Bioleaching of heavy metal from woody biochar using Acidithiobacillus ferrooxidans and activation for adsorption

Waste derived modified biochar as promising functional material for enhanced water remediation potential

The waste management and water purification are daunting environmental challenges. Biochar, a carbonaceous material prepared from diverse organic waste (agricultural, household residues and municipal sewage sludge) has garnered substantial attention due to its excellent attributes, including carbon content, cation exchange efficacy, ample specific surface area, and structural robustness. Thus, the present review comprehensively analyzes bio waste-derived biochar with a particular emphasis on water remediation applications. This article primarily delves into various strategies for modifying biochar, elucidating the underlying mechanisms behind these modifications and their potential for bolstering pollutant removal efficiency. Furthermore, it addresses the impact of functionalization on both biochar stability and cost for commercialization. Lastly, the article outlines key developments, SWOT analysis, and future prospects, offering insights into the practical execution of biochar applications at a larger scale. Therefore, this article paves the way for future research to deepen the understanding of modified biochar with mechanisms for exploring water remediation applications in a more sustainable manner.

Removal of antimonite and antimonate in aqueous solution by mugwort biochar modified by Acidithiobacillus ferrooxidans after pyrolysis

In the research, iron oxides-biochar composites (ALBC) were prepared from pristine biochar modified by Acidithiobacillus ferrooxidans (A. ferrooxidans) and pyrolyzed at 500 °C and 700 °C in order to remove antimonite (Sb(III)) and antimonate (Sb(V)) from water. The results indicated that biochar prepared at 500 °C and 700 °C (ALBC500 and ALBC700) were loaded with Fe₂O₃ and Fe₃O₄, respectively. In bacterial modification systems, ferrous iron and total iron concentrations decreased continuously. The pH values of bacterial modification systems including ALBC500 increased first and then decreased to a stable state, while the pH values of bacterial modification systems with ALBC700 continued to decrease. The bacterial modification systems can facilitate the formation of more jarosites by A. ferrooxidans. ALBC500 had optimal adsorbing capacities for Sb(III) (18.81 mg·g^-1) and Sb(V) (14.64 mg·g^-1). The main mechanisms of Sb(III) and Sb(V) adsorption by ALBC were electrostatic interaction and pore filling.

Synergistic remediation of lead pollution by biochar combined with phosphate solubilizing bacteria

Pb(II) is extreme toxic to biological cells, which limits the restoration of Pb(II) by functional strains. This study examined a Pb(II)-tolerant phosphate solubilizing bacteria(PSB) Ochrobactrum sp. J023 combined with corn stover biochar to enhance the immobilization of Pb(II). The results showed that the removal rate of Pb(II) by biochar combined with phosphate-solubilizing bacteria was as high as 71.30 %. SEM-EDS showed that more disordered crystals appeared on the surface of biochar treated with bacteria. XRD analysis indicated that the mineralization products of Pb(II) in biochar combined strain system were mainly in Pb₅(PO₄)₃OH and Pb₅(PO₄)₃Cl. FT-IR analysis revealed that there were more phosphate groups involved in the mineralization process when biochar was added. XPS verified the formation of PbO or lead-containing precipitates in this system, and the amount of lead precipitates was larger. The mechanism of lead fixation by strain combined with biochar can be regarded that the strain regulates the microenvironment of the biochar surface, enhances the release of phosphate and promotes the generation of stable pyroxite. Moreover, biochar composition and porous structure not only provide nutrient elements for strains, but also protect and promote the metabolism of strains. Biochar adsorption also reduces the loss of available phosphorus, which helps PSB to fix Pb sustainably and effectively. This suggests that the synergistic effect of PSB-biochar can not only effectively reduce the mobility and bioavailability of Pb(II), but also increase the sustainability of remediation. Therefore, the combination of phosphate solubilizing bacteria and biochar is a promising approach to the remediation of heavy metal pollution.

