Impact of deashing treatment on biochar structural properties and potential sorption mechanisms of phenanthrene

Recent advances in biochar application for water and wastewater treatment: a review

In the past decade, researchers have carried out a massive amount of research on the application of biochar for contaminants removal from aqueous solutions. As an emerging sorbent with great potential, biochar has shown significant advantages such as the broad sources of feedstocks, easy preparation process, and favorable surface and structural properties. This review provides an overview of recent advances in biochar application in water and wastewater treatment, including a brief discussion of the involved sorption mechanisms of contaminants removal, as well as the biochar modification methods. Furthermore, environmental concerns of biochar that need to be paid attention to and future research directions are put forward to promote the further application of biochar in practical water and wastewater treatment.

Effect of deashing on activation process and lead adsorption capacities of sludge-based biochar

To explore the effect of inorganic minerals on activation process and lead adsorption of sludge-based biochar, sludge-based biochar was pre-deashed using hydrochloric acid or hydrofluoric acid followed by potassium acetate activation. The results indicate that hydrochloric or hydrofluoric acid deashing can improve the pore parameters of sludge-based biochars and promote subsequent activation effect of potassium acetate. The specific surface area of biochar activated by potassium acetate after hydrochloric acid and hydrofluoric acid pretreatment increased from 583.36 m²/g to 718.70 m²/g and 991.55 m²/g, respectively. The enhancement of pore structure is conducive to enhancing the physical adsorption of lead on sludge-based biochar, while the chemical adsorption is not significantly affected at the same time. Thereby, the biochar and activated biochar pretreated with hydrofluoric acid showed better lead adsorption capacities (16.70 and 49.47 mg/g) than untreated biochar (7.56 and 38.49 mg/g).

The ratio of H/C is a useful parameter to predict adsorption of the herbicide metolachlor to biochars

Biochar adsorbent was produced by pyrolyzing traditional Chinese medicinal herb residue at 300, 500 and 750 °C (referred to as biochar-300, biochar-500 and biochar-750). Basic physical and chemical analyses, Fourier transform infrared spectroscopy (FT-IR), and thermodynamic analyses were performed to elucidate adsorption and properties of biochar. Biochar adsorption capacity of herbicide metolochlor, as measured by batch-type adsorption experiments by Freundlich constant K_f (mg^1-n Lⁿ kg^-1), followed the order: biochar-750 > biochar-300 > biochar-500. Thermodynamic analysis suggested that adsorption of metolachlor on biochar was a spontaneous process. The adsorption isotherm for the biochar produced at the highest pyrolysis temperature was characteristic for adsorption process driven by a high surface area of biochar (85.30 m² g^-1), while the adsorption process for the biochar produced at the lowest temperature was controlled by its higher content of organic matter (39.06%) and abundant functional groups. The FT-IR spectra also showed that the biochar prepared at the lowest temperature had the highest number of surface groups. In general, pore-filling induced by the large surface area of the biochar was the dominant adsorption mechanism. When the H/C value was >0.5, the adsorption mechanism of biochar was dominated by surface chemical bond, while pore-filling played a major role when the H/C value was <0.5.

Differential roles of ash in sorption of triclosan to wood-derived biochars produced at different temperatures

Biochar is composed of carbonaceous and inorganic (ash) fractions. The structural properties of carbonaceous fractions and the composition of ash in biochar are both variable with pyrolysis temperature. However, it is unknown whether ash may play different roles in sorption of organic compounds to the carbonaceous fraction of biochars produced at different temperatures. Hence, in this study, the pristine biochars produced at 300-900°C and their corresponding deashed biochars were investigated, and the combined roles of carbonaceous fraction and ash in sorption of triclosan were compared. The results showed that the biochars produced at 300-400°C had high content of uncarbonized organic structure with dominating partition effect. The combination of uncarbonized organic structure and ash had comparable or even higher sorption coefficient (K_D ) for triclosan at low concentration compared with a single uncarbonized organic structure. However, for the biochars produced at 600-900°C, which were mainly composed of carbonized or graphitized carbon structure, ash had significant effect on triclosan sorption by reducing surface adsorption and pore filling effect. The combination of carbonaceous fraction and ash decreased K_D values for triclosan at any tested concentrations. In addition, the results of pH effect on sorption indicated that ash possibly decreased the electrostatic repulsion of deprotonated phenolic hydroxyl between biochars and triclosan. Accordingly, it will be more valuable to design biochars for pollutant sorption from the perspective of combined role of carbonaceous fraction and ash rather than a single role of carbonaceous fraction.

An examination of the role of biochar and biochar water-extractable substances on the sorption of ionizable herbicides in rice paddy soils

The application of biochar as a soil amendment can increase concentrations of soil organic matter, especially water-extractable organic substances. Due to their mobility and reactivity, more studies are needed to address the potential impact of biochar water-extractable substances (BWES) on the sorption of herbicides in agricultural soils that are periodically flooded. Two paddy soils (100 and 700 years of paddy soil development), unamended or amended with raw (BC) or washed biochar (BCW), were used to test the influence of BWES on the sorption behavior of the herbicides azimsulfuron (AZ) and penoxsulam (PE). The adsorption of AZ to biochar was much stronger than that to the soils, and it was adsorbed to a much larger extent to BC than to BCW. The depletion of polar groups in the BWES from the washed biochar reduced AZ adsorption but had no effect on PE adsorption. The adsorption of AZ increased when the younger soil (P100) was amended with BC and decreased when it was amended with BCW. In P700, which has lower dissolved organic carbon (DOC) content than P100, the adsorption of AZ increased regardless of whether biochar was raw or washed. The adsorption of PE slightly decreased when P100 was amended with BC or BCW and slightly increased when P700 was amended with BC or BCW. In order to evaluate compositional differences in the biochar and BWES before and after the washing treatment, we performed solid-state ¹³C NMR spectroscopy of BC and BCW, and high resolution mass spectrometry of BWES. Our observations stress the importance of proper consideration of soil and biochar properties before their incorporation into paddy soils, since biochar may reduce or increase the mobility of AZ and PE depending on soil properties and time of application.

Characterization of peanut-shell biochar and the mechanisms underlying its sorption for atrazine and nicosulfuron in aqueous solution

The aim of the present study was to investigate the sorption of atrazine and nicosulfuron onto several experimentally produced biochars, as well as to understand the influence of biochar structure on sorption mechanisms. Nine biochars were generated by pyrolyzing peanut shell at 300, 450, or 600 °C and exposing samples to each of the several deashing treatments: none, water or HCl. The sorption of atrazine and nicosulfuron by the nine biochars were evaluated. Biochars were characterized via elemental analyzer, BET-N₂ surface area, FTIR and XPS. Three kinetic models were used to fit the sorption kinetics data and both the Freundlich and dual-mode models described the sorption isotherms well. All the biochar samples exhibited high sorption affinity for both atrazine and nicosulfuron. The sorption mechanisms of the biochar included hydrophobic partition, π-π electron donor-acceptor interactions, H-bonding, and pore-filling mechanism, and these mechanisms were dependent on both the degree of biochar carbonization and the concentration of atrazine or nicosulfuron. Ash could bind to atrazine and nicosulfuron by specific interactions but played a negative role in the sorption, especially on high pyrolyzing temperature biochars. These results will facilitate the production of efficient and cheap adsorbents for reducing the risk of atrazine and nicosulfuron.

Acidic surface functional groups control chemisorption of ammonium onto carbon materials in aqueous media

Elucidation of mechanistic insight into the interaction of carbon materials' physicochemical surface properties and ammonium (NH₄⁺) adsorption in aqueous media was made by conducting a systematic study using a wide range of carbon materials. Three types of biochars (rice husk, poultry litter, and enhanced poultry litter) and activated carbons (fresh and aged coconut shell-based and charcoal-based) were used for investigating the NH₄⁺ adsorption mechanism. Poultry litter biochar, with lowest surface area (3 m² g^-1) and largest pore diameter (29 nm), showed the highest NH₄⁺ adsorption capacity (0.34 mg NH₄⁺g^-1), while charcoal-based activated carbon, with the highest surface area (1133 m² g^-1) and small pore diameter (6 nm), had the least NH₄⁺ adsorption capacity (0.09 mg NH₄⁺g^-1). The value of Freundlich isotherm constant 'n' was >1 for all tested carbon materials indicating chemisorption as the dominant sorption mechanism. Aging of the carbon surface resulted in 30% increase in NH₄⁺ retention. Surface chemical properties that most influenced NH₄⁺ chemisorption on to carbon materials were found to be acidic surface functional groups (ASFGs), elemental composition, ash content, and pH. The optimal conditions for NH₄⁺ adsorption, regardless of type and source of carbon materials, were solution pH of 8, a high amount of ash content, and carboxyl, carbonyl, and phenolic functional groups. Evaluation of CEC and ASFGs indicated that CEC and ASFGs are not equivalent terms. Through this study, conducted on carbon adsorbents derived from different sources, with different surface physical and chemical properties, we established that ASFGs, and not CEC, play a critical role in ammonium chemisorption on carbon materials. The study showed that low cost and eco-friendly biochars, with optimal surface chemistry, can replace expensive activated carbons for NH₄⁺ remediation in aqueous media.

