Cadmium removal by MgCl2 modified biochar derived from crayfish shell waste: Batch adsorption, response surface analysis and fixed bed filtration

Investigating the Dewatering Efficiency of Sewage Sludge with Optimized Ratios of Electrolytic Manganese Residue Components

As an industrial waste residue, Electrolytic Manganese Residue (EMR) can greatly promote sludge dewatering and further particle-size optimization can significantly strengthen sludge dewaterability. In this study, the effects of ammonium sulfate, calcium sulphate dihydrate, and manganese carbonate in EMR on sludge dewatering performance were investigated using the response surface optimization method. It was found that the optimized ratio of three components in EMR was 1.0:1.6:2.2 based on capillary suction time (CST), specific resistance of filtration (SRF), and zeta potential of dewatered sludge. The composition ratio of particle-size optimized EMR was modified based on the above optimization, resulting in a significant increase in sludge dewatering performance (CST and SRF reduced by 8.7% and 11.2%, respectively). Compared with those in original sludge, the content of bound extracellular polymeric substances in the conditioned sludge with optimized ratio was drastically reduced while that of soluble extracellular polymeric substances was slightly increased, which was in accordance with the decline of fluorescence intensity. These findings indicated the disintegration of extracellular polymeric substances, the enhancement of hydrophobicity, and dewatering properties of the sludge. In summary, optimized EMR can effectively intensify the dewaterability of sludge, providing a competitive solution for dewatering and further disposal of sludge.

Silica-magnesium coupling in lignin-based biochar: A promising remediation for composite heavy metal pollution in environment

Lignin hydrothermal silica-carbon material served as a backbone for MgCl2 activation to prepare lignin-based silicon/magnesia biochar (ALB/Si-Mg) for Cd2+, Pb2+, Cu2+, and Zn2+ removal from water and soil environment. Characterization studies revealed a 1017.71-fold increase in the specific surface area of ALB/Si-Mg compared to the original lignin biochar (ALB), producing abundant oxygen functional groups (OC-O, Si-O, Mg-O), and mineral matter (Mg2SiO4 and MgO). Crucially, batch adsorption experiments demonstrated that the adsorption capacity of ALB/Si-Mg for Cd2+, Pb2+, Cu2+, and Zn2+ was 848.17, 665.07, 151.84, and 245.78 mg/g, which were 29.09-140.45 times of the ALB. Soil remediation experiments showed that applying ALB/Si-Mg increased soil effective silicon (109.04%-450.2%) and soil exchangeable magnesium (276.41%-878.66%), enhanced plant photosynthesis, and notably reduced the bioavailability of heavy metals in soil as well as the content of heavy metals in Pakchoi, thereby promoting Pakchoi growth and development. The presence of oxygen-containing functional groups on ALB/Si-Mg, along with Mg2SiO4 and MgO nanoparticles, enhanced the adsorption capacity for heavy metals through the promotion of heavy metal precipitation, ion exchange, and complexation mechanisms. This study establishes the groundwork for the coupling of silica and magnesium elements in biochar and the remediation of composite heavy metal environmental pollution.

Sodium hydroxide/magnesium chloride multistage activated sludge biochar: interfacial chemical behavior and Cd(II) adsorption performance

To enhance the adsorption performance of municipal sludge biochar on Cd(II), modified sludge biochar was prepared by sodium hydroxide/magnesium chloride (NaOH/MgCl2) graded activation, and the Cd(II) adsorption performance on sludge biochar (BC), NaOH-activated sludge biochar (NBC) and NaOH/MgCl2 activated sludge biochar (NBC-Mg) was investigated. The results showed that NaOH/MgCl2 graded activation upgraded the surface structure and enhanced the graphitization of sludge biochar. The adsorption experiments indicated that the adsorption kinetic and adsorption isotherm for Cd(II) were in accordance with the pseudo second-order kinetic and Langmuir model. The adsorption capacity of NBC-Mg (143.49 mg/g) for Cd(II) was higher than that of BC (50.40 mg/g) and NBC (85.20 mg/g). The mechanism of Cd(II) adsorption included ion exchange, complexation, cation-π interaction, and mineral precipitation. After five regeneration, the removal efficiency of Cd(II) by NBC-Mg remained above 90%. This work indicated that sludge biochar prepared by multistage activation could be an effective material for Cd-containing wastewater treatment.

Developing a sorptive material of cadmium from pyrolysis of hen manure

A large amount of manure is generated from concentrated animal feeding operations (CAFOs), leading to serious environmental issues and hazardous risks from pathogens, such as methicillin-resistant Staphylococcus aureus. Therefore, developing an effective method for manure disposal is essential. Thus, in this study, we suggest the use of CO2 in pyrolysis of hen manure (HM) as an effective method to convert the carbon in HM into syngas (especially carbon monoxide (CO)). HM was used and tested as the model compound. From the results of thermo-gravimetric analysis, the decarboxylation of CaCO3 in HM in the presence of N2 was realized at temperatures ranging from 638 to 754 °C. The Boudouard reaction was observed at ≥ 664 °C in the presence of CO2. Despite the lack of occurrence of the Boudouard reaction, more CO formation was observed in the presence of CO2 at ≥ 460 °C. This was deemed as a homogeneous reaction induced by CO2. Considering the high Ca content of HM, HM biochar in N2 and CO2 were used as adsorbent for removal of Cadmium (Cd), which is toxic heavy metal. The adsorption capacities of HM_N2 and HM_CO2 were 302.4 and 95.7 mg g-1, respectively. The superior performance of HM_N2 is mainly attributed to the presence of Ca(OH)2, which provides favorable (alkaline) conditions for precipitation and ion exchange. Our results indicate the environmental benefits from using CO2. Specifically, CO2 (representative greenhouse gas) converted into fuel. Given this, pyrolysis of HM in the presence of CO2 was achieved at ≤ 640 °C, and the atmospheric condition should be switched from CO2 to N2 at ≥ 640 °C to ensure the decarboxylation of CaCO3.

Biochar as Alternative Material for Heavy Metal Adsorption from Groundwaters: Lab-Scale (Column) Experiment Review

The purpose of this manuscript is to present a review of laboratory experiments (including methodology and results) that use biochar, a specific carbon obtained by a pyrolysis process from different feedstocks, as an alternative material for heavy metal adsorption from groundwater. In recent years, many studies have been conducted regarding the application of innovative materials to water decontamination to develop a more sustainable approach to remediation processes. The use of biochar for groundwater remediation has particularly attracted the interest of researchers because it permits the reuse of materials that would be otherwise disposed of, in accordance with circular economy, and reduces the generation of greenhouse gases if compared to the use of virgin materials. A review of the different approaches and results reported in the current literature could be useful because when applying remediation technologies at the field scale, a preliminary phase in which the suitability of the adsorbent is evaluated at the lab scale is often necessary. This paper is therefore organised with a short description of the involved metals and of the biochar production and composition. A comprehensive analysis of the current knowledge related to the use of biochar in groundwater remediation at the laboratory scale to obtain the characteristic parameters of the process that are necessary for the upscaling of the technology at the field scale is also presented. An overview of the results achieved using different experimental conditions, such as the chemical properties and dosage of biochar as well as heavy metal concentrations with their different values of pH, is reported. At the end, numerical studies useful for the interpretation of the experiment results are introduced.

