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With the goal of combining the advantages of ball-milling and biochar technologies, a variety of ball-milled biochars (BM-biochars) were synthesized, characterized, and tested for nickel (Ni(II)) removal from aqueous solution. Ball milling increased only the external surface area of low temperature biochars, but still dramatically enhanced their ability to sorb aqueous Ni(II). For higher temperature biochars with relatively low surface area, ball milling increased both external and internal surface area. Measurements of pH, zeta potential, stability, and Boehm titration demonstrated that ball milling also added oxygen-containing functional groups (e.g., carboxyl, lactonic, and hydroxyl) to biochar's surface. With these changed, all the BM-biochars showed much better Ni(II) removal efficiency than unmilled biochars. Ball-milled 600 °C bagasse biochar (BMBG600) showed the greatest Ni(II) adsorption capacity (230–650 compared to 26–110 mmol/kg for unmilled biochar) and the adsorption was dosage and pH dependent. Compared with the unmilled biochar, BMBG600 also displayed faster adsorption kinetics, likely due to an increase in rates of intra-particle diffusion in the latter. Experimental and modeling results suggest that the increase in BM-biochar's external and internal surface areas exposed its graphitic structure, thus enhancing Ni(II) adsorption via strong cation-π interaction. In addition, the increase in acidic surface functional groups enhanced Ni(II) adsorption by BM-biochar via electrostatic interaction and surface complexation. Ball milling thus has great potential to increase the efficiency of environmentally friendly biochar for various environmental applications. [ABSTRACT FROM AUTHOR]

Novel adsorbents were produced through the grinding of biochars of different feedstock and pyrolysis temperature in a planetary ball mill. The removal effectiveness and mechanisms of aqueous methylene blue by these adsorbents were examined. Ball milled sugarcane bagasse biomass pyrolyzed at 450 °C (BMBG450) had the highest methylene blue sorption capacity thus was chosen for further study. Compared to unmilled bagasse biochar (BG450), BMBG450 had greater specific surface area, larger pore volume, smaller hydrodynamic radius, stronger negative zeta potential (about 1.6-fold increase), and more oxygen-containing functional groups (1.05 mmol/g increase). These characteristics resulted in much greater methylene blue removal capacity (354 mg/g Langmuir maximum adsorption capacity vs. 17.2 mg/g of original BG450). The increased in BM–biochar’s external and internal surface areas exposed its graphitic structure and oxygen-containing functional groups, thus enhancing methylene blue adsorption via π–π interaction and electrostatic attraction. Experimental and modeling results suggest external mass transfer as the rate-limiting adsorption step for BG450 and surface diffusion as the rate-limiting adsorption step for BMBG450. BM–biochars had a lower equilibrium dosage and shorter reactor detention time when applied in a completely mixed flow reactor (CMFR). [ABSTRACT FROM AUTHOR]

As the first of its kind, a novel biochar/iron oxide composite (BM-Fe-HC) was successfully prepared by simply ball milling iron-laden biochar (Fe-HC). The performance and mechanisms of Cr(VI) removal by BM-Fe-HC were investigated. Ball milling effectively reduced particle size, increased specific surface area, more importantly, enhanced the distribution and increased the exposure of iron oxides on biochar surface. As a result, Cr(VI) removal by BM-Fe-HC showed fast kinetics and large adsorption capacity with the Langmuir maximum capacity of 48.1 mg/g, higher than that of other biochar/iron composites reported in the literature. Acidic pH promoted Cr(VI) removal while competition ions (Cl-, SO 4 2- and PO 4 3-) inhibited Cr(VI) removal by BM-Fe-HC. Comparison of pre- and post-adsorption samples revealed that iron oxides of the BM-Fe-HC played the dominant role in the adsorption and reduction of Cr(VI) during the removal. After adsorption, part of adsorbed Cr(VI) was reduced by Fe(II) and then stabilized by Fe(III) in the form of amorphous Cr x Fe 1−x (OH) 3 on the composite surface. All the results demonstrate that novel ball-milled biochar/iron oxide composites can be used as an effective adsorbent to remove Cr(VI) from water. [Display omitted] • Ball milling iron-laden biochars produced novel biochar/iron oxide composites • Ball milling increased the exposure of iron oxides on biochar surface • Ball-milled biochar/iron oxide composites showed enhanced removal of Cr(VI) • Iron oxides of the composites are the main sites that can adsorb and reduce Cr(VI) [ABSTRACT FROM AUTHOR]

