Unmodified Biochar Research Articles

Synthesis of MgO-Coated Canna Biochar and Its Application in the Treatment of Wastewater Containing Phosphorus

In order to treat phosphorus-containing wastewater and realize the resource utilization of wetland plant residues, biochar was prepared by the pyrolysis of canna aquatic plant waste at 700 °C, and the adsorption characteristics of phosphorus by MgO-modified biochar (MBC) were explored. The main results are as follows: the adsorption capacity of the MBC was eight times that of unmodified biochar (BC), and the adsorption capacity was up to 244 mg/g. The isothermal adsorption data were consistent with the Langmuir equation, which indicates monolayer adsorption. The functional groups changed little before and after the modification, but a new diffraction peak appeared after the modification. Compared with the standard card, it was suggested that there were MgO crystals with a higher purity. SEM images showed that the BC had a smooth surface, an obvious pore structure, and a thin pore wall, while the MBC had a rough surface and a layered structure, which can provide more adsorption sites for phosphate adsorption. In addition, an XPS analysis showed that Mg3(PO4)2 crystals appeared on the surface of the MBC after adsorption. The mechanism analysis showed that MgO is an important substance for MBC to adsorb phosphorus, and electrostatic adsorption and complex precipitation play key roles. In the test to verify the removal of actual phosphorus-containing wastewater by MBC, it was found that the removal rates for wastewater with 2.06 mg/L and 199.8 mg/L of phosphorus by MBC were as high as 93.4–93.9% and 99.2–99.3%, respectively. MBC can be used as an efficient adsorbent for phosphorus removal.

Cadmium immobilization in soil using phosphate modified biochar derived from wheat straw

The phosphate-modified biochar (BC) immobilizes cadmium (Cd), yet little is known about how phosphate species affect Cd detoxification in contaminated soils. We developed phosphate-modified biochar through the pyrolysis of wheat straw impregnated with three types of phosphate: mono‑potassium phosphate (MKP), dipotassium hydrogen phosphate (DKP), and tripotassium phosphate (TKP). The Cd adsorption mechanism of modified biochar was investigated by biochar characterization, adsorption performance evaluation, and soil incubation tests. The results demonstrated that the efficiency of biochar in immobilizing Cd2+ followed the order: TKP-BC > DKP-BC > MKP-BC. The TKP-BC had the highest orthophosphate content, the fastest adsorption rate, and the largest adsorption capacity (Langmuir) of 257.28 mg/g, which is 6.31 times higher than that of the unmodified BC (CK). In contrast, pyrophosphate was predominant in MKP-BC and DKP-BC. The primary adsorption mechanism for Cd2+ was precipitation, followed by cation exchange, as evidenced by the formation of CdP minerals on the BC surface, and an increase of K+ in solution (compared to water-soluble K+) and a decrease of K+ in the biochar during adsorption. Desorption of Cd from the TKP-BC after adsorption was 9.77 %–12.39 % at a pH of 5–9, much lower than that of CK. The soil incubation test showed the diethylenetriaminepentaacetic acid extracted Cd of TKP-BC, MKP-BC, and DKP-BC was reduced by 67.93 %, 18.41 % and 31.30 % over CK, respectively. Using the planar optodes technique, we also found that TKP-BC had the longest effect enhancing in situ soil pH. This study provides a theoretical basis for developing heavy metal pollution control technology using green remediation materials and offers insights into the remediation mechanisms.

