Adsorption removal of natural organic matters in waters using biochar

Co-selective effect of dissolved organic matter and chlorine on the bacterial community and their antibiotic resistance in biofilm of drinking water distribution pipes

The proliferation of pathogenic bacteria and antibiotic resistance genes (ARGs) in the biofilm of drinking water distribution pipes poses a serious threat to human health. This work adopted 15 polyethylene (PE) pipes to study the co-selective effect of dissolved organic matter (DOM) and chlorine on the bacterial community and their antibiotic resistance in biofilm. The results indicated that ozone and granular activated carbon (O3-GAC) filtration effectively removed lignins and proteins from DOM, and chlorine disinfection eliminated carbohydrate and unsaturated hydrocarbons, which both contributed to the inhibition of bacterial growth and biofilm formation. After O3-GAC and disinfection treatment, Porphyrobacter, unclassified_d_bacteria, and Sphingopyxis dominated in the biofilm bacterial community. Correspondingly, the bacterial metabolism pathways, including the phosphotransferase system, phenylalanine, tyrosine and tryptophan biosynthesis, ABC transporters, and starch and sucrose metabolism, were downregulated significantly (p < 0.05), compared to the sand filtration treatment. Under such a situation, extracellular polymeric substances (EPS) secretion was inhibited in biofilm after O3-GAC and disinfection treatment, postponing the interaction between EPS protein and pipe surface, preventing bacteria, especially pathogens, from adhering to the pipe surface to form biofilm, and restraining the spread of ARGs. This study revealed the effects of various water filtration and disinfection processes on bacterial growth, metabolism, and biofilm formation on a molecular level, and validated that the O3-GAC filtration followed by chlorine disinfection is an effective and promising pathway to control the microbial risk of drinking water.

Simultaneous removal of nutrients and pharmaceuticals and personal care products using two-stage woodchip bioreactor-biochar treatment systems

The co-occurrence of nutrients and pharmaceuticals and personal care products (PPCPs) in sewage effluent can degrade water quality of the receiving watersheds. This study investigated the simultaneous removal of excess nutrients and PPCP contaminants by developing a novel woodchip bioreactor and biochar (B2) treatment system. The result revealed that woodchip bioreactors could effectively remove nitrate via a denitrification process and adsorb some PPCPs. Biochar as a secondary treatment system significantly reduced the concentrations of PPCPs and dissolved reactive phosphorus (DRP) (p < 0.05), compared to the woodchip bioreactor. The removal efficiencies of all targeted contaminants by the B2 system were evaluated using various hydraulic retention times (HRTs) and biochar types (pelletized versus granular biochar). Longer HRTs and smaller biochar particles (granular biochar) could enhance the removal efficiencies of targeted contaminants. Average contaminant removals were 77.25 % for nitrate-N, 99.03 % for DRP, 69.51 % for ibuprofen, 73.65 % for naproxen, 91.09 % for sitagliptin, and 96.96 % for estrone, with woodchip bioreactor HRTs of 12 ± 1.4 h and granular biochar HRTs of 2.1 ± 0.1 h. Notably, the second-stage biochar systems effectively mitigated by-products leaching from woodchip bioreactors. The presence of PPCPs in the woodchip bioreactors enriched certain species, such as Methylophilus (69.6 %), while inhibiting other microorganisms and reducing microbial community diversity. Furthermore, a scaled-up B2 system was analyzed and assessed, indicating that the proposed engineering treatment system could provide decades of service in real-world applications. Overall, this study suggests that the B2 system has promising applications for addressing emerging and conventional contaminants.

