Application of biochar for the removal of pollutants from aqueous solutions

Influence of cross-sectional aspect ratio on biochar segregation in a bubbling fluidized bed

In this study, computational particle fluid dynamics was applied to investigate the segregation characteristics of biochar in a bubbling fluidized bed. The aspect ratio of the bubbling fluidized bed was changed and the effects of the aspect ratio on the segregation characteristics were investigated. The segregation characteristics of a mixture of biochar and sand particles were analyzed in terms of bubble size distribution, pressure fluctuations, and mixing index. As the aspect ratio increased, the bubble size decreased, leading to a clearer segregation of biochar and sand particles. The mixing index of the biochar and sand particles decreased as the aspect ratio increased.

Herbal plants- and rice straw-derived biochars reduced metal mobilization in fishpond sediments and improved their potential as fertilizers

Fishpond sediments are rich in organic carbon and nutrients; thus, they can be used as potential fertilizers and soil conditioners. However, sediments can be contaminated with toxic elements (TEs), which have to be immobilized to allow sediment reutilization. Addition of biochars (BCs) to contaminated sediments may enhance their nutrient content and stabilize TEs, which valorize its reutilization. Consequently, this study evaluated the performance of BCs derived from Taraxacum mongolicum Hand-Mazz (TMBC), Tribulus terrestris (TTBC), and rice straw (RSBC) for Cu, Cr, and Zn stabilization and for the enhancement of nutrient content in the fishpond sediments from San Jiang (SJ) and Tan Niu (TN), China. All BCs, particularly TMBC, reduced significantly the average concentrations of Cr, Cu, and Zn in the overlying water (up to 51% for Cr, 71% for Cu, and 68% for Zn) and in the sediments pore water (up to 77% for Cr, 76% for Cu, and 50% for Zn), and also reduced metal leachability (up to 47% for Cr, 60% for Cu, and 62% for Zn), as compared to the control. The acid soluble fraction accounted for the highest portion of the total content of Cr (43-44%), Cu (38-43%), and Zn (42-45%), followed by the reducible, oxidizable, and the residual fraction; this indicates the high potential risk. As compared with the control, TMBC was more effective in reducing the average concentrations of the acid soluble Cr (15-22%), Cu (35-53%), and Zn (21-39%). Added BCs altered the metals acid soluble fraction by shifting it to the oxidizable and residual fractions. Moreover, TMBC improved the macronutrient status in both sediments. This work provides a pathway for TEs remediation of sediments and gives novel insights into the utilization of BC-treated fishpond sediments as fertilizers for crop production.

Purification mechanism of city tail water by constructed wetland substrate with NaOH-modified corn straw biochar

The pollution of corn straw to the environment had attracted much attention. The preparation and alkali modification of corn straw biochar as the constructed wetland (CW) substrate was conducive to solving the environment pollution caused by straw and improving the purification effect of CW. The NaOH modification mechanism of corn straw biochar was analyzed by measuring the surface morphology, element content, specific surface area (SSA), pore volume, crystal structure, surface functional groups and CO₂ adsorption. Biochar prepared under relatively optimal NaOH-modified conditions was used as the vertical flow CW substrate to treat city tail water. The results showed that controlling the modification condition of NaOH (< 1.0 mol·L^-1, ≤ 24 h) was conducive to prevent the biochar structure destruction and C element reduction. The SSA and pore volume of NaOH (0.1 mol·L^-1) modified biochar are 360 m²·g^-1 and 0.109 cm³·g^-1, respectively. The biochar adsorption for CO₂ conformed to the Langmuir and Freundlich isothermal adsorption theoretical model (R² > 0.9). The maximum adsorption capacity of CO₂ by modified biochar with NaOH (0.1 mol·L^-1) was 64.516 cm³·g^-1 and increased by 10.3%. The city tail water treated by CW with plants showed that the removal rates of ammonia nitrogen, total nitrogen and nitrate nitrogen reached about 90%. The research results improved the utilization value of straw, realized straw carbon sequestration and promoted the progress of CW technology.

Integration of biochar into Ag3PO4/α-Fe2O3 heterojunction for enhanced reactive oxygen species generation towards organic pollutants removal

A biochar (BC) harbored Ag₃PO₄/α-Fe₂O₃ type-Ⅰ heterojunction (Ag-Fe-BC) was prepared by a hydrothermal-impregnation method to transfer active center of heterojunctions. The electrochemical and spectroscopic tests demonstrated that BC enhanced the catalytic performance of the heterojunction by enhancing photocurrent, reducing fluorescence intensity, and facilitating separation of electron-hole pairs. The photocatalytic activity showed the Ag-Fe-BC (5:1:3) could degrade Rhodamine B (20 mg/L) by up to 92.7%, which was 3.35 times higher than Ag₃PO₄/α-Fe₂O₃. Tetracycline and ciprofloxacin (20 mg/L) were degraded efficiently by 58.3% and 79.4% within 2 h, respectively. Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species (ROS) consisted of singlet oxygen (¹O₂) and superoxide (·O₂^-). Excellent RhB adsorption and electrons capturing capacity of BC facilitated electron-hole pairs separation and ROS transferring to target organics followed by elevated degradation. Thus, a facile method was proposed to synthesize a highly efficient visible-light responsive photocatalyst for degradation of various organics in water.

The Reuse of Biomass and Industrial Waste in Biocomposite Construction Materials for Decreasing Natural Resource Use and Mitigating the Environmental Impact of the Construction Industry: A Review

The construction industry is the world's largest emitter of greenhouse gases. The CO₂ emission levels in the atmosphere are already reaching a tipping point and could cause severe climate change. An important element is the introduction of a technology that allows for the capture and sequencing of carbon dioxide levels, reducing both emissions and the carbon footprint from the production of Portland cement and cement-based building materials. The European Union has started work on the European Climate Law, establishing the European Green Deal program, which introduces the achievement of climate neutrality in the European Union countries. This includes a new policy of sustainable construction, the aim of which is to develop products with a closed life cycle through proper waste management. All efforts are being made to create generated waste and thus to support their production and/or use as substitutes for raw materials to produce biocomposites. This article reviews environmental issues and characterizes selected waste materials from the agri-food, mineral, and industrial sectors with specific properties that can be used as valuable secondary raw materials to produce traditional cements and biocomposite materials, while maintaining or improving their mechanical properties and applications.

Effects of pyrolysis temperature and aging treatment on the adsorption of Cd2+ and Zn2+ by coffee grounds biochar

As an in-situ immobilization material for heavy metals, biochar can exist in the environment for thousands of years, while whether the natural aging would affect its heavy metals adsorption performance still remains unclear. Therefore, the coffee grounds biochar (CGB) was prepared under different pyrolysis temperatures (300, 500 and 700 °C) in this study, and the simulated artificial aging treatment was carried out to investigate the effects of pyrolysis temperature and aging treatment on Cd²⁺ and Zn²⁺ (both separate and combined conditions) adsorption performance of CGB. The result revealed that Fresh-CGB adsorption performance increased with increasing pyrolysis temperature, while the relationship was not so clear with Aged-CGB where adsorption performance peaked at medium pyrolysis temperature (500 °C) but reduced again as pyrolysis temperature increased to 700 °C. The changes of Aged-CGB adsorption performance for Cd²⁺ and Zn²⁺ represented the long-term performance of naturally aging biochar in environment, and a mid-range pyrolysis temperature would seem most appropriate for long-term application of biochar. The X-ray Diffraction (XRD) result revealed that the degree of graphitization of CGB increased with increasing pyrolysis temperature, which represents a stronger environmental stability as the weight loss of CGB300, CGB500 and CGB700 after aging treatment was 2.38%, 0.66%, and 0%, respectively. The EDS and FTIR results suggested that ion-exchange and complexation between CGB/Aged-CGB with Cd²⁺/Zn²⁺ played a dominant role in adsorption processes. In addition, the selectivity for Cd²⁺ was significantly improved after the aging treatment. This is desirable given the stronger toxicity of Cd²⁺ relative to Zn²⁺. In general, this study provides new insights into the practical application of biochar from the perspective of long-term effects.

