rate of rice seeds. Together, these results provide guidance for the application of modified biochar firstly as an adsorbent of phosphate and subsequently as a soil remediator.

Occurrence, toxicity, impact and removal of selected non-steroidal anti-inflammatory drugs (NSAIDs): A review

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most frequently used pharmaceuticals for human therapy, pet therapeutics, and veterinary feeds, enabling them to enter into water sources such as wastewater, soil and sediment, and seawater. The control of NSAIDs has led to the advent of the novel materials for treatment techniques. Herein, we review the occurrence, impact and toxicity of NSAIDs against aquatic microorganisms, plants and humans. Typical NSAIDs, e.g., ibuprofen, ketoprofen, diclofenac, naproxen and aspirin were detected at high concentrations in wastewater up to 2,747,000 ng L-1. NSAIDs in water could cause genotoxicity, endocrine disruption, locomotive disorders, body deformations, organs damage, and photosynthetic corruption. Considering treatment methods, among adsorbents for removal of NSAIDs from water, metal-organic frameworks (10.7-638 mg g-1) and advanced porous carbons (7.4-400 mg g-1) were the most robust. Therefore, these carbon-based adsorbents showed promise in efficiency for the treatment of NSAIDs.

Density functional theory study on the formation mechanism of CaClOH in municipal solid waste incineration fly ash

Municipal solid waste incineration (MSWI) fly ash is defined as a kind of hazardous waste because of its high levels of multiple pollutants. The main component of MSWI fly ash is CaClOH, and the characteristics have not achieved consensus. And density functional theory (DFT) was used to calculate the formation process of CaClOH in this study, which mainly included HCl adsorption on CaO (0 0 1) surface and Ca(OH)2 (0 0 1) surface and the surface reaction process. The reaction mechanism was investigated. The results showed that the maximum adsorption energies of HCl on CaO and Ca(OH)2 surfaces reached - 195.17 kJ/mol and - 83.48 kJ/mol, respectively, representing strong chemisorption. The chemisorption process was shown as the adsorption of H atom on O site, and the adsorption capacity was reflected in the adsorption range of O site. The significant electron density overlap between O site and H atom meant that a new chemical bond formed, which made the adsorption structure stable. The adsorption energy of multi-HCl adsorption on the crystal surfaces was not proportional to the number of HCl molecule, indicating that the adsorption processes were influenced by each other. After surface reaction, the H-Cl bond was broken completely, and the structure of CaO and Ca(OH)2 changed to new structures. According to transition state (TS) search, the formation of CaClOH had a higher priority, easier than that of CaCl2, explaining the presence of CaClOH in fly ash. The study provides helpful information for the solidification treatment of fly ash.

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.

Biochar for the Removal of Emerging Pollutants from Aquatic Systems: A Review

Water contaminated with emerging pollutants has become a serious environmental issue globally. Biochar is a porous and carbon-rich material produced from biomass pyrolysis and has the potential to be used as an integrated adsorptive material. Many studies have shown that biochar is capable to adsorb emerging pollutants from aquatic systems and could be used to solve the water pollution problem. Here, we provided a dual perspective on removing emerging pollutants from aquatic systems using biochar and analyzed the emerging pollutant removal efficiency from the aspects of biochar types, pollutant types and coexistence with heavy metals, as well as the associated mechanisms. The potential risks and future research directions of biochar utilization are also presented. This review aims to assist researchers interested in using biochar for emerging pollutants remediation in aquatic systems and facilitate research on emerging pollutants removal, thereby reducing their environmental risk.

Sewage sludge derived biochar for environmental improvement: Advances, challenges, and solutions

With the rapid growth yield of global sewage sludge, rational and effective treatment and disposal methods are becoming increasingly needed. Biochar preparation is an attractive option for sewage sludge treatment, the excellent physical and chemical properties of sludge derived biochar make it an attractive option for environmental improvement. Here, the current application state of sludge derived biochar was comprehensively reviewed, and the advances in the mechanism and capacity of sludge biochar in water contaminant removal, soil remediation, and carbon emission reduction were described, with particular attention to the key challenges involved, e.g., possible environmental risks and low efficiency. Several new strategies for overcoming sludge biochar application barriers to realize highly efficient environmental improvement were highlighted, including biochar modification, co-pyrolysis, feedstock selection and pretreatment. The insights offered in this review will facilitate further development of sewage sludge derived biochar, towards addressing the obstacles in its application in environmental improvement and global environmental crisis.