Iron-modified biochar effectively mitigates arsenic-cadmium pollution in paddy fields: A meta-analysis

The escalating problem of compound arsenic (As) and cadmium (Cd) contamination in agricultural soils necessitates the urgency for effective remediation strategies. This is compounded by the opposing geochemical behaviors of As and Cd in soil, and the efficacy of biochar treatment remains unclear. This pioneering study integrated 3780 observation pairs referred from 92 peer-reviewed articles to investigate the impact of iron-modified biochar on As and Cd responses across diverse soil environments. Regarding the treatments, 1) biochar significantly decreased the exchangeable and acid-soluble fraction of As (AsF1, 20.9%) and Cd (CdF1, 24.0%) in paddy fields; 2) iron-modified biochar significantly decreased AsF1 (32.0%) and CdF1 (27.4%); 3) iron-modified biochar in paddy fields contributed to the morphological changes in As and Cd, mainly characterized by a decrease in AsF1 (36.5%) and CdF1 (36.3%) and an increase in the reducible fraction of As (19.7%) and Cd (39.2%); and 4) iron-modified biochar in paddy fields increased As (43.1%) and Cd (53.7%) concentrations in the iron plaque on root surfaces. We conclude that iron-modified biochar treatment of paddy fields is promising in remediating As and Cd contamination by promoting the formation of iron plaque.

Removal of cadmium from aqueous solution by magnetic biochar: adsorption characteristics and mechanism.

Experiments were conducted to investigate the potential of the efficient resource utilization of waste cow manure and corn straw in an agricultural ecosystem. In this study, a magnetic cow manure and straw biochar were synthesized by a co-precipitation method, and cadmium (Cd(II)) was removed by adsorption in aqueous solution. Several physicochemical characterization techniques were applied, including SEM, BET, Zeta, FTIR, Raman, XPS, and VSM. The effects of pH value, magnetic biochar content, adsorption kinetics, and isothermal adsorption on the adsorption of Cd(II) were investigated. The physicochemical characterizations revealed that the physical and chemical properties of the magnetic biochar were substantially changed compared to the unmodified biochar. The results showed that the surface of the biochar became rough, the number of oxygen (O)-containing functional groups increased, and the specific surface area increased. The results of the adsorption experiments showed that the adsorption capacity was affected by pH, magnetic biochar addition, Cd(II) concentration, and adsorption time. The adsorption kinetics and isothermal adsorption experiments showed that the Cd(II) adsorption processes of the cow manure and corn straw magnetic biochars were consistent with the Freundlich model and pseudo-second-order kinetic model. The results also showed that the Cd(II) adsorption effect of cow manure magnetic biochar was found to be more effective than that of corn straw magnetic biochar. The optimal conditions for Cd(II) adsorption were 800 ℃ for cow manure magnetic biochar, with a pH value of 5 and 0.14g biochar addition, and 600 ℃ for straw magnetic biochar with a pH value of 8 and 0.12g biochar addition. In conclusion, the cow manure magnetic biochar was an effective adsorbent for the absorption of Cd(II) in wastewater.

Influences of phosphorus-modified biochar on bacterial community and diversity in rhizosphere soil.

Root-associated bacteria play a vital role in the soil ecosystem and plant productivity. Previous studies have reported the decline of bacterial community and rhizosphere soil quality in the cultivation of some medicinal plants (i.e., Pseudostellaria heterophylla). Phosphorus (P)-modified biochar has the potential to improve soil health and quality. However, its influence on the bacterial community and diversity in the rhizosphere of medicinal plants is not well understood. Therefore, this study aims to investigate the effects of P-modified biochar on the bacterial community and diversity in the rhizosphere of P. heterophylla. Soil samples were collected from the rhizosphere of 4-month P. heterophylla under control (no biochar), 3% unmodified and 3% P-modified biochar treatments, respectively. Compared with control and unmodified biochar treatment, P-modified biochar significantly increased the relative abundance of plant-beneficial bacteria (P < 0.05), particularly Firmicutes, Nitrospirae and Acidobacteria. The relative abundance of Bacillus, belonging to Firmicutes, was dramatically raised from 0.032% in control group to 1.723% in P-modified biochar-treated group (P < 0.05). These results indicate the potential enhancement of soil quality for the growth of medicinal plants. The application of biochar significantly increased bacterial richness and bacterial diversity (P < 0.05). P modification of biochar did not have significant effects on soil bacterial richness (P > 0.05), while it reduced Shannon and increased Simpson diversity index of soil bacterial communities significantly (P < 0.05). It indicates a decrease in bacterial diversity. This research provides a new perspective for understanding the role of P-modified biochar in the rhizosphere ecosystem.

