Application of biochar for the removal of pollutants from aqueous solutions

Synergistic construction of green tea biochar supported nZVI for immobilization of lead in soil: A mechanistic investigation

Biochar-based nanocomposites with functional materials provide an excellent prospect in reactivity and stability. Most biochar reported have no reusability upon aging and offer the risk of release of immobilized components after short-term immobilization. To overcome this, we developed nano zero-valent iron (nZVI) impregnated magnetic green tea biochar (nZVI@GTBC) and studied its performance in immobilizing Pb and long-term effectiveness in the soil. The reactive nZVI units were obtained from iron oxide solution by reducing with polyphenol solution (green tea extract) and were successively stabilized by impregnation onto the remaining green tea waste matrix through co-precipitation technique. Finally, the magnetic biochar was developed from the above nZVI impregnated green tea waste through oven drying and slow pyrolysis technique in different temperature range (150-650 °C). The synthesized nZVI@GTBC biochar was characterized and studied by XRD, FTIR, Raman, UV-Vis, TG/DSC, XPS, SEM, and TEM. The nZVI@GTBC obtained with a particle size of 130 nm and surface charge of +2.8 C/m² at 450 °C. Moreover, colloidal stability and mobility experiments were considered to explain the transport behavior and stability of bare nZVI and magnetic nZVI@GTBC in the soil. The immobilization of Pb by pristine nZVI, GTBC, and nZVI@GTBC was compared and explained under different soil pH conditions. The bioavailability of Pb content before and after immobilization was investigated through leaching experiments. Further, thirty days of soil incubation were carried out to examine different species of Pb according to the Tessier sequential extraction scheme. The study suggested that nZVI@GTBC enhanced the immobilization efficiency by 19.38% in comparison with pristine nZVI and 57.14% in comparison with bare GTBC biochar.

Competitive sorption and availability of coexisting heavy metals in mining-contaminated soil: Contrasting effects of mesquite and fishbone biochars

Mesquite and fishbone were pyrolyzed to produce biochar (MBC and FBC, respectively) at different temperatures. The effects of the MBC and FBC on the removal of single and competitive metals (Cd, Pb, Zn, and Cu) from aqueous solutions were evaluated. A greenhouse pot experiment was also conducted using wheat plants with the mining-contaminated soils. In the presence of MBC or FBC (dosages of 15 and 30 g kg^-1), the bioavailability of co-existing Cd, Pb, Zn, Cu, Mn, and Fe were assessed. The results clearly indicated competitive adsorption among metals with the highest adsorption preference toward Pb. The removal efficiency and partition coefficient (PC) values of heavy metals for FBCs were higher than those for MBCs. These two values increased with MBC pyrolysis temperature under both single- and multi-metals adsorption conditions. Applying FBC to mining soil resulted in the highest reduction in most NH₄NO₃-extractable heavy metals, reducing their availability to wheat plants. At the highest application dosage of 30 g kg^-1, the highest metal immobilization, which accounted for 40.0% and 43.0% for Pb, 61.7% and 66.2% for Cu, 48.3% and 55.6% for Zn, and 32.7% and 33.8% for Cd, was achieved following the application of FBC400 and FBC600, respectively. However, applying MBC lead to a significant reduction in the availability of Cu and Pb but not that of Zn and Cd. FBC is thus more effective in removing heavy metal from aqueous solutions, as well as in immobilizing co-existing heavy metals in contaminated mining soil. It could, therefore, be an effective sorbent and immobilizing agent.

Co-processing of common plastics with pistachio hulls via hydrothermal liquefaction

Mixed, wet, plastic streams containing food waste residues are being increasingly collected at point of use, but are extremely challenging to recycle and are therefore largely sent to landfill. While a challenging waste problem, this also represents an underutilised feedstock, which could be co-processed with biomass, increasing the scope of products, easing out seasonal variation in biomass production and increasing the production capacity of a traditional biorefinery. One promising method of biomass conversion is hydrothermal liquefaction (HTL), where lignocellulosic residues are broken down in water at high temperatures and pressures to produce a bio-crude oil, a solid residue and an aqueous fertiliser. In this study, the co-processing of common plastic waste with pistachio hulls was assessed to investigate the suitability of the HTL approach. The HTL of pistachio hulls was undertaken at 350 °C over 15 and 60 min, with four commonly used plastics: polyethylene, polypropylene, PET and nylon-6, in blends of up to 20 wt% plastic to biomass. A novel FT-IR method was developed to estimate the conversion of plastics in the system, and the product phases were fully analysed. High yields of up to 35% bio-crude were achieved, and under optimal conditions, nylon-6 and PET were found to break down almost completely in the system. PET generated numerous products that distributed predominantly into the aqueous phase; the major decomposition product of nylon-6 was found to be the monomer ∊-caprolactam, also largely partitioning into the aqueous phase. The polyolefins were less reactive; a limited degree of decomposition formed oxidised products, which distributed into the bio-crude phase. This result represents a highly promising method for waste plastic valorisation.

Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

Cr(VI) contamination has posed great threat to both the ecosystem and human health for its carcinogenic and mutagenic nature. A highly effective adsorbent for the removal of Cr(VI) was prepared and its adsorption mechanism was thoroughly discussed in this study. In detail, magnetic BiFeO₃ and kenaf biochar were loaded on cross-linked chitosan to obtain chitosan-kenaf biochar@BiFeO₃ (CKB) for improving adsorption capacity towards Cr(VI). The adsorption process of Cr(VI) onto CKB was evaluated as a function of the pH, the existence of competing ions, the initial concentration of Cr(VI) and contact time. The results show that CKB exhibits the highest adsorption capacity under the optimal pH 2.0. The presence of competing ions such as Ca²⁺, NO₃⁻, SO₄²⁻, and Cl⁻ decreases the adsorption capacity; among them, Ca²⁺ and NO₃⁻ show the greatest hindrance. By studying the effect of initial Cr(VI) concentration on the adsorption capacity, it was found that CKB in the solution was enough to remove Cr(VI) for all treatments (10–200 mg/L). The adsorption experimental data were well fitted with pseudo-first-order model, suggesting that chemisorption is not the dominant rate-limiting step. Freundlich isotherm model can better explain the adsorption process, indicating a non-ideal adsorption towards Cr(VI) on a heterogeneous surface of CKB. A 2^5-1 Fractional Factorial Design (FFD) showed that pH and initial concentration of Cr(VI) have significant influence on Cr(VI) adsorption in our reaction system. In general, excellent adsorption efficiency of CKB indicates that it may be a good candidate for the remediation of Cr(VI)-contaminating wastewater.

