Effect of production temperature on lead removal mechanisms by rice straw biochars

Physicochemical properties and performance of non-woody derived biochars for the sustainable removal of aquatic pollutants: A systematic review

Biochar is a carbon-rich material produced from the partial combustion of different biomass residues. It can be used as a promising material for adsorbing pollutants from soil and water and promoting environmental sustainability. Extensive research has been conducted on biochars prepared from different feedstocks used for pollutant removal. However, a comprehensive review of biochar derived from non-woody feedstocks (NWF) and its physiochemical attributes, adsorption capacities, and performance in removing heavy metals, antibiotics, and organic pollutants from water systems needs to be included. This review revealed that the biochars derived from NWF and their adsorption efficiency varied greatly according to pyrolysis temperatures. However, biochars (NWF) pyrolyzed at higher temperatures (400-800 °C) manifested excellent physiochemical and structural attributes as well as significant removal effectiveness against antibiotics, heavy metals, and organic compounds from contaminated water. This review further highlighted why biochars prepared from NWF are most valuable/beneficial for water treatment. What preparatory conditions (pyrolysis temperature, residence time, heating rate, and gas flow rate) are necessary to design a desirable biochar containing superior physiochemical and structural properties, and adsorption efficiency for aquatic pollutants? The findings of this review will provide new research directions in the field of water decontamination through the application of NWF-derived adsorbents.

The immobilization of cadmium by rape straw derived biochar in alkaline conditions: Sorption isotherm, molecular binding mechanism, and in-situ remediation of Cd-contaminated soil

The issue of cadmium (Cd) contamination in alkaline soils is escalating, necessitating the prompt implementation of effective passivation strategies. Biochar has gained significant attention for its potential in immobilizing heavy metals; however, the suitability of biochar as a remediation material and its micro-scale interaction mechanisms with Cd under alkaline conditions remain unclear. Rape straw (RS) were pyrolyzed at 400 °C (RB400) and 700 °C (RB700) to produce biochar. Adsorption and soil incubation experiments were carried out to assess the feasibility of using rape straw derived biochar pyrolyze at different temperatures and understanding their remediation mechanisms in alkaline environments. The sorption capacity for Cd immobilization was evaluated using sorption isotherms, revealing that RB700 exhibited enhanced Cd sorption performance with a maximum sorption capacity of 119.33 mg g-1 calculated from the Langmuir isotherm equation at pH 8. Cd L3-edge X-ray absorption near-edge structure (XANES) spectroscopy analysis confirmed that the dominant sorption species of Cd were organic Cd in RB400, with CdCO3 precipitation increased to 73.9% in RB700. Solid-state 13C nuclear magnetic resonance (13C-NMR) spectroscopy demonstrated that aromatic and carboxyl C functional groups are involved in the organic sorption of Cd through complexation and Cd2+-π interactions in alkaline solutions. The precipitation of CdCO3 in RB700 may resulted in a more effective passivation effect compared to RB400, leading to a significant 15.54% reduction in the DTPA-Cd content in Cd-contaminated soil. These findings highlight the effective Cd passivation Cd in alkaline environments by rape straw derived biochar, providing new molecular insights into the Cd retention mechanism of biochar. Furthermore, it presents novel ideas for improving remediation approaches for alkaline Cd-contaminated soils.

Effect of biochar, zeolite and bentonite on physiological and biochemical parameters and lead and zinc uptake by maize (Zea mays L.) plants grown in contaminated soil

Heavy metals (HMs) are common contaminants with major concern of severe environmental and health problems. This study evaluated the effects of organo-mineral amendments (mesquite biochar (MB), zeolite (ZL) and bentonite (BN) alone and in combination) applied at different rates to promote the maize (Zea mays L.) growth by providing essential nutrient and improving the soil physio-chemical properties under zinc (Zn) and lead (Pb) contamination. Result revealed that the incorporation of organo-mineral amendments had significantly alleviated Pb and Zn contamination by maize plants and improved the physiological and biochemical attributes of plants. Combined application of organo-mineral amendments including BMA-1, BMA-2 and BMA-3 performed excellently in terms of reducing Pb and Zn concentrations in both leaves (19-60%, 43-75%, respectively) and roots (24-59%, 42-68%, respectively) of maize. The amendments decreased the extractable, reducible, oxidisable and residual fractions of metals in soil and significantly reduced the soil DTPA-extractable Pb and Zn. BMA-1 substantially improved antioxidant enzyme activities in metal-stressed plants. This study indicated that combined use of organo-mineral amendments can effectively reduce the bioavailability and mobility of Pb and Zn in co-contaminated soils. Combined application of organo-mineral amendments could be viable remediation technology for immobilization and metal uptake by plants in polluted soils.

Sustainable management of campus fallen leaves through low-temperature pyrolysis and application in Pb immobilization

Realizing campus sustainability requires the environmental-friendly and economical treatment of tremendous fallen leaves. Producing fallen leaf biochar at a low temperature is a candidate approach. In this study, six common types of fallen leaves on the campus were pyrolyzed at 300 °C. The obtained biochars were characterized and the adsorption mechanisms of lead (Pb) by the fallen leaf biochars were investigated. The adsorption capacity of leaf biochar for Pb was relatively high, up to 209 mg/g (Yulania denudata leaf biochar). Adsorption of Pb onto active sites was the rate-limiting step for most leaf biochars. But for Platanus leaf biochar, intraparticle diffusion of Pb2+ dominated owing to the lowest adsorption capacity. However, the highest exchangeable Pb fraction (27%) indicated its potential for removing aqueous Pb2+. Ginkgo and Prunus cerasifera leaf biochar immobilized Pb by surface complexation and precipitation as lead oxalate. Hence, they were suitable for soil heavy metal remediation. This study shed the light on the sustainable utilization of campus fallen leaves and the application of fallen leaf biochars in heavy metal remediation.

Effective biosorption of Al ions from drinking water by lignocellulosic biomass rice straw

High concentration of aluminum (Al) in drinking water is a major intake source of it and can result in serious diseases. Rice straw (RS) as lignocellulosic biomasses has great potential to peak up metal ions from aqueous environment, however, feasibility of Al3+ removal by RS has not been investigated yet. The present study aimed to evaluate the capacity of RS as a novel biosorbent for Al3+ from drinking water. Biosorption characteristics of RS were surveyed through several biological and physiochemical techniques. Additionally, isotherm, kinetic and thermodynamic studies were evaluated using various common models. BET profiles revealed the presence of textural mesoporosity on heterogeneous surface, which leading to improve the biosorption capacity. SEM-EDS analysis confirmed the morphological changes as irregularly particles of Al3+ on external surface via physical mechanism. The results of bioassays and FTIR analysis showed carboxylic and hydroxyl groups in lignin and pectin as the main Al3+ binding site. The batch experimental results showed the maximum biosorption capacity of 283.09 mg/g and removal efficiency of 94.86% for Al3+ at biosorbent dosage of 0.05 g/100 mL, contact time of 50 min, pH 7.5, and temperature of 30 °C. The Freundlich model has the best match and suggests the biosorption process as a multi-layer. According to the results of free activation energy, biosorption process was also physical. As thermodynamic result, the biosorption behavior was found spontaneous and endothermic. Consequently, results showed RS as an economical biosorbent for reducing Al3+ of drinking water. Meanwhile, it can be considered as one of the most appropriate methods for management of rice paddies waste.

