Effect of pyrolysis temperature and correlation analysis on the yield and physicochemical properties of crop residue biochar

Review on biochar as a sustainable green resource for the rehabilitation of petroleum hydrocarbon-contaminated soil

Petroleum pollution is one of the primary threats to the environment and public health. Therefore, it is essential to create new strategies and enhance current ones. The process of biological reclamation, which utilizes a biological agent to eliminate harmful substances from polluted soil, has drawn much interest. Biochars are inexpensive, environmentally beneficial carbon compounds extensively employed to remove petroleum hydrocarbons from the environment. Biochar has demonstrated an excellent capability to remediate soil pollutants because of its abundant supply of the required raw materials, sustainability, affordability, high efficacy, substantial specific surface area, and desired physical-chemical surface characteristics. This paper reviews biochar's methods, effectiveness, and possible toxic effects on the natural environment, amended biochar, and their integration with other remediating materials towards sustainable remediation of petroleum-polluted soil environments. Efforts are being undertaken to enhance the effectiveness of biochar in the hydrocarbon-based rehabilitation approach by altering its characteristics. Additionally, the adsorption, biodegradability, chemical breakdown, and regenerative facets of biochar amendment and combined usage culminated in augmenting the remedial effectiveness. Lastly, several shortcomings of the prevailing methods and prospective directions were provided to overcome the constraints in tailored biochar studies for long-term performance stability and ecological sustainability towards restoring petroleum hydrocarbon adultered soil environments.

A novel two stages chemical activation of pinewood waste for removing organic micropollutants from water and wastewater

The prevalent presence of pharmaceuticals in aquatic ecosystems underscores the necessity for developing cost-effective techniques to remove them from water. The utilization of affordable precursors in producing activated carbon, capable of rivaling commercial alternatives, remains a persistent challenge. The adsorption of diclofenac and ciprofloxacin onto a novel pinewood-derived activated carbon (FPWAC) was explored, employing a sequential activation process involving ammonium nitrate (NH4NO3) treatment followed by sodium hydroxide (NaOH) activation. The produced FPWAC was then thoroughly characterized by employing several techniques. The removal of diclofenac and ciprofloxacin in water and real wastewater effluent was examined in batch tests. The optimum removal conditions were an FPWAC dosage of 1 g L-1, pH 6, mixture concentration of 25 mg L-1, and a temperature of 25 °C. The FPWAC was able to remove both pharmaceuticals for up to six cycles, with more than 95% removal for water and 90% for wastewater in the first cycle. The adsorption performance fitted well with the non-linear Freundlich isotherm for both pollutants. The kinetics of adsorption of diclofenac followed a pseudo-first-order model, while ciprofloxacin showed adherence to the pseudo-second-order model. FPWAC proved its potency as a low-cost adsorbent for pharmaceutical removal from wastewater.

Boosting acetaminophen degradation in water by peracetic acid activation: A novel approach using chestnut shell-derived biochar at varied pyrolysis temperatures

In this study, biochar derived from chestnut shells was synthesized through pyrolysis at varying temperatures from 300 °C to 900 °C. The study unveiled that the pyrolysis temperature is pivotal in defining the physical and chemical attributes of biochar, notably its adsorption capabilities and its role in activating peracetic acid (PAA) for the efficient removal of acetaminophen (APAP) from aquatic environments. Notably, the biochar processed at 900 °C, referred to as CN900, demonstrated an exceptional adsorption efficiency of 55.8 mg g-1, significantly outperforming its counterparts produced at lower temperatures (CN300, CN500, and CN700). This enhanced performance of CN900 is attributed to its increased surface area, improved micro-porosity, and a greater abundance of oxygen-containing functional groups, which are a consequence of the elevated pyrolysis temperature. These oxygen-rich functional groups, such as carbonyls, play a crucial role in facilitating the decomposition of the O-O bond in PAA, leading to the generation of reactive oxygen species (ROS) through electron transfer mechanisms. This investigation contributes to the development of sustainable and cost-effective materials for water purification, underscoring the potential of chestnut shell-derived biochar as an efficient adsorbent and catalyst for PAA activation, thereby offering a viable solution for environmental cleanup efforts.

Alteration of soil pH induced by submerging/drainage and application of peanut straw biochar and its impact on Cd(II) availability in an acidic soil to indica-japonica rice varieties

The effects of soil pH variations induced by submergence/drainage and biochar application on soil cadmium (Cd) availability to different rice (Oryza sativa L.) varieties are not well understood. This study aims to investigate the possible reasons for available Cd(II) reduction in paddy soil as influenced by biochar and to determine Cd(II) absorption and translocation rates in different parts of various rice varieties. A pot experiment in a greenhouse using four japonica and four indica rice varieties was conducted in Cd(II) contaminated paddy soil with peanut straw biochar. The results indicated that the submerging led to an increase in soil pH due to the consumption of protons (H+) by the reduction reactions of iron/manganese (Fe/Mn) oxides and sulfate (SO42-) and thus the decrease in soil available Cd(II) contents. However, the drainage decreased soil pH due to the release of protons during the oxidation of Fe2+, Mn2+, and S2- and thus the increase in soil available Cd(II) contents. Application of the biochar increased soil pH during soil submerging and inhibited the decline in soil pH during soil drainage, and thus decreased soil available Cd(II) contents under both submerging and drainage conditions. The indica rice varieties absorbed more Cd(II) in their roots and accumulated higher amounts of Cd(II) in their shoots and grains than the japonica rice varieties. The Cd(II) sensitive varieties exhibited a greater absorption and translocation rate of Cd(II) compared to the tolerant varieties of both indica and japonica rice. Biochar inhibited the absorption and accumulation of Cd(II) in the rice varieties, which ultimately lowered the Cd(II) contents in rice grains below the national food safety limit (0.2 mg kg-1). Overall, planting japonica rice varieties in Cd(II) polluted paddy soils combined with the use of biochar can effectively reduce Cd(II) content in rice grains which protects human health against Cd(II) toxicity.

Large-scale soil application of hydrochar: Reducing its polycyclic aromatic hydrocarbon content and toxicity by heating

The beneficial roles of hydrochar in carbon sequestration and soil improvement are widely accepted. Despite few available reports regarding polycyclic aromatic hydrocarbons (PAHs) generated during preparation, their potential negative impacts on ecosystems remain a concern. A heating treatment method was employed in this study for rapidly removing PAHs and reducing the toxicity of corn stover-based hydrochar (CHC). The result showed total PAHs content (∑PAH) decreased and then sharply increased within the temperature range from 150 °C to 400 °C. The ∑PAH and related toxicity in CHC decreased by more than 80% under 200 °C heating temperature, compared with those in the untreated sample, representing the lowest microbial toxicity. Benzo(a)pyrene produced a significant influence on the ecological toxicity of the hydrochar among the 16 types of PAHs. The impact of thermal treatment on the composition, content, and toxicity of PAHs was significantly influenced by the adsorption, migration, and desorption of PAHs within hydrochar pores, as well as the disintegration and aggregation of large molecular polymers. The combination of hydrochar with carbonized waste heat and exhaust gas collection could be a promising method to efficiently and affordably reduce hydrochar ecological toxicity.

Straw pyrolysis for use in electricity storage installations

A concept has been proposed for an installation designed to store excess electricity periodically occurring on the grid. Excess electricity will be used for straw pyrolysis. The main pyrolysis product, gas, will be used to generate electricity using a combustion generator to feed back power into the grid during periods of shortage. The resulting biochar from the pyrolysis can be introduced into the soil to improve soil quality and play a significant role in carbon sequestration. The system uses an electrically heated reactor with a screw conveyor. To preliminarily assess the feasibility of this system, experiments were carried out using wheat straw at temperatures of 300, 400, 500, 600, and 700 °C for the pyrolysis reactor. The resulting gas-to-feedstock mass ratio ranged from 29.04 % at 300 °C to 52.7 % at 700 °C reactor temperature, the biochar mass yield ratio to feedstock varied from 39.41 % to 27.36 % (at 700 °C), and the pyrolysis liquid ranged from 31.55 % to 27.36 % (at 700 °C). The pyrolytic liquid contained a high water content relative to its mass, reaching up to 95.2 % at 700 °C, rendering it less suitable as an energy feedstock. At a reactor temperature of 700 °C, the energy value of the gas produced from the feedstock was twice that of the electricity used for the pyrolysis process. These results suggest the feasibility and operation of the proposed installation.