Activated biochar derived from Enteromorpha with high specific surface area for efficient removal of phenanthrene: Experiments, mechanism and DFT calculations

Conversion of solid marine waste into innovative nanomaterials has been successfully developed for removing organic pollutants from aqueous solutions. In this study, activated biochar (HTST) was successfully synthesized using a straightforward three-step method involving pretreatment, carbonization, and chemical regulation. Multiple characterization techniques revealed the presence of abundant three-dimensional hierarchical porous structures in the samples, along with amorphous and active functional group structures such as -COOH, -OH, -NHR, -CC, and C-O. Notably, the prepared sample exhibited a remarkable specific surface area (SBET) of 3284.52 m2/g, which was close to 1700 times larger than that of the raw biomass. Additionally, the highest removal efficiency could reach approximately 100% under neutral condition, while the adsorption capacity even achieved up to 782.37 mg/g within 2 h at room temperature. Calculations simulation not only highlighted the significance of the π-π conjugation between sample and pollutant molecules, but deeply explored the bonding interaction of active functional groups on the surface, whereas adsorption energies of different configurations had the following order: ΔE(-NHR) = 0.75194674 eV > ΔE(-OH) = 0.72502369 > ΔE(-COOH) = 0.71488135 > ΔE(-CC-) = 0.53852269 eV. Moreover, the adsorption activities for the optimized configuration were further analyzed based on the LUMO-HOMO energy gap and electric distribution. This work presents a viable synthesis method for low-cost nanomaterials and offers new insights into the exceptional adsorption properties of advanced adsorbents for wastewater treatment.

Effects of biochar and vermicompost on growth and economic benefits of continuous cropping pepper at karst yellow soil region in Southwest China

Recently, biochar (B) and vermicompost (V) have been widely used as amendments to improve crop productivity and soil quality. However, the ameliorative effects of biochar and vermicompost on the continuous cropping of pepper under open-air conditions, particularly in the karst areas of southwestern China, remain unclear. A field experiment was conducted to study the effects of biochar and vermicompost application, alone or in combination, on the yield, quality, nutrient accumulation, fertilizer utilization, and economic benefits of continuous pepper cropping from 2021 to 2022. The experiment included six treatments: CK (no fertilizer), TF (traditional fertilization of local farmers), TFB (TF combined with biochar of 3000 kg·ha-1), TFV (TF combined with vermicompost of 3000 kg·ha-1), TFBV1 (TF combined with biochar of 1500 kg·ha-1 and vermicompost of 1500 kg·ha-1), and TFBV2 (TF combined with biochar of 3000 kg·ha-1 and vermicompost of 3000 kg·ha-1). Compared with the TF treatment, biochar and vermicompost application alone or in combination increased the yield of fresh pod pepper by 24.38-50.03% and 31.61-88.92% in 2021 and 2022, respectively, whereas the yield of dry pod pepper increased by 14.69-40.63% and 21.44-73.29% in 2021 and 2022, respectively. The application of biochar and vermicompost reduced the nitrate content and increased the vitamin C (VC) and soluble sugar content of the fruits, which is beneficial for improving their quality. Biochar and vermicompost application alone or in combination not only increased nutrient uptake but also significantly improved agronomic efficiency (AE) and recovery efficiency (RE). In addition, although the application of biochar or vermicompost increased production costs, the increase in yield improved net income (ranging from 0.77 to 22.34% in 2021 and 8.82 to 59.96% in 2022), particularly in the TFBV2 treatment. In conclusion, the use of biochar and vermicompost amendments had a positive effect on the productivity and economic benefits of continuous pepper cropping, and the co-application of biochar and vermicompost could be an effective nutrient management strategy for the continuous cropping of pepper in the karst mountain areas of southwest China.

Analysis of natural photocatalysts derived from spartina alterniflora with superior removal performance of pollutant

