Abstract: At a local scale, snow cover is influenced by terrain properties, and it affects water availability across some arid and semiarid regions. This study aimed to quantify the spatial heterogeneity of snow cover due to topographic effects based on moderate-resolution image spectroradiometer (MODIS) snow cover products, processed with spatial and backward temporal filters. A snow-dominant region in the middle section of the northern Tianshan Mountains in China was selected, and the snow cover ratio (SCR) and the number of snow cover days (SCD) were investigated. The results suggest that MODIS images are biased toward underestimation of the snow cover in the study region, and the error is primarily manifested within the elevation band of 1 500–2 500 m. The snow cover is mainly affected by elevation, and snow mostly accumulates above 3 800 m. In addition, the differences in SCR and SCD between the south- and north-facing slopes are more significant than those between the east- and west-facing slopes. Notably, the north-facing slopes have the maximum values of SCR and SCD, whereas the south-facing slopes have the minimum values of SCR and SCD. Furthermore, the impact of slope gradients on snow cover varies across seasons. Snow cover on a sloped surface decreases with the slope gradient during winter, while it tends to increase with the slope gradient during the other seasons. Overall, this study presents a useful perspective on the variance in regional snow cover and provides guidance for the water resources management of snow meltwater with different terrain features.
Abstract: Excess reactive phosphorus (PO4) in waterways can lead to eutrophication. A low-cost approach to reducing PO4 levels in surface water was evaluated using the alum-based water treatment residual (Al-WTR) or Al-WTR augmented with powdered activated carbon (PAC-WTR). Batch adsorption-desorption and continuous flow column experiments were performed to assess the specific adsorption capacities under various concentration and flow conditions. Both Al-WTR and PAC-WTR exhibited the ability to adsorb PO4. The overall, cumulative sorbed amount after a 28-d desorption step for Al-WTR was 33.93 mg/kg, significantly greater than the PAC-WTR value of 24.95 mg/kg (p < 0.05). The continuous flow column experiments showed a theoretical PO4 uptake of 9.00 mg/g for Al-WTR and 7.14 mg/g for PAC-WTR over 720 h. When surface water was used, the Al-WTR and PAC-WTR columns removed 67.4% and 62.1% of the PO4, respectively. These results indicated that Al-WTR was more effective for in-field evaluation.
Abstract: Phosphorus adsorption tests were carried out using poly-aluminum chloride sludge (PACS), which was collected from a water treatment plant in Nanjing. The amount of phosphorus adsorbed by PACS increased quickly within the first hour and reached equilibrium after about 48 h. The adsorption behavior of PACS for phosphorus is consistent with the Langmuir adsorption isotherm equation (R2 > 0.99) and parallel first-order kinetic equation (R2 > 0.98). With the increase of the PACS concentration, the adsorption capacity of PACS for phosphorus decreased, and the removal rate increased. The results of batch tests showed that the adsorption capacities of PACS for phosphorus ranged from 1.64 to 1.13 mg/g when the pH value varied from 4 to 10. However, the adsorption capacity of PACS was not evidently influenced by temperature. In comparison with the ion exchange resin, the adsorption capacity of PACS was barely inhibited by competitive ions, such as , , and Cl−. The PACS surface after adsorption became smooth, and the vibration peaks of Al–O and Al–OH shifted. Both HCl and NaOH have a strong desorption effect on PACS after adsorption saturation, and with higher concentrations of HCl and NaOH, the desorption effect was stronger. Results of column adsorption experiments showed that with lower phosphorus and hydraulic loads, the adsorption column took longer to reach saturation. This indicated that PACS could be used as an efficient material for removal of phosphorus from water. This study provides a new treatment method with PACS.
Abstract: In this experiment, cobalt ferrite-supported activated carbon (CF-AC) was developed and characterized via the wet impregnation method for the removal of Cr and Pb(II) ions from tannery wastewater. Batch adsorption was carried out to evaluate the effect of experimental operating conditions (pH of solution, contact time, adsorbent dose, and temperature), and the removal efficiencies of Cr and Pb(II) ions by the developed adsorbents were calculated and recorded for all experimental conditions. These variables were estimated and reported as removal efficiencies of 98.2% for Cr and 96.4% for Pb(II) ions at the optimal conditions of 5, 0.8 g, 80 min, and 333 K for pH, adsorbent dose, contact time, and temperature, respectively. The equilibrium for the sorption of Cr and Pb(II) ions was studied using four widely used isotherm models (the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherm models). It was found that the Freundlich isotherm model fit better with the coefficient of determination (R2) of 0.948 4 and a small sum of square error of 0.000 6. The maximum adsorption capacities (Qm) of Pb(II) and Cr adsorbed onto CF-AC were determined to be 6.27 and 23.6 mg/g, respectively. The adsorption process conformed well to pseudo-second order kinetics as revealed by the high R2 values obtained for both metals. The thermodynamic parameters showed that adsorption of Cr and Pb(II) ions onto CF-AC was spontaneous, feasible, and endothermic under the studied conditions. The mean adsorption energy (E) values revealed that the adsorption mechanism of Cr and Pb(II) by CF-AC is physical in nature. The results of the study showed that adsorbent developed from CF-AC can be efficiently used as an environmentally friendly alternative adsorbent, for removal of Cr and Pb(II) ions in tannery wastewater.