Machine learning models for predicting biochar properties from lignocellulosic biomass torrefaction

This study developed six machine learning models to predict the biochar properties from the dry torrefaction of lignocellulosic biomass by using biomass characteristics and torrefaction conditions as input variables. After optimization, gradient boosting machines were the optimal model, with the highest coefficient of determination ranging from 0.89 to 0.94. Torrefaction conditions exhibited a higher relative contribution to the yield and higher heating value (HHV) of biochar than biomass characteristics. Temperature was the dominant contributor to the elemental and proximate composition and the yield and HHV of biochar. Feature importance and SHapley Additive exPlanations revealed the effect of each influential factor on the target variables and the interactions between these factors in torrefaction. Software that can accurately predict the element, yield, and HHV of biochar was developed. These findings provide a comprehensive understanding of the key factors and their interactions influencing the torrefaction process and biochar properties.

Untapped potential of food waste derived biochar for the removal of heavy metals from wastewater

The presence of heavy metals in water pose a serious threat to both public and environmental health. However, the advances in the application of low cost biochar based adsorbent synthesize from various feedstocks plays an effective role in the of removal heavy metals from water. This study implies the introduction of novel method of converting food waste (FW) to biochar through pyrolysis, examine its physiochemical characteristics, and investigate its adsorption potential for the removal of heavy metals from water. The results revealed that biochar yield decreased from 18.4 % to 14.31 % with increase in pyrolysis temperature from 350 to 550 °C. Likewise, increase in the pyrolysis temperature also resulted in the increase in the ash content from 39.87 % to 42.05 % thus transforming the biochar into alkaline nature (pH 10.17). The structural and chemical compositions of biochar produced at various temperatures (350, 450, and 550 °C) showed a wide range of mineralogical composition, and changes in the concentration of surface functional groups. Similarly, the adsorption potential showed that all the produced biochar effectively removed the selected heavy metals from wastewater. However a slightly high removal capacity was observed for biochar produced at 550 °C that was credited to the alkaline nature, negatively charged biochar active sites due to O-containing functional groups and swelling behavior. The results also showed that the maximum adsorption was recorded at pH 8 at adsorbent dose of 2.5 g L-1 with the contact time of 120 min. To express the adsorption equilibrium, the results were subjected to Langmuir and Freundlich isotherms and correlation coefficient implies that the adsorption process follows the Freundlich adsorption isotherm. The findings of this study suggest the suitability of the novel FW derived biochar as an effective and low cost adsorbent for the removal of heavy metals form wastewater.

In-situ registration subtraction image segmentation algorithm for spatiotemporal visualization of copper adsorption onto corn stalk-derived pellet biochar by micro-computed tomography

The non-homogeneous structure and high-density ash composition of biochar matrix pose significant challenges in characterizing the dynamic changes of heavy metal adsorption onto biochar with micro-computed tomography (Micro-CT). A novel in-situ registration subtraction image segmentation method (IRS) was developed to enhance micro-CT characterization accuracy. The kinetics of Cu(II) adsorption onto pellet biochar derived from corn stalks were tested. Respectively, the IRS and traditional K-means algorithms were used for image segmentation to the in-situ three-dimensional (3D) visual characterization of the Cu(II) adsorption onto biochar. The results indicated that the IRS algorithm reduced interference from high-density biochar composition, and thus achieved more precise results (R2 = 0.95) than that of K-means (R2 = 0.72). The visualized dynamic migration of Cu(II) from surface adsorption to intraparticle diffusion reflexed the complex mechanism of heavy metal adsorption. The developed Micro-CT method with high generalizability has great potential for studying the process and mechanism of biochar heavy metal adsorption.

Biochar-based materials as remediation strategy in petroleum hydrocarbon-contaminated soil and water: Performances, mechanisms, and environmental impact

Petroleum contamination is considered as a major risk to the health of humans and environment. Biochars as low-cost and eco-friendly carbon materials, have been widely used for the removal of petroleum hydrocarbon in the environment. The purpose of this paper is to review the performance, mechanisms, and potential environmental toxicity of biochar, modified biochar and its integration use with other materials in petroleum contaminated soil and water. Specifically, the use of biochar in oil-contaminated water and soil as well as the factors that could influence the removal ability of biochar were systematically evaluated. In addition, the modification and integrated use of biochar for improving the removal efficiency were summarized from the aspects of sorption, biodegradation, chemical degradation, and reusability. Moreover, the functional impacts and associated ecotoxicity of pristine and modified biochars in various environments were demonstrated. Finally, some shortcoming of current approaches, and future research needs were provided for the future direction and challenges of modified biochar research. Overall, this paper gain insight into biochar application in petroleum remediation from the perspectives of performance enhancement and environmental sustainability.

Carbon-based adsorbents for the mitigation of polycyclic aromatic hydrocarbon: a review of recent research

Accumulation of polycyclic aromatic hydrocarbons (PAH) poses significant dangers to the environment and human health. The advancement of technology for cleaning up PAH-contaminated environments is receiving more attention. Adsorption is the preferred and most favorable approach for cleaning up sediments polluted with PAH. Due to their affordability and environmental friendliness, carbonaceous adsorbents (CAs) have been regarded as promising for adsorbing PAH. However, adsorbent qualities, environmental features, and factors may all significantly impact how well CAs remove PAH. According to growing data, CAs, most of which come from laboratory tests, may be utilized to decontaminate PAH in aquatic setups. However, their full potential has not yet been established, especially concerning field applications. This review aims to concisely summarize recent developments in CA, PAH stabilization processes, and essential field application-controlling variables. This review analysis emphasizes activated carbon, biochar, Graphene, carbon nanotubes, and carbon-nanomaterials composite since these CAs are most often utilized as adsorbents for PAH in aquatic systems.

A review on photocatalytic attribution and process of pyrolytic biochar in environment

Biochar has attracted significant attention due to its excellent environmental benefits and extensive applications. Recently, a consensus has been accepted that biochar can act as a photocatalyst and trigger effective photocatalytic reactions in the environment, which is important to energy conversion and the cycle of elements. However, its photocatalytic processes and the corresponding environmental impacts need to receive more and due attention. In this review, we provide a comprehensive summary of the underlying correlations among the pyrolytic evolution of biomass, the structure characteristic of biochar, and the resultant photocatalytic performance. Moreover, the photocatalytic processes and the influence of environmental factors were elaborately investigated on biochar. Finally, future tendencies and challenges in the photocatalysis of biochar have been prospected in the environmental field. This review has offered innovative insights into the photocatalytic essential of biochar and highly enhanced the understanding of its environmental impact.

Utilization of biochar for remediation of heavy metals in aqueous environments: A review and bibliometric analysis

Biochar usage for removing heavy metals from aqueous environments has emerged as a promising research area with significant environmental and economic benefits. Using the PICO approach, the research question aimed to explore using biochar to remove heavy metals from aqueous media. We merged the data from Scopus and the Web of Science Core Collection databases to acquire a comprehensive perspective of the subject. The PRISMA guidelines were applied to establish the search parameters, identify the appropriate articles, and collect the bibliographic information from the publications between 2010 and 2022. The bibliometric analysis showed that biochar-based heavy metal remediation is a research field with increasing scholarly attention. The removal of Cr(VI), Pb(II), Cd(II), and Cu(II) was the most studied among the heavy metals. We identified five main clusters centered on adsorption, water treatment, adsorption models, analytical techniques, and hydrothermal carbonization by performing keyword co-occurrence analysis. Trending topics include biochar reusability, modification, acid mine drainage (AMD), wastewater treatment, and hydrochar. The reutilization of heavy metal-loaded spent biochar includes transforming it into electrodes for supercapacitors or stable catalyst materials. This study provides a comprehensive overview of biochar-based heavy metal remediation in aquatic environments and highlights knowledge gaps and future research directions.