Ammonia removal and simultaneous immobilization of manganese and magnesium from electrolytic manganese residue by a low-temperature CaO roasting process

A large amount of open-dumped electrolytic manganese residue (EMR) has posed a severe threat to the ecosystem and public health due to the leaching of ammonia (NH4+) and manganese (Mn). In this study, CaO addition coupled with low-temperature roasting was applied for the treatment of EMR. The effects of roasting temperature, roasting time, CaO-EMR mass ratio and solid-liquid ratio were investigated. The most cost-effective and practically viable condition was explored through response surface methodology. At a CaO: EMR ratio of 1:16.7, after roasting at 187 °C for 60 min, the leaching concentrations of NH4+ and Mn dropped to 10.18 mg/L and 1.05 mg/L, respectively, below their discharge standards. In addition, the magnesium hazard (MH) of EMR, which was often neglected, was studied. After treatment, the MH of the EMR leachate was reduced from 60 to 37. Mechanism analysis reveals that roasting can promote NH4+ to escape as NH3 and convert dihydrate gypsum to hemihydrate gypsum. Mn2+ and Mg2+ were mainly solidified as MnO2 and Mg(OH)2, respectively. This study proposes an efficient and low-cost approach for the treatment of EMR and provides valuable information for its practical application.

Characterization of Water Vapor Sorption Performance and Heat Storage of MIL-101 (Cr) Complex MgCl2, LiCl/LaCl3 System for Adsorptive Thermal Conversion

Adsorption heat conversion systems can provide heating and cooling across time and space in a more environmentally friendly way. Porous materials are potential candidates for water-based adsorption thermal conversion, in which a metal-organic framework (MOF) has a larger specific surface area and porosity than other porous matrices. However, many MOFs with high saturated adsorption capacity have great deficiencies in performance at low water vapor partial pressure, which hinder their application in adsorption thermal conversion. To improve the water vapor adsorption performance of MIL-101 (Cr), different contents of magnesium chloride, lithium chloride, and lanthanum chloride are mixed into MIL-101 (Cr) by an impregnation method. The properties and structures of the materials are characterized by XRD, SEM, nitrogen adsorption tests, water vapor adsorption tests, TG, FTIR, and so on. The results show that the saturated water vapor adsorption capacity of the sample impregnated with salt increases by 1.5-2.3 times, up to 2.24 g/g, compared with that of the unimpregnated sample. When the partial pressure of water vapor is 0.3, the adsorption capacity increases by 5.3-7.5 times and reaches 0.68 g/g at most. The maximum heat storage density of impregnated samples can be increased by 866 J/g. Impregnated MgCl2 can greatly improve the adsorption and thermal conversion performance of MOF, and impregnated MgCl2 and the proper amount of LiCl can further improve the performance of the material system. Our experiments show that the composite impregnation of magnesium chloride and the proper amount of lithium chloride can improve the application performance of the MOF materials in the adsorption thermal conversion process.

Adsorption characteristics and mechanisms of Cd(II) from wastewater by modified chicken manure biochar

Due to the threat to food supply and human health posed by cadmium-contaminated wastewater, a highly effective adsorbent is under necessary development to remove cadmium from wastewater. In this study, four new types of modified biochars with different modifier concentrations were prepared from chicken manure using K2FeO4 as a modifier, and the modified biochar KFBC1 with the best adsorption effect was obtained through optimal experiments. Various characterization analyses have shown that KFBC1 has a rough surface structure, abundant pore structure, and a large number of functional groups. Additionally, iron oxides are introduced on the surface of the biochar, which provided a favorable condition for the adsorption of Cd(II) in wastewater. The adsorption performance of Cd(II) on the biochar before and after modification was investigated through batch adsorption experiments. The adsorption kinetic model of KFBC1 to Cd(II) in solution was in accordance with the quasi-secondary kinetic model, and the adsorption isothermal model was in accordance with the Langmuir model, with a maximum adsorption capacity of 330.06 mg/g, which was 5.15 fold of pristine BC. Meanwhile, the adsorption rate of Cd(II) by KFBC1 was positively correlated with dosage and pH. Pore adsorption, ion exchange, surface precipitation, interaction with -π electrons, and complexation of oxygen-containing functional groups on the surface were considered as important mechanisms for the removal of Cd(II) by KFBC1. According to the results, KFBC1 is a novel and efficient adsorbent that can be used as a treatment agent for cadmium-contaminated wastewater.

Saccharomyces cerevisiae additions normalized hemocyte differential genes expression and regulated crayfish (Procambarus clarkii) oxidative damage under cadmium stress

Because China produces the most crayfish in the world, safe solutions must be improved to mitigate the risks of ongoing heavy metal stressors accumulation. This study aimed to use Saccharomyces cerevisiae as a bioremediation agent to counteract the harmful effect of cadmium (Cd) on crayfish (Procambarus clarkia). Our study used three concentrations of S. cerevisiae on crayfish feed to assess their Cd toxicity remediation effect by measuring total antioxidant capacity (TAC) and the biomarkers related to oxidative stress like malondialdehyde (MDA), protein carbonyl derivates (PCO), and DNA-protein crosslink (DPC). A graphite furnace atomic absorption spectroscopy device was used to determine Cd contents in crayfish. Furthermore, the mRNA expression levels of lysozyme (LSZ), metallothionein (MT), and prophenoloxidase (proPO) were evaluated before and following the addition of S. cerevisiae. The results indicated that S. cerevisae at 5% supplemented in fundamental feed exhibited the best removal effect, and Cd removal rates at days 4th, 8th, 12th, and 21st were 12, 19, 29.7, and 66.45%, respectively, which were significantly higher than the basal diet of crayfish. The addition of S. cerevisiae increased TAC levels. On the other hand, it decreased MDA, PCO, and DPC, which had risen due to Cd exposure. Furthermore, it increased the expression of proPO, which was reduced by Cd exposure, and decreased the expression of LSZ and MT, acting in the opposite direction of Cd exposure alone. These findings demonstrated that feeding S. cerevisiae effectively reduces the Cd from crayfish and could be used to develop Cd-free crayfish-based foods.

Adsorption properties and mechanism of suaeda biochar and modified materials for tetracycline

Adsorption was an available way to eliminate Tetracycline (TC) from waste water. Suaeda biochar (800SBC) and iron modified biochar (Fe-800SBC) were prepared using pyrolysis under oxygen-limiting conditions. BET and SEM showed that the surface of Fe-800SBC was rougher, and the specific surface area (SBET) was 7 times that of 800SBC. There existed pore filling, ion exchange, metal ion complexation, hydrogen bonds and cation-π interaction mechanism. Both 800SBC and Fe-800SBC conformed to quasi-second-order kinetics model, belonged to chemisorption. Fe-800SBC conformed to Elovich model too. The adsorption process of 800SBC conformed to Freundlich and Sips L-F models, Fe-800SBC conformed to the Sips L-F and Temkin models, identifying the presence of physical and chemical adsorption during adsorption. Response surface method (RSM) was used to optimize important process parameters. The quadratic model was sufficient to predict TC removal response in the range of studied parameters.

