Ball milling as a mechanochemical technology for fabrication of novel biochar nanomaterials

Recent advancements in antimony (Sb) removal from water and wastewater by carbon-based materials: a systematic review

Antimony (Sb) has been classified as a high-priority contaminant in the environment. Sb contamination resulting from the use of antimony-containing compounds in industry necessitates the development of efficient methods to remove it from water and wastewater. Adsorption is a highly efficient and reliable method for pollutants removal owing to its availability, recyclability, and low cost. Recently, carbonaceous materials and their applications for the removal of Sb from the aqueous matrices have received special attention worldwide. Herein, this review systematically summarizes the occurrence and exposure of Sb in the environment and on human health, respectively. Different carbon-based adsorbents have been classified for the adsorptive removal of Sb and their adsorption characteristics have been delineated. Recent development in the adsorption performance of the adsorbent materials for improving the Sb removal from the aqueous medium has been outlined. Further, to develop an understanding of the effect of different parameters like pH, competitive ions, and dissolved ions for Sb adsorption and subsequent removal have been discussed. A retrospective analysis of literature was conducted to present the adsorption behavior and underlying mechanisms involved in the removal of Sb using various adsorbents. Moreover, this study has identified emerging research gaps and emphasized the need for developing modified/engineered carbonaceous adsorbents to enhance Sb adsorption from various aqueous matrices.

Remarkable synergy between sawdust biochar and attapulgite/diatomite after co-ball milling to adsorb methylene blue

Biochar has been recognized as a promising sustainable adsorbent for removing pollutants from wastewater. In this study, two natural minerals, attapulgite (ATP) and diatomite (DE) were co-ball milled with sawdust biochar (pyrolyzed at 600 °C for 2 h) at ratios of 10-40% (w/w) and examined the ability of methylene blue (MB) to be removed from aqueous solutions by them. All the mineral-biochar composites sorbed more MB than both ball milled biochar (MBC) and ball milled mineral alone, indicating there was a positive synergy in co-ball milling biochar with these minerals. The 10% (w/w) composites of ATP:BC (MABC10%) and DE:BC (MDBC10%) had the greatest MB maximum adsorption capacities (modeled by Langmuir isotherm modeling) and were 2.7 and 2.3 times that of MBC, respectively. The adsorption capacities of MABC10% and MDBA10% were 183.0 mg g^-1 and 155.0 mg g^-1 at adsorption equilibrium, respectively. These improvements can be owing to the greater content of oxygen-containing functional groups and higher cation exchange capacity of the MABC10% and MDBC10% composites. In addition, the characterization results also reveal that pore filling, π-π stacking interactions, hydrogen bonding of hydrophilic functional groups, and electrostatic adsorption of oxygen-containing functional groups also contribute prominently to the adsorption of MB. This, along with the greater MB adsorption at higher pH and ionic strengths, suggests the roles in MB adsorption was an electrostatic interaction and an ion exchange mechanism. These results demonstrate that mineral-biochar composites prepared by co-ball milling treatment were promising sorbents of ionic contaminants for environmental applications.

Remediation of polybrominated diphenyl ethers contaminated soil in the e-waste disposal site by ball milling modified zero valent iron activated persulfate

Hydrophobic organic compounds (HOCs) in e-waste disposal sites are difficult to remove effectively. There is little reported about zero valent iron (ZVI) coupled with persulfate (PS) to achieve the removal of decabromodiphenyl ether (BDE209) from soil. In this work, we have prepared the flake submicron zero valent iron by ball milling with boric acid (B-mZVI^bm) at a low cost. Sacrifice experiments results showed that 56.6% of BDE209 was removed in 72 h with PS/B-mZVI^bm, which was 2.12 times than that of micron zero valent iron (mZVI). The morphology, crystal form, atomic valence, composition, and functional group of B-mZVI^bm were determined by SEM, XRD, XPS, and FTIR, and the results indicated that the oxide layer on the surface of mZVI is replaced by borides. The results of EPR indicated that hydroxyl radical and sulfate radical played the dominant role in the degradation of BDE209. The degradation products of BDE209 were determined by gas chromatography-mass spectrometry (GC-MS), accordingly, the possible degradation pathway was further proposed. The research suggested that ball milling with mZVI and boric acid is a low-cost means of preparing highly active zero valent iron materials. And the mZVI^bm has promising applications in improving the activation efficiency of PS and enhancing the removal of the contaminant.

Microstructural tailoring of porous few-layer graphene-like biochar from kitchen waste hydrolysis residue in molten carbonate medium: Structural evolution and conductive additive-free supercapacitor application

Biomass-derived graphene-like material is a promising candidate for supercapacitor electrodes, while it is critical to controllably convert biomass into structure-tunable graphene. Herein, few-layer graphene-like biochar (FLGBS) was successfully fabricated from waste biomass in molten carbonate medium. Molten carbonate acted as the effective catalyst for graphitizing and the liquid medium for microcrystal relinking to achieve the rearrangement of carbon structure. It was found that the stacking of graphene layer and formation of porous structure were influenced by the volume of reaction medium and biomass pre‑carbonation. Namely, increasing the dosage of molten K₂CO₃ was in favor to form few layer-type graphene structure, but excess dosage could destroy the nanopore structure to expand the aperture. In addition, pre‑carbonation at high temperature impeded the exfoliation of graphene layers. When FLGBSs were applied to fabricate conductive additive-free electrode, they displayed a superior supercapacitor performance (up to 237.4 F g^-1 at 0.5 Ag^-1). This excellent performance should be attributed to the large specific surface area, hierarchical pore structure and graphene-like structure. In short, this work could help to get insights into the structural evolution of biomass carbon to graphene-like biochar in molten carbonate medium and achieve the tailoring of microstructure for further application in energy storage.

Insight into the adsorptive removal of ibuprofen using porous carbonaceous materials: A review

Over the last decade, the removal of pharmaceuticals from aquatic bodies has garnered substantial attention from the scientific community. Ibuprofen (IBP), a non-steroidal anti-inflammatory drug, is released into the environment in pharmaceutical waste as well as medical, hospital, and household effluents. Adsorption technology is a highly efficient approach to reduce the IBP in the aquatic environment, particularly at low IBP concentrations. Due to the exceptional surface properties of carbonaceous materials, they are considered ideal adsorbents for the IBP removal of, with high binding capacity. Given the importance of the topic, the adsorptive removal of IBP from effluent using various carbonaceous adsorbents, including activated carbon, biochar, graphene-based materials, and carbon nanostructures, has been compiled and critically reviewed. Furthermore, the adsorption behavior, binding mechanisms, the most effective parameters, thermodynamics, and regeneration methods as well as the cost analysis were comprehensively reviewed for modified and unmodified carbonaceous adsorbents. The compiled studies on the IBP adsorption shows that the IBP uptake of some carbon-based adsorbents is significantly than that of commercial activated carbons. In the future, much attention is needed for practical utilization and upscaling of the research findings to aid the management and sustainability of water resource.