Graphic abstract Highlights • Governing adsorption mechanisms of heavy metals onto carbon adsorbents are summarized. • Various methods for introduction of oxygen, nitrogen, and sulfur functional groups onto carbon surfaces are categorized. • Effects of various functional groups on heavy metal adsorption onto different carbon materials are discussed. • Perspectives of future work on functionalized carbon adsorbents for heavy metal removal is also presented. Abstract Carbon-based adsorbents such as graphene and its derivatives, carbon nanotubes, activated carbon, and biochar are often used to remove heavy metals from aqueous solutions. One of the important aspects of effective carbon adsorbents for heavy metals is their tunable surface functional groups. To promote the applications of functionalized carbon adsorbents in heavy metal removal, a systematic documentation of their syntheses and interactions with metals in aqueous solution is crucial. This work provides a comprehensive review of recent research on various carbon adsorbents in terms of their surface functional groups and the associated removal behaviors and performances to heavy metals in aqueous solutions. The governing removal mechanisms of carbon adsorbents to aqueous heavy metals are first outlined with a special focus on the roles of surface functional groups. It then summarizes and categorizes various synthesis methods that are commonly used to introduce heteroatoms, primarily oxygen, nitrogen, and sulfur, onto carbon surfaces for enhanced surface functionalities and sorptive properties to heavy metals in aqueous solutions. After that, the effects of various functional groups on adsorption behaviors of heavy metals onto the functionalized carbon adsorbents are elucidated. A perspective of future work on functional carbon adsorbents for heavy metal removal as well as other potential applications is also presented at the end. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Engineered biochar showed strong batch adsorption ability to P in real secondary treated wastewater. • Engineered biochar in fixed-bed columns also effectively removed P from the wastewater. • Commonly used fixed-bed dynamic adsorption models describe the P breakthrough curves well. • Exhaust P-laden biochar promoted mung bean seed germination and seedling growth. Abstract Phosphorus (P), a vital growth-limiting nutrient, is often lost in wastewater discharge, which may not only deteriorate water quality but also accelerate P depletion. In this study, laboratory experiments were conducted to investigate the reclamation and reuse of P from secondary treated wastewater (STWW) by engineered biochar loaded with aluminum oxyhydroxides (AlOOH). Biochar loaded with colloidal and nanosized AlOOH crystalline flakes was successfully produced through direct pyrolysis of hickory wood chips pretreated with aluminum salt. STWW samples were collected from a local wastewater treatment plant to evaluate the P sorption ability of the engineered biochar. The real wastewater was used in batch sorption experiments and the results showed that the engineered biochar effectively removed P from the STWW with relatively fast kinetics (<8 h) and good capacity (8,346 mg-P/kg), mainly through the electrostatic attraction mechanism. When the engineered biochar was packed in fixed-bed columns, it also effective removed P from the real STWW. The P removal efficiencies of the fixed-bed columns were affected by biochar dosage and flow rate. Various fixed-bed filtration models were applied to simulate the column experimental data and the model results matched the experimental breakthrough curves of P well. After the use, the engineered biochar was laden with P and thus significantly stimulated seed (Vigna radiata R. Wilczek) germination and early seedling growth. Findings from this study demonstrate that engineered biochar has promising applications in wastewater treatment because it can not only reduce P level in discharge to benefit the environment but also reclaim it as an agricultural fertilizer to improve P biogeochemical cycling and sustainability. [ABSTRACT FROM AUTHOR]