Abstract: Bioaccumulation and biosorption in microalgae are effective approaches for the removal of heavy metals (HMs) from river water. The objective of this study was to investigate the potential for use of acclimatized microalgae in the removal of HMs from the Yamuna River water as an acclimatizing medium. An active culture of Arthrospira platensis (A. platensis) was acclimatized to HMs up to a concentration of 100 mg/L. It was gradually exposed to increasing concentrations of HMs in five subsequent batches with a step increase of 20 mg/L to acclimatize live cells in the simulated Yamuna River water. The presence of high levels of HMs in the Yamuna River water caused growth inhibition. An empirical growth inhibition model was developed, and it predicted high threshold concentrations of HMs (210.7—424.5 mg/L), producing a positive specific growth rate of A. platensis. A. platensis also showed high average removal efficiencies of HMs, including 74.0% for Cu, 77.0% for Cd, 50.5% for Ni, 76.0% for Cr, 76.5% for Pb, and 63.5 % for Co, from HMs-enriched Yamuna River water. The findings demonstrated that the maximum specific removal amounts of Cu, Cd, Ni, Cr, Pb, and Co were 54.0, 58.0, 39.0, 62.8, 58.9, and 45.3 mg/g, respectively. The maximum yields of the value-added products chlorophyll and phycocyanin were 2.5 mg/g (in a batch of 40 mg/L for Cd) and 1054 mg/g (in a batch of 20 mg/L for Cu), respectively. Therefore, acclimatized A. platensis was proven to be a potential microalga not only for sequestration of HMs but also for production of valuable pigments.
Abstract: Contraction joint shear keys are resilient features of gravity dams that can be considered to increase the sliding safety factors or minimise seismic residual sliding displacements, allowing costly remedial actions to be avoided. This paper presents a novel, robust, and computationally efficient three-dimensional (3D) modelling and simulation strategy of gravity dams, using a series of adjacent cantilever beam elements to represent individual monoliths. These monoliths are interconnected in the longitudinal direction by 3D no-tension link elements representing the lumped shear key stiffness contributions at a particular elevation. The objective is to assess the shear key internal force demands, including the axial force, shear, and moment demands. Shear key demand-capacity ratios can then be assessed with related multi-axial failure envelopes. The 3D link element stiffness coefficients were derived from a series of 3D finite element (FE) solid models with a detailed representation of geometrical features of multiple shear keys. The results from the proposed method based on advanced grillage analysis show strong agreement with reference solutions from 3D FE solid models, demonstrating high accuracy and performance of the proposed method. The application of the proposed advanced grillage method to a dam model with two monoliths clearly shows the advantage of the proposed method, in comparison to the classical approach used in practice.
Abstract: Due to limited flow capacity and the instability of the asymmetric structure of traditional baffle dropshafts, a novel baffle dropshaft with a symmetric structure, adopting the construction shield well directly, is proposed for large-range flow discharge in deep tunnel drainage systems. In this study, a two-phase flow field of the novel baffle dropshaft with three different baffle spacings was simulated at seven different flow rates with a three-dimensional (3D) numerical model verified with experiments, to study hydraulic characteristics of this novel baffle dropshaft. The results show that the novel baffle dropshaft has a remarkable energy dissipation effect. Baffle spacing of the novel baffle dropshaft has a greater effect on flow patterns and baffle pressure distributions than the comprehensive energy dissipation rate. Flow rate is a critical issue for the selection of baffle spacing in the design. Some guidance on baffle spacing selection and structure optimization for the application of this novel baffle dropshaft in deep tunnel drainage systems is proposed.
Abstract: In order to investigate the influence of correlation scale error on the inversion precision of the hydraulic conductivity of the aquifer, the successive linear estimator (SLE) was used to invert the hydraulic conductivity field of a heterogeneous aquifer based on synthetic experiments. By increasing the numbers of observation wells and pumping tests, we analyzed the difference between the estimated and true values of hydraulic conductivity with different correlation scale errors. The relationships between the observation well number and the error in inversion results, and between the pumping test number and the error in inversion results were investigated. The results show that, if the amount of observed head data is insufficient, there will be errors in inversion results with changing correlation scale. Due to the existence of correlation scale error, the improvement of inversion precision gradually slows down with the increase of the amount of observed head data, which indicates that too much observed head data causes data redundancy. Therefore, for the synthetic experiments described in this paper, the observation well number should be less than 41, the pumping test number should be less than 17, and a more suitable method should be selected according to the precision requirements of specific situations in practical engineering.