Customized oxygen-rich biochar with ultrahigh microporosity for ideal solid phase microextraction of substituted benzenes

The synergistic effect of high microporosity and abundant heteroatoms is important for improving the performance of biochar in various fields. However, it is still challenging to create enough micropores for biochar, while simultaneously retaining the heteroatoms from biomass. A series of biochar with variable microstructures was successfully prepared by carbonization and following ball milling on lotus pedicel (LP), watermelon rind (WR), and litchi rind (LR). The pore structures and heteroatoms of biochar were characterized in detail. Notably, high microporosity could be realized by the carbonization of LR, and further ball milling resulted in a higher microporous surface area (1323.4 m²·g^-1) and richer oxygen. Furthermore, the obtained biochar was fabricated as solid phase microextraction (SPME) coatings with uniform morphologies and similar thicknesses to deeply investigate the relationships between the microstructures and extraction performance. The best performance was demonstrated by the LR800BM, with enrichment factors from 1780 to 155,217. Finally, it was coupled with gas chromatography-mass spectrometry (GC-MS) to develop an analytical method with a wide linear range (1-50,000 ng·L^-1), low limits of detection (0.10-1.4 ng·L^-1), good repeatability (0.83 %-7.5 %) and reproducibility (4.2 %-8.9 %). This work provides valuable insights into the structure-performance relationship of biochar, which is important for the design of high-performance biochar-based adsorbents and their applications in the environment.

Effects of ball milling on biochar adsorption of contaminants in water: A meta-analysis

Reckless release of contaminants into the environment causes pollution in various aquatic systems on a global scale. Biochar is potentially an inexpensive and environmentally friendly adsorbent for removing contaminants from water. Ball milling has been used to enhance biochar's functionality; however, global analysis of the effect of ball milling on biochar's capacity to adsorb contaminants in aqueous solutions has not yet been done. Here, we conducted a meta-analysis to investigate the effects of ball milling on the adsorption/removal capacity of biochar for contaminants in aqueous solutions, and to investigate whether ball milling effects are related to biochar production, ball milling, and other experimental variables. Overall, ball milling significantly increased biochar adsorption capacity towards both inorganic and organic contaminants, by 69.9% and 561.9%, respectively. This could be attributed to ball milling increasing biochar surface area by 2.05-fold, pore volume by 2.39-fold, and decreasing biochar pH by 0.83-fold. The positive adsorption effects induced by ball milling varied widely, with the most effective being ball milling for 12 to 24 h at 300 to 400 rpm with a biochar:ball mass ratio of 1:100 on biochars produced at 400-550 °C from wood residues. Based on this meta-analysis, we conclude that ball milling could effectively enhance biochar's ability to remove organic and inorganic contaminants from aquatic systems.

A review on nanoparticles: characteristics, synthesis, applications, and challenges

The significance of nanoparticles (NPs) in technological advancements is due to their adaptable characteristics and enhanced performance over their parent material. They are frequently synthesized by reducing metal ions into uncharged nanoparticles using hazardous reducing agents. However, there have been several initiatives in recent years to create green technology that uses natural resources instead of dangerous chemicals to produce nanoparticles. In green synthesis, biological methods are used for the synthesis of NPs because biological methods are eco-friendly, clean, safe, cost-effective, uncomplicated, and highly productive. Numerous biological organisms, such as bacteria, actinomycetes, fungi, algae, yeast, and plants, are used for the green synthesis of NPs. Additionally, this paper will discuss nanoparticles, including their types, traits, synthesis methods, applications, and prospects.

H2O2 activated moxa ash via ball milling for ultrafast removal of mitoxantrone

As emerging contaminants, antineoplastic drugs are widely used, but their residues in water may cause long-term genotoxicity to aquatic organisms and human beings. Here, waste moxa ash was selected as biomass raw material and modified by ball milling to obtain carbon-based materials with excellent adsorption performance, which were used to remove the antineoplastic drug mitoxantrone (MTX) from water. The experimental results indicate that moxa ash modified by ball milling in hydrogen peroxide exhibits ultrafast removal of MTX (the removal efficiency reaches 97.66% in 1 min and 99.72% in 30 min). The pseudo-second-order kinetics and Freundlich isotherm models accurately describe the MTX adsorption process, and the mechanism of adsorption probably involves pore filling, hydrogen bond, π-π interaction and electrostatic attraction. Not only that, moxa ash also has the ability to remove dyes such as malachite green (97.81%) and methylene blue (99.97%). In this study, a simple and environmentally friendly process was used to convert waste moxa ash into an effective MTX adsorbent, providing a feasible solution for controlling MTX pollution and identifying a circular and economic way to reuse the waste.

Tree-based machine learning model for visualizing complex relationships between biochar properties and anaerobic digestion

The ideal conditions for anaerobic digestion experiments with biochar addition are challenging to thoroughly study due to different experimental purposes. Therefore, three tree-based machine learning models were developed to depict the intricate connection between biochar properties and anaerobic digestion. For the methane yield and maximum methane production rate, the gradient boosting decision tree produced R² values of 0.84 and 0.69, respectively. According to feature analysis, digestion time and particle size had a substantial impact on the methane yield and production rate, respectively. When particle sizes were in the range of 0.3-0.5 mm and the specific surface area was approximately 290 m²/g, corresponding to a range of O content (>31%) and biochar addition (>20 g/L), the maximum promotion of methane yield and maximum methane production rate were attained. Therefore, this study presents new insights into the effects of biochar on anaerobic digestion through tree-based machine learning.

Mitigating soil salinity stress with titanium gypsum and biochar composite materials: Improvement effects and mechanism

Titanium gypsum and biochar are considered effective amendments for mitigating soil salinity stress. However, the knowledge is inadequate regarding their efficiency and application as an improvement. In this study, TG-B composite was prepared by using industrial by-products titanium gypsum and biochar as raw materials and then modified by ball milling method, to characterize its microscopic characteristics and explore the improvement effect on saline-alkali soil and plant growth. Besides, we explored the mechanism of TG-B in improving saline-alkali soil and the dynamic balance of the solution reaction process. Our results showed that the CaSO₄·2H₂O particles in TG-B were finer, dispersed evenly, and contacted fully with soil gelatinous particles, which was more conducive to the improvement of saline-alkali soil. The results of TG-B with different ball milling ratios and different materials dosages indicated that the application rate of TG-B was 5%, and the optimum ratio of TG-B was TG: B (mass ratio) = 10:1, with the best soil improvement effect. The pot experiment proved that the indicators of indicating soil salinity such as pH, EC, SAR, and soluble Na⁺ decreased by 20.74%, 77.24%, 68.77%, and 44.70%, respectively, thus playing a good role in improving saline-alkali soil. In addition, pot experiments demonstrated that compared with the control group, the soil porosity and soil moisture content in the TG-B group increased by 15.95% and 38.71%, respectively, and further improve the structure and diversity of soil bacterial community when compared with titanium gypsum and biochar alone. Finally, the application of TG-B promoted the germination and growth of rice significantly through the synergistic effects of composite material components. These results all suggested that the application of TG-B was an effective strategy to improve soil salinity and promote plant growth. Therefore, it might provide new insights into the utilization of solid waste resources to improve saline-alkali lands.

