Application of biochar for the removal of pollutants from aqueous solutions

Characterization and utilization of biochars derived from five invasive plant species Bidens pilosa L., Praxelis clematidea, Ipomoea cairica, Mikania micrantha and Lantana camara L. for Cd2+ and Cu2+ removal

Exotic invasive plants endanger the integrity of agricultural and natural systems throughout the world. Thus, the development of cost-effective and economic application of invasive plants is warranted. Here, we characterized fifteen biochars derived from five invasive plants at different temperatures (300, 500, and 700 °C) by determining their yield, ash content, pH, CEC, surface area, elementary composition, functional groups, and mineral composition. We conducted batch adsorption experiments to investigate the adsorption capacity and efficiency for Cd²⁺ and Cu²⁺ in wastewater. Our results suggest that all invasive plants are appropriate for biochar production, temperature and plant species had interacting effects on biochar properties, and the biochars pyrolyzed at 500 and 700 °C exhibited high metal adsorption capacity in neutral (pH = 7) solutions. The adsorption kinetics can be explained adequately by a pseudo-second-order model. BBC500 (Bidens pilosa L. derived biochar at 500 °C) and MBC500 (Mikania micrantha) exhibited higher metal equilibrium adsorption capacities (38.10 and 38.02 mg g^-1 for Cd²⁺, 20.01 and 20.10 mg g^-1 for Cu²⁺) and buffer abilities to pH than other biochars pyrolyzed at 500 °C. The Langmuir model was a better fit for IBC500 (Ipomoea cairica), MBC500, and LBC500 (Lantana camara L.) compared to the Freundlich model, whereas the opposite was true for BBC500 and PBC500 (Praxelis clematidea). These results suggest that the adsorption of metals by IBC500, MBC500, and LBC500 was mainly monolayer adsorption, while that by BBC500 and PBC500 was mainly chemical adsorption. Our results are important for the utilization and control of invasive plants as well as the decontamination of aqueous pollution.

Development and Characterization of Composite Carbon Adsorbents with Photocatalytic Regeneration Ability: Application to Diclofenac Removal from Water

This paper presents results related to the development of a carbon composite intended for water purification. The aim was to develop an adsorbent that could be regenerated using light leading to complete degradation of pollutants and avoiding the secondary pollution caused by regeneration. The composites were prepared by hydrothermal carbonization of palm kernel shells, TiO2, and W followed by activation at 400 °C under N2 flow. To evaluate the regeneration using light, photocatalytic experiments were carried out under UV-A, UV-B, and visible lights. The materials were thoroughly characterized, and their performance was evaluated for diclofenac removal. A maximum of 74% removal was observed with the composite containing TiO2, carbon, and W (HCP25W) under UV-B irradiation and non-adjusted pH (~5). Almost similar results were observed for the material that did not contain tungsten. The best results using visible light were achieved with HCP25W providing 24% removal of diclofenac, demonstrating the effect of W in the composite. Both the composites had significant amounts of oxygen-containing functional groups. The specific surface area of HCP25W was about 3 m2g−1, while for HCP25, it was 160 m2g−1. Increasing the specific surface area using a higher activation temperature (600 °C) adversely affected diclofenac removal due to the loss of the surface functional groups. Regeneration of the composite under UV-B light led to a complete recovery of the adsorption capacity. These results show that TiO2- and W-containing carbon composites are interesting materials for water treatment and they could be regenerated using photocatalysis.

Static and Dynamic Investigations on Leaching/Retention of Nutrients from Raw Poultry Manure Biochars and Amended Agricultural Soil

In this study, nutrients release/adsorption from/by raw poultry manure-derived biochar produced at a pyrolysis temperature of 600 °C (RPM-B) was assessed under static and dynamic conditions. Batch sequential leaching experiments of RPM-B for a total contact time of 10 days showed that both phosphorus and potassium were slowly released but with higher amounts compared to various other animal- and lignocellulosic-derived biochars. The cumulated released P and K amounts were assessed to 93.6 and 17.1 mg g−1, which represent about 95% and 43% of their original contents in the RPM-B, respectively. The column combined leaching/adsorption experiments showed that amending an alkaline sandy agricultural soil with two doses of RPM-B (at 5% and 8% w:w) resulted in an efficient retention of NO3-N and NH4-N, and on the contrary, important leached amounts of PO4-P, K+, Mg2+, and Ca2+ but with relatively slow kinetic release rates for a long period. Even after 40 days of dynamic leaching, these latter nutrients continued to be released with kinetic rates lower than 10 mg kg−1 d−1. Thus, compared to synthetic fertilizers, RPM-B valorization as organic amendment for poor semiarid soils could be considered as an attractive, eco-friendly, and sustainable waste recycling option.

Current Trends of Arsenic Adsorption in Continuous Mode: Literature Review and Future Perspectives

Arsenic is a toxic element for humans and a major pollutant in drinking water. Natural and anthropogenic sources can release As into water bodies. The countries with the greatest arsenic contamination issues lack the affordable technology to attain the maximum permitted concentrations. Adsorption can be a highly efficient and low-cost option for advanced water treatment, and the development of new cheap adsorbents is essential to expand access to water with a safe concentration of arsenic. This paper aims to review the state of the art of arsenic adsorption from water in continuous mode and the latest progress in the regeneration and recovery of arsenic. The disposal of the exhausted bed is also discussed. Fixed-bed column tests conducted with novel adsorbents like binary metal oxides and biosorbents achieved the highest adsorption capacities of 28.95 mg/g and 74.8 mg/g, respectively. Iron-coated materials presented the best results compared to adsorbents under other treatments. High recovery rates of 99% and several cycles of bed regeneration were achieved, which can aggregate economic value for the process. Overall, further pilot-scale research is recommended to evaluate the feasibility of novel adsorbents for industrial purposes.