Cadmium and lead removal by Mg/Fe bimetallic oxide-loaded sludge-derived biochar: batch adsorption, kinetics, and mechanism

Biochar is a valuable adsorbent for the removal of heavy metals from water, and it is important to explore ways to increase its heavy metal adsorption capacity. In this study, Mg/Fe bimetallic oxide was loaded onto sewage sludge-derived biochar to enhance its heavy metal adsorption capacity. Batch adsorption experiments for the removal of Pb(II) and Cd(II) were performed to evaluate the removal efficiency of Mg/Fe layer bimetallic oxide-loaded sludge-derived biochar ((Mg/Fe)LDO-ASB). The physicochemical properties of (Mg/Fe)LDO-ASB and corresponding adsorption mechanisms were studied. The maximum adsorption capacities of (Mg/Fe)LDO-ASB for Pb(II) and Cd(II), which were calculated by isotherm model, were 408.31 and 270.41 mg/g, respectively. Adsorption kinetics and isotherms analysis showed that the dominant adsorption process of Pb(II) and Cd(II) uptake by (Mg/Fe)LDO-ASB was spontaneous chemisorption and heterogeneous multilayer adsorption, and film diffusion was the rate-limiting step. SEM-EDS, FTIR, XRD, and XPS analyses revealed that the Pb and Cd adsorption processes of (Mg/Fe)LDO-ASB involved oxygen-containing functional group complexation, mineral precipitation, electron-π-metal interactions, and ion exchange. The order of their contribution was as follows: mineral precipitation (Pb: 87.92% and Cd: 79.91%) > ion exchange (Pb: 9.84% and Cd: 16.45%) > metal-π interaction (Pb: 0.85% and Cd: 0.73%) > oxygen-containing functional group complexation (Pb: 1.39% and Cd: 2.91%). Mineral precipitation was the main adsorption mechanism, and ion exchange played a crucial role in Pb and Cd adsorption.

The importance of presoaking to improve the efficiency of MgCl2-modified and non-modified biochar in the adsorption of cadmium

Investigating the effect of presoaking, as one of the most important physical factors affecting the adsorption behavior of biochar, on the adsorption of heavy metals by modified or non-modified biochar and presoaking mechanism is still an open issue. In this study, the water presoaking effect on the kinetics of cadmium (Cd) adsorption by rice husk biochar (produced at 450 °C, B1, and at 600 °C, B2) and the rice husk biochar modified with magnesium chloride (B1 modified with MgCl₂, MB1, and B2 modified with MgCl₂, MB2) was investigated. Furthermore, the effect of pH (2, 5, and 6), temperature (15, 25, and 35 °C), and biochar particle size (100 and 500 µm) on the kinetics of Cd adsorption was also investigated. Results revealed that the content of Cd adsorbed by the presoaked biochar was significantly higher than that by the non-presoaked biochar. The highest Cd adsorption capacity of MB2 and MB1 was 98.4 and 97.6 mg g^-1, respectively, which was much better than that of B1 (7.6 mg g^-1) and B2 (7.5 mg g^-1). The modeling of kinetics results showed that in all cases pseudo-second-order model was well-fitted (R²>0.99) with Cd adsorption data. The results also indicated that the highest Cd adsorption values were observed at pH 6 in presoaked MB1 with size of 100 µm as well as at the temperature of 35 °C in presoaked MB2, indicating the optimum conditions for this process. The presoaking process was not affected by biochar size and pH, and the difference in adsorbed Cd content between presoaked biochars and non-presoaked ones was also similar. However, the temperature had a negative effect on presoaking. The presoaking process decreased micropores (<10 µm) in the biochars but had no effect on biochar hydrophobicity. Therefore, presoaking, which could significantly increase Cd adsorption and reduce equilibrium time by reducing the micropores of biochars, is suggested as an effective strategy for improving the efficiency of modified biochars or non-modified ones in the adsorption of contaminants (Cd) from aquatic media.

Selective removal behavior of lead and cadmium from calcium-rich solution by MgO loaded soybean straw biochars and mechanism analysis

Modified biochars has great potential for removing heavy metals from aquatic environments, but the removal of heavy metals by biochars is usually significantly affected by the co-presence of the macro amount of metal ions, such as Ca. Enhancing the ion exchange capacity of biochar by increasing its alkali metal content is a very prospective method to improve its selectivity. In this paper, MgO loaded biochar (MBC) was synthesized by co-pyrolysis of soybean straw and MgCl₂·6H₂O for selective remove Pb and Cd from calcium-rich wastewater. MBC exhibited excellent selective adsorption performance for Pb and Cd in calcium-rich wastewater due to the successful loading of MgO. The adsorption capacities of MBC for Pb and Cd were 582.57 and 167.40 mg/g, and the removal efficiency of Ca below 2.5% with an initial concentration of 800 mg/L. The ion exchange capacities of Pb and Cd enhanced almost 27 and 23 times than BC. By analyzing the results of BET, XRD, SEM-EDS, XPS and FTIR, the adsorption mechanisms of MBC were mainly including ion exchange, precipitation with minerals, and interaction with oxygen-containing functional groups. The easy preparation method and high selective adsorption capacity makes MBC an ideal alternative for efficiently selective removal Pb and Cd from calcium-rich wastewater.

Nano-chlorapatite modification enhancing cadmium(II) adsorption capacity of crop residue biochars

Cadmium (Cd) contamination in rivers or lakes has attracted worldwide concerns. Biochar pyrolyzed form crop residues (CR) could adsorb Cd(II) from aquatic environments, while the removal capacity of single CR biochar is relatively low. Nano-chlorapatite (nClAP) modification can enhance metal scavenging ability, but little is known about the behaviors and mechanisms of Cd(II) adsorption by nClAP-modified CR biochars. In this study, the influences of feedstock type, pyrolysis temperature, nClAP modification and aquatic environments on Cd(II) adsorption of biochars derived from rice (RB) and wheat (WB) husks were investigated comprehensively. Results showed that the pristine RB and WB showed low and similar Cd(II) adsorption capacities, while the rise of pyrolysis temperatures from 300 to 600 °C significantly improved the adsorption capacities. The Cd(II) adsorption of both RB and WB was regarded as monolayer chemical processes controlled by chemical precipitation, surface complexation and cation exchange mechanisms. Moreover, the nClAP modification notably enhanced Cd(II) adsorption capacities from 13.2 to 39.9 mg·g^-1 of pristine biochars to 25.2-60.7 mg·g^-1 of modified biochars attributed to the improved contribution of Cd(II)-phosphate precipitation. Among all biochars, the nClAP-modified RB and WB pyrolyzed at 500 °C had the highest Cd(II) adsorption capacities with 60.7 and 48.3 mg·g^-1, respectively. These biochars could maintain good adsorption performances under the neutral-alkaline (pH 6-8), low ionic strength, high dissolved organic matter and all oxidation-reduction potential conditions. In conclusion, this study reveals the importance of nClAP modification to optimize Cd(II) adsorption of CR biochars, which provides a promising future for its practical application in aquatic Cd(II) scavenging.