Using the Conditional Process Analysis Model to Characterize the Evolution of Carbon Structure in Taxodium ascendens Biochar with Varied Pyrolysis Temperature and Holding Time

Temperature determines biochar structure during pyrolysis. However, differences in holding time and feedstock types may affect this relationship. The conditional process analysis model was used in this paper to investigate the potential to affect this mechanism. The branch and leaf parts of Taxodium ascendens were separately pyrolyzed at 350, 450, 650, and 750 °C, and kept for 0.5, 1, and 2 h at each target temperature. We measured the fixed carbon and ash contents and the elemental composition (C, H, O and N) of the raw materials and their char samples. After plotting a Van Krevelen (VK) diagram to determine the aromatization of chars, the changes in the functional groups were analyzed using Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS). The results revealed that pyrolysis at temperatures between 450 and 750 °C accounted for the aromatization of biochar because the atomic H/C ratio of branch-based chars (BC) decreased from 0.53-0.59 to 0.15-0.18, and the ratio of leaf-based chars (LC) decreased from 0.56-0.68 to 0.20-0.22; the atomic O/C ratio of BC decreased from 0.22-0.27 to 0.08-0.11, while that of LC decreased from 0.26-0.28 to 0.18-0.21. Moreover, the average contents of N (1.89%) and ash (13%) in LC were evidently greater than that in BC (N:0.62%; Ash: 4%). Therefore, BC was superior to LC in terms of the stability of biochar. In addition, the increasing ID/IG and ID/I(DR+GL) ratios in BC and LC indicated an increasing amount of the amorphous aromatic carbon structure with medium-sized (2~6 rings) fused benzene rings. According to the CPA analysis, an extension of the holding time significantly enhanced the increase in aromatic structures of LC with temperature. But this extension slightly reduced the growth in aromatic structures of BC. All indicate that holding time and feedstock types (branch or leaf feedstock) could significantly affect the variation in biochar aromatic structure with respect to temperature.

Navigating Pyrolysis Implementation-A Tutorial Review on Consideration Factors and Thermochemical Operating Methods for Biomass Conversion

Pyrolysis and related thermal conversion processes have shown increased research momentum in recent decades. Understanding the underlying thermal conversion process principles alongside the associated/exhibited operational challenges that are specific to biomass types is crucial for beginners in this research area. From an extensive literature search, the authors are convinced that a tutorial review that guides beginners particularly towards pyrolysis implementation, from different biomasses to the thermal conversion process and conditions, is scarce. An effective understanding of pre-to-main pyrolysis stages, alongside corresponding standard methodologies, would help beginners discuss anticipated results. To support the existing information, therefore, this review sought to seek how to navigate pyrolysis implementation, specifically considering factors and thermochemical operating methods for biomass conversion, drawing the ideas from: (a) the evolving nature of the thermal conversion process; (b) the potential inter-relatedness between individual components affecting pyrolysis-based research; (c) pre- to post-pyrolysis' engagement strategies; (d) potential feedstock employed in the thermal conversion processes; (e) the major pre-treatment strategies applied to feedstocks; (f) system performance considerations between pyrolysis reactors; and (g) differentiating between the reactor and operation parameters involved in the thermal conversion processes. Moreover, pre-pyrolysis activity tackles biomass selection/analytical measurements, whereas the main pyrolysis activity tackles treatment methods, reactor types, operating processes, and the eventual product output. Other areas that need beginners' attention include high-pressure process reactor design strategies and material types that have a greater potential for biomass.

Synthesis of tapioca starch/palm oil encapsulated urea-impregnated biochar derived from peppercorn waste as a sustainable controlled-release fertilizer

Nutrient leaching and volatilization cause environmental pollution, thus the pursuit of developing controlled-release fertilizer formulation is necessary. Biochar-based fertilizer exhibits slow-release characteristic, however the nutrient release mechanism needs to be improved. To overcome this limitation, the approach of applying encapsulation technology with biochar-based fertilizer has been implemented in this study. Black peppercorn waste was used to synthesize urea-impregnated biochar (UIB). Central composite design was used to investigate the effects of pyrolysis temperature, residence time and urea:biochar ratio on nitrogen content of UIB. The optimum condition to synthesize UIB was at 400 °C pyrolysis temperature, 120 min residence time and 0.6:1 urea:biochar ratio, which resulted in 16.07% nitrogen content. The tapioca starch/palm oil (PO) biofilm formulated using 8 g of tapioca starch and 0.12 µL of PO was coated on the UIB to produce encapsulated urea-impregnated biochar (EUIB). The UIB and EUIB pellets achieved complete release of nitrogen in water after 90 min and 330 min, respectively. The nutrient release mechanism of UIB and EUIB was best described by the Higuchi model and Korsmeyer-Peppas model, respectively. The improvement of water retention ratio of UIB and EUIB pellets was more significant in sandy-textural soil as compared to clayey-textural soil. The EUIB derived from peppercorn waste has the potential to be utilized as a sustainable controlled-release fertilizer for agriculture.

In-situ retention of nitrogen, phosphorus in agricultural drainage and soil nutrients by biochar at different temperatures and the effects on soil microbial response

This study conducted a two-year experiment to investigate the impacts of biochar with various temperatures (350 °C, 500 °C, and 650 °C), on the reduction of pollutants in agricultural runoff and the enhancement of soil fertility. The results showed that the biochar significantly reduced the concentrations of total nitrogen and total phosphorus in farmland runoff. Moreover, higher-temperature biochar demonstrated greater efficacy in decreasing pollutants in farmland drainage. Treatment with RB650 resulted in a reduction of the total nitrogen and total phosphorus output load by 29.31-30.67 % and 21.92-25.21 %, respectively, compared to RB350. Furthermore, biochar exhibited substantial enhancements in soil fertility. This was supported by heightened soil organic matter content, increased availability of nutrients, and a noteworthy (P < 0.05) upsurge in pH, organic matter, total nitrogen, and total phosphorus content observed in the second year following the application of biochar. Biochar has the potential to enhance soil enzyme activity and affect microbial community composition, thereby facilitating nutrient cycling. The findings illustrated the regenerative and recyclable characteristics of biochar's adsorption activity throughout crop growth. This process enables sustained improvement in soil nutrient retention capacity and fertility. Thus, it emphasizes the potential of biochar as an in-situ model for nutrient retention and recycling, offering an effective approach to mitigate agricultural non-point source (NPS) pollution and enhance soil fertility.

Insight into the impacts of pyrolysis time on adsorption behavior of Pb2+ and Cd2+ by Mg modified biochar: Performance and modification mechanism

Co-pyrolysis biomass and alkaline metals can effectively improve the adsorption performance of heavy metals (HM). Nevertheless, the researchers have ignored the relationship between the change of alkaline metal morphology and adsorption during pyrolysis. In this article, according to control the pyrolysis time (30, 60, and 180 min) synthesized Magnesium (Mg) modified biochar (MBCX) by using MgCl2·6H2O and soybean straw under 400 °C. The sorption capacities of MBC60 and MBC180 for Pb2+/Cd2+ increased by 38.65%/213.29%, 44.57%/230.36%, and the selectivity coefficient of Pb2+/Cd2+ increased by 113.28%/209.49%, 213.58%/253.62%, respectively, compared with MBC30. Additionally, the characterization results demonstrated that MgO dominated the surface phases of MBC60 and MBC180, whereas MgCl2 dominated the surface phases of MBC30. Moreover, according to the results of DFT calculation, the adsorption energy (Eads) of MgO for Pb2+ (-0.537 eV) and Cd2+ (-0.347 eV) was lower than that of MgCl2 (Pb2+: 0.37 eV, Cd2+: -0.185 eV), so that, MBC60 and MBC180 had higher sorption capacities for Pb2+ and Cd2+ than MBC30. Therefore, this work provides a new sight to clear the mechanism for modified biochar by alkali metal oxide and practical and theoretical guidance for adsorbent preparation with high adsorption ability for HMs.