Recent developments in modification of biochar and its application in soil pollution control and ecoregulation

Soil pollution has become a real threat to mankind in the 21st century. On the one hand, soil pollution has reduced the world's arable land area, resulting in the contradiction between the world's population expansion and the shortage of arable land. On the other hand, soil pollution has seriously disrupted the soil ecological balance and significantly affected the biodiversity in the soil. Soil pollutants may further affect the survival, reproduction and health of humans and other organisms through the food chain. Several studies have suggested that biochar has the potential to act as a soil conditioner and to promote crop growth, and is widely used to remove environmental pollutants. Biochar modified by physical, chemical, and biological methods will affect the treatment efficiency of soil pollution, soil quality, soil ecology and interaction with organisms, especially with microorganisms. Therefore, in this review, we summarized several main biochar modification methods and the mechanisms of the modification and introduced the effects of the application of modified biochar to soil pollutant control, soil ecological regulation and soil nutrient regulation. We also introduced some case studies for the development of modified biochars suitable for different soil conditions, which plays a guiding role in the future development and application of modified biochar. In general, this review provides a reference for the green treatment of different soil pollutants by modified biochar and provides data support for the sustainable development of agriculture.

Impregnating biochar with Fe and Cu by bioleaching for fabricating catalyst to activate H2O2

Biochar is an excellent support material for heterogeneous catalyst in Fenton reaction. However, fabrication of heterogeneous catalyst supported by biochar normally adopts chemical impregnation which is costly and difficult in post-treatment. Here, impregnation by bioleaching driven by Acidithiobacillus ferrooxidans was developed. Bioleaching was particularly effective in loading iron to biochar. Iron loading amount was 225.5 mg/g after 10-g biochar was treated in bioleaching containing 40-g FeSO₄·7H₂O for 60 h. When copper was added into bioleaching, simultaneous impregnation with iron and copper could be achieved. Impregnation mechanism for iron was jarosite formation on biochar surface and adsorption for copper. For the high metal content, after pyrolysis, the final composites could activate hydrogen peroxide to decolorize dye effectively. With 15 mg as-synthesized Cu-Fe@biochar containing 254.3 mg/g iron and 33.4 mg/g copper, 50 mg/L reactive red 3BS or methylene blue could be decolorized completely in 20 min in a 100-mL solution by 16-mM H₂O₂ at pH 2.5. Compared with existing impregnation methods, bioleaching was facile, cheap and green, and deserved more concern. KEY POINTS: • High amount of Fe is loaded to biochar uniformly as jarosite by bioleaching. • Cu is adsorbed onto biochar during bioleaching. • Synthesized Cu-Fe@biochar is an excellent photo-Fenton catalyst.

Characteristics of Cu(II)-modified aerobic granular sludge biocarbon in removal of doxycycline hydroxide

In this study, the biocarbon derived from aerobic granular sludge with different nutritive proportions was modified by Cu(NO₃)₂•3H₂O (Cu-BC) to improve its adsorption capacity of doxycycline hydrochloride (DOX). The surface area, pores, functional groups, and element composition of biocarbon were characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectrometer, X-ray diffraction (XRD), the X-ray photoelectron spectrometer, and Fourier transform infrared spectrometry (FT-IR), respectively. Effects of DOX concentration, initial pH, and background electrolyte on adsorption effects of composite were analyzed. Furthermore, the adsorption kinetics, isotherm, thermodynamics, and diffusion model were investigated. Results demonstrated that biocarbons which were prepared with aerobic granular sludge under different nutritive proportions presented different performances. The BET specific surface area of Cu-NaAC/AGS-BC was 260.1592 m²/g, and the micropore volume was 0.054101 cm³/g. The BET specific surface area of Cu-GLC /AGS-BC was only 10.6821 m²/g, and the micropore volume was 0.008687 cm³/g. Both kinds of modified biochar contain a large number of oxygen-containing functional groups. The highest adsorption efficiency of Cu-BC could reach 99.54%. The adsorption of DOX on two modified biocarbons conforms to the pseudo-second-order dynamic model and Temkin isothermal model.