Hydrated manganese oxide (HMO) nanoparticles were impregnated into a peanut shell-derived biochar (BC) to obtain a remarkable nanocomposite adsorbent, HMO-BC, which overcomes the technical barriers of singly applying either HMO or BC in practical heavy metal-containing wastewater treatment. HMO-BC can effectively sequestrate Pb(II) and Cd(II) in a wide pH range of 3–7 and exhibited more preferable sorption than bare BC in the presence of high-level competing cations. BC also significantly lowered the Mn leaching at acidic pH. Fixed-bed column adsorption tests showed that the effective treatment volume of HMO-BC for a simulated Pb(II)- or Cd(II)-laden wastewater is about 4–6 times higher than that of the BC host. In addition, HMO-BC was effective in removing Pb(II) from a real Pb-containing electroplating wastewater to discharge limit (0.2 mg L − 1 ) with treatable volume of 525 BV, much higher than that of the bare BC (60 BV). More importantly, the saturated HMO-BC can be thoroughly regenerated for repeated uses without any observable capacity loss. Such attractive results of HMO-BC were attributed to the complementary effect of its two components. The embedded HMO nanoparticles provide preferable capture of target cations through specific inner-sphere complexation, as illustrated by XPS spectra of Pb 4f 7/2 and O1s, while the non-diffusive negatively charged oxygen-containing groups bound to BC facilitate the pre-enrichment and permeation of Pb(II) and Cd(II) cations into the pore channels prior to their preferable sorption through the Donnan membrane effect. [ABSTRACT FROM AUTHOR]

Arsenate (As(V)) removal ability by nanoscale zero-valent iron (nZVI) is compromised by aggregation of nZVI particles. In this work, pine derived biochar (PB) was used as a supporting material to stabilize nZVI for As(V) removal. The biochar supported nZVI (nZVI/BC) was synthesized by precipitating the nanoparticles on carbon surfaces. Experiments using batch and continuous flow, completely mixed reactors (CMRs) were carried out to investigate the removal of As(V) by the nZVI/BC from aqueous solutions. Batch experiments showed that nZVI/BC had high As(V) removal capacity in a wide range of pH (3–8). Kinetic data revealed that equilibrium was reached within 1 h and the isotherm data showed that the Langmuir maximum adsorption capacity of the nZVI/BC for As(V) at pH 4.1 was 124.5 g kg −1 . As(V) (100 mg L −1 ) adsorption in anoxic condition was about 8% more than in oxic conditions, where As(V) reduction was observed in anoxic condition. The performance of the nZVI/BC in flowing condition was evaluated in CMRs at influent As(V) concentrations of 2.1 and 5.5 mg L −1 and the adsorbent removed 100% and 90% of the As(V), respectively. Furthermore, the nZVI/BC composite is magnetic which facilitates collection from aqueous solutions. [ABSTRACT FROM AUTHOR]

Dissolved organic matter released from biochar (biochar-derived DOM, BDOM) could dominate the environmental behavior and fate of trace metals by forming BDOM-metal complexes. Here general, heterospectral as well as moving-window (MW) two-dimensional correlation spectroscopy (2DCOS) analyses of synchronous fluorescence and Fourier transform infrared spectra were employed to explore the heterogeneous binding characteristics between sludge BDOM and Cu(II). The results revealed that Cu-BDOM binding first occurred in the fulvic-like (368–380 nm), then humic-like (428 nm) fluorescent fractions, followed by infrared groups of phenolic hydroxyl groups, carboxylate, C OH of polysaccharide groups, C C of aromatic carbon, CH of aliphatics and C O C of aliphatic ethers. The binding affinity of the hydrophilic groups was stronger than that of hydrophobic groups in BDOM towards Cu(II). Fluorescence components in BDOM played a decisive role in the binding of Cu(II) with trace concentration (1 μM), while infrared functional groups made a substantial contribution in the complexation of Cu(II) with higher concentration (10–100 μM). The concentration of final configuration transformation point (11.7 μmol/mg in this study) by MW2DCOS analysis was suggested as an actual binding threshold that was helpful for evaluating their environmental behaviors. [Display omitted] • Hydrophilic sites were binded towards Cu(II) prior to hydrophobic sites. • Oxygen-containing functional groups preferred to bind with Cu(II) than aromatics. • Fluorescence response was prior to vibration changes of infrared functional groups. • Final configuration transformation point was suggested as actual binding threshold. • Moving-window 2DCOS provides a new insight in understanding dynamic binding process. [ABSTRACT FROM AUTHOR]

