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The use of carbon-rich sorbents to remove and/or immobilize perfluoroalkyl substances (PFAS) in contaminated environmental scenarios is attracting increasing interest. The identification of key sorbent properties responsible for PFAS sorption and the development of models that can predict the distribution coefficients (Kd) for PFAS sorption in these materials are crucial in the screening of candidate materials for environmental remediation. In this study, sorption kinetics, sorption isotherms, and the effects of pH, calcium concentration and dissolved organic carbon (DOC) content on PFAS sorption were evaluated in four representative carbon-rich materials: two biochars with contrasting properties, a compost, and charcoal fines rejected by the metallurgical industry. Subsequently, the sorption of seven PFAS with numbers of fluorinated carbons ranging from 4 to 11 was evaluated in a total of ten carbon-rich materials, including activated carbons, so as to build up a Kd prediction model. The sorption of PFAS increased with greater fluorinated chain length, suggesting that hydrophobic interactions play a major role in sorption and electrostatic interactions a minor one. These results were confirmed by a principal component analysis, which revealed that the CORG/O molar ratio and the specific surface area of the material were the two main sorbent properties affecting PFAS sorption. Furthermore, the DOC content in solution had a negative effect on PFAS sorption. Using this information, a simple Kd prediction model applicable to a wide range of materials and PFAS was developed, using only a few easily-derived physicochemical properties of sorbent (CORG/O molar ratio and SSA) and PFAS (number of CF2), and was externally validated with data gathered from the literature.

Biochar is an adsorbent widely used to remove contaminants from polluted water. A series of biochar from corn straw, corncob and corn starch was prepared through one-step pyrolysis. The biochar was characterized, and the capacity for triazine pesticide (TRZ) removal from water was compared. P doped biochar from corn straw (CSWP) was able to remove six TRZs (>96%) from water after shaking five times. The removal was more rapid than that by four other commonly used adsorbents. The physicochemical properties of CSWP were characterized systematically, and carboxyl and metaphosphates on CSWP were found to provide adsorption sites. The experimental data were best fitted by a pseudo-second-order kinetic model and the Freundlich model. Adsorption equilibrium of atrazine on CSWP occurred within 20 min, and the maximum adsorption capacity reached up to 79.6 mg g−1 at 25 °C. The adsorption mechanism of CSWP for atrazine includes Van der Waals' forces, hydrogen bonding, electrostatic interactions and pore filling. CSWP can be reused at least five times and shows strong potential as a candidate for the rapid and efficient removal of TRZs.

Rice (Oryza sativa L.) was cultivated in a Cd-contaminated soils with rice straw biochar (BC) and water-washed rice straw biochar (W-BC) were applied to investigate the underlying mechanisms and possible reasons for biochar's weakening effects on the immobilization of Cd in soil-rice system. The results indicated that W-BC reduced the Cd concentration in pore water as well as in the roots and shoots of rice by 26.24%, 53.23% and 62.47% respectively. On the contrary, there was an increase in Cd contents by 50.27% in pore water, 2.32% in the roots, and 12.80% in the shoots of rice under BC treatment. Furthermore, Cd content in rice shoot was significantly and positively correlated with Cl− addition to the soil (P

Biochar (BC) is as an emerging and promising adsorbent for the removal of pollutants from aqueous solutions in water treatment given its porous structure, large surface area, and numerous O-functional groups. However, the effects of BC on the formation of disinfection byproducts (DBPs) during the disinfection process of water treatment remains largely unknown. This study investigated the influence of aqueous solution chemistry on DBP formation in the presence of BC during chlorination. BC samples prepared from different biomass precursors (wheat straw, peanut shells, and shaddock peel) with different pyrolysis temperatures were compared, and the effects of aqueous solution chemistry were systematically investigated. Results indicated that DBPs could be formed during disinfection with BC. Certain intermediate DBP products would undergo base catalysis to form trichloromethane (TCM) via hydrolysis as pH increased. This phenomenon would increase TCM content, as well as decrease chloral hydrate and 1,1-dichloro-2-propanone content. The increment in inorganic ion (NaCl) content showed negligible effects on DBP formation during BC chlorination. DBP formation was restrained in the presence of humic acid (HA) because the number of active sites on BC that participated in the reaction decreased when BC adsorbed HA.

The elucidation of interactions between the dissolved black carbon (DBC) in biochar and hydrophobic organic contaminants (HOCs) is crucial for controlling the environmental behavior of HOCs. The complicated chemical structures of DBCs result in diverse interaction mechanisms between DBCs and HOCs, which were driven by different chemical structures in DBCs. In the present study, ten DBCs were extracted from rice straw and corncob biochars and their chemical structures were characterized and analyzed. The binding of phenanthrene (Phen) with DBC were studied through fluorescence quenching experiments. DBCs with low concentration (1 mg C/L) were found to complex with high amounts of Phen per unit mass. No significant difference was found in the amount of the bound Phen per unit amount of DBC when the concentration of DBC increased beyond >5 mg C/L. The dominant mechanisms involved in the binding of Phen by DBCs are speculated to be hydrophobic interactions, π–π electron donor–acceptor (EDA), and chemical partition, which was driven by the fatty carbon chain, aromatic rings, and quinone groups or ester groups, respectively. This study elucidates the interactions between DBC and Phen, which is of great significance for understanding the environmental behavior of HOCs.

A novel chitosan-modified kiwi branch biochar (CHKB) was successfully fabricated as cut-price modified biochar to remove Cd (II) from wastewater. Characterization experiments with SEM-EDS, FTIR and XPS suggested that CHKB had more cations and surface functional groups compared with the original kiwi biochar (KB). The adsorption experiment results of Cd (II) on CHKB showed that the adsorption isotherms can be described best by the Langmuir model and that the pseudo-second-order model fits the Cd (II) adsorption kinetics well, indicating that the process was monolayer and controlled by chemisorption. CHKB exhibited the Langmuir maximum adsorption capacity of Cd (II) (126.58 mg g-1), however, that of KB is only 4.26 mg g-1. The adsorption ability of CHKB was improved by the increase of the surface area and abundant surface functional groups (-OH, -NH, C=O and so on). And the cation exchange, electrostatic interaction, surface complexation and precipitation were main mechanisms in the sorption of Cd (II) on CHKB. In addition, CHKB can be regenerated and reused for Cd (II) sorption by the eluent of EDTA-2Na. Excellent adsorption performance, low-cost, and environmental-friendly made CHKB become the fantastic adsorbent to remove Cd (II) in wastewater.