Spartina alterniflora, as an invasive alien species, has been studied in terms of its potential use in immobilization and synergistic photocatalysis against dye contaminants for the first time. Microscopic characterization and Fourier transform infrared (FTIR) spectroscopy results confirmed the presence of abundant 3D wormhole-like pore structures and active functional groups (-OH, -NH2, CO, Si-O-Si). Moreover, the existence of SiO2 was connected the metal oxides with polar groups, which could proceed entire reaction procedure subsequently. Transition metal oxides (such as Fe2O3, TiO2, MnO2 and NiO) contained in photocatalysts might effectively promote the organics decomposition by the visible light excitation. The highest dye removal efficiency of 92.03% could be reached with the addition of 0.02 g photocatalyst. The capture experiment confirmed that the h+ was the dominant active substance during the photocatalytic degradation process. Density functional theory (DFT) calculations verified that the functional groups (-COOH, -OH and -NH2) were exceptional adsorption sites for catalyst, and the calculated adsorption energy were all negative with the order of SRHH-NH2 (-2.712688 eV) < SRHH-OH (-2.075601 eV) < SRHH-COOH (-1.283141 eV), which confirmed that interface interaction effectively bound cationic dyes through the formation of hydrogen bonds at the catalysts-water interface, further accelerating the reaction rate of the entire photocatalytic reduction of dye molecules. Therefore, this work provides a feasible synthesis of natural photocatalysts using solid waste, which suggests excellent adsorption and photocatalysis properties for the treatment of organic industrial pollutant.

Eco-geological consequences of textile processing wastes: Risk assessment, elemental dissolution kinetics, and health hazard potential

Although substantial quantities of toxic wastes are generated from textile industries, the characteristics of textile processing wastes (TPWs) have yet scantily been investigated from ecological and agricultural perspectives. Here, the eco-geological consequences of TPWs are evaluated by considering three types of sludges (i.e., silk fibre sludge (SFS), dye mixed silk processing sludge (DSPS), and cotton processing wastewater sludge (CPWS)). The predominance of certain components between different wastes (e.g., fibrous substances in silk industry wastes (i.e., SFS and DSPS) and amorphous materials in cotton processing wastes (i.e., CPWS)) is accounted for by the use of different raw materials in different industries. According to the FTIR and other characterization analyses, all three types of TPWs were rich in carbonaceous compounds and nutrients (e.g., CNPK) because of their biological origin. Further, high accumulation of toxic metals (e.g., Cd, Cr, Cu, Zn, Pb, and Mn) was apparent with chemical-processing routes. The principal component analysis indicated strong relationships between certain environmental variables (e.g., moisture content and bulk density) and bioavailability of several metals (e.g., Cd, Zn, Cu, and Mn), while C levels in TPWs were tightly associated with Cr levels. According to the Visual MINTEQ model, the dissolution-precipitation dynamics of potentially toxic elements (e.g., Pb, Cr, and Zn) in TPWs are predicted to be controlled by the levels of phosphates/chlorides/sulphates in line with the textile processing steps employed in different factories. The great toxicity potential of CPWS (e.g., relative to SFS and DSPS) is recognized to pose significant metal-induced hazards to ecosystems and human health over time. Among the three TPWs, SFS could be prescribed for agricultural application after proper treatment (e.g., via valorization techniques) with the aid of its benign nature and high nutrient (Total N: 3.83%; available P: 118.6 mg kg^-1) value.

Perturbation and strengthening effects of DOM on the biochar adsorption pathway

Biochar is an effective adsorbent commonly used in pollutants adsorption. However, natural constituents, such as dissolved organic matter (DOM), could affect pollutants adsorption. In this study, we analyzed the mechanisms underlying phenol adsorption on pine biochar under perturbation by fertilizer-derived DOM. In addition, biochar property alterations were characterized and further analyzed. The results showed that phenol and DOM combined to a certain extent in the adsorption system. DOM affected the adsorption pathway, which increased the biochar adsorption efficiency for phenol. The addition of DOM₂ promoted phenol adsorption efficiency (70.31%), with total DOM adsorption capacity of 61.45 mg g^-1 onto biochar.

Assessment and prediction of the effect of ageing on the adsorption of nonylphenol in black carbon-sediment systems