Recent Developments in Chitosan-Based Adsorbents for the Removal of Pollutants from Aqueous Environments

The quality of water is continuously under threat as increasing concentrations of pollutants escape into the aquatic environment. However, these issues can be alleviated by adsorbing pollutants onto adsorbents. Chitosan and its composites are attracting considerable interest as environmentally acceptable adsorbents and have the potential to remove many of these contaminants. In this review the development of chitosan-based adsorbents is described and discussed. Following a short introduction to the extraction of chitin from seafood wastes, followed by its conversion to chitosan, the properties of chitosan are described. Then, the emerging chitosan/carbon-based materials, including magnetic chitosan and chitosan combined with graphene oxide, carbon nanotubes, biochar, and activated carbon and also chitosan-silica composites are introduced. The applications of these materials in the removal of various heavy metal ions, including Cr(VI), Pb(II), Cd(II), Cu(II), and different cationic and anionic dyes, phenol and other organic molecules, such as antibiotics, are reviewed, compared and discussed. Adsorption isotherms and adsorption kinetics are then highlighted and followed by details on the mechanisms of adsorption and the role of the chitosan and the carbon or silica supports. Based on the reviewed papers, it is clear, that while some challenges remain, chitosan-based materials are emerging as promising adsorbents.

O-doped Graphitic Granular Biochar Enables Pollutants Removal via Simultaneous H2O2 Generation and Activation in Neutral Fe-free Electro-Fenton Process

H₂O₂ generation by 2-electron oxygen electroreduction reaction (2eORR) has attracted great attention as an alternative to the industry-dominant anthraquinone process. Electro-Fenton (EF) process, which relies on the H₂O₂ electrogeneration, is regarded as an important environmental application of H₂O₂ generation by 2eORR. However, its application is hindered by the relatively expensive electrode materials. Proposing cathode materials with low cost and facile synthetic procedures are the priority to advance the EF process. In this work, a composite cathode structure that uses graphitic granular bamboo-based biochar (GB) and stainless steel (SS) mesh (GBSS) is proposed, where SS mesh functions as current distributor and GB supports synergistic H₂O₂ electrogeneration and activation. The graphitic carbon makes GB conductive and the oxygen-containing groups serve as active sites for H₂O₂ production. 11.3 mg/L H₂O₂ was produced from 2.0 g GB at 50 mA after 50 min under neutral pH without external O₂/air supply. The O-doped biochar further increased the H₂O₂ yield to 18.3 mg/L under same conditions. The GBSS electrode is also effective for H₂O₂ activation to generate ·OH, especially under neutral pH. Ultimately, a neutral Fe-free EF process enabled by GBSS cathode is effective for removal of various model organic pollutants (reactive blue 19, orange II, 4-nitrophenol) within 120 min, and for their partial mineralization (48.4% to 63.5%). Long-term stability of the GBSS electrode for H₂O₂ electrogeneration, H₂O₂ activation, and pollutants degradation were also examined and analyzed. This work offers a promising application for biomass waste for removals of organic pollutants in neutral Fe-free EF process.

Highly efficient removal of thallium in wastewater by MnFe2O4-biochar composite

Thallium (Tl), is a highly toxic trace metal in the natural environment. Emerging Tl pollution in waters has gradually become a global concern. However, limited removal technologies are available for Tl-containing wastewater. Herein, MnFe₂O₄-biochar composite (MFBC) was successfully fabricated via coprecipitation method as a novel and efficient adsorbent for treating Tl(I)-contaminated wastewater. It was found that the MFBC, with a specific surface area of 187.03 m²/g, exhibited high performance across a wide pH range of 4-11, with the superior Tl(I) removal capacity (170.55 mg/g) based on Langmuir model (pH 6.0, a dosage of 1 g/L). The removal mechanisms included physical and chemical adsorption, ion exchange, surface complexation, and oxidation. This investigation revealed that MFBC is a promising and environmentally friendly adsorbent with a low cost, large specific surface area, magnetic properties, and high efficiency for the removal of Tl(I) from wastewater.

State-of-the-Art Char Production with a Focus on Bark Feedstocks: Processes, Design, and Applications

In recent years, there has been a surge of interest in char production from lignocellulosic biomass due to the fact of char’s interesting technological properties. Global char production in 2019 reached 53.6 million tons. Barks are among the most important and understudied lignocellulosic feedstocks that have a large potential for exploitation, given bark global production which is estimated to be as high as 400 million cubic meters per year. Chars can be produced from barks; however, in order to obtain the desired char yields and for simulation of the pyrolysis process, it is important to understand the differences between barks and woods and other lignocellulosic materials in addition to selecting a proper thermochemical method for bark-based char production. In this state-of-the-art review, after analyzing the main char production methods, barks were characterized for their chemical composition and compared with other important lignocellulosic materials. Following these steps, previous bark-based char production studies were analyzed, and different barks and process types were evaluated for the first time to guide future char production process designs based on bark feedstock. The dry and wet pyrolysis and gasification results of barks revealed that application of different particle sizes, heating rates, and solid residence times resulted in highly variable char yields between the temperature range of 220 °C and 600 °C. Bark-based char production should be primarily performed via a slow pyrolysis route, considering the superior surface properties of slow pyrolysis chars.