The demand for ultrapure water (UPW) in the semiconductor industry has increased in recent years, while the idea to use reclaimed water instead of tap water for UPW production has also attracted more attention. However, since urea concentration in reclaimed water is higher than that in tap water, UPW production has not been efficient. To resolve this problem, this study aims to develop a new spent coffee grounds based biochar (SCG-BC)/persulfate catalytic system as a pretreatment unit. The objective is to enhance urea removal from reclaimed water so that UPW production is more effective. In this study, the biochar used was prepared from spent coffee grounds with detailed characterization. Results strongly suggested that the urea removed by SCG-BC/persulfate catalytic system was very encouraging (up to 73%). The best possible dosages for SCG-BC and persulfate for urea removal were 0.2 and 2.0 g L−1, respectively. Furthermore, this system could remove urea effectively in a wide range of pH (3–10). Moreover, the characterizations of SCG-BC (graphite C, defective edges and functional groups, i.e. –OH, C O, carboxyl C–O) helped to activate persulfate in the catalytic process. OH• and SO4• − were all involved in this process, while the SO4• − was the main radical for urea degradation.

Microbe induced iron (Fe) reduction play an important role in arsenic (As) transformation and the related secondary mineral formation. Meanwhile biochar could react as electron transfer shuttle for this process. Impact of biochar and model electron transfer shuttle anthraquinone-2,6-disulfonate (AQDS) on the chemical/biological iron reduction of As (Ⅲ)-adsorbed ferrihydrite and the solid-liquid redistribution of As in M1 buffer were studied. Fe reduction results in the release of As adsorbed on ferrihydrite into the solution. Under abiogenic conditions, both biochar and AQDS promoted ferrous production, the chemical oxidation of As(III) and As release. Inoculate with Shewanella oneidensis MR-1, AQDS has greater electronic shuttle function than biochar (with the maximum Fe (Ⅱ) contents: 154 mg/L > 76.6 mg/L respectively). However, only 12.8 mg/L As was released in the presence of AQDS, which was much lower than that in the presence of biochar (21.6 mg/L), and may be associated with the transformation of As speciation and the formation of secondary minerals. XRD and EDX-SEM confirmed that the As could be fixed by the generated secondary mineral vivianite. The relative contents of vivianite in biological control and AQDS addition were 2.7% and 18.4%, respectively. This study provides information on the transformation and migration of As and Fe with the addition of biochar under anaerobic conditions, which is potential to understand the mechanism of As(III)-contaminated soil remediation.

Considering the adverse effects of heavy metals (HMs) on agriculture soil, in-situ immobilization has been paid great attention worldwide. P-modified biochar/hydrochar along with synthetic zeolite for efficient HMs immobilization in contaminated soil becomes a promising choice. In this study, H3PO4-modified hydrochar (BPH) derived from banana peels, and Na-X zeolite (ZL) prepared from coal gangue was applied individually and synergistically (1%BPH, 2%BPH 1%ZL, 2%ZL, and 1%BPH+1%ZL) to remediate a farmland soil polluted by Cd, Cu, and Pb near the coal-mining area. Compared with the mono-application of these two amendments, their combination significantly improved the soil organic carbon (SOC), electric conductivity (EC), and dehydrogenase activity. Besides, the addition of 1%CLH+1%ZL remarkably reduced the Cd, Cu, and Pb bioavailability by 67.01%, 57.01%, and 78.72%, respectively, in the soil after 100 d incubation by transforming these metals to more stable forms. The order of the HMs immobilization capacity for these two amendments was as follows: Pb > Cu > Cd. Moreover, the dominated immobilization mechanism of their synergistic application was that BPH could immobilize HMs by precipitation, complexation, and π−π electron-donor-acceptor interaction. The precipitation and complexation blocked the surface pores of BPH. The sustained release of phosphorus groups and radicals was prevented. This obstacle was possibly alleviated by adding ZL. Besides, the formation of cationic bridging, the enhancement of soil properties, and the physical adsorption of these amendments were also conducive to HMs immobilization in soil. This work indicated that co-application of BPH and ZL possibly was an excellent choice for immobilizing HMs in soil.

A novel biochar electrode Bio-Fe3O4/CF used for electroreduction of nitrate was prepared by the hydrothermal synthesis method. The results showed that the growth of spherical Fe3O4 on the surface of smooth biochar can significantly increase the nitrate reduction rate. Besides, the presence of Cl and Br in the solution could promote the conversion of NH4+ to N2, thereby regulating the element nitrogen in the solution. Mechanistic analysis showed that the interconversion of Fe (II) and Fe (III) facilitates the transfer of electrons to nitrate. This study not only provides a biochar electrode material for the efficient removal of nitrate but also simply reveals regulation of halogen in solution, which provides a particular theoretical and data basis for nitrate removal.

The threat posed by the degradation of the soil environment by metal (-oid)s has been lead to the improvement of existing or search for new remediation methods; in this case, the application of environmentally friendly nanomaterials falls into this trend. The study applied a technique of aided phytostabilization for the immobilization of metal (-oid)s in soil with the application of nanosized halloysite and biochar (nBH), along with Lolium perenne L. Its effectiveness was assessed in terms of changing temperature conditions (16 cycles of freeze and thaw cycles, (FTC)) on the content of As, Cu, Pb and Zn in the soil, roots, and above-ground parts of the tested plant, chemical fraction distributions of metal (-oid)s and their stability (based on reduced partition index, Ir). The biomass yield in nBH-amended soil was 2-fold higher compared to control soil, but it decreased by 1.6-fold after FTC. nBH facilitated more bioaccumulation of As, Pb and Zn than Cu in plant roots, before than after FTC. nBH increased pH in phytostabilized soil, but it was not affected by changing FTC. In soil nBH-phytostabilized total concentration of metal (-oid)s significantly decreased compared to control soil, for As and Cu below permissible value, regardless of FTC. Soil amendment and changing temperature conditions affected metal (-oid)s redistribution in soil. As a result, the stability of As increased from 0.50 to 0.66, Cu from 0.49 to 0.52, Pb from 0.36 to 0.48 and Zn from 0.39 to 0.47. These findings suggest that nBH can immobilize metal (-oid)s in phytostabilized soil under changing temperature conditions.

In this study, biochar derived from spent coffee grounds (SCGB) was used to adsorb norfloxacin (NOR) in water. The biochar properties were interpreted by analysis of the specific surface area, morphology, structure, thermal stability, and functional groups. The impacts of pH, NOR, and ion's present on SCGB performance were examined. The NOR adsorption mode of SCGB is best suited to the Langmuir model (R2 = 0.974) with maximum absorption capacity (69.8 mg g−1). By using a Response Surface Method (RSM), optimal adsorption was also found at pH of 6.26, NOR of 24.69 mg L−1, and SCGB of 1.32 g L−1. Compared with biochars derived from agriculture such as corn stalks, willow branches, potato stem, reed stalks, cauliflower roots, wheat straw, the NOR adsorption capacity of SCGB was 2–30 times higher, but less than 3–4 times for biochars made from Salix mongolica, luffa sponge and polydopamine microspheres. These findings reveal that spent coffee grounds biochar could effectively remove NOR from aqueous solutions. Approaching biochar derived from coffee grounds would be a promising eco-friendly solution because it utilizes solid waste, saves costs, and creates adsorbents to deal with emerging pollutants like antibiotics.