Black carbon (BC) is a promising sediment amendment, as proven by its considerable adsorption capacity for hydrophobic organic pollutants and accessibility, but its reliability when used for the removal of pollutants in natural sediments still needs to be evaluated. For example, the ageing process, resulting in changing of surface physicochemical properties of BC, will decrease the adsorption capacity and performance of BC when applied to sediment pollution control. In this study, how the ageing process and BC proportion affect the adsorption capacity of BC-sediment systems was modelled and quantitatively investigated to predict their adsorption capacity under different ageing times and BC additions. The results showed that the ageing process decreased the adsorption capacity of both BC-sediment systems, due to the blockage of the non-linear adsorption sites of BC. The adsorption capacity of rice straw black carbon (RC)-sediment systems was higher than that of fly ash black carbon (FC)-sediment systems, indicating that RC is more efficient than FC for nonylphenol (NP) pollution control in sediment. The newly established model for the prediction of adsorption capacity fits the experimental data appropriately and yields acceptable predictions, especially when based on parameters from the Freundlich model. However, to fully reflect the influence of the ageing process on BC-sediment systems and make more precise predictions, it is recommended that future work considering more factors and conditions, such as modelling of the correlation between the adsorption capacity and the pore volume or specific surface area of BC, be applied to build an accurate and sound model.

Facile Ball-Milling Synthesis of CuO/Biochar Nanocomposites for Efficient Removal of Reactive Red 120

With the goal of improving the removal of anionic contaminants, copper oxide (CuO)-modified biochar (BC) nanocomposites were successfully prepared through simply ball milling CuO particles with BC. The physicochemical properties of the fabricated CuO/BC nanocomposites were systematically characterized by a series of techniques; their adsorption performances were assessed, and the main adsorption mechanism was revealed. X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses of the nanocomposites showed the strong interaction between CuO and BC and confirmed the success of the ball-milling syntheses. Because of strong electrostatic attraction between the embedded CuO nanoparticles and reactive red (RR120), the composited adsorbents exhibited excellent RR120 removal. The 10%-CuO/BC nanocomposite achieved the best RR120 removal efficiency (46%), which is much higher than that of pristine BC (20%). In addition, the adsorption was insensitive to the change of solution initial pH (4-10). The 10%-CuO/BC also showed fast adsorption kinetics (equilibrium time < 3 h) and extremely high adsorption capacity (Langmuir maximum capacity of 1399 mg g^-1) to RR120 in aqueous solutions. Findings from this study demonstrate not only the strong feasibility of ball-milling synthesis of BC-based nanocomposites but also the promising potential of the CuO/BC nanocomposites to remove aqueous anionic contaminants.

Polyethyleneimine modification of activated fly ash and biochar for enhanced removal of natural organic matter from water via adsorption

In this study, fly ash (FA) and biochar (BC), two common industrial byproducts, were activated and surface-modified with polyethyleneimine (PEI) to enhance their capacities to remove natural organic matter (NOM) from water via adsorption. Different fluorescent components were identified using fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) to explore the individual adsorption behaviors of different organic constituents in a bulk NOM. The NOM adsorption was quantitatively examined via adsorption isotherm and kinetics models. Compared to the pristine adsorbents, the functionalized adsorbent with increased surface area and positive surface charge achieved higher NOM adsorption. By evaluating the adsorptive behaviors of UV-absorbing and fluorescent moieties, it was concluded that the operative mechanism of adsorption included electrostatic attraction, hydrogen bonding, and π-π interaction. At the optimal pH of 3, the surface-modified FA and BC (i.e., FA-PEI and BC-PEI) had adsorption capacities for NOM that were ∼3 times higher than the capacities of the pristine materials. Due to its aromatic features, π-π interaction may have enhanced BC and BC-PEI selective adsorption of aromatic NOM components compared to FA and FA-PEI. Kinetic modelling showed that the mesopores of FA-PEI were available for NOM adsorption and diffusion of NOM molecules into the mesoporous structures was rate-limiting. On the other hand, PEI-modification may have further reduced NOM diffusion through the narrow micropores in BC such that external adsorption primarily occurred on BC-PEI. The modified adsorbents showed a faster adsorption kinetics than the pristine counterparts and a high durability in repeated adsorption-desorption cycles.