Efficient and Stable Rice Husk Bioderived Silica Supported Cu2S-FeS for One Pot Esterification and Transesterification of a Malaysian Palm Fatty Acid Distillate

A novel heterogeneous catalyst composite (CuS-FeS/SiO2) derived from rice husk silica was engineered following pyrolysis, chemical precipitation, and chemical redox technique. The resulting catalyst was applied to the conversion of palm fatty acid distillate to biodiesel. The presence of CuS and FeS on the catalyst was verified using X-ray diffraction and Fourier transform infrared spectroscopy, nitrogen physisorption, scanning electron microscopy (FESEM) with energy dispersive X-ray (EDS) spectroscopy, and temperature-programmed desorption of NH3 (TPD-NH3), inductively coupled plasma-atomic emission spectrometry (ICP-AES), and TGA; a specific surface area of approximately 40 m2·g−1 was identified. The impact of independent variables, i.e., reaction temperature, reaction duration, methanol:oil ratio and catalyst concentration were evaluated with respect to the efficacy of the esterification reaction. The greatest efficiency of 98% with a high productivity rate of 2639.92 µmol·g−1·min−1 with k of 4.03 × 10−6 mole·S−1 was achieved with the following parameters: temperature, 70 °C; duration, 180 min; catalyst loading, 2 wt.%; and methanol to oil ratio, 15:1. The CuS-FeS/SiO2 catalyst showed relatively high stability indicated by its ability to be reused up to five times.

Phosphate adsorption improvement using a novel adsorbent by CaFe/LDH supported onto CO2 activated biochar

It is imperative to remove phosphate from the aquatic system. This nutrient in excess can cause environmental problems such as eutrophication. Therefore, aiming to enhance phosphate removal, this work presents a novel adsorbent developed from the construction of Ca²⁺/Fe³⁺ layer double hydroxides (CaFe/LDH) supported onto biochar physically activated with CO₂ [CaFe/biochar (CO₂)]. Pristine biochar was produced from the pyrolysis of Eucalyptus saligna sawdust, activated with CO₂, and then impregnated with CaFe/LDH. The CaFe/biochar (CO₂) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET). The characterization confirmed a proper synthesis of the new adsorbent. Experiments were conducted in the form of batch adsorption. Results indicated that the optimum pH and adsorbent dosage were 2.15 and 0.92 g L^-1, respectively. Adsorption kinetics, isotherms, and thermodynamics were also evaluated. Adsorption kinetics and isotherms were better fitted by the pseudo n order and Freundlich models, respectively. Results also indicated a better adsorption capacity (99.55 mg·g^-1) at 55 °C. The thermodynamic indicators depicted that the adsorption process was favorable, spontaneous, and endothermic. Overall, CaFe/biochar (CO₂) could be potentially applied for the adsorptive removal of phosphate from an aqueous solution.

Cow Dung-Based Biochar Materials Prepared via Mixed Base and Its Application in the Removal of Organic Pollutants

Cow dung (CD) is a waste product of livestock production. Improper disposal of a large amount of CD will cause environmental pollution. In this work, three biochar materials based on CD (BMCD) were prepared by using three types of base, including KOH, NaOH, and mixed base (MB, a mixture of equal mass NaOH and KOH) as activators to investigate the different physicochemical properties of BMCDs (BMCD-K, BMCD-Na, and BMCD-MB). The objective was to verify the effectiveness of MB activation in the preparation of biochar materials. The results show that MB has an effect on the structural characteristics of BMCDs. In particular, the surface area and total pore volume, the specific surface area, and the total pore volume of BMCD-MB (4081.1 m² g⁻¹ and 3.0118 cm³ g⁻¹) are significantly larger than those of BMCD-K (1784.6 m² g⁻¹ and 1.1142 cm³ g⁻¹) and BMCD-Na (1446.1 m² g⁻¹ and 1.0788 cm³ g⁻¹). While synthetic dye rhodamine B (RhB) and antibiotic tetracycline hydrochloride (TH) were selected as organic pollutant models to explore the adsorption performances, the maximum adsorption capacities of BMCD-K, BMCD-NA and BMCD-MB were 951, 770, and 1241 mg g⁻¹ for RhB, 975, 1051, and 1105 mg g⁻¹ for TH, respectively, which were higher than those of most adsorbents. This study demonstrated that MB can be used as an effective activator for the preparation of biochar materials with enhanced performance.