The interaction between biochars from distinct pyrolysis temperatures and multiple pollutants determines their combined cytotoxicity

Biochar (BC) has been widely used for soil remediation and pollutant removal from environmental water. The pollutant-adsorbing BC often exerts different cytotoxicity from pollutant-free BC. However, how adsorption of multiple pollutants alters the cytotoxicity of BC and how to modulate such toxicity are still unclear. By preparing BCs from two different materials (Banana peel (BP) and corn stalk (CS)) at two pyrolysis temperatures (300 °C and 500 °C, namely BP300-BC, BP500-BC, CS300-BC, and CS500-BC, respectively), we systemically investigated factors that affect the combined cytotoxicity of pollutant-adsorbing BC in Human normal rectal mucosal cells (FHC). The reduction of Cr(VI) to Cr(III) occurred on BC, in particular on BC prepared at 300 °C, in which larger amount of organic matters were left. The presence of Cu(II) promoted the release of Cr from BC once entering cells, which was more obvious for BC prepared at 500 °C. The changes in valence states and release rates of Cr adsorbed on BC prepared at different pyrolysis temperatures together caused reduced cytotoxicity of BP300-BC-Cr-Cu but enhanced cytotoxicity of BP500-BC-Cr-Cu, compared to the same amount of mixture of Cr(VI)-Cu(II). Our findings offer insight understanding of how pyrolysis temperature and the adsorbed multiple pollutants affect the combined cytotoxicity of BC-pollutant complex, allowing for safe applications of BC in future.

Efficient remediation of antibiotic pollutants from the environment by innovative biochar: current updates and prospects

The increased antibiotic consumption and their improper management led to serious antibiotic pollution and its exposure to the environment develops multidrug resistance in microbes against antibiotics. The entry rate of antibiotics to the environment is much higher than its exclusion; therefore, efficient removal is a high priority to reduce the harmful impact of antibiotics on human health and the environment. Recent developments in cost-effective and efficient biochar preparation are noticeable for their effective removal. Moreover, biochar engineering advancements enhanced biochar remediation performance several folds more than in its pristine forms. Biochar engineering provides several new interactions and bonding abilities with antibiotic pollutants to increase remediation efficiency. Especially heteroatoms-doping significantly increased catalysis of biochar. The main focus of this review is to underline the crucial role of biochar in the abatement of emerging antibiotic pollutants. A detailed analysis of both native and engineered biochar is provided in this article for antibiotic remediation. There has also been discussion of how biochar properties relate to feedstock, production conditions and manufacturing technologies, and engineering techniques. It is possible to produce biochar with different surface functionalities by varying the feedstock or by modifying the pristine biochar with different chemicals and preparing composites. Subsequently, the interaction of biochar with antibiotic pollutants was compared and reviewed. Depending on the surface functionalities of biochar, they offer different types of interactions e.g., π-π stacking, electrostatic, and H-bonding to adsorb on the biochar surface. This review demonstrates how biochar and related composites have optimized for maximum removal performance by regulating key parameters. Furthermore, future research directions and opportunities for biochar research are discussed.

Effects of wetland plant biochars on heavy metal immobilization and enzyme activity in soils from the Yellow River estuary

The purpose of this study was to assess the effects of wetland plant biochars on the enzyme activity in heavy metal contaminated soil. The biochars were produced from Phragmites australis (PB), Suaeda salsa (SB), and Tamarix chinensis (TB) under different pyrolysis temperatures and times. The detected pyrolysis products showed that the ash, pH, electrical conductivity, and carbon content of the biochars increased significantly, while the production rate of the biochars decreased with increasing pyrolysis temperature and time. The results of the adsorption experiments indicated that biochar addition could effectively reduce the concentration of Pb and/or Cd in the Pb²⁺/Cd²⁺ single or mixed solutions, but the Pb²⁺ and Cd²⁺ in the mixed solution indicated a competitive adsorption. A 30-day incubation experiment was conducted using salt marsh soil amended with different biochar application rates to investigate the short-term effects of biochar addition on Pb and Cd immobilization. The PB and SB significantly immobilized Pb within the first 15 days, but Pb remobilized within the next 15-day period. In contrast, TB addition did not significantly fix Pb. Moreover, biochar addition promoted the conversion of Cd from the residue to the less immobile fractions. The addition of three types of plant biochar had no significant effect on the urease activity in wetland soil but significantly increased soil sucrase activity. PB and SB significantly promoted catalase activity, while TB significantly inhibited soil catalase activity. According to the adsorption effect, the fixation effect, and the promotion of enzyme activities, the Suaeda salsa biochars are suitable for the remediation of heavy metal pollution in wetland soils.

Efficient removal of pefloxacin from aqueous solution by acid-alkali modified sludge-based biochar: adsorption kinetics, isotherm, thermodynamics, and mechanism

In this paper, one kind of acid-alkali modified sludge-based biochar (ASBC) was synthesized, characterized, and employed as adsorbent for the removal of pefloxacin. The characterization results showed that the specific surface area (SSA) of ASBC (53.381 m²/g) was significantly higher than that of SBC (24.411 m²/g). ASBC had a rougher surface, larger particle distribution, lower zero point charge, and richer functional groups (e.g., C-O and O-H) than SBC. The adsorption capacity of ASBC was 1.82 times than that of SBC. After 8 adsorption cycles in reuse experiment, the adsorption capacity of ASBC for pefloxacin still reached 144.08 mg/L, indicating that ASBC has good reusability. Static experiments showed that the optimal pH value was 6.0 in the adsorption of pefloxacin on SBC and ASBC. The result of adsorption kinetics indicated that the pseudo-second-order model could describe well the adsorption process. The Freundlich model was better than the Langmuir model to describe the adsorption of pefloxacin by ASBC, indicating that the adsorption process was mainly multilayer adsorption. Thermodynamic result showed that the adsorption of pefloxacin by ASBC was spontaneous and endothermic. The removal mechanism of pefloxacin by ASBC is mainly the substitution reaction and π-π EDA interaction. In summary, acid-alkali modified biochar is an effective adsorbent for pefloxacin in aqueous solution, and has great application prospects.

Assessing the efficiency and mechanism of zinc adsorption onto biochars from poultry litter and softwood feedstocks

The efficiency and adsorption mechanism of zinc removal was assessed in aqueous solution using four biochars from multiple biomass residues (poultry litter and three tree species). The effect of pH, kinetic effects, and isotherm fittings were investigated, as well as zinc-laden biochar using x-ray diffraction and absorption near edge structure. Sorbent load results showed softwood biochar exhibited the greatest zinc removal from both deionized (15 mg_Zn/L) and mining influenced river water (10 mg_Zn/L). The Langmuir isotherm was the best fit for the majority of the biochars. Exchangeable cations contributed most for the adsorption mechanism from the softwood biochars, while precipitation was greatest contribution for the poultry litter biochar. Overall, our results suggest that biochars from Douglas Fir trees are more efficient at removing zinc from aqueous solutions (up to 19.80 mg_Zn/g) compared to previously studied biochars (0.61 to 11.0 mg_Zn/g) and should be used for future remediation efforts.