Stabilization of anaerobic co-digestion of biowaste using activated carbon of coffee ground biomass

Process instability commonly encountered in anaerobic co-digestion (AcoD) of organic fractions of municipal solid wastes (OFMSWs) is addressed by utilizing hydrochar (CB-HTC) and activated hydrochar (ACB-HTC) derived from coffee ground biomass. Addition of CB-HTC or ACB-HTC shortened the lag phase resulting in high biogas yield of 68.57 Nl/kg oTS or 102.86 Nl/kg oTS, respectively within the first week. Improvement in biogas yield (~5% higher than the control) was due to unique properties which prevented washout of consortia of bacteria useful for AcoD and subsequently led to a more stable process. An increase in either OLR [1.0 kg oTS/(m³*d) to 1.5 kg oTS/(m³*d)] or temperature (36.5 °C to 42.5 °C) did not lead to increase in ammonium-nitrogen or TKN in reactors amended with hydrochars. Likewise, ratio of VFA/TA was within 0.2-0.3 after the fourth week in ACB-HTC treated reactor. Addition of ACB-HTC greatly improved nutrient retention in the digestate.

The addition of biochar as a sustainable strategy for the remediation of PAH-contaminated sediments

The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH-contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi-PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m² g^-1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low-temperature biochar-amended sediments. Finally, biochar is effective in co-application with Fe²⁺ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.

Increasing straw surface functionalities for enhanced adsorption property

A simple low-temperature partial-oxidation process was demonstrated as an effective technology for reed straw modification towards environmental remediation. At an optimal temperature of 180 °C, the straw materials exhibited a remarkable colour change from light yellow to dark brown, increased methylene blue (MB) uptake by 1.8 times, enhanced removal efficiency from 34.5% to 92.8%, and a high yield of 77.2%. Spectroscopic characterization and Boehm titration proved that the amount of surface oxygen (O)-containing functional groups significantly increased after modification. A strong linear correlation (R² = 0.93) existed between total amounts of O-containing functional groups and MB uptake for modification temperatures below 180 °C, whereas blockage of the pore entrances and competition with metallic cations must be taken into account for samples generated from excess heating (>180 °C). These results provided insights into designing promising technologies for sustainable environmental management through reutilization of agricultural waste.

Study on the denitrification and dephosphorization of the aqueous solution by Chitosan/4A Zeolite/Zr based Zeolite

The ternary hybrid material chitosan/4A Zeolite/Zr based Zeolite was synthesized by using 4A zeolite molecular sieve, Zr-zeolite and chitosan acetic acid solution as starting materials. The prepared composite were characterized by SEM, FT-IR and XRD. The experimental conditions such as the concentration of chitosan acetic acid solution, mass ratio of mass ratio of chitosan acetic acid solution, 4A zeolite molecular sieve and Zr-zeolite functional material, the optimum calcination temperature were optimized. Under this optimum conditions, the denitrification and dephosphorization effect can reach more than 70% when pH value was at 3-9. Dynamics research results showed that the ammonia nitrogen and phosphorus removal progress by chitosan/4A Zeolite/Zr based Zeolite was in accordance could be well described by the pseudo-second-order kinetic model, and the adsorption rate is up to 6.439 g/min. The isothermal adsorption process was in accordance with Freundlich model.

Batch study for Pb2+ removal by polyvinyl alcohol-biochar macroporous hydrogel bead

In this paper, a novel adsorbent which used polyvinyl alcohol, alginate and biochar was successfully made and been used to remove lead from aqueous solutions. Batch experiments were carried out to evaluate the adsorption capacities of Pb (II) on this bead. Experimental data were analysed by the model equations like Langmuir and Freundlich and adsorption kinetic constants were determined using pseudo-first-order (PFO) and pseudo-second-order (PSO). In this study, the adsorption characteristics of Pb (II) were well fitted by the Langmuir isotherm model and pseudo-second-order (PSO) kinetic model. The adsorption of Pb (II) onto PVA-biochar beads are spontaneous and exothermic at 303-333 K by the evidence of the changes in standard Gibbs free energy, standard enthalpy and standard entropy. The maximum adsorption capacity for Pb (II) was estimated to be 176.40 mg/g, which is comparable with other adsorbents. While the maximum adsorption increased varying the pH of initial solution from 2 to 6, the effect on the adsorption amount by the sodium ion concentration is not very large. The results of EDS spectra indicated that the existence of lead in polyvinyl alcohol (PVA)-biochar bead after adsorption, which proving the adsorption of lead. In XPS spectrum, the observed Pb elements also demonstrated that the lead was adsorbed by PVA-biochar bead.

Coconut husk biochar amendment enhances nutrient retention by suppressing nitrification in agricultural soil following anaerobic digestate application

Anaerobic digestate and biochar are by-products of the biogasification and pyrolysis of agricultural wastes. This study tested the hypothesis that combined application of anaerobic pig/cattle manure digestate and coconut husk (CH) biochar can improve soil nutrient conditions, whilst minimizing atmospheric and groundwater pollution risks. Microcosms simulated digestate application to agricultural soil with and without CH biochar. Ammonia volatilization and nutrient leaching were quantified after simulated heavy rainfalls. Archaeal and bacterial community and abundance changes in soils were quantified via next generation sequencing and qPCR of 16S rRNA genes. Nitrifying bacteria were additionally quantified by qPCR of functional genes. It was found that CH biochar retarded nitrate leaching via slower nitrification in digestate-amended soil. CH biochar reduced both nitrifying archaea and bacteria abundance in soil by 71-83 percent in the top 4 cm soil layer and 66-80 percent in the deeper soil layer one month after the digestate application. Methanotroph abundances were similarly reduced in the CH biochar amended soils. These findings demonstrate combined benefits of anaerobic digestate and CH biochar application which are relevant for the development of a more circular rural economy with waste minimization, renewable energy production, nutrient recycling and reduced water pollution from agricultural land.