Exogenous application of carbon nanoparticles alleviates drought stress by regulating water status, chlorophyll fluorescence, osmoprotectants, and antioxidant enzyme activity in Capsicum annumn L

Drought is one of the most important abiotic stresses that has a huge negative effect on crop yield. Carbon nanoparticles (CNPs) have received greater attention for their impact on the plants under abiotic stress conditions. However, it is urgently required to apply CNPs to the chili pepper (Capsicum annuum L. cv. Kaskada), which has not yet been studied. The goal of this study was to find out how CNPs affect the growth of chili pepper plants, chlorophyll pigments, proline content, and the activity of antioxidant enzymes when the plants are stressed by drought. Therefore, we synthesized and functionalized CNPs of oil fly ash by one-pot ball milling fabrication. X-ray photoelectron spectroscopy (XPS) was used to identify oxidative moieties on the CNPs surface after exposure to nitric and acetic acids. In the present study, functionalized CNPs were sprayed onto the leaves of 20-day-old plants at various concentrations (6 and 12 mg L^-1) to determine their effects. We demonstrate that drought stress considerably reduces the plant height, fresh weight (FW), and dry weight (DW). Nevertheless, the exogenous application of functionalized CNPs caused an increase in relative water content (RWC), chlorophyll stability index (CSI), and chlorophyll fluorescence (Fv/Fm) under drought stress. Exogenous functionalized CNPs dramatically increased proline content under drought by reducing abscisic acid (ABA) content in the leaves. When subjected to drought stress, functionalized CNPs boosted antioxidant activities such as superoxide dismutase (SOD) and catalase (CAT) activity. Overall, the positive effects of CNPs on chili pepper seedlings open up new possibilities for developing innovative agricultural techniques, especially when plants are grown in drought conditions.

Ball-milling: A sustainable and green approach for starch modification

Ball-milling is a low-cost and green technology that offers mechanical actions (shear, friction, collision, and impact) to modify and reduce starch to nanoscale size. It is one of the physical modification techniques used to reduce the relative crystallinity and improve the digestibility of starch to their better utility. Ball-milling alters surface morphology, improving the overall surface area and texture of starch granules. This approach also can improve functional properties, including swelling, solubility, and water solubility, with increased energy supplied. Further, the increased surface area of starch particles and subsequent increase in active sites enhance chemical reactions and alteration in structural transformations and physical and chemical properties. This review is about current information on the impact of ball-milling on the compositions, fine structures, morphological, thermal, and rheological characteristics of starch granules. Furthermore, ball-milling is an efficient approach for the development of high-quality starches for applications in the food and non-food industries. There is also an attempt to compare ball-milled starches from various botanical sources.

Yerba mate: From waste to activated carbon for supercapacitors

Developing technological solutions that use yerba mate waste as precursors is key to reducing the environmental impact caused by the lack of treatment and its accumulation in landfills. Due to their physicochemical properties, these residues can be used to develop activated carbons. Activated carbon is a versatile material with a high surface area that can be used for energy storage. In this work, yerba mate residues were valued by producing chemically activated carbon to be used as electrode material in supercapacitors. Activated carbons were developed through chemical activation in two steps with KOH. Variables such as impregnation ratio and activation temperature are studied. The developed carbons were characterized by physicochemical and electrochemical techniques. They were found to have high surface areas, up to 1800 m² g^-1, with a hierarchical porous distribution. A maximum specific capacitance of 644 F g^-1 at 0.1 A g^-1, and power values of ca 32,000 W kg^-1, at 33 A g^-1 were found. All the synthesized carbons have excellent electrochemical properties and are suitable for use as active material in supercapacitors.

Twice-milled magnetic biochar: A recyclable material for efficient removal of methylene blue from wastewater

Although magnetic modification has potential for preparing recyclable biochar, the traditional preparation methods of loading magnetic materials on biochar will probably lead to pore blockage and consequently remarkable adsorption recession. Herein, a preparation method was developed in which ball milled biochar was loaded with ultrafine magnetite and then milled for a second time, thus generating a magnetic, recyclable biochar with minimal pore blockage. The deposits of magnetite did not significantly wrap the biochar, although a decreased sorption performance was still detectable. Benefitting from the extra milling step, surface functional groups and specific surface areas of the adsorbents were largely restored, thus leading to a 93.8 % recovery adsorption of 84.6 ± 2.5 mg/L on methylene blue. Meanwhile, the recyclability of the material was not affected. The adsorption was driven by multiple interactions. These twice-milled magnetic biochar is quite outstanding for sustainable removal of aqueous contaminants with its recyclability and high sorption efficiency.

Co-pyrolysis technology for enhancing the functionality of sewage sludge biochar and immobilizing heavy metals

Sewage sludge (SS) is a frequent and challenging issue for countries with big populations, due to its massive output, significant hazard potential, and challenging resource utilization. Pyrolysis can simultaneously realize the reduction, harmlessness and recycling of SS. Co-pyrolysis offers a wide range of potential in terms of increasing product quality and immobilizing heavy metals (HMs), thanks to its capacity to use additives to address the mismatch between SS characteristics and pyrolysis. High-value utilization potential of SS biochar is the key to evaluating the advancement of treatment technology. A further requirement for using biochar resources is the immobilization and bioavailability reduction of HMs. Due to the catalytic and synergistic effects in the co-pyrolysis process, co-pyrolysis SS biochar exhibits enhanced functionality and has been applied in soil improvement, pollutant adsorption and catalytic reactions. This review focuses on the research progress of different additives in improving the functionality of biochar and influencing the behavior of HMs. The key limitation and challenges in SS co-pyrolysis are then discussed. Future research prospects are detailed from seven perspectives, including pyrolysis process optimization, co-pyrolysis additive selection, catalytic mechanism research of process and product, biochar performance improvement and application field expansion, cooperative immobilization of HMs, and life cycle assessment. This review will offer recommendations and direction for future research paths, while also assist pertinent researchers in swiftly understanding the current state of SS pyrolysis research field.

Lithium storage performance and mechanism of nano-sized Ti2InC MAX phase

Fine powders of MAX phases (a family of layered carbides/nitrides) have been showing great promise in energy storage applications. A feasible method of obtaining nano-sized MAX phase particles is critical to realizing the practical application of the vast MAX phase family in more technologically important fields. Herein, ball milling, a commercial and feasible method, is employed to prepare nano-sized Ti₂InC, which delivers a high specific capacity of 590 mA h g^-1 after 500 cycles and maintains 574.4 mA h g^-1 after 600 cycles at 0.1 A g^-1 when used as a lithium storage anode. Compared with other methods (e.g., partial etching), decreasing the size of Ti₂InC particles by ball milling can preserve the exfoliated indium (In) atoms, which have great volumetric and gravimetric capacities. In situ XRD analysis indicates that the capacity of the nano-sized Ti₂InC primarily comes from the lithiation of elemental In exfoliated from Ti₂InC, and in particular, the exfoliated In atoms by ball milling can increase the initial capacity. The lithiation/delithiation cycle can effectively activate and even exfoliate the Ti₂InC grains, which accounts for the increasing capacity upon cycling.

A critical review on mechanochemical processing of fly ash and fly ash-derived materials

Fly ash (FA) is a solid, fine powder that constitutes a by-product obtained when coal, biomass, municipal solid waste or a mixture of these are combusted. This review article focuses on the mechanochemistry of coal fly ash (CFA), as well as highlights the issue of fly ash from municipal solid waste (MSW). In general, FA is regarded as a waste of public concern (since it contains hazardous components), which is primarily consumed in the construction industry, as well as in chemical synthesis and environmental engineering. However, the actual amount of FA recycled is still less than the amount produced, with the reuse rate of only up to 30 %. Due to its relatively low reactivity and heterogeneity, FA is commonly landfilled in huge quantities. Nevertheless, the physical and chemical properties of FA can be tailored, for example, by mechanical forces, ultimately leading to a higher value-added product. Currently, mechanochemistry (MC) is drawing attention in chemical synthesis, pollution remediation and waste management, especially as a possible solution for various drawbacks of conventional syntheses and processes. Mechanochemical processing of FA can be considered eco-friendly, inexpensive and efficient, in particular for processing tons of readily available fly ash already stored in ponds or landfills. With the aim of highlighting the hidden potential and facilitating the favorable use of FA, this article deals with FA as an environmentally challenging material, FA reactivity and recycling through mechanochemical processing, mechanochemical stabilization of heavy metals in FA, as well as up-to-date challenges for life cycle assessment (LCA) in evaluating FA-derived materials. Furthermore, all these full-potential aspects of FA mechanochemistry have not been addressed before, which is a valuable contribution to the existing literature.