Preparation of spiramycin fermentation residue derived biochar for effective adsorption of spiramycin from wastewater

Spiramycin (SPI) fermentation residue (SFR) is classified as hazardous waste in China because of the residual antibiotics in it. SFR disposal in the traditional way is costly and wasteful of resources. In this study, pyrolysis method was adopted to covert SFR to biochar for SPI removal from wastewater, and the SPI adsorption performance was investigated. The results showed that the optimal pyrolysis temperature was 700 °C as the prepared biochar BC700 exhibited the highest SPI removal efficiency. The specific surface area of BC700 was 451.68 m²/g, and the maximum adsorption capacity was 147.28 mg/g. The adsorption mechanism involved electrostatic interaction, pore filling, π-π interaction, hydrogen bonding, and the participation of C-C and O-CO functional groups in the adsorption. No residual SPI was detected in BC700 indicating the detoxification of SFR was achieved. Moreover, after recycling for 5 times, the SPI removal efficiency was still higher than 80.0%. Therefore, this study could provide a promising method for SFR disposal.

Recent Advances of Biochar-Based Electrochemical Sensors and Biosensors

In the context of accelerating the global realization of carbon peaking and carbon neutralization, biochar produced from biomass feedstock via a pyrolysis process has been more and more focused on by people from various fields. Biochar is a carbon-rich material with good properties that could be used as a carrier, a catalyst, and an absorbent. Such properties have made biochar a good candidate as a base material in the fabrication of electrochemical sensors or biosensors, like carbon nanotube and graphene. However, the study of the applications of biochar in electrochemical sensing technology is just beginning; there are still many challenges to be conquered. In order to better carry out this research, we reviewed almost all of the recent papers published in the past 5 years on biochar-based electrochemical sensors and biosensors. This review is different from the previously published review papers, in which the types of biomass feedstock, the preparation methods, and the characteristics of biochar were mainly discussed. First, the role of biochar in the fabrication of electrochemical sensors and biosensors is summarized. Then, the analytes determined by means of biochar-based electrochemical sensors and biosensors are discussed. Finally, the perspectives and challenges in applying biochar in electrochemical sensors and biosensors are provided.

Removal of Phosphate from Aqueous Solution by Zeolite-Biochar Composite: Adsorption Performance and Regulation Mechanism

Recently, rampant eutrophication induced by phosphorus enrichment in water has been attracting attention worldwide. However, the mechanisms by which phosphate can be eliminated from the aqueous environment remain unclear. This study was aimed at investigating the adsorption performance and regulation mechanisms of the zeolite-biochar composite for removing phosphate from an aqueous environment. To do this, physicochemical properties of the zeolite-biochar composite were assessed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area (SSA) analyzer, and transmission electron microscopy (TEM). Adsorption tests were performed to evaluate the adsorption ability of the composite material for mitigating excess phosphorus in the aqueous environment. The findings evinced that the phosphorus removed by PZC 7:3 (pyrolyzed zeolite and corn straw at a mass ratio of 7:3) can reach 90% of that removed by biochar. The maximum adsorption capacities of zeolite, biochar, and PZC 7:3 were 0.69, 3.60, and 2.41 mg/g, respectively. The main mechanism of phosphate removal by PZC 7:3 was the formation of thin-film amorphous calcium-magnesium phosphate compounds through ligand exchange. This study suggests that PZC 7:3 is a viable adsorbent for the removal of phosphate from aquatic systems.

Effects of Biochar Production Methods and Biomass Types on Lead Removal from Aqueous Solution

Biochar has proven its potential in removing heavy metal ions from water. The objective of this study was to evaluate locally obtained biomass feedstocks for biochar production and their efficiency as a sorbent for aqueous lead (Pb2+) removal. The biomass feedstocks consisted of avocado seed, avocado peel, grapefruit peel, and brown seaweed, which represent agricultural and marine biomasses. The biochar materials were produced in two different methods: (1) a laboratory tube furnace at 300 °C and (2) a Do-It-Yourself (DIY) biochar maker, “BioCharlie Log”. The biochars were characterized for selected physicochemical properties, and batch adsorption tests with 10 mg Pb2+ L−1 were conducted. All biochars exhibited >90% Pb2+ removal with the avocado seed and grapefruit peel biochars being the most effective (99%) from the tube-furnace-produced biochars. BioCharlie-produced-biochars showed similar Pb2+ removal (90–97%) with brown seaweed and avocado seed biochars being the most effective (97%). Land-based biochars showed a higher carbon content (>53%) than the brown seaweed biochar (28%), which showed the highest ash content (68%). Our results suggested that oxygen-containing surface functional groups in land-based biochar and mineral (ash) fraction in marine-based biochar play a key role in Pb2+ removal.

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.

Physicochemical modification of corn straw biochar to improve performance and its application of constructed wetland substrate to treat city tail water

Corn straw is rich in resources, and the preparation of biochar as the constructed wetland (CW) substrate is an effective measure to realize high-value resource utilization. The objective of this paper was to improve the treatment effect of CW on city tail water, the freeze-thaw cycles (FTCs) modification and chemical modification (KMnO₄, NaOH and H₂SO₄) of straw biochar and the utilization of modified straw biochar in CW were studied. The modification characteristics of straw biochar were discussed through scanning electron microscope, element determination, pore structure determination, X-ray diffraction analysis, Fourier transform infrared reflection analysis, CO₂ adsorption and desorption experiment and application experiment of CW (no plants and plants). The results show that under the influence of strong oxidation of KMnO₄, the combination of KMnO₄ and FTCs modification is easy to cause the destruction of biochar structure, and the content of carbon element is reduced. Except for the combined modification of NaOH and FTCs, other composite modifications have little effect on the crystal structure and functional groups of straw biochar. The adsorption capacity of CO₂ by FTCs modified biochar increased by 20.4%, and the adsorption capacity of CO₂ by H₂SO₄ and FTCs composite modified biochar increased by 23.0%. The effect of H₂SO₄ modification of straw biochar based on FTCs modification is obviously better than that of NaOH and KMnO₄. The research results are of great significance to improve the material structure of biochar and the purification effect of CW on city tail water.