• MO-L-BC was fabricated using a biochar with enlarged pore structure as the carrier. • Sb(III) and Cu(II) adsorption on MO-L-BC can achieve equilibria within 15 min. • Oxidation of the sorbed Sb(III) to Sb(V) caused by the loaded MO was identified. • MO-L-BC can effectively treat synthetic wastewater in high flow column settings. Antimony and copper pollution pose significant threat to water quality security, and their advanced treatment is still a great challenge. In this study, we fabricated a hybrid adsorbent (denoted as MO-L-BC) through dispersing manganese oxide (MO) inside a biochar with enlarged pore structure (namely L-BC). The used carrier L-BC possessed a high proportion of large pores (>2 nm) (87%), and thus lowered the diffusion resistance of target pollutants in pore region of MO-L-BC. Consequently, Sb(III) and Cu(II) adsorption onto MO-L-BC achieved equilibrium within 15 min, and their effective coefficients of intra-particle diffusion (D) were calculated to be 8.6 × 10−8 and 1.5 × 10−7 cm2 s−1, respectively, which were only one-order magnitude lower than that in aqueous phase. XPS analysis indicated that 53.3% of the sorbed Sb(III) was oxidized to Sb(V) by the impregnated MO. Coexisting substances such as HCO 3 −, SO 4 2−, NO 3 −, Ca2+, Mg2+ and humic acid up to 20 times higher concentration than target contaminants (Sb(III) or Cu(II)) caused only < 20% drop in sorption capacity of MO-L-BC, and the mutual effect of Sb(III) and Cu(II) was also not noticeable. The fixed-bed column adsorption tests showed that MO-L-BC can achieve the tertiary treatment of either the singly polluted (Sb(III) or Cu(II)) or the co-contaminated wastewater at a high flow rate of 0.27 m h−1, with effective treatment volumes larger than400 BV, and the saturated MO-L-BC can be effectively regenerated. MO-L-BC is a promising engineered biochar to treat Sb(III) and/or Cu(II) contaminated water especially under high-flow conditions. [ABSTRACT FROM AUTHOR]

Biochar is a promising agent for wastewater treatment, soil remediation, and gas storage and separation. This review summarizes recent research development on biochar production and applications with a focus on the application of biochar technology in wastewater treatment. Different technologies for biochar production, with an emphasis on pre-treatment of feedstock and post treatment, are succinctly summarized. Biochar has been extensively used as an adsorbent to remove toxic metals, organic pollutants, and nutrients from wastewater. Compared to pristine biochar, engineered/designer biochar generally has larger surface area, stronger adsorption capacity, or more abundant surface functional groups (SFG), which represents a new type of carbon material with great application prospects in various wastewater treatments. As the first of its kind, this critical review emphasizes the promising prospects of biochar technology in the treatment of various wastewater including industrial wastewater (dye, battery manufacture, and dairy wastewater), municipal wastewater, agricultural wastewater, and stormwater. Future research on engineered/designer biochar production and its field-scale application is discussed. Based on the review, it can be concluded that biochar technology represents a new, cost effective, and environmentally-friendly solution for the treatment of wastewater. Image 1 • Biochar technologies in various wastewater treatment are elucidated. • Feedstock pre-treatment and post-treatment effect on biochar production is reviewed. • Biochar as an innovative adsorbent to remove aqueous contaminants is discussed. • Future perspectives of biochar technology in wastewater treatment are summarized. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are widely accumulated in sediments and thus impose great risks to the ecosystem and public health. There is increasing effort on the development of technologies for remediation of PAH-contaminated sediments. Adsorption is one of the most promising remediation technologies is to PAH-contaminated sediments. Carbonaceous adsorbents (CAs) have been considered desirable for adsorbing PAHs due to their cost-effective and eco-friendly nature. The effectiveness of CAs in removal of PAHs, however, can be greatly affected by adsorbent properties, sediment characteristics, and environmental conditions. An accumulating evidence largely from laboratory experiments has shown that CAs can be used for immobilization and decontamination of PAHs in sediments, however, their full potential has not been demonstrated, particularly with respect to field applications. The present review aims to summarize the current progress on CA physical and chemical properties, and mechanisms of the stabilization of PAHs in sediments as well as key factors controlling field applications. In addition, potential environmental effects associated with CA-mediated PAH stabilization is also discussed. Among various CAs, activated carbon and biochar are the most commonly used adsorbents for sediment remediation and thus are the focuses of this review. • Applications of CAs in immobilization and decontamination of PAHs in sediments are reviewed. • Influences of characteristics of CAs and PAHs, and remediation conditions are discussed. • Physical and chemical mechanisms of CAs for PAH remediation in sediments are summarized. • Negative effects associated with CA remediation of PAH-contaminated sediments are discussed. [ABSTRACT FROM AUTHOR]