Biochar as environmental armour and its diverse role towards protecting soil, water and air

Biochar has been of considerable importance for various environmental applications in recent years. It has exhibited substantial advantages like favourable structural and surface properties, easy process of preparation and widely available feedstocks. These set of exceptional properties make it an efficient, cost-effective and environment friendly source for diversified elimination of pollutants. The heterogeneity of physico-chemical properties offers a possibility for biochar to optimize its efficacy for targeted applications. This review aims to highlight the critical role that biochar plays in various environmental applications, be it in soil, water or air. In particular the article offers a comprehensive review of the recent research findings and updates related to the diversified role of biochar. Also, the interaction of pollutants with biochar functional groups and the impact of variation of parameters on biochar attribute relevant to specific pollutant removal, modifications, mechanisms involved and competence for such removal has been discussed. Different technologies for production of biochar have also been summarized with an emphasis on post treatment of biochar, such as modification and doping. In addition to this, the underlying gaps in the studies carried out so far and recommendations for future research areas in biochar have also been deliberated.

Red Yeast Improves the Potential Safe Utilization of Solid Waste (Phosphogypsum and Titanogypsum) Through Bioleaching

Phosphogypsum (PG) and titanium gypsum (TG), as a by-product (solid waste) in phosphate fertilizer and titanium dioxide industry, are causing serious environmental hazards. The resource/harmless application of PG and TG is the development trend in the future. The biological function of red yeast (Rho: Rhodotorula mucilaginosa) can effectively reduce the concentration of pollutants in the environment and has the potential of biological flotation/purification of mineral solid waste. In this study, the bioremediation mechanism and safe utilization efficiency of Rho for different contents of PG and TG were explored by using its biological flotation function. The X-ray fluorescence spectrometry (XRF) results showed that F was the main toxic element in PG and TG, and Pb and Cd did not reach the detection limit. The processing capacity of Rho for PG (>10 g/ml) is higher than that of TG (<5 g/ml). After bioleaching by Rho, the proportion of F in PG and TG solid decreased by 61.45–63.79% and 49.45–59.19%, respectively. The results of three-dimensional fluorescence, extracellular polymeric substance (EPS) extraction, X-ray diffraction (XRD), and scanning electron microscopy (SEM) confirmed that Rho could accelerate the release of harmful elements (F) in PG and TG. SEM showed that Rho cells and secretions adhered and wrapped on PG/TG, causing PG/TG decomposition and fragmentation. In addition, the adsorption of EPS and the formation of Ca₅(PO₄)₃F are two main ways for Rho to remove F. Furthermore, under the condition of high concentration bioleaching, Rho can accelerate the release and utilization of P in PG, which is not only for the re-precipitation of Ca₅(PO₄)₃F but also conducive to the reproduction and utilization of microorganisms. Meanwhile, the purification/safe reuse of PG by Rho is easier than that of TG. Therefore, the toxicity of PG and TG bioleaching by Rho can be greatly reduced, suggesting the huge potential of Rho in soil improvement and remediation.

Enhanced removal of cadmium from wastewater with coupled biochar and Bacillus subtilis

Shortcomings of individual biochar or microbial technologies often exist in heavy metal removal from wastewater and may be circumvented by coupled use of biochar and microorganisms. In this study, Bacillus subtilis and each of three biochars of different origins (corn stalk, peanut shell, and pine wood) were coupled forming composite systems to treat a cadmium (Cd, 50 mg/L) wastewater formulated with CdCl₂ in batch tests. Biochar in composite system enhanced the activity and Cd adsorption of B. subtilis. Compared with single systems with Cd removal up to 33%, the composite system with corn stalk biochar showed up to 62% Cd removal, which was greater than the sum of respective single B. subtilis and biochar systems. Further analysis showed that the removal of Cd by the corn stalk composite system could be considered to consist of three successive stages, that is, the biochar-dominant adsorption stage, the B. subtilis-dominant adsorption stage, and the final biofilm formation stage. The final stage may have provided the composite system with the ability to achieve prolonged steady removal of Cd. The biochar-microorganism composite system shows a promising application for heavy metal wastewater treatment.