Efficient removal of uranium(VI) from aqueous solution by a novel phosphate-modified biochar supporting zero-valent iron composite

Uranium (U) is an important strategic resource as well as a heavy metal element with both chemical and radiotoxicity. At present, the rapid and efficient removal of uranium from wastewater remains a huge challenge for environmental protection and ecological security. In this paper, phosphate-modified biochar supporting nano zero-valent iron (PBC/nZVI) was triumphantly prepared and fully characterized. The introduction of polyphosphate can greatly increase the specific surface area of biochar pores, and then the zero-valent iron can be evenly distributed on the surface of material, thus leading to excellent removal performance of the PBC/nZVI for U(VI). The theoretical maximum U(VI) removal capacity of PBC/nZVI was up to 967.53 mg/g at pH 5. The results of adsorption kinetics, isotherm, and thermodynamics showed that the adsorption of uranium by PBC/nZVI was a monolayer physical adsorption and endothermic reaction. And the PBC/nZVI has favorable selectivity toward uranium against the interference of coexisting metal ions. Further mechanism studies show that the excellent uranium removal performance of PBC/nZVI is mainly attributed to the synergistic effect of physical adsorption and chemical reduction. This work proves that the PBC/nZVI has a wide application prospect in the field of uranium wastewater treatment.

Removal of Cd2+ from wastewater to form a three-dimensional fiber network using Si-Mg doped industrial lignin-based carbon materials

In this study, SiMg doped industrial lignin-based carbon materials (SLCs) were prepared by water bath silicification and MgCl₂ activation to remove Cd²⁺ from aqueous solutions. What's more, the doping of SiMg jointly promoted the excellent physicochemical properties of the material, e.g., high specific surface area, good pore volume, and numerous oxygen-containing groups. The Cd²⁺ batch adsorption experiments proved that SLCs have good Cd²⁺ removal capacity within pH 3-7, and the adsorption model demonstrated the adsorption process as a physicochemically complex process. The maximum adsorption of Cd²⁺ in the SLC was 665.35 mg/g, and the contributing factors to the removal of Cd²⁺ were as follows: ion exchange (59.36 %) > Cd²⁺ precipitation (24.93 %) > oxygen-containing functional group complexation (14.79 %) > Cd²⁺-π interactions (0.92 %). In addition, the complexation of SiO, MgO, and Cd precipitates allowed the formation of a three-dimensional fiber mesh structure. The application of SLCs has the potential to eliminate Cd²⁺ pollution in water bodies, and its preparation is simple and environmentally friendly. Finally, this study provides a theoretical basis for an in-depth understanding of the mechanism of heavy metal adsorption by inorganic nonmetals in combination with metal oxides.

Efficient removal of Cd2+ by diatom frustules self-modified in situ with intercellular organic components

The organic modification of three-dimensional porous diatom frustules (biosilica) and their fossils (diatomite) is promising in heavy metal adsorption. However, the preparation of such materials involves complex processes, high costs, and environmental hazards. In this study, organic-biosilica composites based on in situ self-modification of diatoms were prepared by freeze-drying pretreatment. Freeze-drying resulted in the release of the intercellular organic components of diatoms, followed by loading on the surface of their diatom frustules. The bio-adsorbent exhibits outstanding Cd²⁺ adsorption capacity (up to 220.3 mg/g). The adsorption isotherms fitted the Langmuir model and the maximum adsorption capacity was 4 times greater than that of diatom biosilica (54.1 mg/g). The adsorption kinetics of Cd²⁺ was adequately described by a pseudo-second-order model and reached equilibrium within 30 min. By combining focused ion beam thinning with transmission electron microscopy-energy dispersive X-ray spectroscopy, the internal structure of the composite and the Cd²⁺ distribution were investigated. The results showed that the organic matter of the composite adsorbed approximately 10 times more Cd²⁺ than inorganic biosilica. The adsorption mechanism was dominated by complexation between the abundant organic functional groups (amide, carboxyl, and amino groups) on the surfaces of composite and Cd²⁺. The bio-adsorbent was demonstrated to have wide applicability in the presence of competitive cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) and under a wide range of pH (3-10) conditions. Thus, the self-modification of diatoms offers a promising organic-inorganic composite for heavy metal remediation.

An attempt to enhance the adsorption capacity of biochar for organic pollutants - Characteristics of CaCl2 biochar under multiple design conditions

Activators affect the physical and chemical properties of carbon products. However, the effects of different activation mechanisms and pyrolysis conditions on the properties of carbon products still need to be explored. In this study, we obtained a new biochar by impregnation of reed powder with an alkali metal salt (CaCl2) under a specific pyrolysis procedure and pyrolysis conditions. Impregnation by CaCl2 can reduce the activation energy of the biomass while capturing and immobilizing oxygenated organic matter during pyrolysis. The new biochar has a high adsorption capacity of organic matters, for example Bisphenol A (BPA). The adsorption results showed that the modified biochar demonstrated a 364.5 % improvement in the adsorption capacity compared to the original biochar. The final performance enhancement was correlated with the confinement conditions of the environment and the procedure of pyrolysis. These procedures ultimately changed the pore distribution, functional group type, aromaticity, and degree of defects of the modified biochar. This study is important to screen synthetic pathways for identifying compounds with excellent adsorption effects.

Biochar for the removal of contaminants from soil and water: a review

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.

Graphical Abstract

First "unsaturated soils" view towards quantitative adsorption and immobilization mechanisms of Cd by biochar in soils during aging

Instead of traditional batch and column experiments with large water-soil ratios, this study investigated the behaviors and mechanisms of Cd adsorption and immobilization by biochar in unsaturated soils, in which the soil moisture conditions were closer to those in the actual field. The transport, transformation, and immobilization of cadmium (Cd) by pristine and KMnO₄-modified biochars in unsaturated soils were investigated during a 48-week mild aging process. Biochar acidified with HCl solution was employed to quantify the contributions of mineral and non-mineral components in biochar to Cd adsorption and immobilization in unsaturated soils with a three-layer mesh method. The behaviors and mechanisms of Cd adsorption by biochar in unsaturated soils significantly differed from those in aqueous solutions. The equilibrium times of Cd adsorption by biochar in unsaturated soils (weeks) were much longer than those in aqueous solutions (hours). The percentages of the Cd adsorbed by pristine and modified biochar remained relatively constant relative to the total Cd in unsaturated soils, which accounted for 39.50-49.39 % and 57.35-68.94 %, respectively. The contribution of mineral components to Cd adsorption dominated in both unsaturated soils (45.00-94.09 %) and aqueous solutions (70.73-95.51 %). The process of Cd immobilization in unsaturated soils was that biochar firstly adsorbed the exchangeable Cd from the soil, and then converted it to relatively stable Cd. After aging for 48 weeks, the contributions of non-mineral components to Cd immobilization dominated in unsaturated soil with a low concentration (1.23 mg·kg^-1), and the contributions of mineral components to Cd immobilization dominated in unsaturated soil with medium-high concentrations (4.08-51.26 mg·kg^-1).