Nanobiochar paper based electrochemical immunosensor for fast and ultrasensitive detection of microcystin-LR

A portable, cheap and sensitive paper type electrochemical immunosensor was developed with conductive nanobiochar paper as the conductive layer and utilized for sensitive detection of microcystin-LR (MCLR) toxin in water. The paper immunosensor was constructed by coating of highly conductive and dispersible nanobiochar particle (nBC) and anti-MCLR antibody on the filter paper via dipping-drying method. The presence of MCLR could be specifically quantified amperometrically by the nBC-paper immunosensor with the response time of less than 5 min, and the lowest detection limit of 17 pM (0.017 μg/L) was achieved. Moreover, the proposed immunosensor exhibited high selectivity, reproducibility and storage stability, and was also used for environmental water detection with satisfactory recovery. The successful fabrication of low cost and ubiquitous biochar based paper type electrochemical immunosensing system would have significant value for the development of highly cost-effective electrochemical device.

Sustainable Chromium (VI) Removal from Contaminated Groundwater Using Nano-Magnetite-Modified Biochar via Rapid Microwave Synthesis

This study developed a nano-magnetite-modified biochar material (m-biochar) using a simple and rapid in situ synthesis method via microwave treatment, and systematically investigated the removal capability and mechanism of chromium (VI) by this m-biochar from contaminated groundwater. The m-biochar was fabricated from reed residues and magnetically modified by nano-Fe₃O₄. The results from scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterisations confirmed the successful doping of nano-Fe₃O₄ on the biochar with an improved porous structure. The synthesised m-biochar exhibited significantly higher maximum adsorption capacity of 9.92 mg/g compared with that (8.03 mg/g) of the pristine biochar. The adsorption kinetics followed the pseudo-second-order model and the intraparticle diffusion model, which indicated that the overall adsorption rate of Cr(VI) was governed by the processes of chemical adsorption, liquid film diffusion and intramolecular diffusion. The increasing of the pH from 3 to 11 significantly affected the Cr(VI) adsorption, where the capabilities decreased from 9.92 mg/g to 0.435 mg/g and 8.03 mg/g to 0.095 mg/g for the m-biochar and pristine biochar, respectively. Moreover, the adsorption mechanisms of Cr(VI) by m-biochar were evaluated and confirmed to include the pathways of electrostatic adsorption, reduction and complexation. This study highlighted an effective synthesis method to prepare a superior Cr(VI) adsorbent, which could contribute to the effective remediation of heavy metal contaminations in the groundwater.

Reaction of Substituted Phenols with Lignin Char: Dual Oxidative and Reductive Pathways Depending on Substituents and Conditions

Biomass chars are known to be intrinsically redox-reactive toward some organic compounds, but the mechanisms are still unclear. To address this, a char made anoxically at 500 °C from dealkaline lignin was reacted either in the fresh state or after 180-day aging in air with p-nitrophenol (NO₂-P), p-hydroxybenzaldehyde (CHO-P), phenol (H-P), or p-methoxyphenol (MeO-P). The reactions were carried out under oxic or anoxic conditions. Degradation occurred in all cases. Both oxidation and reduction products were identified, with yields dependent on the presence or absence of air during reaction or storage. They included oligomers, amines, and ring-hydroxylated compounds, among others. Exposure to air suppressed sorption, annihilated reducing sites, and provided a source of reactive oxygen species that assisted degradation. Sorption suppression was due to the incorporation of hydrophilic groups by chemisorption of oxygen, and possibly blockage of sites by products. Fresh char has comparable electron-donating and accepting capacity, whereas there is a preponderance of electron-accepting over donating capacity in aged char. Under anoxic conditions, both oxidation and reduction occurred. Under oxic conditions or after aging in air, oxidation predominated, and linear free energy relationships were found between the rate constant and the Hammett or Brown substituent electronic parameter or the standard electrode potential of the phenol. The results demonstrate that chars possess heterogeneous redox activities depending on reaction pairs, reaction conditions, and aging.

The key role of persistent free radicals on the surface of hydrochar and pyrocarbon in the removal of heavy metal-organic combined pollutants

We show that persistent free radicals (PFRs) on the surface of biochar can produce hydroxyl radicals (•OH) by catalyzing H₂O₂ to facilitate the removal of the combined pollutant BPA-Cr(VI). Microstructure characterization showed that the structures of pyrocarbon and hydrochar were significantly different when prepared at different temperatures. As the preparation temperature and preparation time for biochar increased, the concentration of PFRs first increased and then decreased. When biochar, PFRs, and H₂O₂ were present in the same solution, the single pollutants BPA and Cr(VI) as well as the combined pollutant BPA-Cr(VI) could be removed effectively, with removal rates greater than 90%. However, when PFRs, BPA, H₂O₂, and Cr(VI) were present in the same solution, Cr(VI) competed with H₂O₂ for electrons and promoted the removal of BPA. The results of this study could be applied to sludge recycling and be used to develop approaches to catalytically degrade combined pollutants.

