The degradation of high-altitude hydropower reservoir slopes limits slope stability and ecological restoration. This work proposes phosphate-enhanced co-composting, which transforms municipal sludge and forestry residues (sawdust and fallen leaves) into a high-quality soil amendment suitable for degraded topsoils in the Shuangjiangkou reservoir area. The co-composting process was optimized by adjusting the carbon/nitrogen (C/N) ratio, bulking agent composition, and the phosphate dosage. A C/N ratio of 25 with a sawdust–leaves composite produced stable thermophilic conditions, increased microbial enzymatic activity, accelerated organic matter decomposition, and minimized ammonium loss. Moderate phosphate addition of 0.6 mmol P/g dry solid reduced composting time to 16 days and enhanced nutrient retention. Field application of the mature compost at a 9% addition rate significantly improved the treated soils, increasing organic matter from 5.20 to 44.53 g/kg and decreasing bulk density from 1.40 to 1.31 g/cm3, while nutrient contents and heavy metal concentrations met regulatory requirements. The phosphate-enhanced co-composting strategy provides an efficient and safe solution for soil amendment in high-altitude hydropower reservoir regions, particularly contributing to carbon neutrality by promoting organic carbon stabilization, reducing waste-related emissions, and enhancing soil carbon sequestration. These findings demonstrate a low-carbon pathway linking waste management, ecological restoration, and renewable energy infrastructure development.

Crop production is threatened by both water scarcity and poor soil water retention in arid or semi-arid regions. At the same time, the industrial-scale accumulation of municipal sludge creates substantial environmental and resource pressures. The goal of this work was to recycle municipal sludge into a low-cost, environmentally friendly, and multifunctional sludge-based water-retaining material (SBWRM) for enhancing soil water retention capacity and nutritional status. Sludge was used as the primary raw material, and extracellular polymeric substances were extracted using a combined alkaline ultrasonic method. These extracts were then mixed with polyvinyl alcohol to prepare the sludge-based material. The water retention capacity of the material, as well as its effects on seed germination and plant growth in a planting substrate, were systematically evaluated. The results suggested that the SBWRM achieved a maximum water retention capacity of 18.7 times its own weight. The addition of 40% SBWRM effectively promoted ryegrass seed germination and plant height, increased soil moisture and pH value, and enhanced the nutrient contents of nitrogen, phosphorus, and potassium. The findings indicate that SBWRM can effectively enhance water conservation, soil quality, and nutrient supply, thereby providing a practical approach for utilizing sludge resources and supporting ecological restoration in agricultural systems.

Sludge dewatering is a key step in the overall process of sludge treatment and disposal. In this study, ferric tannate was synthesized by chemically complexing tannic acid with Fe₂(SO₄)₃ under various conditions and then was innovatively employed to enhance electrochemical conditioning (ECC) for municipal sludge dewatering. The optimal preparation conditions of ferric tannate were determined as a tannic acid to iron ion molar ratio of 0.8:10, pH of 10, and reaction time of 2 h. Subsequently, ferric tannate-enhanced ECC was investigated under different dosages and operating parameters. The optimal conditions were identified as ferric tannate dosage of 20% total solid, voltage of 50 V, and reaction time of 30 min, under which capillary suction time, specific resistance to filtration, and water content of dewatered sludge cake decreased by 84.3%, 84.2%, and 17.6%, respectively. Results of the mechanism analysis indicated that ferric tannate effectively reduced sludge viscosity, increased zeta potential, and neutralized the negative surface charges via charge neutralization, hydrophobic interactions, and hydrogen bonding. Meanwhile, adsorption bridging promoted floc aggregation and particle growth. Compared with the ECC process alone, the addition of ferric tannate in the ferric tannate-enhanced ECC process generated more ^•OH, promoting the extracellular polymeric substance degradation and protein removal, thereby improving sludge hydrophobicity. Furthermore, the floc structure was reconstructed into a more compact and smooth morphology, facilitating the release of bound water during filtration. These findings provide new technical and theoretical support for the development of eco-friendly and efficient sludge conditioning and dewatering processes.

The resource utilization of urban river sediments is often hindered by their high-water content, poor mechanical properties, and potential environmental risks. In this study, a composite stabilization system based on mayenite (CA) and coconut-shell biochar (BC) was developed to simultaneously improve the engineering performance and environmental safety of contaminated sediments. The effects of initial water content, CA dosage, CA particle size, BC dosage, and BC particle size were systematically investigated using unconfined compressive strength (UCS) tests. The optimal conditions were 70% initial water content, 40% CA (250 mesh), and 20% BC (200 mesh), achieving a maximum UCS of 2.31 ± 0.11 MPa. Microstructural analyses revealed distinct functional roles of the two stabilizers. CA primarily provided mechanical stabilization by forming cementitious hydration products that bound sediment particles into a dense, continuous matrix, whereas BC mainly enhanced environmental stabilization through pore refinement and adsorption-assisted contaminant retention. As a result, the CA–BC composite significantly reduced the leaching of heavy metals, chemical oxygen demand, total nitrogen, and total phosphorus compared to CA stabilization alone. This study demonstrates that CA and BC play complementary roles in sediment stabilization, with CA dominating mechanical reinforcement and BC enhancing environmental stability, providing an effective strategy for the sustainable reuse of dredged sediments in geotechnical engineering.