Nano-biochar: recent progress, challenges, and opportunities for sustainable environmental remediation

Nano-biochar in soil ecosystems: Occurrence, transport, and negative environmental risks

Nano-biochar (nano-BC) in the soil environment has begun to attract great attention owing to its better dispersion and stronger migration ability than bulk-biochar (bulk-BC) for soil remediation. Here we review the behaviors of nano-BC during sorption and transit in soil ecosystems as well as the consequences of nano-BC that have been observed. The ability of nano-BC to absorb organic and heavy metal contaminants are well-established, and this feature may significantly affect the distribution of these pollutants within the soil matrix. Beyond its potential to exert adverse ecotoxicological impacts on soil fauna, nano-BC also alters the soil's microbial and enzymatic activities, plant growth, and physicochemical properties. The vertical and horizontal transport of nano-BC may be facilitated by soil flora. Pollutants associated with nano-BC may disperse further in soil as a result of its movement. Prior to the widespread application of nano-BC in soil ecosystems, future research should focus on assessing the environmental risks associated with the unforeseen negative effects of nano-BC on human health and plant life.

Lactiplantibacillus plantarum as a sustainable solution for monocrotophos degradation and plant growth enhancement

In the present study, characterization of bacterial isolate from fermented foods based on the morphology, biochemical, and molecular analysis identified Lactiplantibacillus plantarum. The bacterium was tested for its ability to degrade monocrotophos (MCP) at a concentration of 1000 ppm. The dephosphorylation potential of this bacterial enzyme against organophosphate substrates including MCP was analyzed. The Lactiplantibacillus plantarum phosphatase showed optimal activity at 40 °C and 6 pH. The Michaelis-Menten constant was found to be 238.14 µM while Vmax is 357.14 µmol/min.ml for MCP as a substrate. The enzyme activity was enhanced by metal ions such as Mn2+, Mg2+, and Ca2+ and inhibited by K+, Zn2+, and Fe2+ ions. Plant growth promotion assays of Lp. plantarum exhibited characteristic traits including phosphate solubilization, cellulase, catalase, and xylanase activities. The degradation of MCP was confirmed based on the presence of acetamide and trimethyl phosphate as intermediate metabolites, confirmed by FTIR and GC-MS analysis. Thus, L. plantarum is a suitable candidate for phosphate solubilization, plant growth promotion, and bio-fertilizer application.

Remediating contaminated environmental systems: the role of plants in cadmium removal

Cadmium (Cd) is one of the most harmful heavy metals in the environment, negatively impacting plant growth and development. However, phytoremediation which is an environmentally friendly and cost-effective technique can be used to treat Cd contaminated environments. It effectively removes Cd from polluted soil and water through processes, such as phytoextraction, phytostabilization, phytostimulation, phytofiltration, and phytotransformation. Numerous research has shown evidences that biological, physical, chemical, agronomic, and genetic methods are being utilized to improve phytoremediation. A special group of plants known as hyperaccumulator plants further enhance Cd removal, turning polluted areas into productive land. These plants accumulate Cd in root cell vacuoles and aerial parts. Despite the morphological and genetic variations, different plant species remediate Cd at different rates using either one or multiple mechanisms. To improve the effectiveness of phytoremediation, it is essential to thoroughly understand the mechanisms that control the accumulation and persistence of Cd in plants, including absorption, translocation, and elimination processes. However, what missing in understanding is in depth of idea on how the limitations of phytoremediation can be overcome. The limitations of phytoremediation can be addressed through various strategies, including natural and chemical amendments, genetic engineering, and natural microbial stimulation, broadly categorized into soil amelioration and plant capacity enhancement approaches. This review presents a concise overview of the latest research on various plants utilized in Cd phytoremediation and the different methods employed to enhance this process. Moreover, this review also underscores the creditability of phytoremediation technique to remediate Cd pollution as it offers a promising approach for eliminating Cd from contaminated sites and restoring their productivity. Additionally, we recommend directing future research toward enhancing the biochemical capabilities of plants for remediation purposes, elucidating the molecular mechanisms underlying the damage caused by Cd in plants, and understanding the fundamental principles regulating the enrichment of Cd in plants.

Engineered biochar for in-situ and ex-situ remediation of contaminants from soil and water

Tailoring physical and chemical properties of biochar enhances its selectivity, treatability, and efficiency in contaminant remediation. Thus, engineered biochar has emerged as a promising remedy for both in-situ and ex-situ remediation of polluted soil and water. Several factors influence the effectiveness of engineered biochar, including feedstock sources, pyrolysis conditions, surface functionalization, mode of application, and site characteristics. The advantages and disadvantages of different modification approaches to engineered biochar and their specific treatability for in-situ and ex-situ remediation are obscure and must be adequately addressed. This review critically evaluates the application of engineered biochar for on/off-spot contamination management, taking into account the long-term stability and biocompatibility prospects. The properties of engineered biochar resulting from modification with clay minerals, nanoparticles, polymers, surfactants, and oxidants/reductants were critically reviewed. Recent progress and advances in remediation mechanisms and modes of application were elaborated for the effective removal of organic and inorganic contaminants, including heavy metals, pesticides, dyes, polycyclic aromatic hydrocarbons, per- and poly-fluoroalkyl substances, and agrochemicals. Several crucial parameters influence in-situ remediation, including the distribution of contaminants, background electrolytes, hydraulic conductivity, as well as dispersion and stability of adsorbents. Ex-situ remediation of pollutants relies heavily on adsorption or degradation kinetics, background electrolytes, adsorbent dose, and pollutant concentrations. In addition, factors restricting the application of engineered biochar were highlighted for long-term sustainable contaminant management and maintaining low environmental impact. Finally, the challenges and future perspectives of utilizing engineered biochar for field-scale demonstration of contaminated sites are proposed.