Pb(ΙΙ), Cd(ΙΙ), and Mn(ΙΙ) adsorption onto pruning-derived biochar: physicochemical characterization, modeling and application in real landfill leachate

The aim of this study was to systemically evaluate how different pyrolysis temperatures (400, 550, and 700 °C) and particle sizes (1-2 mm and 63-75 µm) were influenced biochar evolution, made from urban pruning waste, during pyrolysis process and to establish their relationships with biochar potential for removal of lead (Pb), cadmium (Cd), and manganese (Mn) from real municipal solid waste landfill leachate. The effects of pH (2-7), contact time (30-300 min) and adsorbent dosage (0.1-5 g L-1) on heavy metals removal were also examined. The results showed that physicochemical properties of biochar were greatly influenced by pyrolysis temperature. Particle size, however, showed little influence on biochar characteristics (p > 0.05). The yield, volatile matter, hydrogen and oxygen contents, and surface functional groups decreased consistently with increasing pyrolysis temperature. An increase in the pH, electrical conductivity, ash, fixed carbon, and specific surface area values was also found. In biochar samples formed at high temperatures (i.e., 550 and 700 °C), Fourier transform infrared spectroscopy-FTIR studies confirmed the increase in aromaticity. Field emission scanning electron microscopy-FESEM images showed differences in the microporous structure and lower size pores at higher temperatures. Biochar pyrolyzed at 700 °C with a particle size of 63-75 µm (i.e., Lv700-63) showed the highest removal efficiency performance. Pb and Cd ions were completely removed (100%) by 0.2 g L-1 Lv700-63 at 7.0 pH and contact times of 120 and 90 min, respectively. The maximum percentage removal of Mn was 86.20% at optimum conditions of 0.2 g L-1 Lv700-63 dosage, 7.0 pH, and 180 min contact time. The findings suggests that the surface complexation, π-electron coordination, and cation exchange were the dominant mechanisms for the Pb, Cd, and Mn removal onto Lv700-63.

Biotoxicity attenuation and the underlying physicochemical mechanism of biochar aged under simulated natural environmental conditions

Biochar (BC), with the benefits of enhancing soil fertility, absorbing heavy metals, carbon sequestration, and mitigating the greenhouse effect, has been extensively used for soil remediation. However, the long-term changes in the biotoxicity of BC under complex environmental conditions, which are the key factors influencing the sustainable application of BC in soil, are still unclear. Herein, the biotoxicity of BC aged with various processes, including dry‒wet cycle (DW) aging, freeze‒thaw cycle (FT) aging, ultraviolet irradiation (UV) aging, and low molecular weight organic acid (OA) aging, was systematically investigated by Escherichia coli (E. coli) culture experiments. The toxicity attenuation rate (%·week-1) was proposed to more concisely and clearly compare the influence of different aging methods on BC toxicity. The results indicated that after 5 weeks of aging, the toxicity attenuation rate during the four aging modes followed the order OA aging > FT aging > UV aging > DW aging. BC was nontoxic after 1 week of OA aging, 4 weeks of FT aging, 7 weeks of UV aging, and 14 weeks of DW aging. Spectroscopic characterizations revealed that humic acids in the dissolved organic matter of BC were the main reason for the biotoxicity. In addition, the attenuation of environmentally persistent free radicals on BC during aging was also an important factor for reducing environmental toxicity. This work provides insight into the detoxification mechanism of the BC aging process under ordinary environmental conditions and guidance for the safe application of BC in soil.

Combined effects of microcystin-LR and rice straw-derived biochar on the hepatic antioxidant capacity of zebrafish: Insights from LC-MS/MS-based metabolomics analysis

Microcystin-LR (MC-LR) produced by cyanobacteria blooms poses a serious risk to aquatic organisms. Rice straw-derived biochar (BC) is gradually being utilized as an effective adsorbent to remove water pollutants. In the present study, the combined toxicity of MC-LR and BC on hepatic antioxidant capacity and metabolic phenotype of zebrafish (Danio rerio) were conducted due to the increasing concern of eutrophication in aquatic environments. Female zebrafish were exposed to solutions of MC-LR (10 μg/L) and BC (100 μg/L) individually and in combination for 30 days. The results indicated that sub-chronic MC-LR exposure induced oxidative stress and metabolic disorders, with a significant elevation of several amino acids, glucose as well as unsaturated fatty acids. Metabolic pathway analysis showed that the ascorbate and aldarate metabolism and biosynthesis of unsaturated fatty acids were affected under MC-LR stress. Significantly increased MDA levels along with significantly decreased CAT and GPx activities were observed in the MC-LR group. Nevertheless, MDA levels, antioxidant enzyme activities, and the relevant gene expressions (cat1, nrf2a, HO-1, keap1a) returned to baseline in the co-exposure group. These findings revealed that MC-LR resulted in metabolic disorders of protein, sugar, and lipid related to energy production, and BC could relieve MC-LR-induced metabolic disorder and oxidative stress in the liver of zebrafish. However, the potential risk of BC-induced metabolic disorder should not be neglected. Our present results highlight the potential of BC as a tool for mitigating the negative impacts of MC-LR on aquatic organisms in blooms-contaminated water.

Biochar for soil remediation: A comprehensive review of current research on pollutant removal

Biochar usage in soil remediation has turned out to be an enticing topic recently. Biochar, a product formed by pyrolysis of organic waste, which is rich in carbon, has the aptitude to ameliorate climate change by sequestering carbon while also enhancing soil quality and crop yields. Two-edged implications of biochar on soil amendment are still being discussed yet, clarity on the long-term implications of biochar on soil health and the environment is not yet achieved. As a result, it is crucial to systematically uncover the pertinent information regarding biochar remediation, as this can serve as a roadmap for future research on using biochar to remediate contaminated soils in mining regions. This review endeavors to bring forth run thoroughly the latest state of research on the use of biochar in soil remediation, along with its potential benefits, limitations, challenges, and future scope. By synthesizing existing literature on biochar soil remediation, this review aims to provide insights into the potential of biochar as a sustainable solution for soil remediation. Specifically, this review will highlight the key factors that influence the effectiveness of biochar for soil remediation and the potential risks associated with its use, as well as the current gaps in knowledge and future research directions.

Investigation on Pb2+ adsorption characteristics by AAEMs-rich biochar in aqueous solution: Performance and mechanism

Biochar derived from soybean straw with AAEMs (alkali and alkaline earth metals) enrichment could efficiently remove heavy metals from contaminated water. In this study, the influences of pyrolysis temperature on the physicochemical property and adsorption performance of soybean straw biochar were investigated. The contributions of different adsorption mechanisms were analyzed quantitatively. The results show that the soybean straw biochar exhibits excellent Pb2+ adsorption performance (157.2-227.2 mg g-1), with an order of BC800 > BC400 > BC600 > BC700 > BC500. The mechanisms of metal ion exchange (37.49%-72.58%) and precipitation with minerals (22.38%-58.03%) mainly control the Pb2+ adsorption, whereas complexation with organic functional groups (OFGs) and cation-Cπ interaction make the less contribution. The order of cation exchange capacity (CEC) is BC400 > BC800 > BC700 > BC600 > BC500, showing a high correlation (0.965) with the contribution of metal ion exchange with AAEMs. Moreover, Ca exhibits the strongest exchange capacity. The contribution of precipitation is consistent with the variation of soluble CO32- content in biochar. These results suggest that soybean straw biochar rich in AAEMs is a prospective adsorbent for Pb2+ elimination.

Techno-economic assessment of doxycycline recovery using rice straw biochar: A circular economic execution

The non-scientific disposal of antibiotics has resulted in massive contamination of the bioactive molecules in the aquatic ecosystem. The presence of antibiotics in the effluents limits the biodegradation of micropollutants by affecting the micro-ecological balance. Hence this study aims to remove doxycycline antibiotics from wastewater using biochar. Elemental analysis of the biochar revealed C, Si and N as most abundant content while BET analysis confirmed the mesoporous nature of the adsorbent. The XRD and Raman spectra confirmed amorphic sp2 carbon dominant structure in the biochar. The adsorption mechanism was predicted, correlating the charge distribution and FTIR analysis. The effects of different process parameters were studied using CCD, ANOVA, and RSM. Moreover, the different kinetic models revealed that the pseudo-second-order kinetics model was the best fit and film layer diffusion was the dominant contributor. The isotherm study indicated the high adsorption capacity of the biochar and its non-ionic nature. Thermodynamics study established the spontaneity and exothermic nature. The results suggested no significant change in antibiotic removal efficiency across different system (pond water (97.13%), river water (98.11%), seawater (96.84%), tap water (99.13%), and distilled water (99.74%)). For the desorption of the antibiotic from the biochar surface, 90% ethanol was the most efficient (98.9%), and upon recrystallization by solvent evaporation, 98.7% of the antibiotic of the initial load was recovered. Hence, the implementation of this described process would enable resource recovery along with water treatment, which is not possible with existing approaches. The cost analysis of the whole process revealed that biochar preparation was the bulk expense and the process would be self-sustainable even if the price of the recovered antibiotic would be set at less than half ($41/kg) of the current market price ($94/kg) of the API. Thus, the process endorses a successful circular economy approach toward societal and economic sustainability.