Effective removal of carbamazepine and diclofenac by CuO/Cu2O/Cu-biochar composite with different adsorption mechanisms

In this study, the CuO/Cu₂O/Cu-biochar composite (CBC) was fabricated by calcining Cu²⁺-loaded cauliflower root at 500 °C. The CBC displayed the higher specific surface area and total pore volume than raw biochar, which attributed to Cu²⁺ acting as a pore-forming agent in the synthesis process. The adsorption experiments indicated that CBC could remove 88.96% diclofenac and 93.02% carbamazepine, which was nearly double higher than the raw biochar. The film diffusion mainly controlled the adsorption rate. Meanwhile, the common adsorption mechanisms for two pollutants were deemed to hydrogen-bonding interaction, π-π interaction and micropore filling effect, and copper oxide particles providing more adsorption sites. In addition, the adsorption of diclofenac involved electrostatic attraction. Lastly, the higher adsorption capacity of carbamazepine than diclofenac on CBC was mainly attributed to two mechanisms: Lewis acid-base interaction enhancing the adsorption of carbamazepine and size exclusion effect reducing the adsorption of diclofenac. Therefore, the study provided a possible method that Cu-contaminated biomass converted to CuO/Cu₂O/Cu-biochar, which could achieve win-win results.

Enhanced adsorption of Pb(II) by nitrogen and phosphorus co-doped biochar derived from Camellia oleifera shells

We describe the synthesis of a series of novel nitrogen- and phosphorus-enriched biochar (activated carbon, AC) nanocomposites via the co-pyrolysis of Camellia oleifera shells (COSs) with different weight ratios of ammonium polyphosphate (APP) (w_APP: w_COSs = 1-3:1). The physicochemical characteristics of these nanocomposites (APP@ACs) were investigated via X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption/desorption analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results revealed that the APP@ACs exhibited richer N- and P-containing functional groups than unmodified AC. In addition, the removal performance of APP@AC-3 with respect to Pb(II) (723.6 mg g^-1) was greatly improved relative to unmodified AC (264.2 mg g^-1). Kinetic and equilibrium data followed the pseudo-second-order kinetic model and Langmuir model, respectively. The removal mechanism could be attributed to partial physisorption and predominant chemisorption. The N₂ adsorption/desorption isotherms demonstrated that pore-volume properties could be an effective physical trap for Pb(II). Furthermore, the XPS and FTIR analysis revealed that the chemical removal mechanism of the APP@ACs is surface complexation via N-containing and P-containing functional groups. These findings indicate that the co-pyrolysis of COSs and APP leads to the formation of nitrogen- and phosphorus-containing functional groups that facilitate excellent activated carbon-based (biochar) adsorption performance.

Biochar Aging: Mechanisms, Physicochemical Changes, Assessment, And Implications for Field Applications

Biochar has triggered a black gold rush in environmental studies as a carbon-rich material with well-developed porous structure and tunable functionality. While much attention has been placed on its apparent ability to store carbon in the ground, immobilize soil pollutants, and improve soil fertility, its temporally evolving in situ performance in these roles must not be overlooked. After field application, various environmental factors, such as temperature variations, precipitation events and microbial activities, can lead to its fragmentation, dissolution, and oxidation, thus causing drastic changes to the physicochemical properties. Direct monitoring of biochar-amended soils can provide good evidence of its temporal evolution, but this requires long-term field trials. Various artificial aging methods, such as chemical oxidation, wet-dry cycling and mineral modification, have therefore been designed to mimic natural aging mechanisms. Here we evaluate the science of biochar aging, critically summarize aging-induced changes to biochar properties, and offer a state-of-the-art for artificial aging simulation approaches. In addition, the implications of biochar aging are also considered regarding its potential development and deployment as a soil amendment. We suggest that for improved simulation and prediction, artificial aging methods must shift from qualitative to quantitative approaches. Furthermore, artificial preaging may serve to synthesize engineered biochars for green and sustainable environmental applications.

Heavy Metal Sorption by Sludge-Derived Biochar with Focus on Pb2+ Sorption Capacity at μg/L Concentrations

Municipal wastewater management causes metal exposure to humans and the environment. Targeted metal removal is suggested to reduce metal loads during sludge reuse and release of effluent to receiving waters. Biochar is considered a low-cost sorbent with high sorption capacity for heavy metals. In this study, heavy metal sorption to sludge-derived biochar (SDBC) was investigated through batch experiments and modeling and compared to that of wood-derived biochar (WDBC) and activated carbon (AC). The aim was to investigate the sorption efficiency at metal concentrations comparable to those in municipal wastewater (<1 mg/L), for which experimental data are lacking and isotherm models have not been verified in previous works. Pb2+ removal of up to 83% was demonstrated at concentrations comparable to those in municipal wastewater, at pH 2. SDBC showed superior Pb2+ sorption capacity (maximum ~2 mg/g at pH 2) compared to WDBC and AC (<0 and (3.5 ± 0.4) × 10−3 mg/g, respectively); however, at the lowest concentration investigated (0.005 mg/L), SDBC released Pb2+. The potential risk of release of other heavy metals (i.e., Ni, Cd, Cu, and Zn) needs to be further examined. The sorption capacity of SDBC over a metal concentration span of 0.005–150 mg Pb2+/L could be predicted with the Redlich–Peterson model. It was shown that experimental data at concentrations comparable to those in municipal wastewater are necessary to accurately model and predict the sorption capacity of SDBC at these concentrations.