Effect of Biochar on Micronutrient Availability and Uptake Into Leafy Greens in Two Urban Tropical Soils With Contrasting Soil pH

Biochars have been proposed as a novel biotechnology to increase crop yields in acidic soils due to a liming effect. However, the application of biochar to soils with a neutral soil pH is less likely to improve yield. A rise in pH typically increases the availability of macronutrients (e.g., PO43-, NO3-) but biochar is known to immobilize some elements due to a pH increase and adsorption on the biochar surface. Therefore, biochar application may reduce the uptake of important micronutrients (e.g., Cu, Fe, and Zn) into the edible portions of food crops. Before recommending indiscriminate biochar application to tropical soils, an understanding of the potentially negative impacts of biochar application to contrasting soil types should be fully appreciated to prevent unintended consequences. Our aim was to determine the impact of biochar amendment to an acidic soil and a neutral soil on micronutrient availability and uptake into leafy greens. We produced biochars from 3 different organic feedstock materials (corn cobs, rice husk and teak sawdust) and applied these in pot experiments to an acidic tropical soil (pH 4.5) and a neutral tropical soil (pH 6.9) collected from urban farms in Tamale and Kumasi, respectively, in Ghana. We grew leafy greens (Amaranthus, Corchorus, and Lettuce) and measured their growth and the uptake of Cu, Fe, and Zn, alongside supporting measurements of soil pH and micronutrient availability in the soil. We also measured water soluble Cu, Fe, and Zn in the soils amended with biochars pyrolyzed at different temperatures. The corn cobs biochar increased soil pH and considerably increased plant growth in the acidic soil from Tamale. In the neutral soil from Kumasi we found that, while corn cob biochar increased soil pH, rice husk biochar decreased soil pH. Furthermore, corn cob biochar considerably reduced plant growth in the neutral soil. The concentration of micronutrients in the edible portions of leafy greens was not greatly affected by biochar application, but the total uptake (i.e., concentration multiplied by biomass) of micronutrients into leaves was generally increased by biochar application in the acidic (Tamale) soil and application of the corn cob biochar generally decreased total uptake of micronutrients in the neutral (Kumasi) soil. Our results highlight the need for site-specific information on biochar feedstock and soil pH prior to recommending biochar application to tropical urban soils so that the benefits can be optimized and unintended consequences can be prevented.

Emerging application of biochar as a renewable and superior filler in polymer composites

Biochar is conventionally and widely used for soil amendment or as an adsorbent for water treatment. Nevertheless, the need for transition to renewable materials has resulted in an expansion of biochar for use as a filler for polymer composites. The aim is to enhance the physical, chemical, mechanical and rheological properties of the polymer composite. The reinforcement of biochar into a polymer matrix however is still new, and limited reports are focusing on the effects of biochar towards polymer composite properties. Hence, this review highlights the unique properties of biochar and its effect on the crystallization, thermal, flammability, electrical conductivity, and mechanical properties of polymer composites. This review does not solely summarize recent studies on biochar-polymer-based composites, but also offers insights into a new direction of biochar as a renewable and superior polymer filler in the future.

Optimization of the raw materials of biochars for the adsorption of heavy metal ions from aqueous solution

In this paper, the material types were preferentially selected for different kinds of heavy metals, the effect of calcination temperatures on metal adsorption was investigated, and the adsorption mechanism was explored and summarized. The results show that the pseudo-first-order kinetic was better to fit the adsorption of heavy metals. The biomass type and pyrolysis temperature had an effect on the rate at which heavy metals were absorbed. Based on their adsorbed capacity, 350 °C pyrolyzed corn stalk char, 550 °C pyrolyzed peanut shell char, 450 °C pyrolyzed peanut shell char, 450 °C pyrolyzed peanut shell char, and 500 °C pyrolyzed wheat stalk char were shown to be the best adsorbents for Cr₂O₇^2-, Cd²⁺, Cu²⁺, Zn²⁺ and Pb²⁺, respectively. The largest adsorption rate were in the order of Cr⁶⁺ (Cr₂O₇^2-, 0.5380 /min) > Pb²⁺ (0.2276 /min) > Cd²⁺ (0.1354 /min) > Cu²⁺ (0.1273 /min) > Zn²⁺ (0.1000 /min), which might be positively related to the ion radius. Meanwhile, the yield of biomass decreased from 43.9% to 29.0% with the increase of pyrolysis temperature from 350 °C to 550 °C. In addition, the specific surface area and functional groups of the biochar, as well as the ionic radius and initial concentration of heavy metals affect the adsorption rate.

Preparation, characterization, and application of modified magnetic biochar for the removal of benzotriazole: process optimization, isotherm and kinetic studies, and adsorbent regeneration

The adsorption of benzotriazole (BTA) by chemically modified magnetic biochar (MMBC) as a cheap and abundant biosorbent was investigated and optimized using response surface methodology (RSM). Initially, the MMBC composite was synthesized and characterized by scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and Brunauer-Emmett-Teller (BET) techniques. The characterization results confirmed the existence of Fe₃O₄ in the composite structure, which had uniformly dispersed over biochar (BC) with porous texture. Moreover, the presence of Zn and Cl elements in EDX analysis indicated that the magnetic biochar (MBC) had been modified successfully. The effects of chemical modification methods on the adsorption capacity of magnetic biochar were investigated. Maximum BTA removal efficiency was demonstrated by MMBC, modifying using ZnCl₂ (>99%). Optimization was carried out based on reaction time, BTA concentration and the concentration of adsorbent. Optimum experimental conditions for the removal of BTA from aqueous solutions were found to be 35 min of reaction time, 0.55 g/L of adsorbent, and 50 mg/L of initial BTA concentration. At these optimal conditions, the predicted BTA adsorption efficiency was 92.6%. The adsorption process followed the Avrami fractional-order reaction kinetic and the Langmuir adsorption isotherm with the maximum adsorption capacity of 563.1 mg/g. The values of thermodynamic parameters demonstrated that the adsorption of BTA on ZnCl₂-MBC is endothermic and spontaneous. Under optimum usage of MMBC, the adsorptive removal efficiency of BTA non-significantly decreased from 99.2 to 93.9% after the 5th cycle. Thus, MMBC can be recommended as an environmentally friendly and cost-effective adsorbent to remove micropollutants from water.

Facile synthesis of a novel magnetic covalent organic frameworks for extraction and determination of five fungicides in Chinese herbal medicines

A novel magnetic covalent organic framework was synthesized via one step coating approach with solvothermal reaction employing 2,4,6-tris(4-aminophen-yl)-1,3,5-triazine and 2,4,6-triformylphloroglucinol as two building blocks by covalent bonding. The prepared magnetic covalent organic frameworks were properly characterized by different techniques and employed as adsorbent of magnetic solid phase extraction. An analytical method was developed for simultaneous determination of five fungicides in two Chinese herbal medicine samples via magnetic solid phase extraction coupled to UHPLC-MS/MS analysis. Under optimized magnetic solid phase extraction conditions, the method exhibited satisfactory recoveries (74.0-109.6%) with the relative standard deviations of 0.4-4.6%, low limits of detection (0.003-0.015 μg kg^-1 ), and good linearity (R² > 0.9960). Compared with the traditional extraction method, the proposed method required a lower amount of adsorbent (3 mg) and extraction time (5 min). The adsorbent also had favourable reusability (not less than 8 times). Therefore, the magnetic covalent organic frameworks could be a promising adsorbent for the extraction and quantitation of pesticide residues in Chinese herbal medicines. This article is protected by copyright. All rights reserved.

Biochar from fungiculture waste for adsorption of endocrine disruptors in water

The agricultural residues are ecofriendly alternatives for removing contaminants from water. In this way, a novel biochar from the spent mushroom substrate (SMS) was produced and assessed to remove endocrine disruptor from water in batch and fixed-bed method. SMS were dried, ground, and pyrolyzed. Pyrolysis was carried out in three different conditions at 250 and 450 °C, with a residence time of 1 h, and at 600 °C with a residence time of 20 min. The biochar was firstly tested in a pilot batch with 17α-ethinylestradiol (EE2) and progesterone. The residual concentrations of the endocrine disruptors were determined by HPLC. The biochar obtained at 600 °C showed the best removal efficiency results. Then, adsorption parameters (isotherm and kinetics), fixed bed tests and biochar characterization were carried out. The Langmuir model fits better to progesterone while the Freundlich model fits better to EE2. The Langmuir model isotherm indicated a maximum adsorption capacity of 232.64 mg progesterone/g biochar, and 138.98 mg EE2/g biochar. Images from scanning electrons microscopy showed that the 600 °C biochar presented higher porosity than others. In the fixed bed test the removal capacity was more than 80% for both endocrine disruptors. Thus, the biochar showed a good and viable option for removal of contaminants, such as hormones.