Reviewing the role of biochar in paddy soils: An agricultural and environmental perspective

The main challenge of the twenty-first century is to find a balance between environmental sustainability and crop productivity in a world with a rapidly growing population. Soil health is the backbone of a resilient environment and stable food production systems. In recent years, the use of biochar to bind nutrients, sorption of pollutants, and increase crop productivity has gained popularity. This article reviews key recent studies on the environmental impacts of biochar and the benefits of its unique physicochemical features in paddy soils. This review provides critical information on the role of biochar properties on environmental pollutants, carbon and nitrogen cycling, plant growth regulation, and microbial activities. Biochar improves the soil properties of paddy soils through increasing microbial activities and nutrient availability, accelerating carbon and nitrogen cycle, and reducing the availability of heavy metals and micropollutants. For example, a study showed that the application of a maximum of 40 t ha-1 of biochar from rice husks prior to cultivation (at high temperature and slow pyrolysis) increases nutrient utilization and rice grain yield by 40%. Biochar can be used to minimize the use of chemical fertilizers to ensure sustainable food production.

Biochar applications for treating potentially toxic elements (PTEs) contaminated soils and water: a review

Environmental pollution with potentially toxic elements (PTEs) has become one of the critical and pressing issues worldwide. Although these pollutants occur naturally in the environment, their concentrations are continuously increasing, probably as a consequence of anthropic activities. They are very toxic even at very low concentrations and hence cause undesirable ecological impacts. Thus, the cleanup of polluted soils and water has become an obligation to ensure the safe handling of the available natural resources. Several remediation technologies can be followed to attain successful remediation, i.e., chemical, physical, and biological procedures; yet many of these techniques are expensive and/or may have negative impacts on the surroundings. Recycling agricultural wastes still represents the most promising economical, safe, and successful approach to achieving a healthy and sustainable environment. Briefly, biochar acts as an efficient biosorbent for many PTEs in soils and waters. Furthermore, biochar can considerably reduce concentrations of herbicides in solutions. This review article explains the main reasons for the increasing levels of potentially toxic elements in the environment and their negative impacts on the ecosystem. Moreover, it briefly describes the advantages and disadvantages of using conventional methods for soil and water remediation then clarifies the reasons for using biochar in the clean-up practice of polluted soils and waters, either solely or in combination with other methods such as phytoremediation and soil washing technologies to attain more efficient remediation protocols for the removal of some PTEs, e.g., Cr and As from soils and water.

Qualitative and quantitative analysis for Cd2+ removal mechanisms by biochar composites from co-pyrolysis of corn straw and fly ash

Removal of heavy metals (e.g., Cd) from contaminated water using waste-converted adsorbents is promising, but the efficiency still needs to be improved. Here, we prepared a functional biochar composite as novel Cd adsorbents by co-pyrolysis of two typical solid wastes, i.e., agricultural corn straw and industrial fly ash. The adsorption behavior and mechanism were investigated using batch and column adsorption experiments and modern characterization techniques. Results showed that alkali-modified fly ash (AMFA) was loaded onto the surface of the corn straw biochar as some fine particle forms, with quartz (SiO₂) and silicate being the main mineral phases on the surface. The maximum sorption capacity fitted by Langmuir model for functionalized biochar composite (FBC700) was up to 137.1 mg g^-1, which was 7.7 times higher than that of the original corn straw biochar (BC700). Spectroscopic analysis revealed that adsorption mechanisms of Cd onto the FBC700 included mainly precipitation and ion exchange, with complexation and Cd-π interaction also contributing. The AMFA could effectively improve the mineral precipitation with Cd. The adsorption columns filled with FBC700 exhibited a longer breakthrough time than that filled with BC700. The adsorption capacity calculated by Thomas model for FBC700 was also approximately 6.0 times higher than that for BC700, showing that FBC700 was more suited to practical applications. This study provided a novel perspective for recycling solid wastes and treating Cd-contaminated water.

Producing Metal Powder from Machining Chips Using Ball Milling Process: A Review

In the pursuit of achieving zero emissions, exploring the concept of recycling metal waste from industries and workshops (i.e., waste-free) is essential. This is because metal recycling not only helps conserve natural resources but also requires less energy as compared to the production of new products from virgin raw materials. The use of metal scrap in rapid tooling (RT) for injection molding is an interesting and viable approach. Recycling methods enable the recovery of valuable metal powders from various sources, such as electronic, industrial, and automobile scrap. Mechanical alloying is a potential opportunity for sustainable powder production as it has the capability to convert various starting materials with different initial sizes into powder particles through the ball milling process. Nevertheless, parameter factors, such as the type of ball milling, ball-to-powder ratio (BPR), rotation speed, grinding period, size and shape of the milling media, and process control agent (PCA), can influence the quality and characteristics of the metal powders produced. Despite potential drawbacks and environmental impacts, this process can still be a valuable method for recycling metals into powders. Further research is required to optimize the process. Furthermore, ball milling has been widely used in various industries, including recycling and metal mold production, to improve product properties in an environmentally friendly way. This review found that ball milling is the best tool for reducing the particle size of recycled metal chips and creating new metal powders to enhance mechanical properties and novelty for mold additive manufacturing (MAM) applications. Therefore, it is necessary to conduct further research on various parameters associated with ball milling to optimize the process of converting recycled copper chips into powder. This research will assist in attaining the highest level of efficiency and effectiveness in particle size reduction and powder quality. Lastly, this review also presents potential avenues for future research by exploring the application of RT in the ball milling technique.

Dynamic removal of Pb(II) by live Dunaliella salina: a competitive uptake and isotherm model study

The main aim of this study is modeling of a continuous biosorption system for the removal of Pb(II) ions in the aqueous conditions using live Dunaliella salina microalgae. The live microalgae can grow in saline water and opens new opportunities in varying the amount and properties of biosorbent. The effects of five parameters, including pH, optical density of algae as a factor indicating the adsorbent dosage, injection time, contact time, and initial concentration of Pb(II), were optimized by means of response surface methodology (RSM) based on the central composite design (CCD). Dunaliella salina algae showed maximum Pb(II) biosorption with 96% efficiency. For the selective Pb(II) uptake in the presence of Cd(II) and Ni(II), binary and ternary systems of ions were chosen. The mutual effect of each heavy metal ion in all systems on the total uptake percentage was also examined. The ion selectivity was investigated in the presence of diverse heavy metal ions, and the Pb(II) uptake percentage was determined to be 80%. Both Langmuir and Freundlich isotherm models were suitable for describing multicomponent binary and ternary systems depending on the presence of competitive ions in the mixture. Main functional groups and surface properties of the Dunaliella salina were identified by Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectrometry. Hence, effective heavy metal ion uptake, simple design, and cost-effective cultivation confirmed live Dunaliella salina as suitable microalgae for purifying contaminated water in an economic and safe manner.