Preparation and study of straw porous biochar with aromatic ring structure for adsorption performance and mechanism toward TNT red water

2,4,6-Trinitrotoluene (TNT) production processes generate a substantial amount of toxic wastewater. Therefore, it is crucial to identify efficient and sustainable methods for treating this wastewater. This paper explores the application of sustainable biomass-derived carbon produced from rice straw for the adsorption of 2,4,6-trinitrotoluene (TNT) red water. The rice straw-derived biochar (SBC) materials were synthesized by two-step reactions through hydrothermal carbonization and chemical activation with KOH. Characterization of the fabricated biochar was conducted using various techniques. Here, the chemical oxygen demand (COD) was used as an evaluation index for adsorption efficiency. The adsorption kinetics showed a good fit with the pseudo-second-order model, and the adsorption equilibrium was achieved in 30 min. The biochar's high surface area (1319 m2/g) and large pore volume (1.058 cm3/g) gave it a large adsorption capacity. The Langmuir model exhibited better correlation for equilibrium data analysis, with a maximum adsorption capacity of 173.9 mg/g at 298 K. The SBC was found to have a high removal effect over a wide pH range (from 1 to 13) and showed remarkable stability after undergoing five desorption-adsorption cycles using ethanol and acetone as eluent. The results provide a simple and low-cost method for the efficient treatment of TNT red water.

Reduced and oxidized rice straw biochar for hexavalent chromium adsorption: Revisiting the mechanism of adsorption

Surface oxygen functional groups of biochar were tuned by oxidation and reduction of biochar for establishing Cr(VI) adsorption mechanism. Oxygen functional groups (OFGs) on the surface of leached rice straw biochar (LBC4-6) obtained from pyrolysis at 400, 500 and 600 °C, were oxidized to furnish OBC4-6 using modified Hummer's method. Reduced biochar RBC4-6 were obtained by esterification and NaBH4/I2 reduction of oxidized biochar (OBC4-6). The modified biochar were characterized by increase in O/C and H/C ratio, respectively, in case of OBC4-6 and RBC4-6. The Cr(VI) adsorption by modified biochar LBC4-6, OBC4-6, and RBC4-6 showed optimum conditions of pH 3 and dose 0.1 g/L with a good non-linear fit for Langmuir & Freundlich isotherm. The maximum adsorption (Qm) followed the trend: OBC4 (17.47 mg/g) > RBC4 (15.23) > OBC5 (13.23) > LBC4 (10.23) > RBC5 (9.83) > OBC6 (9.60) > RBC6 (7.24) > LBC5 (6.32) > LBC6 (5.98). The adsorption kinetics for adsorption of Cr(VI) on to modified biochar fits pseudo second order (PSO), Elovich and intraparticle diffusion kinetics, showing a chemisorptions in case of biochar L/O/RBC4-6. The lower temperature modified biochar O/RBC4 show better Cr(VI) adsorption. X-ray Photoelectron Spectroscopy (XPS) studies establish optimum OFGs for reduction of Cr(VI) and chelation of the reduced Cr(III). Adsorption and stripping cycles show the oxidized and reduced biochar as better adsorbents with excellent stripping of Cr up to >98 % upon desorption with 1 M NaOH.

Enhanced soil P immobilization and microbial biomass P by application of biochar modified with eggshell

Phosphate fertilizers have been excessively applied in agricultural production, bringing the risk of phosphorus (P) loss to nearby river systems and low utilization efficiency. In this study, eggshell-modified biochars prepared by pyrolysis of eggshell and corn straw or pomelo peel were applied to soil for enhancing P immobilization and utilization. The structure and properties of modified biochars before and after P adsorption were analyzed using the Brunauer-Emmett-Teller (BET) nitrogen adsorption method, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The eggshell-modified biochar performed an excellent adsorption performance for P (up to 200 mg/g), which was well described by the Langmuir model (R2 > 0.969), showing monolayer chemical adsorption with homogenous surface. The Ca(OH)2 appeared on the surface of eggshell modified biochars and changed to Ca5(PO4)3(OH) and CaHPO4(H2O)2 after P adsorption. The release of immobilized P by modified biochar increased with decreased pH. In addition, pot experiments of soybean indicated that the combined application of modified biochar and P fertilizer significantly increased the content of microbial biomass P in soil, raising from 4.18 mg/kg (control group) to 51.6-61.8 mg/kg (treatment group), and plants height increased by 13.8-26.7%. Column leaching experiments showed that P concentration in the leachate decreased by 97.9% with the modified biochar application. This research provides a new perspective that the eggshell-modified biochar could serve as a potential soil amendment for enhancing P immobilization and utilization.

Characteristics of dissolved organic matter composition in biochar: Effects of feedstocks and pyrolysis temperatures

Biochar has widely used in soil pollution remediation due to its advantages of high efficiency and environmental sustainability. Dissolved organic matter (DOM) released by biochar plays a non-negligible role in the migration and transformation of pollutants in environment, and its composition was regarded as main impact factor. In this study, 28 biochar were investigated to detect the effect of pyrolysis temperature and feedstock on DOM content and components. Results showed that the content of DOM released from biochar at low pyrolysis temperatures (300-400 ℃) was higher than that from high pyrolysis temperatures (500-600 ℃). In addition, the specific UV-Visible absorbance at 254 nm (SUVA254) results expressed that DOM from peanut shell biochar (PSBC), rice husk biochar (RHBC) and bamboo biochar (BBC) had higher humification at high temperatures. Moreover, one fulvic acid-like (C2) and two humic acid-like (C1, C3) substances were main fluorescent components of biochar-derived DOM identified by parallel factor analysis based on excitation emission matrices fluorescence spectroscopies (EEM-PARAFAC). With the increase of pyrolysis temperature, humic acid substances content gradually decreased. The correlation analysis results revealed that pyrolysis temperatures and O/C, H/C, DOM content, the biological index (BIX), humification index (HIX), C1% and C3% was negatively correlated (p < 0.001). Thus, the pyrolysis temperatures take important roles in composition of DOM released from biochar, and this research would provide a reference for the application of biochar in the environment.

Production and characterization of graphene oxide-engineered biochars and application for organic micro-pollutant adsorption from aqueous solutions

In this study, conventional and Graphene Oxide-engineered biochars were produced and thoroughly characterized, in order to investigate their potential as adsorptive materials. Two types of biomass, Rice Husks (RH) and Sewage Sludge (SS), two Graphene Oxide (GO) doses, 0.1% and 1%, and two pyrolysis temperatures, 400 °C and 600 °C were investigated. The produced biochars were characterized in physicochemical terms and the effect of biomass, GO functionalization and pyrolysis temperature on biochar properties was studied. The produced samples were then applied as adsorbents for the removal of six organic micro-pollutants from water and treated secondary wastewater. Results showed that the main factors affecting biochar structure was biomass type and pyrolysis temperature, while GO functionalization caused significant changes on biochar surface by increasing the available C- and O- based functional groups. Biochars produced at 600 °C showed higher C content and Specific Surface Area, presenting more stable graphitic structure, compared to biochars produced at 400 °C. Micro-pollutant adsorption rates were in the range of 39.9%-98.3% and 9.4%-97.5% in table water and 28.3%-97.5% and 0.0%-97.5% in treated municipal wastewater, for the Rice Husk and Sewage Sludge biochars respectively. The best biochars, in terms of structural properties and adsorption efficiency were the GO-functionalized biochars, produced from Rice Husks at 600 °C, while the most difficult pollutant to remove was 2.4-Dichlorophenol.