Sorption of ionic and neutral species of pharmaceuticals to loessial soil amended with biochars

To clarify the impact of biochar amendment on soil sorption for coexisting pharmaceuticals, wheat straw-derived biochars pyrolyzed at 300 and 700 °C (labeled as WS300 and WS700, respectively) were prepared. Batch experiments on ketoprofen (KTP), atenolol (ATL) and carbamazepine (CBZ) sorption to biochars, loessial soil and biochar-amended soils were conducted. The results indicated that sorption affinity of different species of pharmaceuticals to WS300 and WS700 was in the order of cationic ATL > neutral CBZ > anionic KTP. Cationic ATL had the highest sorption to biochars due to electrostatic attraction. Coexisting ATL, CBZ and KTP competed for the shared adsorption sites on carbonized phase of biochars, and π-π interactions were proposed to be the main sorption mechanism. Sorption coefficients (K_d) and nonlinearity of ATL, CBZ and KTP to soil increased when biochar was added (5% by weight), especially for WS700 with higher specific surface area. K_d values of the three pharmaceuticals to WS700-amended soil in either single solute or bisolute system were one to two orders of magnitude higher than those to soil, indicating the promoting role of WS700 in sorption of coexisting pharmaceuticals in soil. The study demonstrated the enhanced and competitive sorption of ionic and neutral species of pharmaceuticals to soil amended with biochars, which is helpful in designing biochar as effective sorbents for immobilization of pharmaceuticals in soil remediation.

Insights into the roles of the morphological carbon structure and ash in the sorption of aromatic compounds to wood-derived biochars

Currently, it is still lack of systematic and in-depth knowledge regarding the co-effect of carbon-based fractions and ash in the sorption behavior of biochars. Therefore, pristine wood-derived biochars (PBCs) produced at different temperatures and their corresponding de-ashed versions (DBCs) were used to determine the roles of carbon's morphological structure and ash in sorption of aromatic compounds (toluene, m-toluidine, and m-nitrotoluene) to biochars. The results showed that biochars produced at 300-400 °C (mainly uncarbonized organic matter, UCOM) and 900 °C (turbostratic carbon, TC) may have stronger partition effect and pore filling effect with π-π interaction, respectively, and thus have greater sorption coefficients (Lg K_d) than biochars produced at 600 °C (pyrogenic amorphous carbon, PAC), which are probably dominated by surface hydrophobic effect. Meanwhile, TC had a greater Lg K_d than UCOM at low adsorbate concentrations (C_e), but exhibited an opposite trend at high C_e. The Lg K_d values of DBCs are always greater than those of PBCs, indicating ash has an inhibitory effect on sorption of aromatic compounds to biochars. Furthermore, the role of ash in sorption behavior of PBCs would vary with solution pH. At a neutral pH, PBCs have the maximum sorption quantity for aromatic compounds due to the formed cation-π bond between cations of ash and aromatic compounds. However, the acidic pH enhanced the dissolution of cations in ash and the basic pH enhanced the hydroxylation of cations in ash. Therefore, both acidic and basic pH weakened the cation-π bond between ash and aromatic compounds and decreased the sorption of aromatic compounds on PBCs. The results suggest that de-ashed biochars with more UCOM or TC are effective sorbents for sequestration of aromatic compounds, and provide a well-designed method for improving the sorption efficiency of biochars.

Humic Acid Can Enhance the Mineralization of Phenanthrene Sorbed on Biochars

Biodegradation of hydrophobic organic contaminants by bacteria has been widely studied, but how dissolved organic matter (DOM) may affect their removal if accumulated on biochars is poorly understood. To address this knowledge gap, microbial mineralization of phenanthrene (PHE) spiked on various biochars by Mycobacterium vanbaalenii PYR-1 in the presence of humic acid (HA, a model DOM) at two concentrations was investigated. Our findings showed that HA greatly increased the rate and extent of PHE mineralization. This could be attributed to enhanced PHE desorption by HA, which facilitated access to it by bacteria in the aqueous phase. Furthermore, the high HA affinity for PHE facilitated PHE flow toward the bacterial cells with HA acting as a carrier in the aqueous phase. The mineralization enhancement of PHE by HA within 480 h was negatively influenced by the aromatic carbon contents and micropore volumes in biochars. This shows the importance of the physicochemical properties of biochars in altering the HA effect. Results of this study provide novel information on how to achieve complete removal of PHE accumulated on biochars with a strong sorption affinity for it, using a microbial technique and natural DOM.

Removal of tylosin and copper from aqueous solution by biochar stabilized nano-hydroxyapatite

Antibiotics and heavy metals are frequently detected simultaneously in water environment. Effective elimination methods for antibiotics and heavy metals pollution should deserve our attention. This study investigates the adsorption performance of biochar modified with nano-hydroxyapatite (nHAP) on tylosin (TYL) and Cu from water simultaneously. Composite adsorbents of nHAP and biomass, derived from three waste residues, which were wood-processing residues (WR), wheat straw (WS) and Chinese medicine residues (CMR), were prepared. According to the results of orthogonal experiment, the degree of influence of the three factors on TYL and Cu were the pyrolysis temperature > the proportion of nHAP and biomass > the sources of biomass, and pyrolysis temperature> the sources of biomass> the proportion of nHAP and biomass, respectively. The optimum conditions for nHAP@biochar were screened. At pH < 7.0, the adsorption quality of TYL increased with pH increased, while at pH > 7.0, the adsorption quality of TYL changed slightly. At low pH, Cu and TYL could compete for the same adsorption sites on nHAP@biochars. The adsorption amount of TYL and Cu were both increased with increasing of the temperature. Compared with Langmuir model, Freundlich model could better fit the TYL adsorption on nHAP@biochars, with K_f values of TYL 62.35 (mmol/kg) (L/mmol)ⁿ (WR1) and 4.84 (mmol/kg) (L/mmol)ⁿ (CMR1), respectively.

Enhanced biochar stabilities and adsorption properties for tetracycline by synthesizing silica-composited biochar

The silica-composited biochars (SBC) were synthesized by adding silica particulates into bamboo biomass during pyrolysis at 700 °C to examine the effect of silica addition on biochar stabilities and adsorption properties for tetracycline (TC). Silica addition increased the total pore volume and average pore diameter of biochar due to the abundant mesopores in SBC, but decreased specific surface area due to the blockage of biochar pore with silica particles. Biochar stability was obviously enhanced with silica addition due to the decreased atomic ratio of H/C and O/C, the reduced C loss amount after chemical oxidation treatment, and the increased thermal stability. The adsorption capacities of SBC for TC were greatly enhanced with silica addition and increased with the increasing silica addition amount, which can be attributed to the facilitating effect of π-π electron donor acceptor (EDA) interaction and pore-filling effect. In addition, silica addition can also effectively enhance the oxidation resistance of biochar for TC adsorption, since the decreased degree (δ) of TC adsorption amounts on the biochars after chemical oxidation decreased with the increasing silica addition level. The observed positive correlations between δ values and the corresponding C loss amount of biochars after chemical oxidation suggested that the high carbon stability was favorable for the maintenance of biochar adsorption capacity. These results can provide a new way to improve biochar stabilities, aging resistance, and adsorption properties for organic pollutants.