Adsorption of 17β-estradiol from aqueous solution by raw and direct/pre/post-KOH treated lotus seedpod biochar

Five biochars derived from lotus seedpod (LSP) were applied to examine and compare the adsorption capacity of 17β-estradiol (E2) from aqueous solution. The effect of KOH activation and the order of activation steps on material properties were discussed. The effect of contact time, initial concentration, pH, ionic strength and humic acid on E2 adsorption were investigated in a batch adsorption process. Experimental results demonstrated that the pseudo second-order model fitted the experimental data best and that adsorption equilibrium was reached within 20 hr. The efficiency of E2 removal increased with increasing E2 concentration and decreased with the increase of ionic strength. E2 adsorption on LSP-derived biochar (BCs) was influenced little by humic acid, and slightly affected by the solution pH when its value ranged from 4.0 to 9.0, but considerably affected at pH 10.0. Low environmental temperature is favorable for E2 adsorption. Chemisorption, π-π interactions, monolayer adsorption and electrostatic interaction are the possible adsorption mechanisms. Comparative studies indicated that KOH activation and the order of activation steps had significant impacts on the material. Post-treated biochar exhibited better adsorption capacity for E2 than direct treated, pre-treated, and raw LSP biochar. Pyrolyzed biochar at higher temperature improved E2 removal. The excellent performance of BCs in removing E2 suggested that BCs have potential in E2 treatment and that the biochar directly treated by KOH would be a good choice for the treatment of E2 in aqueous solution, with its advantages of good efficiency and simple technology.

Use of microalgae based technology for the removal of antibiotics from wastewater: A review

The antibiotic resistance induced by the release of antibiotics to the environment has urged research towards developing effective technologies for antibiotic removal from wastewater. Traditional technologies such as activated sludge processes are not effective for antibiotic removal. Recently, microalgae-based technology has been explored as a potential alternative for the treatment of wastewater containing antibiotics by adsorption, accumulation, biodegradation, photodegradation, and hydrolysis. In this review, the toxicities of antibiotics on microalgae, the mechanisms of antibiotic removal by microalgae, and the integration of microalgae with other technologies such as ultraviolet irradiation (photocatalysis), advanced oxidation, and complementary microorganism degradation for antibiotic removal were discussed. The limitations of current microalgae-based technology and future research needs were also discussed.

Impact of spent mushroom substrate on Cd immobilization and soil property

This study aims to evaluate the potential of fresh spent mushroom substrate (SMS) in Cd immobilization and soil improvement, compared with spent mushroom substrate biochar (SMSB) and spent mushroom substrate compost (SMSC). A simulating remediation experiment was conducted with soil at Cd concentration of 0.6, 1.2, 1.8, and 2.4 mg kg^-1 and amendment addition ratio of 0.5%, 1%, 2%, and 4% for 90 days. At the end of incubation, it was found that 4%SMS addition showed the best effect both on Cd immobilization and soil improvement. It decreased Cd exchangeable fraction ratio by 52.77% (16.30% higher than 4%SMSC) and increased residual fraction ratio by 65.28% (36.34% and 49.64% higher than 4%SMSB and 4%SMSC, respectively); increased soil pH, EC, and CEC by 10.43% (3.83% higher than 4%SMSC), 11.54%, and 29.72%; and increased urease activity, sucrase activity, and catalase activity by 125.61% (43.90% and 8.54% higher than 4%SMSB and 4%SMSC, respectively), 79.46% (35.35% and 14.02% higher than 4%SMSB and 4%SMSC, respectively), and 75.68% (29.73% higher than 4%SMSB), compared with control treatment (CK) respectively. The results demonstrate that 4%SMS can be used as amendments for cadmium-contaminated soils.

Ex situ evaluation of the effects of biochars on environmental and toxicological availabilities of metals and polycyclic aromatic hydrocarbons

The present study experimented five biochars, one made from wood (400 °C, 12 h) and four made from miscanthus cultivated on contaminated soils (temperature 400/600 °C, duration 45/90 min). They were used as amendments at a 2% application rate on soil, cultivated or not cultivated with ryegrass, contaminated with (i) metals (Cd, Pb, and Zn), (ii) eight polycyclic aromatic hydrocarbons (PAHs), and (iii) a mix of metals and PAHs. The objectives were (i) to compare the effectiveness of the five biochars on soil parameters and pollutant availability and (ii) to determine the influence of soil multicontamination and ryegrass cultivation on biochar effectiveness. The results showed that biochar application did not necessarily lead to lower pollutant extractability and metal bioaccessibility. However, differences were highlighted between the biochars. The miscanthus biochars produced at 600 °C (BM600) showed higher effectiveness at decreasing metal extractability than the miscanthus biochars produced at 400 °C (BM400) due to its better sorption characteristics. In addition, ryegrass cultivation did not impact pollutant availability but modified metal bioaccessibility, especially for the soil amended with the BM600 and the woody biochar. Moreover, the presence of PAHs also negatively impacted the metal bioaccessibility in the soil amended with the BM600, and, on the contrary, positively impacted it in the soil amended with the BM400. Complementary studies are therefore necessary to understand the mechanisms involved, particularly in a context where soils requiring remediation operations are often multicontaminated and vegetated.

Recycling supercapacitor activated carbons for adsorption of silver (I) and chromium (VI) ions from aqueous solutions

In this study, we reported on the recycling of carbon materials from spent commercial supercapacitors and its application as low-cost adsorbent for high-efficiency removal of Ag(I) and Cr(VI) ions from aqueous solutions. Adsorption kinetics and isotherms, and effects of initial pH were carried out to investigate the adsorption performance of the recycled supercapacitor activated carbon (RSAC), whereas a series of characterizations such as SEM, EDX, BET, XPS, XRD and FTIR were employed to detailedly analyse the adsorption mechanism. The RSAC showed maximal adsorption capacity for Ag(I) and Cr(VI) of 104.0 and 96.3 mg g^-1, respectively, with adsorbent dosage of 2 g L^-1 and initial ions concentration of ∼2000 mg L^-1 at room temperature (23 ± 1 °C), and the adsorption was rapid and influenced by the initial pH value. The outstanding adsorption performance of RSAC was attributed to the high specific surface area (1403 m² g^-1) and abundant multifarious oxygenic groups which could participate in the electrostatic attraction and reduction reaction of Ag(I) and Cr(VI) during the adsorption process. Furthermore, the predominate species of the adsorbed toxic Ag(I) and Cr(VI) on the surface of RSAC was metallic silver particle (about 2 μm) and harmless Cr(III), respectively, thus it was possible for further recycling and disposal.

