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The efficient exploitation and utilization of deep geothermal energy can alleviate the energy crisis in the world today. The high thermal conductivity and low-density cementing composite (HTLDC) is helpful to improve the extraction efficiency of deep geothermal energy. In this paper, the optimal formulation of HTLDC is obtained by theoretical analysis, orthogonal test, matrix analysis, SEM, XRD, MIP and other methods. Then the basic properties, microstructure and performance changes at different temperatures are studied. The results show that the best formula of HTLDC is 0.8 W/S ratio, 60 wt% cement, 9 wt% graphite, 15 wt% quartz powder, 6 wt% silica fume, 3 wt% fly ash and 7 wt% admixture. The density of HTLDC is 1.53 g/cm3. The thermal conductivity is 1.6702 W/(m·K), which is 94.71 % higher than that of conventional low density cementing material (CLDC). The 48 h compressive strength is 7.63 MPa, which is 40.77 % higher than CLDC. The content of Ca(OH) 2 is as high as 68.9 %, which is 20 times higher than CLDC. The harmful porosity is only 15.6 %, which is 46.65 % lower than CLDC. The thermal conductivity of HTLDC increases rapidly and then tends to be stable with the increase of temperature. The maximum growth rate of thermal conductivity is 0.0026 W/(m·K2), which is 136 % higher than that of CLDC. The thermal conduction mechanism of HTLDC is consistent with the heat conduction pathway theory. HTLDC has a good high-temperature resistance due to the SiO 2 participates in the hydration reaction and generates C 5 S 6 H 5 and C 6 S 6 H with the increase of temperature. The research results can provide strong technical support for the efficient exploitation of deep geothermal energy. • The formula of HTLDC is obtained by orthogonal test, AHP and matrix analysis. • HTLDC has good thermal conductivity, high temperature resistance and low density. • The HTLDC thermal conduction mechanism conforms to heat conduction pathway theory. • HTLDC can be used for cementing deep geothermal wells with the depth of 5000 m. [ABSTRACT FROM AUTHOR]

Water quality assessment is a crucial step in water resource management and pollution prevention, and is essential for achieving sustainable development. Current methods for evaluating water quality often fall short of meeting the needs of water resource management due to the lacks of accuracy and applicability. In this paper, an enhanced water quality evaluation system was established by Principal Component Analysis / Factor Analysis (PCA/FA), Analytic Hierarchy Process / Entropy Weight Method / Game Theory (AHP/EWM/GT) and Variable Fuzzy Set Theory (VFST). The accuracy of this method was verified by evaluating the water quality of a landfill in a karst area and comparing with the conventional evaluation models. The results indicated that the highest influence on groundwater quality in the study area came from human factor, dissolved solid factor, biological factor, and nutritional factor. The quality of surface water and groundwater in the study area was primarily Grade Ⅱ, accounting for 62.5% and 75%, respectively. The predominant groundwater type was HCO 3 -Ca·Mg, which was strongly affected by karstification. The NH 3 -N and TP in the surface water had the highest variability, and the variation coefficients of K+, Na+, Ca2+, Cl−, NH 3 -N, NO 3 −, TDS, and TH in the groundwater were greater than 1. The surface water quality gradually improved between 2018 and 2019. Overall, the groundwater quality in the southern and central regions was inferior to that in the northern and surrounding areas. There could be a hydraulic link between the surface water and landfill in the research location, while karstification and leachate primarily impacted the groundwater. The water quality evaluation method established in this study can make a significant contribution to water resource management, which has important practical significance for environmental protection and indirect social value to the public. [Display omitted] • PCA/FA is used to reduce the dimension and determine the evaluation index. • The comprehensive weight is obtained by GT coupling AHP and EWM. • An improved VFST water quality evaluation model is established and verified. • The hydrochemical features and water-quality temporospatial variation are analyzed. [ABSTRACT FROM AUTHOR]

Straw and urine have always been two major problems in rural environmental management worldwide. Realizing the recycle of resources is possible to solve the dual problems of resources and environment. In this study, synthetic urine was proposed as a pretreatment method for wheat straw. The effects and application potential of synthetic urine on anaerobic fermentation of wheat straw were explored by comparing the start-up time, pH, methane production and other parameters of dry anaerobic fermentation system with four other traditional pretreatment and non-pretreatment (control). The results showed that the synthetic urine can effectively destroy the fiber structure of straw and beneficial to control the pH in the optimal range to avoid acidogenesis, speeding up the methanogenesis process (10 d). Compared with the control group, the total solid gas production rate and volume gas production rate after pretreatment with 1: 3 dilution of synthetic urine increased by 56.3% and 100%, reaching 195.73 mL g−1 and 1.20 m3 (m3 d) −1. The startup time of the system is also shortened by 11 d. Compared with other pretreatment groups, the methanogenesis process after synthetic urine pretreatment was the shortest (39 d), and the maximum methane production reached 121.5 mL g−1 VS. These results provide evidence that the synthetic urine has good potential to co-ferment with straw to increase bioenergy production in rural areas. Image 1 • A new fermentation mode for wheat straw to control rural environmental pollution. • Synthetic urine pre-treatment shortened start-up time by more than 10 d. • The volumetric gas production rate doubled to 1.2 m3 m−3·d−1. • Methane production process shortened to 39 d. • The maximum methane yield of 121.5 mL g−1 VS was achieved. [ABSTRACT FROM AUTHOR]