Nanoscale zero-valent iron (nZVI) has been extensively used to remove various pollutants. However, the rapid deactivation due to aggregation and surface passivation severely limits its practical application. In this study, a novel composite with nZVI supported by pinecone biochar (nZVI-PBC) was successfully synthesized and used for the removal of high concentration Cr(VI) from aqueous solution in the presence of Shewanella oneidensis MR-1 (MR-1). The results showed that the nZVI-PBC coupling with MR-1 (nZVI-PBC/MR-1) exhibited an excellent removal performance for high concentration Cr(VI) compared to the nZVI-PBC alone. Under optimal conditions, 100 mg/L Cr(VI) could be removed completely by nZVI-PBC/MR-1 within 48 h, while only 39.50% of Cr(VI) was removed by nZVI-PBC alone. The improvement of Cr(VI) removal is due to the dissolution of the surface passivation layer of nZVI-PBC, formation of sorbed Fe(II) in the presence of MR-1, and an important role of extracellular polymeric substance (EPS) derived from MR-1. X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near-edge structure spectra (XANES) confirmed that most Cr(VI) was reduced to insoluble Cr(III) and formed Cr2O3, CrxFe1-x(OH)3 and FeCr2O4 precipitates, and a small amount of unreduced Cr(VI) was immobilized through adsorption and complexation. The results suggest that nZVI-PBC/MR-1 can effectively overcome the limitations of nZVI and achieve highly efficient removal of high concentration Cr(VI).

The iron (Fe) cycle in the rice-soil system affects arsenic (As) uptake by rice. The effect of Fe on As uptake can be influenced by the addition of biochar, but has not been thoroughly investigated. In this study, the effects of maize straw-derived biochar (MB) on Fe and As translocation were determined by analysing the Fe and As concentrations in pore water, dithionite-citrate-bicarbonate (DCB) extracts, and rice plants. As-contaminated soils were supplemented with 0 or 1% biochar and 0 or 90 mg kg−1 P, and rice plants were grown for 70 d. Results indicated that biochar addition increased the concentrations of Fe and As in pore water, while P did not affect them. Additionally, biochar promoted the accumulation of Fe and As in roots. However, the rice biomass increased by 28% upon biochar addition, indicating that the rice plants became more tolerant to As toxicity with biochar. Specifically, biochar increased the root triphenyl tetrazolium chloride (TTC) reductive intensity, reduced the root H2O2 concentration, and promoted iron plaque (IP) formation. Moreover, the positive correlation between IP/DCB-extractable As and crystalline Fe on the rice root surface indicated that crystalline Fe appeared to be the determinant species of IP and played a central role in As segregation. In addition, biochar increased both crystalline Fe formation on the root surface and the Fe content in the cell wall, which enhanced As sequestration. Overall, rice could effectively tolerate As stress under biochar treatment since As could be retained on the root surface and root cell wall with MB.

Agrowaste biochars [sugarcane straw (SS), rice husk (RH), poultry manure (PM), and sawdust (SW)] were synthesized at different pyrolysis temperatures (350, 450, 550, and 650 °C) to evaluate their potential to retain highly mobile herbicides, such as hexazinone and tebuthiuron that often contaminate water resources around sugarcane plantations. A new low field nuclear magnetic resonance approach based on decay due to diffusion in internal magnetic field (NMR-DDIF) was successfully used to determine biochar's porosity and specific surface area (SSA) to clear the findings of this work. SSA of pores with diameters >5.0 μm increased with pyrolysis temperatures and seemed to dictate biochar's retention, which was >70% of the applied amounts at 650 °C. These macropores appear to act as main arteries for herbicide intra-particle diffusion into smaller pores, thus enhancing herbicides retention. Biochar granulometry had little, but herbicide aging had a significant effect on sorption, mainly of tebuthiuron. However, soils amended with 10,000 kg ha−1 of the biochars showed low sorption potential. Therefore, higher than usual biochar rates or proper incorporation strategies, i.e., surface incorporation, will be needed to remediate areas contaminated with these highly mobile herbicides, thus precluding their leaching to groundwaters.

Heavy metal contamination in water bodies is currently in an area of greater concern due to the adverse effects on human health. Despite the good adsorption performance of biochar, various modifications have been performed on the pristine biochar to further enhance its adsorption capability, at the same time overcome the difficulty of particles separation and mitigate the secondary pollution issues. In this review, the feasibility of chitosan-modified magnetic biochar for heavy metal removal from aqueous solution is evaluated by critically analysing existing research. The effective strategies that applied to introduce chitosan and magnetic substances into the biochar matrix are systematically reviewed. The physicochemical changes of the modified-biochar composite are expounded in terms of surface morphology, pore properties, specific surface area, surface functional groups and electromagnetism. The detailed information regarding the adsorption performances of various modified biochar towards different heavy metals and their respective underlying mechanisms are studied in-depth. The current review also analyses the kinetic and isotherm models that dominated the adsorption process and summarizes the common models that fitted well to most of the experimental adsorption data. Moreover, the operating parameters that affect the adsorption process which include solution pH, temperature, initial metal concentration, adsorbent dosage, contact time and the effect of interfering ions are explored. This review also outlines the stability of modified biochar and their regeneration rate after cycles of heavy metal removal process. Lastly, constructive suggestions on the future trends and directions are provided for better research and development of chitosan-modified magnetic biochar.

The United Nations estimates the rate of deforestation over 10 million hectares per year, with additional infested wood available due to drought, bark beetle calamity and other damage vectors. Processing the hard-to-reach infested wood into biochar via mobile pyrolysis units seems to be a good option for fire prevention. However, since most biochar is currently produced mainly from biological waste, there is not enough experience with wood biochar on a large scale. Review of current knowledge, followed by techno-economic assessment reveals that following the chemical composition of the feedstock, wood biochar outperforms other types of biochar in terms of high porosity. Therefore, wood biochar shows excellent results in increasing the amount of plant-available water content in soil and appears to be an excellent tool for recycling nutrients (especially into plant-available forms of phosphorus and nitrogen). The overall positive effects of biochar application change from abiotic to biotic over time because as it decays, many of its physical properties disappear, but it can boost soil microbial communities on which soil fertility depends. As global climate change creates a wide range of factors that damage forest cover, wood biochar consequently represents untapped potential in the field of soil, nutrient, and energy management.