Phosphorus recovery and reuse in water bodies with simple ball-milled Ca-loaded biochar

The demand to control eutrophication in water bodies and the risk of phosphorus scarcity have prompted the search for treatment technologies for phosphorus recovery. In this study, ball-milled Ca-loaded biochar (BMCa@BC) composites were prepared with CaO and corn stover biochar as raw materials by a new ball-milling method to recover phosphorus from water bodies. Experimental results demonstrated that BMCa@BC could efficiently adsorb phosphorus in water bodies with an excellent sorption capacity of 329 mg P/g. Hydrogen bonding, electrostatic attraction, complexation, and surface precipitation were involved in adsorption process. In addition, phosphorus recovered by BMCa@BC had high bioavailability (86.7 % of TP) and low loss (3.3 % of TP) and was a potential slow-release fertilizer. P-laden BMCa@BC significantly enhanced seed germination and growth in planting experiments, proving that it could be used as a substitute for P-based fertilizer. After five cycles of regeneration, BMCa@BC still showed good adsorption recovery and the P-enriched desorption solution could be recovered as Ca-P products with the fertilizer value. Overall, BMCa@BC has good cost-effectiveness and practical applicability in phosphorus recovery. This provides a new way to recover and reuse phosphorus effectively.

Current research trends on emerging contaminants pharmaceutical and personal care products (PPCPs): A comprehensive review

Pharmaceutical and personnel care products (PPCPs) from wastewater are a potential hazard to the human health and wildlife, and their occurrence in wastewater has caught the concern of researchers recently. To deal with PPCPs, various treatment technologies have been evolved such as physical, biological, and chemical methods. Nevertheless, modern and efficient techniques such as advance oxidation processes (AOPs) demand expensive chemicals and energy, which ultimately leads to a high treatment cost. Therefore, integration of chemical techniques with biological processes has been recently suggested to decrease the expenses. Furthermore, combining ozonation with activated carbon (AC) can significantly enhance the removal efficiency. There are some other emerging technologies of lower operational cost like photo-Fenton method and solar radiation-based methods as well as constructed wetland, which are promising. However, feasibility and practicality in pilot-scale have not been estimated for most of these advanced treatment technologies. In this context, the present review work explores the treatment of emerging PPCPs in wastewater, via available conventional, non-conventional, and integrated technologies. Furthermore, this work focused on the state-of-art technologies via an extensive literature search, highlights the limitations and challenges of the prevailing commercial technologies. Finally, this work provides a brief discussion and offers future research directions on technologies needed for treatment of wastewater containing PPCPs, accompanied by techno-economic feasibility assessment.

Waste to catalyst: Role of agricultural waste in water and wastewater treatment

Presently, owing to the rapid development of industrialization and urbanization activities, a huge quantity of wastewater is generated that contain toxic chemical and heavy metals, imposing higher environmental jeopardies and affecting the life of living well-being and the economy of the counties, if not treated appropriately. Subsequently, the advancement in sustainable cost-effective wastewater treatment technology has attracted more attention from policymakers, legislators, and scientific communities. Therefore, the current review intends to highlight the recent development and applications of biochars and/or green nanoparticles (NPs) produced from agricultural waste via green routes in removing the refractory pollutants from water and wastewater. This review also highlights the contemporary application and mechanism of biochar-supported advanced oxidation processes (AOPs) for the removal of organic pollutants in water and wastewater. Although, the fabrication and application of agriculture waste-derived biochar and NPs are considered a greener approach, nevertheless, before scaling up production and application, its toxicological and life-cycle challenges must be taken into account. Furthermore, future efforts should be carried out towards process engineering to enhance the performance of green catalysts to improve the economy of the process.

Mechanochemical Synthesis of TiO2-CeO2 Mixed Oxides Utilized as a Screen-Printed Sensing Material for Oxygen Sensor

TiO₂ and CeO₂ are well known as oxygen sensing materials. Despite high sensitivity, the actual utilization of these materials in gas detection remains limited. Research conducted over the last two decades has revealed synergistic effects of TiO₂-CeO₂ mixed oxides that have the potential to improve some aspects of oxygen monitoring. However, there are no studies on the sensing properties of the TiO₂-CeO₂ obtained by mechanochemical treatment. We have tested the applicability of the mechanochemically treated TiO₂-CeO₂ for oxygen detection and presented the results in this study. The sensing layers are prepared as a porous structure by screen printing a thick film on a commercial substrate. The obtained structures were exposed to various O₂ concentrations. The results of electrical measurements showed that TiO₂-CeO₂ films have a significantly lower resistance than pure oxide films. Mixtures of composition TiO₂:CeO₂ = 0.8:0.2, ground for 100 min, have the lowest electrical resistance among the tested materials. Mixtures of composition TiO₂:CeO₂ = 0.5:0.5 and ground for 100 min proved to be the most sensitive. The operating temperature can be as low as 320 °C, which places this sensor in the class of semiconductor sensors working at relatively lower temperatures.

Recent progresses, challenges, and opportunities of carbon-based materials applied in heavy metal polluted soil remediation

The application of carbon-based materials (CBMs) for heavy metal polluted soil remediation has gained growing interest due to their versatile properties and excellent remediation performance. Although the progresses on applications of CBMs in removing heavy metal from aqueous solution and their corresponding mechanisms were well known, comprehensive review on applications of CBMs in heavy metal polluted soil remediation were less identified. Therefore, this review provided insights into advanced progresses on utilization of typical CBMs including biochar, activated carbon, graphene, graphene oxide, carbon nanotubes, and carbon black for heavy metal polluted soil remediation. The mechanisms of CBM remediation of heavy metals in soil were summarized, mainly including physical adsorption, precipitation, complexation, electrostatic interaction, and cationic-π coordination. The key factors affecting the remediation effect include soil pH, organic matter, minerals, microorganisms, coexisting ions, moisture, and material size. Disadvantages of CBMs were also included, such as: potential health risks, high cost, and difficulty in achieving co-passivation of anions and cations. This work will contribute to our understanding of current research advances, challenges, and opportunities for CBMs remediation of heavy metal-contaminated soils.