Mitigation of arsenic release by calcium peroxide (CaO2) and rice straw biochar in paddy soil

Biochar has a great potential in the stabilization of soil heavy metals; however, the application can actually enhance the mobility of Arsenic (As) in soil. Here, a biochar-coupled calcium peroxide system was proposed to control the increase in As mobility caused by biochar amendment in paddy soil environment. The capability of rice straw biochar pyrolyzed at 500 °C (RB) and CaO₂ to control As mobility was evaluated by incubation for 91 days. CaO₂ encapsulation was performed for pH control of CaO₂, and As mobility was evaluated using a mixture of RB + CaO₂ powder (CaO₂-p), and RB + CaO₂ bead (CaO₂-b), respectively. The control soil solely and RB alone were included for comparison. The combination of RB with CaO₂ exhibited remarkable performance in controlling As mobility in soil, and As mobility decreased by 40.2% (RB + CaO₂-p) and 58.9% (RB + CaO₂-b) compared to RB alone. The result was due to high dissolved oxygen (6 mg L^-1 in RB + CaO₂-p and RB + CaO₂-b) and calcium concentrations (296.3 mg L^-1 in RB + CaO₂-b); oxygen (O₂) and Ca²⁺ derived from CaO₂ is able to prevent the reductive dissolution and chelate-promoted dissolution of As bound to iron (Fe) oxide by biochar. This study revealed that the simultaneous application of CaO₂ and biochar could be a promising way to mitigate the environmental risk of As.

One-step self-assembly of Fe-biochar composite for enhanced persulfate activation to phenol degradation: Different active sites-induced radical/non-radical mechanism

Persulfate (PS) activation by nanoscale zerovalent iron (nZVI) is promising for water purification, while is limited due to its easy agglomeration and oxidation. Herein, nZVI encapsuled in carbon matrix shell was synthesized via one-step carbothermal reduction. The core-shell structure effectively inhibited oxidation and agglomeration of nZVI core, and graphitized porous structures facilitated phenol binding with maximal adsorption capacity of 117.10 mg/g achieved by nZVI_0.6-BC₈₀₀. Both reactive oxygen species (SO₄^•-, O•H, O₂^•- and ¹O₂) and electron transfer process resulted in phenol decomposition. Owing to diversified active sites, the nZVI_0.6-BC₈₀₀/PS system could completely degrade phenol degradation within short time, and exhibited great adaptation to extensive pH range (3.0-9.0) and coexisting substances. Additionally, the nZVI_0.6-BC₈₀₀/PS system could maintain over 85% removal of phenol after three recycles or 50 days of storage, and was highly-efficient to different water environments, thus proposing rational design of iron-carbon catalyst with potential in water treatment.

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.

Fir sawdust as a low-cost and easily recyclable adsorbent: efficient removal of Pb(II), Cu(II), and Zn(II) contaminants from wastewater

The main pollution sources of heavy metals are the arbitrary discharge of industrial wastewater and waste residues, which cause serious harm to the water environment, soil environment, and human health. In this study, following the principle of waste utilization, a gel adsorbent (AA-SW-AMPS) was prepared by microwave-assisted chemical cross-linking using fir sawdust as raw material. A scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and swelling dynamic experiments were used to investigate the microstructure, reaction mechanism, and water absorption performance of AA-SW-AMPS. The N₂ adsorption-desorption curve shows that the porous structure of AA-SW-AMPS creates 240.75 cm²/g of specific surface area to enable excellent heavy-metal sorption. It was determined by adsorption experiments that the optimal adsorption state was when the dosage of AA-SW-AMPS was 5 g/L, the pH of the solution was 5, the adsorption time was 45 min, and the initial heavy metal ion concentration was 250 mg/L. In addition, the adsorption mechanism was investigated using adsorption dynamics, adsorption isotherm, and Materials Studio simulation. The results show that the maximum adsorption capacities of AA-SW-AMPS for Pb(II), Cu(II), and Zn(II) were 253.49 mg/g, 237.29 mg/g, and 232.15 mg/g, respectively, and the adsorption mechanism is monolayer chemisorption. The adsorbent showed great potential in removing heavy metals from wastewater.

Recent advances in biochar amendments for immobilization of heavy metals in an agricultural ecosystem: A systematic review

Over the last several decades, extensive and inefficient use of contemporary technologies has resulted in substantial environmental pollution, predominantly caused by potentially hazardous elements (PTEs), like heavy metals that severely harm living species. To combat the presence of heavy metals (HMs) in the agrarian system, biochar becomes an attractive approach for stabilizing and limiting availability of HMs in soils due to its high surface area, porosity, pH, aromatic structure as well as several functional groups, which mostly rely on the feedstock and pyrolysis temperature. Additionally, agricultural waste-derived biochar is an effective management option to ensure carbon neutrality and circular economy while also addressing social and environmental concerns. Given these diverse parameters, the present systematic evaluation seeks to (i) ascertain the effectiveness of heavy metal immobilization by agro waste-derived biochar; (ii) examine the presence of biochar on soil physico-chemical, and thermal properties, along with microbial diversity; (iii) explore the underlying mechanisms responsible for the reduction in heavy metal concentration; and (iv) possibility of biochar implications to advance circular economy approach. The collection of more than 200 papers catalogues the immobilization efficiency of biochar in agricultural soil and its impacts on soil from multi-angle perspectives. The data gathered suggests that pristine biochar effectively reduced cationic heavy metals (Pb, Cd, Cu, Ni) and Cr mobilization and uptake by plants, whereas modified biochar effectively reduced As in soil and plant systems. However, the exact mechanism underlying is a complex biochar-soil interaction. In addition to successfully immobilizing heavy metals in the soil, the application of biochar improved soil fertility and increased agricultural productivity. However, the lack of knowledge on unfavorable impacts on the agricultural systems, along with discrepancies between the use of biochar and experimental conditions, impeded a thorough understanding on a deeper level.

Effect of montmorillonite biochar composite amendment on thallium bioavailability in contaminated agricultural soils and its mitigated health risk

Little information is available on the effect of clay minerals and biochar composite on the remediation and bioavailability of thallium in agricultural soils. This study thus investigated the influence of montmorillonite biochar composite (Mnt-BC) amendment on the remediation of agricultural soil contaminated artificially by Tl and its potential health risks. Herein, bok choi was cultured to estimate the efficiency of soil Mnt-BC amendments through the bioavailability of Tl of the vegetable. Results showed that Tl bioavailability was significantly reduced in Mnt-BC-amended soils, mainly ascribed to the elevated soil pH and other improved soil properties of high functional groups (-OH, -COOH), negative charges, and exchangeable cations after amendment. Specifically, the highest immobilization efficiency of Tl in soils was observed in 2.5% treated soils with 79.11%, while in plant leaves the highest reduction of Tl was estimated to be 75.1% compared to the control treatment. Hence, the amendment dosage improved the immobilization of Tl in soil and subsequently reduced Tl uptake by the vegetable. Furthermore, from target hazard quotient (THQ) estimation, Mnt-BC amendment can lower the potential health risk while consuming such cultured bok choi in Tl-contaminated soils. Considering the environmental friendliness and high efficiency of Mnt-BC, it could be used as a potential soil amendment to remediate agricultural soils contaminated by Tl.

Multicomponent adsorption of heavy metals onto biogenic hydroxyapatite: Surface functional groups and inorganic mineral facilitating stable adsorption of Pb(Ⅱ)

Due to the coexistence of various heavy metals in the contaminated environment, it is essential to comprehensively study the multicomponent adsorption of heavy metals in order to tackle these combined pollutants. Herein, the adsorption processes of Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) by biogenic hydroxyapatite (BHAp) were investigated in single and multicomponent systems. The maximum adsorption capacity for Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) by BHAp in single system reached 311.16, 82.05 and 92.54 mg g^-1, respectively, while adsorption capacity for Cu(Ⅱ) and Cd(Ⅱ) in multicomponent system decreased more obviously than that of Pb(Ⅱ). Furthermore, the stability of Cu(Ⅱ) and Cd(Ⅱ) adsorbed on BHAp was indeed influenced in multicomponent system. By means of the characterization analysis, it was found that ion exchange was more instrumental in the adsorption processes of Cu(Ⅱ) and Cd(Ⅱ) in single system than in multicomponent system. Significantly, it was observed that the proportion of generally stable Pb(II) adsorbed on BHAp exceeded 95% in both single and multicomponent systems. This result might be due to the in-site growth of stable crystals of Pb_xCa_10-x(PO₄)₆(OH)₂, which was synergistically induced by surface functional groups and inorganic mineral of BHAp, and was unaffected by the coexistence of Cu(Ⅱ) and Cd(Ⅱ).