Herein, the major biochar properties were correlated with electron transfer of zerovalent iron (ZVI) and contribution of biomass constituents to biochar property was ascertained to optimize electron transfer of ZVI. To this end, five respective stalk-type and wood-type lignocellulosic biomasses were pyrolzed at 600 °C to prepare biochars to harbor ZVI (ZVI/BC). Thermogravimetric analysis demonstrated woody biomasses decomposed more intensively at higher temperature relative to stalky biomass. ZVI/BC were characterized with Raman, X-ray diffraction, and electrochemical analyses including electron donating capacity (EDC) and electron accepting capacity (EAC). Pearson correlation and partial least-squares (PLS) analyses confirmed that Cr(VI) reduction capacity was negatively related to Tafel corrosion potential and intensity ratio of ID/IG, but significantly positively-related to EDC of BC, in which EDC was a predominant attribute to contribute to reductive capacity toward Cr(VI) reduction. That is, greater EDC and higher graphitic carbon structure of biochar due to cellulose and hemicellulose components favor electron transfer of ZVI toward Cr(VI) reduction.

Chromium (Cr) pollution in water has become an environmental and social problem because of the highly toxic nature of Cr(VI). Biochar has been widely used in Cr-containing wastewater treatment due to its adsorption advantage and intrinsic electron-donating ability. In this paper, Cr(VI) was taken as the target pollutant, and corn-straw derived biochar (BC) and its iron-modified counterpart (BC–Fe) were taken as the main adsorbents. The effects of fulvic acid (FA) and lactic acid (LA) on the adsorption efficiency of BC and BC-Fe in aqueous solution were discussed, and the internal reaction mechanism was revealed by SEM, FTIR, XPS, and Zeta potential analysis. The results showed that the BC-Fe pyrolyzed at 600 °C (i.e., BC-Fe600) had good magnetic property and adsorption effect across a wide pH range (pH 3–9) (the maximum removal efficiency was 96%). At the same time, LA had a concentration-dependent promoting effect on Cr(VI) adsorption in the BC600. However, the addition of FA and LA both inhibited the adsorption of Cr(VI) by BC-Fe600 at pH = 5 and 7, with LA showing a more inhibiting effect on Cr(VI) removal (decreased by 16.09% at pH 5) than FA (decreased by 2.09% at pH 5). The addition of FA and LA caused the surface potential of BC-Fe600 to drop, resulting in an increasing electrostatic repulsion between Cr(VI) and the material. However, LA increased the reduction of Cr(VI) on BC-Fe600, possibly through the combined effects of the electron-donating ability of LA and the photolysis of Fe(III)-lactate complexes.

The current study was dedicated to finding the effect of soil amendments (biochar and compost) on plants belonging to Poaceae and Fabaceae families. Plants selected for the phytoremediation experiment included wheat (Triticum aestivum), maize (Zea mays), white clover (Trifolium repens), alfalfa (Medicago sativa), and ryegrass (Lolium multiflorum). The physiological and microbial parameters of plants and soil were affected negatively by the 4 % TPHs soil contamination. The studied physiological parameters were fresh and dried biomass, root and shoot length, and chlorophyll content. Microbial parameters included root and shoot endophytic count. Soil parameters included rhizospheric CFUs and residual TPHs. Biochar with wheat, maize, and ryegrass (Fabaceae family) and compost with white clover and alfalfa (Poaceae family) improved plant growth parameters and showed better phytoremediation of TPHs. Among different plants, the highest TPH removal (68.5 %) was demonstrated by ryegrass with compost, followed by white clover with biochar (68 %). Without any soil amendment, ryegrass and alfalfa showed 59.55 and 35.21 % degradation of TPHs, respectively. Biochar and compost alone removed 27.24 % and 6.01 % TPHs, respectively. The interactive effect of soil amendment and plant type was also noted for studied parameters and TPHs degradation.

Constructed wetland is considered a promising approach for water remediation due to its high efficiency, low operation costs, and ecological benefits, but the large amounts of wetland plant biomass need to be properly harvested and utilized. Recently, wetland plant derived biochar has drawn extensive attention owing to its application potential. This paper provides an updated review on the production and characteristics of wetland plant derived biochar, and its utilization in soil improvement, carbon sequestration, environmental remediation, and energy production. In comparison to hydrothermal carbonization and gasification, pyrolysis is a more common technique to convert wetland plant to biochar. Characteristics of wetland plant biochars varied with plant species, growth environment of plant, and preparation conditions. Wetland plant biochar could be a qualified soil amendment owing to its abundant nutrients. Notably, wetland plant biochar exhibited considerable sorption capacity for various inorganic and organic contaminants. However, the potentially toxic substances (e.g. heavy metal and polycyclic aromatic hydrocarbons) retained in wetland plant biochar should be noticed before large-scale application. To overcome the drawbacks from the scattered distribution, limited productivity, and seasonal operation of constructed wetlands, the economic feasibility of wetland plant biochar production system could be improved via using mobile pyrolysis unit, utilizing local waste heat, and exploiting all the byproducts. Future challenges in the production and application of wetland plant derived biochar include the continuous supply of feedstock and proper handling of potentially hazardous components in the biochar.

Biochars were produced from pine feedstock pretreated with aqueous base, NaOH, at pH 9 and 11, and alkali and alkaline earth metals (AAEMs) Na, K, Ca, and Mg at 10−3 and 1 M. The effects of base and AAEM feedstock pretreatment on biochar surface area, pore size distribution, and adsorption capacity of two organic micropollutants (OMPs), 2,4-dichlorophenoxyacetic acid and sulfamethoxazole, from surface water with background dissolved organic matter (DOM) were evaluated. Base pretreatment significantly increased surface area within micropores ( 2 nm in diameter. The catalytic activity of AAEMs, assessed by generation of non-micropore surface area, decreased in the following order: Ca > K > Na > Mg. All pretreated biochars outperformed untreated biochar for OMP adsorption. Biochar pretreated by aqueous base at pH 11 showed over an order of magnitude increase in OMP adsorption, nearly matching the performance of commercial activated carbon. OMP adsorption from surface water was positively correlated with biochar micropore surface area and negatively correlated with non-micropore surface area, which was linked to higher levels of DOM competition. Base and AAEM pretreatment of biochar feedstocks can increase OMP adsorption for water treatment applications by tuning pore structure and surface area.