Ball milling enhanced Cr(VI) removal of zero-valent iron biochar composites: Functional groups response and dominant reduction species

Zero-valent iron biochar composites (ZVI/BC) have been widely used to remove Cr(VI) from water. However, the application of ZVI/BC prepared by the carbothermal reduction was limited by the non-uniform dispersion of ZVI on the biochar surface. In this work, ball milling technique was introduced to modify ZVI/BC. Results showed that after ball milling, the maximum Langmuir adsorption capacity for Cr(VI) was 117.7 mg g-1 (298 K) which was 2.08 times higher than ZVI/BC. The initial adsorption rate of the Elovich model increased from 4.57 × 102 mg g-1 min-1 to 3.74 × 109 mg g-1 min-1 after ball milling. Dispersibility of ZVI on biochar surface and contact between ZVI and biochar were improved by the ball milling, thus accelerating the electron transfer. Besides, ball milling increased the content of oxygen-containing functional groups in biochar, contributing to the chemisorption of Cr(VI). The response sequence of oxygen-containing functional groups was analyzed by two-dimensional correlation spectroscopy, indicating that Cr(VI) preferentially complexed with phenolic -OH. Shielding experiments showed that Fe (0) was the dominant reducing species with a contribution of 73.4%, followed by surface-bound Fe(II) (21.3%) and dissolved Fe2+ (5.24%). Density functional theory calculations demonstrated that ball milled ZVI/BC improved the adsorption affinity and electron transfer flux towards Cr(VI) by introducing phenolic -OH and Fe (0). Combining all the textural characterization, the Cr(VI) removal mechanism of the ball milled ZVI/BC could be proposed as adsorption, reduction, and precipitation. Eventually, stable Cr-Fe oxides (FeOCr2O3 and Cr1·3Fe0·7O3) were formed. This work not only provides a simple method to modify ZVI/BC to remove Cr(VI) in water efficiently and rapidly, but also improves the mechanistic insight into the Cr(VI) removal by iron-carbon composites via the response sequence of functional group analysis and the quantitative analysis of reducing species.

Engineered biochar effects on soil physicochemical properties and biota communities: A critical review

Biochar can be effectively used in soil amendment, environmental remediation as well as carbon sequestration. However, some inherent characteristics of pristine biochars (PBCs) may limit their environmental applications. To improve the physicochemical properties of PBCs and their effects on soil amendment and pollution remediation, appropriate modification methods are needed. Engineered biochars (EBCs) inevitably have a series of effects on soil physicochemical properties and soil biota after being applied to the soil. Currently, most studies focus on the effects of PBCs on soil physicochemical properties and their amendment and remediation effects, while relatively limited studies are available on the impacts of EBCs on soil properties and biota communities. Due to the differences of biochars modified by various methods on soil physicochemical properties and biota communities, the impact mechanisms are different. For a better understanding of the recent advances in the effects of EBCs on soil physicochemical properties and biota communities, a systematic review is highly needed. In this review, the development of EBCs is firstly introduced, and the effects of EBCs on soil physicochemical properties and biota communities are then systematically explored. Finally, the suggestions and perspectives for future research on EBCs are put forward.

Contrasting effects of different field-aged biochars on potential methane oxidation between acidic and saline paddy soils

There is recognition that biochar addition is an appropriate measure to mitigate methane (CH₄) emissions by promoting potential methane oxidation (PMO) in the field. However, the mechanism for different field-aged biochars and effective duration after field application are not well documented. Based on a long-term field experiment, biochar was field aged and separated from two contrasting acidic (Ba) and saline (Bs) paddy fields. Then, the effects of different aged biochars on PMO in acidic and saline paddy soils were explored by incubation experiment. There were five treatments for each soil group: soil without biochar (CK), biochar-enriched paddy soil (2 or 6 years) (NB), fresh biochar amendment (Bf), aged biochar separated from acidic paddy soil amendment (Ba), and aged biochar separated from saline paddy soil amendment (Bs). Results showed that saline paddy soils had a significantly higher PMO than acidic paddy soils under treatment without biochar, and that PMO in acidic paddy soil was enhanced by various biochar amendments, whereas those biochar amendments had no significant effects on PMO in saline paddy soil. PMO was positively correlated with pmoA abundance, N consumption rate and pH of soil-biochar mixture. Aged biochar separated from different fields had conflicting influences on soil pH, N consumption rate and PMO. Ba lost its initial effect on changing PMO as compared to Bf treatment when added back into acidic paddy soil. To the contrary, the acidic paddy soil NB treatment containing biochar added six years before possessed the highest value of PMO among all ten treatments. This study suggested that acidic paddy soil with biochar amendment could mitigate CH₄ emissions by promoting PMO for a prolonged period, though aged biochar separated from the same field had a limited impact on reducing CH₄ emissions.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

Biochar-mediated removal of pharmaceutical compounds from aqueous matrices via adsorption

Pharmaceutical is one of the noteworthy classes of emerging contaminants. These biologically active compounds pose a range of deleterious impacts on human health and the environment. This is attributed to their refractory behavior, poor biodegradability, and pseudopersistent nature. Their large-scale production by pharmaceutical industries and subsequent widespread utilization in hospitals, community health centers, and veterinary facilities, among others, have significantly increased the occurrence of pharmaceutical residues in various environmental compartments. Several technologies are currently being evaluated to eliminate pharmaceutical compounds (PCs) from aqueous environments. Among them, adsorption appears as the most viable treatment option because of its operational simplicity and low cost. Intensive research and development efforts are, therefore, currently underway to develop inexpensive adsorbents for the effective abatement of PCs. Although numerous adsorbents have been investigated for the removal of PCs in recent years, biochar-based adsorbents have garnered tremendous scientific attention to eliminate PCs from aqueous matrices because of their decent specific surface area, tunable surface chemistry, scalable production, and environmentally benign nature. This review, therefore, attempts to provide an overview of the latest progress in the application of biochar for the removal of PCs from wastewater. Additionally, the fundamental knowledge gaps in the domain knowledge are identified and novel strategic research guidelines are laid out to make further advances in this promising approach towards sustainable development.

Valorization of ball-milled waste red mud into heterogeneous catalyst as effective peroxymonosulfate activator for tetracycline hydrochloride degradation

Red mud (RM), a kind of iron-rich industrial waste produced in the alumina production process, can be utilized as a potential iron-based material for the removal of refractory organic pollutants from wastewater in advanced oxidation processes (AOPs). In this work, high-iron RM (rich in iron) was activated in a ball mill and applied as an effective activator of peroxymonosulfate (PMS) for tetracycline hydrochloride (TC-HCl) degradation. Compared with that of unmilled RM (69.7%), the TC-HCl decomposition ratios of ball-milled RM (BM-RM) (72.2%-92.0%) were all improved in the presence of PMS. Systematic characterization suggested that ball milling could optimize the physicochemical properties of RM, such as increased surface area, increased oxygen vacancies, enhanced electrical conductivity, and increased exposure of Fe(II) sites, all of which could effectively improve RM for PMS activation to degrade TC-HCl. The quenching experiments and electron paramagnetic resonance technique revealed that ¹O₂ and SO₄·^- contributed dominantly to the TC-HCl degradation. Ultra performance liquid chromatography mass spectrometry analysis combined with density functional theory calculation revealed that the degradation pathways of TC-HCl were driven by hydroxylation, N-demethylation and dehydration in BM-RM/PMS system. Based on quantitative structure-activity relationship prediction using the Toxicity Estimation Software Tool software, the toxicity of almost all intermediates was significantly reduced. An obvious inhibition effect on TC-HCl was occurred in the presence of Cl^-, whereas the presences of NO₃^- and SO₄^2- had little effect. However, HCO₃^- improved TC-HCl removal efficiency. BM-RM had a wide working pH range (pH = 3-11) and showed good stability and reusability in use. Overall, this work not only offers a simple and promising approach to improve the catalytic activity of RM, but also opens new insights into the ball-milled RM as an effective PMS activator for wastewater treatment.