The effect of adsorption on the fate of colloidal polystyrene microplastics in drinking water distribution system pipe scales

With microplastics (MPs) being continuously found in various environments, the pollution of water supply systems by MPs is receiving increasing attention. As the sediment in drinking water distribution systems (DWDSs), pipe scales act as the interface for complex reactions between bulk water and pipe surfaces. Consequently, the fate of MPs in pipe scales requires exploration, especially colloidal MPs. In this study, MPs were detected in different pipe scale layers, with concentrations of 0.32-3.10 items g^-1. Subsequently, the adsorption interaction mechanisms between pipe scales and colloidal polystyrene microplastics (PSMPs) were investigated through batch adsorption experiments. The findings indicated that pipe scales showed a potential adsorption capacity for PSMPs. The adsorption kinetics and isotherms results demonstrated that the PSMP adsorption process was physically dominant and complicated. van der Waals and electrostatic interactions, hydrogen bonding, and pore filling were the main adsorption mechanisms. These results verify that colloidal MPs can be adsorbed by pipe scales, demonstrating that pipe scales play an essential role in the fate of colloidal MPs in DWDSs and the quality and security of drinking water. The secondary release of MPs from pipe scales is also worthy of attention due to the environmental and health risks.

Efficient removal of cadmium by salts modified-biochar: Performance assessment, theoretical calculation, and quantitative mechanism analysis

Modified biochar is a feasible adsorbent to solve cadmium pollution in water. However, few studies could elucidate the mechanism of cadmium adsorption by biochar from a molecular perspective. Furthermore, traditional modification methods are costly and have the risk of secondary contamination. Hence, several environmentally friendly sodium salts were used to modify the water chestnut shell-based biochar and employ it in the Cd²⁺ adsorption in this work. The modification of sodium salt could effectively improve the specific surface area and aromaticity of biochar. Na₃PO₄ modified biochar exhibited the highest Cd²⁺ adsorption capacity (112.78 mg/g). The adsorption of Cd²⁺ onto biochar was an endothermic, monolayer, chemisorption process accompanied by intraparticle diffusion. Microscopically, the enhancement of aromatization after modification made Cd²⁺ more likely to interact with the regions rich in π electrons and lone pair electrons. This study provided a new research perspective and application guidance for heavy metal adsorption on biochar.

Enhanced removal of Cd2+ from water by AHP-pretreated biochar: Adsorption performance and mechanism

The sesame straw-derived biochar was successfully prepared via alkaline hydrogen peroxide (AHP) pretreatment in this study. Systematic experimental characterizations, 15 relevant batch and column adsorption models, combined with density functional theory (DFT) calculation were used to investigate the performances and micro-mechanisms of Cd²⁺ adsorption onto biochar. We found AHP-pretreatment could greatly improve the adsorption performance of biochar for Cd²⁺. The maximum Cd²⁺ adsorption capacity of AHP-pretreated biochar (87.13 mg g^-1) was much larger than that of unpretreated biochar. Cd²⁺ adsorption was mainly dominated by the chemisorption of the homogeneous surface monolayer. The hydroxyl and carboxyl groups on the surface of biochar provided preferential adsorption sites, and liquid film diffusion and intra-particle diffusion were two dominant rate-controlling steps. Our results showed that ion exchange, co-precipitation, surface complexation, and Cd²⁺-π interaction were the dominant adsorption mechanisms. Especially, DFT calculations well-identified that lone-pair electrons during complexation and π electrons during coordination were provided by oxygen-containing functional groups and aromatic rings, respectively. The experimental breakthrough curves fitted better with the theoretical value of the BJP model, compared to Thomas, Yoon-Nelson, and EXY models. Overall, our study provides a promising method for Cd²⁺ removal from wastewater and resource utilization of agricultural wastes.

Insights on ball milling enhanced iron magnesium layered double oxides bagasse biochar composite for ciprofloxacin adsorptive removal from water

Both ciprofloxacin (CIP) and sugarcane bagasse have brought enormous pressure on environmental safety. Here, an innovative technique combining Fe-Mg-layered double oxides and ball milling was presented for the first time to convert bagasse-waste into a new biochar adsorbent (BM-LDOs-BC) for aqueous CIP removal. The maximum theoretical adsorption capacity of BM-LDOs-BC reached up to 213.1 mg g^-1 due to abundant adsorption sites provided by well-developed pores characteristics and enhanced functional groups. The results of characterization, data fitting and environmental parameter revealed that pore filling, electrostatic interactions, H-bonding, complexation and π-π conjugation were the key mechanisms for CIP adsorptive removal. BM-LDOs-BC exhibited satisfactory environmental safety and outstanding adsorption capacity under various environmental situations (pH, inorganic salts, humic acid). Moreover, BM-LDOs-BC possessed excellent reusability. These superiorities illustrated that BM-LDOs-BC was a promising adsorbent and created a new avenue for rational placement of biowaste and high-efficiency synthesis of biochar for antibiotic removal.

Manganese oxide-modified biochar derived from discarded mushroom-stick for the removal of Sb(III) from aqueous solution

In this study, discarded mushroom-stick, which is widely available, was selected as a precursor to prepare MnO₂-modified biochar (MBC) for Sb(III) removal. Several characterisation methods (SEM, BET, XPS, FT-IR, and XRD) were used to explore the mechanisms of antimony adsorption onto MBC. The results showed that MBC is a mesoporous material with a fluffy structure and a higher specific surface area (23.56 and 32.09 m²·g^-1) than PBC600 (13.62 m²·g^-1), exhibiting superior and stable adsorption capacities for Sb(III) (50.30 mg·g^-1 for 1/30MBC600 and 64·12 mg·g^-1 for 1/20MBC600) across a wide pH range (pH 4-8). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy analyses indicated that the main oxides and functional groups involved in the adsorption were manganese oxides and hydroxyl groups. Forty-four per cent of the adsorbed Sb(III) was oxidised to Sb(V) by manganese oxides or hydroxyl groups both on the surface of biochar and in solution. According to adsorption kinetics and isotherms, the adsorption process of Sb(III) is chemisorption, which includes monolayer and multilayer heterogeneous chemisorption processes. To sum up, MBC is an excellent adsorbent for the capture of Sb(III) from contaminated water with strong potential for future application.