Soil quality management through effective utilization of agricultural residue is the cynosure of intense global research. Therefore, we have explored the pyrolytic conversion of a locally available agricultural residue, the areca nut husk (AH), into biochar (BC) as a sustainable option towards residue management. The AH was carbonized at 250–400 °C, and residence times of 30–90 min. Subsequent detailed analysis revealed areca nut husk biochar (AHBC) formed at 250 °C with 60 min residence time, had the highest soil organic matter yield index (SOMYI), the lowest H/C and O/C ratio, and an average particle size of 1191.6 nm. Further characterization exposed the highly porous structure of prepared AHBC with oxygenated functional groups attached to its surface. The application of AHBC in conjunction with vetiver (Chrysopogon zizanioides L.) was used as a novel agrotechnological approach to assess soil quality improvement. Various doses of AHBC (5 t ha−1, 10 t ha−1, and 15 t ha−1) were applied in the experimental soils, and the principal component analysis (PCA) revealed that the 15 t ha−1 dose was optimum for the growth of the vetiver. AHBC amendment in soil resulted in increase of plant height and relative water content. This could be attributed to the increase in organic carbon, cation exchange capacity, and nutrients in the soil. Application of AHBC along with vetiver could be a simple, yet effective option, for sustainable agricultural residue and soil management.

The discharge of effluents from the textile industry is a multidimensional problem that affects the ecosystem in many ways. Though many new technologies are being developed, it remains to be seen which of those can be practiced in a real scenario. The current investigation attempts to absorb the Malachite Green, an effluent from textile dye using Chinese Fan Palm Seed Biochar. Accordingly, biochar was prepared using fruits of Chinese Fan Palm (Livistona chinensis) tree. The fruit also yielded a significant amount of biochar and bio-oil. 1.346 kg of fresh and cleaned fruit was fast pyrolyzed at 500 °C in a laboratory-scale Pyrolyzer resulting in 0.487 kg of biochar and 0.803 L of bio-oil. The remaining fruit matter was converted to gaseous products. The kinetics of dye removal were studied and the parameters were determined. The study advocates that the Langmuir isotherm model simulates the adsorption experiment, to a good extent. From the plot, the maximum (monolayer) adsorption capacity, Qm was determined to be 21.4 mg/g. The suitability of the Langmuir isotherm model onto biochar was established by the high correlation coefficient, R2 that was higher than 0.97.

Chemical degradation is one of the crucial methods for the remediation of hydrophobic organic compounds (HOCs) in soil/sediment. The sequestration effect of black carbon (BC) can affect the adsorption state of HOCs, thereby affecting their chemical degradability. Our study focused on the chemical degradability of 2-Chlorobiphenyl (PCB1) sequestrated on the typical BC (fly ash (FC), soot (SC), low-temperature biochar (BC400) and high-temperature biochar (BC900)) by iron-nickel bimetallic nanomaterials (nZVI/Ni) based on TENAX desorption technology. The results showed that PCB1 adsorbed in various states were simultaneously dechlorinated by nZVI/Ni. Specifically, rapid-desorption-state PCB1 tended to degrade more easily than resistant-desorption-state PCB1. Moreover, the degradation mechanism varied according to the type of BC. In the case of FC and SC, the degradation rate was lower than the desorption rate for the PCB1 in rapid and slow desorption states, and the degradation rate of PCB1 in the resistant desorption state was negligible. The PCB1 on FC and SC was first desorbed from BC and then degraded. However, in terms of BC400 and BC900, the degradation rate was higher than the desorption rate, and the degradation rate of the resistant-desorption-state PCB1 was 1.4 × 10−2 h−1 and 4.1 × 10−2 h−1, respectively. The graphitized structure of BC900 can directly transfer electrons, so more than 90% of the resistant-desorption-state PCB1 could be degraded. In addition, BC may affect the longevity of nZVI/Ni, thereby affecting its degradability. Therefore, the chemical degradability of BC-adsorbed HOCs should be comprehensively evaluated based on the adsorption state and the properties of BC.

Hydrogen sulfide (H2S) can influence methanotrophic activities and be adsorbed by biochar (BC); however, the impact of H2S on BC in stimulating the methane (CH4) oxidation capacity of landfill cover soil (LCS) has not been clarified. Thus, batch incubation experiments were conducted to observe the effect of H2S on the CH4 oxidation capacity of and microbial communities in BC-amended LCS. Three landfill gas conditions were considered: 5 % CH4 and 15 % oxygen (O2) (5 M), 10 % CH4 and 10 % O2, and 20 % CH4 and 5 % O2 (20 M) by volume, with H2S concentrations of 0, 100, 250, and 1000 ppm, respectively. Another series was conducted using LCS subjected to pre-H2S saturation under the 20 M gas condition. In the 5 M gas condition suitable for the dominant methanotroph Methylocaldum (type I), the BC retained its ability to stimulate the CH4 oxidation capacity of LCS (enhancement of 41–108 %) in the presence of H2S. Additionally, when H2S ≤ 250 ppm, the BC exhibited a relatively consistent impact of H2S on both CH4 oxidation capacity and microbial communities in LCS, independent of the CH4 or O2 concentrations. This result could be attributed to the different pathways of H2S metabolism for the LCS and BC-amended LCS. Furthermore, when saturated adsorption of H2S occurred for the LCS, the CH4 oxidation capacity for BC-amended LCS was higher than that for non-amended LCS, which demonstrated the ability of BC in alleviating the inhibition of H2S on CH4 oxidation due to its excellent H2S adsorption under even anoxic environments.

The widespread use of per- and polyfluoroalkyl substances (PFASs)-related products such as aqueous film-forming foams (AFFF) has led to increasing contamination of groundwater systems. The concentration of PFASs in AFFF-impacted groundwater can be several orders of magnitude higher than the drinking water standard. There is a need for a sustainable and effective sorbent to remove PFASs from groundwater. This work aims to investigate the sorption of PFASs in groundwater by biochar column. The specific objectives are to understand the influences of PFASs properties and groundwater chemistry to PFASs sorption by biochar. The PFASs-spiked Milli-Q water (including 19 PFASs) and four aqueous film-forming foams (AFFF)-impacted groundwater were used. The partitioning coefficients (log Kd) of long chain PFASs ranged from 0.77 to 4.63 while for short chain PFASs they remained below 0.68. For long chain PFASs (C ≥ 7), log Kd increased by 0.5 and 0.8 for each CF2 moiety of PFCAs and PFSAs, respectively. Dissolved organic matter (DOM) was the most influential factor in PFASs sorption over pH, salinity, and specific ultraviolet absorbance (SUVA). DOM contained hydrophobic compounds and metal ions which can form DOM-PFASs complexes to provide more sorption sites for PFASs. The finding is useful for executing PFASs remediation by biochar filtration column, especially legacy long chain PFASs, for groundwater remediation.