Adsorption-desorption behavior of carbendazim by sewage sludge-derived biochar and its possible mechanism

Biochar application in agricultural soil for environmental remediation has received increasing attention, however, few studies are focused on sewage sludge based biochar. The present study evaluated the effect of raw sewage sludge and sewage sludge based biochars produced at different pyrolysis temperatures (100-700 °C) on the adsorption-desorption of carbendazim in soil. Sewage sludge derived biochar significantly enhanced the sorption affinity and limited the desorption capacity of the soil for carbendazim. A maximum removal efficiency of 98.9% and a greatest value of 144.05 ± 0.32 μg g-1 sorption capacity occurred in soil amended with biochar pyrolyzed at 700 °C (BC700). As the pyrolysis temperature and the amendment rate of biochars increased, the sorption of carbendazim was promoted and desorption was further inhibited. The adsorption-desorption hysteresis index of carbendazim was consistently higher in soils amended with biochars (>0.85) than in the unamended soil (0.42-0.68), implying that carbendazim could be immobilized in soil amended with sewage sludge derived biochars. The partition effect was dominant in the sorption process for carbendazim in the biochar-soil mixtures. This study will be helpful for the disposal of sewage sludge and its utilization, and it is the first report for the study the sorption-desorption process of carbendazim in soil amended with sewage sludge derived biochar. Furthermore, these findings may be also useful for understanding the distribution and transport of carbendazim in the environment and will be of great significance in remediation strategies for contaminated soil.

The application of machine learning methods for prediction of metal sorption onto biochars

The adsorption of six heavy metals (lead, cadmium, nickel, arsenic, copper, and zinc) on 44 biochars were modeled using artificial neural network (ANN) and random forest (RF) based on 353 dataset of adsorption experiments from literatures. The regression models were trained and optimized to predict the adsorption capacity according to biochar characteristics, metal sources, environmental conditions (e.g. temperature and pH), and the initial concentration ratio of metals to biochars. The RF model showed better accuracy and predictive performance for adsorption efficiency (R² = 0.973) than ANN model (R² = 0.948). The biochar characteristics were most significant for adsorption efficiency, in which the contribution of cation exchange capacity (CEC) and pH_H2O of biochars accounted for 66% in the biochar characteristics. However, surface area of the biochars provided only 2% of adsorption efficiency. Meanwhile, the models developed by RF had better generalization ability than ANN model. The accurate predicted ability of developed models could significantly reduce experiment workload such as predicting the removal efficiency of biochars for target metal according to biochar characteristics, so as to select more efficient biochar without increasing experimental times. The relative importance of variables could provide a right direction for better treatments of heavy metals in the real water and wastewater.

Influence of organic carbon fractions of freshwater biofilms on the sorption for phenanthrene and ofloxacin: The important role of aliphatic carbons

Sorption to biofilms is thought to be a crucial process controlling the fate of trace organic contaminants in aquatic systems. The organic composition of biofilms is regarded as the determining factor in the sorption mechanism of biofilm organic carbon fractions; however, its role is not well known. Here, the sorption of phenanthrene and ofloxacin was modeled with classic and emerging organic contaminants, respectively, by comparatively investigating nine type of freshwater biofilms cultured in a river, lake, and reservoir in spring, summer, and autumn. The chemical features of the nine biofilms were analyzed using elemental analysis, infrared spectroscopy, X-ray photoelectron spectroscopy, and carbon-13 nuclear magnetic resonance. Results showed that the freshwater biofilms were aliphatic-rich natural amorphous solid substances with O-containing functional groups, and their surface polarity was significantly lower than their bulk polarity. All the isotherms of phenanthrene and ofloxacin sorption by the biofilms were linear. The organic carbon-normalized partition coefficient values for phenanthrene and ofloxacin on the nine biofilms ranged from 91.9 to 364.2 L g^-1 and 3.2 to 43.2 L g^-1, respectively. The van der Waals interaction between a majority of aliphatic carbon (73.4%-83.9%) in biofilms and the two sorbates was much stronger than π-π interactions between a minority of aromatic carbon (12.7%-21.7%) and sorbates. The surface polarity of the biofilms regulated polar interactions including the hydrogen bonding and electron donor-acceptor interactions. Both the aliphatic carbon and surface polarity in the biofilms enhanced the sorption of phenanthrene and ofloxacin. The sorption characteristics and mechanisms of polycyclic aromatic hydrocarbons and antibiotics on biofilms shown in our present and previous studies are different from those of other ubiquitous natural solid materials such as soils and sediments. This study provides insight into the importance of aliphatic carbon fractions of freshwater biofilms for the sorption of classic and emerging organic contaminants.

Sunflower stalk-derived biochar enhanced thermal activation of persulfate for high efficient oxidation of p-nitrophenol

Sunflower stalk-derived biochars (BC) were prepared at various temperatures (i.e., 500, 650, and 1000 °C) and demonstrated as a highly efficient catalyst in persulfate (PS) activation for the oxidation of p-nitrophenol (PNP) at 60 °C. The apparent PNP oxidation rate constant in the BC500 (0.1543 L mol^-1 S^-1), BC650 (0.6062 L mol^-1 S^-1), or BC1000 (2.1379 L mol^-1 S^-1) containing PS system was about 2, 8 and 28 times higher than that in PS/PNP (0.0751 L mol^-1 S^-1) system, respectively. The effect of reaction temperature on PNP oxidation was also investigated. Furthermore, the radical quenching tests and electron paramagnetic resonance spectroscopy (EPR) were employed to investigate the sulfate and hydroxyl radicals for PNP oxidation. The Raman results suggested that the defective sites on biochars possess vital role for oxidation of PNP in PS system. The possible activation pathway of PS/BC was proposed that the defective sites on BC were involved for weakening the O-O bond in PS and subsequently cleaving O-O bond by heat to generate sulfate radical. The oxidation of PNP at low concentration (below 100 μg L^-1) was completely removed in urban wastewater by PS/BC system within 30 min. This work would provide new insights into PS activation by BC catalyst and afford a promising method for organic pollutant removal in high-temperature wastewater.

Combining bulk characterization and benzene polycarboxylic acid molecular markers to describe biochar properties

The physicochemical properties of biochar determined its sorption of organic contaminations, and the environmental aging process changed the biochar properties. However, the correlation between biochar heterogeneous properties and their sorption characteristics is unclear. In this study, peanut shell biochars were produced at 200-700 °C, and HNO₃/H₂SO₄ was used to oxidize 400 °C biochar for 2-10 h to simulate the enhanced aging process of biochar in the environment. Benzene polycarboxylic acid (BPCA) molecular markers, and bulk characterization were analyzed to describe biochar physicochemical properties and to further predict the sorption characteristics to bisphenol A (BPA). For pristine biochars, the mellitic acid/BPCAs (B6CA/BPCAs) increased with the raise of pyrolysis temperature and the H/C atomic ratio was positively correlated with benzenepentacarboxylic acid/B6CA (B5CA/B6CA) (P < 0.01), which indicated the increased aromatic condensation. After HNO₃/H₂SO₄ treatment, the aromaticity (H/C ratio) decreased while the highly condensed components in biochars were enriched (increased B6CA/BPCAs values). Multiple regression models were adopted to establish a quantitative relationship between biochar heterogeneous properties and their sorption of BPA. Both nonlinearity coefficient N values (N = 0.08 + 0.103 B5CA/B6CA + 0.721 (O + N)/C, R² = 0.985) and single-point sorption coefficients log K_d (log K_d = 1.236 + 0.006 BPCAs + 1.449 (O + N)/C, R² = 0.936) could be estimated combining molecular markers and polarity parameters for biochars.

Sorption mechanisms of lead on silicon-rich biochar in aqueous solution: Spectroscopic investigation

Unraveling sorption mechanisms of lead (Pb) to silicon (Si)-rich biochar at molecular scale in aqueous solution are essential for the effective application of the biochars to the remediation of Pb and other metal(loid)s pollution in the environment. Thus, this study investigated the contributions of phytoliths and other compounds to the Pb sorption on Si-rich coconut fiber biochar (CFB500) and the corresponding sorption mechanisms using spectroscopic techniques, including the micro-X-ray fluorescence (μ-XRF), X-ray absorption fine structure (XAFS), scanning electron microscopy combined with energy dispersive X-ray spectroscopy, and X-ray diffraction. The μ-XRF and XAFS results showed that K, Ca, Cu, Mn, and Fe were released and significantly related to Pb in Pb-loaded CFB500; four major Pb species were formed with similar structures to lead carboxylate (e.g., Pb(C₂H₃O₂)₂), Pb₃(PO₄)₂, PbSiO₃, and PbCO₃. On phytoliths in CFB500, Pb²⁺ ions were mainly sorbed on the sites of silicate with a structure similar to PbSiO₃. The contribution of binding sites for Pb²⁺ sorption was ascribed to the outer-wall of carbon skeleton of CFB500, which was stronger than that provided by the mineral oxide aggregate and phytoliths on CFB500. Organic carbon functional groups, inorganic carbonates, silicates and phosphates on CFB500 mostly dominated the sorption sites for Pb²⁺. Our results suggest that CFB500 was a promising material for the remediation of Pb-contaminated aqueous environments (e.g., wastewater).