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

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

Enhanced Adsorption of Cu2+ from Aqueous Solution by Sludge Biochar Compounded with Attapulgite-Modified Fe

Three types of modified sludge biochar were produced for the adsorption of copper in aqueous solutions via the calcium-based magnetic (CaCO3, Fen+) treatment (CA–BC), nanozero-valent iron (nZVI) treatment (nZVI–BC), and iron (Fe3+) treatment (FA–BC) of raw biochar. The results suggested that the adsorption capacity for Cu2+ of calcium-based magnetic attapulgite/sludge biochar (CA–BC) prepared from CaCO3, FeCl3, and FeSO4 is 38.01% greater than that of unmodified biochar and 6.41% to 17.5% greater than that of the other biochar. The CA-BC contained a variety of ferrite-containing and hydroxide-functional groups, as well as a more developed pore structure. The existence of H+ reduced the adsorption capacity of the biochar for Cu2+. A high initial concentration of Cu2+ could increase Cu2+ adsorption on CA–BC. Combined with theoretical calculations, the adsorption efficiency of CA–BC in different systems was explored. The results revealed that CA–BC achieved a maximum removal rate of 92.644% at a pH of 6 with a reaction time of 157 min and an initial Cu2+ concentration of 2.813 mg/L. These results suggest that CA–BC shows great potential for removing Cu2+ from aqueous solutions.

The regulation of biochar surface potential to achieve rapid capacitive deionization

Capacitive deionization (CDI) is a promising desalination technology. In the design and fabrication of high-performance CDI electrodes, the modification of activated carbon is widely adopted to improve the desalination capacity. In this work, aiming at the regulation of surface potential, activated carbon was doped with N and S, showing improved conductivity, wettability, and optimized pore structure. The difference in the potential of zero charge (Epzc) generated by the heteroatom doping was employed to enlarge the actual adsorption voltage window, and to improve the salt adsorption capacity (SAC) and total salt adsorption capacity at long periods. SAC of 14.4 mg g-1 was achieved with a high average salt absorption rate (ASAR) of 8.2 mg g-1 min-1 under 1.2 V in a 500 mg L-1 NaCl solution. Moreover, the total SAC of asymmetric configuration of N, S-doped biochar of 50 cycles achieved 545.8 mg g-1, 19.7% more than that of the symmetric configuration of unmodified biochar. The doping of N and S atoms on biochar brings excellent electrochemical performance and desalination capacity, and the rational utilization of Epzc after heteroatom doping provides a reasonable method for the design of CDI configuration.

Biochar modification methods and mechanisms for salt‐affected soil and saline‐alkali soil improvement: A review

AbstractThe continuous growth of the world's population has led to an increased demand for food. Biochar (BC) contains valuable functional groups and nutrients, which have been demonstrated to enhance soil properties and boost crop yield. Nonetheless, unmodified BC exhibits significant alkalinity and a large salt concentration; thus, its efficacy in improving saline‐alkali soil remains a matter of contention. Therefore, scholars aim to address the aforementioned limitations by adapting BC. In this paper, a summary is given of the methods used to modify BC and the effects of modified BC on salt‐affected soil and saline‐alkali soil properties, including pH, nutrients and microbial activity. The effects and principles of different modifiers and modification methods on BC's physicochemical properties (porosity and functional group content and type, etc.) were revealed. Furthermore, the principle of soil improvement by modified BC varies depending on the modification method. Although modified BC can effectively enhance salt‐affected soil, its excessive application and improper selection of modifiers can aggravate Na+ toxicity or introduce other pollutants into salt‐affected soil. Therefore, using modified BC with care is imperative according to the actual situation. In this review, we provide a detailed introduction to the methods and principles of BC modification for saline‐alkali soil. Furthermore, we identify the shortcomings and future research directions in this field. These insights are valuable when choosing proper BC modification methods for salt‐affected soil.