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

The present investigation deals with removal of lead (Pb+2) ions from waste water using biosorbent prepared from seeds of Artocarpus heterophyllus (SBAh) and Syzygium cumini (SBSc). Biosorbents surface has been characterized through FT-IR spectroscopy to probe the presence of functional groups. Response surface methodology enabled optimized conditions (Pb+2 concentration 2 μg/mL, pH 5.8 and bioadsorbent dose 60 mg) resulted in Pb+2 removal ~96% for SBAh and ~93% for SBSc at agitation speed 300 rpm. The adsorption capacity has been found to be 4.93 mg/g for SBAh and 3.95 mg/g for SBSc after 70 min. At optimal experimental conditions, kinetics of biosorption was explained well by inter-particle diffusion model for SBAh (R2 = 0.99) whereas Elovich model best fitted for SBSc (R2 = 0.98). Further, both the biosorbents followed Temkin adsorption isotherm model.

With rising concerns in the practical application of biochar for the remediation of environment influenced by various organic contaminants, a critical review to facilitate insights the crucial role that biochar has played in wastewater and polluted soil decontamination is urgently needed. This research therefore aimed to describe different intriguing dimensions of biochar interactions with organic contaminants, which including: (i) an introduction of biochar preparation and the related physicochemical properties, (ii) an overview of mechanisms and factors controlling the adsorption of organic contaminants onto biochar, and (iii) a summary of the challenges and an outlook of the further research needs in this issue. In the light of the survey consequences, the appearance of biochar indicates the potential in substituting the existing costly adsorbents, and it has been proved that biochar is one promising adsorbent for organic pollutants adsorption removal from water and soil. However, some research gaps, such as dynamic adsorption, potential environmental risks, interactions between biochar and soil microbes, novel modification techniques, need to be further investigated to facilitate its practical application. This research will be conductive to better understanding the adsorption removal of organic contaminants by biochar.

Soils functions, fertility, and microbial abundance may alter in various ways by the biochar amendments to the soil. This study revealed the way of pyrolysis temperature influences the biochar quality and its addition for improving soil properties. The SS biochar was synthesized via pyrolysis and characterized by SEM and FTIR for studying surface images and chemical functional groups. The biochar upon addition with soil was studied for physiological parameters of plants like seed germination index, root length, shoot length, biomass, metal (loid) analysis of soil, SS and SS biochar, total organic content, C: N ratio, NPK values, etc. Besides, combinations of biochar: soil {1:3 (25% + 75%), 1:1 (50% + 50%), and 3:1 (75% + 25%)} ratios were used for studying the effect of biochar on soil microbial community. The 16S rRNA metagenomic analysis revealed the dominance of phyla: Proteobacteria, Actinobacteria, and Acidobacteria that influence the soil nutrient cycle when applied at ratio 1:3. This study highlights the valorization of SS into biochar and studied the effect of biochar augmentation with soil; its impact on soil nutrients, microbial abundance, and plant biomass enhancement. The greener approach also mitigates and helps in the sustainable management of solid wastes, thus reducing GHGs emissions and improves nutrient cycling.

Pyrolysis of agricultural biomass is a promising technique for producing renewable energy and effectively managing solid waste. In this study, groundnut shell (GNS) was processed at 500 °C in an inert gas atmosphere with a gas flow rate and a heating rate of 10 mL/min and 10 °C/min, respectively, in a custom-designed fluidized bed pyrolytic-reactor. Under optimal operating conditions, the GNS-derived pyrolytic-oil yield was 62.8 wt.%, with the corresponding biochar (19.5 wt.%) and biogas yields (17.7 wt.%). The GC-MS analysis of the GNS-based bio-oil confirmed the presence of (trifluoromethyl)pyridin-2-amine (18.814%), 2-Fluoroformyl-3,3,4,4-tetrafluoro-1,2-oxazetidine (16.23%), 5,7-dimethyl-1H-Indazole (11.613%), N-methyl-N-nitropropan-2-amine (6.5%) and butyl piperidino sulfone (5.668%) as major components, which are used as building blocks in the biofuel, pharmaceutical, and food industries. Furthermore, a 2 × 5 × 1 artificial neural network (ANN) architecture was developed to predict the decomposition behavior of GNS at heating rates of 5, 10, and 20 °C/min, while the thermodynamic and kinetic parameters were estimated using a non-isothermal model-free method. The Popescu method predicted activation energy (Ea) of GNS biomass ranging from 111 kJ/mol to 260 kJ/mol, with changes in enthalpy (ΔH), Gibbs-free energy (ΔG), and entropy (ΔS) ranging from 106 to 254 kJ/mol, 162–241 kJ/mol, and −0.0937 to 0.0598 kJ/mol/K, respectively. The extraction of high-quality precursors from GNS pyrolysis was demonstrated in this study, as well as the usefulness of the ANN technique for thermogravimetric analysis of biomass.

In this study, a novel biochar-supported zero-valent iron (ZVI) composite was synthesised by a one-pot co-pyrolysis reduction method, and was used to remove Cu(II) and Cr(VI). The raw materials for the composite were derived from natural bagasse/straw and goethite. Scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry (TG), and Brunauer-Emmett-Teller (BET) analysis were used to characterise the biochar and biochar-supported ZVI composites. Batch removal experiments on the effects of the initial pH and citric acid concentrations were performed as well as kinetic studies and isotherm experiments. The composite materials showed better Cu(II) and Cr(VI) removal performance than single biochar and mineral. The removal of Cu(II) and Cr(VI) is pH-dependent, and proceeds via heterogeneous multilayer chemisorption. Electrochemical analysis revealed that straw biochar-supported ZVI composite exhibited greater electrical conductivity and electron transfer rate than pure biochar and ZVI. FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) elucidated the uptake mechanism, showing that Cu(II) and Cr(VI) were easily adsorbed onto the biochar surface and were then reduced by ZVI. These results indicate that biochar-supported ZVI composite is effective for heavy metal remediation, which is economical, environment-friendly, and suitable for mass production.

With the quick increase in industrialization and urbanization, a mass of sludge has been produced on the account of increased wastewater treatment facilities. Sewage sludge (SS) management has become one of the most crucial environmental problems because of the existence of various pollutants. However, SS is a carbon-rich material, which has favored novel technologies for biochar production, which can be utilized for dissimilar applications. This review systematically analyzes and summarizes the pretreatment, modification, and especially application of sewage sludge-derived biochar (SSBC), based on published literature. The comparative assessment of pretreatment technology such as pyrolysis, hydrothermal carbonization, combustion, deashing, and co-feeding is presented to appraise their appropriateness for SS resource availability and the production of SSBC. In addition, the authors summarize and analyze the current modification methods and divide them into two categories: physical properties and surface chemical modifications. The applications of SSBC as absorbent, catalyst and catalyst support, electrode materials, gas storage, soil amendment, and sold biofuel are reviewed in detail. Furthermore, the discussion about the existing problems and the direction of future efforts are presented at the end of each section to envisage SS as a promising opportunity for resources rather than a nuisance.