Preparation and Characterization of Biochars Obtained from Biomasses for Combustible Briquette Applications

Renewable energies have been considered as alternative, clean, available, and ecological sources of energy. The production of biochar from biomass by thermochemical means is considered an efficient method of converting biomass for energy production. In this study, the biochars were produced from the biomasses of peanut shells and sugar cane bagasse at different pyrolysis temperatures (400°C, 450°C, and 500°C). The biomass samples and their produced biochars were characterized using calorific value, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and energy dispersive X-ray spectrometry (SEM and EDX), compressibility index, and combustion behavior in order to analyze their potential. Experimental results showed that biochar has better fuel qualities compared to raw biomass. We also found that increasing the pyrolysis temperature clearly improved the calorific value, the morphology, the porosity of the biochars as well as the compressibility index of the biochars. The interest of this study was to produce renewable biochar from peanut shell waste and sugar cane bagasse for use as solid fuel.

Effect of Pyrolysis Temperature on the Sorption of Cd(II) and Se(IV) by Rice Husk Biochar

This study investigated the removal of metal cations (Cd(II)) and metalloid anions (Se(IV)) from their aqueous solution by using agricultural waste (rice husk biochar). Rice husk biochar samples were prepared under 300, 500, and 700 °C pyrolysis conditions and their physicochemical properties were characterized. Aqueous Cd(II) and Se(IV) sorption kinetics and isotherms of rice husk biochar were studied. The results showed that the yield of rice husk biochar decreased from 41.6% to 33.3%, the pH increased from 7.5 to 9.9, and the surface area increased from 64.8 m²/g to 330.0 m²/g as the pyrolysis temperature increased from 300 °C to 700 °C. Under the experimental conditions, at increasing preparation temperatures of rice husk biochar, the sorption performance of Cd(II) and Se(IV) was enhanced. The sorption capability and sorption rate were considerably higher and faster for Cd(II) ions than for Se(IV) ions. Cd(II) sorption was found to reach equilibrium faster, within 150 min, while Se(IV) sorption was slower and reached equilibrium within 750 min. The maximum sorption capacities of cadmium and selenium by rice husk biochar were 67.7 mg/g and 0.024 mg/g, respectively, according to Langmuir model fitting.

Potential application of spent mushroom compost (SMC) biochar as low-cost filtration media in heavy metal removal from abandoned mining water: a review

Overpopulation and rapid development have put an increasing burden on the environment, leading to various water crisis. Importing water from abandoned mines as an alternative raw water source could be the next answer to alleviate water scarcity problems globally. However, due to its high heavy metals content, there is a need to find an economical and effective method to remove heavy metals before reusing it as potable water source. Biochar, a low-cost and carbon-rich biosorbent, has received increasing attention on its application as a remediating agent to remove heavy metals from water. Previous studies have revealed the potential properties of biochar as a heavy metal removal agent including high cation exchange capacity, high surface area, active surface functional groups, as well as efficient adsorption. Apparently, the most important factor influencing the sorption mechanism is the type of feedstock materials. Spent mushroom compost (SMC), a waste product from mushroom cultivation, has been found as an excellent biosorbent. SMC has received global attention as it is low cost and eco-friendly. It also has been proved as an efficient heavy metals remover from water. Nevertheless, its application as biochar is still scarce. Therefore, this review focuses on the potential of transforming SMC into modified biochar to remove heavy metals, especially from abandoned mining water. The present review emphasizes the current trends in adsorption methods for heavy metal removal from water, assembles data from previous studies on the feedstock of biosorbents to biochars, and discusses the potentials of SMC as a biochar for water treatment.

Effects of biochar particle size and dosage on the desiccation cracking behavior of a silty clay

Desiccation cracking can significantly change the integrity of soils, and potentially result in the instability of infrastructure as well as the migration of contaminants. Biochar is regarded as a promising low-carbon material for geotechnical applications, including cracking prevention. This study investigates the effects of biochar particle size and dosage on the desiccation cracking characteristics of a silty clay. For samples with fine biochar particles (<0.25 mm), coarser primary cracks initiate first, followed by finer secondary cracks regardless of biochar dosage. Quantitative analysis of the cracking characteristics at the stable stage shows that the surface crack ratio, the number of crack segments, the total length of cracks and the average width of cracks decreased by 31.29%, 30.78%, 14.18%, and 20.45% after 10% biochar addition. For samples with coarse biochar particles (>0.25 mm), cracks initiate simultaneously on the soil surface, and primary and secondary cracks are difficult to distinguish after drying, especially in high dosage samples. In the presence of 10% biochar, the surface crack ratio and average width of cracks decreased by 28.64% and 62.84%, but the number of crack segments and total length of cracks increased by 163.39% and 42.13%. Microstructure and image processing analysis of soil cracks indicate that biochar affects the crack initiation and propagation process by altering the soil microstructure and thereby the crack parameters. The contact between biochar and soil particles transitions from close contact to loose contact as the size of the biochar particles increases. In general, the application of 10% biochar with fine particle size had the best performance in inhibiting soil cracking.

Adsorption of pollutants in wastewater via biosorbents, nanoparticles and magnetic biosorbents: A review

Adsorption has gained much attention as one of the efficient approaches to remediate the contaminants in wastewater. Herein, this critical review focuses on the preparation, modification, application and regeneration of the biosorbents, nanoparticles and magnetic biosorbents for the wastewater treatment in recent 5 years (2017-2021). Among these materials, the development of magnetic biosorbents is attractive owing to their variable active sites, high specific surface area, easy separation and low cost. To improve the adsorption performance of biosorbents, the chemical activations such as acid, alkali and salt activations of biosorbents are discussed. In general, the oxidation reaction in acid, alkali and salt activations increases the porosity of biosorbents. The surface characteristics, surface chemistry of the biosorbents and magnetic biosorbents such as electrostatic interaction, π-π interaction and hydrogen bonding are highlighted. Ionic compounds are separated through ion exchange, surface charge and electrostatic interactions while the organic pollutants are removed via hydrophobicity, π-π interactions and hydrogen bonding. The effect of solution pH, adsorbent dosage, initial concentration of pollutants, adsorption duration and temperature on the adsorption capacity, and removal efficiency are discussed. Generally, an increase in adsorbent dosage resulted in a decrease in adsorption capacity due to the excessive active sites. On the other hand, a higher initial concentration or an increase in contact time of adsorbent increased the driving force, subsequently enhancing the adsorption capacity. Finally, this review will be concluded with a summary, challenges and future outlook of magnetic biosorbents. It is anticipated that this review will provide insights into engineering advanced and suitable materials to achieve cost-effective and scalable adsorbents for practical and sustainable environmental remediation.

