This paper presents a constitutive model for biotreated sand, developed within the framework of thermodynamic theory, to describe its mechanical behavior under undrained shear conditions. The model incorporates a reinforcement index and a hardening index to account for bonding effects. Undrained triaxial shear tests are conducted to validate the constitutive model. The results demonstrate the model's capacity to accurately predict the undrained shear behavior of biotreated sand under various reinforcement levels and initial confining pressures. It effectively captures the evolution of deviatoric stress, pore pressure, and stress paths. Furthermore, the model accounts for energy dissipation and the degradation of inter-grain bonding during undrained shearing, providing a theoretical foundation for the engineering application of biotreated sand.

Recently, the biostimulation has received attention due to its sustained mineralization, environmental adaptability and lower cost. In the current study, a series of isotropic consolidated undrained triaxial shear (CU) tests were performed on biocemented soil treated through biostimulation approach to examine the effect of cementation levels on the undrained shear behaviors. The test results demonstrate that the biocementation generated by the biostimulation approach can improve the shear behaviors remarkably, with the observed changes in stress-strain relationship, pore water pressure, stress path, stiffness development, and strength parameters. The variations of the strength parameters, i.e., effective cohesion and effective critical state friction angle, with increasing cementation treatment cycles can be well fitted by an exponential function and a linear function, respectively, while the variation of the effective peak-state friction angle is relatively small. The increased shear strength, stiffness, effective cohesion, and strain softening phenomenon of biocemented soils are related to the densification, increased particle surface roughness, and raised interparticle bonding caused by biostimulation approach. The liquefaction index decreases with the increase in cementation treatment cycles, especially at lower initial mean effective stress (100 and 200 kPa), indicating that the biostimulation approach may be a viable method for anti-liquefaction of soil.

This study introduces a novel method for stabilising expansive subgrade soils by integrating microbially induced calcite precipitation (MICP) process with a synergistic combination of waste sugarcane bagasse and recycled polyester fibres. This innovative approach aims to enhance strength properties and reduce volume susceptibility. The study demonstrates increases in Unconfined Compressive Strength (UCS), Split Tensile Strength (STS), and California Bearing Ratio (CBR), while substantially decreasing linear shrinkage, swell strains and pressures, indicating improved soil stability. The study also investigates the microstructural and chemical transformations through SEM-EDS, FTIR, and DSC-TGA, further corroborated by 16S metagenomic sequencing to understand microbial dynamics. Optimal stabilisation results were obtained with 0.5% fibre content and a four-day mellowing period, enhancing soil structure and durability by calcite precipitation and leveraging the combined benefits of natural and synthetic fibres. These fibres strengthen the soil structure and facilitate calcite nucleation, ensuring lasting stability, particularly valuable for stabilising expansive subgrade soils.

The objective of the current study is to explore the effect of biostimulation treatment methods on the mechanical properties and microstructure characteristics of biocemented soil. Biostimulated microbially induced carbonate precipitation (MICP) is an eco-friendly and economical soil reinforcement measure. It relies on the stimulation of the urease-producing bacteria (UPB) in situ for the MICP process. Different biostimulation treatment methods involve different oxygen availability, stimulation solution content and distribution, and number of biostimulation treatments. There may be differences in the effect of UPB stimulation and biocementation when different biostimulation treatment methods are used. In this study, four biostimulation treatment methods, i.e., unsaturated single biostimulation treatment (USBT), unsaturated multiple biostimulation treatments (UMBT), saturated single biostimulation treatment (SSBT) and saturated-unsaturated-combined single biostimulation treatment (CSBT), were used to stimulate native UPB in soil columns, and then, the same cementation treatment was applied to the soil columns. Subsequently, the mechanical behavior and microstructural properties of the biocemented soil were investigated. The results indicated that the saturated single biostimulation treatment was more conducive to stimulating native UPB to induce CaCO3 precipitation. Samples subjected to the saturated single biostimulation treatment exhibited higher CaCO3 precipitation content (CCP), dry density, unconfined compressive strength (UCS) and lower permeability within the same cementation treatment cycle (NC). However, UCS was not only determined by CCP, but was also regulated by CaCO3 spatial distribution and precipitation pattern. This study could help guide the selection of biostimulation treatment methods.