Recent Progress in Biochar-Based Photocatalysts for Wastewater Treatment: Synthesis, Mechanisms, and Applications

Biochar (BC) is a carbon-rich material produced from pyrolysis of biomass. In addition to its low toxicity, environmental compatibility, and low cost, BC has the desired advantages of well-developed mesoporous structure and abundant surface functional groups. In recent years, BC-based photocatalysts (BCPs) have played a significant role in many environmental fields. In this paper, we highlight the current progress and several exciting results of BCPs by focusing on their synthesis, characterization, mechanisms, and applications in wastewater treatment. Details on various preparation methods include sol–gel, hydrothermal/solvothermal, ultrasound, calcination, and in situ methods are summarized and discussed. The underlying mechanisms and the applications of BCPs for different semiconductors are reviewed. Furthermore, some future trends and potentials are outlined.

Dissolved organic matter (DOM) removal from biotreated coking wastewater by chitosan-modified biochar: Adsorption fractions and mechanisms

To effectively remove dissolved organic matter (DOM) from actual biotreated coking wastewater (BTCW), a reusable and low-cost chitosan-biochar (CB) was prepared. From the results, CB (52%) exhibited superior removal efficiency compared to that of biochar (12%) and a faster adsorption rate. Analysis of the DOM fractions, molecular weight distribution, fluorescent components, and molecular compositions indicated that chitosan modification made more kinds of DOM components (e.g., hydrophilic substances) have an affinity with biochar. The material characterization and removal characteristics jointly proved that the adsorption efficiency was promoted by the change in pore size distribution and increase in functional groups that provide bonding sites for DOM via hydrogen bonding, acid-base reactions, and electrostatic interactions. Moreover, compared to traditional adsorbent activated carbon, CB exhibited superior removal efficiency and cost-effectiveness. These results demonstrated that CB is a potential alternative adsorbent for advanced DOM treatment of BTCW.

Experimental and theoretical aspects of biochar-supported nanoscale zero-valent iron activating H2O2 for ciprofloxacin removal from aqueous solution

Ciprofloxacin has been frequently detected in water environment, and its removal has become a significant public concern. Biochar-supported nanoscale zero-valent iron (BC/nZVI) to activate hydrogen peroxide (H₂O₂) has many advantages on promoting the removal of organic contaminants. In this paper, the BC/nZVI activating H₂O₂ degradation of ciprofloxacin was systematically investigated by experimental and theoretical approaches. The morphologies and property analysis showed that nZVI particles distributed uniformly on the biochar surface, which mainly include ^-OH, >CO and COC and CO groups. Different reaction conditions were compared to define the optimal conditions for ciprofloxacin removal in BC/nZVI/H₂O₂ system. More than 70% of ciprofloxacin was removed in the optimal conditions: acidic condition (pH 3∼4), low doses of H₂O₂ (20 mM), and temperature of 298 K. The hydroxyl radical (^•OH) oxidation was the primary pathway in BC/nZVI/H₂O₂ degradation of ciprofloxacin process. The theoretical calculation indicated that hydrogen atom abstraction (HAA) pathways were the dominant oxidation pathways contributing 92.3% in overall second‒order rate constants (k) of ^•OH and ciprofloxacin. The current results are valuable to evaluate the application of BC/nZVI activating H₂O₂ degradation of ciprofloxacin and other fluoroquinolone antibiotics in water treatment plants.

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

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

Removal of 2,4,6-trichlorophenol from water by Eupatorium adenophorum biochar-loaded nano-iron/nickel

From the perspective of waste utilization, the invasive species, Eupatorium adenophorum was used to prepare biochar, which was then loaded with iron/nickel bimetals. Compared with pure biochar, the biochar-loaded nano-iron/nickel bimetals have a significant effect on the removal of 2,4,6-trichlorophenol (2,4,6-TCP) from water, and their degradation rate can be increased by 39.7%-71.6% under different conditions. Several factors can influence the removal of 2,4,6-TCP, including the load ratio, pH of the solution, concentration of 2,4,6-TCP, and coexisting ions in water (HCO₃^-, SO4₂^-, NO₃^-). Based on the density functional model (DET), Ni can activate H₂ (produced in the reaction between nano-Fe and H₂O) to convert to H^*, which can then substitute Cl. The activation energy is 109.5 kJ/mol, indicating the reaction is easy to take place.