Effect of using powdered biochar and surfactant on desorption and biodegradability of phenanthrene sorbed to biochar

The present study aimed to investigate the relationship between the desorption and biodegradability of phenanthrene sorbed to biochars by employing two approaches that may change the desorption and biodegradability: the use of powdered biochars and nonionic surfactants. Biochars derived from two feedstocks (rice husk and sewage sludge; pyrolyzed at 500 °C but showing different aromaticity) were used. When the biochars were powdered to obtain particles <250 μm the mass fractions of the desorbed phenanthrene at ∼80 days (f_des) increased from 0.303 to 0.431 for sewage sludge biochars. On the other hand, f_des for rice husk biochars remained virtually unchanged (from 0.264 to 0.255). The mass fractions of the biodegraded phenanthrene (f_bio) increased from 0.191 to 0.306 for rice husk biochars and from 0.077 to 0.168 for sewage sludge biochars. When a nonionic surfactant was added at the sub-critical micelle concentration (CMC), f_bio increased by 4.7 times and 8.3 times for rice husk and sewage sludge biochars. For both types of biochars, f_bio was larger than f_des when the surfactant was added. This study suggests that the addition of nonionic surfactants can be considered if the inhibition of microbial activity is of concern in soils and sediments treated by biochar.

Adsorption capacity of phenanthrene and pyrene to engineered carbon-based adsorbents produced from sewage sludge or sewage sludge-biomass mixture in various gaseous conditions

Adsorption of phenanthrene (PHE) and pyrene (PYR) by engineered carbon-based adsorbents produced from sewage sludge in an atmosphere of nitrogen (N₂) or carbon dioxide (CO₂) at temperatures of 500, 600, and 700 °C was investigated. The addition of willow to the SSL decreased the biochar adsorption capacity. However, there was an increase in the adsorption capacity after changing N₂ to CO₂. The addition of willow to SSL and the type of carrier gas affected the mechanism of adsorption. The adsorption of PHE and PYR on the SSL-derived adsorbents produced in N₂ occurred through pore filling. The adsorption on the SSL-derived adsorbents with willow followed the mechanism of π-π electron-donor-acceptor (EDA) interactions and hydrophobic interactions. A similar mechanism was observed with regard to the biochars produced from SSL in atmosphere of CO₂. For the SSL-derived adsorbents with willow in CO₂, the adsorption mechanism was observed to vary between PHE and PYR.

Characteristics and mechanisms of chlorpyrifos and chlorpyrifos-methyl adsorption onto biochars: Influence of deashing and low molecular weight organic acid (LMWOA) aging and co-existence

The effects of inherent minerals in biochars and low molecular weight organic acids (LMWOAs) on chlorpyrifos and chlorpyrifos-methyl adsorption by biochars are unclear. We examined the sorption of chlorpyrifos and chlorpyrifos-methyl onto giant reed-derived biochars before and after deashing or LMWOA aging. The effect of citric acid (CA) as a co-solute on the sorption of chlorpyrifos and chlorpyrifos-methyl was also investigated. With increasing temperature (300-600 °C), the adsorption capacity of biochars increased from 4.32 to 14.8 mg/g for chlorpyrifos and from 15.0 to 50.5 mg/g for chlorpyrifos-methyl. This can be explained by the fact that higher temperature biochar had more aromatic units and pores for capturing more sorbates. The deashing and LMWOA aging treatments exposed more carbon surfaces and improved the porosity of biochar, thus favoring sorption. Further, the deashing treatment resulted in greater sorption enhancement, when compared with the LMWOA aging treatment. At pH 6.5, CA^2- and CA^3- chelated Ca²⁺ via bridging at CA concentration below 10 mmol/L, thus reducing the competition of Ca²⁺ for aromatic surfaces and COO^-/OH groups. When the CA concentration was above 20 mmol/L, CA^2-, CA^3-, and [Ca(CA)₂]^x- inhibited the sorption of chlorpyrifos and chlorpyrifos-methyl by competing for carbon sites and pores of biochar. These findings will help guide the practical application of biochar in pesticide-contaminated water and soil, and to better understand the role of biochar in the transport, fate, and bioavailability of organophosphorus pesticides in the rhizosphere.

Characteristics of wood-derived biochars produced at different temperatures before and after deashing: Their different potential advantages in environmental applications

Ash in biochar has great influence on the characteristics of biochars. This study systematically compared the differences in physico-chemical properties between pristine biochars (PBCs) and deashed biochars (DBCs) produced at different temperatures (300-900 °C), and specifically analyzed their different advantages in environmental applications. In terms of all the PBCs and DBCs, PBC of 900 °C and the corresponding DBC have the highest degree of graphitization that is recalcitrant in environment, they are benefit for carbon sequestration. PBC of 300 °C and the corresponding DBC have the highest content of O-containing functional groups and aliphaticity that is labile in environment, they are potential carbon source for the growth of soil organisms. PBCs of 300-400 °C have the greatest releasable PO₄^3- content (0.418-0.441 mg/g), and PBCs of 700-900 °C have highest pH (9.28-9.59) and mineral elements content (11.58-12.64 mg/g), they are potential provision of P, and acid soil amendments with potential provision of mineral elements, respectively. DBCs of 300-400 °C possess less competitive cations including Ca, Mg, Al, Fe, and Zn (1.49-2.01 mg/g) and highest content of O-containing functional groups, they are good sorbents for heavy metals, meanwhile these DBCs have the lowest pH (4.49-4.70) that are potential amendments for alkaline soil. Moreover, DBCs of 900 °C have the highest surface area (SA) (351 m²/g), the most developed porosity, and the highest releasable NH₄⁺ content (0.052 mg/g), they are good sorbents for hydrophobic organic pollutants and potential provision of N. This study gives an effective guidance for selecting the suitable biochars-design (deashing or non-deashing) according to their applications in environment.

Insight into interaction between biochar and soil minerals in changing biochar properties and adsorption capacities for sulfamethoxazole

Biochars produced from wheat straw at 400 °C (BC400) and 700 °C (BC700) were treated with three typical soil minerals to examine the effects of soil minerals on biochar properties and adsorption capacity for sulfamethoxazole (SMX). Mineral treatment enlarged the surface area and pore size of biochar, and the electron donating capacity (EDC) of the mineral-treated biochars also increased due to the increased phenolic group in BC400 and the enhanced conjugated π-electron system in BC700, respectively, which in turn affected the adsorption capacity of biochars for SMX. The adsorption of SMX on BC700 was increased after mineral treatment due to the facilitating effect of π-π electron donor-acceptor interaction as indicated by the positive correlation of surface adsorption amount (Q_A) of SMX with EDC of biochars (R² = 0.92-0.96). In contrast, mineral treatment decreased SMX adsorption on BC400, which could be attributed to the potential association of organic matter with minerals via coprecipitation and adsorption, in addition to the weak adsorption capacities of soil minerals for SMX. These results can provide a new insight for better understanding the interaction between biochar and soil minerals and its effect on adsorption capacity of biochar for organic pollutants.

Quantitative evaluation of relationships between adsorption and partition of atrazine in biochar-amended soils with biochar characteristics

Atrazine (ATZ) adsorption in two natural soils amended with biochars produced from different feedstocks at 300, 500, and 700 °C were investigated; further, the relationships between the surface and partition adsorption capacities of ATZ in biochar-amended soils with biochar characteristics were quantitatively evaluated. The results revealed that high aromaticity, hydrophobicity, and low polarity of biochar facilitated ATZ adsorption. The addition of selected biochars significantly increased the adsorption of ATZ on paddy soil (PS) and black soil (BS) by 5.2–7.5 times and 2.3–4.2 times, respectively. On the contrary, the degree of increase in surface adsorption was much higher than that in partition adsorption, mainly due to the role of the specific adsorption of ATZ on biochar. Meanwhile, the respective contributions of surface and partition adsorptions to the total ATZ adsorption on biochar-amended soil changed with different addition amounts of biochar. The multiple nonlinear regression analysis demonstrated the linear dependence of H/C ratio, (O + N)/C ratio, and specific surface area (SSA) of biochar on the surface adsorption capacity of biochar-amended PS and BS, as well as the linear dependence of organic carbon and ash contents on the partition adsorption capacity of biochar-amended PS and the linear dependence of the H/C ratio and SSA on the partition adsorption capacity of biochar-amended BS. In biochar-amended soil systems, interactions between biochar and soil could affect ATZ adsorption, and organic matter in biochar might compensate for the role of soil organic matter in the competition for adsorption sites with a decrease in the biochar pyrolysis temperature.