Biochar mediated uranium immobilization in magnetite rich Cu tailings subject to organic matter amendment and native plant colonization

Organic matter (OM) amendments and plant colonization can accelerate mineral weathering and soil formation in metal mine tailings for ecological rehabilitation. However, the weathering effects may dissolve uranium (U)-bearing minerals (e.g., ianthinite) and increase U dissolution in porewater and seepages. The present study aimed to characterize the U solubility and distribution among different fractions and investigate if biochar (BC) could decrease soluble U levels and facilitate U immobilization in the OM-amended and plant-colonized tailings. A native plant species, Red Flinders grass (Iseilema vaginiflorum) was cultivated in the tailings for four weeks, which were amended with sugarcane residue (SR) with or without BC addition. The results showed that OM amendment and plant colonization increased porewater U concentrations by almost 10 folds from ~ 0.2 mg L^-1 to > 2.0 mg L^-1. The BC addition decreased porewater U concentrations by 40%. Further micro-spectroscopic analysis revealed that U was immobilized through adsorption onto BC porous surfaces, via possibly complexing with oxygen-rich organic groups. Besides, the BC amendment facilitated U sequestration by secondary Fe minerals in the tailings. These findings provide important information about U biogeochemistry in Cu-tailings mediated by BC, OM and rhizosphere interactions for mitigating potential pollution risks of tailings rehabilitation.

Removal of potentially toxic elements from contaminated soil and water using bone char compared to plant- and bone-derived biochars: A review

Conversion of hazardous waste materials to value-added products is of great interest from both agro-environmental and economic points of view. Bone char (BC) has been used for the removal of potentially toxic elements (PTEs) from contaminated water, however, its potential BC for the immobilization of PTEs in contaminated water and soil compared to bone (BBC)- and plant (PBC)-derived biochars has not been reviewed yet. This review presents an elaboration for the potentials of BC for the remediation of PTEs-contaminated water and soil in comparison with PBC and BBC. This work critically reviews the preparation and characterization of BC, BBC, and PBC and their PTEs removal efficiency from water and soils. The mechanisms of PTE removal by BC, BBC, and PBC are also discussed in relation to their physicochemical characteristics. The review demonstrates the key opportunities for using bone waste as feedstock for producing BC and BBC as promising low-cost and effective materials for the remediation of PTEs-contaminated water and soils and also elucidates the possible combinations of BC and BBC aiming to effectively immobilize PTEs in water and soils.

Chitosan-modified biochar: Preparation, modifications, mechanisms and applications

The chitosan-modified biochar composite, as a carbohydrate polymer, has received increasing attention and becomes a research hotspot. It is a promising impurity adsorption material, which has potential application value in the agricultural environment fields such as soil improvement and sewage purification. The composite can combine the advantages of biochar with chitosan, and the resulting composite usually exhibits a great improvement in its surface functional groups, adsorption sites, stability, and adsorption properties. In addition, compared to other adsorbents, the composite truly achieves the concept of "waste control by waste". In this paper, the preparation method, composite classification, adsorption mechanism, and models of biochar modified by chitosan are introduced, meanwhile, we also review and summarize their effects on the decontamination of wastewater and soil. In addition to common heavy metal ions, we also review the adsorption and removal of some other organic/inorganic pollutants, including (1) drug residues; (2) dyes; (3) phosphates; (4) radionuclides; (5) perfluorochemicals, etc. Moreover, challenges and prospects for the composite are presented and further studies are called for the chitosan-biochar composite. We believe that the composite will lead to further achievements in the field of environmental remediation.

Design of nitrogen-phosphorus-doped biochar and its lead adsorption performance

The surface properties of the adsorbents and the acidic environment have an influence effect on Pb adsorption. In order to further improve the adsorption performance of biochar, we herein reported an effective method to synthesize high-adsorbed biochar by co-doping with nitrogen and phosphorus. After atom doping, the N/P co-doped biochar (NP-BC) showed the enhanced adsorption capacity for lead ion (Pb²⁺). The adsorption kinetics, isotherm, pH value, and influencing factors were studied. The results show that the synthesized NP-BC has high Pb²⁺ adsorption capacity in aqueous solution, and can be maintained with various environmental interference factors including pH, natural organic matter, and other metal ions. High adsorption performance shows that the material may be well used to remove Pb²⁺ in various water bodies. Various characterization experiments prove that surface properties contribute to Pb²⁺ adsorption, and the high performance of NP-BC is mainly due to the surface complexation between functional groups and Pb²⁺. This work demonstrates that the surface functional groups of biochar are critical to the development of high-performance heavy metal adsorbents.

Biochar Adsorbents for Arsenic Removal from Water Environment: A Review

Arsenic intake can cause human health disorders to the lungs, urinary tract, kidney, liver, hyper-pigmentation, muscles, neurological and even cancer. Biochar is potent, economical and ecologically sound adsorbents for water purification. After surface modifications, adsorption capacity of biochar significantly increased due to high porosity and reactivity. Adsorption capacities of the biochar derived from the municipal solid waste and KOH mixed municipal solid waste were increased from 24.49 and 30.98 mg/g for arsenic adsorption. Complex formation, electrostatic behavior and ion exchange are important mechanisms for arsenic adsorption. Organic arsenic removal using biochar is a major challenge. Hence, more innovative research should be conducted to achieve one of the 17 sustainable development goals of the United Nations i.e. "providing safe drinking water for all". This review is focused on the arsenic removal from water using pristine and modified biochar adsorbents. Recent advances in production methods of biochar adsorbents and mechanisms of arsenic removal from water are also illustrated.

Biochar-based slow-release of fertilizers for sustainable agriculture: A mini review

Increasing global population and decreasing arable land pose tremendous pressures to agricultural production. The application of conventional chemical fertilizers improves agricultural production, but causes serious environmental problems and significant economic burdens. Biochar gains increasing interest as a soil amendment. Recently, more and more attentions have been paid to biochar-based slow-release of fertilizers (SRFs) due to the unique properties of biochar. This review summarizes recent advances in the development, synthesis, application, and tentative mechanism of biochar-based SRFs. The development mainly undergoes three stages: (i) soil amendment using biochar, (ii) interactions between nutrients and biochar, and (iii) biochar-based SRFs. Various methods are proposed to improve the fertilizer efficiency of biochar, majorly including in-situ pyrolysis, co-pyrolysis, impregnation, encapsulation, and granulation. Considering the distinct features of different methods, the integrated methods are promising for fabricating effective biochar-based SRFs. The in-depth understanding of the mechanism of nutrient loading and slow release is discussed based on current knowledge. Additionally, the perspectives and challenges of the potential application of biochar-based SRFs are described. Knowledge surveyed from this review indicates that applying biochar-based SRFs is a viable way of promoting sustainable agriculture.