Simultaneous adsorption of toxic metals in binary systems using peanut and sheanut shells biochars

Converting peanut and sheanut shells into biochar is a smart strategy for recycling agricultural waste. Biochar was produced from peanut and sheanut shells at temperatures of 350 ± 5 °C and 700 ± 5 °C. The adsorption capacities for lead (Pb²⁺), cadmium (Cd²⁺) and mercury (Hg²⁺) in the binary systems were evaluated. In the binary systems with concentrations of 5 : 5 mg/L, 10 : 10 mg/L, 25 : 25 mg/L and 50 : 50 mg/L the removal efficiencies of GB350, SB350, GS350, GB700, SB700 and GS700 were 100% for Pb²⁺ and 88.70%–99.46% for Cd²⁺, 98.20%–100% for Pb²⁺ and 100% for Hg²⁺, 79.30%–100% for Cd²⁺ and 99.96%–100% for Hg²⁺. The higher adsorption percentages of Pb²⁺, Cd²⁺ and Hg²⁺ by the biochar in the binary systems indicated that the pH values of the solutions were good and suitable for adsorption. The biochar from peanut and sheanut shells showed excellent capacity to remove Pb, Cd and Hg in the binary systems. The Langmuir model (0.3351 ≤ R² ≤ 0.9901) was more suitable than the Freundlich model (0.0014 ≤ R² ≤ 0.9994) for the adsorption of toxic metal ions onto the biochar in the binary systems. The interactive effects of the binary mixtures in the aqueous solution of Pb²⁺, Cd²⁺, and Hg²⁺ were found to be either antagonistic or synergistic. Peanut and sheanut shell biochar were rich in calcium, potassium, magnesium, and sodium, and phosphates affected the mechanisms of Pb and Cd adsorption. The high sulphur content might have influenced the mechanism of Hg adsorption in the aqueous solutions on peanut and sheanut shell biochar. These results suggest that peanut and sheanut shell biochar have enormous potential and are suitable for adsorption of Pb²⁺, Cd²⁺ and Hg²⁺ in wastewater and polluted soil. Therefore, their effectiveness should be further tested in an actual water polluted environment.

Toxicological effect assessment of aged biochar on Escherichia coli

Biochar (BC) is a biomass material that has a wide range of applications on the remediating heavy metals. In this experiment, we prepared BC (300 ºC, 500 ºC, and 700 ºC) and applied them to adsorb lead ions (Pb²⁺) to simulate BC treatment of Pb²⁺-contaminated soil. The retention capacity of BC for heavy metals was altered by means of bacterial culture, and the heavy metals released by BC can have toxicological effects on bacteria. This approach was used to assess the effects of long-term application of BC in heavily contaminated land with heavy metals on soil microorganisms. The results show that Escherichia coli survived in the medium containing lower doses of Pb²⁺-aged BC prepared at 300 ºC and 500 ºC (25 mg/L and 50 mg/L), depending on its ability of tolerating a certain amount of Pb²⁺. The addition of 100 mg/L Pb²⁺-aged BC prepared at 700 ºC not only significantly inhibited the growth of E. coli, but also promoted the release of citric acid from E. coli, which in turn triggered BC releasing more Pb²⁺. It is hoped that this will provide foundation to support the long-term application of BC in the remediation of heavy metal contaminated soils.

Optimization of target biochar for the adsorption of target heavy metal ion

The purpose of this work is to study the pyrolysis conditions of target biochar suitable for target heavy metal ion, to characterize the optimized target biochar, and to study the adsorption performance of biochar. With Cu²⁺ and Zn²⁺ as the target pollutants, the pyrolysis conditions involved in the preparation process as pyrolysis temperature, pyrolysis time, and heating rate were evaluated and optimized from Box–Behnken Design (BBD), response surface methodology (RSM) and desirability function, the optimized pyrolysis conditions of target biochar for Cu²⁺ (Cu-BC) and Zn²⁺ (Zn-BC) were obtained. The optimum pyrolysis parameters for Cu-BC and Zn-BC were pyrolysis time of 3.09 and 2.19 h, pyrolysis temperature of 425.27 and 421.97 °C, and heating rate of 19.65 and 15.88 °C/min. The pseudo-second-order kinetic and Langmuir isotherm model proved to be the best fit for the equilibrium data, with a maximum adsorption capacity (Q_max) fitted by Langmuir model were 210.56 mg/g for Cu²⁺ by Cu-BC and 223.32 mg/g for Zn²⁺ by Zn-BC, which were both higher than the Q_max of unoptimized biochar (BC) for Cu²⁺ (177.66 mg/g) and Zn²⁺ (146.14 mg/g). The physical properties, chemical structure, surface chemistry properties of Cu-BC and Zn-BC were characterized by Zeta potential meter, Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). This study puts forward a new perspective for optimizing target biochar production for special environmental application.

Energy-efficient biochar production for thermal backfill applications

The function of engineered thermal backfills surrounding underground pipelines of the crude oil industry is to prohibit heat migration for the design period of 25 to 50 years. Biochar is suitable for reconstituting standard thermal backfill material since it is biochemically inert and has a low heat conductivity. However, the preparation of biochar from biomass involves an energy-intensive pyrolysis process. This study aims to make biochar production energy-efficient via optimizing the pyrolysis temperatures, specifically for thermal backfill applications. Ten distinct biochars were prepared by pyrolyzing two waste biomass, i.e., water hyacinth (WH) and sugarcane bagasse (SB), at temperatures ranging from 300 to 700 °C. The biochars were assessed based on their thermal conductivity, energy consumption, yield, and stability in soil for the design period. The thermal conductivity of produced biochars varied in a narrow range of 0.10 to 0.13 W m^-1 K^-1 with different pyrolysis temperatures, which is possibly due to marginal differences in their microstructure, mineralogy, and physicochemical properties. The findings revealed that the biochar produced at lowest pyrolysis temperature (300 °C) consumed least energy and produced maximum yield. However, it was not suitable for thermal backfill applications due to its inadequate carbon stability in soil. Therefore, the current study recommends a pyrolysis temperature of 400 °C for thermal backfill applications. The recommended pyrolysis temperature was found to be at least 60% energy efficient in comparison to pyrolysis at 700 °C for both the feedstocks. This study provides crucial insight into the role of pyrolysis temperature for tailoring biochar production for intended applications.

Effect of Pyrolysis Temperature on Removal Efficiency and Mechanisms of Hg(II), Cd(II), and Pb (II) by Maize Straw Biochar

Pyrolysis temperature significantly affects the properties of biochar, which in turn can affect the removal of heavy metal ions and the underlying mechanism. In this work, biochars from the pyrolysis of maize straw at 300, 400, and 500 °C (BC300, BC400, and BC500, respectively) and wheat straw at 400 °C (WBC400) were investigated. The influence of production temperature on the adsorption of Hg2+, Cd2+, and Pb2+ by maize straw biochar was investigated by the characterization of the biochars and by adsorption tests. The adsorption capacities of maize and wheat straw biochar were compared in an adsorption experiment. Biochar BC400 showed the best physical and chemical properties and had the largest number of surface functional groups. The pseudo-second-order kinetic model was more suitable for describing the adsorption behavior of metal ions to biochar. The Langmuir model better fit the experimental data. Biochar BC400 had a higher adsorption speed and a stronger adsorption capacity than WBC400. The sorption of Pb2+ and Hg2+ to maize straw biochar followed the mechanisms of surface precipitation of carbonates and phosphates and complexation with oxygenated functional groups and delocalized π electrons. The adsorption mechanism for Cd2+ was similar to those of Hg2+ and Pb2+, but precipitation mainly occurred through the formation of phosphate. In the multi-heavy-metal system, the adsorption of Cd2+ by BC400 was inhibited by Pb2+ and Hg2+. In summary, BC400 biochar was most suitable for the adsorption effect of heavy metals in aqueous solution.

Improved adsorption properties of tetracycline on KOH/KMnO4 modified biochar derived from wheat straw

Modification of pristine biochars has received increasing attentions due to the significant potential in enhancing adsorption performance. In this work, the co-modification of KOH and KMnO₄ on biochar (K-Mn-BC) was performed, with the effect of KOH/KMnO₄ modification on biochar properties and their adsorption toward tetracycline (TC) being extensively explored. Results showed that KOH/KMnO₄ modification can significantly regulate biochars to form hierarchical structure. The obtained K-Mn-BC was characterized with a high specific surface area (1524.6 m² g^-1) and total pore volume (0.85 cm³ g^-1). In addition, the K-Mn-BC exhibited a high adsorption capacity of 584.19 mg g^-1 toward TC at 318 K, and pseudo-second-order (R²:0.993～0.998) and Langmuir (R²: 0.834～0.874) models can fit well with the adsorption behavior. Moreover, the obtained K-Mn-BC can efficiently adsorb TC within a wide pH range (3.0-10.0), and were not affected by the co-existing ions. The possible mechanisms for the high adsorption capacity were ascribed to the pore filling and π-π interaction, following by hydrogen bonding and metal complexation. The obtained K-Mn-BC is a suitable adsorbent for TC removal from water due to the hierarchical structure, high adsorption capacity, and stable adsorption effect.