Low-emission and energetically efficient co-gasification of coal by incorporating plastic waste: A modeling study

The issues of global plastic waste generation and demand for hydrogen energy can be simultaneously resolved by gasification process. In this regard, feasibility and efficiency of steam and air co-gasification of coal by incorporating five different and prevalent types of plastic waste were investigated in this modeling study. All steam and air coal/plastic waste co-gasification types were multi-objective optimized utilizing a response surface methodology. The best co-gasification types were selected using VIekriterijumsko KOmpromisno Rangiranje (VIKOR) analysis. Overall, the results showed that incorporating plastic waste into coal gasification improved hydrogen concentration in the syngas and increased normalized carbon dioxide production due to the high carbon content of plastic waste and activation of water-gas and CO shift reactions. VIKOR analysis revealed that steam coal/low density polyethylene was the best optimized co-gasification type with hydrogen concentration of 62.8 mol %, normalized carbon dioxide production of 2.60 g/mol, based on the feedstock entering the system, and energy efficiency of 76.6%. Increasing gasifier temperature enhanced hydrogen concentration and decreased normalized carbon dioxide production. The energy efficiency was markedly improved by increasing the moisture content and decreasing the ratio of steam/feedstock. This study confirmed the hypothesis of efficient utilization of plastic waste in coal/plastic waste co-gasification.

Simultaneous immobilization of arsenic, lead and cadmium by magnesium-aluminum modified biochar in mining soil

Owing to the human activities such as smelting and mining, arsenic (As), lead (Pb) and cadmium (Cd) seriously polluted the soil of non-ferrous metal mining areas, thus efficient methods for the simultaneous immobilization of the three heavy metals are urgently needed. In the present study, Mg-Al modified biochars (MABs) were synthesized through a simple one-pot pyrolysis method to immobilize the three heavy metals. According to the BET (Brunauer-Emmett-Teller) test method, MABs had larger specific surface areas than biochar. Compared to the materials obtained at 300 °C and 700 °C, MAB with a pyrolysis temperature of 500 °C (MAB 500) had a significant immobilization effect on As, Pb and Cd in the Gansu mining area. Compared with BC, the removal efficiencies of As, Pb and Cd increased from -62%, 17% and 5% to 52%, 100% and 66%, respectively. And the toxicity characteristic leaching procedure (TCLP) test showed that the leaching concentrations of the three heavy metals in the treated soil were all lower than the standard value. X-ray photoelectron spectroscopy and kinetic experiments showed that there were various mechanisms in the immobilization process of the three heavy metals, and the large specific surface area and the multi-Mg/Al-OH of MABs play an important role in this process. More charges were provided by larger specific surface for ion exchange with heavy metals. In addition, larger specific surface area also provided more adsorption sites. More complex sites were provided by Mg/Al-OH to form Mg/Al-O-M then immobilize the heavy metals. In summary, the immobilization mechanism may involve electrostatic attraction, precipitation/co-precipitation, and surface complexation.

Mitigation of organic fouling of ultrafiltration membrane by high-temperature crayfish shell biochar: Performance and mechanisms

The paper applied crayfish shell (CFS) biochar to the mitigation of ultrafiltration (UF) membrane fouling induced by humic acid (HA) and sodium alginate (SA). Results indicated that the high adsorption capacity of CFS800 to HA made it effective in alleviating the irreversible membrane fouling induced by HA, and the cross-linking reaction between the hydroxyl calcium components on CFS800 and SA reduced the reversible membrane fouling induced by SA rapidly. Further analysis showed that the "hydrogel flocs" generated by the cross-linking reaction would accumulate on the surface of the substrate membrane and form an amorphous hydrogel layer to intercept the subsequent foulant and purify the water quality further. Meanwhile, the mitigation performance of CFS800 was twice more than that of commercial powder activated carbon (PAC), and the dosage was the main factor affecting its practical application performance and thus could be considered as a promising material in alleviating membrane fouling induced by HA and SA. More importantly, the findings of the present study gave a new sight towards the application of biochar.

Nickel-loaded shrimp shell biochar enhances batch anaerobic digestion of food waste

This study evaluated the effectiveness of shrimp shell biochar (SBC) and nickel (Ni) loaded SBC in increasing methane yield during anaerobic digestion of food waste. The results indicated that the methane yields of control (without SBC), SBC, SBC loaded with the low concentration of Ni, and SBC loaded with the high concentration of Ni were 81.8, 116.1, 134.7, and 99.2 mL/(g·VS), respectively. SBC promoted the efficiency and stability of the whole anaerobic digestion process including hydrolysis, volatile fatty acid conversion and methanogenesis. While the invigorating effect of loaded Ni at the low concentration of 0.88 mg/g was mainly concentrated in methanogenesis, the inhibition effect of the high Ni concentration was comprehensive. SBC helped Methanosarcina proliferation, and low concentration Ni promoted the number and activity of Methanosarcina and Methanosaeta. The results show that biochar loaded with a low level of trace elements such as Ni can promote the anaerobic digestion process.

Enhanced removal of P(V), Mo(VI) and W(VI) generated oxyanions using Fe-MOF as adsorbent from hydrometallurgical waste liquid: Exploring the influence of ionic polymerization

Environmentally hazardous P(V), Mo(VI) and W(VI) generated oxyanions exist widely in the waste liquid of nonferrous hydrometallurgy. In this work, Fe-MOF material was simply prepared via solvothermal synthesis and then used as an adsorbent to remove P(V), Mo(VI) and W(VI) oxyanions from hydrometallurgical waste liquid. Several important parameters, including solution pH, oxyanion concentration, contact time, adsorbent amount, temperature and coexistent heavy metal ions, were systematically investigated. The results demonstrate that adsorption process was almost pH-independent over a broad range of pH 3.0-10.0. The adsorption efficiency was strongly associated with the chemical species of oxyanions. The higher polymerisation degree of oxyanions was more favourable for removal efficiency. Additionally, the maximum removal efficiencies for P(V), Mo(VI) and W(VI) oxyanions under optimum conditions were approximately 100%. Furthermore, the adsorption kinetics and isotherms of oxyanions on the adsorbent separately belonged to the pseudo-second-order and Langmuir isotherm models. XPS analysis revealed that inner-sphere complexation played a dominant role in the adsorption removal process. Fe-MOFs with pH-independent properties, abundant binding sites and high stability are prospective adsorbents for treating waste liquids in the hydrometallurgical industry.

Efficient adsorptive removal of fluoroquinolone antibiotics from water by alkali and bimetallic salts co-hydrothermally modified sludge biochar

Fluoroquinolones are one of most commonly used antibiotics for preventing and treating bacterial infections and their unsatisfactory removal by conventional wastewater treatment technology have aroused widespread attention. A novel adsorbent of KMSBC was the first time synthesized and tested to adsorb three typical fluoroquinolone antibiotics of CIP, NOR and OFL from water. The characterization analysis showed that KMSBC possessed the superior porous structure, abundant functional groups and greater graphitic degree. Together with kinetics, isotherms, thermodynamics and critical factors (e.g., biochar dose, reaction time/temperature, fluoroquinolone antibiotics concentration, pH, co-existing ionic strength and HA concentration) analysis suggested that pore filling, π-π conjugation, H-bonding and electrostatic interaction were the key mechanisms for fluoroquinolone antibiotics adsorption by KMSBC. KMSBC exhibited the optimum adsorption performance at pH = 5 despite the adsorbates. The maximum adsorption capacity of KMSBC for CIP, NOR and OFL were 49.9, 55.7 and 47.4 mg/g at 25 °C, respectively. Also, KMSBC exhibited the good magnetic sensitivity and stability with the leaching concentrations of Fe were far below than environmental limit (GB5749-2006) at various pH (from 3 to 12), ionic strength and HA concentrations. Additionally, KMSBC performed a stable sustainable adsorption performance in recycles by NaOH regeneration. Thus, KMSBC had the potential to be a promising adsorbent for fluoroquinolone antibiotics removal with favorable adsorption capacity, environmental security and easy regeneration performance.