Waste shrimp shell-derived hydrochar as an emergent material for methyl orange removal in aqueous solutions

Shrimp processing and consumption generate large amounts of waste shrimp shell (WSS) rich in chitin and protein. Herein, we successfully synthesized WSS-based hydrochar (WSH) adsorbent through deproteinization and deacetylation followed by hydrothermal carbonization (HTC) and acid washing. For comparison, another hydrochar (CCH) adsorbent was synthesized from HTC of commercial chitosan under identical conditions. Specifically, WSH contained rich nitrogen-containing functional groups with a long aliphatic chains structure. Acid etching of calcium carbonate in WSS led to a higher specific surface area of WSH (12.65 m²/g) which was nearly 6 times higher than that of CCH (2.13 m²/g). The lower deacetylation degree of WSH was responsible for higher amide I and amino groups retained therein. Under an optimal initial solution pH of 4.0, WSH could rapidly achieve a superb adsorption capacity of 755.08 mg/g for methyl orange molecule. Moreover, the adsorption process followed a pseudo-second-order kinetics model and was well described by a monolayer adsorption pattern based on the Langmuir isotherm model with correlation coefficients higher than 0.9989. Prominent adsorption performance of WSH for methyl orange was mainly attributed to electrostatic interactions, while steric hindrance effect had a detrimental impact on the adsorption capacity of CCH. Superb adsorption capacity and excellent regeneration performance suggest WSH could be a promising and affordable adsorbent candidate for anionic dye removal.

Design and Preparation of Chitosan-Crosslinked Bismuth Ferrite/Biochar Coupled Magnetic Material for Methylene Blue Removal

Biochar obtained by pyrolysis of the fiber plant kenaf was mixed with bismuth ferrite (BiFeO₃) in a chitosan-containing acetic acid solution, magnetized, and modified to prepare a chitosan-crosslinked BiFeO₃/biochar coupled magnetic material. The adsorption properties of the composite were investigated using methylene blue dissolved in water, and the effects of external conditions, such as pH, methylene blue concentration, reaction time, and temperature, on the adsorption performance were studied. The adsorption data were fitted and analyzed with kinetic and isotherm models, and the results showed that the BiFeO₃/biochar coupled magnetic material effectively adsorbed methylene blue. The amounts adsorbed onto this magnetic material increased with increasing initial methylene blue concentration, reaction time, and temperature, and the adsorption performance improved under neutral and alkaline conditions. The pseudo-first-order kinetic and Langmuir isotherm models satisfactorily fitted the adsorption data, showing that the adsorption of methylene blue involved both chemical and physical adsorption. The maximum adsorption capacity of methylene blue onto the BiFeO₃/biochar coupled magnetic material reached 18.942 mg·g⁻¹ at 25 °C, confirming the excellent dye binding activity of this material.

Food Waste Materials as Low-Cost Adsorbents for the Removal of Volatile Organic Compounds from Wastewater

The aim of this work was to study the potential of food waste materials (banana peel, potato peel, apple peel, lemon peel, coffee waste, decaf coffee waste, grape waste, and carob peel) as low-cost adsorbents for the removal of aliphatic and aromatic volatile organic compounds (VOCs) from wastewater. The ability of examined food waste materials to adsorb VOCs from synthetic multi-component standard solutions was evaluated and the examined food waste materials showed high removal efficiency. Performances of coffee waste, grape waste, and lemon peel were detailed by using Trichloroethylene and p-Xylene in mono-component standard solutions. The adsorption capacity of the three selected food wastes was determined by using linear Langmuir and Freundlich isotherm models. Two errors functions, average percentage error (APE) and the chi-square test (χ²), were used for isotherm optimization prediction. Freundlich isotherm well described the adsorption of VOCs on the considered materials. According to the obtained results, a multilayer, physical, and cooperative adsorption process was hypothesized, particularly evident when the VOCs’ concentrations are high. This was confirmed by the high adsorption efficiency percentages (E% > 80%) of VOCs from a real polluted matrix (urban solid waste leachate), containing high concentrations of total organic content.

Efficient removal of Cd (II) from contaminated water and soils using nanoparticles from nitrogen fertilizer industry waste

BACKGROUND

Cadmium (Cd) is used extencively in many industries and can cause environmenal pollution and severe damage to human health. As millions of tons of lime-based solid by-product from nitrogen fertilizer industry (NFIB) are produced each year, the main purpose of this study was to develop a novel, efficient and cheap nanoscale sorbent from NFIB for remediation of Cd (II) contaminated soil and water to protect and preserve public and ecosystem health.

METHODS

A novel nanoscale adsorbent was developed from the nitrogen fertilizer industry byproduct (NFIB) and was characterized using X-ray diffraction(XRD) and scanning electron microscope (SEM). Batch sorption equilibrium and kinetic experiments were conducted to evaluate the efficiency of nano- NFIB (nNFIB) in sequestering Cd(II) in contaminated soil and water.

RESULTS

The results of adorption equilibrium and kinetics experiments revealed that Langmuir and power function models best described Cd adsorption on bulk NFIB and nNFIB as evidenced by high R²(determination coefficient) and low SE(standard error of estimates) values. The Langmuir maximum adsorption capacity (q푞_max) of nNFIB for Cd(II) was 100 mg g^-1 which is twenty times higher than that of Bulk NFIB. The distinguishing features of NIFB nanoparticles involve efficient removal of Cd(II) from contaminated water (>90%) and enhancement of Cd (II) immobilization (146%) in cotaminated soil.Fourier Transmission Infrared (FTIR) spectra of Cd(II) contaminated water and soil before and after nNFIB application revealed the important rule of calcite nanoparticles in Cd(II) sequestration.

CONCLUSIONS

The accessibility, low cost, and Cd sequestration efficiency of nNFIB nominate it to be an economic and a promised adsorbent for environmental remediation.

Activated carbon biochar from municipal waste as a sorptive agent for the removal of polyaromatic hydrocarbons (PAHs), phenols and petroleum based compounds in contaminated liquids

Wastewater (WW) sludge cake is problematic to dispose of with treatment unable to remove organic pollutants. Typical disposal options include landfill or deposition on agricultural land, at considerable expense and environmental impact. Pyrolysis can recycle this waste to biochar however, additional unwanted organic pollutants are generated, differing in composition and volume according to the feedstock. These pollutants can be captured in solvent impingers or 'scrubbers' to avoid environmental release but lead to alternative waste. Both activated carbon and biochar are proven clean-up methods for organic pollutants with pine wood biochar showing changes in extraction selectivity with preparation temperature. Activated carbon biochar (ACB) from pine wood has also been successfully compared as a substitute at reduced cost and improved efficacy. To our knowledge, ACB from sludge cake has remained untested along with its application to clean-up solvent scrubbers. We have investigated this material from two WW treatment plants (UK and Ghana) as a sorbent, generated at 400 and 700 °C, to minimise contamination of liquids from pyrolysis and, petrochemicals in the event of a spill. This study confirmed the use and selective production of ACB for preferential clean-up of specific pollutants. Despite high temperature pine wood ACB proving most effective in removing petrochemical mixtures (>76%) extractions of equivalent repeatability and reasonable recovery were achieved with low temperature sludge cake ACB. This re-use of waste sludge cake offers improved thermochemical (recycling) and WW process efficiency, limiting the environmental impact and overall operational costs, minimising waste for disposal.