Sustainable exploitation and safe utilization of biochar: Multiphase characterization and potential hazard analysis

Pyrolysis temperature determines the multiphase (solid and dissolved) structure of biochar (BC). In this study, the temperature-dependent evolution of characteristics and potential hazards of three crop (cotton, alfalfa, and wheat) residue BC were systematically investigated. The results showed that pyrolysis temperature significantly affected the elemental composition and morphology of BC. A higher pyrolysis temperature led to a higher aromatization and graphitization degree of BC. A numerical relationship between pyrolysis temperature and BC surface properties (functional groups, carbonization degree) was established. Pyrolysis temperature controlled the content, composition, and functional group evolution of BC-derived dissolved organic matter. Although the amount of potentially toxic elements (PTEs) in BC was concentrated after pyrolysis, the potentially risk of PTEs significantly decreased. The spin concentration of persistent free radicals in BC prepared at 500 °C was the highest. These findings will hopefully offer comprehensive guidance for sustainable utilization of crop straw and fit-for-purpose exploitation of BC.

Use of local waste for biochar production: Influence of feedstock and pyrolysis temperature on chromium removal from aqueous solutions

Sediment enrichment with biochar, a high-carbon material produced by the pyrolysis of biomass, is a promising remediation strategy for metal pollution. The metal immobilization capacity of biochar can be explained by its porous structure, surface functional groups, pH greater than 7, and cation exchange capacity. However, the effectiveness in reducing metal bioavailability depends on the physicochemical characteristics of the biochar, which are strongly associated with the process conditions and feedstock. The aims of this study were to analyze the effect of pyrolysis temperature on the properties of biochars derived from different locally available biomass materials, biochar potential to adsorb Cr, and biochar phytotoxicity in seed germination. Poultry litter (PL), maize straw, the macrophyte Juncus imbricatus, and phytoremediation wastes from the macrophyte previously exposed to Cr were pyrolyzed into biochar at 300 °C and 600 °C. The properties and capacity of biochar to remove Cr from the aqueous phase were determined. Finally, a germination assay was performed to evaluate biochar phytotoxicity. Biochar yield decreased with increasing pyrolysis temperature, whereas ash content and pH increased. Biochar C content and total surface area increased with temperature. Biochar Cr removal capacity improved under the highest temperature, reaching a maximum sorption value of 13.7 mg g^-1 Cr at 300 °C in PL biochar and of 42.6 mg g^-1 Cr at 600 °C in J. imbricatus biochar. Despite the comparatively high metal content in the biochar, the germination indices of all biochars produced at 600 °C were higher than 80%, suggesting no phytotoxicity. Considering the metal sorption capacity and the phytotoxicity, biochars produced from J. imbricatus, PL, and phytoremediation residues at 600 °C were suitable for use in the removal of Cr from water. Integr Environ Assess Manag 2023;19:717-725. © 2022 SETAC.

Development of sludge-based activated char sorbent with enhanced hydrophobicity for oil spill cleanup

Recovery of oil spilled on surface waters by the use of sorbents remains one of the primary oil spill response options available. To improve on this response measure, we have successfully fabricated an activated char (AC) sorbent material by pyrolysis of sewage sludge (SS), a readily available waste product generated across the world from wastewater treatment plants. The inherent Fe-minerals in SS texture were converted to magnetic Fe₃O₄ particles during the pyrolysis reaction. The AC provided a unique means to recover the sorbent after the oil sorption process with a magnetic field. Meanwhile, a superhydrophobic sorbent material with a water contact angle of 152.2° was created by the treatment of AC with myristic acid which could float on the water surface. Feasibility studies at the laboratory-scale were conducted with motor oil and light crude oil to evaluate its potential use in spill response operations. Results showed a sorption capacity of about 8.5 and 10.7 g/g for motor oil and light crude oil, respectively. Following the recovery of the test oils by ethanol stripping, the material could be recycled up to 5 times with trivial loss in sorption capacity. This research proposes a framework for the development of a highly efficient sorbent material for oil spill response operations from SS waste.

Applications of agricultural residue biochars to removal of toxic gases emitted from chemical plants: A review

Crop residues are representative agricultural waste materials, massively generated in the world. However, a large fraction of them is currently being wasted, though they have a high potential to be used as a value-added carbon-rich material. Also, the applications of carbon-rich materials from agricultural waste to industries can have economic benefit because waste-derived carbon materials are considered inexpensive waste materials. In this review, valorization methods for crop residues as carbon-rich materials (i.e., biochars) and their applications to industrial toxic gas removals are discussed. Applications of crop residue biochars to toxic gas removal can have significant environmental benefits and economic feasibility. As such, this review discussed the technical advantages of the use of crop residue biochars as adsorbents for hazardous gaseous pollutants and greenhouse gases (GHGs) stemmed from combustion of fossil fuels and the different refinery processes. Also, the practical benefits from the activation methods in line with the biochar properties were comprehensively discussed. The relationships between the physico-chemical properties of biochars and the removal mechanisms of gaseous pollutants (H₂S, SO₂, Hg⁰, and CO₂) on biochars were also highlighted in this review study. Porosity controls using physical and chemical activations along with the addition of specific functional groups and metals on biochars have significantly contributed to the enhancement of flue gas adsorption. The adsorption capacity of biochar for each toxic chemical was in the range of 46-76 mg g^-1 for H₂S, 40-182 mg g^-1 for SO₂, 80-952 μg g^-1 for Hg⁰, and 82-308 mg g^-1 CO₂, respectively. This helps to find suitable activation methods for adsorption of the target pollutants. In the last part, the benefits from the use of biochars and the research directions were prospectively provided to make crop residue biochars more practical materials in adsorption of pollutant gases.

Migration electric-field assisted electrocoagulation with sponge biochar capacitive electrode for advanced wastewater phosphorus removal

Migrating electric field-assisted electrocoagulation (MEAEC) is a three-electrode electrochemical system, including waste flour-derived sponge biochar (SBC) as an adsorption electrode for efficient phosphorus removal from wastewater. The SBC was applied in the MEAEC system as a pseudo capacitance electrode with low energy consumption and reached an excellent effluent level (0.12 mg/L) with a 200-s treatment time in 1 mg/L phosphate synthetic wastewater. The SBC adsorption electrode had a total charge capacitance of 1.14 F/g with abundant micropores. Continuous charging and discharging at a constant voltage over 100 cycles demonstrated the excellent durability of the biochar electrodes. The energy demand of SBC-MEAEC was only 0.0058 kWh/m³ for 90% phosphate removal, which was 65% less than that of the control. The use of SBC in the MEAEC system greatly enhanced phosphate removal at low concentrations. In the SBC-MEAEC system, the electro-desorption synchronous electrocoagulation process demonstrated efficient concentration and release of ions after electro-adsorption. These results indicate that MEAEC with an SBC electrode could achieve a high level of phosphate removal with a much lower energy consumption than in previous studies. The recovered concentrated phosphorus flocs also contained fewer metal impurities than those in previous electrochemical approaches. The proposed desorption synchronous electrocoagulation utilizing waste-derived SBC electrodes provides a cost-effective pathway to treat low phosphorous-containing wastewater.

