Compared to the limited performance of other high-efficiency urea products, humic acid urea (HAU) increased the grain yield of winter wheat as well as of summer maize. However, the effect of adding different amounts of humic acid (HA) on the fate of urea and comprehensive economic and environmental evaluations remains unclear. Four treatments (no urea (CK), common urea (U), HAU0.5, and HAU5) were compared in a 2-year winter wheat-summer maize rotation system. Compared to U, the grain yield of HAU treatments increased by 4.48-11.25 %, regardless of crop type, planting year, or HA addition level; this was partly attributable to the increased storage of soil available N, as confirmed by a simultaneous 15N tracing microplot experiment in the first winter wheat season. HAU inhibited the loss of reactive N (NH3 volatilization, N2O emission, and NO3--N leaching loss). The C footprint based on the yield and areas calculations for HAUs was 7.01-13.48 % and 3.53-5.54 % lower than that of U, respectively. Annual environmental damage costs and annual net ecosystem economic benefits were decreased and increased by 14.89 %- 19.11 % and 6.38 %-9.23 %, respectively. Few agronomic and environmental differences were found between HAU5 and HAU0.5, although the former locked more 15N nutrients in the topsoil. This combined experiment using 15N tracer and field lysimeters showed that more nutrients from HAU were absorbed by crops and converted into grains, reducing the environmental risk of greenhouse gas emissions due to the release of unused nutrients from common U into farmland.

Magnesia carbonation can be adopted as a soil solidification technology for geotechnical engineering. Recent studies have shown that urea decomposition under the catalyzation of ureolytic bacteria can provide a carbon source for magnesia carbonation. Although many related studies have been reported, the mechanical behaviour of the magnesia solidified soil, especially its durability and long-term performance, still require further deep investigations. Besides, the use of plant urease instead of bacteria for magnesia carbonation is also of research interest and requires further studies. In this study, we used crude soybean urease for the catalyzation of urea decomposition in order to provide carbon source for magnesia carbonation (soybean urease intensified magnesia carbonation, SIMC). The mechanical behaviour and durability of SIMC solidified soil under drying-wetting and soaking conditions in acid rain solution were investigated. For SIMC samples, the addition of urea and urease as internal carbon sources led to a much higher strength compared with those without them. The optimum urea concentration was 2 mol/L, and higher concentrations could have negative impact on the strength. As for magnesia, the highest strengths were obtained when the addition was 8 %. During the drying-wetting cycles and soaking tests with acid rain water, there was a generally moderate decreasing trend in strength for the SIMC samples with more drying-wetting cycles or soaking durations. However, the strength reduction ratio, which was defined as the long-term strength in acid environment to that in neutral environment, was much higher compared to the PC samples, implying a much stronger resistance to acid rain water. The mineralogical analysis revealed that hydrated magnesium carbonates were the major effective cementing materials.

Tufa, a loose and porous calcium carbonate deposit, is vulnerable to weathering, which can heighten the risk of geological hazards. This study investigated the potential of microbial-induced calcite precipitation (MICP) to stabilize weathered tufa by isolating urease-producing bacteria from Jiuzhaigou, Sichuan Province. Two strains with the highest urease activity, identified as Stenotrophomonas sp. (U1) and Lysinibacillus boronitolerans (U2), were selected for mixed cultures (Mc). The physiological characteristics and calcification capacity of the strains (U1, U2, and Mc), along with the mechanical properties of treated tufa columns (SCU-1, SCU-2, and SCM), were analyzed. The findings revealed that these strains effectively induced the formation of CaCO3. Mc demonstrated strong growth dynamics (OD600 = 3.9 +/- 0.1) and urease activity (865 +/- 17 U/ml), leading to enhanced CaCO3 production. Furthermore, MICP significantly improved the compressive and shear strength of the weathered tufa, with the SCM sample showing superior results compared to SCU-1 and SCU-2. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses confirmed that Mc produced a greater quantity of CaCO3 in the crystalline form of calcite. Overall, the results indicate that MICP represents a promising environmental protection technology that can effectively enhance the engineering properties of weathered tufa.