Effect of terminal temperature on the morphology and potentially toxic metals concentrations of biochars derived from paper and kitchen waste

This study investigated the morphology and potentially toxic metal concentrations of paper waste-based biochar (PB) and kitchen waste-based biochar (KB) obtained at 500 and 700 °C. The morphology and potentially toxic metals (Cr, Mn, Cu, Cd, Pb, Zn, Ag, and Ba) concentrations in the biochars were determined by SEM and FT-IR analysis. The Cr, Mn, Cu, and Cd concentrations in PB were low, while the Ba content was relatively high at 0.1 mg∙kg^-1. An increase in the terminal temperature led to an increase in the concentrations of Fe/Mn oxide-bound potentially toxic metals of PB, and a decrease in the concentrations of organic matter-bound potentially toxic metals. The Fe/Mn oxide-bound Cr, Mn, Cu, Pb, and Zn concentrations of KB decreased with an increase in the terminal temperature. Therefore, increasing the terminal temperature could reduce the bioavailability of potentially toxic metals in PB and KB. The environmental risk of the different biochars when used for soil remediation was assessed by the potential ecological risk index (RI), and a case study of a Tibetan soil was also conducted. The potentially toxic metal concentrations leached from both PB and KB were lower than the relevant standards. The findings showed that both PB and KB can be safely used for soil remediation.

Evaluating the protection of bacteria from extreme Cd (II) stress by P-enriched biochar

Cadmium cations (Cd²⁺) are extremely toxic to organisms, which limits the remediation of Cd by microorganisms. This study investigated the feasibility of applying biochar to protect bacteria from extreme Cd²⁺ stress (1000 mg/L). An alkaline biochar (RB) and a slightly acidic biochar (SB) were selected. SB revealed a higher Cd²⁺ removal than RB (15.5% vs. 4.8%) due to its high surface area. Addition of Enterobacter sp. induced formation of Cd phosphate and carbonate on both SB and RB surface. However, Cd²⁺ removal by RB enhanced more evidently than SB (78.9% vs. 30.2%) due to the substantial microbial regulation and surficial alkalinity. Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and geochemical modeling (GWB) all confirmed that the formation of stable Cd phosphate on RB was superior to that in SB. These biomineralization, together with biochar pore structure, protect bacterial cells from Cd stress. Moreover, the alkalinity of biochar promoted the formation of carbonate, which strengthened the decline of Cd²⁺ toxicity. The protection by RB was also confirmed by the intense microbial respiration and biomass (PLFA). Furthermore, this protection induced a positive feedback between P-abundant biochar and Enterobacter sp.: biochar provides P source (the most common limiting nutrient) to support microbial growth; bacteria secrete more organic acids to drive P release. This study therefore elucidated the protection of bacteria by P-enriched biochar based on both physic-chemical and microbial insights.