Urban soil pollution by heavy metals (HMs) is a pressing problem in the development of urban agriculture (UA). In this context, the use of amendments, such as biochar, and phytoremediation are considered potentially cost-effective alternatives to conventional methods, and can be also combined to improve the remediation of soils from HMs. A pot experiment was performed to investigate the combined effect of berseem clover (Trifolium alexandrinum, L.) and biochar amendment in remediating a sandy soil collected near a shooting range area co-contaminated with Cd, Cr, Cu, Ni, Pb, and Zn. The biochar, obtained from a wood-chip gasifier fed with a mix of Douglas (Pseudotsuga menziesii, Mirb.) and Black Pine (Pinus nigra, J.F.Arnold) wood, was applied at two rates (0.8% and 1.6%, w/w). Eighteen weeks after sowing, all plants were harvested. The roots and aboveground tissues of the crops were separately collected and analyzed. The tested biochar effectively adsorbed the HMs (Cd, Cr, Cu, Ni, Pb, and Zn) from the soil. Biochar increased DW production of aboveground and root tissues. Moreover, biochar significantly reduced the concentration of Cr, Cu, Ni, and Pb in the aboveground tissues of berseem clover, although a significant reduction was not detected for Cd and Zn. Results indicated that berseem clover was a Cr, Ni and Pb excluder. However, this species can be considered suitable for Cu phytoextraction and Cd and Zn phytostabilization of slightly polluted urban soil. Only the Cu levels in the aerial biomass were below the acceptable limit for use as fodder.

Herbicides are commonly used globally. However, residual herbicides in soils for ages often result in phytotoxicity and serious yield loss to subsequent crops. In this paper, the multi-walled carbon nanotubes (MWCNTs) were utilized to amend the herbicide polluted soil, and the adsorption performance of herbicides to MWCNTs amended soil was studied. Results indicate efficient alleviation of herbicide-induced phytotoxicity to rice and tobacco due to MWCNTs amendment. When 0.4% MWCNTs were applied, the concentration of sulfentrazone that inhibited the same rice height by 50% (IC50) increased to more than 3 times that of pure soil. When the MWCNTs were used to alleviate the phytotoxicity of quinclorac to tobacco, the MWCNTs not only alleviated the phytotoxicity of quinclorac but also promoted the growth of tobacco. The MWCNTs amended soil significantly increased the adsorption of herbicide to soil than biochar. The soil microbial analysis shows that MWCNTs had no significant effect on soil microbial community diversity, but the long-term exposure to MWCNTs could change the structure of the soil microbial community. Above all, our results highlighted the potential implication of the MWCNTs to ensure crop production by promoting crop growth and reducing the residual bioavailability of herbicides.

The sorption isotherms of polychlorinated biphenyls (PCBs) on carbons (coal based activated carbon named AC and hardwood derived biochar named BC) and natural organic matter (NOM) loaded carbons were examined and carbon-water partition coefficients (KC-W-PCB) were calculated. The purpose was to accurately predict the effectiveness of in-situ carbon treatments on the sediment impacted with hydrophobic organic chemicals (HOCs). For 1 month sorption, AC KC-W-PCB values were significantly higher than BC, corresponding to the much larger surface area (particularly in mesopores) for AC. BC KC-W-PCB values were correlated with PCB total surface area (TSA) and octanol-water partition coefficient (logKow). After loading with NOM, AC adsorption to PCBs strongly reduced and the fitted Freundlich exponents (n) decreased with increasing NOM level. However, NOM loading slightly impacted BC sorption and exhibited an opposite effect on BC n values. It is illustrated that the sorption mechanisms are different between AC and BC thereby the influences of NOM on sorption characteristics differ vastly. As the sorption time increased from 1 month to 6 months, an increase is observed in BC sorption extent but simultaneously NOM reduction effect on BC sorption increases, implying that more accurately evaluating BC application as an in-situ sorbent amendment for HOC impacted sediment need further investigation. On the contrary, AC adsorption attenuation caused by NOM coating greatly decreases over time, encouraging AC application as a sediment amendment.

Because of rapid development in the livestock industry, the production of chicken manure has subsequently increased, which may contribute to environmental pollution. In this regard, in-vessel composting of biochar amended chicken manure and sawdust mixtures was investigated to find out the effect of biochar at the ratios of 0% (control), 3% (T1), 5% (T2), and 10% (T3) on ammonia and greenhouse gases (GHGs) emission, compost quality, pathogenic contaminants and phytotoxicity. The composting process was performed in 100-L, pilot-scale, plastic, cylindrical vessels for 50 days. The addition of biochar (3%, 5%, and 10%) increased the thermophilic temperature with a significant reduction in gaseous emissions (ammonia and CO2), microbial pathogens (Escherichia coli and Salmonella sp.), and phytotoxicity (Lepidium sativum seed germination assay) compared with that of the control compost products. However, according to the obtained results with in-vessel composting, the amendment of 10% biochar showed the most significant effects concerning the quality of the compost nutrients. The study reveals that the addition of biochar during in-vessel chicken manure composting is beneficial in the reduction of gaseous emissions and pathogenic microorganisms apart from improvement in plant nutrients.

The extensive use of imidacloprid (IMI) has led to its being frequently detected in natural water, also caused the potential damage to the ecosystem. Development of efficient, green and sustainable technique is demanded to eliminate this problem. A novel biochar (KMCBC) derived from agriculture waste of corn cob was first time co-modified by potassium hydroxide (KOH), ferric chloride (FeCl3) and zinc chloride (ZnCl2), which showed the greater adsorption amount (410 mg g−1 at 298 K) for imidacloprid (IMI). Pseudo-second-order kinetic and Langmuir isotherm models fitted well with the experimental data, together with the physicochemical characterization analysis, demonstrating that the adsorption process of IMI by KMCBC might be mainly controlled by micropore filling, π-π electron donor-acceptor and functional groups interactions (H-bonding and complexation). Additionally, the thermodynamics parameters suggested that IMI adsorption in this study was a spontaneous, endothermic and randomly increasing process. Besides, KMCBC owned the easy separation performance and promising environmental safety, also exhibited a high selective adsorption capacity regardless of solution pH (its optimum adsorption performance for IMI was obtained at pH = 5), inorganic ions strength and humic acid (HA) concentrations. The regenerated KMCBC (synergistic ultrasound/ethanol) could sustainably and efficiently adsorb IMI in the reuse cycles. Therefore, this study provided an efficient, green and sustainable adsorbent of KMCBC for IMI removal.