High-temperature technology survey and comparison among incineration, pyrolysis, and gasification systems for water resource recovery facilities

Solids from wastewater treatment undergo processing to reduce mass, minimize pathogens, and condition the products for specific end uses. However, costs and contaminant concerns (e.g., per- and polyfluoroalkyl substances [PFAS]) challenge traditional landfill and land application practices. Incineration can overcome these issues but has become complicated due to evolving emissions regulations, and it suffers from poor public perception. These circumstances are driving the re-emergence of pyrolysis and gasification technologies. A survey of suppliers was conducted to document differences with technologies. Both offer advantages over incineration with tailored production of a carbon-rich solid, currently less stringent air emission requirements, and lower flue gas flows requiring treatment. However, incineration more simply combines drying and thermal processing into one reactor. Equipment costs provided favor pyrolysis and gasification at lower capacities but converge with incineration at higher capacities. Long-term operational experience will confirm technology competitiveness and elucidate whether pyrolysis and gasification warrant widespread adoption. PRACTITIONER POINTS: Pyrolysis and gasification systems are gaining traction in the wastewater industry with several full-scale installations operating, in construction, or design Several advantages, but some disadvantages, are considered in comparison with incineration Organic contaminants, including PFAS, will undergo transformation and potentially complete mineralization through each process.

Adsorption behavior and performance of ammonium onto sorghum straw biochar from water

Sorghum has been widely used for liquor production and brewing, but how to make efficiently utilize sorghum straw (SS) has become an urgent problem. Meanwhile, the wastewater produced by winemaking is typical organic wastewater with a high ammonium concentration. To solve the problem of resource utilization of SS and remove ammonium from water, SS was used to prepare biochar as an adsorbent for ammonium adsorption. Batch adsorption experiments were carried out to study the influencing factors and adsorption mechanisms of ammonium onto sorghum straw biochar (SSB). The results showed that the adsorption capacity of SSB was much higher than that of SS. The SSB pyrolyzed at 300 °C had the highest adsorption capacity. The favorable pH was 6–10, and the optimal dosage was 2.5 g/L. The adsorption process and behavior conformed to the pseudo-second-order kinetic and Langmuir isotherm adsorption models. The maximum ammonium adsorption capacity of SSB at 45 °C was 7.09 mg/g, which was equivalent to 7.60 times of SS. The ammonium adsorption of SS and SSB was mainly chemical adsorption. The regeneration test indicated that SSB had good regeneration performance after three adsorption-regeneration cycles. This work suggests that SSB could be potentially applied to sewage treatment containing ammonium to achieve the purpose of resource recycling.

Ni(II), Cr(VI), Cu(II) and nitrate removal by the co-system of Pseudomonas hibiscicola strain L1 immobilized on peanut shell biochar

At present, the improvement of nitrate and mixed heavy metals removal in wastewater by microorganism are urgently needed. Previous studies have shown that Pseudomonas hibiscicola strain L1 exhibited Ni(II) removal ability under aerobic denitrification. In this study, the characteristics of the free strain L1, peanut shell biochar (PBC) and further the co-system of strain L1 immobilized on PBC were investigated for the removal of Ni(II), Cr(VI), Cu(II) and nitrate in mix-wastewater. The results illustrated that strain L1 could remove 15.51% - 32.55% of Ni(II) (20-100 mg·L^-1), and removal ratios by co-system were ranked as Ni(II) (81.17%) > Cu(II) (45.84%) > Cr(VI) (38.21%). Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) images indicated that the strain L1 immobilized well on PBC and had vigorous biological activity; the crystals of Ni(OH)₂, Cu(OH)₂ and CrO(OH) etc. were formed on surface of co-system with various functional groups participated in. In Sequential Batch Reactor (SBR), the pollutant removal ratios by co-system were higher than that by free strain L1. This study illustrated that the co-system of strain L1 immobilized on PBC was qualified to be applied for practical scenarios of effective heavy metal removal of electroplating mix-wastewater.

Magnetically Recyclable Loofah Biochar by KMnO4 Modification for Adsorption of Cu(II) from Aqueous Solutions

Novel KMnO₄-modified loofah biochar loaded with nano-Fe₂O₃ (FMLB) was successfully synthesized for Cu(II) adsorption. Nitrogen adsorption method, scanning electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, and other characterization measurements were used to evaluate the physical and chemical properties of FMLB and nano-Fe₂O₃-loaded biochar (FLB). The results show that the adsorption behavior of Cu(II) can be best fitted by the Langmuir isotherm model and the pseudo-second-order (PSO) kinetic model, indicating that the surface of FMLB was composed of homogeneous adsorption, and chemical adsorption dominated the adsorption process under optimal reaction conditions. The adsorption capacity of FMLB is improved by 42.86% compared to FLB, and it remained over 75% after four cycles. The inner-sphere complexes with manganese oxide (MnO _x ) and oxygen-containing functional groups, as well as electrostatic interaction, physical adsorption, and ion exchange, play important roles in Cu(II) adsorption. The saturation magnetization of FMLB was 10.41 emu/g, ensuring that it can be easily separated from aqueous solutions. Therefore, magnetically recyclable biochar modified by KMnO₄ is a feasible method for Cu(II) adsorption.

Use of Biochar from Rice Husk Pyrolysis: Part A: Recovery as an Adsorbent in the Removal of Emerging Compounds

One of the main products of pyrolysis is char. For the better performance and improvement of its physicochemical properties, it is necessary to make temperature changes. In this study, different temperatures have been tested for the pyrolysis of rice husk, and the biochar obtained from the process went through an evaluation to test its yield in the removal of emerging compounds such as azithromycin (AZT) and erythromycin (ERY). For this, pyrolysis of rice husk has been carried out at temperatures of 450, 500, 550, and 600 °C, and the biochars have been characterized by ultimate analysis and proximate analysis, as well as specific surface area tests. Then, different adsorption tests have been carried out with a 200 mg L^-1 drug (AZT and ERY) solution prepared in the laboratory. All biochars have been found to present removal percentages higher than 95%. Therefore, obtaining biochar from rice husk at any temperature and using it in the removal of high-molecular-weight compounds are quite suitable.

Processing of natural fibre and method improvement for removal of endocrine-disrupting compounds

Persistent endocrine-disrupting compounds (EDCs) in bodies of water are a concern for human health and constitute an environmental issue, even if present in trace amounts. Conventional treatment systems do not entirely remove EDCs from discharge effluent. Due to the ultra-trace level of EDCs which affect human health and pose an environmental issue, developing new approaches and techniques to remove these micropollutants from the discharged effluent is vital. This review discusses the most common methods of eliminating EDCs through preliminary, primary, secondary and tertiary treatments. The adsorption process is favoured for EDC removal, as it is an economical and straightforward option. The NABC aspects, which are the need, approach, benefits and challenges, were analysed based on existing circumstances, highlighting biochar as a green and renewable adsorbent for the removal of organic contaminants. From the environmental point of view, the effectiveness of this method, which uses natural fibre from the kenaf plant as a porous and economical biochar material with a selected lignocellulosic biomass, provides insights into the advantages of biochar-derived adsorbents. Essentially, the improvement of the natural fibre as an adsorbent is a focus, using carbonisation, activation, and the physiochemical process to enhance the adsorption ability of the material for pollutants in bodies of water. This output will complement sustainable water management approaches presented in previous studies for combating the emerging pollutant crisis via novel green and environmentally safe options.