Adsorption of copper(II) and lead(II) from seawater using hydrothermal biochar derived from Enteromorpha

The objective of this research was to evaluate the capacity of Enteromorpha derived biochar to adsorb heavy metals from seawater. The biochar characteristics were determined, and isothermal and kinetic data were obtained using batch experiments. Copper [Cu(II)] and lead [Pb(II)] adsorption by the biochar was favored by high pH conditions, while elevated salinity had a relatively weak negative effect on adsorption. The Langmuir isotherm and adsorption kinetics pattern enabled interpretation of the equilibrium and kinetics of Cu(II) and Pb(II) removal by the biochar. The maximum removal rates of Cu(II) and Pb(II) by the biochar in 60 min were estimated to be 91% and 54%, respectively. A model describing the adsorption processes was developed to predict the efficiency of heavy metal removal by the biochar. The outcomes of the present study indicate that Enteromorpha derived biochar could be an effective and environmentally friendly adsorbent for removing heavy metals from marine environments.

Metal-free activation of persulfates by corn stalk biochar for the degradation of antibiotic norfloxacin: Activation factors and degradation mechanism

This study investigated the degradation of norfloxacin by persulfate activated with corn stalk biochar. The results demonstrate that corn stalk biochar is a green and low-cost carbon material with excellent catalytic activity for the metal-free activation of persulfate to degrade norfloxacin. The removal rate of norfloxacin increased with the increase in the dosage of persulfate, but the increased ratio gradually decreased. With alcohols and phenols as free radical trapping agents, it was determined that norfloxacin degradation by SO- 4· and HO· in the biochar/persulfate system occurred mainly on the surface or boundary layer of biochar. pH has an important effect on norfloxacin degradation in the biochar/persulfate system. Norfloxacin degradation performances under different initial pH conditions are decreased according to the following order: (initial pH 6.5) > (initial pH 3.4) > (initial pH 10.6). The effects of pH on norfloxacin degradation in the biochar/persulfate system was mainly realized through affecting norfloxacin adsorption on corn stalk biochar surface.

Optimization of biochar preparation from the stem of Eichhornia crassipes using response surface methodology on adsorption of Cd2

In this study, preparation of Eichhornia crassipes stem biochar (ECSBC) was optimized and applied for the removal of Cd²⁺ from aqueous solution. To obtain the best adsorption capacity of ECSBC, the response surface methodology (RSM) was used to optimize the preparation conditions of ECSBC (OECSBC). The interactions among heating time (X₁), heating temperature (X₂) and heating rate (X₃) were designed by Box-Behnken Design (BBD) experiments. The software gave seventeen runs experiment within the optimal conditions towards two response variables (removal rate and adsorption capacity for Cd²⁺). The results showed that the mathematical model could fit the experimental data very well and the significance of the influence factors followed the order as heating temperature (X₂) > heating rate (X₃) > heating time (X₁), and the influence of interaction term is: X₁ and X₂ (heating time and heating temperature) > X₂ and X₃ (heating temperature and heating rate) > X₁ and X₃ (heating time and heating rate). Based on the analysis of variance and the method of numerical expected function, the optimal conditions were heating time of 2.42 h, heating temperature of 393 °C, and heating rate of 15.56 °C/min. Under the optimum conditions, the predicted the maximum removal rate and adsorption capacity were 85.2724% and 21.168 mg/g, respectively, and the experimental value of removal rate and adsorption capacity for Cd²⁺ were 80.70% and 20.175 mg/g, respectively, the deviation from the predicted value were 5.36% and 4.69%. The results confirmed that the RSM can optimize the preparation conditions of ECSBC, and the adsorption capacity of OECSB was improved.

β-Cyclodextrin-loaded minerals as novel sorbents for enhanced adsorption of Cd2+ and Pb2+ from aqueous solutions

The use of minerals to capture heavy metal pollution is limited by their capacity. Here, β-cyclodextrin (β-CD) with a good ability to capture heavy metals is loaded onto the surface of zeolite and vermiculite to adsorb lead and cadmium ions. Using epichlorohydrin (EPI) as a crosslinking agent, β-CD is loaded onto zeolite and vermiculite, as confirmed by a characterization analysis. Isothermal adsorption of Cd²⁺ and Pb²⁺ by the loaded minerals is tested at different concentrations, while contact time, pH, and kinetic and thermodynamic characteristics of the adsorption processes are analyzed. The amount of β-CD and crosslinker loaded onto a unit mass of zeolite is higher than that of vermiculite due to the unique porous structure of the zeolite surface. After β-CD loading, the adsorption saturation of zeolite for Cd²⁺ and Pb²⁺ are 93.06 and 175.25 mg/g, respectively. The adsorption saturation of Cd²⁺ and Pd²⁺ by β-CD-loaded vermiculite is 68.65 and 126.35 mg/g, respectively. The mechanism study revealed that the adsorption process of lead and cadmium ions by β-CD-loaded minerals was combined by diffusional movement with a chemical exchange of ionizable protons or cations, as well as by chemical bonding among heavy metal ions and functional groups (-OH, -COOH and CO).

Effect of fulvic acid coating on biochar surface structure and sorption properties towards 4-chlorophenol

Fulvic acid (FA) in soil ubiquitously affected the long-term benefits of biochars as soil amendments. The sorption of ionizable organic pollutants on biochars was complicated by FA because of the presence of ionic groups. To investigate the effect of FA coating on the interaction between biochars and 4-chlorophenol (4-CP), sorption isotherms at pH 4.0 and 12.0 and pH-sorption edge curves were generated. The biochars derived from platane wood were pyrolyzed at 300°C, 500°C and 700°C, resulting in low-, medium- and high-temperature biochars, respectively. The FA coating increased the surface area of the low-temperature biochar but decreased those of the medium- and high-temperature biochars. After coating biochars with FA, the aromaticity and the surface charge of the biochars decreased, but the content of oxygen-containing functional groups, especially carboxyl groups, on the biochar surfaces increased. The results from the sorption isotherm and pH-sorption edge curves showed that FA coating inhibited the sorption under alkaline conditions but did not change the sorption under acidic conditions, which indicated that coating by FA not only occupied the sorption sites but also strengthened the hydrogen bonding between 4-CP and biochars. As determined by characterization of biochars before and after coating, the number of carboxyl groups on the biochar surface increased after coating, which participated in hydrogen bonding with the hydroxyl groups of non-dissociated 4-CP. This research indicated that FA in the soil influenced the interaction between biochar with 4-CP, and the influences varied mainly due to the formation of hydrogen bonds at different pH values. This study could help us better understand the environmental behavior of biochar after aging, and provided a reference for sustainable utilization of biochar.