Synergistic approach for synthesis of functionalized biochar for efficient adsorption of Lopinavir from polluted water

The COVID-19 pandemic has led to a significant increase in antibiotic consumption, along with a 70% rise in antiviral drug concentrations in aquatic ecosystems. For the effective adsorption of antibiotics, biochar was modified by incorporating layered double hydroxide (LDH) through hydrothermal method. The results showed that LDH provides additional hydroxyl groups, positive surface charges and ion exchange. Whereas biochar component provides a larger specific surface area (467.8 m2/g). Batch adsorption experiments of biochar @ layered double hydroxide (BC@LDH) showed enhanced adsorption performance (832.9 mg/g), compared to pristine LDH (420.3 mg/g) and unmodified biochar (548.5 mg/g). Adsorption data were best interpreted (R2 = 0.99) by pseudo second order, Freundlich, and Temkin isotherm models. Adsorption was a synergism of LDH and biochar physiochemical properties, whereas pore-filling was the primary mechanism. The recyclability of BC@LDH confirmed its good structural stability. This study introduces a sustainable and efficient method for synthesizing a versatile adsorbent with superior antibiotic removal.

Assessing pollutant sorption efficiency of modified and unmodified biochar with Bacillus cereus on contaminated lake water: implications for Oryza sativa seedling and Artemia franciscana larvae viability

Assessing pollutant sorption efficiency of modified and unmodified biochar with Bacillus cereus on contaminated lake water: implications for Oryza sativa seedling and Artemia franciscana larvae viability

Dynamic simulation analysis of city tail water treatment by constructed wetland with biochar substrate.

Constructed wetland (CW) is an important method of ecological water treatment, and CW has obvious advantage in treating low-pollution water. In order to improve the treatment efficiency of CW, the first-order and second-order kinetics simulations of pollutant removal in CW were carried out to optimize operating conditions. The experimental study of city tail water treatment under unmodified biochar (different additions) or different modified biochar conditions showed that the first-order kinetic equation relatively accurately reflect the removal of pollutants by substrate. The relatively optimal range of biochar addition (2.21-3.79%) in the first-order kinetic analysis covered the relatively optimal mass ratio (2.95%). The first-order kinetic equation fitting showed that the half-life of ammonia nitrogen removal by NaOH (0.1 mol·L-1)-modified biochar was reduced by about 10% without plant. The half-life of total phosphorus removal by KMnO4 (0.1 mol·L-1) modified biochar was reduced by about 50%. The half-life of chemical oxygen demand removal by H2SO4 (0.75 mol·L-1) + 8 freeze-thaw cycles modified biochar was reduced by about 9.0%. When the half-life was small, the pollutant removal rate was high. The results of this study further confirmed the effectiveness of the simulation results of pollutant removal in CW with biochar by the first-order kinetic equation. This study further optimized the CW operating conditions and improved the treatment efficiency of nitrogen and phosphorus in the CW.

Adsorption of phosphorus in water by metal-modified large-size biochar: Realizing the recovery and recycling of phosphorus