Statistical optimization, kinetic, equilibrium isotherm and thermodynamic studies of copper biosorption onto Rosa damascena leaves as a low-cost biosorbent

In this study, Rosa damascena leaf powder was evaluated as a biosorbent for the removal of copper from aqueous solutions. Process variables such as the biosorbent dose, pH, and initial copper concentration were optimized using response surface methodology. A quadratic model was established to relate the factors to the response based on the Box-Behnken design. Analysis of variance (ANOVA) was used to assess the experimental data, and multiple regression analysis was used to fit it to a second-order polynomial equation. A biosorbent dose of 4.0 g/L, pH of 5.5, and initial copper concentration of 55 mg/L were determined to be the best conditions for copper removal. The removal of Cu2+ ions was 88.7% under these optimal conditions, indicating that the experimental data and model predictions were in good agreement. The biosorption data were well fitted to the pseudo-second-order and Elovich kinetic models. The combination of film and intra-particle diffusion was found to influence Cu2+ biosorption. The Langmuir and Dubinin-Radushkevich isotherm models best fit the experimental data, showing a monolayer isotherm with a qmax value of 25.13 mg/g obtained under optimal conditions. The thermodynamic parameters showed the spontaneity, feasibility and endothermic nature of adsorption. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the biosorbent before and after Cu2+ biosorption, revealing its outstanding structural characteristics and high surface functional group availability. In addition, immobilized R. damascena leaves adsorbed 90.7% of the copper from aqueous solution, which is more than the amount adsorbed by the free biosorbent (85.3%). The main mechanism of interaction between R. damascena biomass and Cu2+ ions is controlled by both ion exchange and hydrogen bond formation. It can be concluded that R. damascena can be employed as a low-cost biosorbent to remove heavy metals from aqueous solutions.

Pyrolysis of grape bagasse to produce char for Cu(II) adsorption: a circular economy perspective

Based on cleaner production and circular economy concepts, chars were produced through thermochemical conversion of grape bagasse and then used as adsorbents to uptake Cu(II) from aqueous media since Cu(II) is a common element found in fungicides to treat grapevines. The grape bagasse and char characteristics were investigated through several analytical techniques (TGA, SEM, XRD, FTIR, and BET). Three chars were obtained using different pyrolysis temperatures: 700, 800, and 900 °C. The materials had similar removal percentages and adsorption capacity. The char produced at 700 °C was chosen due to its lower production cost. Studies were conducted on the adsorbent dosage and pH effect, adsorption kinetics, isotherms, and thermodynamics. The most efficient dosage was 1.5 g L-1, and the pH was 5.5. The kinetic study showed that the equilibrium was reached in 60 min and the pseudo-second-order model presents the best fit. After the temperature influence study (25, 35, 45, and 55 °C), it was possible to verify that Cu(II) adsorption through char was favored at 55 °C. The Freundlich model showed the best fit for the experimental data. The highest removal percentage was 96.56%, and the high maximum adsorption capacity was 42 mg g-1. The thermodynamic study shows the adsorption as a spontaneous process, favorable, and endothermic.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-02792-8.

Approach to an efficient pretreatment method for rice straw by deep eutectic solvent for high saccharification efficiency

Deep eutectic solvent comprising choline chloride (ChCl) and acetic acid (AA) was used for rice straw (RS) pretreatment. Effect of ChCl: AA molar ratio, time and temperature on lignin removal and retainment of total carbohydrate content (TCC) in pretreatment process were evaluated by central composite design (CCD) approach. The pretreatment temperature and molar ratio of AA to ChCl played a significant role in delignification. The optimized conditions for RS pretreatment were 1:3.59 (ChCl:AA molar ratio), 126 °C and 150 min. ChCl:AA pretreated RS (CApRS) gave 83.1% delignification, 679 mg/g_CApRS TCC and 83.7% pretreatment efficiency. CApRS contained enriched cellulose content, 0.73 g/g_CApRS as compared with 0.43 g/g_{raw RS} in raw RS. CApRS showed 31% higher crystallinity index, 17-fold higher surface area than raw RS. The morphological study of CApRS displayed porous surface. Saccharification of CApRS by commercial cellulase gave total reducing sugar of 18.8 g/L in hydrolysate with saccharification efficiency, 92.2%.

Enhanced Nutrient Removal in A2N Effluent by Reclaimed Biochar Adsorption

The excessive nitrogen and phosphorus discharged into the water environment will cause water eutrophication and thus disrupt the water ecosystem and even exert biological toxicities. In this study, the absorption removal of nitrogen and phosphorus from the anaerobic tank in an anaerobic−anoxic/nitrifying system using four different kinds of biowaste-reclaimed biochars were investigated and compared. The effects of temperature and pH on nutrient adsorption removal were further investigated. The four kinds of biochar were successfully prepared and well characterized using a scanning electron microscope, fourier transform infrared spectroscopy, X-ray diffraction and Brunner−Emmet−Teller methods. Generally, there was no significant change in chemical oxygen demand (COD) and NH4+-N removal efficiencies when treated by the different biochars, while the activated sludge biochar (ASB) displayed the highest total phosphorus (TP) removal efficiency. The initial TP concentrations (<40 mg/L) displayed no remarkable effects on the TP adsorption removal, while the increase of temperature generally enhanced TP and NH4+-N adsorptions on the ASB. Besides, the increase of pH significantly promoted NH4+-N removal but depressed TP removal. Moreover, the adsorption process of TP by the ASB complies with the secondary kinetic model, suggesting the chemical precipitation and physical electrostatic interaction mechanisms of TP adsorption removal. However, the adsorption of NH4+-N conformed to the inner-particle diffusion model, indicating that the NH4+-N adsorption was mainly involved with pore diffusions in the particles.

Remediation of emerging metal pollutants using environment friendly biochar- Review on applications and mechanism

Bioremediation of heavy metals has become a major environmental concern due to their bio resistant nature and tendency to accumulate. Application of various technologies, involving physical and chemical working principles are applied and passive uptake using sorption involving eco-friendly substrates gained significant attention. Biochar, a cheaper and efficient material, offers good potential due to the greater ease of production, treatment and disposal. This review focuses on the effective application of biochar to treat water contaminated by three specific heavy metals: chromium, lead and arsenic. The on-field applications like soil amendment, industrial wastewater treatment and groundwater treatment using biochar are highlighted. The review article describes the feedstock available for biochar production, various production processes and the importance of optimum conditions like pyrolysis temperature, rate and retention time for various feedstocks reported in literature. The energy requirement of the production process can be supplied by its own energy output. Various modifications that are suitable for the biochar from distinct feedstocks are also discussed. The removal performance of biochar at different working conditions like pH, initial concentration of pollutant and adsorbent dose are consolidated. The highest removal efficiencies reported were by coconut shell biochar (Cr - 99.9%), canola straw biochar (Pb - 100%) and perilla leaf biochar (As - 100%). The adsorption mechanism is explained with reference to kinetics, isotherms, and molecular dynamics. Adsorption mechanism of most of the biochars was found to fit either Freundlich or Langmuir isotherm.

Efficient removal of Cd2+ from aqueous solution with a novel composite of silicon supported nano iron/aluminum/magnesium (hydr)oxides prepared from biotite

Taking low cost silicate minerals to develop efficient Cd²⁺ adsorption materials was favorable to the comprehensive utilization of minerals and remediation of environmental pollution. In this study, a composite of silicon supported nano iron/aluminum/magnesium (hydr)oxides was prepared with biotite by combining acid leaching and base precipitation process, which was used to remove Cd²⁺. Cd²⁺ adsorption behaviors were in accordance of pseudo-second order kinetic model and Langmuir model, and the obtained maximal Cd²⁺ adsorption capacity was 78.37 mg/g. Increasing pH and temperature could accelerate the removal of Cd²⁺. The activation energy was calculated as 66.05 kJ/mol, meaning that Cd²⁺ removal process was mainly depended on chemical adsorption. XRD and SEM results showed that this composite was a micro-nano structure of layered silica supported nano iron/aluminum/magnesium (hydr)oxides. Cd²⁺ removal mechanisms were consisted of surface complexation and ion exchange between Cd²⁺ and other metal ions, and the ion exchange interaction played the major role. These results indicated that a novel efficient utilization way for silicate minerals was developed.