Fe-Mn-Ce oxide-modified biochar composites as efficient adsorbents for removing As(III) from water: adsorption performance and mechanisms

In this study, a novel Fe-Mn-Ce oxide-modified biochar composite (FMCBC) was synthesized via pyrolysis to enhance the adsorption capacity of biochar (BC). Scanning electron microscopy-energy-dispersive X-ray spectroscopy confirmed that Fe, Mn, and Ce were successfully loaded onto the surface of the BC. A series of adsorption experiments showed that the FMCBC exhibited improved adsorption of As(III) in an aqueous environment. The adsorption process was well expressed by the pseudo-second-order kinetic model. The adsorption capacity of FMCBC reached 8.74 mg L^-1, which was 3.27 times greater than that of BC. The pH of the solution significantly influenced the adsorption of As(III), where the amount of As(III) adsorbed by FMCBC was maximized at pH 3. A high phosphate concentration inhibited adsorption, whereas nitrate and sulfate ions promoted As(III) adsorption and increased the FMCBC adsorption capacity. Similarly, with increasing humic acid concentration, the adsorption capacity of FMCBC for As(III) decreased; however, a low concentration of humic acid promoted adsorption. X-ray photoelectron spectroscopy analysis revealed that the adsorption of As(III) by FMCBC occurred through redox and surface complexation reactions. Therefore, FMCBC has excellent potential for purifying arsenic-contaminated water.

Facile Preparation of Charcoal Nanomaterial from Fishery Waste with Remarkable Adsorption Ability

In this study, modified activated fishbone charcoal (MAFC) was successfully prepared to remove emulsified oil from oily wastewater. Various characteristic techniques, including SEM, XRD, FTIR, and BET, were employed to investigate the morphology, texture, and surface properties of as-prepared samples. BET results demonstrated that the specific surface area of fishbone charcoal increased from 69.8 m2/g to 206.0 m2/g after treatment with K2CO3 as an activating agent, while the total pore volume of MAFC increased from 0.003 cm3/g to 0.3 cm3/g, accompanied by the formation of abundant pore structures. It was observed that 90.1% of emulsified oil (100 mg/L) was successfully removed by MAFC under our experimental conditions. The results of a kinetic and isotherm model analysis indicated that the adsorption experimental data were not only consistent with the Langmuir adsorption isotherm but were also well-described by the pseudo-second-order adsorption model. It is expected that this highly efficient and inexpensive MAFC can be a promising bio-adsorbent for removing organic pollutants from industrial wastewater.

High-performance porous biochar from the pyrolysis of natural and renewable seaweed (Gelidiella acerosa) and its application for the adsorption of methylene blue

A high-performance porous biochar adsorbent prepared by facile thermal pyrolysis of seaweed (Gelidiella acerosa) is reported. The textural characteristics of the prepared seaweed biochar (SWBC) and the performance in the adsorption of methylene blue (MB) dye were evaluated. The batch experiment for the adsorption of MB was conducted under different parameters, such as temperature, pH, and initial concentration of MB in the range of 25-400 mg/L. The developed SWBC exhibited a relatively high surface area, average pore size, and pore volume of 926.39 m²/g, 2.45 nm, and 0.57 cm³/g, respectively. The high surface area and pristine mineral constituents of the biochar promoted a high adsorption capacity of 512.67 mg/g of MB at 30 °C. The adsorption isotherm and kinetics data best fitted the Langmuir and pseudo-second-order equations. The results indicate that SWBC is efficient for MB adsorption and could be a potential adsorbent for wastewater treatment.