Use of Biochar in agriculture

The objective of this review is to show in a general way how biochar (BC) can be obtained and its effects on the physicochemical properties of soils and physiological behavior of cultivated plants. BC is a product rich in carbon that comes from the pyrolysis of biomass, generally of vegetable origin. BC is obtained by the decomposition of organic matter exposed to temperatures between 200-900 ºC in an atmosphere with low oxygen availability (pyrolysis), which can be slow, intermediate or fast. Depending on the biomass and the temperature used in its production, BC can contain high levels of elements such as carbon, nitrogen, oxygen, hydrogen, sulfur, among others. The main sources to produce biochar are forest, agroindustrial and manure residues. BC quality and physical-chemical characteristics will depend not only on the type of waste or plant material for production, but also on the plant photosynthetic apparatus. The high carbon contents present in organic matter, which are more resistant to biological and chemical decomposition, are stabilized by the pyrolysis process. When incorporated into the soil, BC remains stable for longer periods of time and is not volatilized into the atmosphere; this allows BC to be considered as an important compound for the mitigation of the impacts of polluting substances. Additionally, it has been found that BC application improves the physicochemical characteristics of the soil, including fertility. This improvement generates positive responses in the physiological behavior of cultivated plants such as the increase of germination, accumulation of dry matter, photosynthetic rate, yield and quality of the harvested organ. BC use opens important doors for the sustainable management of agriculture in Colombia. It can be considered in production systems exposed to heavy metals such as vegetables and perennial species, in order to reduce the impact of these substances on human health.

Adsorption of Cd2+ on GO/PAA hydrogel and preliminary recycle to GO/PAA-CdS as efficient photocatalyst

In this work, a GO (graphene oxide)/PAA (poly acrylic acid) hydrogel was prepared by graft polymerization between GO and AA. It was employed as highly efficient adsorbent for Cd²⁺ removal from wastewater. The GO/PAA-Cd²⁺ composite after the adsorption process was recycled through in-situ precipitation to obtain GO/PAA-CdS composites. During the synthesis process, the amounts of GO and AA were optimized to enable the hydrogel with maximum adsorption of Cd²⁺ (316.4 mg/g at 25 °C). The structure and chemical composites of GO/PAA hydrogel were investigated through FTIR spectra, Raman spectra, and TGA. The adsorption kinetics and isotherms of Cd²⁺ on GO/PAA were analyzed. The synthesized products served as an efficient adsorbent for Cd²⁺ and a suitable matrix for the CdS quantum dots formation which was confirmed by various characterizations, including XPS, SEM-EDS and HRTEM. The roles of GO and PAA in the successive adsorption-photocatalyst process were proved to be complementary: PAA improved the adsorption of Cd²⁺ while GO enhanced the photocatalyst efficiency. The photodegradation rate of MB (30 mg/L) was over 90% within 2 h.

Enhanced Pb immobilization via the combination of biochar and phosphate solubilizing bacteria

Application of biochar in heavy metal remediation suffers from lack of long-term stability. Phosphate-solubilizing bacteria (PSB) are able to elevate P release and the subsequent reaction with Pb to form stable pyromorphite. This study investigated the feasibility of applying PSB modified biochar to enhance immobilization of Pb²⁺. An alkaline biochar produced from rice husk (RB) and a slightly acidic biochar produced from sludge (SB) were selected. It showed that the biochars can effectively remove Pb²⁺ via adsorption, i.e., aqueous Pb concentrations after RB and SB addition were reduced by 18.61 and 53.89% respectively. The addition of PSB increased the Pb²⁺ removal for both biochars (to 24.11 and 60.85%, respectively). In particular, PSB significantly enhanced the formation of stable pyromorphite on surface of SB. This is due to that the evenly distributed PSB enhanced P release and regulated pH on the biochar surface. Moreover, small particles (<0.074 mm) showed their higher ability to induce the formation of pyromorphite, for both RB and SB. Nevertheless, SB demonstrated higher capability of sorption, together with its more abundant P content, which provided a more suitable platform to attract PSB to immobilize heavy metals. Therefore, the combination of biochar and PSB is a promising candidate material for heavy metal remediation. However, the types and particle size distribution of biochar should be addressed.