A review of biochar-based sorbents for separation of heavy metals from water

Biochar is the low-cost and environmental-friendly material which has shown a great potential for separation of heavy metals from water. The previous studies have established a superior role of biochar over other materials, such as activated carbon and inorganic sorbents (iron based) in efficient removal of toxic heavy metals from aqueous systems. Among the various factors influencing heavy metals sorption ability of biochar, types of feedstock/biomass and pyrolysis temperature play a significant role. The goal of this review is to increase our understanding of heavy metals sorption behavior by biochars - this is important as heavy metals sorption is driven based on biochar type, heavy metals species which involve numerous mechanisms, including the physical binding, complexation, ion exchange, surface precipitation and electrostatic interactions. In addition, this review paper describes various approaches to improve heavy metal sorption capacity of biochars by steam and acids/bases activations and impregnation of biochar-based composites with minerals, organic compounds and carbon-rich materials. The physical/chemical activation of biochars can improve the surface area, thus leading to their improved functionality, while modification/pretreatment methods help in synthesizing composites using biochar as a supporting media to develop new sorbents with efficient surface attributes for heavy metals removal from aqueous solutions.

Comparative production of biochars from corn stalk and cow manure

The aim of the present work was to compare corn stalk (CS) and cow manure (CM) for hydrochar production at different reaction temperatures (180-260 °C) and retention times (1-4 h). CM and CS resulted in hydrochars with significantly different physicochemical properties; however, both led to similar yields (30-65%). CM-derived hydrochar had a lower carbon content but a higher nitrogen and ash content than CS-derived hydrochar. CM-derived hydrochar demonstrated potential as a soil amendment due to its higher content of nitrogen, the presence of surface functional groups and higher specific surface area in comparison to CS-derived hydrochar. In comparison, CS-derived hydrochar demonstrated suitability as a solid fuel due to its high heating value and low ignition temperature. This study revealed that the composition of lignocellulose significantly impacted the properties and thus potential applications of hydrochar.

Photo-induced redox coupling of dissolved organic matter and iron in biochars and soil system: Enhanced mobility of arsenic

Dissolved organic matter (DOM) elucidated from biochars enhances the dissolution of iron oxides and reduction of iron. However, given that reduction mechanism of iron (Fe(III)) in the practical biochar applications for soil amendment and environmental remediation have not been fully elucidated, this study laid great emphasis on the photo-induced Fe(II) liberated from DOM-Fe(III) complexes. Thus, pyrolysis of biomass was carried out at 300 °C to maximize DOM release from biochars. Moreover, three different biomass samples (rice straw (R), granular sludge (G) from an anaerobic digester, and spent coffee grounds (C)) were chosen as carbon substrates for biochars preparation. To demonstrate the transformation of Fe(III), 1 and 5 wt% biochar was applied to the clean (S1) and arsenic-contaminated (S2) soil with/without the light. The results indicate that the light condition produces more Fe(II). The amount of Fe(II) accounts for 25.3, 28.6, and 30.7% of total iron under the light with 5 wt% GB, RB, and CB in S1, and 10.6, 13.1, and 13.8% in S2. This study demonstrates that Fe(II) is generated more under ultraviolet irradiation than visible light and dark condition. In addition, a control experiment without biochar showed that DOM plays an important role in the reduction of Fe(III). The mobility of arsenic increased under the light condition since the intermediates of DOM photo-degradation accelerates the dissolution of iron oxides and arsenic competes with DOM for the adsorption. Therefore, there was no significant correlation between the elution of arsenic and the formation of Fe(II) during the reductive dissolution of iron oxide under the light condition.

Functional and structural roles of wiry and sturdy rooted emerged macrophytes root functional traits in the abatement of nutrients and metals

Macrophytes root functional traits (RFTs) play central roles in the cycling of aquatic contaminants, and there is evidence that emerged macrophytes differ in macronutrients (N and P) and heavy metals (Cd, Cr, Cu, Ni, Pb, V, Zn) abatement due to difference in RFTs. However, it remains ambiguous what root type of emerged macrophytes and their RFTs play more significant roles in the mineralization and removal of nutrients and heavy metals in aquatic systems. There is a clear need of intensive investigation on fibrous- and thick-root emerged macrophytes and their diverse RFTs in previous literatures to identify appropriate plants for phytoremediation technology. Morphological, physiological, anatomical, and symbiotic RFTs of fibrous-root emerged macrophytes favour the nutrients and heavy metals uptake. Thick-root emerged macrophytes with greater root rhizomes, lignifications and suberization illustrate tolerance under higher stress. Besides higher removal abilities of fibrous-root macrophytes, their limited lifespan and stress tolerance are the challenges for long-term removal of metals. Thus, it is still infancy to wrap up at once that the fibrous-root macrophytes and their RFTs are equally efficient for removal of heavy metals from aquatic ecosystems. Several advance techniques include cisgenesis intragenesis, symbiotic endophytes, and plant-harboring microbes are emerging to improve the RFTs of plants. These techniques need to be employed in emerged macrophytes to achieve desirable RFTs and targets. Still, these macrophytes require advanced studies on emerging contaminants, such as pharmaceutical and personal care products, organic carbon stability, and mitigation of greenhouse gases emission.

Influence of amendments on metal environmental and toxicological availability in highly contaminated brownfield and agricultural soils

The immobilizing effects of wood biochar (BW2%) and iron grit (Z1%) applied alone or in combination (BW2% + Z1%) to agricultural (M750) and brownfield (MAZ) soils highly contaminated by metals were assessed in a greenhouse experiment. The results showed that Z1% and BW2% + Z1% were the most efficient amendments to reduce Cd, Cu, Pb, and Zn mobility, environmental availability, and phytoavailability in the M750 soil. The oxidation of Z1% allowed part of the Cu and Zn pools present in exchangeable or carbonate-bound forms (labile fraction) to complex in less mobile forms. In this soil, the metal chemical extractions (0.01 M CaCl₂ and 0.05 M EDTA) and the DGT (diffusive gradient in thin films) devices to assess metal in soil solution and soil pore water (SPW) also highlighted the immobilizing characteristic of Z1%. In most cases, the addition of BW2% to Z1% (BW2% + Z1%) did not improve this effect, except for the dissolved Pb and Zn concentrations in the M750 soil solution. It was also observed that Cd, Pb, and Zn passed throughout DGT mimicking the biological cell membrane were reduced by all amendments of the M750 soil corroborating metal concentrations measured in rye grass shoots. In the MAZ soil, metals were less available as shown by their low extractability rate, low capacity of metal resupply from the solid phase to pore water, and low phytoavailability. The poor metal availability could be explained by the high levels of carbonate and organic matter contents in this soil. Nevertheless, a decrease of the Cu environmental availability and the Cu concentrations in rye grass shoots grown on the MAZ soil was also observed in the soil amended with Z1% alone or in combination with BW2%. From a health point of view, the most effective amendment to reduce human exposure through ingestion of soil particles for the M750 and MAZ soils was BW2% for Cd and BW2% + Z1% for Pb. However, the presence of rye grass minimized the amendments' beneficial effects.