Efficient activation of persulfate by Nickel-supported cherry core biochar composite for removal of bisphenol A

In this study, low-cost and easily obtained biochar was chosen to prepare nickel-modified biochar materials (Ni/BC) through a one-step activation pyrolysis method. Characterization with X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy proved the existence of Ni⁰ and NiO nanocrystals in Ni/BC catalyst. The optimal Ni_0.5/BC exhibited excellent peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation efficiency toward bisphenol A (BPA) degradation. The Ni_0.5/BC (0.03 g) reacted with 1.0 g L^-1 PMS or PDS could completely remove 20 mg L^-1 BPA in 10 min with the first-order kinetic constants (k₁) of 0.322 min^-1 (PMS) and 0.336 min^-1 (PDS). More importantly, the composite has better structural and functional attributes for the BPA degradation with universal applicability at wide pH and temperature range, proving as a better degradation mediator with high adaptation for numerous organic pollutants. Catalytic activity decreased slightly even after 4 cycles. Based on the quenching experiment and electron paramagnetic resonance, it was found that SO₄^•-, •OH and ¹O₂ were the dominant active species in BPA degradation process. Therefore, this work not only supplies a promising catalyst for the removal of organic contaminants, but also is beneficial for the further development of alternative catalysts for sulfate radical based advanced oxidation processes.

Simultaneous removal of lead, manganese, and copper released from the copper tailings by a novel magnetic modified biosorbent

Potentially toxic elements including lead (Pb), manganese (Mn), and copper (Cu) released from copper tailings would cause severe long-term environmental risks and potential threats to human health. To prevent these negative effects caused by the release of the metals, a novel magnetic carboxyl groups modified bagasse with high adsorption affinity and strong magnetism was synthesized through an in-situ precipitation method and used to simultaneously remove Pb, Mn, and Cu from the eluate of copper tailings. Results showed that release of Pb, Mn, and Cu from the copper tailings was pH, time, and particle size dependent, and maximum concentrations of them released in the eluate was 1.7, 1.9, and 4.1 mg L^-1 under weak acid conditions. Batch adsorption experiment showed that the as-synthesized magnetic modified bagasse could selectively absorb Pb, Mn, and Cu from a complex solution with adsorption capacity of 137.3, 13.1, and 90.0 mg g^-1, respectively. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy-mapping (EDS-mapping) demonstrated that Pb, Mn, and Cu interacted with the magnetic modified biosorbent mainly through coordination and ion exchange. Column experiments showed that higher than 99.5% of the released Pb, Mn, and Cu could be simultaneously removed by the magnetic modified bagasse, and the maximum concentrations of them released in the eluate of the copper tailings were all decreased to lower than 0.01 mg L^-1, which reached the discharge standards. After recycled by a magnet, the magnetic modified bagasse could be collected easily and used repeatedly. Because of the high efficiency and easy recovery, the used method had great practical application value in removal of potentially toxic elements released from metallic tailings.

Production of biochar from crop residues and its application for anaerobic digestion

Anaerobic digestion (AD) is a viable and cost-effective method for converting organic waste into usable renewable energy. The efficiency of organic waste digestion, nonetheless, is limited due to inhibition and instability. Accordingly, biochar is an effective method for improving the efficiency of AD by adsorbing inhibitors, promoting biogas generation and methane concentration, maintaining process stability, colonizing microorganisms selectively, and mitigating the inhibition of volatile fatty acids and ammonia. This paper reviews the features of crop waste-derived biochar and its application in AD systems. Four critical roles of biochar in AD systems were identified: maintaining pH stability, promoting hydrolysis, enhancing the direct interspecies electron transfer pathway, and supporting microbial development. This work also highlights that the interaction between biochar dose, amount of organic component in the substrate, and inoculum-to-substrate ratio should be the focus of future research before deploying commercial applications.

Removal and recovery of phosphorus from secondary effluent using layered double hydroxide-biochar composites

Removal of phosphorus (P) from wastewater and its recovery as a fertilizer are solutions to both P pollution control and resource recycling for agriculture. In this study, various layered double hydroxide biochar composites (LDH/BCs), namely, Zn-Al-LDH/BC, Mg-Al-LDH/BC, and Mg-Fe-LDH/BC, were synthesized to remove P from secondary effluents and then applied as fertilizers. Batch experiments showed that LDH/BCs could adsorb P in fast kinetics, with adsorption capacities ranging 35.19-55.76 mg P/g. A dynamic experiment was performed under different column heights and flow rates, and the results fitted well with Thomas model (R² > 0.90). These LDH/BCs effectively removed P in the continuous mode, even when treating secondary effluents. Furthermore, when the used LDH/BCs applied as fertilizers, the adsorbed Mg-Al-LDH/BC and Mg-Fe-LDH/BC stimulated crop growth; however, Zn-Al-LDH/BC did not. These differences were attributed to not only the availability of P, but also the stimulation or inhibition of photosynthetic pigment synthesis in crops by adsorbents. Overall, we synthesized LDH/BCs, which effectively removed and recovered P from secondary effluents, and investigated the factors influencing the effects of LDH/BCs on crops. We suggest that both P availability and physiological influences of adsorbents on crops should be considered when using adsorbents as fertilizers.

Identifying biotic and abiotic processes of reversing biochar-induced soil phosphorus leaching through biochar modification with MgAl layered (hydr)oxides

Biochar (BC) as a increasing widely adopted soil amendments showed potential threat to soil P leaching, but the relevant mechanisms were not clear enough and relevant strategy should be proposed to address the P leaching induced by BC application. In this study, effects of ordinary corn straw BC, and a fabricated Mg/Al-LDHs modified biochar (LBC) on soil P availability, adsorption, fraction and mobility were compared and investigated by conducting the column and incubation experiments at biochar to soil rate of 1 %, 2 % and 4 % (w/w). Chemical sequential extraction methods and various solid-state method (i.e., three-dimensional excitation emission matrix (EEM), x-ray diffraction (XRD), scanning electron micrograph (SEM) and P K-edge X-ray absorption near edge structure (XANES)) were utilized to give deep insights into the P mobilization and immobilization mechanisms by respectively applying the BC and LBC. Results of incubation experiments showed that applying the LBC reduced the labile P with significant CaP transformation to Al-retained P, while ordinary BC promoted the Fe/Al-P transformation to labile dibasic calcium phosphate and monobasic calcium phosphate evidenced by the EEM analysis, in-situ XANES investigation and chemical sequential extraction methods. Results of phosphatase and microbial analyses indicated that the decreased labile P after 30 days' incubation and the mitigated P leaching in LBC treatment were dominantly ascribed to abiotic processes of inorganic P transformation and (de)sorption. This research gave deep insights into abiotic and biotic processes of ordinary biochar promoting soil P leaching, and important implications for applying engineered biochar in reducing P leaching and improving soil productivity.