Simultaneous adsorption of As(III) and Pb(II) by the iron-sulfur codoped biochar composite: Competitive and synergistic effects

Simultaneous elimination of As(III) and Pb(II) from wastewater is still a great challenge. In this work, an iron-sulfur codoped biochar (Fe/S-BC) was successfully fabricated in a simplified way and was applied to the remediate the co-pollution of As(III) and Pb(II). The positive enthalpy indicated that the adsorption in As-Pb co-pollution was an endothermic reaction. The mechanism of As(III) removal could be illustrated by surface complexation, oxidation and precipitation. In addition to precipitation and complexation, the elimination mechanism of Pb(II) also contained ion exchange and electrostatic interactions. Competitive and synergistic effects existed simultaneously in the co-contamination system. The suppression of As(III) was ascribed to competitive complexation of the two metals on Fe/S-BC, while the synergy of Pb(II) was attributed to the formation of the PbFe₂(AsO₄)₂(OH)₂. Batch experiments revealed that Fe/S-BC had outstanding ability to remove As(III) and Pb(II), regardless of pH dependency and interference by various coexisting ions. The maximum adsorption capacities of the Fe/S-BC for As(III) and Pb(II) were 91.2 mg/g and 631.7 mg/g, respectively. Fe/S-BC could be treated as a novel candidate for the elimination of As(III)-Pb(II) combined pollution.

Non-metal activated peroxydisulfate by straw biochar for tetracycline hydrochloride oxidative degradation: catalytic activity and mechanism

In this study, stalk biochar (BC) was prepared by a high-temperature pyrolysis process and used as a non-metallic catalyst to activate peroxydisulfate (PDS) to degrade tetracycline hydrochloride (TCH). Various characterization results showed that BC had a hollow tubular structure, irregular folds, and important active sites such as oxygen-containing functional groups. Under the optimal reaction conditions, the degradation rate of TCH reached 98.1% within 120 min. In addition, the degradation performance was satisfactory and similar under acidic and near neutral pH, and higher temperature promoted the degradation of TCH. The SO₄·^-, ·OH, and ¹O₂ generated by PDS activation were reactive oxygen species (ROS), which degraded TCH through free radical/non-radical synergistic pathways. Quenching experiments proved that the generated SO₄·^- and ·OH might be the dominant reactive oxygen species (ROS) during the oxidative reaction. The research results will provide a theoretical basis for the application of PDS activated by non-metallic catalysts in the remediation of tetracycline antibiotics pollution.

Pyrolytic biochar from plastic film waste addition on farmland for maize growth improvement: Process and effect study

Pyrolyzing and returning to farmland is one of the potential methods for farmland plastic film waste. This study explored both pyrolyzation and activation optimum conditions of a mixture of plastic film (polyethylene) and maize straw (MPS) in a 1:5 ratio to produce MPS-char, investigated the action of the char on the maize seedling stage (for 30 days). The results showed that the char promoted the root to be more advanced than aboveground part, therefore, this study experimentally clarified the role MPS-char played when added to the soil. The functional groups of the char were varied by the participation of polyethylene. Carbon-based groups were observed, such as carbonyl or carboxyl groups, which could constitute an NH₄⁺ absorption release system to increase the existence of urea in soil, therefore the average nitrogen concentration was improved by 16.18 %. However, the shallow soil temperature increased by 2.03 °C, and the deep soil temperature slightly decreased with the effect of MPS-char. While, the soil moisture content was slightly reduced in the second half of the experiment, and the soil oxygen content increased by 7.64 % throughout the whole experiment. Overall, returning MPS-char to farmland showed a positive effect on maize growth, which was caused by the variation of both chemical and physical properties. This variation provides opportunities for further promotion of rhizosphere development.

Review of biochar production via crop residue pyrolysis: Development and perspectives

Worldwide surge in crop residue generation has necessitated developing strategies for their sustainable disposal. Pyrolysis has been widely adopted to convert crop residue into biochar with bio-oil and gas being two co-products. The review adopts a whole system philosophy and systematically summarises up-to-date knowledge of crop residue pyrolysis processes, influential factors, and biochar applications. Essential process design tools for biochar production e.g., cost-benefit analysis, life cycle assessment, and machine learning methods are also reviewed, which has often been overlooked in prior reviews. Important aspects include (a) correlating techno-economics of biochar production with crop residue compositions, (b) process operating conditions and management strategies, (c) biochar applications including soil amendment, fuel displacement, catalytic usage, etc., (d) data-driven modelling techniques, (e) properties of biochar, and (f) climate change mitigation. Overall, the review will support the development of application-oriented process pipelines for crop residue-based biochar.

Machine learning and statistical analysis for biomass torrefaction: A review

Torrefaction is a remarkable technology in biomass-to-energy. However, biomass has several disadvantages, including hydrophilic properties, higher moisture, lower heating value, and heterogeneous properties. Many conventional approaches, such as kinetic analysis, process modeling, and computational fluid dynamics, have been used to explain torrefaction performance and characteristics. However, they may be insufficient in actual applications because of providing only some specific solutions. Machine learning (ML) and statistical approaches are powerful tools for analyzing and predicting torrefaction outcomes and even optimizing the thermal process for its utilization. This state-of-the-art review aims to present ML-assisted torrefaction. Artificial neural networks, multivariate adaptive regression splines, decision tree, support vector machine, and other methods in the literature are discussed. Statistical approaches (SAs) for torrefaction, including Taguchi, response surface methodology, and analysis of variance, are also reviewed. Overall, this review has provided valuable insights into torrefaction optimization, which is conducive to biomass upgrading for achieving net zero.

Optimization via response surface methodology of palm kernel shell biochar for supplementary cementitious replacement

The use of sustainable materials in the construction industry has been on the rise recently. Studies have proven that the use of conventional concrete and its raw materials has a negative impact on the environment. Research on incorporating biochar as a supplementary cementitious material has been recently evolving and has shown that the attributes of biochar are highly affected by the pyrolysis parameters. These attributes have enhanced the properties of biochar concrete and mortar composite. This paper identifies the different physiochemical properties exhibited by palm kernel shell biochar through optimization by response surface methodology. Focusing on some of the properties of biochar that have proven beneficial when used as a cement replacement. Very limited research has used optimization tools for the production of biochar with the intention of using it as a cement substitute. Pyrolysis was conducted by a tubular furnace at different temperature ranges from 200 °C to 800 °C. The biomass and biochar have been analyzed with TGA and FESEM-EDX. The targeted biochar properties and selected responses are the yield, carbon, oxygen, silica, and potassium content. The optimized parameters obtained are 409 °C, 15 °C/min, 120 min with responses of 38.2% yield, 73.37% carbon, 25.48% oxygen, 0.39% potassium and 0.44% silica. Thermal properties of the palm kernel shell biochar affected by the pyrolysis factors such as temperature, heating rate and residence time have also been discussed. In conclusion, this study supports and encourages the use of palm waste, which is abundant in Malaysia, as a supplementary cementitious material to promote sustainable growth in construction.

Sewage sludge derived biochar for environmental improvement: Advances, challenges, and solutions

With the rapid growth yield of global sewage sludge, rational and effective treatment and disposal methods are becoming increasingly needed. Biochar preparation is an attractive option for sewage sludge treatment, the excellent physical and chemical properties of sludge derived biochar make it an attractive option for environmental improvement. Here, the current application state of sludge derived biochar was comprehensively reviewed, and the advances in the mechanism and capacity of sludge biochar in water contaminant removal, soil remediation, and carbon emission reduction were described, with particular attention to the key challenges involved, e.g., possible environmental risks and low efficiency. Several new strategies for overcoming sludge biochar application barriers to realize highly efficient environmental improvement were highlighted, including biochar modification, co-pyrolysis, feedstock selection and pretreatment. The insights offered in this review will facilitate further development of sewage sludge derived biochar, towards addressing the obstacles in its application in environmental improvement and global environmental crisis.