Sewage biogas efficient purification by means of lignocellulosic waste-based activated carbons

The present paper evaluates the efficiency of sustainable activated carbons obtained from the valorization of lignocellulosic waste in removing siloxanes and volatile organic compounds for the purification of anaerobic digester biogas. Pyrolized and non-pyrolized lignocellulosic residues generated in food and wood industries were used as precursor materials to obtain experimental adsorbents by a chemical activation process using several activating agents. The highest porosity was obtained by non-pyrolized residue activated by K₂CO₃ at 900 °C. The performance of the experimental materials was compared with that of commercial activated carbons in gas adsorption tests of siloxanes (octamethylcyclotetrasiloxane and hexamethyldisiloxane) and volatile organic compounds (toluene and limonene). The waste-based activated carbons developed in this work proved to be more efficient for the removal of both siloxanes and VOCs than the commercial samples in most of the conditions tested. Adsorption capacities correlated with porosity, while the more relevant pore size depends on the adsorbate.

Phytoextraction of Cd from a contaminated soil by tobacco and safe use of its metal-enriched biomass

Successful phytoextraction produces a large quantity of contaminated biomass, which will cause secondary pollution unless properly treated. This study investigated the disposal of contaminated tobacco biomass after phytoextraction. We detected significantly high Cadmium concentrations in tobacco, especially in their stems and leaves. From the latter, nearly all the Cd and nicotine were removed by extractions with 0.5% HCl + 70% ethanol, and the nicotine completely recovered via steam distillation, whereas the protein content remained unaffected in the leaves, thus making them safe for use as animal feed. The highest biochar yield was 47%, obtained after slow pyrolysis at 300 °C. In this case, the biochar contained the highest amount of nutrients and metals. From stem biochar, 87% of Cd and a large amount K along with several other elements were extracted by deionized water at pH 1. After acid-extraction, metals were formed precipitation and then separated from the K-enriched solution when the pH was adjusted to 11 by using drops of 40% KOH. Therefore, with improved technology to remove metals and recover nutrients and nicotine from biomass, tobacco is an ideal candidate as profit yielding crop for use in phytoextraction while also providing renewable resources.

Characterization of modified biochars prepared at low pyrolysis temperature as an efficient adsorbent for atrazine removal

In this study, biochars (BC, ZnBC, and PBC) produced from wheat straw at relatively lower pyrolysis are successfully fabricated using different pretreatment techniques (without and with ZnCl₂ or H₃PO₄). The specific surface area (SSA), elemental analysis, and Fourier transform infrared spectra (FTIR) are used to analyze physicochemical properties of unmodified and modified biochars. ZnBC and PBC show higher specific surface area and more micropore structure than pure BC. Kinetic models (pseudo-first order, pseudo-second order, and intra-particle diffusion) as well as isotherm models (Langmuir and Freundlich) are applied to analyze adsorption behavior. Adsorption on biochars can be better fitted by the pseudo-second-order and intra-particle diffusion models, indicating that micropores and mesopores play important roles on adsorption process and chemisorption is dominant. The adsorption process is also affected by physical and chemical adsorption. In conclusion, biochar is a low-cost, effective, and environment-friendly adsorbent implicating in the environment for pesticide removal. Graphical abstract.

Pyrolytic behavior of a zero-valent iron biochar composite and its Cu(ii) removal mechanism

The reduction behavior of Fe³⁺ during the preparation of a zero-valent iron cocoanut biochar (ZBC8-3) by the carbothermic reduction method was analyzed. Fe³⁺ was first converted into Fe₃O₄, which was subsequently decomposed into FeO, and finally reduced to Fe⁰. A minor amount of γ-Fe₂O₃ was produced in the process. The isothermal thermodynamic data for the removal of Cu(ii) over ZBC8-3 followed a Langmuir model. The Langmuir equation revealed a maximum removal capacity of 169.49 mg g⁻¹ at pH = 5 for ZBC8-3. The removal of Cu(ii) over ZBC8-3 fitted well to a pseudo-first-order equation, which suggested that the rate limiting step of the process was diffusion. The Cu(ii) removal mechanism on ZBC8-3 involved the reduction of Cu(ii) by Fe⁰ to produce Cu⁰ and Cu₂O, while C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C, C–O–, and –O–H formed a complex with Cu(ii).

