Biogrouting, a method to enhance soil properties using microorganisms and mechanical techniques, has shown great potential for soil improvement. Most studies focus on small sand columns in labs, but recent tests used 0.5 m plastic boxes filled with sand stabilized with microorganisms and fly ash. The experiments, conducted over 30 days, applied injection and infusion methods with microbial fluids, maintaining groundwater levels to simulate field conditions. Mechanical properties were analyzed through unconfined compressive strength (UCS) tests on extracted samples. Researchers also assessed calcium carbonate distribution and shear strength. Results showed water saturation significantly influenced vertical stress (qu), while UCS correlated with the permeability of sand containing varying calcium carbonate levels. Bacillus safensis, a resilient bacterium used in this process, can withstand extreme conditions. After completing its task, it enters a dormant state and reactivates when needed. The bacteria produce calcium carbonate by binding calcium with enzymes, which cements soil particles, enhancing strength and stability. center dot Testing enzymes on microbes and natural soil center dot Installation settings for drip tools using infusion center dot Soil resistance testing after stabilization using UCS

Biomineralization technology is a promising method for soil cementation, enhancing its mechanical properties. However, its application in mitigating slope surface erosion caused by rainfall has not been fully explored. This study experimentally examined the feasibility of using plant-based enzyme-induced carbonate precipitation (PEICP) to reduce slope surface rainfall erosion through simulated rainfall tests. The effects of biotreatment cycles (N) and rainfall intensity (Ri) on erosion resistance were evaluated. The results demonstrated that increasing the biotreatment cycles improved the bio-cementation level, as evidenced by enhanced surface strength, increased calcium carbonate content (CCC) and thicker crust layers. Specifically, as the biotreatment cycles (N) increased from 2 to 6, the crust layer thickness expanded from 5.2 mm to 15.7 mm, with surface strength rising from 38.3 kPa to 244.3 kPa. Likewise, the CCC increased significantly from 1.09% to 5.32%, further reinforcing the soil structure and enhancing erosion resistance. Slopes treated with six biotreatment cycles exhibited optimal erosion resistance across rainfall intensities ranging from 45 to 100 mm/h. Compared to untreated slopes, biotreated slopes showed significant reductions in soil loss, with a decrease to below 10% at N = 4 and near-complete erosion resistance at N = 6. These findings highlight the potential of PEICP technology for improving slope stability under rainfall conditions.

Natural cementation of rock debris is a spontaneous geochemical process that plays an important role in geotechnical stabilization. The focus of this study is to analyze the natural cementation phenomenon in mudslide-prone areas using mineralogical and biological methods. We analyzed the formation of the natural cementation phenomenon by studying its mineral composition, elemental endowment distribution, mechanical properties, and community structure. Similarly, simulated cementation experiments of rock debris by carbonate mineralizing bacteria were carried out in the laboratory to assess the feasibility of biomineralization in the stabilization of rock and soil. The results show that the natural cementation of rock debris in mudslide-prone areas is caused by the formation of calcite under chemical action, and microorganisms also contribute to it; this cementation has multiple environmental protection significance, including improving the compressive properties of rock debris (up to 2.58 Mpa), slowing down or preventing the occurrence of geologic hazards such as slumps, landslides, etc., and significantly decreasing the migratory properties of heavy metal ions and its ecological risks. Laboratory simulation conditions showed that carbonate mineralizing bacteria were enabled to utilize the Ca2+ provided by weathering to achieve rapid cementation of the rock debris, which played an important role in the increase of their compressive strength and the improvement of their pore parameters. This study provides a theoretical basis for future engineering applications of biomineralization technology.

Ferromanganese nodules (FMNs), simultaneously termed as manganese nodules, are metallic concretions typically found in the B horizon of iron and manganese-rich soils. These nodules are primarily formed through the biomineralization process driven by favorable redox reactions and microbial activity. The formation of FMNs in the soil is governed by complex geochemical interactions and influenced by both biotic and abiotic factors, such as temperature, pH, organic matter, redox potential (Eh), wet/dry cycles, and nucleation sites. FMNs typically vary in size, ranging from a few microns to several centimeters, and exhibit diverse shapes, from spherical to irregular. These nodules play a crucial role in nutrient cycling and the adsorption of heavy metals, including phosphorus, lead, copper, zinc, cobalt, and nickel, thereby improving soil quality and preventing metal leaching into aquatic environments. The ion exchange during redox reactions, complexation, occlusion, and adsorption are the key mechanisms through which heavy metals can become immobilized in soil FMNs. The formation of FMNs involves Mn-oxidizing bacteria, such as Bacillus, Pedomicrobium, Erythrobacter, Pseudomonas putida, Geobacter, and Leptothrix discophora, which use specific functional genes such as mnxG, moxA, mopA, CumA, ombB, omaB, OmcB, and mofA to facilitate manganese oxidation. This process reacts with geological material, resulting in the precipitation of metal leachates and the development of metal oxide coatings that serve as nucleation sites for FMNs. Such microbial activities are not only essential for FMNs formation but also for trapping heavy metals in soil, highlighting their importance in soil biogeochemical cycling and ecological functions. However, further research is needed to unravel the complex biogeochemical interactions that influence FMNs growth and composition, as well as to understand the stabilization and release dynamics of nutrients and heavy metals, and the roles of microbial communities and functional genes involved in these processes, particularly in relation to soil fertility and plant nutrition.