Agro-Wastes are identified as to manufacture potential valuable organic biochar fertilizer product economically while also managing the waste. Biochar (BC) produced from agriculture waste is helps to improve the soil because of its neutral pH, addition of organic carbon to the soil and lower salt index values. This study focused on the development of nano-biochar into a more enhanced biochar product where it was checked whether the biochar derived from wheat straw can absorb nutrients and then act as support matter for releasing micro-nutrients and macro-nutrients for the plants on slow liberation basis. Wheat biochar (WBC) and wheat nano-biochar (WBNC) were synthesized by pyrolysis at two different temperatures and nutrients were fused into the WBC via impregnation technique. Physical parameters such as Proximate, Ultimate analysis & other were also studied and inspected by standard control procedures. Studies were also carried out on water retention (WR), water absorbance (WA), swelling ratio (SR) and equilibrium water content (EWC) for all samples; data was collected and compared for the better sample. Slow-release studies performed portrayed the release pattern of nutrients for prolonged periods, which are very important for the plant growth, yield and productivity. Overall, the experimental results displayed that BNC produced at 350 °C showed promising features of (SI:0.05, SR: 3.67, WA:64%, EWC:78.6%, FC:53.05% and pH:7.22), is a good substance however the nano-biochar has improved results; environmental friendly & could be utilized as a potential fertilizer on slow release for sustainable and green agriculture application.

Biochar prepared from various feedstock materials has been utilized in recent years as a potential stabilizing agent for heavy metals in smelter-contaminated soils. However, the effectiveness of animal bone-derived biochar and its potential for the stabilization of contaminants remains unclear. In the present study, sheep bone-derived biochar (SB) was prepared at low (500 °C; SBL) and high temperatures (800 °C; SBH) and amended a smelter-contaminated soil at 2, 5, and 10% (w/w). The effects of SB on soil properties, bioavailable Zn and Cd and their geochemical fractions, bacterial community composition and activity, and the response of plant attributes (pigments and antioxidant activity) were assessed. Results showed that the SBH added at 10% (SBH10) increased soil organic carbon, total nitrogen, and phosphorus, and also increased the oxidizable and residual Zn and Cd fractions at the expense of the bioavailable fractions. The SBH10 lowered the Zn and Cd contents in maize roots (by 57 and 60%) and shoot (by 42 and 61%), respectively, compared to unamended control. Additionally, SBH10 enhanced urease (98%) and phosphates (107%) activities, but reduced dehydrogenase (58%) and β-glucosidase (30%) activities. Regarding the effect of the pyrolysis temperature, SBH enhanced the activity of Acidobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Verrucomicrobia, Chlorobi, and Microgenomates, but reduced Actinobacteria and Parcubacteria in comparison to SBL. However, only the SBL10 reduced the Proteobacteria community (by 9%). In conclusion, SB immobilized Zn and Cd in smelter-affected soils, enhanced the bacterial abundance and microbial function (urease, phosphates), and improved plant growth. However, validation of the results, obtained from the pot experiment, under field conditions is suggested.

This article aims to discuss (1) the incorrect identification of Cr(III) and Cr(VI) binding energies in the Cr 2p XPS (X-ray photoelectron spectroscopy) spectra of the laden adsorbent (the nZVI-BC sample after Cr(VI) adsorption), (2) misconception regarding the Weber–Morris intraparticle diffusion model, and (3) inconsistency between the experiential data and the Thomas adsorption rate constants. The authors hope that our comments are beneficial for other researchers to avoid the undesirable mistakes.

Soil contamination in mining areas is an important environmental concern. In these areas, phytoremediation is often impeded because of the low fertility and pH. Assisted phytoremediation is increasingly being used in polluted areas. Biochar could assist plant growth via enhanced soil fertility. An experiment was performed in a mining soil (RIII) from the mining area of Riotinto (Spain) contaminated with Cu, Pb, Zn and As in order to study: (i) The effects of biochar on soil fertility; (ii) Biochar temperature of preparation effect and (iii) Effect of biochar on phytoremediation potential. A mesocosm experiment was designed using Brassica napus as test specie. Soil (RIII) was treated with rabbit manure biochars prepared at 450 °C (BM450) and 600 °C (BM600) at a rate of 10% in mass and incubated for 60 days with or without Brassica napus. Results showed that the combination of BM450 or BM600 with Brassica napus growth decreased the amount of As, Cu, Co, Cr, Se and Pb in the soil. Values of bioaccumulation factor (BAF) for Cd were particularly elevated (>10) in the unamended soil and reached values higher than 1 for other elements, indicating the potential of Brassica napus to accumulate several heavy metals. Translocation Factor (TF) was reduced for Co, Cr, Cd, Cu, Ni, Zn, Pb and As after biochar addition indicating root accumulation of these metals. In all cases, biochar addition increased biomass production. Finally, the addition of BM450 increased GMea index indicating also an improvement on soil quality.

Used baby diaper consists of a combination of decomposable cellulose, non-biodegradable plastic materials (e.g. polyolefins) and super-absorbent polymer materials, thus making it difficult to be sorted and separated for recycling. Microwave pyrolysis was examined for its potential as an approach to transform used baby diapers into value-added products. Influence of the key operating parameters comprising process temperature and microwave power were investigated. The pyrolysis showed a rapid heating process (up to 43 °C/min of heating rate) and quick reaction time (20–40 min) in valorizing the used diapers to generate pyrolysis products comprising up to 43 wt% production of liquid oil, 29 wt% gases and 28 wt% char product. Microwave power and operating temperature were observed to have impacts on the heating rate, process time, production and characteristics of the liquid oil and solid char. The liquid oil contained alkanes, alkenes and esters that can potentially be used as chemical additives, cosmetic products and fuel. The solid char contained high carbon, low nitrogen and free of sulphur, thus showing potential for use as adsorbents and soil additives. These observations demonstrate that microwave pyrolysis has great prospect in transforming used baby diaper into liquid oil and char products that can be utilised in several applications.

Wood-based biochar, as a metal-free heterogeneous activator of peroxydisulfate (PDS), was successfully prepared by pyrolysis of polar sawdust for efficient removal of Acid Orange 7 (AO7). The results demonstrate PDS could be effectively activated by wood-based biochar, and AO7 was rapidly eliminated in a wide range of pH value (3.0–10.0) with AO7 removal achieved ≥ 99.3% after 14 min reaction. The dominant reactive species in the biochar/PDS system were verified via radical quenching tests and electron paramagnetic resonance (EPR) technique. It is speculated that sulfate radicals (SO4•−) and hydroxyl radicals (•OH) were formed on the surface of biochar. Based on the results of X-ray photoelectron spectroscopy (XPS), π-electron density and oxygen-containing functional groups (especially C–OH) on biochar surface were active centers for the catalytic reaction. Recycle experiments of biochar for 4 runs were carried out and the regeneration method of the catalyst was also studied.