Adsorption of atrazine (ATZ) in two natural soils amended with different biochars was investigated, and the relationships of adsorption capacity of biochar-amended soils with biochar characteristics were also quantitatively evaluated.

Phenol adsorption on biochar prepared from the pine fruit shells: Equilibrium, kinetic and thermodynamics studies

Biochar samples were prepared from pine fruit shell (PFS) biomass using slow pyrolysis for 1 h at three different temperatures (350, 450 and 550°C). Batch experiments were carried out for the biosorption of phenol onto these biochars. The effect of biosorption experimental parameters such as adsorbent dosage, ionic strength, initial solution pH, contact time and temperatures has been investigated. Experimental equilibrium data were fitted to Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms by non-linear regression method. The experimental kinetic data were also fitted to Lagergren pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models by non-linear regression method. Determination coefficient (R²), chi-squared (χ²) and error function (F_error%) were used to determine the optimum isotherm and kinetic by non-linear regression method. Kinetics results were best described by pseudo-second order model for phenol onto three biochars. Thermodynamic parameters were estimated and implied that the adsorption process is spontaneous and exothermic in nature.

Levels of persistent toxic substances in different biochars and their potential ecological risk assessment

This study investigated the levels of persistent toxic substances, such as 16 polycyclic aromatic hydrocarbons (Σ16PAHs) and heavy metals (Cu, As, Cd, Zn, Pb, Ni, Mo, and Cr) in biochars produced from crop residues (walnut shell, corn cob, corn straw, rice straw, and rice husk) at different heat treatment temperatures (HTTs, 250, 400, and 600 °C). The levels of Σ16PAHs in different biochars were 0.47-7.11 mg kg^-1, with naphthalene and phenanthrene contributing the most. The Σ16PAHs had the positive correlations with H/C and (O + N)/C, but had negative correlations with biochar surface areas. This finding indicates the increasing hydrophobic π-π interactions between the PAHs and the aromatic sheets of biochars and even the trapping of PAHs within the micropores with the increase of HTTs. The levels of heavy metals in rice residue-derived biochars were significantly higher than those in other biochars. The heavy metals had positive correlations with ash contents in the biochars, indicating the enrichment of heavy metals in the ash. The potential ecological risks of PAHs and heavy metals (dosage: 1%, w/w; frequency: 1) were minimal according to the risk quotient of negligible concentrations (RQ_NCs: 2.50-47.40, << 800) and maximum permissible concentrations (RQ_MPCs: 0.02-0.48, << 1) for PAHs and the potential ecological risk indexes (PERI: 0.01-0.28, << 150) for heavy metals.

Insight into mechanism of aged biochar for adsorption of PAEs: Reciprocal effects of ageing and coexisting Cd2

Biomass derived biochar is a stable carbon-rich product with potential for soil amendment. Introduced into the natural environment, biochar will naturally experience 'ageing' processes that are liable to change its physicochemical properties and the mobility of sorbed pollutants over the longer term. To elucidate the reciprocal effects of biochar ageing and heavy metal adsorption on the affinity of biochar for organic pollutants, we systematically assessed the adsorption of diethyl phthalate (DEP), representative of phthalic acid esters (PAEs), to fresh and aged biochars with and without coexistence of Cd²⁺. Long-term oxidative ageing was simulated using 5% H₂O₂ and applied to biochar samples made from corn cob, maize straw and wheat straw made by pyrolysis at both 450 °C and 650 °C. Our results showed that biochar made at lower temperature (450 °C) and from straw exhibited the higher adsorption capacity, owing to their greater polarity and abundance of O-containing functional groups. The adsorption of DEP onto fresh biochars was found to be driven by van der Waals force and H-bonding. Biochar made at the higher temperature (650 °C) displayed higher carbon stability than that produced at lower pyrolysis temperature. Oxidized biochar showed lower adsorption capacity than fresh biochar owing to the formation of three-dimensional water clusters on biochar surface, which blocked accessible sites and decreased the H-bonding effect between DEP and biochars. The coexistence of Cd²⁺ suppressed the sorption of DEP, via competition for the same electron-rich sites. This indicates that cation/π-π EDA interactions are the primary mechanism for PAE and Cd²⁺ stabilization on biochar. Our study sheds light on the mechanism of organic pollutant sorption by biochar, as well as the potential susceptibilities of this sorption to ageing effects in the natural environment.

Phosphorus sorption capacity of biochars varies with biochar type and salinity level

Biochar is recognized as an effective material for recovering excess nutrients, including phosphorus (P), from aqueous solutions. Practically, that benefits the environment through reducing P losses from biochar-amended soils; however, how salinity influences P sorption by biochar is poorly understood and there has been no direct comparison on P sorption capacity between biochars derived from different feedstock types under non-saline and saline conditions. In this study, biochars derived from wheat straw, hardwood, and willow wood were used to compare P sorption at three levels of electrical conductivity (EC) (0, 4, and 8 dS m^-1) to represent a wide range of salinity conditions. Phosphorus sorption by wheat straw and hardwood biochars increased as aqueous solution P concentration increased, with willow wood biochar exhibiting an opposite trend for P sorption. However, the pattern for P sorption became the same as the other biochars after the willow wood biochar was de-ashed with 1 M HCl and 0.05 M HF. Willow wood biochar had the highest P sorption (1.93 mg g^-1) followed by hardwood (1.20 mg g^-1) and wheat straw biochars (1.06 mg g^-1) in a 25 mg L^-1 P solution. Although the pH in the equilibrium solution was higher with willow wood biochar (~ 9.5) than with the other two biochars (~ 6.5), solution pH had no or minor effects on P sorption by willow wood biochar. The high sorption rate of P by willow wood biochar could be attributed to the higher concentrations of salt and other elements (i.e., Ca and Mg) in the biochar in comparison to that in wheat straw and hardwood biochars; the EC values were 2.27, 0.53, and 0.27 dS m^-1 for willow wood, wheat straw, and hardwood biochars, respectively. A portion of P desorbed from the willow wood biochar; and that desorption increased with the decreasing P concentration in the aqueous solution. Salinity in the aqueous solution influenced P sorption by hardwood and willow wood but not by wheat straw biochar. We conclude that the P sorption capacity of the studied biochars is dependent on the concentration of the soluble element in the biochar, which is dependent on the biochar type, as well as the salinity level in the aqueous solution.

Effects of biochar input on the properties of soil nanoparticles and dispersion/sedimentation of natural mineral nanoparticles in aqueous phase

Upon addition to or otherwise entering soils and waters, biochar particles inevitably interact with natural mineral nanoparticles (NPs). We explored the impacts of two biochars made from charring peanut shells at 300 and 600°C (P300 and P600) on the characteristics of soil NPs extracted from brown soil and laterite soil. The dispersion or sedimentation of montmorillonite (Mon), kaolinite (Kao), goethite (Goe), and hematite (Hem) in the aquatic phase were investigated in the presence of P300 and P600 or their nano samples (NP300 and NP600). P300 and P600 increased the organic C fraction in the soil NPs extracted from brown soil, and decreased the amount of Fe-associated NPs. However, no significant influence was observed in the organic C and mineral phases of laterite soil NPs by P300 and P600. Goe and Hem were slightly adsorbed to P300 at pH6.5, while Goe or Hem homoaggregates formed and settled onto P600. NP300 and NP600 significantly reduced the dispersion of Goe and Hem in the aquatic environment via heteroaggregation, but there was no interaction between NP300 or NP600 and Mon or Kao. These findings are helpful for understanding the interaction between natural minerals and biochars, and the potential fate and ecological services of biochar-mineral complexes in soil and water.