Activated multi-walled carbon nanotubes decorated with zero valent nickel nanoparticles for arsenic, cadmium and lead adsorption from wastewater in a batch and continuous flow modes

Nickel nanoparticles (NiNPs) supported on activated multi-walled carbon nanotubes (MWCNTs) were used as an adsorbent applied towards Pb(II), As(V) and Cd(II) remediation from industrial wastewater. The result revealed the hydrophilic surface of MWCNTs-KOH was enhanced with the incorporation of NiNPs enabling higher surface area, functional groups and pore distribution. Comparatively, the removal of Pb(II), As(V) and Cd(II) on the various adsorbents was reported as NiNPs (58.6 ± 4.1, 46.8 ± 3.7 and 40.5 ± 2.5%), MWCNTs-KOH (68.4 ± 5.0, 65.5 ± 4.2 and 50.7 ± 3.4%) and MWCNTs-KOH@NiNPs (91.2 ± 8.7, 88.5 ± 6.5 and 80.6 ± 5.8%). Using MWCNTs-KOH@NiNPs, the maximum adsorption capacities of 481.0, 440.9 and 415.8 mg/g were obtained for Pb(II), As(V) and Cd(II), respectively. The experimental data were best suited to the Langmuir isotherm and pseudo-second order kinetic model. The fitness of experimental data to the kinetic models in a fixed-bed showed better fitness to Thomas model. The mechanism of metal ion adsorption onto MWCNTs-KOH@NiNPs show a proposed electrostatic attraction, surface adsorption, ion exchange, and pore diffusion due to the incorporated NiNPs. The nanocomposite was highly efficient for 8 adsorption cycles. The results of this study indicate that the synthesized nanocomposite is highly active with capacity for extended use in wastewater treatment.

Effects of H3PO4 modified biochar on heavy metal mobility and resistance genes removal during swine manure composting

In this research, static composting treatments of swine manure with forced ventilation were conducted to study the effects of biochar (BC) and H₃PO₄ modified biochar (BP) addition on heavy metals (HMs) stabilization, profiles of antibiotic resistance genes (ARGs), heavy metals resistance genes (MRGs) and bacterial communities during swine manure composting. After 42 days of the composting, compared to control (CK), BC and BP decreased the concentration of diethylenetriamine pentaacetic acid extractable Cu and Zn by 12.04%, 15.15% and 26.91%, 36.50%, respectively. Furthermore, BC and BP treatments reduced the total abundances of nine ARGs by 4.02% and 66.21%, and five MRGs by 53.66% and 58.81%, compared to CK in the compost product. Network analysis and square structural equation model analysis revealed that the decrease of ARGs and MRGs in BP treatment was related tothe change in bacterial community during the composting, rather than differences in co-selection pressure.

Key particle properties of shells for cadmium chemisorption

Previous studies on cadmium adsorption of calcium carbonate have found that polymorph, and, crystallinity are influential factors for adsorbing cadmium ions. The predominant factor for cadmium adsorption has yet to be elucidated because these factors are linked. To overcome this, here each factor is investigated separately. First, atmospheric grinding prepared surf clam (aragonite phase) and scallop (calcite phase) shells with similar crystallite sizes and specific surface areas. Using adsorption isotherm models, kinetics, X-ray diffraction analysis, and TEM observations, both calcite and aragonite react with cadmium to form cadmium carbonate. The chemisorption follows the adsorption mechanism reported in the literature. Based on the Langmuir isotherm model fitting, the maximum adsorbed amount for the ground surf clam shells is 633.3 mg/g, while that for scallop shells is 195.8 mg/g. Then fine surf clam shell particles with a similar specific surface area, and with a relatively wide range of the aragonite ratio, and crystallite size are prepared via a combination of grinding and a subsequent calcination process. Our experiments where one explanatory variable is changed at a time demonstrate that the polymorph ratio and crystallite size of the ground shells play key roles in the chemisorption.

Preparation and characterization of lignin-derived hard templated carbon(s): Statistical optimization and methyl orange adsorption isotherm studies

In this study, lignin-derived zeolite templated carbon materials were fabricated to remove the organic contaminant, methyl orange. Response surface methodology with Box-Behnken design was used to optimize the adsorption parameters. Based on Box-Behnken design, a quadratic model was developed to correlate the adsorption variables with the response, removal efficiency. Analysis of variance revealed the adsorbent dosage as the most influential adsorption variable. Lignin derived ZSM-5 (PZ) and mordenite (PM) templated carbon materials exhibited high surface area; 476.0 and 716.0 m²/g respectively. The maximum theoretical adsorption capacity of PZ and PM for methyl orange was 514.0 and 225.0 mg/g, respectively. The experimental kinetic data best fitted to pseudo-second-order model for both the adsorbents. PZ adsorbent was also utilized to treat real wastewater containing dyes and achieved 40 % methyl orange removal efficiency. Adsorption thermodynamic study revealed the process as spontaneous, exothermic and also indicated the increment in entropy after adsorption.

Quantitative analysis on the mechanism of Cd2+ removal by MgCl2-modified biochar in aqueous solutions

In this study, a pristine biochar (BC) and MgCl₂-modified biochar (MBC) were prepared using Pennisetum sp. straw for removing Cd²⁺ from aqueous solutions. Scanning electron microscope (SEM) imaging combined with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), as well as the surface area and porosity analyses were used to reveal the physico-chemical characteristics of the pristine and modified adsorbents. Results suggested that MgCl₂ impregnation during the synthesis had enhanced the specific surface area and pore volume of the biochar. Batch adsorption experiments indicated that the Cd²⁺ adsorption data of MBC fitted the Langmuir isothermal and pseudo-second order kinetic models, indicating a chemical adsorption was undergoing in the system. The maximum adsorption capacity of Cd²⁺ on MBC was 763.12 mg/g, which was 11.15 times higher than that of the pristine BC. The Cd²⁺ removal by MBC was mainly attributed to the mechanisms in an order: Cd(OH)₂ precipitation (73.43%) > ion exchange (22.67%) > Cd²⁺-π interaction (3.88%), with negligible contributions from functional group complexation, electrostatic attraction and physical adsorption. The MBC could thus be used as a promising adsorbent for Cd²⁺ removal from aqueous solutions.