Performance improvement of PES membrane decorated by Mil-125(Ti)/chitosan nanocomposite for removal of organic pollutants and heavy metal

The Mil-125(Ti)-CS nanocomposite was successfully synthesized and characterized by using scanning electron microscopy (SEM) images, Fourier-transform infrared (FTIR) analysis and X-ray diffraction (XRD). Then, to improve the membrane performance, the synthesized Mil-125(Ti)-CS nanocomposite was embedded into the polyethersulfone (PES) membrane matrix. The nanofiltration membranes were fabricated via phase inversion method. Presence of chitosan in the structure of Mil-125(Ti) has increased the compatibility of nanoparticles with the polymer and also improved the hydrophilicity of the resulted membranes. The water contact angle of bare membrane (58°) was reduced to 40° by blending of 1 wt% nanocomposite led to increasing the pure water flux. However, the incorporation of more than 1 wt% of the nanocomposite caused the accumulation of nanocomposites and this was reduced the pore radius and permeability. The membrane containing 1 wt% nanocomposite was displayed the highest flux recovery ratio (FRR) ∼ 98% in bovine serum albumin (BSA) filtration. The membranes containing Mil-125(Ti)-CS also showed good performance against fouling. The performance of membranes was evaluated by treatment of six reactive dyes, antibiotic (cefixime), heavy metal, NaCl and Na₂SO₄ solutions. Addition of Mil-125(Ti)-CS NPs at low concentrations resulted in membranes with high pure water flux, higher separation efficiency, and remarkable anti-fouling behavior.

Pyrolysis and gasification at water resource recovery facilities: Status of the industry

Wastewater treatment generates solids requiring subsequent processing. Costs and contaminant concerns (e.g., per- and polyfluoroalkyl substances [PFAS]) are challenging widely used landfilling and land application practices. These circumstances are partly driving the re-emergence of pyrolysis and gasification technologies along with beneficial reuse prospects of the char solid residual. Previously, technologies experienced operational challenges leading to revised configurations, such as directly coupling a thermal oxidizer to the reactor to destroy tar forming compounds. This paper provides an overview of pyrolysis and gasification technologies, characteristics of the char product, air emission considerations, and potential fate of PFAS and other pollutants through the systems. Results from a survey of viable suppliers illustrate differences in commercially available options. Additional research is required to validate performance over the long-term operation and confirm contaminant fate, which will help determine whether resurging interest in pyrolysis and gasification warrants widespread adoption. PRACTITIONER POINTS: Pyrolysis and gasification systems are re-emerging in the wastewater industry. Direct coupling of thermal oxidizers and other modifications offered by contemporary systems aim to overcome past failures. Process conditions when coupled with a thermal oxidizer will likely destroy most organic contaminants, including PFAS, but requires additional research. Three full-scale facilities recently operated, several in construction or design that will provide operating experience for widespread technology adoption consideration.

Biosorption of V(V) onto Lantana camara biochar modified by H3PO4: Characteristics, mechanism, and regenerative capacity

Biochar has been widely recognized as an environmentally efficient adsorbent for removing heavy metals. However, considering the weak adsorption performance of the original biochar to the oxygen-containing anion, the adsorption of vanadium by biochar has rarely been investigated. This study proposes that H₃PO₄ activated biochar made from an invasive plant species growing near mines is a novel material to be investigated for V(V) recovery and reuse. As a noxious, invasive plant, Lantana camara L. (LC) has become widely naturalized around the world. Biochar was prepared from LC by pyrolysis at different conditions (200 °C, 350 °C, 500 °C, and 650 °C). The adsorption effect of biochar with and without P pretreatment on V(V) in aqueous solution was compared. The results show that biochar prepared from LC impregnated with H₃PO₄ (MLBC) had the highest adsorption capacity at 500 °C, and the maximal adsorption capacity fitted by Langmuir model was 77.38 mg g^-1, which was considerably higher than that of untreated biochar (LBC, 5.89 mg g^-1). The adsorption procedure was substantially fitted by the Langmuir isotherm and the pseudo-second-order kinetic. Additionally, the interaction of V(V) on MLBC is pH-dependent, and slightly acidic conditions are more favorable for adsorption. The characterization results indicated that electrostatic interaction, complexation reaction, and redox reaction were the primary mechanisms. After three cycles of adsorption, the final maximal adsorption capacity of MLBC remained at 76.03% of that of the virgin sample, demonstrating that MLBC had a recyclable capability to eliminate and restore V(V) from aqueous solutions.

Pristine and engineered biochar for the removal of contaminants co-existing in several types of industrial wastewaters: A critical review

Biochar has been widely studied as an adsorbent for the removal of contaminants from wastewater due to its unique characteristics, such as having a large surface area, well-distributed pores and high abundance of surface functional groups. Critical review of the literature was performed to understand the state of research in utilizing biochars for industrial wastewater remediation with emphasis on pollutants that co-exist in wastewater from several industrial activities, such as textile, pharmaceutical and mining industries. Such pollutants include organic (such as synthetic dyes, phenolic compounds) and inorganic contaminants (such as cadmium, lead). Multiple correspondence analyses suggest that through batch equilibrium, columns or constructed wetlands, researchers have used mechanistic modelling of isotherms, kinetics, and thermodynamics to evaluate contaminant removal in either synthetic or real industrial wastewaters. The removal of organic and inorganic contaminants in wastewater by biochar follows several mechanisms: precipitation, surface complexation, ion exchange, cation-π interaction, and electrostatic attraction. Biochar production and modifications promote good adsorption capacity for those pollutants because biochar properties stemming from production were linked to specific adsorption mechanisms, such as hydrophobic and electrostatic interactions. For instance, adsorption capacity of malachite green ranged from 30.2 to 4066.9 mg g^-1 depending on feedstock type, pyrolysis temperature, and chemical modifications. Pyrolyzing biomass at above 500 °C might improve biochar quality to target co-existing pollutants. Treating biochars with acids can also improve pollutant removal, except that the contribution of precipitation is reduced for potentially toxic elements. Studies on artificial intelligence and machine learning are still in their infancy in wastewater remediation with biochars. Meanwhile, a framework for integrating artificial intelligence and machine learning into biochar wastewater remediation systems is proposed. The reutilization and disposal of spent biochar and the contaminant release from spent biochar are important areas that need to be further studied.

The Use of Gigantochloa Bamboo-Derived Biochar for the Removal of Methylene Blue from Aqueous Solution

In this study, locally grown bamboo (Gigantochloa spp.) was used as feedstock for pyrolysis production of biochar under various pyrolysis temperatures (400–800°C). The resultant biochars were tested for their performance in adsorptive removal of the methylene blue (MB) dye. The scope of the adsorption experiment includes the effects of adsorbent dosage, solution pH, initial adsorbate concentration, and contact time. The adsorption data confirmed that pyrolysis temperature has a significant effect on adsorptive performance, whereas biochar pyrolysed at 500°C (BC500) has the highest adsorptive performance with the maximum adsorption capacity (derived from the Langmuir model) being 86.6 mg g-1. Basic characterisations (SEM, EDX, XRD, FTIR, and BET) were carried out for BC500 where FTIR and SEM confirmed the adsorption of MB onto the biochar, while the BET data showed the reduction of the BET surface area, total pore volume, and pore diameter after the adsorption process.