Speciation of phosphorus in plant- and manure-derived biochars and its dissolution under various aqueous conditions

Phosphorus (P) in biochar serves as both a P source for plant growth and a contributor to water eutrophication, thus prioritizing the efficient management of P in biochar. This study employed solid- and solution- state ³¹P-nuclear magnetic resonance and X-ray diffraction analyses to explore the impact of feedstock and heating treatment temperature (HTT) on P species of biochars. The effects of ambient temperature, coexisting anions, pH and nutrient solution on P release were also investigated to study the effect of various environmental factors on P release from biochars. P species in both plant- and manure- derived biochars were dominated by inorganic orthophosphate and pyrophosphate (mainly calcium-bound-phosphates). The HTT of biochar showed a negative impact upon its pyrophosphate content. Compared with plant biochars, manure biochars contained higher P but had a lower release degree. Release of P from biochars was controlled by diffusion-dissolution process and was enhanced by higher ambient temperature, co-existing anions, and both acidic and alkaline conditions but inhibited by coexisting Hoagland nutrients. Anion-induced increase in P release was more significant for plant biochars than manure biochars. These findings help to adjust favorable environmental conditions for the full utilization of P in biochars.

A review on the demineralisation of pre- and post-pyrolysis biomass and tyre wastes

Pyrolysis is an attractive technology to convert low-cost carbonaceous waste materials into fuels, energy and other value added products goods. During pyrolysis, the inorganic minerals present in the feedstock can cause problems to the equipment and give side reactions. Besides, the minerals present in the chars can hinder their possible applications. Therefore, it seems necessary to eliminate said contaminants in order to valorise the aforementioned goods. Demineralisation is a process widely used for purifying materials that are contaminated with inorganic matter. Although this technique is commonly used with waste materials that will undergo pyrolysis, or the products obtained from it, the studies analysing this practise are rather scattered. The aim of this paper was to compile and review the current literature concerning the demineralisation of carbonaceous waste (tyres and lignocellulosic biomass) materials. The chemistry involved, feedstock type and the effect of performing the purifying step before or after pyrolysis were addressed in this work. The review revealed that biomass samples should be demineralised before pyrolysis in order to affect not only the char but also the bio-oil quality. Depending on the form in which the minerals are linked to the structure, the solvent chosen will vary (from water to strong acids). However, water is the most popular option due to its price and easy disposal. In tyres, demineralisation should be performed after pyrolysis using strong acid and subsequently base. Due to the crosslinked chemical structure, rubber is highly resistant to chemicals thus the pre-treatment has to be avoided.

Effect of minerals on the stability of biochar

The stability of biochar is a major determinant of its potential for carbon sequestration. In previous studies, the biochar stability was evaluated by analyzing the oxidation resistance property of biochar, for which, K₂Cr₂O₇/H₂O₂ oxidation and thermogravimetric analysis (TGA) were widely used to measure the high oxidation resistance of biochars. In this study, rice straw (RI)- and swine manure (SW)-derived biochars produced at different heating treatment temperatures (HTTs) and their corresponding de-ashed biochars and iron-biochars were selected to investigate the effect of minerals on these biochars stability. There was a significantly positive correlation between carbon remaining values (CRVs) obtained after K₂Cr₂O₇/H₂O₂ oxidation and ash (mineral) contents of biochars (p < 0.05). Moreover, the decreasing CRVs of most biochars were observed after de-ashing treatment. These K₂Cr₂O₇/H₂O₂ oxidation results indicated that endogenous minerals in biochars can protect biochars from chemical oxidation. On the other hand, the R₅₀ (C recalcitrance index) values of iron-biochars (33.3-57.4%) were lower than those of corresponding biochars (38.6-60.8%), indicating that Fe-bearing mineral formed in biochars can promote the thermal decomposition of biochars. In H₂O₂ oxidation, the different change trend of CRVs between biochars produced at 450 °C and biochars produced at 600 °C after iron mineral treatment showed that the effect of exogenous Fe-bearing mineral on biochar stability was related to biochar category regulated by HTTs. This study indicated that endogenous minerals could increase biochar stability, and exogenous Fe-bearing minerals had dissimilar effects on different kinds of biochars, which critically regulates the potential of biochar for long-term carbon sequestration.

Reduced bioavailability and plant uptake of polycyclic aromatic hydrocarbons from soil slurry amended with biochars pyrolyzed under various temperatures

Biochar has high potential for organic pollutant immobilization due to its powerful sorption capacity. Nevertheless, potential risks may exist when biochar-sorbed organic pollutants are bioavailable. A direct plant exposure assay in combination with an organic solvent extraction experiment was carried out in this study to investigate the bioavailability of polycyclic aromatic hydrocarbons (PAHs) with the application of pine needle biochars pyrolyzed under different temperatures (100, 300, 400, and 700 °C; referred as P100-P700 accordingly). Biochar reduced solvent extractability and plant uptake of PAHs including naphthalene (Naph), acenaphthene (Acen), phenanthrene (Phen), and pyrene (Pyr), especially for three- and four-ring PAHs (Phen and Pyr) with high-temperature biochar. Plant uptake assay validates with organic solvent extraction for bioavailability assessment. Sorption of PAHs to biochars reduced plant uptake of PAHs in roots and shoots by lowering freely dissolved PAHs. Aging process reduced the bioavailability of PAHs that were bound to biochar. High pyrolysis temperature can be recommended for biochar preparation for purpose of effectively immobilizing PAHs, whereas application of moderate-temperature biochar for PAH immobilization should concern the potential risks of desorption and bioavailability of PAHs.

Insight into Multiple and Multilevel Structures of Biochars and Their Potential Environmental Applications: A Critical Review

Biochar is the carbon-rich product of the pyrolysis of biomass under oxygen-limited conditions, and it has received increasing attention due to its multiple functions in the fields of climate change mitigation, sustainable agriculture, environmental control, and novel materials. To design a "smart" biochar for environmentally sustainable applications, one must understand recent advances in biochar molecular structures and explore potential applications to generalize upon structure-application relationships. In this review, multiple and multilevel structures of biochars are interpreted based on their elemental compositions, phase components, surface properties, and molecular structures. Applications such as carbon fixators, fertilizers, sorbents, and carbon-based materials are highlighted based on the biochar multilevel structures as well as their structure-application relationships. Further studies are suggested for more detailed biochar structural analysis and separation and for the combination of macroscopic and microscopic information to develop a higher-level biochar structural design for selective applications.

Isolation and characterization of biochar-derived organic matter fractions and their phenanthrene sorption

Chemical composition and pollutant sorption of biochar-derived organic matter fractions (BDOMs) are critical for understanding the long-term environmental significance of biochar. Phenanthrene (PHE) sorption by the humic acid-like (HAL) fractions isolated from plant straw- (PLABs) and animal manure-based (ANIBs) biochars, and the residue materials (RES) after HAL extraction was investigated. The HAL fraction comprised approximately 50% of organic carbon (OC) of the original biochars. Results of XPS and ¹³C NMR demonstrated that the biochar-derived HAL fractions mainly consisted of aromatic clusters substituted by carboxylic groups. The CO₂ cumulative surface area of BDOMs excluding PLAB-derived RES fractions was obviously lower than that of corresponding biochars. The sorption nonlinearity of PHE by the fresh biochars was significantly stronger than that of the BDOM fractions, implying that the BDOM fractions were more chemically homogeneous. The BDOMs generally exhibited comparable or higher OC-normalized distribution coefficients (K_oc) of PHE than the original biochars. The PHE logK_oc values of the fresh biochars correlated negatively with the micropore volumes due to steric hindrance effect. In contrast, a positive relationship between the sorption coefficients (K_d) of BDOMs and the micropore volumes was observed in this study, suggesting that pore filling could dominate PHE sorption by the BDOMs. The positive correlation between the PHE logK_oc values of the HAL fractions and the aromatic C contents indicates that PHE sorption by the HAL fractions was regulated by aromatic domains. The findings of this study improve our knowledge of the evolution of biochar properties after application and its potential environmental impacts.