Benzo[a]pyrene (BaP) is a highly carcinogenic persistent organic pollutant, and biostimulation is an effective strategy to enhance its degradation. This study utilized Bacillus subtilis MSC4 as a BaP-degrading bacterium to investigate the effects of two different fermentation waste liquids as stimulants on BaP degradation. The mechanisms were analyzed and compared at both the cellular and molecular levels. The results showed that the stimulation percentages of yeast Yarrowia lipolytica extracellular metabolites (YEMs) and Lactobacillus plantarum fermentation waste solution (LPS) on the biodegradation of BaP reached 52.8% and 63.4%, respectively, compared to B treatment without biostimulant. Physiological analyses showed that both stimulants repaired cell morphology, more than doubled bacterial biomass, increased EPS secretion, enhanced bacterial activity, and significantly reduced oxidative stress by lowering ROS levels to 75-78% of those in the BaP-stressed group, allowing for repair of oxidative damage. Transcriptomic analysis indicated that both stimulants upregulated pathways related to central carbon metabolism, enhancing cell proliferation and energy supply. Additionally, YEMs promoted electron transport and BaP transmembrane transport and upregulated the synthesis of various monooxygenases, while LPS induced the upregulation of genes encoding quercetin dioxygenase and played a more active role in biofilm formation and enhancing BaP bioavailability. This study reveals the shared and distinct mechanisms by which YEMs and LPS enhance BaP biodegradation, providing theoretical guidance for the application of YEMs and LPS in the bioremediation of BaP-contaminated environments.

Expanding on the challenges of expansive soils to civil infrastructure, this research delves into the synergistic application of microbially induced calcium carbonate precipitation (MICP) through bio-stimulation and natural fiber reinforcement to mitigate soil swell-shrink behavior and enhance soil strength. This research diverges from traditional methods by addressing their economic and environmental limitations. The dual strategy of bio-stimulation with natural fiber reinforcement was assessed through laboratory tests, including unconfined compression, 1D swell, linear shrinkage tests, and microstructural analysis. This methodology involved preparing solutions to foster bacterial growth and strategically adding jute fibers to enhance the soil matrix. Results revealed significant improvements in soil strength (up to 186%), and reductions in swell strain (up to 85%) and swell pressure (up to 90%), with the optimal jute fiber content at 1.5%. Additionally, a significant increase in calcium carbonate content (163-176%) highlighted bio-stimulation's role in soil stabilization. SEM analysis showed that bio-stimulation and jute fiber reinforcement transformed the soil microstructure, enhancing cohesion and reducing deformability. These outcomes highlight the promise of combining bio-stimulated MICP with natural fiber reinforcement as an eco-friendly and efficient approach to soil stabilization. They also add to the growing body of knowledge on tackling the issues posed by expansive soils in civil engineering applications.

This study elucidates the findings of a computational investigation into the stimulation characteristics of natural reservoir systems enhanced by high-voltage electropulse-assisted fluid injection. The presented methodology delineates the comprehensive rock-fracturing process induced by electropulse and subsequent fluid injection, encompassing the discharge circuit, plasma channel formation, shockwave propagation, and hydro-mechanical response. A hydromechanical model incorporating an anisotropic plastic damage constitutive law, discrete fracture networks, and heterogeneous distribution is developed to represent the natural reservoir system. The results demonstrate that high-voltage electropulse effectively generates intricate fracture networks, significantly enhances the hydraulic properties of reservoir systems, and mitigates the adverse impact of ground stress on fracturing. The stimulationenhancing effect of electropulse is observed to intensify with increasing discharge voltage, with enhancements of 118.0%, 139.5%, and 169.0% corresponding to discharge voltages of 20 kV, 40 kV, and 60 kV, respectively. Additionally, a high-voltage electropulse with an initial voltage of U0 1/4 80 kV and capacitance C 1/4 5 mF has been shown to augment the efficiency of injection activation to approximately 201.1% compared to scenarios without electropulse. Under the influence of high-voltage electropulse, the fluid pressure distribution diverges from the conventional single direction of maximum stress, extending over larger areas. These innovative methods and findings hold potential implications for optimizing reservoir stimulation in geo-energy engineering. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Compost tea is widely recognized for its beneficial effects on crop growth and soil health. However, its efficacy varies depending on the composition of the feedstock and brewing conditions. This study investigates the chemical composition and agronomic impact of compost tea prepared from a commercial mixture of plant residues and animal manure. Standard chemical analyses, combined with solid-state 13C CPMAS NMR spectroscopy, were employed to characterize the organic chemistry of the feedstock. High-throughput sequencing of bacterial and eukaryotic rRNA gene markers was used to profile the microbiota. Compost tea was applied to three crops, Allium cepa, Beta vulgaris, and Lactuca sativa, grown in protected Mediterranean environments on volcanic soils. The 13C CPMAS NMR analysis revealed that the feedstock is predominantly composed of plant-derived tissues, including grass straw, nitrogen-fixing hay, and animal manure, with a significant presence of O-alkyl-C and di-O-alkyl-C regions typical of sugars and polysaccharides. Additionally, the chemical profile indicated the presence of an aliphatic fraction (alkyl-C), characteristic of lipids such as waxes and cutins. The compost tea microbiome was dominated by Pseudomonadota, with Pseudomonas, Massilia, and Sphingomonas being the most prevalent genera. Compost tea application resulted in significant yield increases, ranging from +21% for lettuce to +58% for onion and +110% for chard. Furthermore, compost tea application reduced slug damage and enhanced the shelf life of lettuce. These findings highlight the bio-stimulant potential of this standardized compost tea mixture across different vegetable crops.