Biochar finds extensive use in adsorbing phosphorus (P) from wastewater abundant in P content. Most biochars carry negative surface charges, causing electrostatic repulsion towards anions. However, as P commonly exists as anions in water, the P adsorption capacity of biochar remains limited. Moreover, conventional biochar used for P adsorption presents challenges in recycling due to its small particle size. This study presented a novel approach wherein metal-modified large-size (1–2 mm) walnut shell biochars were created using Fe, Mg, and Ca additives at varying ratios. This innovation aims to enhance P adsorption capacity and recyclability. Experimental findings revealed that unmodified biochar (BC) exhibited minimal P adsorption capacity (0.34 mg/g), while all metal-modified biochars (MBCs) demonstrated elevated P adsorption capabilities (1.06–25.60 mg/g). Among the distinct MBCs, Ca-MBCs displayed the highest P adsorption capacity (25.60 mg/g), trailed by Mg-MBCs (23.58 mg/g) and Fe-MBCs (5.99 mg/g). Furthermore, both isotherm and kinetic adsorption analyses suggested that the P adsorption mechanism for MBCs predominantly involves chemical adsorption. However, desorption studies post-adsorption indicated suboptimal desorption efficiencies for P (19.16–26.07%) in MBCs, posing challenges for their application as fertilizers. Therefore, it is essential to enhance simultaneous P adsorption and desorption capabilities of biochar.

Development of a novel three-dimensional biofilm-electrode system (3D-BES) loaded with Fe-modified biochars for enhanced pollutants removal in landfill leachate

Different mass ratio iron (Fe)-loaded biochars (FeBCs) were prepared from food waste and used in the three-dimensional biofilm-electrode systems (3D-BES) as particular electrodes for landfill leachate treatment. Compared to the unmodified biochar (BC), specific surface area of Fe-loaded biochars (FeBC-3 with a Fe: biochar of 0.2:1) increased from 63.01 m2/g to 184.14 m2/g, and pore capacity increased from 0.038 cm3/g to 0.111 cm3/g. FeBCs provided more oxygen-containing functional groups and exhibited excellent redox properties. Installed with FeBC-3 as particular electrode, both NH4+-N and chemical oxygen demand COD removals in 3D-BESs were well fitted with the pseudo-first-order model, with the maximum removal efficiencies of 98.6 % and 95.5 %, respectively. The batch adsorption kinetics experiments confirmed that the maximum NH4+-N (7.5 mg/g) and COD (21.8 mg/g) adsorption capacities were associated closely with the FeBC-3 biochar. In contrast to the 3D-BES with the unmodified biochar, Fe-loaded biochars significantly increased the abundance of microorganisms being capable of removing organics and ammonia. Meanwhile, the increased content of dehydrogenase (DHA) and electron transport system activity (ETSA) evidenced that FeBCs could enhance microbial internal activities and regulate electron transfer process among functional microorganisms. Consequently, it is concluded that Fe-loaded biochar to 3D-BES is effective in enhancing pollutant removals in landfill leachate and provided a reliable and effective strategy for refractory wastewater treatment.

Removal of methyl blue and malachite green from water using biodegradable magnetic Tamarindus Indica fruit seed biochar: Characterization, equilibrium study, modelling and thermodynamics

The removal of hazardous dyes from water by magnetic biosorbents has received a lot of interest in recent studies. This is because they are inexpensive and simple to separate from the solution phase. In this study, nano-magnetic Tamarindus indica fruit seed biochar was combined with iron to create a green nano-magnetic/ biochar (BC) composite (nM-BC). Compared to unmodified biochar, modified biochar composite significantly improved the ability to adsorb methyl blue (MB) and malachite green (MG). The Dubinin-Radushkevich, Scathard, Freundlich, Langmuir, and Temkin models were used to analyze the adsorption equilibrium data, and the Langmuir isotherm (R2 =0.952–0.995) provided a good match to the results. Saturated BC adsorption capacities for MB and MG were 3.055 mg/g and 5.577 mg/g, respectively, while nM-BC values for MB and MG were 3.326 mg/g and 20.408 mg/g, respectively. The adsorption process is accurately described by the pseudo-second-order kinetic model. BC and nM-BC both passed four reusability tests. Utilizing FT-IR and SEM instruments BC and nM-BC were characterized. The study demonstrates that biochar can be enhanced with nano-iron which has a potent ability to remove dyes utilizing a green manufacturing approach.