A new cutting-edge review on the bioremediation of anaerobic digestate for environmental applications and cleaner bioenergy

Circular agriculture and economy systems have recently emerged around the world. It is a long-term environmental strategy that promotes economic growth and food security while reducing negative environmental consequences. Anaerobic digestion (AD) process has a high contribution and effective biodegradation route for bio-wastes valorization and reducing greenhouse gases (GHGs) emissions. However, the remaining massive digestate by-product contains non-fermented organic fractions, macro and/or micro-nutrients, heavy metals, and metalloids. Direct application of digestate in agriculture negatively affected the properties of the soil due to the high load of nutrients as well as the residuals of GHGs are emitted to the environment. Recycling and valorizing of anaerobic digestate is the main challenge for the sustainable biogas industry and nutrients recovery. To date, there is no global standard process for the safe digestate handling. This review described the biochemical composition and separation processes of anaerobic digestate. Further, advanced physical, chemical, and biological remediation's of the diverse digestate are comprehensively discussed. Moreover, recycling technologies such as phyco-remediation, bio-floc, and entomoremediation were reviewed as promising solutions to enhance energy and nutrient recovery, making the AD technology more sustainable with additional profits. Finally, this review gives an in-depth discussion of current biorefinery technologies, key roles of process parameters, and identifies challenges of nutrient recovery from digestate and prospects for future studies at large scale.

Synthesis and Adsorbent Performance of Modified Biochar with Ag/MgO Nanocomposites for Heat Storage Application

Heat storage is a major problem in the world. Many research is going on the heat storage application. This research investigates the novel Ag/MgO/biochar nanocomposites for heat storage. Ag/MgO/biochar nanocomposites were fabricated using solvent-free ball milling techniques. According to several analytical measurements, the Ag/MgO nanoparticles in biochar are uniformly dispersed across the carbon interface. This type of adsorbent material has been characterized by different techniques such as X-ray diffraction pattern analysis (XRD), FTIR analysis, scanning electron microscope (SEM), and transmission electron microscope (TEM) as all indicate the surface morphology and successful ball milling synthesis of Ag/MgO nanocomposites. The UV visible spectroscopy wavelength range of AgNPs and MgONPs is 330 nm and 470 nm, respectively. FTIR analysis revealed that different functional groups of modified biochar nanocomposites such as O-H group are 3728 cm-1 and for C-H bond is 932 cm-1, C-O group is 1420 cm-1, and C=O is 1785 cm-1, respectively. Adsorption tests showed that 1.0 gL-1 dosage with 60% phosphate removal, an ion, and 0.2 gL-1 of dosages that had 85% methylene blue decomposition, a charged synthetic dye, were the lowest absorption levels. This research suggests that ball milling offers the advantages of stabilization and chemical adaptability for customized remediation of different atmospheric contaminants. Ball milling is a facile and feasible process to fabricate carbon-metal-oxide nanomaterials.

Responses of microbial necromass carbon and microbial community structure to straw- and straw-derived biochar in brown earth soil of Northeast China

Soil microbial organisms are conducive to SOC sequestration. However, little attention has been given to the contributions of living MBC and microbial necromass carbon to the SOC pool under biochar and straw amendments. The aims of the study were to explore (1) the effects of maize straw and biochar on MBC, POC, MAOC, DOC and microbial necromass carbon; (2) the contribution of MBC and microbial necromass carbon to the SOC pool; and (3) the relationships among the soil microbial community structure, microbial necromass carbon and other SOC fractions under maize straw and biochar application for nine consecutive years. Three treatments were studied: CK (applied chemical fertilizer only), BC (biochar applied annually at a rate of 2.625 t ha⁻¹ combined with chemical fertilizer), and SR (straw applied annually at a rate of 7.5 t ha⁻¹). Both biochar and straw increased the SOC contents after nine successive maize plant seasons; the DOC and MAOC contents were also increased by biochar and straw amendments. Biochar had advantages in increasing POC contents compared to straw. Biochar and straw increased MBC contents by 48.54% and 60.83% compared to CK, respectively. Straw significantly increased the Galn, GluN, MurA, ManN and total amino contents (P < 0.05); however, biochar significantly increased the Galn and GluN contents (P < 0.05) but had no impact on the MurA contents and decreased the ManN contents. Biochar mainly increased the fungal-derived necromass carbon contents but had no effect on the bacterial-derived necromass carbon, and straw increased both the bacterial- and fungal-derived necromass carbon contents. Straw had no influence on the ratios of microbial necromass carbon accounting for SOC and MAOC, but biochar decreased the ratios in the current study. Similarly, biochar mainly increased the fungal PLFA and total PLFA contents compared to CK, but straw increased bacterial PLFAs, fungal PLFAs and Actinomycetes PLFAs. Maize yield were increased by 7.44 and 9.16% by biochar and straw application, respectively. These results indicate that biochar stimulates fungal activities and turnover to contribute to the stable soil carbon pool and that biochar also improves POC contents to improve the soil organic carbon sink.

Mobilization of contaminants: Potential for soil remediation and unintended consequences

Land treatment has become an essential waste management practice. Therefore, soil becomes a major source of contaminants including organic chemicals and potentially toxic elements (PTEs) which enter the food chain, primarily through leaching to potable water sources, plant uptake, and animal transfer. A range of soil amendments are used to manage the mobility of contaminants and subsequently their bioavailability. Various soil amendments, like desorbing agents, surfactants, and chelating agents, have been applied to increase contaminant mobility and bioavailability. These mobilizing agents are applied to increase the contaminant removal though phytoremediation, bioremediation, and soil washing. However, possible leaching of the mobilized pollutants during soil washing is a major limitation, particularly when there is no active plant uptake. This leads to groundwater contamination and toxicity to plants and soil biota. In this context, the present review provides an overview on various soil amendments used to enhance the bioavailability and mobility of organic and inorganic contaminants, thereby facilitating increased risk when soil is remediated in polluted areas. The unintended consequences of the mobilization methods, when used to remediate polluted sites, are discussed in relation to the leaching of mobilized contaminants when active plant growth is absent. The toxicity of targeted and non-targeted contaminants to microbial communities and higher plants is also discussed. Finally, this review work summarizes the existing research gaps in various contaminant mobilization approaches, and prospects for future research.

Hydroxyapatite tailored hierarchical porous biochar composite immobilized Cd(II) and Pb(II) and mitigated their hazardous effects in contaminated water and soil

A novel composite of hydroxyapatite tailored hierarchical porous biochar (HA-HPB) was synthesized and used for the adsorptive immobilization of Cd(II) and Pb(II) in water and soil. The hierarchical porous biochar (HPB) was prepared from rice husk through a molten-salt-assisted pyrolysis approach; then, a series of HA-HPB (with 0.5, 1, 2, 3, and 4 g of HPB) was prepared with co-precipitation procedure. All HA-HPBs, particularly HA-3HPB, revealed significantly higher removal efficiency of Cd(II) and Pb(II) (≥99.5%) in water than pristine biochar (5.79 - 24.12%). The immobilization efficiency of HA-3HPB for Cd(II) and Pb(II) was slightly inhibited by the ionic strength and co-existing cations. The Langmuir adsorption capacities of Cd(II) and Pb(II) were 88.1 and 110.2 mg/g, respectively. Ion exchange, complexation, cation-π interaction, and precipitation were the key mechanisms involved in the immobilization of Cd(II) and Pb(II) using HA-3HPB. The HA-3HPB reduced the availability of soil Cd (63.5 - 87.8%) and Pb (64.6 - 92.9%) compared to the unamended soil, and thus reduced their content in the Chinese cabbage shoots by 69.3 -95.4% for Cd and 66.5 -97.2% for Pb. These findings demonstrate the effectiveness of HA-HPB for remediation of Cd(II) and Pb(II) contaminated water and soil and mitigating the potential risks.