To improve the reinforcement effect of MICP technology on fine-grained soil, and consider the fine particle size and activity characteristics of red mud, the experiment of red mud strengthening MICP solidified fine-grained soil was designed and carried out. Combined with mechanical test and microstructural analysis, the enhancing mechanism of red mud on microbial solidified fine-grained soil was comprehensively evaluated. The results show that: (1) Red mud can significantly improve the production of cement during microbial reinforcement of fine-grained soils; the optimal dosage of red mud is 20 %, which increases the strength by 34.6 % and the production of cement by 42.9 %, compared with conventional MICP. (2) After red mud was incorporated into the soil, the pore volume and pore diameter of the treated soil were significantly reduced, and the overall compactness was further improved. (3) The enhancement mechanism of microbial consolidation of fine-grained soils by red mud is mainly due to the presence of chemically active b-C2S and calcium oxide in red mud. These active calcium-based components undergo hydration and carbonation reactions under the action of microbial mineralization, generating calcium carbonate and hydrated calcium silicate, which improves the cement yield and enhances the intergranular bond strength, compactness and overall reinforcement effect of the treated soil. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Lime is a popularly adopted binder for improving the mechanical properties and controlling the volume change behavior of problematic clayey soils. However, lime treatment offers certain limitations due to the durability issues arising from varying physico-chemical conditions exacerbated by climatic stresses or clay mineralogy. Lime-treated soils rich in mineral montmorillonite have experienced severe durability issues, with considerable strength decline, eventually falling below the minimum standards required for its application as a construction material. In this study, the innovative approach of carbon mineralization is adopted to augment the inadequate mechanical strength in the treated soil rich in mineral montmorillonite through carbonate cementation. Extensive mechanical and microstructure characterization techniques comprising unconfined compressive strength tests, scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and mercury intrusion porosimetry (MIP) techniques were performed to identify the mechanism behind strength deterioration in lime-clay composites cured for 24 months in ambient conditions (99 % relative humidity and temperatures of 25 degrees C and 40 degrees C). The results show that the unconfined compressive strength of treated soils reduced drastically beyond 9 months of curing. The newly derived parameter, effective precipitation factor from cementation levels, and macroporosity measurements at varying curing periods helped reveal the deterioration mechanism in the lime-clay composites. Accelerated carbonation of these composites resulted in a maximum of 74 % strength increment with a corresponding 15 % decrease in macroporosity. Carbonation enabled the nucleation of voluminous carbonates that fill and bridge the inter-aggregate pores of these composites via contact cementation, as evidenced by the micro-level images. In addition to rehabilitating deteriorated earthwork due to aging, the technique mitigates carbon emissions by capturing 37 % of CO2 released during lime production into stable carbonate minerals, promoting environmental sustainability.

Multiple-heavy-metal contamination in soil, such as the simultaneous presence of AsO43-, Cd2+ and Pb2+, which can reduce crop yields and damage human health, is a serious issue to be addressed. Herein, the MgFe-LDHs (layered double hydroxides) intercalated with carbonate and nitrate (MgFe-CO3 and MgFe-NO3) were synthesized by Separate Nucleation and Aging Steps and ion-exchange method, respectively. The MgFe-CO3 demonstrated the maximum saturation adsorption capacity of 55.86, 543.48 and 1597.4 mg g(-1) for single AsO43-, Cd2+ and Pb2+ in aqueous solution, while MgFe-NO3 exhibited 92.50, 387.59 and 869.56 mg g(-1), respectively. Kinetic and thermodynamic results for mineralization of single AsO43-, Cd2+ and Pb2+ fitted well with the pseudo-second-order kinetic model and Langmuir isotherm model, indicating the occurrence of chemisorption and monolayer adsorption for both MgFe-CO3 and MgFe-NO3. Furthermore, simultaneous mineralization of AsO43-, Cd2+ and Pb2+ with >99.0 % efficiency in 240 min in aqueous solution and >81.1 % efficiency in 14 days in soil can be achieved by both MgFe-CO3 and MgFe-NO3. Preliminary red bean seedlings cultivation experiments indicated that the released Mg2+ ions from MgFe-CO3 and MgFe-NO3 were capable to promote the emergence and growth of red bean seedlings. Detailed XRD and XPS results demonstrated that the AsO43- anions were adsorbed on the laminate of LDHs, whereas the Pb-3(OH)(2)(CO3)(2) was the mineralization product for both MgFe-CO3 and MgFe-NO3. In terms of Cd2+, CdCO3 was obtained as a mineralization product for MgFe-CO3, while CdCO3 and Cd(OH)(2) can be detected due to the slow transformation of MgFe-NO3 to MgFe-CO3 in air.