Enhanced removal efficiency of bensulfuron-methyl by a novel boron doping biochar-based Acinetobacter YH0317 at a lower temperature

Biochar-based bacteria are regarded as an efficient strategy for remediating organic pollutants in aquatic environments. Herein, a strain named Acinetobacter YH0317 that could degrade bensulfuron-methyl (BSM) at a lower temperature (15 °C) was isolated from a paddy rice field with long-term BSM application. Then Acinetobacter YH0317 was loaded on unmodified biochar (BC) and boron doping biochar (BBC). Results showed that BBC-based YH0317 significantly enhanced the removal efficiency of BSM (71.8–99.1%) compared with BC-based YH0317 (41.9–44.0%) and YH0317 alone (18.1–20.7%) in 24 h. BBC promoted the growth of YH0317 and secretion of extracellular secretions by providing a carrier and shelter for YH0317. The electrochemical analysis suggested BBC improved the electron transfer rate, which ultimately facilitated the removal of BSM. Hydroponic experiments indicated that BBC-based YH0317 effectively improved the growth of soybean. This work reports a novel BBC-based Acinetobacter YH0317 that could effectively remediate BSM contamination in the water environment.

Adsorption Characteristics of Heavy Metals Pb2+ and Zn2+ by Magnetic Biochar Obtained from Modified AMD Sludge.

Acid mine drainage (AMD) sludge can be used to prepare adsorbent materials for the removal of heavy metals in water, which is an effective means for its resource utilization. Magnetic modified biochar (MMB), which can be recovered by magnetic separation, was prepared from sludge generated from the carbonate rock neutralization treatment of AMD and rice straw agricultural waste. Unmodified biochar (UMB) was obtained from rice straw and chemically modified and treated by ultraviolet radiation to produce MMB. The Pb2+ and Zn2+ adsorption capacities of UMB and MMB were investigated. Simultaneously, the materials were characterized by SEM, FTIR, BET, and ZETA. The results showed that the specific surface area (130.89 m2·g-1) and pore volume (0.22 m2·g-1) of MMB were significantly increased compared to those of UMB (9.10 m2·g-1 and 0.05 m2·g-1, respectively). FTIR images showed that MMB was successfully loaded with Fe3O4. The adsorption process of Pb2+ and Zn2+ onto MMB was consistent with the Langmuir adsorption isotherm and second-order kinetic models, with maximum adsorption capacities of 329.65 mg·g-1 and 103.67 mg·g-1, respectively. In a binary system of Pb2+ and Zn2+, MMB preferentially binds Pb2+. The adsorption efficiencies of MMB reached >80% for Pb2+ and Zn2+.

Characteristics and mechanisms of sulfamethoxazole adsorption onto modified biochars with hierarchical pore structures: Batch, predictions using artificial neural network and fixed bed column studies

A series of modified biochar with hierarchical pore structures (ZnxBC1, x = 0.5, 1, 2, 3) was obtained by ZnCl2 and investigated the adsorption performance of sulfamethoxazole (SMX). The structure and composition of ZnxBC1 were well characterized by the material analysis technique. Compared with unmodified biochar (BC), the specific surface area, pore volume, and adsorption capacity of ZnxBC1 significantly increased. The ZnxBC1 performed a significant adsorption capacity of SMX with the maximum adsorption amount of 597.57 mg/g, leading to a 54-fold increase in that of BC (11.04 mg/g). Multiple linear regression analysis showed that the quantitative relationship of qe with Vmeso and Vmicro was qe = 360.74*Vmeso + 871.58*Vmicro-22.26, which was the novelty of the study to the analysis of SMX adsorption capacity on the different Vmeso/Vmicro ratios of adsorbents. Based on the batch experiment results, an artificial neural network (ANN) model with a topology of 5:5:10:1 was developed to sufficiently describe the adsorption data (R2 > 0.99), and possessed good predictability in different water quality conditions. Additionally, both static adsorption and dynamic adsorption experiments of Zn1BC1 showed excellent regeneration properties. Overall, the ZnCl2 modified biochar with the properties of rapid adsorption rate, high adsorption capacity, multiple reuses, and low-cost performed the potential utilization for the removal of SMX, and the effect of pore structure of biochar on SMX adsorption could guide the design and preparation of efficient antibiotics adsorbents.