Characterization and application of magnetic biochar for the removal of phosphorus from water

Activated biochars were prepared from residues of medium density fiberboard (MDF) produced by the furniture industry. Biomass residue was pre-treated with FeCl3 in two different FeCl3:biomass ratios (0.5:1 and 1:1, w/w) aiming to produce a matrix embedded with iron oxide. The pyrolysis process produced maghemite on the biochar surface and its magnetic properties were confirmed by its attraction to a hand magnet and its magnetic susceptibility. Samples were also characterized using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), surface area by BET-N2, Fourier transform infrared (FTIR), X-ray diffraction, magnetic susceptibility, and cation exchange capacity (CEC). Magnetic biochar exhibited up to twelve-fold higher surface area than the non-magnetic biochar, which varies according the maghemite particles content. Iron oxide on biochar surface also contributed for increasing CEC around ten-fold compared to non-magnetic biochars. Phosphorus adsorption isotherms showed that these magnetic biochars have high capacity to sorb oxyanions like phosphate, especially at lower pH. Thus, these magnetic biochars could be used to clean water bodies contaminated with oxyanions in acidic conditions.

Effects of biochar on methane emission from paddy soil: Focusing on DOM and microbial communities

Biochar can be used as a soil amendment. However, it generally possesses unique physicochemical properties and complex organics, which could affect soil methanogenesis. In this study，straw-based biochars obtained at 300 °C (BC300), 500 °C (BC500) and 700 °C (BC700) were added to the paddy soil. Compared with the blank group, BC300 significantly increased paddy soil methane emissions by about 38%. However, this promoting effect gradually disappeared with the increase of pyrolysis temperature, and the inhibition even appeared in the BC700 group with the methane reduction by 18.2%. This might be related to the organics released from biochar. Van Krevelen (VK) diagram showed that the aromaticity of BC700 and BC500 were significantly higher than BC300. Fluorescent analysis further revealed that BC300 increased the amount of degradable fluorescent organics in the soil, which could provide more substrate for methane production. Moreover, as pyrolysis temperature increased, the fluorescent organics released were more likely to be non-biodegradable humus. In addition, it was shown that BC700 could adsorb some inherent organics in the soil, and thus reduced the total organic content and inhibited soil methane emissions. Microbial analysis showed that methanogenesis had a positive correlation with the abundance of syntrophic bacteria (e.g. Desulfobacca and Clostridium) which had ability to further degrade various types of organics and provided substrates to the methanogens. This article provides a deeper understanding regarding for the effects of biochar on methane emission from paddy soil in terms of organics and microbial perspectives.

Review: Efficiently performing periodic elements with modern adsorption technologies for arsenic removal

Arsenic (As) toxicity is a global phenomenon, and it is continuously threatening human life. Arsenic remains in the Earth's crust in the forms of rocks and minerals, which can be released into water. In addition, anthropogenic activity also contributes to increase of As concentration in water. Arsenic-contaminated water is used as a raw water for drinking water treatment plants in many parts of the world especially Bangladesh and India. Based on extensive literature study, adsorption is the superior method of arsenic removal from water and Fe is the most researched periodic element in different adsorbent. Oxides and hydroxides of Fe-based adsorbents have been reported to have excellent adsorptive capacity to reduce As concentration to below recommended level. In addition, Fe-based adsorbents were found less expensive and not to have any toxicity after treatment. Most of the available commercial adsorbents were also found to be Fe based. Nanoparticles of Fe-, Ti-, Cu-, and Zr-based adsorbents have been found superior As removal capacity. Mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.) removed As efficiently from water. Oxidation of AsO₃^3- to AsO₄^3-and adsorption of oxidized As on the mixed element-based adsorbent occurred by different adsorbents. Metal organic frameworks have also been confirmed as good performance adsorbents for As but had a limited application due to nano-crystallinity. However, using porous materials having extended surface area as carrier for nano-sized adsorbents could alleviate the separation problem of the used adsorbent after treatment and displayed outstanding removal performances.

Environmental remediation in circular economy: End of life tyre magnetic pyrochars for adsorptive removal of pharmaceuticals from aqueous solution

We demonstrate a challenge-based innovation of End of Life Tyres (ELTs) pyrolysis for magnetic pyrochar production and synthesis with evidence of its use as low cost, novel adsorbent for pharmaceuticals removal from aqueous solutions. Magnetic tyre pyrochar (MTC) derived from ELTs at Technology Readiness Level 3-7 (TRL3-7), was tested for the removal of ciprofloxacin (CIP), propranolol (PRO) and clomipramine (CLO), from water, at varied pH and ionic strengths. The morphological and chemical properties of the adsorbents were assessed using Brunauer Emmett Teller (BET) surface area, Vibrating Sample Magnetometer (VSM), Fourier Transform Infrared (FTIR), Scanning Electron Microscope coupled with Energy Dispersive X-ray (SEM-EDS), elemental analysis and zeta potential measurements. MTC showed excellent adsorption efficiency of 85%, 90% and 92% for CIP, PRO and CLO respectively, higher than that of the non-magnetic tyre pyrochar (TC), due to the larger surface area, and porosity and lower polarity. Adsorption of the compounds onto MTC was highly pH dependent, and favourable at low ionic strength. The experimental data were well described by pseudo-second order kinetic and Freundlich isotherm models. Based on FTIR and zeta potential analysis, the interaction mechanisms were explained by cation-π, π-π EDA, cation exchange, electrostatic repulsion and hydrophobic effect. In the context of the circular economy, this ELTs based low cost magnetic adsorbent (estimated at $299/t) can be potentially used at full-scale industrial wastewater treatment for elimination of drugs from aqueous solutions, offering sustainable environmental remediation.