High adsorptive potential of calcined magnetic biochar derived from banana peels for Cu2+, Hg2+, and Zn2+ ions removal in single and ternary systems

The use of banana peel as a sustainable and low-cost precursor for the fabrication of effective biochar was exploited. Here, calcined magnetic biochar (CMB) was fabricated and characterized. CMB possesses surface acidic functional groups (-OH and COO^-), porous structures, high saturation magnetization (39.55 emu/g), and larger surface area than the non-magnetic biochar (CB). The CMB adsorption performance (72.8, 75.9, and 83.4 mg/g for Zn²⁺, Cu²⁺, and Hg²⁺, respectively at pH 6) in a single component was described suitably by pseudo-second order kinetic model, Langmuir, and Redlich-Peterson adsorption isotherms. Notably, the selectivity factor values in the extended Langmuir isotherm indicated that CMB has higher adsorption affinity toward Hg²⁺ than Cu²⁺ and Zn²⁺ in the multi-component system. Owing to its high adsorption efficiency and fast and easy separation, the calcined magnetic biochar is considered promising and effective for the purification of heavy metal-bearing wastewater.

Degradation of phenanthrene and fluoranthene in a slurry bioreactor using free and Ca-alginate-immobilized Sphingomonas pseudosanguinis and Pseudomonas stutzeri bacteria

Biodegradation studies of three- and four-ring polycyclic aromatic hydrocarbons (PAHs) (phenanthrene [PHE] and fluoranthene [FLU]) were conducted using free and Ca-alginate-immobilized Sphingomonas pseudosanguinis strain J1-q (S1) and Pseudomonas stutzeri strain (S2) in bench-scale sediment slurry reactors. In this study, the effects of sodium alginate (SA) dosage on the characteristics of immobilized bacterial beads were investigated. The results indicated a 3% alginate concentration was optimal for immobilizing bacteria for PHE and FLU degradation. Scanning electron microscopy (SEM) images of the immobilized beads showed the presence of honeycomb structures and abundant interstices in the beads, which provided adequate space for microorganism adhesion and proliferation. The biodegradation of PHE and FLU using both free and immobilized bacteria fit a first-order reaction model well. The degradation efficiencies of PHE and FLU using immobilized bacteria were higher than those of free bacteria in sediment slurry reactors. The removal percentages of PHE and FLU using immobilized indigenous bacteria strain S1 after 42 d were 63.16% and 56.94%, respectively, which were higher than the removal percentages of exogenous strain S2.

A novel Fe3O4/graphene oxide/citrus peel-derived bio-char based nanocomposite with enhanced adsorption affinity and sensitivity of ciprofloxacin and sparfloxacin

To create more active adsorption sites on biochar, the Fe₃O₄/GO/citrus peel-derived magnetic bio-nanocomposite (mGOCP) with hierarchically porous architectures was synthesized by a facile one-pot hydrothermal approach for efficient removal of fluoroquinolone antibiotics ciprofloxacin (CIP) and sparfloxacin (SPA). The characterization analysis of bio-nanocomposites showed that the incorporation of GO could ensure relatively higher surface area (1556 cm² g^-1), more abundant pore structure, and higher thermal stability within mGOCP bio-nanocomposites than Fe₃O₄/citrus peel-derived magnetic bio-nanocomposites (mCP). And the mGOCP-1% attained outstanding adsorption capacity for CIP (283.44 mg g^-1) and SPA (502.37 mg g^-1), respectively. The primary adsorption mechanisms for CIP and SPA included π-π electron donor-acceptor interaction, H-bonding, hydrophobic interaction and electrostatic interaction. Overall, the surface morphology and structural composition of biochars could be regulated with GO to facilitate the adsorption capacity. Moreover, the developed mGOCP could be extended as a potential adsorbent for removal of other emerging organic pollutants in water.

Coating magnetic biochar with humic acid for high efficient removal of fluoroquinolone antibiotics in water

As antibiotics are widely consumed, fluoroquinolones (FQs) behave to have huge hidden danger to human health. Various agricultural residues have potential to produce biochar rich in porous structure for adsorption of contaminants. In this study, potato leaves and stems were pyrolyzed at 500 °C under anoxic condition for biochar (BC) preparation. At the same conditions, magnetic biochar (MBC) and humic acid (HA) coated magnetic biochar (HAB) were also prepared. In particular, characterizations of HAB showed the extensive coating of HA on MBC surface and introducing more oxygen-containing groups, which may promote the adsorption capacity of biochar. Three typical FQs (ciprofloxacin (CIP), norfloxacin (NOR) and enrofloxacin (ENR)) were used as target contaminants to further investigate the adsorption property of HAB. Compared with BC and MBC, novel adsorbent HAB due to introduction of HA exhibited better FQs adsorption ability, and its maximum adsorption capacity for CIP, NOR and ENR were 1.80, 1.67 and 1.70 times higher than those of MBC and were 3.40, 2.88, 2.96 times higher than those of raw BC, respectively. Pseudo-second-order kinetic model and Langmuir isotherm model could describe the process of FQs adsorbed on HAB more appropriately, and thermodynamic results illustrated that the sorption process was spontaneous and endothermic. In addition, FQs adsorption by HAB was increased with initial solution pH from 3.0 to 10.0, while it was slightly decreased with ionic strength rising (0.001-0.1 M CaCl₂). Combined with FTIR results, high FQs removal efficiency could be attributed to electrostatic, hydrophobic, H-bond and π-π EDA interactions.

Interaction with low molecular weight organic acids affects the electron shuttling of biochar for Cr(VI) reduction

Biochar can act as "electron shuttle" in soil redox reactions. It is possible that biochar accepts the electrons from low molecular weight organic acids (LMWOAs) in soil and then transfer them to the acceptors, e.g., Cr(VI). This study evaluated the interaction between seven soil LMWOAs and peanut shell biochar (BC) as well as its effect on the electron shuttling of biochar for Cr(VI) reduction. Both redox reactions and sorption process occurred during the interaction of biochar and LMWOAs, which altered the contents of Cr(VI) reduction-relevant groups (i.e., CO and CO) on the surface of biochar. The redox reactions were more important to the electron transfer between biochar produced at 400℃ (BC400) and LMWOAs due to the repeated cycle of reduction-oxidation of surface functional groups. The reduction rate of Cr(VI) by LMWOAs mediated by BC400 was 1.10-7.09 × 10^-3 h^-1, among which tartaric acid had the best reduction efficiency due to its highest reducing capability. For biochar produced at 700℃ (BC700), the sorption process of LMWOAs was the key factor to the direct electron shuttling process through the conjugated structure of biochar. The reduction rate of Cr(VI) by LMWOAs mediated by BC700 was significantly higher and ranged 7.40-864 × 10^-3 h^-1, with the oxalic acid having the best reduction efficiency due to its highest sorption capacity by BC700. The results obtained from this study can help to establish the linkage between biochar and LMWOAs in soil electron network, which better explains the multifunctional roles of biochar during the redox processes such as Cr(VI) reduction in soil.