Does the Incorporation of Biochar into Biodegradable Mulch Films Provide Agricultural Soil Benefits?

The pollution caused by plastic mulch film in agriculture has garnered significant attention. To safeguard the ecosystem from the detrimental effects of plastic pollution, it is imperative to investigate the use of biodegradable materials for manufacturing agricultural plastic film. Biochar has emerged as a feasible substance for the production of biodegradable mulch film (BDM), providing significant agricultural soil benefits. Although biochar has been widely applied in BDM manufacturing, the effect of biochar-filled plastic mulch film on soil carbon stock after its degradation has not been well documented. This study provides an overview of the current stage of biochar incorporated with BDM and summarizes its possible pathway on soil carbon stock contribution. The application of biochar-incorporated BDM can lead to substantial changes in soil microbial diversity, thereby influencing the emissions of greenhouse gases. These alterations may ultimately yield unforeseen repercussions on the carbon cycles. However, in light of the current knowledge vacuum and potential challenges, additional study is necessary to ascertain if biochar-incorporated BDM can effectively mitigate the issues of residual mulch film and microplastic contamination in agricultural land. Significant progress remains necessary before BDM may fully supplant traditional agricultural mulch film in agricultural production.

Ammonium capture Kinetic, Capacity, and Prospect of Rice Husk Biochar produced by different pyrolysis conditions

This study explores the potential application of rice husk biochars, categorized by their pH (acidic, pH 5.98; neutral, pH 7.02; and alkali, pH 11.21) and particle sizes (micron-scale and sub-centimeter) in aquatic ecosystems for efficient removal of ammonium (NH4+). To assess the NH4+ adsorption capacity of the rice husk biochars, both NH4+ adsorption kinetics and isotherms were employed. Additionally, we propose future prospects for utilizing rice husk biochar as an efficient adsorbent based on a review of previous studies. Our findings suggest that the NH4+adsorption capacity of rice husk biochars is primarily influenced by their surface characteristics, specifically surface area of rice husk biochars and loss of acidic functional groups. In this study, the neutral rice husk biochars, which had the highest surface area at 9.86 m2 g-1, exhibited the highest NH4+adsorption performance at 1.12 mg g-1 (micron-scale) and 0.94 mg g-1 (sub-centimeter) compared to acidic and alkali rice husk biochars. Additionally, particle size control proves to be a promising strategy for enhancing adsorption efficiency of rice husk biochars, with the micron-scale rice husk biochars being 1.19-fold higher than sub-centimeter ones. However, before implementing biochar-based pollutant removal strategies in aquatic ecosystems, several considerations (e.g., the potential harmfulness of inner components in biochar, side effects of biochar on aquatic life, and tracking the fate of biochar in aquatic ecosystems) must be addressed. By addressing these concerns, we can expect to expand the practical application of biochar for remediation in aquatic environments, contributing to the effective management of pollutants.

From Bulk to Nano: Formation, Features, and Functions of Nano-Black Carbon in Biogeochemical Processes

Globally increasing wildfires and widespread applications of biochar have led to a growing amount of black carbon (BC) entering terrestrial ecosystems. The significance of BC in carbon sequestration, environmental remediation, and the agricultural industry has long been recognized. However, the formation, features, and environmental functions of nanosized BC, which is one of the most active fractions in the BC continuum during global climate change, are poorly understood. This review highlights the formation, surface reactivity (sorption, redox, and heteroaggregation), biotic, and abiotic transformations of nano-BC, and its major differences compared to other fractions of BC and engineered carbon nanomaterials. Potential applications of nano-BC including suspending agent, soil amendment, and nanofertilizer are elucidated based on its unique properties and functions. Future studies are suggested to develop more reliable detection techniques to provide multidimensional information on nano-BC in environmental samples, explore the critical role of nano-BC in promoting soil and planetary health from a one health perspective, and extend the multifield applications of nano-BC with a lower environmental footprint but higher efficiency.