Ball milling potassium ferrate activated biochar for efficient chromium and tetracycline decontamination: Insights into activation and adsorption mechanisms

Herein, novel Fe-biochar composites (MBC_BM500 and MBC_BM700) were synthesized through K₂FeO₄ co-pyrolysis and ball milling, and were used to eliminate Cr(VI)/TC from water. Characterization results revealed that higher temperature promoted formation of zero-valent iron and Fe₃C on MBC_BM700 through carbothermal reduction between K₂FeO₄ and biochar. The higher specific surface area and smaller particle size of MBC_BM500/700 stemmed from the corrosive functions of K and the ball milling process. And the maximal uptake amount of MBC_BM700 for Cr(VI)/TC was 117.49/90.31 mg/g, relatively higher than that of MBC_BM500 (93.86/84.15 mg/g). Furthermore, ion exchange, pore filling, precipitation, complexation, reduction and electrostatic attraction were proved to facilitate the adsorption of Cr(VI), while hydrogen bonding force, pore filling, complexation and π-π stacking were the primary pathways to eliminate TC. This study provide a reasonable design of Fe-carbon materials for Cr(VI)/TC contained water remediation, which required neither extra modifiers nor complex preparation process.

Bioaugmentation of Methanosarcina thermophila grown on biochar particles during semi-continuous thermophilic food waste anaerobic digestion under two different bioaugmentation regimes

This study presents the effect of bioaugmentation of thermophilic anaerobic digestion of food waste with Methanosarcina thermophila grown on a wood-derived biochar. Two different supplementation regimes were tested, namely a single bioaugmentation (SBABC) in which 10% v/v of the microbes grown on biochar (1 g/L) is added at setup of the reactors, versus a routine bioaugmentation (RBABC) wherein the same amount of supplements were added over 10 feeding cycles. The optimally performing 'R' and 'S' reactors had increased methane yields by 37% and 32% over their respective controls while reactors SBABC 2 and 3 produced 21.89% and 56.09% higher average methane yield than RBABC 2 and 3, respectively. It appears that a single dose bioaugmentation is advantageous for improving AD as analysed in terms of average methane yield and VFA production. This study provides the basis for understanding how biochar and bioaugmentation can be used for engineering sustainable pilot-scale AD processes.

Norfloxacin adsorption and subsequent degradation on ball-milling tailored N-doped biochar

N-doping is an effective way to modify biochar for enhancing the adsorption capacity. The synthesis of N-doped biochar by the ball-milling method has been attractive due to its facile and eco-friendly approach with low energy consumption. However, the commonly used N-precursor NH₃·H₂O is environmentally harmful. It is needed to prepare safe and non-toxic N-doped biochar for large-scale production. Here, a urea N-doped biochar (U-MBC) was prepared by the ball-milling method and used for norfloxacin (NOR) removal. The results showed that U-MBC exhibited almost 4-fold higher adsorption capacity for NOR than pristine biochar in a wide pH range (3-9). The adsorption enhancement was owing to the enhancement of H-bonds, π-π electron donor-acceptor, and pore-filling interactions due to the N-doping and ball-milling method. Additionally, 89% of adsorbed NOR can be further removed after 6 h milling. The regenerated U-MBC still had a good adsorption capacity (46.27 mg g^-1) and performed well in three cycles. The knowledge gained from this study could encourage researchers to use urea or similar safe N-precursors with the ball-milling method for the large-scale production of N-doped biochar to remove antibiotic organic pollutants in the environment.

Biological Applications of Ball-Milled Synthesized Biochar-Zinc Oxide Nanocomposite Using Zea mays L

Nanotechnology is one of the vital and quickly developing areas and has several uses in various commercial zones. Among the various types of metal oxide-based nanoparticles, zinc oxide nanoparticles (ZnO NPs) are frequently used because of their effective properties. The ZnO nanocomposites are risk-free and biodegradable biopolymers, and they are widely being applied in the biomedical and therapeutics fields. In the current study, the biochar-zinc oxide (MB-ZnO) nanocomposites were prepared using a solvent-free ball-milling technique. The prepared MB-ZnO nanocomposites were characterized through scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet–visible (UV) spectroscopy. The MB-ZnO particles were measured as 43 nm via the X-ray line broadening technique by applying the Scherrer equation at the highest peak of 36.36°. The FTIR spectroscope results confirmed MB-ZnO’s formation. The band gap energy gap values of the MB-ZnO nanocomposites were calculated as 2.77 eV by using UV–Vis spectra. The MB-ZnO nanocomposites were tested in various in vitro biological assays, including biocompatibility assays against the macrophages and RBCs and the enzymes’ inhibition potential assay against the protein kinase, alpha-amylase, cytotoxicity assays of the leishmanial parasites, anti-inflammatory activity, antifungal activity, and antioxidant activities. The maximum TAC (30.09%), TRP (36.29%), and DPPH radicals’ scavenging potential (49.19%) were determined at the maximum dose of 200 µg/mL. Similarly, the maximum activity at the highest dose for the anti-inflammatory (76%), at 1000 μg/mL, alpha-amylase inhibition potential (45%), at 1000 μg/mL, antileishmanial activity (68%), at 100 μg/mL, and antifungal activity (73 ± 2.1%), at 19 mg/mL, was perceived, respectively. It did not cause any potential harm during the biocompatibility and cytotoxic assay and performed better during the anti-inflammatory and antioxidant assay. MB-ZnO caused moderate enzyme inhibition and was more effective against pathogenic fungus. The results of the current study indicated that MB-ZnO nanocomposites could be applied as effective catalysts in various processes. Moreover, this research provides valuable and the latest information to the readers and researchers working on biopolymers and nanocomposites.

Aggregation kinetics of biochar nanoparticles in aqueous environment: Interplays of anion type and bovine serum albumin

The colloidal particles, especially those at the nanoscale, are the most active part of the pyrogenic carbon (biochar). Increasingly applied biochar has resulted in a large number of biochar nanoparticles (NPs) being released into the environment. The aggregation of biochar NPs affects their environmental behavior and fate. The complex effects of anion type (Cl^-, SO₄^2-) and protein (bovine serum albumin, BSA) on the aggregation of wheat straw biochar (WB) and pinewood biochar (PB) NPs in solutions were investigated by the time-resolved dynamic light scattering method. The critical coagulation concentration (CCC) of WB and PB NPs in Na₂SO₄ solution was higher than their CCCs in NaCl solution, which was consistent with the Hofmeister series that SO₄^2-, a kosmotrope anion, increased the interaction between water molecules, thus enhancing the hydrophobic interactions between biochar NPs in solution and promoting their aggregation, while Cl^-, a chaotropic agent, exhibited the opposite effect. When BSA was added into the solution, BSA was adsorbed on the surface of biochar NPs and BSA corona was formed, which inhibited the aggregation of biochar NPs by inducing steric force. The enhanced stability of biochar NPs by BSA was more significant in NaCl than in Na₂SO₄ solution because BSA corona had a more negatively charged surface and a more steric structure in NaCl solution, thus generating stronger electrical repulsion and steric hindrance. The classical DLVO theory and the XDLVO theory incorporating the steric repulsion (in the presence of BSA) were used to interpret the aggregation and dispersion of biochar NPs. Through this study, we found that anion type indirectly affected the aggregation of biochar NPs by influencing the interaction between water molecules, while the aggregation of BSA-biochar NPs conjugates is mainly influenced by the surface charge and structure of BSA corona.