Influence of pyrolysis temperature on sludge biochar: the ecological risk assessment of heavy metals and the adsorption of Cd(II)

Pyrolysis of sludge to biochar can not only reduce the sludge volume, toxic organic compound, and pathogens, but also be applied as effective adsorbents. However, the immobilization of heavy metals in the sludge and the properties of the biochar greatly rely on the pyrolysis temperature. In this paper, municipal sludge biochar (SBC) was prepared from 400 to 1000 °C. Pyrolysis immobilized heavy metals in sludge and the potential ecological risk of heavy metals significantly decreased to low level at temperature above 500 °C. At 700 °C, the adsorption capacity of Cd(II) reached a maximum (120.24 mg·g^-1). The Cd(II) adsorption fitted the Pseudo-second-order model, indicating the existence of chemical adsorption. The adsorption capacity increased along with the initial pH and slowed down after pH reached 5.5. The existence of coexisting cations (Ca²⁺ and Na⁺) and anions (SO₄^2- and NO₃^-) displayed different degree of inhibitory action on Cd(II) adsorption. The SEM, XRD, FTIR, and XPS analysis of sludge biochar before and after adsorption revealed that there were CdCO₃, CdSO₄, Cd₂SiO₄, Cd₃(PO₄)₂, and Cd₉(PO₄)₆ appearing on the surface of sludge biochar, suggesting that the adsorption of Cd(II) by SBC included co-precipitation, ion exchange, coordination with π electrons, and complexation. It was confirmed that different properties formed by pyrolysis temperature made a difference in adsorption mechanism of sludge biochar.

Influence of pyrolysis temperature on the physicochemical properties of biochars obtained from herbaceous and woody plants

This work aimed to investigate the effect of pyrolysis temperature on the yield and properties of biochars synthesized from herbaceous and woody plants. Four typical materials, including two herbaceous plants (rice straw, corn straw) and two woody plants (camellia oleifera shells, garden waste), were used in the experiments under five operating temperatures (from 300 °C to 700 °C, with an interval of 100 °C). The results showed biochar derived from herbaceous plants had a significantly higher pH (from 7.68 to 11.29 for RS), electrical conductivity (EC, from 6.5 Ms cm-1 to 13.2 mS cm-1 for RS), cation exchange conductivity (CEC, from 27.81 cmol kg-1 to 21.69 cmol kg-1 for RS), and ash content (from 21.79% to 32.71% for RS) than the biochar from woody plants, but the volatile matter (VM, from 42.23% to 11.77% for OT) and specific surface area (BET, from 2.88 m2 g-1 to 301.67 m2 g-1 for OT) in the woody plant-derived biochar were higher. Except for CEC and VM, all the previously referred physicochemical characteristics in the as-prepared biochars increased with the increasing pyrolysis temperature, the H/C and O/C values of herbaceous and woody plant-derived biochar were lower than 0.9 and 0.3, respectively, confirming their potential as the material for carbon sequestration. The results revealed that biochar made from herbaceous plants was more suitable for acidic soil amendments. In contrast, woody plant-derived biochar were recommended to remove heavy metals in environmental remediation and water treatment.

Adsorption performance and mechanism of cationic and anionic dyes by KOH activated biochar derived from medical waste pyrolysis

The massive generation of medical waste (MW) results in a series of environmental, social, and ecological problems. Pyrolysis is one such approach that has attracted more attention because of the production of value-added products with lesser environmental risk. In this study, the activated biochar (ABC600) was obtained from MW pyrolysis and activated with KOH. The adsorption mechanism of activated biochar on cationic (methylene blue) and anionic (reactive yellow) dyes were studied. The physicochemical characterization of biochar showed that increasing pyrolysis temperature and KOH activation resulted in increased surface area, a rough surface with a clear porous structure, and sufficient functional groups. MB and RYD-145 adsorption on ABC600 was more consistent with Langmuir isotherm (R² ≥ 0.996) and pseudo-second-order kinetics (R² ≥ 0.998), indicating chemisorption with monolayer characteristics. The Langmuir model fitting demonstrated that MB and RYD-145 had maximum uptake capacities of 922.2 and 343.4 mg⋅g^-1. The thermodynamics study of both dyes showed a positive change in enthalpy (ΔH°) and entropy (ΔS°), revealing the endothermic adsorption behavior and randomness in dye molecule arrangement on activated-biochar/solution surface. The activated biochar has excellent adsorption potential for cationic and anionic dyes; hence, it can be considered an economical and efficient adsorbent.

Synthesis of carbon molecular sieves from agricultural residues: Status, challenges and prospects

Adsorption is the most promising technology used in the gas separation and purification process. The key success of this technology relies on the selection of an adsorbent. Activated carbon and zeolites are the most commonly used adsorbents in the separation of particular gas from gaseous mixtures. Activated carbon deriving from fossil and biomass-based resources has wide pore size distribution and thereby results in lower selectivity. Whereas, zeolites synthesized from natural minerals are expensive which increases the cost of the purification process. Taking this into concern, the quest for synthesizing low-cost and effective adsorbents has gained greater attention in recent years. Carbon Molecular Sieves (CMSs), are considered as an attractive alternative to replace the conventional adsorbents. Furthermore, CMSs exhibit higher selectivity and adsorption capacity, due to their narrow micropore size distribution (0.3-0.5 nm). CMSs are synthesized from any organic carbonaceous precursor with low inorganic content. Since most of the agricultural residues fall under this category, they can be used as a feedstock for CMSs production. The synthesis of CMSs involves three stages: carbonization, activation, and pore modification. In this review, physicochemical characteristics of various agricultural residues, the effects of carbonization process parameters, activation methods, and pore modification techniques adopted for producing CMSs are comprehensively discussed. The effect of deposition temperature, time, and flow rate of depositing agent on pore characteristics of CMSs is briefed. The prospects and challenges in CMSs production are also studied. The insights in this review provide guidelines for synthesizing CMSs from agro-residues.

Phytoremediation plants (ramie) and steel smelting wastes for calcium silicate coated-nZVI/biochar production: Environmental risk assessment and efficient As(V) removal mechanisms

Arsenic is one of the most common and harmful pollutants in environment throughout the world, especially in aqueous solutions. In this study, two kinds of industrial solid wastes (Oxide scale (OS) and Blast furnace slag (BFS)) and one kind of phytoremediation plant waste (Ramie stalk) were used to prepare an environmentally friendly, low-cost, and efficient calcium silicate coated nano zero-valent iron (nZVI)/biochar composite (BOS) for As(V) adsorption. The potential environmental risks of BOS and their effects on removal of arsenic ions from aqueous media were investigated. The adsorption mechanism was explored and discussed based on XRD, SEM-EDS, XPS, etc. The results suggested that the environmental risk and heavy metals toxicity in BOS by co-pyrolysis were significantly reduced compared to the original materials, and no additional contaminant was observed in the subsequent experiments. Simultaneously, the BOS showed excellent As(V) removal capacity (>99%) and regenerative properties. The As(V) removal mechanisms are mainly ascribed to the complexation and co-precipitation between Fe and As, and the hydrogen bond between CO functional group of BOS and As. The mechanism of enhanced nZVI activity for As(V) removal was revealed. A protective layer of Ca₂SiO₄ was formed on the surface of nZVI during the co-pyrolysis process to prevent the passivation of nZVI. During the reaction process, the Ca₂SiO₄ covering the nZVI surface would be continuously detached to expose the fresh surface of nZVI, thus providing more redox activity and adsorption sites. This study provides a new way to treat and recycle industrial steel solid wastes and phytoremediation plant wastes, and the produced calcium silicate coated-nZVI/biochar composite is proposed to be a very promising material for practical remediation of As(V)-contaminated water bodies.