• HMO-K-BC was prepared by employing a macro-mesoporous biochar as the carrier. • Pb(II) and Cd(II) adsorption onto HMO-K-BC can reach equilibria within 7.5 min. • The intraparticle diffusivity of HMO-K-BC is much higher than common adsorbents. • HMO-K-BC can treat simulated and real wastewater in high flow column settings. Porous carrier supported metal oxide composites possess significant potential for sequestration of heavy metals from various waters. However, slow diffusion of targeted metal ions within the micropores of the porous carriers is a key technical barrier limiting practical application of these hybrid adsorbents, particularly in high flow systems. In this study, we first synthesized a biochar with enlarged pore channel (namely K-BC) by adding KHCO 3 during the biochar pyrolysis process and then employed the K-BC as a supporter to fabricate a new manganese oxide-based composite (namely HMO-K-BC). It is striking that the effective intra-particle diffusion coefficient D of Pb(II) inside the K-BC is comparable to that in aqueous solution (1.5 × 10−6 v.s. 2.1 × 10−6 cm2 s−1). Although the D value of Pb(II) inside the HMO-K-BC was reduced to 1.8 × 10−7 cm2 s−1, it is still 1–2 orders of magnitude higher than that of conventional adsorbents such as activated carbon, ion exchanger and biochar. As a result, the HMO-K-BC can rapidly sequestrate Pb(II) and Cd(II) within 7.5 min. The HMO-K-BC can also selectively remove Pb(II) and Cd(II) in the presence of high level Ca(II) and humic acid. Column tests further showed that HMO-K-BC was able to effectively treat simulated and real Pb(II)- and Cd(II)-polluted wastewater in a high-flow system with superficial liquid velocity of 0.53 m h−1 (20 BV h−1). All the results manifest that expanding pores of biochar is a promising measure for promoting the practical application of biochar supported composites in wastewater treatment. [ABSTRACT FROM AUTHOR]

• Ball milling improved the physicochemical characteristics of biochar. • Ball-milled biochars showed enhanced adsorption of VOCs. • VOC adsorption onto ball-milled biochars was controlled by surface adsorption and partition mechanisms. • Adsorbed VOCs were completely desorbed from ball-milled biochars. Hickory wood was pyrolyzed at 300 °C, 450 °C, and 600 °C to produce biochars, which were then modified by ball milling. The pristine and ball-milled biochars were used to remove volatile organic compounds (VOCs) including acetone, ethanol, chloroform, cyclohexane, and toluene. Compared with the corresponding pristine one, each ball-milled biochar showed significantly improved structural characteristics. Their specific surface area (SSA) increased by 1.4–29.1 times, average pore size (APS) decreased slightly, and the hydrophilicity and polarity were also enhanced according to the elemental analysis. The adsorption of VOCs by ball-milled biochar increased by 1.3–13.0 folds, and the maximum adsorption capacity of acetone was up to 103.4 mg/g. The adsorption of polar VOCs (acetone, ethanol, and chloroform) onto ball-milled biochars was mainly controlled by surface adsorption process, which was affected by the SSA, APS, and volatile organic matter of the biochars, as well as the properties of the VOCs. The adsorbed VOCs were completely desorbed from the ball-milled biochars at relatively low temperature (≤115.2 °C). Reusability experiments with five adsorption-desorption cycles showed that ball-milled biochar had an excellent reusability for all VOCs. Ball-milled biochars can therefore be used as an effective and regenerable adsorbent for the removal of VOCs. [ABSTRACT FROM AUTHOR]