Production and beneficial impact of biochar for environmental application: A comprehensive review

This review focuses on a holistic view of biochar, production from feedstock's, engineering production strategies, its applications and future prospects. This article reveals a systematic emphasis on the continuation and development of biochar and its production methods such as Physical engineering, chemical and bio-engineering techniques. In addition, biochar alternatives such as nutrient formations and surface area made it a promising cheap source of carbon-based products such as anaerobic digestion, gasification, and pyrolysis, commercially available wastewater treatment, carbons, energy storage, microbial fuel cell electrodes, and super-capacitors repair have been reviewed. This paper also covers the knowledge blanks of strategies and ideas for the future in the field of engineering biochar production techniques and application as well as expand the technology used in the circular bio-economy.

Treatment of nano-oil polluted wastewater in an expanded bed adsorption column based on carboxymethyl cellulose-cellulose-nickel composite beads

In the present work, spherical carboxymethyl cellulose-cellulose-nickel (CMC-C-Ni) composite beads as novel adsorbent was synthesized to make a stable expanded bed adsorption (EBA) column for the treatment of the oily wastewater collected from the downstream of rapeseed industry. The morphology and structure of the CMC-C-Ni composite beads were studied by scanning electron microscopy (SEM) and optical microscope. The SEM images revealed that the synthesized composite beads were spherical with porous structure. The pore size of the beads was in the range of 90-200 nm. The physical characteristics of the CMC-C-Ni composite beads including wet density, porosity, and water content were respectively in the ranges of 1.23-1.63 g/cm³, 82.29-90.75%, and 52-76%. The factor of bed expansion in the range of 2-3 was corresponded with Richardson-Zaki equation. The results showed that by increasing the fluid viscosity, the terminal settling velocity (U_t) was reduced. The expansion index values were between 2.77 and 3.14 that were close to 4.8 (commonly utilized index in the laminar flow regimes). CMC-C-Ni composite beads were tested when the velocity of fluid was ˂ 700 cm/h, and the D_axl was found to be ˂ 1 × 10^-5 m²/s (steady state).

Efficient absorptive removal of Cd(Ⅱ) in aqueous solution by biochar derived from sewage sludge and calcium sulfate

Biochar derived from co-pyrolysis of sewage sludge and calcium sulfate was used to remove Cd(II) from aqueous solution. The results showed that the Cd(Ⅱ) adsorption better followed Freundlich model, and the maximum adsorption capacities were 109.0 mg/g (288 K), 127.9 mg/g (298 K) and 145.4 mg/g (308 K). The Cd(Ⅱ) removal was a multi-layer adsorption process dominated by chemisorption, which was also a spontaneous and endothermic process. The contribution of physisorption gradually increased as the Cd(Ⅱ) initial concentration. The Cd(Ⅱ) removal process which better followed pseudo-second-order kinetic model, was divided into three stages. The first (0-0.3 h) and second stages (0.3-2 h) were separately controlled by liquid film diffusion/intraparticle diffusion/chemical reaction and liquid film diffusion/chemical reaction, while the third stage (0.3-24 h) was the dynamic equilibrium process. The speciation distribution of Cd on biochar surface was mainly CdCO₃/CdOOC and CdO/CdSiO₃, indicating coprecipitation, ion exchange and complexation contributed more to the Cd(Ⅱ) removal.

Sustainable removal of cadmium from contaminated water using green alga - Optimization, characterization and modeling studies

This research study reported the feasibility of cadmium removal using green algae, Caulerpa scalpelliformis, under controlled environmental conditions. The algal biosorbent could effectively remove cadmium under broad range of test conditions, namely, initial pH (3-6), adsorbent mass (0.5-2.5 gL^-1) and shaking speed (60-100 rpm). The best operating conditions were identified using Central Composite Design under Response Surface methodology and found to be pH - 4.9, adsorbent mass - 2.1 gL^-1 and shaking speed - 90 rpm. Equilibrium studies were conducted and monolayer sorption was identified as the mechanism, confirmed by Langmuir isotherm (R² = 0.9920). The maximum Cd uptake achieved at optimal conditions was 111.11 mg g^-1. The kinetic constants of the best fit model (pseudo second order) were determined. The thermodynamic feasibility was verified (ΔG ^ͦ < 0) and the biosorption process was found to be endothermic (ΔH ^ͦ > 0). The mass transfer studies shows that the mass transfer coefficient was inversely related to the temperature. Presence of favorable surface functional groups and enhanced surface area confirmed the suitability of the synthesized biosorbent for effective removal of cadmium.

CFD analysis and RSM optimization of obstacle layout in Tesla micromixer

As a kind of fast and efficient mixing equipment, micromixer has been applied to chemical reaction detection. Its application can not only save experimental samples but also reduce the experimental time. In micromixers, Tesla structure is widely used due to its simple structure and special flow mechanism. In this paper, CFD and response surface method are used to analyze and verify the flow field of the configuration of adding diamond obstacles in the Tesla mixer. The results show that the order of layout parameter weight from large to small is obstacle size > vertical offset > horizontal offset. And the Desirability was 0.806, the optimal diamond obstacle size is 46.35 μm and the optimal lateral offset is 18.78 μm. In addition, a constant value OF 20 μm is predicted as the optimal vertical offset of the micromixer. Compared with the Tesla-type micromixer without obstacles, the diamond-shaped barrier Tesla-type micromixer designed in this paper has higher mixing rate and lower pressure drop under the same conditions, which can be applied to chemical reactors, and can also help to improve the accuracy of chemical reaction. It can be demonstrated that the presented optimal design method of obstacles layout in Tesla mixer is a simple and effective technology to improve the liquid mixing in microfluidic devices, and it has a broad application prospect in chemical engineering.

Facile fabrication of AgI/Sb2O3 heterojunction photocatalyst with enhanced visible-light driven photocatalytic performance for efficient degradation of organic pollutants in water

The construction of heterojunction is considered as a promising approach to designing highly effective visible-light driven photocatalysts. In this research, the AgI/Sb₂O₃ heterojunction photocatalyst was synthesized by a simple in situ deposition-precipitation procedure, which was supported by XPS results. Among the prepared samples, the 60% AgI/Sb₂O₃ samples exhibited the best ARG degradation ratio (98.3%) in 1 h under visible light irradiation, while the pure Sb₂O₃ and AgI exhibited almost none photocatalytic performance. The trapping experiments and EPR proved that the photo-generated ·O₂^- and ·OH made major contributions to the photocatalytic degradation of ARG by the 60% AgI/Sb₂O₃ samples. The enhanced photocatalytic performance of AgI/Sb₂O₃ heterojunction photocatalysts was ascribed to that the e^- produced in the CB of AgI would be transferred to the empty CB of Sb₂O₃, which could effectively promote separation of photo-induced carries. More importantly, the transfer of electrons from AgI to Sb₂O₃ would be in favor of restraining the reduction of Ag⁺ to Ag⁰ resulting in the good stability of heterojunction photocatalysts. The heterojunction photocatalyst provided in this work might be a prospective candidate for decontamination of water.