Similarities and differences in adsorption mechanism of dichlorvos and pymetrozine insecticides with coconut fiber biowaste sorbent

In this study, the similarities and differences of the adsorption mechanisms between dichlorvos and pymetrozine and coconut fiber biowaste sorbent (CF-BWS) were investigated. CF-BWS was produced using the slow pyrolysis process at 600 °C for 4 h. HCl acid modification was used to improve the specific surface area. The properties of CF-BWS were analyzed by SEM, FT-IR, BET, and pHpzc. The adsorption kinetics of dichlorvos and pymetrozine on the CF-BWS were well explained by the pseudo-second-order model. The adsorption isotherms for both insecticides were followed the Langmuir isotherm. The difference in molecular structures and surface chemistry caused the difference in adsorption mechanisms of both insecticides. The pore-filling and the hydrophobic interactions were the key mechanisms for both insecticide adsorptions. However, the π-π electron donor-acceptor interaction played the major role in the pymetrozine adsorption but hardly impacted on the adsorption of dichlorvos. The hydrogen bonding mechanism was pronounced in the pymetrozine adsorption, but it had little influence on the dichlorvos adsorption. The CF-BWS is exhibited as an excellent material for the removal of both pollutants and has high potential to be used further as the adsorbent in water treatment process.

Novel lanthanum doped biochars derived from lignocellulosic wastes for efficient phosphate removal and regeneration

Phosphorus reduction from wastewater is vital to mitigate eutrophication of receiving waters. In this study, discarded lignocellulose biochar loaded with lanthanum (defined as La-biochar) was applied for phosphate adsorption. Based on the design of response surface methodology, La-biochar displayed a high phosphate adsorption capacity of 36.06 mg P/g, strong pH-compatibility from 3 to 12, favorable selectivity for phosphate among foreign ions (Cl^-, SO₄^2-, CO₃^2-, HCO₃^- and NO₃^-), excellent reusability with 92.3% desorption efficiency and retained 85% adsorption capacity after five recycles. The adsorption law of La-biochar perfectly matched with the pseudo-second-order model and the Langmuir model. Moreover, real wastewater adsorption experiments indicated the removal of total phosphorus within 20 min. Ligand exchange, electrostatic attraction, and complexation mechanisms contributed to phosphate adsorption on La-biochar. Overall, the La-biochar material could be applied as a potential sustainable building block for the preconcentration of phosphorus for practical pollutant purification.

Ni-doped MIL-53(Fe) nanoparticles for optimized doxycycline removal by using response surface methodology from aqueous solution

This study proposes a facile one-pot solvothermal method to prepare Ni-doped MIL-53(Fe) nanoparticles as high-performance adsorbents for doxycycline removal. The morphology and structure of the samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infrared spectrum and thermogravimetric analysis. These results reveal that nickel was doped into MIL-53(Fe) successfully via a facile reaction, and the obtained Ni-doped MIL-53(Fe) nanoparticles showed excellent stability. The adsorption activities were evaluated in terms of the removal efficiencies of doxycycline (DOX) in aqueous solution. According to the response surface quadratic model (RSM), the optimal adsorption conditions were concentration of DOX 100 mg/L, temperature 35 °C, ionic strength 5 g/L and pH 7. The as-synthesized Ni-doped MIL-53(Fe) nanoparticles showed better adsorption capacity of 397.22 mg/g compared with other adsorbents. The investigation of adsorption mechanism demonstrated that the adsorption process was dominated by electrostatic and π-π stacking interactions. The Ni-doped MIL-53(Fe) nanoparticles with improved adsorption activities would have a great potential in DOX removal from aqueous environment.

Functionalized Biochar/Clay Composites for Reducing the Bioavailable Fraction of Arsenic and Cadmium in River Sediment

Biochar has frequently been used for the treatment of heavy metal pollution in water and soil; its effect on contaminated sediments requires further research. To improve the ability of biochar to immobilize heavy metals in sediment, we prepared a functionalized biochar/attapulgite composite by pyrolysis of the clay attapulgite and zinc chloride-pretreated rice straw biomass. Compared with the original biochar, the biochar/attapulgite composite had a large increase in specific surface area, pore volume, oxygen-containing functional groups, and cation exchange capacity. Biochar effectively improved the dispersibility of attapulgite as a matrix. The results showed that the biochar/attapulgite composite effectively reduced the bioavailable fraction of arsenic (As) and cadmium (Cd) in river sediment, which was a great improvement compared with the raw biochar. After the sediment was treated with different biochar/attapulgite composites, the concentrations of As and Cd in the overlying water and the porewater, and the content of acid-extractable and toxicity characteristic leaching procedure (TCLP)-extractable As and Cd in the solid phase of the sediment decreased significantly. Both zinc chloride activation and attapulgite improved As and Cd immobilization in sediment when we used the biochar/attapulgite composite. The results suggest that biochar/attapulgite composite can be used as an efficient in situ sorbent amendment to improve the heavy metal immobilization ability of the sediment. Environ Toxicol Chem 2019;38:2337-2347. © 2019 SETAC.

Consecutive reduction of Cr(VI) by Fe(II) formed through photo-reaction of iron-dissolved organic matter originated from biochar

Employing biochar for environmental remediation has been widely practiced. Nonetheless, the reduction mechanisms of hexavalent chromium (Cr(VI)) in the presence of biochar have not been fully elucidated (i.e., direct or indirect reduction of Cr(VI) by biochar). In particular, the effect of light on Cr(VI) reduction by biochar was rarely reported. Thus, to clarify the reduction mechanisms of Cr(VI) by biochar at the fundamental level, this study laid great emphasis on the photo-induced reduction of Cr(VI) in the application of biochar. Biochar releases dissolved organic matter (DOM), the DOM can extract Fe(III) from soil by complexation, and the complexes can be photo-reacted under the light. In these respects, Fe(II) formed by the photo-induced reaction of DOM-Fe(III) was particularly evaluated in this study. To evaluate that, three biomass samples (rice straw, granular sludge from an up-flow anaerobic sludge blanket, and spent coffee ground) were torrefied to biochar. To circumvent the adsorption of Cr(VI) onto biochar, biochar extractives (served as a source for DOM) and Fe(III) solution were tested with/without UV light to prove Fe(II) formation. This study experimentally proved that the more Fe(II) under the UV radiation was formed in the co-existence with biochar extractives and Fe(III). All experimental data from three biochar samples were indeed very similar. Cr(VI) reduction by Fe(II) from GB, RB, and CB reached up to 96, 79, and 100%, respectively. The different reduction efficiency signified that the low molecular weight of organic acids, such as oxalate, were more sensitive to the UV light, thereby resulting in the enhanced Fe(II) formation. Such Fe(II) formation subsequently led to the high reduction efficiency of Cr(VI).