Application of biochar in advanced oxidation processes: supportive, adsorptive, and catalytic role

The advanced oxidation processes (AOPs), especially sulphate radical (SO₄^•-)-based AOPs (SR-AOPs), have been considered more effective, selective, and prominent technologies for the removal of highly toxic emerging contaminants (ECs) due to wide operational pH range and relatively higher oxidation potential (2.5-3.1 V). Recently, biochar (BC)-based composite materials have been introduced in AOPs due to the dual benefits of adsorption and catalytic degradation, but the scientific review of BC-based catalysts for the generation of reactive oxygen species (ROSs) through radical- and non-radical-oriented routes for EC removal was rarely reported. The chemical treatments, such as acid/base treatment, chemical oxidation, surfactant incorporation, and coating and impregnation of minerals, were applied to make BC suitable as supporting materials (SMs) for the loading of Fenton catalysts to boost up peroxymonosulphate/persulphate/H₂O₂ activation to get ROSs including ^•OH, SO₄^•-, ¹O₂, and O₂^•- for targeted pollutant degradation. In this review, all the possible merits of BC-based catalysts including supportive, adsorptive, and catalytic role are summarised along with the possible route for the development prospects of BC properties. The limitations of SR-AOPs especially on production of non-desired oxyanions, as well as disinfection intermediates and their potential solutions, have been identified. Lastly, the knowledge gap and future-oriented research needs are highlighted.

Mechanisms for the removal of Cd(II) and Cu(II) from aqueous solution and mine water by biochars derived from agricultural wastes

The capacity of biochars derived from agricultural wastes to remove Cd(II) and Cu(II) from aqueous solution and contaminated mine water was evaluated using laboratory-based batch sorption experiments. To examine immobilization of heavy metals, biochars produced in a commercial-scale mobile pyrolizer from feedstocks: poultry litter; lucerne shoot; vetch shoot; canola shoot; wheat straws; and sugar-gum wood, were tested in a liquid-based system. Biochars were characterized by FTIR, XPS and XRD before and after the mine water treatment. Lucerne biochar had the highest Langmuir sorption capacity of Cd(II) (6.28 mg g^-1) and vetch-derived biochar had the highest Cu(II) sorption capacity (18.0 mg g^-1) at pH 5.5. All the biochars exhibited higher sorption capacity for Cu(II) than for Cd(II). The smaller ionic radius and higher electronegativity of Cu(II), and the PO₄^3-, CO₃^2- and N-containing functional groups of biochars enhanced their binding affinity. The results demonstrated that poultry litter-derived biochar was effective at removal of the Cd(II) and Cu(II) from mine water up to the levels recommended by the World Health Organisation. The results revealed that precipitation with CO₃^2- and PO₄^3-, complexation with -OH and -COOH groups and electrostatic interaction with O-containing surface functional groups were the main mechanisms involved in the removal of multi-metals by biochars, and that selection of feedstock materials for biochar production is important to maximise remediation of multi-metals in contaminated water.

Properties and adsorption mechanism of magnetic biochar modified with molybdenum disulfide for cadmium in aqueous solution

In this paper, we present the preparation of MoS₂-modified magnetic biochar (MoS₂@MBC) as a novel adsorbent by a simple hydrothermal method. MoS₂@MBC contains abundant S-containing functional groups that facilitate efficient Cd(II) removal from aqueous systems. We employed various characterization techniques to explore the morphology, surface area, and chemical composition of MoS₂@MBC; these included Brunauer-Emmett-Teller analysis scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction,. The results indicated the successful decoration of the surface of MoS₂@MBC with iron and MoS₂, and a higher surface area of MoS₂@MBC than that of unmodified biochar. Moreover, adsorption properties including thermodynamics and kinetics were investigated along with the effects of pH, humic acid, and ionic strength on the Cd(II) adsorption onto MoS₂@MBC. The O-, C-, S-, and Fe-containing functional groups on the surface of MoS₂@MBC led to an electrostatic attraction of Cd(II) and strong Cd-S complexation. The Langmuir and pseudo second-order models fitted best for the batch adsorption experiments results. The adsorption capacity of MoS₂@MBC (139 mg g^-1 on the basis of the Langmuir model) was 7.81 times higher than that of pristine biochar. The adsorption process was found to be pH-dependent. The experimental results indicated that MoS₂@MBC is an effective adsorbent for removing Cd(II) from water solutions. Further, the adsorption process involved the complexation of Cd(II) with oxygen-based functional groups, ion exchange, electrostatic attraction, Cd(II)-π interactions, metal-sulfur complexation, and inner-surface complexation. This work provides new insights into the Cd(II) ions removal from water via adsorption. It also demonstrates that MoS₂@MBC is an efficient and economic adsorbent to treat Cd(II)-contaminated water.