One-step synthesis of garlic peel derived biochar by concentrated sulfuric acid: Enhanced adsorption capacities for Enrofloxacin and interfacial interaction mechanisms

This study put forward a one-step carbonization method by concentrated sulfuric acid to prepare garlic peel derived biochar, and the synthetic conditions were optimized by L₁₆(4⁵) orthogonal experiments. Notably, in order to study the differences between the proposed synthetic method and the conventional pyrolysis method, the concentrated sulfuric acid carbonized garlic peels biochar (CSGPB) was compared with pyrolysis derived garlic peel biochar (HTGPB) in characterization and adsorption capacities for Enrofloxacin (ENR). Results showed that CSGPB exhibited more graphite-like structures with more active functional groups on the surface, and the equilibrium adsorption capacity of CSGPB (142.3 mg g^-1) was 13.7 times of HTGPB (10.4 mg g^-1) under identical conditions. Moreover, the adsorption behaviors including adsorption kinetics, isotherms and thermodynamics of CSGPB for ENR were fully investigated and discussed. Based on the above experiments, density functional theory (DFT) simulations were performed to reveal the interfacial interaction and adsorption mechanism. Results showed π-π interaction between quinolone moieties of ENR and graphite-like structures in CSGPB might be the dominant mechanism. As for the functional groups, the adsorption energies were -40.46, -15.21 and -5.96 kJ mol^-1 for -SO₃H, -OH and -COOH, respectively, which indicated -SO₃H was the most active functional groups on the surface of CSGPB. This study provided a new sustainable perspective for the design of efficient biochars, and explored the interfacial interaction mechanism of antibiotics removal on biochars.

Enhanced adsorption of metal ions onto Vetiveria zizanioides biochar via batch and fixed bed studies

The study highlights the potential of Vetiveria Zizanioides derived biochar for heavy metal removal in multicomponent systems. Biochar efficiency varies with pH, metal ion concentration and residence time. Maximum removal efficiency was found to be 66.34, 67.23, 46.54, 69.92, 68.23 and 63.34% for Arsenic, Copper, Nickel, Cadmium, Lead and Chromium at 90 min respectively. Ternary system revealed that Copper ions have inhibitory effect on Lead ions and have lower adsorption capacity than binary system. Multicomponent isotherm model was used to analyse simultaneous adsorption of metal ions and shows a good fit with modified Langmuir model for binary and ternary systems. Fixed-bed column was tested for scale-up feasibility and maximum adsorption capacity of 139, 130, and 123 mg/g for Lead, Copper, and Nickel ions were obtained at 1.5 L/h and a bed height of 12 cm. In fixed bed column, multicomponent sequence provides more protection against premature exhaustion of biochar.

Characterization of halophyte biochar and its effects on water and salt contents in saline soil

Biochar is a beneficial soil amendment; however, biochar-based properties are mainly determined by the feedstocks and the pyrolysis temperature. Nevertheless, considering the vast biomass of halophyte, little is known about how the halophyte-derived biochar improves saline soils. In this study, we firstly produced biochars by using three different halophytes, including Tamarix chinensis (recretohalophyte), Suaeda salsa (euhalophyte), and Phragmites australis (pseudo-halophyte) at 300, 500, and 700 °C, and compared their chemical and physical properties. We applied halophyte (Tamarix chinensis and Phragmites australis) biochars (pyrolysis at 500 °C) into 0-20 cm saline soil at 2% and 4% (w/w) rates to investigate the saline soil water, salt, and pH dynamics in a 12-month column experiment. The results showed that as the pyrolytic temperature increase, biochar yield and pore diameter decreased by 37.5-44.0% and 34.6-89.7%, respectively; in contrast, biochar pH, specific surface area, and total volume increased by 24.8-47.8%, 3-37 times and 1-9 times, respectively. The halophyte types significantly controlled biochar carbon and dissolved salt content and electrical conductivity. Halophyte biochar application can increase soil water and salt content, and application of 4% of Tamarix chinensis-derived biochar can increase more soil moisture than the soil salinity, and it can maintain soil pH at a stable level, which would be a potential way to improve saline soil properties. The results are valuable for choosing halophyte types and optimizing pyrolytic temperatures for halophyte biochar production through specific environmental usage.

Alleviation of microcystin-LR-induced hepatic lipidosis and apoptosis in zebrafish by use of rice straw-derived biochar

Microcystin-LR (MC-LR), mainly released by Microcystis aeruginosa, is posing a tremendous risk to aquatic animals and human health. Meanwhile, biochar (BC) is gradually be used as a sustainable adsorbent to immobilize and remove water pollutants. In our study, we for the first time conducted a full-scale investigation on lipid metabolism and its regulation mechanism of female zebrafish (Danio rerio) exposed to 0, 10 μg/L MC-LR, 100 μg/L BC, and 10 μg/L MC-LR+ 100 μg/L BC. The results indicated that sub-chronic MC-LR exposure induced hepatic lipidosis and apoptosis, including the formation of lipid droplets, significantly elevation of hepatic triglyceride (TG) level as well as significant upregulated expression of lipogenesis-related genes (foxo1a, elovl5, pparγ) and pro-apoptotic genes (bax, casp3). Nevertheless, no significant alteration was observed in the single BC group and the combined exposure group, which indicated that BC may solely functioned as an absorbent agent to lower MC-LR bioaccumulation in zebrafish liver and alleviate MC-LR-induced hepatotoxicity. Our findings revealed that the utilization of rice straw-derived BC can adsorb and immobile MC-LR in the water, subsequently alleviated the MC-LR-induced hepatic lipidosis and apoptosis in female zebrafish. On the basis of fish health, it is urgent to explore the feasibility of using environmentally friendly materials like BC to adsorb pollutants in water.

Magnetically Modified Biosorbent for Rapid Beryllium Elimination from the Aqueous Environment

Although both beryllium and its compounds display high toxicity, little attention has been focused on the removal of beryllium from wastewaters. In this research, magnetically modified biochar obtained from poor-quality wheat with two distinct Fe_xO_y contents was studied as a sorbent for the elimination of beryllium from an aqueous solution. The determined elimination efficiency was higher than 80% in both prepared composites, and the presence of Fe_xO_y did not affect the sorption properties. The experimental q_max values were determined to be 1.44 mg/g for original biochar and biochar with lower content of iron and 1.45 mg/g for the biochar with higher iron content. The optimum pH values favorable for sorption were determined to be 6. After the sorption procedure, the sorbent was still magnetically active enough to be removed from the solution by a magnet. Using magnetically modified sorbents proved to be an easy to apply, low-cost, and effective technique.

Effects of different order spiking on bioavailability and ecological risk of phenanthrene in mangrove sediment-biochar system

Biochar shows unique advantage in decreasing the bioavailability of phenanthrene and has huge potential into the in-situ remediation of contaminated sediment. The different order spiking influences the bioavailability and ecological risk of phenanthrene, this study provides a comprehensive investigation of biochar (derived from mangrove Kandelia obovata -sediment system under three conditions: I) co-addition of biochar and sediment; II) biochar and subsequently sediment addition (after biochar adsorption reached equilibrium); III) sediment and subsequently biochar addition (after sediment adsorption reached equilibrium). It was observed that the adsorption capability under model I and III was much smaller than that under model II (p < 0.05). Regardless of time, K. obovate - biochar significantly (p < 0.05) increase the sorption of phenanthrene in sediment -water system. The results provide valuable studies for further in-situ remediation of phenanthrene and engineering applications.