A novel nanocomposite of Liquidambar styraciflua fruit biochar-crosslinked-nanosilica for uranyl removal from water

Biochar adsorption has been protruded as a sustainable green and economic process for water remediation. This technology is facing high challenges in removing different pollutants, owning to the stable chemical and physical features of biochar. Therefore, a novel nanocomposite of Liquidambar styraciflua fruit biochar-crosslinked-nanosilica (BC-Gl-NSi) was synthesized and characterized (surface area = 60.754 m² g^-1 and particle size = 17.32-36.25 nm). The designed BC-Gl-NSi nanocomposite was explored for removal of uranyl ions by the batch adsorption technique under the influence of different factors including temperature, contact time, nanocomposite dosage, pH, uranyl ion concentration as well as co-existing ions. The adsorption process was principally confirmed to rely on the solution pH and reached 86.3% in pH 4.0. The results showed also that one-minute contact duration was sufficient to reach the maximum extraction of uranyl (30.0 mg L^-1). Besides, [BC-Gl-NSi] exhibited excellent selectivity and good recovery of uranyl ions with other competing ions.

Microwave assisted hydrothermal preparation of rice straw hydrochars for adsorption of organics and heavy metals

A series of rice straw hydrochars were produced through a microwave-assisted hydrothermal treatment method, characterized and used for the adsorption of three organics and two heavy metals from aqueous solutions. The hydrochars have carbon contents from 37.44% to 43.31%, are rich in oxygen containing functional groups, and the equilibrium of hydrothermal carbonization reactions could be reached rapidly in microwave environment. The hydrochars can effectively adsorb the model pollutants, the maximum adsorption capacities of Congo red, berberine hydrochloride and 2-naphthol at 298 K and initial concentration of 0.5 mg/mL were 222.1, 174.0 and 48.7 mg/g, respectively, and those of Zn²⁺ and Cu²⁺ were 112.8 and 144.9 mg/g, respectively. Adsorption thermodynamic parameters were calculated. These results suggest that microwave-assisted hydrothermal treatment is an effective method for the rapid production of hydrochars, and rice straw hydrochars are promising adsorbents for the removal of water pollutants such as organics and heavy metals.

High-efficiency removal of Pb(II) and humate by a CeO2-MoS2 hybrid magnetic biochar

This work prepares a novel CeO₂-MoS₂ hybrid magnetic biochar (CMMB) for the adsorptive removal of Pb(II) and humate from aqueous solution. The CMMB was evaluated against magnetic biochar (MB). The results showed that CMMB exhibited strong magnetic separation ability. Hybridization of CMMB greatly improved Pb(II) and humate removal compared to MB, with >99% Pb(II) and humate removed within 6 h. Pb(II) and humate removal capacities of CMMB were 263.6 mg/g and 218.0 mg/g, respectively, with negligible influence of ion strength in the range of 0-0.1 mol/L NaNO₃. Pb(II) removal mechanism involved predominately with electrostatic attraction, Cπ-Pb(II) bond interaction, and surface adsorption and complexation combined processes; while pore-filling, partition effect and π-π interaction contributed to the adsorption of humate. Overall, the introduction of graphene-like MoS₂ materials into biochar benefits both of the biomass resources recovery and environmental protection.

Synthesis and Characterization of Novel Fe-Mn-Ce Ternary Oxide⁻Biochar Composites as Highly Efficient Adsorbents for As(III) Removal from Aqueous Solutions

The widespread pollution of water bodies with arsenic (As) necessitates the development of efficient decontamination techniques. To address this issue, we herein prepare Fe-Mn-Ce ternary oxide-biochar composites (FMCBCs) using impregnation/sintering methods and examined their physicochemical properties, morphologies, and As(III) removal performances. The specific surface area of FMCBCs increased with increasing Ce content and enhanced the quantity of surface functional groups (–OH, –COOH). The adsorption of As(III) on FMCBCs was well represented by pseudo-second-order kinetics, and the As(III) adsorption capacity of the best-performing FMCBCs (8.47 mg g⁻¹ for FMCBC₃) exceeded that of BC by a factor of 2.9. At pH = 3, the amount of adsorption of As(III) by FMCBCs reached a maximum, and the increased ionic strength could enhance adsorption capacity of FMCBCs. Moreover, an As(III) removal efficiency of ~99% was observed for FMCBC₃ at a dosage of 8 g L⁻¹, which highlighted its great potential as an absorbent for As(III) removal from contaminated water.