Review on biochar as a sustainable green resource for the rehabilitation of petroleum hydrocarbon-contaminated soil

Petroleum pollution is one of the primary threats to the environment and public health. Therefore, it is essential to create new strategies and enhance current ones. The process of biological reclamation, which utilizes a biological agent to eliminate harmful substances from polluted soil, has drawn much interest. Biochars are inexpensive, environmentally beneficial carbon compounds extensively employed to remove petroleum hydrocarbons from the environment. Biochar has demonstrated an excellent capability to remediate soil pollutants because of its abundant supply of the required raw materials, sustainability, affordability, high efficacy, substantial specific surface area, and desired physical-chemical surface characteristics. This paper reviews biochar's methods, effectiveness, and possible toxic effects on the natural environment, amended biochar, and their integration with other remediating materials towards sustainable remediation of petroleum-polluted soil environments. Efforts are being undertaken to enhance the effectiveness of biochar in the hydrocarbon-based rehabilitation approach by altering its characteristics. Additionally, the adsorption, biodegradability, chemical breakdown, and regenerative facets of biochar amendment and combined usage culminated in augmenting the remedial effectiveness. Lastly, several shortcomings of the prevailing methods and prospective directions were provided to overcome the constraints in tailored biochar studies for long-term performance stability and ecological sustainability towards restoring petroleum hydrocarbon adultered soil environments.

Recent advancement of nano-biochar for the remediation of heavy metals and emerging contaminants: Mechanism, adsorption kinetic model, plant growth and development

Even though researches have shown that biochar can improve soil-health and plant-growth even in harsh environments and get rid of harmful heavy metals and new contaminants, it is still not sustainable, affordable, or effective enough. Therefore, scientists are required to develop nanomaterials in order to preserve numerous aquatic and terrestrial species. The carbonaceous chemical known as nano-biochar (N-BC) can be used to get rid of metal contamination and emerging contaminants. However, techniques to reduce hetero-aggregation and agglomeration of nano-biochar are needed that lead to the emergence of emerging nano-biochar (EN-BC) in order to maximise its capacity for adsorption of nano-biochar. To address concerns in regards to the expanding human population and sustain a healthy community, it is imperative to address the problems associated with toxic heavy metals, emerging contaminants, and other abiotic stressors that are threatening agricultural development. Nano-biochar can provide an effective solution for removal of emerging contaminants, toxic heavy metals, and non-degradable substance. This review provides the detailed functional mechanistic and kinetics of nano-biochar, its effectiveness in promoting plant growth, and soil health under abiotic stress. Nonetheless, this review paper has comprehensively illustrated various adsorption study models that will be employed in future research.

Applications of engineered biochar in remediation of heavy metal(loid)s pollution from wastewater: Current perspectives toward sustainable development goals

Environmental pollution of heavy metal(loid)s (HMs) caused adverse impacts, has become one of the emerging concerns and challenges worldwide. Metal(loid)s can pose significant threats to living organisms even when present in trace levels within environmental matrices. Extended exposure to these substances can lead to adverse health consequences in humans. Removing HM-contaminated water and moving toward sustainable development goals (SDGs) is critical. In this mission, biochar has recently gained attention in the environmental sector as a green and alternative material for wastewater removal. This work provides a comprehensive analysis of the remediation of typical HMs by biochars, associated with an understanding of remediation mechanisms, and gives practical solutions for ecologically sustainable. Applying engineered biochar in various fields, especially with nanoscale biochar-aided wastewater treatment approaches, can eliminate hazardous metal(loid) contaminants, highlighting an environmentally friendly and low-cost method. Surface modification of engineered biochar with nanomaterials is a potential strategy that positively influences its sorption capacity to remove contaminants. The research findings highlighted the biochars' ability to adsorb HM ions based on increased specific surface area (SSA), heightened porosity, and forming inner-sphere complexes with oxygen-rich groups. Utilizing biochar modification emerged as a viable approach for addressing lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and chromium (Cr) pollution in aqueous environments. Most biochars investigated demonstrated a removal efficiency >90 % (Cd, As, Hg) and can reach an impressive 99 % (Pb and Cr). Furthermore, biochar and advanced engineered applications are also considered alternative solutions based on the circular economy.

The synergistic potential of biochar and nanoparticles in phytoremediation and enhancing cadmium tolerance in plants

Cadmium (Cd) is classified as a heavy metal (HM) and is found into the environment through both natural processes and intensified anthropogenic activities such as industrial operations, mining, disposal of metal-laden waste like batteries, as well as sludge disposal, excessive fertilizer application, and Cd-related product usage. This rising Cd disposal into the environment carries substantial risks to the food chain and human well-being. Inadequate regulatory measures have led to Cd bio-accumulation in plants, which is increasing in an alarming rate and further jeopardizing higher trophic organisms, including humans. In response, an effective Cd decontamination strategy such as phytoremediation emerges as a potent solution, with innovations in nanotechnology like biochar (BC) and nanoparticles (NPs) further augmenting its effectiveness for Cd phytoremediation. BC, derived from biomass pyrolysis, and a variety of NPs, both natural and less toxic, actively engage in Cd removal during phytoremediation, mitigating plant toxicity and associated hazards. This review scrutinizes the application of BC and NPs in Cd phytoremediation, assessing their synergistic mechanism in influencing plant growth, genetic regulations, structural transformations, and phytohormone dynamics. Additionally, the review also underscores the adoption of this sustainable and environmentally friendly strategies for future research in employing BC-NP microaggregates to ameliorate Cd phytoremediation from soil, thereby curbing ecological damage due to Cd toxicity.