BackgroundUrea-based fertilizers are essential for agricultural productivity but contribute to environmental degradation by releasing soil nitrogen (N) through N leaching and runoff. To address these issues, this study develops and characterizes slow-release composites of thermoplastic starch (TPS) and epoxidized natural rubber (ENR) that incorporate 46-0-0 fertilizer. TPS, recognized for its moisture sensitivity and biodegradability, was blended with ENR to enhance matrix compatibility and optimize nutrient release from the fertilizer. The blending process included different fertilizer concentrations (6.9, 10, 15, and 20 wt%) within various components of the composite.ResultsThe characterization included evaluation of mechanical properties, water absorbance, biodegradability in soil, ammonium release, and ammonium leaching. The TPS/ENR composites exhibited a two-stage decomposition, with TPS dissolving first to provide an initial nutrient boost, followed by the biodegradation of ENR to ensure sustained nutrient delivery. Ammonium release assays demonstrated that TPS/ENR composites delayed nutrient dissolution compared to conventional fertilizers, significantly reducing nitrogen loss through leaching. Notably, the TPS/ENR composite with 6.9 wt% of 46-0-0 fertilizer exhibited the highest efficiency, achieving sustained ammonium release and enhancing soil nitrogen retention while mitigating phytotoxicity in lettuce and maize germination assays.ConclusionsThese findings highlight the potential and environmental benefits of delivering fertilizer in TPS/ENR composites to improve nitrogen fertilizer efficiency in agricultural systems. The slow-release mechanism provides both initial and sustained nutrient supply, addressing the dual challenges of early crop nutritional needs and long-term environmental sustainability.

Cementations bind sand/soil particles via physical and chemical interactions to form composite solids with macroscopic mechanical properties. While conventional cementation processes (e.g., silicate cement production, phosphate adhesive synthesis, and lime calcination) remain energy-intensive, bio-cementation based on ureolytic microbially induced carbonate precipitation (UMICP) has emerged as an environmentally sustainable alternative. This microbial-mediated approach demonstrates comparable engineering performance to traditional methods while significantly reducing carbon footprint, positioning it as a promising green technology for construction applications. Nevertheless, three critical challenges hinder its practical implementation: (1) suboptimal cementation efficiency, (2) uneven particle consolidation, and (3) ammonia byproduct emissions during ureolysis. To address these limitations, strategic intervention in the UMICP process through polymer integration has shown particular promise. This review systematically examines polymer-assisted UMICP (P-UMICP) technology, focusing on three key enhancement mechanisms: First, functional polymers boost microbial mineralization efficacy through multifunctional roles, namely microbial encapsulation for improved survivability, calcium carbonate nucleation site provision, and intercrystalline bonding via nanoscale mortar effects. Second, polymeric matrices enable homogeneous microbial distribution within cementitious media, facilitating uniform bio-consolidation throughout treated specimens. Third, selected polymer architectures demonstrate ammonium adsorption capabilities through ion-exchange mechanisms, effectively mitigating ammonia volatilization during urea hydrolysis. Current applications of P-UMICP span diverse engineering domains, including but not limited to crack repair, bio-brick fabrication, recycled brick aggregates utilization, soil stabilization, and coastal erosion protection. The synergistic combination of microbial cementation with polymeric materials overcomes the inherent limitations of pure UMICP systems and opens new possibilities for developing next-generation sustainable construction materials.

Excessive bromine, iodine and dyes can damage soil structure and aquatic ecosystems. Therefore, capturing toxic bromine, iodine and dyes from nuclear fuel waste and organic waste liquid is crucial for protecting the environment and human health. In this study, a tridentate imide acid monomer was synthesized with various functional groups and structures, including carboxyl (-COOH), amide (-CONH), and imide rings, to construct a new type of hyper-crosslinked poly (amide-imide) (PAI1-PAI4). Subsequently, porous carbons (PAI1-900-PAI4900) were prepared, and urea was doped during the secondary carbonization process. The ammonia gas (NH3) and carbon dioxide (CO2) generated from the high-temperature decomposition of urea can be trapped by the porous structure of the carbon-based derivatives, and these gases then react with the carbon in the porous carbon and the N-H/C-H in the amide groups, thus resulting in carbon-based materials (PAI1-U-900-PAI4-U-900) with multiple nitrogen and oxygen Lewis basic sites (C-N/N-O/C--O/-OH) and a moderate porosity. These materials enhanced the interactions between the adsorbent and bromine, iodine, and anionic dyes, and exhibited selective adsorption effects for bromide and Congo red (CR).