The Cu(ii) removal mechanism on ZBC8-3 involved the reduction of Cu(ii) by Fe⁰ to produce Cu⁰ and Cu₂O, while CC, C–O–, –O–H formed a complex with Cu(ii).

A critical review on sustainable biochar system through gasification: Energy and environmental applications

This review lays great emphasis on production and characteristics of biochar through gasification. Specifically, the physicochemical properties and yield of biochar through the diverse gasification conditions associated with various types of biomass were extensively evaluated. In addition, potential application scenarios of biochar through gasification were explored and their environmental implications were discussed. To qualitatively evaluate biochar sustainability through the gasification process, all gasification products (i.e., syngas and biochar) were evaluated via life cycle assessment (LCA). A concept of balancing syngas and biochar production for an economically and environmentally feasible gasification system was proposed and relevant challenges and solutions were suggested in this review.

Facile synthesis of Cu(II) impregnated biochar with enhanced adsorption activity for the removal of doxycycline hydrochloride from water

In this study, the effect factors and mechanisms of doxycycline hydrochloride (DOX) adsorption on copper nitrate modified biochar (Cu-BC) was investigated. Cu-BC absorbent was synthesized through calcination of peanut shells biomass at 450°C and then impregnation with copper nitrate. The Cu-BC has exhibited excellent sorption efficiency about 93.22% of doxycycline hydrochloride from aqueous solution, which was double higher than that of the unmodified biochar. The experimental results suggest that the adsorption efficiency of DOX on the Cu-BC is dominated by the strong complexation, electrostatic interactions between DOX molecules and the Cu-BC samples. Comprehensively considering the cost, efficiency and the application to realistic water, the Cu-BC hold the significant potential for enhancing the effectiveness to remove DOX from water.

Effects of Biochar-Derived Sewage Sludge on Heavy Metal Adsorption and Immobilization in Soils

The object of this study was to evaluate the effect of sewage sludge biochar on adsorption and mobility of Cr, Mn, Cu, and Zn. Biochar (BC400) was produced via pyrolysis of municipal sewage sludge at 400 °C. Maximum adsorption capacities (q_m) for Zn, Cr, Mn, and Cu were 5.905, 5.724, 5.681, and 5.342 mg·g^-1, respectively, in the mono-metal solution and 2.475, 8.204, 1.01, and 5.415 mg·g^-1, respectively, in the multi-metal solution. The adsorption capacities for Mn, Cu, and Zn decreased in the multi-metal solution due to competitive adsorption, whereas the capacity for Cr increased. Surface precipitation is an important mechanism in the sorption of these metals on BC400. The 360-day incubation experiment showed that BC400 application reduced metal mobility in contaminated soils, which was attributed to the substantial decreases in the acid-soluble fractions of Cr, Mn, Cu, and Zn (72.20%, 70.38%, 50.43%, and 29.78%, respectively). Furthermore, the leaching experiment using simulated acid rain indicated that the addition of BC400 enhanced the acid buffer capacity of contaminated soil, and the concentration of Cr, Mn, Cu, and Zn in the leachate was lower than in untreated soil. Overall, this study indicates that sewage sludge biochar application reduces the mobility of heavy metal in co-contaminated soil, and this adsorption experiment is suitable for the evaluation of biochar properties for remediation.

Biochar as potential sustainable precursors for activated carbon production: Multiple applications in environmental protection and energy storage

There is a growing interest of the scientific community on production of activated carbon using biochar as potential sustainable precursors pyrolyzed from biomass wastes. Physical activation and chemical activation are the main methods applied in the activation process. These methods could have significantly beneficial effects on biochar chemical/physical properties, which make it suitable for multiple applications including water pollution treatment, CO₂ capture, and energy storage. The feedstock with different compositions, pyrolysis conditions and activation parameters of biochar have significant influences on the properties of resultant activated carbon. Compared with traditional activated carbon, activated biochar appears to be a new potential cost-effective and environmentally-friendly carbon materials with great application prospect in many fields. This review not only summarizes information from the current analysis of activated biochar and their multiple applications for further optimization and understanding, but also offers new directions for development of activated biochar.