Comparison of carbonized materials from wastes of different origin for nonylphenol removal by adsorption

The application of carbonized materials (CMs) from solid wastes for the control of hydrophobic organic contaminants is a promising way to treat wastes. In this paper, the physicochemical properties of CMs prepared from industry (fly ash and sewage sludge), plant (rice straw and bamboo fragments), and livestock (chicken manure) were analyzed, their adsorption capacities for nonylphenol were studied, and the relationship between the adsorption capacity and the physicochemical properties of different types of CMs was investigated. The results showed that the adsorption capacities of CMs prepared from plant solid wastes (rice straw and bamboo fragments) far exceeded those of the industrial and livestock solid wastes. The parameter K_f obtained by the Freundlich model showed a significant and positive correlation with carbon content (C%), carboxyl content, specific surface area (SSA), and pore volume, and a negative correlation with ash content (ash%). Compared with CMs produced by the other two types of solid wastes, CMs from the plant solid wastes had the characteristics of a large SSA, rich pore structure (especially mesoporous) and high aromaticity (high C%), which were the main reasons for their superior adsorption capacity. The results could provide a scientific basis for the utilization of solid wastes.

Data processing to support explication about effect of mineral constituents on temperature-dependent structural characterization of carbon fractions in sewage sludge-derived biochar

This dataset is the supplementary data for the summited research article Li et al., 2017 [1] and provides detailed data profiles to support the explication about mineral constituents' effect on temperature-dependent structural characterization of carbon fractions in sewage sludge-derived biochar. The elemental compositions of major inorganics in the sewage sludge were detected by X-ray fluorescence spectrometry (XRF, S2-Ranger, Bruker).The images from scanning electron microscope (SEM) were compared between unwashed and acid-washed samples, and revealed the effect of acid washing on the surface morphology and porosity of sewage sludge and the biochar. Peak deconvolution was conducted for the (002) peak of X-ray diffraction (XRD) patterns from the acid-washed samples, which provided information on structural parameters of the carbon stacking structure and the temperature-dependent structure evolution of sewage sludge biochar. Peak deconvolution was also carried out for Raman data of the samples with/without consideration of mineral constituents (aluminosilicates). Results of Raman peak deconvolution showed structure ordering evolution with pyrolysis temperature and evidenced the contribution of mineral constituents to the Raman signals.

Kinetic and isothermal adsorption-desorption of PAEs on biochars: effect of biomass feedstock, pyrolysis temperature, and mechanism implication of desorption hysteresis

Biochar has the potential to sequester biomass carbon efficiently into land, simultaneously while improving soil fertility and crop production. Biochar has also attracted attention as a potential sorbent for good performance on adsorption and immobilization of many organic pollutants such as phthalic acid esters (PAEs), a typical plasticizer in plastic and presenting a current environmental issue. Due to lack of investigation on the kinetic and thermodynamic adsorption-desorption of PAEs on biochar, we systematically assessed adsorption-desorption for two typical PAEs, dimethyl phthalate (DMP) and diethyl phthalate (DEP), using biochar derived from peanut hull and wheat straw at different pyrolysis temperatures (450, 550, and 650 °C). The aromaticity and specific surface area of biochars increased with the pyrolysis temperature, whereas the total amount of surface functional groups decreased. The quasi-second-order kinetic model could better describe the adsorption of DMP/DEP, and the adsorption capacity of wheat straw biochars was higher than that of peanut hull biochars, owing to the O-bearing functional groups of organic matter on exposed minerals within the biochars. The thermodynamic analysis showed that DMP/DEP adsorption on biochar is physically spontaneous and endothermic. The isothermal desorption and thermodynamic index of irreversibility indicated that DMP/DEP is stably adsorbed. Sorption of PAEs on biochar and the mechanism of desorption hysteresis provide insights relevant not only to the mitigation of plasticizer mobility but also to inform on the effect of biochar amendment on geochemical behavior of organic pollutants in the water and soil.

Effect of biochar particle size on hydrophobic organic compound sorption kinetics: Applicability of using representative size

Particle size of biochar may strongly affect the kinetics of hydrophobic organic compound (HOC) sorption. However, challenges exist in characterizing the effect of biochar particle size on the sorption kinetics because of the wide size range of biochar. The present study suggests a novel method to determine a representative value that can be used to show the dependence of HOC sorption kinetics to biochar particle size on the basis of an intra-particle diffusion model. Biochars derived from three different feedstocks are ground and sieved to obtain three daughter products each having different size distributions. Phenanthrene sorption kinetics to the biochars are well described by the intra-particle diffusion model with significantly greater sorption rates observed for finer grained biochars. The time to reach 95% of equilibrium for phenanthrene sorption to biochar is reduced from 4.6-17.9days for the original biochars to <1-4.6days for the powdered biochars with <125μm in size. A moderate linear correlation is found between the inverse square of the representative biochar particle radius obtained using particle size distribution analysis and the apparent phenanthrene sorption rates determined by the sorption kinetics experiments and normalized to account for the variation of the sorption rate-determining factors other than the biochar particle radius. The results suggest that the representative biochar particle radius reasonably describes the dependence of HOC sorption rates on biochar particle size.

Comparing the adsorption mechanism of Cd by rice straw pristine and KOH-modified biochar

Biochar was considered as an effective and novel sorbent for cadmium (Cd) adsorption from aqueous solution. In this study, the adsorption isotherm investigations were conducted to examine the effect of biochar produced via pyrolysis from rice straw on removing aqueous Cd before and after modification by 2 M KOH solution. Langmuir and Freundlich adsorption isotherms can preferably describe the adsorption process. Results showed that the highest adsorption capacity of pristine rice straw biochar was 12.17 mg g^-1. The chemically modified rice straw biochar showed greater Cd adsorption capacity of 41.9 mg g^-1, which was more than three times that of pristine biochar. Increase of surface area and changes of porous structure, especially the functional groups on the surface of modified biochar, were the major contributors to its more efficient adsorption of Cd. The possible mechanisms for Cd adsorption by biochar mainly involve (1) surface precipitation by forming insoluble Cd compounds in alkaline condition and (2) ion exchange for Cd with exchangeable cations in the biochar, such as calcium ions, which were confirmed by FTIR, XRD, SEM, and zeta potential determination.

Electronic-property dependent interactions between tetracycline and graphene nanomaterials in aqueous solution

Understanding the interactions between graphene nanomaterials (GNMs) and antibiotics in aqueous solution is critical to both the engineering applications of GNMs and the assessment of their potential impact on the fate and transport of antibiotics in the aquatic environment. In this study, adsorption of one common antibiotic, tetracycline, by graphene oxide (GO) and reduced graphene oxide (RGO) was examined with multi-walled carbon nanotubes (MWCNTs) and graphite as comparison. The results showed that the tetracycline adsorption capacity by the four selected carbonaceous materials on the unit mass basis followed an order of GO>RGO>MWCNTs>graphite. Upon normalization by surface area, graphite, RGO and MWCNTs had almost the same high tetracycline adsorption affinity while GO exhibited the lowest. We proposed π-electron-property dependent interaction mechanisms to explain the observed different adsorption behaviors. Density functional theory (DFT) calculations suggested that the oxygen-containing functional groups on GO surface reduced its π-electron-donating ability, and thus decreased the π-based interactions between tetracycline and GO surface. Comparison of adsorption efficiency at different pH indicated that electrostatic interaction also played an important role in tetracycline-GO interactions. Site energy analysis confirmed a highly heterogeneous distribution of the binding sites and strong tetracycline binding affinity of GO surface.

Preparation of biochar from Enteromorpha prolifera and its use for the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous solution

EP-biochar was produced from Enteromorpha prolifera (EP) at temperatures of 200-600°C under limited-oxygen conditions and then activated using HCl and HF. To optimize the sorption of pyrene (PYR) and benzo[a]pyrene (BaP), the effect of the pyrolysis temperature was studied, and the results showed that EP-biochar produced at 500°C gave the highest removal efficiency. The physiochemical properties of EP-biochar pyrolyzed at 500°C were characterized. The examination indicated that the surface area of EP-biochar was 205.32m²/g. The effect of the EP-biochar dosage and initial solution pH on the adsorption were studied in batch adsorption experiments. Kinetic studies indicated that the adsorption processes of PYR and BaP agreed well with a pseudo second-order kinetic model. The sorption equilibrium data were well described by the Langmuir model. Desorption experiments were conducted to test the strength of binding interactions of EP-biochar. The results showed that PYR and BaP were difficult to dissolve in water after adsorption. Regeneration experiments demonstrated that the biochars regenerated at 200°C retained approximately 48% and 40% of their initial PYR and BaP uptake.