Frequent soil drying and wetting cycles significantly affect the mineralization processes of soil organic carbon (SOC) and total nitrogen (STN), impacting soil quality and contributing to nutrient loss. However, the effects of these dry-wet cycles on SOC and STN mineralization in dam soil are not well understood. This study simulated four consecutive wet-dry cycles under five soil moisture gradients of 0% (CK), 5%, 10%, 15%, and 100%, and 100%, across four cycles of 7, 14, 21, and 28 days, to investigate the effects on soil aggregates, enzyme activities, and the mineralization of SOC and STN. The results indicated that soil enzyme activity peaked after two dry-wet cycles and then began to decline. The dry-wet cycles reduced the proportion of soil macro-aggregates while also decreasing the proportions of small and micro-aggregates. In contrast, the 100% treatment conditions exhibited the opposite effect. Dry-wet cycles enhanced the mineralization rates of SOC and STN, with the average mineralization rates under the 10% soil moisture content being the highest-1.78 and 2.38 times greater than the CK treatment for SOC and STN, respectively. The impact of dry-wet cycles on SOC and STN mineralization through the enzyme pathway was greater than through the aggregate pathway. These research findings provide theoretical insights and scientific references for the efficient operation and ecological protection of sedimentation dams in the Loess Plateau.

Biomimetic mineralized mortar (BMM) represents a novel green cementitious material, increasingly recognized for its environmental sustainability. In this study, four typical amino acids including acidic amino acids (aspartic acid, glutamic acid), neutral amino acid (threonine), and basic amino acid (arginine), are employed as crystal modifiers to develop the high-strength BMM (HBMM) based on the biomimetic chemically induced calcium carbonate precipitation (BCICP) method. The mechanical properties and failure morphology of HBMM were evaluated through unconfined compressive strength (UCS) test. The microstructure characteristics of HBMM were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and contact angle test. The results show that amino acid-modified calcium carbonate precipitation can effectively cement loose sand particles and significantly improve the strength of the HBMM. The failure modes of HBMM observed include local failure, vertical splitting failure, shear failure, and splitting- shear mixed failure. Notably, aspartic acid and glutamic acid can induce the formation of vaterite-phase calcium carbonate crystals, while threonine and arginine facilitate the formation of aragonite-phase calcium carbonate crystals. The hydrogen bonding between modified calcium carbonate crystals and silanol groups on the silica surface ensures a tight adhesion of the precipitate to sand surfaces, filling gaps and cementing particles. This study elucidates that using amino acids as modifiers in the BCICP method can significantly enhance the strength of HBMM and influence its microstructure, offering valuable insights for its potential practical applications.

Polyethylene mulching film, which is widely utilized in arid and semi-arid agriculture, leaves residual pollution. A novel approach to addressing this issue is microbial degradation. To screen the strains that degrade polyethylene efficiently and clarify the effect of degrading strains on the turnover of soil organic carbon, a polyethylene-degrading fungus PF2, identified as Trichoderma asperellum, was isolated from long-time polyethylene-covered soil. Strain PF2 induced surface damage and ether bonds, ketone groups and other active functional groups in polyethylene, with 4.15% weight loss after 30 days, where laccase plays a key role in the degradation of polyethylene. When applied to soil, the Trichoderma-to-soil weight ratios were the following: B1: 1:100; B2: 1:200; B3: 1:300 and B4: 1:400. Trichoderma asperellum significantly increased the cumulative CO2 mineralization and soil organic carbon mineralization in the B1 and B2 treatments compared with the control (B0). The treatments B1, B3 and B4 increased the stable organic carbon content in soil. An increase in the soil organic carbon content was observed with the application of Trichoderma asperellum, ranging from 27.87% to 58.38%. A positive correlation between CO2 emissions and soil organic carbon was observed, with the soil carbon pool management index (CPMI) being most correlated with active organic carbon. Trichoderma treatments improved the CPMI, with B3 showing the most favorable carbon retention value. Thus, Trichoderma asperellum not only degrades polyethylene but also contributes to carbon sequestration and soil fertility when applied appropriately.