Metal-Supported Biochar Catalysts for Sustainable Biorefinery, Electrocatalysis and Energy Storage Applications: A Review

Biochar (BCH) is a carbon-based bio-material produced from thermochemical conversion of biomass. Several activation or functionalization methods are usually used to improve physicochemical and functional properties of BCHs. In the context of green and sustainable future development, activated and functionalized biochars with abundant surface functional groups and large surface area can act as effective catalysts or catalyst supports for chemical transformation of a range of bioproducts in biorefineries. Above the well-known BCH applications, their use as adsorbents to remove pollutants are the mostly discussed, although their potential as catalysts or catalyst supports for advanced (electro)catalytic processes has not been comprehensively explored. In this review, the production/activation/functionalization of metal-supported biochar (M-BCH) are scrutinized, giving special emphasis to the metal-functionalized biochar-based (electro)catalysts as promising catalysts for bioenergy and bioproducts production. Their performance in the fields of biorefinery processes, and energy storage and conversion as electrode materials for oxygen and hydrogen evolutions, oxygen reduction, and supercapacitors, are also reviewed and discussed.

Unraveling the molecular mechanisms of Cd sorption onto MnOx-loaded biochar produced from the Mn-hyperaccumulator Phytolacca americana

Engineered biochar represents a promising material for green remediation practices. In this paper, we present an innovative approach to produce MnO_x-loaded biochars by pyrolyzing the biomass of a Mn-hyperaccumulator species (Phytolacca americana). Batch sorption and stirred-flow kinetic experiments were combined with spectroscopic techniques to elucidate the mechanisms behind the Cd sorption onto those biochars, named here as PABCs. The incorporation of MnO_x into the PABCs increased their surface densities of oxygen-containing functional groups. The average Mn leaching (< 9%) from PABCs was lower than that measured for the non-pyrolyzed biomass of P. americana (30-43%). PABCs pyrolyzed at 500 °C had Cd sorption capacities as high as 212-337 mg/g, which achieved by far the best performance reported for biochar materials. The stirred-flow experiments showed that MnO_x loading was instrumental in increasing both the Cd sorption onto PABCs as well as its irreversibility. Extended X-ray absorption fine structure spectroscopy revealed that the Cd immobilization occurred mainly through its association with organic matter (Cd-OM) and, to a lesser extent, with carbonate (CdCO₃) and MnO_x (Cd-MnO_x). In short, MnO_x-loaded biochar prepared from the biomass of a Mn-hyperaccumulator species proved to be an effective, sustainable, and eco-friendly material for remediating Cd-contaminated waters.

Removal of pharmaceuticals from water using sewage sludge-derived biochar: A review

In recent years, considerable attention has been paid to the beneficial utilization of sewage sludge to reduce the risks associated with sludge disposal. Besides other applications of sludge, biochar produced from sludge has also been employed for the elimination of various pollutants from water. This review critically evaluates the recent progress in applications of sludge-based biochar for the adsorption of pharmaceuticals from water. The synthesis techniques of biochar production from sludge and their effects on physicochemical characteristics of produced biochar are discussed. The removal of various pharmaceuticals by sludge-based biochar are described in detail, with the emphasis on the adsorption mechanism and their reusability potential. It is evident from the literature that sludge-based biochar has demonstrated excellent potential for the adsorption of numerous pharmaceuticals from the aqueous phase. The major hurdles and issues related to the synthesis of sludge-based biochar and applications are highlighted, with reference to the adsorption of pharmaceuticals. Finally, a roadmap is suggested along with future research directions to ensure the sustainable production of biochar from sludge and its applications in water treatment.

Characteristics of Cu(II)-modified aerobic granular sludge biocarbon in removal of doxycycline hydroxide

In this study, the biocarbon derived from aerobic granular sludge with different nutritive proportions was modified by Cu(NO₃)₂•3H₂O (Cu-BC) to improve its adsorption capacity of doxycycline hydrochloride (DOX). The surface area, pores, functional groups, and element composition of biocarbon were characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectrometer, X-ray diffraction (XRD), the X-ray photoelectron spectrometer, and Fourier transform infrared spectrometry (FT-IR), respectively. Effects of DOX concentration, initial pH, and background electrolyte on adsorption effects of composite were analyzed. Furthermore, the adsorption kinetics, isotherm, thermodynamics, and diffusion model were investigated. Results demonstrated that biocarbons which were prepared with aerobic granular sludge under different nutritive proportions presented different performances. The BET specific surface area of Cu-NaAC/AGS-BC was 260.1592 m²/g, and the micropore volume was 0.054101 cm³/g. The BET specific surface area of Cu-GLC /AGS-BC was only 10.6821 m²/g, and the micropore volume was 0.008687 cm³/g. Both kinds of modified biochar contain a large number of oxygen-containing functional groups. The highest adsorption efficiency of Cu-BC could reach 99.54%. The adsorption of DOX on two modified biocarbons conforms to the pseudo-second-order dynamic model and Temkin isothermal model.

Adsorption of norfloxacin from aqueous solution on biochar derived from spent coffee ground: Master variables and response surface method optimized adsorption process

In this study, biochar derived from spent coffee grounds (SCGB) was used to adsorb norfloxacin (NOR) in water. The biochar properties were interpreted by analysis of the specific surface area, morphology, structure, thermal stability, and functional groups. The impacts of pH, NOR, and ion's present on SCGB performance were examined. The NOR adsorption mode of SCGB is best suited to the Langmuir model (R² = 0.974) with maximum absorption capacity (69.8 mg g^-1). By using a Response Surface Method (RSM), optimal adsorption was also found at pH of 6.26, NOR of 24.69 mg L^-1, and SCGB of 1.32 g L^-1. Compared with biochars derived from agriculture such as corn stalks, willow branches, potato stem, reed stalks, cauliflower roots, wheat straw, the NOR adsorption capacity of SCGB was 2-30 times higher, but less than 3-4 times for biochars made from Salix mongolica, luffa sponge and polydopamine microspheres. These findings reveal that spent coffee grounds biochar could effectively remove NOR from aqueous solutions. Approaching biochar derived from coffee grounds would be a promising eco-friendly solution because it utilizes solid waste, saves costs, and creates adsorbents to deal with emerging pollutants like antibiotics.

Removal of oxytetracycline promoted by manganese-doped biochar based on density functional theory calculations: Comprehensive evaluation of the effect of transition metal doping

The regulation of surface electrons by non-metal doping of biochar (BC) is environmentally and ecologically significant. However, systematic studies on the regulation of surface electrons by transition metal doping are lacking. The present study is based on the observation that the removal efficiency of oxytetracycline (OTC) by Mn-doped BC is eight times higher than that of undoped BC in 20 min. The effects of Mn doping on the crystal phase formation, persistent free radicals (PFRs), electron density, molecular orbitals, and nucleophilic active sites of BC are investigated, and the intermediate products of OTC are evaluated. Mn doping enhances the signal for sp²-hybridised carbon-carbon double bond, forms more delocalised π-bonds, and promotes the formation of free radicals centred on the carbon atoms. The specific surface area of BC increases, and manganese oxide is formed on the its surface. Density functional theory calculations show that Mn doping accelerates the electron transfer of BC, provides additional electrons for the BC system, and makes this system more ionised. OTC molecules preferentially attack the nucleophilic reaction sites near Mn atoms based on molecular electrostatic potential measurements. Therefore, this study provides new insights into the surface electronic structures regulated by transition metal elements.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.