Difference in characteristics and nutrient retention between biochars produced in nitrogen-flow and air-limitation atmospheres

The different effects of nitrogen-flow (NF) and air-limitation (AL) pyrolysis on the characteristics and nutrient retention of biochars (BCs) are unclear. Hence, in this study, BCs derived from bamboo, corn straw, and wheat straw were produced in AL and NF atmospheres at various temperatures (300-750 °C), and their different characteristics and nutrient retention rates were compared systematically. Nitrogen-flow pyrolysis facilitates C retention and graphitic C formation, and AL pyrolysis improves the polarity and supports the formation of oxygen-containing groups. With increasing pyrolysis temperature, C retention and graphitic C formation in BCs derived from AL pyrolysis decreases more significantly compared with BCs from NF pyrolysis. At 750 °C, the polarity and oxygen-containing groups of BCs derived from AL pyrolysis increase, whereas those from BCs derived from NF pyrolysis decrease. The observations are attributable to the AL and high-temperature-enhanced oxidization and gasification of C. An AL atmosphere with a higher pyrolysis temperature supports porosity and results in a larger specific surface area. Although pyrolysis temperature and atmosphere have negligible effects on nutrient retention, a low pyrolysis temperature facilitates the formation of water-soluble Ca, Mg, and P, and AL pyrolysis facilitates the formation of water-soluble P because the high pyrolysis temperature improves the pH and mineral stability of BCs, and air limitation facilitates the oxidation of organic P into PO₄ ^3- . This study provides a reference for selecting AL or NF pyrolysis based on various pyrolysis temperatures to produce BCs and applying these in C sequestration, contaminant sorption, and soil quantity improvement.

Valorizing Plastic-Contaminated Waste Streams through the Catalytic Hydrothermal Processing of Polypropylene with Lignocellulose

Food waste is a promising resource for the production of fuels and chemicals. However, increasing plastic contamination has a large impact on the efficiency of conversion for the more established biological routes such as anaerobic digestion or fermentation. Here, we assessed a novel route through the hydrothermal liquefaction (HTL) of a model waste (pistachio hulls) and polypropylene (PP). Pure pistachio hulls gave a biocrude yield of 34% (w/w), though this reduced to 16% (w/w) on the addition of 50% PP in the mixture. The crude composition was a complex blend of phenolics, alkanes, carboxylic acids, and other oxygenates, which did not change substantially on the addition of PP. Pure PP does not breakdown at all under HTL conditions (350 °C, 15% solids loading), and even with biomass, there is only a small synergistic effect resulting in a conversion of 19% PP. This conversion was enhanced through using typical HTL catalysts including Fe, FeSO₄·7H₂O, MgSO₄·H₂O, ZnSO₄·7H₂O, ZSM-5, aluminosilicate, Y-zeolite, and Na₂CO₃; the conversion of PP reached a maximum of 38% with the aluminosilicate, for example. However, the PP almost exclusively broke down into a solid-phase product, with no enhancement of the biocrude fraction. The mechanism was explored, and with the addition of the radical scavenger butylated hydroxytoluene (BHT), the conversion of plastic reduced substantially, demonstrating that radical formation is necessary. As a result, the plastic conversion was enhanced to over 50% through the addition of the co-solvent and hydrogen donor, formic acid, and the radical donor, hydrogen peroxide. The addition of formic acid also changed the crude composition, including more carboxylic acids and oxygenated species than the conversion of the biomass alone; however, the majority of the carbon distributed to the volatile organic gas fraction producing an array of short-chain volatile hydrocarbons, which potentially could be repolymerized as a polyolefin or combined with the biocrude for further processing. Catalytic HTL was therefore shown to be a promising method for the valorization of polyolefins with biomass under typical HTL conditions.

Adsorption behaviors on trace Pb2+ from water of biochar adsorbents from konjac starch

Biochar adsorbents used to treat different heavy metals in water are efficient and low-cost. Appropriate raw materials, excellent selectivity and detailed adsorption mechanism are of important for research on biochar adsorbents. In this work, konjac starch was dispersed in polyvinylpyrrolidone (PVP) solution to prepare different sizes hydrophilic carbon spheres (HCSs) by hydrothermal synthesis method. Adsorption kinetics of the HCSs towards Pb2+ is described perfectly by the pseudo-second-order equation. With the temperature increasing, adsorption thermodynamics are more consistent with the Freundlich model. The calculated ΔG, ΔH and ΔS shows the adsorption of the HCSs towards Pb2+ is a spontaneous, endothermic and entropy increase process. In addition, HCSs have excellent selectivity for the adsorption of Pb2+ and Cu2+. HCSs prepared from konjac starch make full use of natural biomass resources, they can be used as a potential adsorbent material in treatment on heavy metal ion from water field.

Removal of antibiotic from the water environment by the adsorption technologies: a review

Antibiotics are known as emergent pollutants because of their toxicological properties. Due to continuous discharge and persistence in the aquatic environment, antibiotics are detected almost in every environmental matrix. Therefore antibiotics that are polluting the aquatic environment have gained significant research interest for their removal. Several techniques have been used to remove pollutants, but appropriate technology is still to be found. This review addresses the use of modified and cheap materials for antibiotic removal from the environment.

Decontamination of xenobiotics in water and soil environment through potential application of composite maize stover/rice husk (MS/RH) biochar-a review

Industries continuously emit xenobiotics into the environment, which increases risks of exposing humans and other biota to xenobiotics. Though various conventional and modern environmental remediation technologies are being employed, some of them are ineffective in removing xenobiotics, while others are costly and not feasible for large-scale utilization. Maize stover (MS) and rice husks (RH) are produced in abundance globally, which make them ideal and cost-effective feedstocks for large-scale biochar production for environmental remediation. Since either type of pristine MS and RH biochar may not be effective in removing some xenobiotics, the incorporation of modifiers into MS/RH biochars can help to form composite MS/RH biochar which in turn can better decontaminate water and soil. Thus, this review paper provides a comprehensive overview of the preparation, characterization, and environmental remediation using pristine and composite MS/RH biochar. Possible areas for composite MS/RH biochar applications and future perspectives of the technology in reducing xenobiotics are also proposed in this paper.