Sorption mechanisms of neonicotinoids on biochars and the impact of deashing treatments on biochar structure and neonicotinoids sorption

To elucidate the sorption affinity of biochars for neonicotinoid pesticides and the influence of biochar structure on sorption mechanisms therein, 24 biochar samples were obtained by pyrolyzing maize straw and pig manure at pyrolyzing temperatures (PTs) of 200-700 °C and by further deashing them using acids, and the sorption of three typical neonicotinoids, imidacloprid, clothianidin and thiacloprid on untreated and acid-deashed biochars were evaluated. All the biochar samples could efficiently adsorb the three neonicotinoids and multiple mechanisms were involved in sorption. With the increasing PTs, hydrophobic partition sorption increased, but had a declined contribution to the total sorption as revealed by a dual-mode model. Besides hydrophobic partition, specific interactions like cation-π electron donor acceptor (EDA) interactions (only for protonated IMI and CLO) and hydrogen bond and contributed much to the sorption on low-PT (≤500 °C) biochars, while the sorption on those high-PT (>500 °C) biochars mainly depended on pore-filling strengthened by cation-π and p/π-π EDA interactions. Thiacloprid showed stronger sorption on untreated biochars compared to imidacloprid and clothianidin, due to its greater ability to form hydrogen bond and hydrophobic interactions. Acid-deashing treatments increased the relative percentage contents of organic carbon, bulk O, aromaticity and O-containing functional groups, surface area and pore volume of biochars. The ash can bind neonicotinoids by specific interactions but played a negative role in the whole sorption on high-PT biochars by covering the inner sorption sites of organic moieties and blocking the micropores in biochars. The results acquired in the present study will help us to get deep insight in the comprehensive sorption mechanisms of polar pesticides on biochar and the effects of biochar structure.

Effects of metal ions and pH on ofloxacin sorption to cassava residue-derived biochar

In this study, the impacts of various cations, cation strength and pH on ofloxacin (OFL) adsorption to cassava residue-derived biochars were determined. The associated adsorption mechanisms are discussed. The biochars were prepared at pyrolysis temperatures ranging from 350°C to 750°C, and labeled as CW350, CW450, CW550, CW650 and CW750. The Freundlich model provided the best fit to describe the adsorption capacity of OFL and the Freundlich coefficient (logK_f) increased with increasing pyrolysis temperature. The inclusion of Zn²⁺ or Al³⁺ increased OFL sorption capacities of five biochars, while Cu²⁺ reduced sorption to CW450 and CW550. No significant impacts on OFL sorption were observed in the presence of K⁺ and Ca²⁺. The concentration of Ca²⁺ affected the adsorption capacity of CW550, but had no significant impact on other biochars. The pH of OFL solution, ranging from 3 to 9, had no significant changes on OFL adsorption by all the tested biochars. Results of FTIR spectra and zeta potential indicated that electrostatic interactions, cationic exchange, metal bridging and micropore filling could be the main sorption mechanism between OFL and biochars. These studies indicated that cassava residue can be converted into biochars that are effective adsorbents for removing OFL from aqueous solution.

Comparison between Soil- and Biochar-Derived Humic Acids: Composition, Conformation, and Phenanthrene Sorption

Biochar-derived organic matter (BDOM) plays an important role in determining biochar's application potential in soil remediation. However, little is known about the physicochemical properties of BDOM and its sorption of hydrophobic organic compounds (HOCs). Humic acids (HAs) were extracted from oxidized biochars produced from plant straws and animal manures at 450 °C, and their sorption of phenanthrene, a representative of HOCs, was investigated. The organic carbon recovery of biochar-derived HAs (BDHAs) was 13.9-69.3%. The ¹³C NMR spectra of BDHAs mainly consisted of aromatic and carboxylic C, while those of soil-derived HAs (SDHAs) contained abundant signals in aliphatic region. BDHAs and SDHAs had comparable CO₂ cumulative surface areas. BDHAs were found to exhibit higher phenanthrene sorption than SDHAs. After the removal of amorphous aromatic components, the logK_oc values of BDHAs were significantly decreased, implying that amorphous aromatic C regulated phenanthrene sorption by BDHAs. In contrast, aliphatic moieties dominated phenanthrene sorption by SDHAs, as evidenced by the enhanced sorption after the removal of amorphous aromatics. This study clearly demonstrated the contrasting characteristics and sorption behaviors of BDHA and SDHA, indicating that biochar addition and subsequent weathering could greatly affect native organic matter properties and the fate of HOCs in biochar-amended soils.

Dynamic changes in atrazine and phenanthrene sorption behaviors during the aging of biochar in soils

The objective of this study was to elucidate the dynamic changes in the properties of biochar-amended soil and their sorption capacity for typical organic contaminants with increasing contact time between biochar and soil. To do so, biochars that were produced from pig manure at two temperatures were added to two soils, and the sorption behaviors of atrazine and phenanthrene (Phen) on soil-biochar mixtures aged for different times were investigated. Soils freshly amended with biochars showed a dramatic increase in the sorption of atrazine (up to 23.4 times at C _e = 0.01 S _w) and Phen (up to 3.12 times at C _e = 0.01 S _w) compared to the bare soils without biochars. The physicochemical properties of soil-biochar mixtures changed with aging time, which in turn affected the sorption capacity. After the biochar produced at 300 °C (BC300) was aged in soil, the sorption of atrazine and Phen by black soil (BS) and fluvo-aquic soil (FS) both increased by different extents, except the sorption of Phen on BS. However, after the biochar produced at 700 °C (BC700) was aged in soil, the sorption of atrazine on the two soils decreased markedly, which was sill 56.3% higher than that on the original soil, while an opposite trend was observed for Phen on the two soils. The complex change patterns could be due to the different dominant sorption mechanisms for different biochars and chemicals.

Comparative study for microcystin-LR sorption onto biochars produced from various plant- and animal-wastes at different pyrolysis temperatures: Influencing mechanisms of biochar properties

Diverse biochars produced from various feedstock sources (i.e., plant- and animal-wastes) at different pyrolysis temperatures (PTs) were characterized for their structural properties and sorption behaviors of aqueous microcystin-LR (MC-LR). Results indicated that MC-LR sorption capability of tested biochars varied as a function of biochar structural properties. Sorption mechanisms involved electrostatic attraction, pore-filling, hydrogen-bonding effect and π-π electron donor-acceptor interaction, but predominant mechanisms varied for different biochars. At the same PT (300 or 600°C), chicken manure-derived biochars (CMBs) exhibited stronger MC-LR sorption than others, with sorption coefficient (K_d) of 6.321-15.529Lg^-1 and 6.354-8.294Lg^-1 at aqueous equilibrium concentration (C_e) of 40 and 200μgL^-1, respectively. Higher mesoporosity, the point of zero charge and total surface groups concentration related to higher ash content of CMBs, which might be indispensable for enhancing MC-LR sorption. This study suggested that CMBs have great potential as low-cost sustainable sorbents to abate MC-LR contamination.

Aging impacts of low molecular weight organic acids (LMWOAs) on furfural production residue-derived biochars: Porosity, functional properties, and inorganic minerals

The aging of biochar by low molecular weight organic acids (LMWOAs), which are typical root-derived exudates, is not well understood. Three LMWOAs (ethanoic, malic, and citric acids) were employed to investigate their aging impacts on the biochars from furfural production residues at 300-600°C (BC300-600). The LMWOAs created abundant macropores in BC300, whereas they significantly increased the mesoporosity and surface area of BC600 by 13.5-27.0% and 44.6-61.5%, respectively. After LMWOA aging, the content of C and H of the biochars increased from 51.3-60.2% and 1.87-3.45% to 56.8-69.9% and 2.06-4.45%, respectively, but the O content decreased from 13.8-24.8% to 7.82-19.4% (except BC300). For carbon fraction in the biochars, the LMWOAs barely altered the bulk and surface functional properties during short-term aging. The LMWOAs facilitated the dissolution of minerals (e.g., K₂Mg(PO₃)₄, AlPO₄, and Pb₂P₂O₇) and correspondingly promoted the release of not only plant nutrients (K⁺, Ca²⁺, Mg²⁺, Fe³⁺, PO₄^3-, and SO₄^2-) but also toxic metals (Al³⁺ and Pb²⁺). This research provided systematic insights on the responses of biochar properties to LMWOAs and presented direct evidence for acid activation of inorganic minerals in the biochars by LMWOAs, which could enhance the understanding of environmental behaviors of biochars in rhizosphere soils.