Fabrication and evaluation of silica embedded and zerovalent iron composited biochars for arsenate removal from water

Complete 2,4,6-trichlorophenol degradation by anaerobic sludge acclimated with 4-chlorophenol: Synergetic effect of nZVI@BMPC and sodium lactate as an external nutrient

Ball-milled plastic char supported nano zero-valent iron (nZVI@BMPC) and their application combined with anaerobic sludge for microbial dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) were investigated. The XRD and FTIR analysis proved composition of zero valent states of iron, and the BET and SEM analysis showed that nZVI was uniformly distributed on the surface of BMPC. Successive addition of 1000 mg/L sodium lactate and nZVI@BMPC enhanced the acclamation of anaerobic sludge and resulted in the degradation of 4-CP within 80 days. The acclimated consortium with nZVI@BMPC completely degraded 2,4,6-TCP into CH4 and CO2, and the key dechlorination route was through 4-CP dechlorinaion and mineralization. The degradation rate of 2,4,6-TCP with nZVI@BMPC was 0.22/d, greater than that without nZVI@BMPC. The dechlorination efficiency was enhanced in the Fe2+/Fe3+ system controlled by nZVI@BMPC and iron-reducing bacteria. Metagenomic analysis result showed that the dominant de-chlorinators were Chloroflexi sp., Desulfovibrio, and Pseudomonas, which could directly degrade 2,4,6-TCP to 4-CP, especially, Chloroflexi bacterium could concurrently be used to mineralize 4-CP. The relative abundance of the functional genes cprA, acoA, acoB, and tfdB increased significantly in the presence of the nZVI@BMPC. This study provides a new strategy can be a good alternative for possible application in groundwater remediation.

Challenges and opportunities for biochar to promote circular economy and carbon neutrality

Biochar, derived from unused biomass, is widely considered for its potential to deal with climate change problems. Global interest in biochar is attributed to its ability to sequester carbon in soil and to remediate aquatic environment from water pollution. As soil conditioner and/or adsorbent, biochar offers opportunity through a circular economy (CE) paradigm. While energy transition continues, progress toward low-emissions materials accelerates their advance towards net-zero emissions. However, none of existing works addresses CE-based biochar management to achieve carbon neutrality. To reflect its novelty, this work provides a critical overview of challenges and opportunities for biochar to promote CE and carbon neutrality. This article also offers seminal perspectives about strengthening biomass management through CE and resource recovery paradigms, while exploring how the unused biomass can promote net zero emissions in its applications. By consolidating scattered knowledge in the body of literature into one place, this work uncovers new research directions to close the loops by implementing the circularity of biomass resources in various fields. It is conclusive from a literature survey of 113 articles (2003-2023) that biomass conversion into biochar can promote net zero emissions and CE in the framework of the UN Sustainable Development Goals (SDGs). Depending on their physico-chemical properties, biochar can become a suitable feedstock for CE. Biochar application as soil enrichment offsets 12% of CO₂ emissions by land use annually. Adding biochar to soil can improve its health and agricultural productivity, while minimizing about 1/8 of CO₂ emissions. Biochar can also sequester CO₂ in the long-term and prevent the release of carbon back into the atmosphere after its decomposition. This practice could sequester 2.5 gigatons (Gt) of CO₂ annually. With the global biochar market reaching USD 368.85 million by 2028, this work facilitates biochar with its versatile characteristics to promote carbon neutrality and CE applications.

Date palm-magnetized biochar for in-situ stabilization of toxic metals in mining-polluted soil: evaluation using single-step extraction methods and phytoavailability

Mining activities provide a pathway for the entry and accumulation of various heavy metals in soil, which ultimately leads to severe environmental pollution. Utilization of various immobilizing agents could restore such contaminated soils. Therefore, in this study, date palm-derived biochars (BCs: produced at 300 °C, 500 °C and 700 °C) and magnetized biochars (MBCs) were employed to stabilize heavy metals (Cd, Pb, Cu and Zn) in mining polluted soil. Metal polluted soil was amended with BCs and MBCs at w/w ratio of 2% and cultivated with wheat (Triticum aestivum L.) in a greenhouse. After harvesting, dry and fresh biomass of plants were recorded. The soil and plant samples were collected, and the concentrations of heavy metals were measured after extracting with water, DTPA (diethylenetriaminepentaacetic acid), EDTA (ethylenediaminetetraacetic acid), and acetic acid. BCs and MBCs resulted in reduced metal availability and uptake, with higher fresh and dry biomass (>36%). MBCs showed maximum decrease (>70%) in uptake and shoot concentration of metals, as these reductions for Cd and Pb reached below the detection limits. Among all single-step extractions, the DTPA-extractable metals showed a significant positive correlation with shoot concentrations of tested metals. Thus, the synthesized BCs and MBCs could effectively be used for stabilizing heavy metals and improve plant productivity in multi-contaminated soils. However, future studies should focus on long term field trials to restore contaminated mining soils using modified biochars.

Remediation of cadmium or arsenic contaminated water and soil by modified biochar: A review

Biochar has a high specific surface area with abundant pore structure and functional groups, which has been widely used in remediation of cadmium or arsenic contaminated water and soil. However, the bottleneck problem of low-efficiency of pristine biochar in remediation of contaminated environments always occurs. Nowadays, the modification of biochar is a feasible way to enhance the performance of biochar. Based on the Web of science™, the research progress of modified biochar and its application in remediation of cadmium or arsenic contaminated water and soil have been systematically summarized in this paper. The main modification strategies of biochar were summarized, and the variation of physicochemical properties of biochar before and after modification were illustrated. The efficiency and key mechanisms of modified biochar for remediation of cadmium or arsenic contaminated water and soil were expounded in detail. Finally, some constructive suggestions were given for the future direction and challenges of modified biochar research.