Pyrolysis Temperature and Application Rate of Sugarcane Straw Biochar Influence Sorption and Desorption of Metribuzin and Soil Chemical Properties

Pyrolysis temperature and application rate of biochar to soil can influence herbicide behavior and soil fertility. The objective was to investigate the effect of soil amendments with application rates of sugarcane straw biochar, produced at different pyrolysis temperatures, on the sorption–desorption of metribuzin in soil. The analysis was performed using high-performance liquid chromatography (HPLC). The treatments were three pyrolysis temperatures (BC350, BC550 and BC750 °C) and seven application rates (0, 0.1, 0.5, 1, 1.5, 5 and 10% w w−1). Amended soil with different application rates decreased H + Al and increased pH, OC, P, K, Ca, Mg, Fe, Mn, CEC and BS contents. Kf values of sorption and desorption of metribuzin were 1.42 and 0.78 mg(1−1/n) L1/n Kg−1, respectively, in the unamended soil. Application rates < 1% of biochar sorbed ~23% and desorbed ~15% of metribuzin, similar to unamended soil, for all pyrolysis temperatures. Amended soil with 10% of BC350, BC550 and BC750 sorbed 63.8, 75.5 and 89.4% and desorbed 8.3, 5.8 and 3.7% of metribuzin, respectively. High pyrolysis temperature and application rates of sugarcane straw biochar show an ability to immobilize metribuzin and improve soil fertility, which may influence the effectiveness in weed control.

Recent Developments in Activated Carbon Catalysts Based on Pore Size Regulation in the Application of Catalytic Ozonation

Due to its highly developed pore structure and large specific surface area, activated carbon is often used as a catalyst or catalyst carrier in catalytic ozonation. Although the pore structure of activated carbon plays a significant role in the treatment of wastewater and the mass transfer of ozone molecules, the effect is complicated and unclear. Because different application scenarios require catalysts with different pore structures, catalysts with appropriate pore structure characteristics should be developed. In this review, we systematically summarized the current adjustment methods for the pore structure of activated carbon, including raw material, carbonization, activation, modification, and loading. Then, based on the brief introduction of the application of activated carbon in catalytic ozonation, the effects of pore structure on catalytic ozonation and mass transfer are reviewed. Furthermore, we proposed that the effect of pore structure is mainly to provide catalytic active sites, promote free radical generation, and reduce mass transfer resistance. Therefore, large external surface area and reasonable pore size distribution are conducive to catalytic ozonation and mass transfer.

How Biochar Derived from Pond Cypress (Taxodium Ascendens) Evolved with Pyrolysis Temperature and Time and Their End Efficacy Evaluation

Biomass type, pyrolysis temperature, and duration can affect biochar properties simultaneously. To further clarify the mechanism of this interaction, the branch and leaf parts of Pond cypress (Taxodium ascendens) were separately pyrolyzed at four peak temperatures (350 °C, 450 °C, 650 °C, and 750 °C) for three different durations (0.5 h, 1 h, and 2 h) in this study. The resulting biochar properties were measured, which included the yield, specific surface area (SSA), pH, EC (electricity conductivity), the bulk and surface elemental composition, and the contents of moisture, ash, fixed carbon, and volatile matter. The results showed that the pyrolysis temperature was more determinant for the modification of all biochar, but the residence time had a significant effect on the yield, pH, and SSA of branch-based biochar (B-biochar) at specific temperatures. However, such a phenomenon only happened on the pH of leaf-based biochar (L-biochar). Results: (1) With the temperature at 350 and 650 °C, the residence time had a significant effect on the yield of B-biochar. (2) The pH of B-biochar and L-biochar varied considerably between durations when the heating temperature hit 650 and 750 °C. (3) The SSA of B-biochar possessed an obvious fluctuation with the time during the pyrolysis from 650 to 750 °C. According to the properties measured above, the principal component and the cluster analysis classified the 24 types of biochar made in this experiment into four groups and revealed that an obvious disparity existed between B-biochar and L-biochar that were pyrolyzed at temperatures ranging from 450 to 750 °C, which suggested that biomass type was the primary factor for biochar-making. All this information can provide valuable references for the optimization of biochar-making in the real world.

Quantitative evaluation of the synergistic effect of biochar and plants on immobilization of Pb

Biochar and plant cooperation in remediation of heavy metal contaminated soil is effective and important, but there still have knowledge gaps of synergistic effect between the two and the synergistic pathway has not been clarified. We prepared the Enteromorpha prolifera biochar at 400 °C and 600 °C (denoted as BC400 and BC600). The Pb fractions changes in soil and Pb toxicity in Brassica juncea were investigated by adding 30 g kg^-1 biochar to soil containing 1200 mg kg^-1 Pb in a pot experiment. There was a significant synergistic effect between biochar and plants on Pb immobilization in soil, according to the "E > 0" of Pb fractions in the interaction equation. Pb immobilization rates of biochar-plant treatments (BJBC4 and BJBC6) were 12.47% and 11.38% higher than biochar treatment (BC4, BC6), and 17.66% and 16.28% plant treatment (BJ). BJBC4 had a better immobilization effect than BJBC6. Biochar alleviated the phytotoxicity of Pb by increasing the antioxidant enzymes activities of plants. These results indicated two synergistic pathways: (1) The high pH and oxygen-containing functional groups of biochar could immobilize Pb through ion exchange, precipitation, or complexation. (2) Biochar enhanced the activity of the antioxidant enzyme system in plants thus improving the Pb tolerance of plants. Statistical analysis methods such as the partial least squares path modeling (PLS-PM) also confirmed the pathways. In a word, clear synergistic effects and pathways could guide the application of biochar and plants in Pb-contaminated soil.

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

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

Energy-efficient biochar production for thermal backfill applications

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

Effects of different low temperature pretreatments on properties of corn stover biochar for precursors of sulfonated solid acid catalysts

In this study, the effects of different pretreatment methods including phosphoric acid (PA), freeze drying (FD) and phosphoric acid-freeze drying combined (PA-FD) pretreatment on corn stover characteristics and pyrolysis of corn stover samples was investigated. The results demonstrated that the physiochemical properties of biochars varied significantly. In comparison, PA pretreatment could effectively remove a large portion of inorganics and improve the fuel characteristics. PA-CSB-600 had a greater HHV, lower O/C and H/C ratios, and a lower biochar energy yield (Y_e), indicating the possibility for an attractive fuel source. PA-FD pretreatment would significantly affected cell volume and caused mechanical damage to corn stover structure. As a sulfonated solid acid catalyst precursor, the results of cellulose catalytic hydrolysis indicated that the density of -SO₃H in FD-CSA was much higher than PA-FD-CSA, but lower surface special area. Specifically, PA-FD-CSB prepared at 600 °C resulted in the maximum increase of cellulose conversion by 34.7-81.3%.

Effects of physical and chemical aging on polycyclic aromatic hydrocarbon (PAH) content and potential toxicity in rice straw biochars

Polycyclic aromatic hydrocarbons in biochars threaten their environmental application. The aging process may affect the concentration of PAHs, potential toxicity, and the properties of biochar. In this study, the aged biochars were obtained by simulated physical aging method (freeze-thaw treatment) and chemical aging method (H₂O₂ chemical oxidation). The PAH contents in biochars were measured, and their potential toxicity was assessed. Meanwhile, the influence of aging process on the physicochemical properties of biochar was also investigated. This study shows that the change of PAH content of aged biochars depended on pyrolysis temperature, ambient temperature, and oxidant concentration. Furthermore, physical and chemical aging process influenced the distribution of different ring PAHs in biochars. High-ring-number PAHs (four, five, six-ring PAHs) appeared in some aged biochar. Aging at ±20 °C and 0.01 M H₂O₂ increased the toxic equivalent quantity of all biochars which may be attributed to the change of the physicochemical properties influencing the different PAH ring distribution in biochars. The contribution of PAHs with different rings to TEQ varied in pristine and aged biochars. Physical and chemical aging process significantly affected the properties of biochars, such as element content, ash content, surface area, pore volume, pH, functional groups, and surface morphology. Correlation analysis confirmed that surface area and pore volume are dominant factors determining the PAH content in the biochars. Therefore, the aging process indeed affected the PAH concentration and toxicity of PAHs in biochar. Assessing PAH behavior in biochar over long timescales should not be overlooked.