Removal of Cu(ii) from aqueous solution using Fe3O4–alginate modified biochar microspheres

Magnetic microspheres (MM) were prepared using calcium alginate (CA) encapsulated biochar (BC) and Fe₃O₄ as a high-performance green absorbent for Cu(ii) removal from aqueous solution.

Enhanced adsorption of methylene blue by citric acid modification of biochar derived from water hyacinth (Eichornia crassipes)

In this work, a novel potential adsorbent, citric acid (CA)-modified biochar, named as CAWB, was obtained from water hyacinth biomass by slow pyrolysis in a N₂ environment at 300 °C. The CA modification focused on enhancing the contaminants adsorption capacity of biochar pyrolyzed at relatively low temperature. Over 90 % of the total methylene blue (MB) could be removed at the first 60 min by CAWB, and the maximum MB adsorption capacity could reach to 395 mg g^-1. The physicochemical properties of CAWB was examined by FTIR, XPS, SEM, and BET analysis. The results indicated that the additional carboxyl groups were introduced to the surface of CAWB via the esterification reaction with CA, which played a significant role in the adsorption of MB. Batch adsorption studies showed that the initial MB concentration, solution pH, background ionic strength, and temperature could affect the removal efficiency obviously. The adsorption process could be well described by the pseudo-second-order kinetic model and Langmuir isotherm. Thermodynamic analysis revealed that the MB adsorption onto CAWB was an endothermic and spontaneous process. The regeneration study revealed that CAWB still exhibited an excellent regeneration and adsorption performance after multiple cycle adsorptions. The adsorption experiments of actual dye wastewater by CAWB suggested that it had a great potential in environmental application.

Simultaneous adsorption of methyl red and methylene blue onto biochar and an equilibrium modeling at high concentration

Methyl red, methylene blue and biochar were used to investigate simultaneous adsorption of dyes onto low-cost adsorbent at different concentrations combinations. Langmuir mixed model could describe the adsorption well at low concentrations. However, it could not describe the adsorption anymore when concentrations of methyl red and methylene blue were higher than 255 and 300 mg L(-1) respectively with 0.5 g L(-1) biochar loading. A new model on the interaction among adsorbed adsorbates at equilibrium was developed. It could describe the adsorption at high concentrations well. According to the experimental results, interaction among dyes molecules would replace the competition onto adsorbent to be the main factor influencing adsorption when amount of adsorbed adsorbates were higher than those required to form a monolayer on all the adsorbing sites of adsorbent. The model was further verified by adsorption with other solute such as glucose or NaCl in solution.

Adsorption of cadmium by biochar derived from municipal sewage sludge: Impact factors and adsorption mechanism

Static equilibrium experiments were carried out to investigate the impact factors and the mechanism of cadmium adsorption on biochar derived from municipal sewage sludge. An appropriate dosage of biochar is sufficient; in the experiment, 0.2% is the optimal dosage for the largest removal capacity, while the removal capacity of biochar reduces with the increasing dosage. pH is another dominant factor of the adsorption process. The removal capacity of biochar is lower than 20 mg·g(-1) when the solution initial pH is lower than 2 pH units, comparatively retaining more than 40 mg·g(-1) at the solution initial pH higher than 3 pH units. Temperature has weak influence on the adsorptive performance. The main mechanism of the adsorption process of biochar for cadmium mainly involves (1) surface precipitation by forming insoluble cadmium compounds in alkaline condition, and (2) ion exchange for cadmium with exchangeable cations in the biochar, such as calcium ions.

Electricity generation from sulfide tailings using a double-chamber microbial fuel cell

Pyrrhotite tailings have the potential to drive electricity generation accompanied by microbial leaching of valuable metals using the double-chamber MFC reactor.