Production of engineered algal biochar through microwave pyrolysis for nutrient recovery from aqueous solution

AbstractBiochar adsorbs contaminants from wastewater. However, biochar's modification, its application in nutrient removal from wastewater, and its mechanism of nutrient removal need to be explored. In this study, nitrate and phosphate were recovered from secondary treated domestic wastewater using microalgal biochar (Spirulina sp.). The biochar was obtained by microwave pyrolysis of algae at 400 W power for 10 min. The biochar was modified using Mg(OH)2 under different conditions. Three pre‐and post‐treated biochars with varied Mg(OH)2 percentages (2%, 4%, and 6% by weight) were produced. All the modifications in biochar improved its specific surface area. Highest specific surface area of the modified biochar reached 33 m2/g compared to 12 m2/g of the unmodified biochar. SEM analysis showed improvement in the porosity of the modified biochars. Modification also introduced ‒OH, ‒C=C‒ and ‒C‒O‒C‒ functional groups on the biochar surface. All these modifications improved the nutrient adsorption capability of the biochar. Adsorption studies indicated that 4% post‐treated biochar (Po4) was the best. The adsorption data fit the pseudo second order kinetic model with R2 being 0.99 and 0.96 for phosphate and nitrate respectively. Among different isotherm models, the Freundlich isotherm model showed the best fit for phosphate and nitrate, with their respective R2 being 0.96 and 0.97, indicating multi‐layer physical‐chemical adsorption, including the intra‐particle diffusion. The equilibrium time for adsorption for nitrate and phosphate was 7 and 6 h, respectively. The optimum pH was 5 and 6 for nitrate and phosphate, respectively, and the optimum dosage was 2 g/L. The maximum adsorption capacity for nitrate and phosphate was 7.9 and 8.9 mg/g, respectively. Po4 showed potential as a fertilizer as it had 5.84 and 3.02 g of extractable phosphate and nitrate per kg of biochar.

Adsorption Characteristics and Mechanism of Ammonia Nitrogen in Water by Nano Zero-valent Iron-modified Biochar

The adsorption performances of ammonia nitrogen (NH+4-N) in water by unmodified biochar are ineffective. In this study, nano zero-valent iron-modified biochar (nZVI@BC) was prepared to remove NH+4-N from water. The NH+4-N adsorption characteristics of nZVI@BC were investigated through adsorption batch experiments. The composition and structure characteristics of nZVI@BC were analyzed using scanning electron microscopy, energy spectrum analysis, BET-N2 surface area (SSA), X-ray diffraction, and FTIR spectra to explore the main adsorption mechanism of NH+4-N by nZVI@BC. The results showed that the composite synthesized at the iron to biochar mass ratio of 1:30 (nZVI@BC1/30) performed well in NH+4-N adsorption at 298 K. The maximum adsorption amount of nZVI@BC1/30 at 298 K was remarkably increased by 45.96% and reached 16.60 mg·g-1. The pseudo-second-order model and Langmuir model fitted well with the adsorption process of NH+4-N by nZVI@BC1/30. There was competitive adsorption between coexisting cations and NH+4-N, and the sequence of coexisting cations to the adsorption of NH+4-N by nZVI@BC1/30 was Ca2+> Mg2+> K+> Na+. The adsorption mechanism of NH+4-N by nZVI@BC1/30 could be mainly attributed to ion exchange and hydrogen bonding. In conclusion, nano zero-valent iron-modified biochar can improve the adsorption performance of NH+4-N and enhance the application potential of biochar in the field of nitrogen removal from water.