Sorptive removal of dissolved organic matter in biologically-treated effluent by functionalized biochar and carbon nanotubes: Importance of sorbent functionality

The sorptive removal of dissolved organic matter (DOM) in biologically-treated effluent was studied by using multi-walled carbon nanotube (MWCNT), carboxylic functionalised MWCNT (MWCNT-COOH), hydroxyl functionalized MWCNT (MWCNT-OH) and functionalized biochar (fBC). DOM was dominated by hydrophilic fraction (79.6%) with a significantly lower hydrophobic fraction (20.4%). The sorption of hydrophobic DOM was not significantly affected by the sorbent functionality (∼10.4% variation) and sorption capacity followed the order of MWCNT > MWCNT-COOH > MWCNT-OH > fBC. In comparison, the sorption of hydrophilic fraction of DOM changed significantly (∼37.35% variation) with the change of sorbent functionality with adsorption capacity decreasing as MWCNT-OH > MWCNT-COOH > MWCNT > fBC. Furthermore, the affinity of adsorbents toward a hydrophilic compound (dinitrobenzene), a hydrophobic compound (pyrene) and humic acid was also evaluated to validate the proposed mechanisms. The results provided important insights on the type of sorbents which are most effective to remove different DOM fractions.

Characterization and alkaline pretreatment of rice husk varieties in Uganda for potential utilization as precursors in the production of activated carbon and other value-added products

In this study, 13 rice husk (RH) varieties from 4 agro-ecological zones in Uganda were characterized, NaOH-pretreated, and evaluated for their potential utilization as precursors for production of bio-oil, ash, char, and activated carbon for selected applications. RH varieties were characterized through particle size analysis, bulk density, proximate and ultimate analyses, specific surface area, pore volume, as well as lignocellulosic and inorganic compositions. Selected RH varieties were subsequently pretreated at NaOH concentrations of 1-4%w/v, using pretreatment ratios of 5 g RH: 40 mL NaOH. Properties varied among RH varieties, suiting them as feedstocks for different applications. Upland rice husk varieties are more suited precursors for production of bio-oil, and activated carbon due to their relatively lower ash content, higher specific surface area, as well as higher volatile matter and fixed carbon contents. Upland rice husks could as well be employed in the preparation of electrodes for electrochemical devices, due to their relatively higher specific surface area. A high ash content (21-32% dry basis) of lowland rice husks presents good prospects for their calcination, since larger amounts of rice husk ash could be obtained, and employed in different applications. Lowland rice husk varieties could also be more suited precursors for production of char for soil amendment, due to their relatively higher ash content, which subsequently increases their char yields. However, alkaline pretreatment of rice husks using 2-4%w/v NaOH can reduce the ash content by as much as 74-93%, depending on the rice husk variety, which paves way for utilizing rice husks with a high ash content in different applications. Aside from ash reduction, the enhanced specific surface area (1.2-1.7 m² g^-1), volatile matter (68-79%db) and fixed carbon (19-24%db) contents of NaOH-pretreated rice husks suggests they are more suited feedstocks than when employed in their raw form, for production of bio-oil, as well as activated carbon.

Adsorption-reduction removal of Cr(VI) by tobacco petiole pyrolytic biochar: Batch experiment, kinetic and mechanism studies

Tobacco petiole biochar (TPBC) was prepared via pyrolysis and used for Cr(VI) removal. Cr(VI) removal efficiency was reduced by pyrolytic temperature (PyT) increase which mainly affected by functional groups rather than specific surface area. According to the optimal pseudo second-order kinetic, the initial adsorption rate was decreased with PyT increase from 355.91 mg·g-1·min-1 (PyT = 300 °C) to 3.44 mg·g-1·min-1 (PyT = 700 °C). The isotherm was optimally explained by Temkin model involved physical absorption with heat of 28.73 J/mol. Simulation result of adsorption-reduction-adsorption process showed the Cr(VI) removal was kinetic controlled by Cr(VI) and Cr(III) adsorptions. TPBC300 was the optimal TPBC for chromium removal from electroplating wastewater with efficiencies of: 66.7% (Cr(VI)) and 21.1% (Cr(tot)).