Functionalized biochars: Synthesis, characterization, and applications for removing trace elements from water

Biochar (BC) has been recognized as an effective adsorbent to remove trace elements (TEs) from water. However, low surface functionality and small pore size can limit the adsorption ability of pristine biochar. These limitations can be addressed by using functionalized biochars which are developed by physical, chemical, or biological activation of biochar to improve their physico-chemical properties and adsorption efficiency. Despite the large amount of research concerning functionalized biochars in recent decades, to our knowledge, no comprehensive review of this topic has been published. This review focuses solely on the synthesis, characterization, and applications of functionalized/engineered biochars for removing TEs from water. Firstly, we evaluate the synthesis of functionalized biochars by physical, chemical, and biological strategies that yield the desired properties in the final product. The following section describes the characterization of functionalized biochars using various techniques (SEM, TEM, EDS, XRD, XANES/NEXAFS, XPS, FTIR, and Raman spectroscopy). Afterward, the role of functionalized biochars in the adsorption of different TEs from water/wastewater is critically evaluated with an emphasis on the factors affecting sorption efficiency, sorption mechanisms, fate of sorbed TEs from contaminated environments and associated challenges. Finally, we specifically scrutinized the future recommendations and research directions for the application of functionalized biochar. This review serves as a comprehensive resource for the use of functionalized biochar as an emerging environmental material capable of removing TEs from contaminated water/wastewater.

Research Progress on Adsorption of Arsenic from Water by Modified Biochar and Its Mechanism: A Review

Arsenic (As) is a non-metallic element, which is widely distributed in nature. Due to its toxicity, arsenic is seriously harmful to human health and the environment. Therefore, it is particularly important to effectively remove arsenic from water. Biochar is a carbon-rich adsorption material with advantages such as large specific surface area, high porosity, and abundant functional groups, but the original biochar has limitations in application, such as limited adsorption capacity and adsorption range. The modified biochar materials have largely enhanced the adsorption capacity of As in water due to their improved physicochemical properties. In this review, the changes in the physicochemical properties of biochar before and after modification were compared by SEM, XRD, XPS, FT-IR, TG, and other characterization techniques. Through the analysis, it was found that the adsorbent dosage and pH are the major factors that influence the As adsorption capacity of the modified biochar. The adsorption process of As by biochar is endothermic, and increasing the reaction temperature is conducive to the progress of adsorption. Results showed that the main mechanisms include complexation, electrostatic interaction, and precipitation for the As removal by the modified biochar. Research in the field of biochar is progressing rapidly, with numerous achievements and new types of biochar-based materials prepared with super-strong adsorption capacity for As. There is still much space for in-depth research in this field. Therefore, the future research interests and applications are put forward in this review.

Biochar Adsorbents for Arsenic Removal from Water Environment: A Review

Arsenic intake can cause human health disorders to the lungs, urinary tract, kidney, liver, hyper-pigmentation, muscles, neurological and even cancer. Biochar is potent, economical and ecologically sound adsorbents for water purification. After surface modifications, adsorption capacity of biochar significantly increased due to high porosity and reactivity. Adsorption capacities of the biochar derived from the municipal solid waste and KOH mixed municipal solid waste were increased from 24.49 and 30.98 mg/g for arsenic adsorption. Complex formation, electrostatic behavior and ion exchange are important mechanisms for arsenic adsorption. Organic arsenic removal using biochar is a major challenge. Hence, more innovative research should be conducted to achieve one of the 17 sustainable development goals of the United Nations i.e. "providing safe drinking water for all". This review is focused on the arsenic removal from water using pristine and modified biochar adsorbents. Recent advances in production methods of biochar adsorbents and mechanisms of arsenic removal from water are also illustrated.

Carbon Nanodots-Embedded Pullulan Nanofibers for Sulfathiazole Removal from Wastewater Streams

Carbon nanodots (CNDs)-embedded pullulan (PUL) nanofibers were developed and successfully applied for sulfathiazole (STZ) removal from wastewater streams for the first time. The CNDs were incorporated into PUL at 0.0%, 1.0%, 2.0%, and 3.0% (w/w) to produce M1, M2, M3, and M4 nanofibers (PUL-NFs), respectively. The produced PUL-NFs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermal gravimetric analysis (TGA) and Differential scanning calorimetry (DSC) and applied for STZ removal from aqueous solutions through pH, kinetics, and equilibrium batch sorption trials. A pH range of 4.0–6.0 was observed to be optimal for maximum STZ removal. Pseudo-second order, intraparticle diffusion, and Elovich models were suitably fitted to kinetics adsorption data (R2 = 0.82–0.99), whereas Dubinin–Radushkevich, Freundlich, and Langmuir isotherms were fitted to equilibrium adsorption data (R2= 0.88–0.99). STZ adsorption capacity of PUL-NFs improved as the amount of embedded CNDs increased. Maximum STZ adsorption capacities of the synthesized PUL-NFs were in the order of: M4 > M3 > M2 > M1 (133.68, 124.27, 93.09, and 35.04 mg g−1, respectively). Lewis acid–base reaction and π-π electron donor–acceptor interactions were the key STZ removal mechanisms under an acidic environment, whereas H-bonding and diffusion were key under a basic environment. Therefore, CNDs-embedded PUL-NFs could be employed as an environmentally friendly, efficient, and non-toxic adsorbent to remove STZ from wastewater streams.