The disposal of tailings in a safe and environmentally friendly manner has always been a challenging issue. The microbially induced carbonate precipitation (MICP) technique is used to stabilise tailings sands. MICP is an innovative soil stabilisation technology. However, its field application in tailings sands is limited due to the poor adaptability of non-native urease-producing bacteria (UPB) in different natural environments. In this study, the ultraviolet (UV) mutagenesis technology was used to improve the performance of indigenous UPB, sourced from a hot and humid area of China. Mechanical property tests and microscopic inspections were conducted to assess the feasibility and the effectiveness of the technology. The roles played by the UV-induced UPB in the processes of nucleation and crystal growth were revealed by scanning electron microscopy imaging. The impacts of elements contained in the tailings sands on the morphology of calcium carbonate crystals were studied with Raman spectroscopy and energy-dispersive X-ray spectroscopy. The precipitation pattern of calcium carbonate and the strength enhancement mechanism of bio-cemented tailings were analysed in detail. The stabilisation method of tailings sands described in this paper provides a new cost-effective approach to mitigating the environmental issues and safety risks associated with the storage of tailings.

This study investigated the effectiveness of enzyme-induced carbonate precipitation (EICP) technology in remediating Pb- and Zn-contaminated sand. The research focused on the immobilization of heavy metals and the enhancement of sand strength. Experimental results demonstrated that urease activity increased linearly with enzyme concentration, stabilizing at 100 g/L with an activity of 18 mmol/min, and reached a peak at a pH of 8. Temperature variations also positively impacted urease activity, and effective remediation levels were achieved at standard room temperature. The EICP method effectively transformed heavy metal ions from a mobile exchangeable state to a stable carbonate-bound state, and removal rates exceeded 80% for Zn2+ and 90% for Pb2+ after three treatment cycles. Furthermore, the technology significantly improved the unconfined compressive strength of contaminated sand, increasing Pb-contaminated sand strength to 0.57 MPa and Zn-contaminated sand strength to 0.439 MPa. These findings highlight the potential of EICP technology as a viable solution for the remediation of heavy metal-contaminated sand, offering both immobilization of contaminants and enhancement of sand mechanical properties.

Significant quantities of bark are generated during wood processing, with the majority being utilized for energy production and soil enhancement. This study investigated the influence of bark particle size and resin type (urea-formaldehyde (UF) and melamine-urea-formaldehyde (MUF)) on the properties of particleboards made from spruce and pine bark. Board samples were fabricated using different bark particle sizes (2 to 5 mm and 5 to 8 mm) and varying adhesive contents (5% and 7%) for both UF and MUF adhesives. Reference particleboards were manufactured using industrial wood particles with the same UF and MUF adhesive contents. The spruce bark consistently outperformed pine bark across most investigated properties. Board samples fabricated from spruce bark particles exhibited higher internal bond (IB) strength and modulus of rupture (MOR), as well as enhanced resistance to water absorption (WA) and thickness swelling (TS), particularly when bonded with urea-formaldehyde (UF) adhesive. Specifically, boards composed of spruce bark, using a combination of bark particle sizes, UF adhesive, and 7% adhesive content, exhibited superior performance in IB strength, water resistance, and modulus of elasticity.

Enzyme-induced carbonate precipitation (EICP) is an appealing bio-cementation technology for soil improvement in geotechnical engineering. This study investigated the bio-reinforcement efficacy of sword bean crude urease (SWCU)-mediated EICP and the enhancement effect of various additives on it. A set of sand column specimens with different bio-cementation levels were prepared. Magnesium chloride, sucrose, xanthan gum, sisal fiber, calcite seeds, and skim milk powder were adopted for comparison. Bio-reinforcement efficacy was evaluated by mechanical properties. SWCU possessed a similar to 127% higher specific activity than entry-level commercial urease while saving over 2000 times the enzyme cost. All specimens treated with SWCU-mediated EICP presented excellent moldability and uniformity for one-time treatment. UCS increased exponentially with bio-cementation level due to the uniformly growing CaCO3 content and crystal size. UCS of similar to 1.8 MPa was achieved in a single treatment using 60 g/L SWCU and 3.0 M urea-CaCl2. SWCU exhibited a superior bio-reinforcement efficiency over soybean crude urease, commercial urease, and bacterial urease, since higher soil strength was achieved at lower CaCO3 content. Magnesium chloride showed the most significant enhancement effect, implying an extensive application prospect of SWCU-mediated EICP in seawater environments. The absence of wet strength, markedly elevated dry strength, and notably higher stiffness and hardness at low stress (load) phase indicated that xanthan gum would be more suitable for windbreak and sand fixation in arid/semi-arid environments. Sisal fiber could also effectively improve soil mechanical properties; however, the labor and time costs caused by its premixing with soil should be considered additionally in practical applications.