The increasing global population has raised concerns about meeting growing food demand. Consequently, the agricultural sector relies heavily on chemical fertilizers to enhance crop production. However, the extensive use of chemical fertilizers can disrupt the natural balance of the soil, causing structural damage and changes in the soil microbiota, as well as affecting crop yield and quality. Biofertilizers and biostimulants derived from microalgae and cyanobacteria are promising sustainable alternatives that significantly influence plant growth and soil health owing to the production of diverse biomolecules, such as N-fixing enzymes, phytohormones, polysaccharides, and soluble amino acids. Despite these benefits, naturally producing high-quality microalgal biomass is challenging owing to various environmental factors. Controlled settings, such as artificial lighting and photobioreactors, allow continuous biomass production, but high capital and energy costs impede large-scale production of microalgal biomass. Sustainable methods, such as wastewater bioremediation and biorefinery strategies, are potential opportunities to overcome these challenges. This review comprehensively summarizes the plant growth-promoting activities of microalgae and elucidates the mechanisms by which various microalgal metabolites serve as biostimulants and their effects on plants, using distinct application methods. Furthermore, it addresses the challenges of biomass production in wastewater and explores biorefinery strategies for enhancing the sustainability of biofertilizers.

Industrial waste and sewage deposit heavy metals into the soil, where they can remain for long periods. Although there are several methods to manage heavy metals in agricultural soil, microorganisms present a promising and effective solution for their detoxification. We isolated a rhizofungus, Aspergillus terreus (GenBank Acc. No. KT310979.1), from Parthenium hysterophorus L., and investigated its growth-promoting and metal detoxification capabilities. The isolated fungus was evaluated for its ability to mitigate lead (25 and 75 ppm) and copper (100 and 200 ppm) toxicity in Triticum aestivum L. seedlings. The experiment utilized a completely randomized design with three replicates for each treatment. A. terreus successfully colonized the roots of wheat seedlings, even in the presence of heavy metals, and significantly enhanced plant growth. The isolate effectively alleviates lead and copper stress in wheat seedlings, as evidenced by increases in shoot length (142%), root length (98%), fresh weight (24%), dry weight (73%), protein content (31%), and sugar content (40%). It was observed that wheat seedlings possess a basic defense system against stress, but it was insufficient to support normal growth. Fungal inoculation strengthened the host's defense system and reduced its exposure to toxic heavy metals. In treated seedlings, exposure to heavy metals significantly upregulated MT1 gene expression, which aided in metal detoxification, enhanced antioxidant defenses, and maintained metal homeostasis. A reduction in metal exposure was observed in several areas, including normalizing the activities of antioxidant enzymes that had been elevated by up to 67% following exposure to Pb (75 mg/kg) and Cu (200 mg/kg). Heavy metal exposure elevated antioxidant levels but also increased ROS levels by 86%. However, with Aspergillus terreus colonization, ROS levels stayed within normal ranges. This decrease in ROS was associated with reduced malondialdehyde (MDA) levels, enhanced membrane stability, and restored root architecture. In conclusion, rhizofungal colonization improved metal tolerance in seedlings by decreasing metal uptake and increasing the levels of metal-binding metallothionein proteins.