Sulfamic acid modified hydrochar derived from sawdust for removal of benzotriazole and Cu(II) from aqueous solution: Adsorption behavior and mechanism

A novel hydrochar adsorbent derived from sawdust (SAHC) was prepared for highly efficient simultaneous removal of benzotriazole (BTA) and Cu(II) from aqueous solution. The prepared adsorbent was characterized by several methods such as SEM, FTIR, and XPS. Batch adsorption experiments showed that the maximum adsorption capacity of SAHC for BTA and Cu(II) was 159.91 and 298.86 mg/g, respectively. Additionally, the study of competitive adsorption showed that the adsorption of Cu(II) was barely affected by the existence of BTA while the BTA adsorption was significantly improved with the coexistence of Cu(II). The study of adsorption mechanism found that Cu(II) could chelate with BTA to form complex, and the complexing-bridging interaction improved BTA adsorption. SAHC exhibited high adsorption ability after six adsorption cycles, which indicated excellent stability and regeneration performance of SAHC. All the results suggested that SAHC could be a promising adsorbent for simultaneous removal of BTA and Cu(II) from wastewater.

Effect of thermotolerant bacterial inoculation on the microbial community during sludge composting

A thermophilic bacterium (Geobacillus stearothermophilus CHB1) was inoculated in a sludge compost, and the effects of the inoculation on the abundance and structure of the bacterial community in the sludge compost were investigated using quantitative PCR and Illumina MiSeq sequencing. The results showed that the high-temperature stage (>50 °C) of the CHB1 and CK (control without inoculum) piles started on days 5 and 8, respectively, and lasted for 7 and 2 days, respectively, indicating the extension of the thermophilic phase by CHB1 inoculation in the sludge compost. At the end of composting, the CHB1 piles showed a higher loss of total organic carbon, lower C/N ratio, and lower moisture content. The abundance of bacteria in the CHB1 piles was significantly higher in the heating and thermophilic phase of composting but were lower than those of the CK in the cooling phase. The richness and diversity of the bacterial community in the thermophilic phase increased after inoculation with CHB1. After inoculation of CHB1, there were higher relative abundances of Firmicutes, Thermopolyspora, Thermobacillus, Thermomonas, Thermomonospora, and Thermovum, which can grow in a high-temperature environment. Furthermore, redundancy analysis indicated that total organic carbon, total nitrogen, C/N ratio, pH, temperature, and moisture were the significant parameters that affected the bacterial community structure during sludge composting. Our findings suggested that inoculation with CHB1 would enhance the quality and efficiency of composting.

Understanding Activation Effects on Low-Temperature Biochar for Optimization of Herbicide Sorption

Activation treatments are often used as a means of increasing a biochar’s sorption capacity for agrochemical compounds but can also provide valuable insight into sorption mechanisms. This work investigates the effects of H2O2 activation on a low-temperature (350 °C) grape wood biochar, evaluates subsequent changes to the removal efficiency (RE) of cyhalofop and clomazone, and elucidates potential sorption mechanisms. Activation by H2O2 decreased the biochar pH, ash content, and C content. Additionally, the biochar O content and surface area increased following activation, and Fourier transform infrared spectroscopy (FTIR) data suggested a slight increase in surface O groups and a decrease in aliphatic C. Cyhalofop RE significantly increased following activation, while clomazone RE was unchanged. The increased sorption of cyhalofop was attributed to pH effects and charge-based interactions with biochar O moieties. Results from this study suggest that H2O2 activation treatments on low-temperature biochars may improve the removal of organic acid herbicides but are of little value in optimizing the removal of polar, non-ionizable herbicides.

Long-term sorption of lincomycin to biochars: The intertwined roles of pore diffusion and dissolved organic carbon

Sequestration of anthropogenic antibiotics by biochars from waters may be a promising strategy to minimize environmental and human health risks of antibiotic resistance. This study investigated the long-term sequestration of lincomycin by 17 slow-pyrolysis biochars using batch sorption experiments during 365 days. Sorption kinetics were well fitted to the Weber-Morris intraparticle diffusion model for all tested biochars with the intraparticle diffusion rate constant (k_id) of 25.3-166 μg g^-1 day^-0.5 and intercept constant (C_id) of 39.0-339 μg g^-1, suggesting that the sorption kinetics were controlled by fast initial sorption and slow pore diffusion. The quasi-equilibrium sorption isotherms became more nonlinear with increasing equilibration time at 1, 7, 30, and 365 days, likely due to increasing abundance of heterogeneous sorption sites in biochars over time. Intriguingly, low-temperature (300 °C) and high-temperature (600 °C) biochars had faster sorption kinetics than intermediate-temperature (400-500 °C) biochars at the long term, which was attributed to greater specific surface area and pore volume of high-temperature biochars and the substantial and continuous release of dissolved organic carbon (DOC) from low-temperature biochars, respectively. DOC release enhanced lincomycin sorption by decreasing biochar particle size and/or increasing the accessibility of sorption sites and pores initially blocked by DOC. Additionally, a large fraction (>75%) of sorbed lincomycin in biochars after a 240-day equilibration could not be extracted by the acetonitrile/methanol extractant. The strong sorption and low extraction recovery demonstrated the great potential of biochars as soil amendments for long-term sequestration of antibiotics in-situ.

Influence of FeONPs amendment on nitrogen conservation and microbial community succession during composting of agricultural waste: Relative contributions of ammonia-oxidizing bacteria and archaea to nitrogen conservation

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe₂O₃ and Fe₃O₄ NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe₂O₃ NPs, reduced total nitrogen (TN) loss, and reserved more NH₄⁺-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH₄⁺-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Effectiveness of Biochar Obtained from Corncob for Immobilization of Lead in Contaminated Soil

BACKGROUND

Recent studies have explored the potential for using biochar as a soil amendment in agriculture. However, it can also be used as a gentle remediation option for contaminant reduction. Biochar is a by-product obtained from the pyrolysis of biomass (organic matter). It is known for its long-lasting chemical properties, wide surface area values, and carbon-richness, which make it an efficient method for the immobilization of organic and inorganic contaminants such as heavy metals.

OBJECTIVE

The aim of the present study was to analyze the efficiency of biochar, obtained from the gasification of corncob, for the immobilization of lead in contaminated soils.

METHODS

In the present study, biochar from corncob was used as an amendment for soil contaminated with lead (extracted from the municipality of Malambo, Colombia) in order to estimate its ability to immobilize leaching lead. A comparison laboratory test applied a modified biochar produced with a 10% hydrogen peroxide chemical treatment. In addition, a pot experiment was done with both biochar by sowing seeds of Pennisetum clandestinum for 33 days. During this period, plant growth was measured for the different amendments of biochar concentrations.

RESULTS

Laboratory tests indicated that unmodified biochar obtained a maximum retention of 61.46% of lead, while the modified biochar obtained only 44.53% retention. In the pot experiments, the modified biochar indicated high germination and growth of seeds (up to 89.8%).

CONCLUSIONS

Although the lead immobilization in soil was positive for both cases, the use of soil with high concentrations of lead (167.62 g/kg) does not indicate biochar's effectiveness for purposes of comparison with the current United States Environmental Protection Agency (USEPA) limit value (400 ppm for bare soil in urban play areas). Therefore, further studies are recommended using soil with lower lead concentration levels.

COMPETING INTERESTS

The authors declare no competing financial interests. One author is an employee of Pure Earth.