Current Issue

2022, Volume 15,  Issue 4

Water Resources
Abstract:
Surf-zone hydrodynamics forced by oblique wave shoaling and breaking on beach slopes were investigated. The results showed that in wavebasin experiments with incident angles in the range of 15°-30°, wave breaking was initiated at a breaker coefficient of around 0.67, which was significantly less than that predicted from empirical relations based on normally incident waves for a given beach slope and deep-water wave steepness. The measurements also showed that subsequent saturated breaking occurred at a breaker coefficient of around 0.47 that was independent of beach slope in the range of 1:10 to 1:100. This result is likely applicable to both oblique and normally incident waves. It is shown that the measured wave heights and longshore velocity profiles in wave-basin studies can be reasonably well predicted by theory with proper adjustments to the process parameters. Best-match formulations were identified for quantifying bottom friction, eddy viscosity, and energy loss due to surface rollers.
Abstract:
Mining activities interfere with the natural groundwater chemical environment, which may lead to hydrogeochemical changes of aquifers and mine water inrush disasters. This study analyzed the hydrochemical compositions of 80 water samples in three aquifers and developed a water source identification model to explore the control factors and potential hydraulic connection of groundwater chemistry in a coal mine. The results showed that the hydrochemical types of the three aquifers were different. The main hydrochemical compositions of the loose-layer, coalbearing, and limestone aquifers were HCO3·Cl-Na, SO4·HCO3-Na, and SO4-Na·Ca, respectively. The correlation, Unmix, and factor analyses showed that the hydrochemical composition of groundwater was controlled by the dissolution of soluble minerals (such as calcite, dolomite, gypsum, and halite) and the weathering of silicate minerals. The factor score plot combined with Q-mode cluster analysis demonstrated no remarkable hydraulic connection among the three aquifers in the study area. The water source identification model effectively identified the source of inrush water. Moreover, the mixing ratio model rationally quantified the contributions of the three aquifers to inrush water.
Abstract:
When choosing sites for monitoring of soil moisture for hydrological purposes, a suitable process that considers the factors influencing soil moisture level should be followed. In this study, two multi-criteria decision-making (MCDM) methods, the multi-influencing factor (MIF) method and the analytical hierarchy process (AHP) method, were used to identify the optimal soil moisture monitoring (SMM) sites in the Dry Creek Catchment in South Australia. The most representative areas for nine SMM sites were obtained using the MIF method, considering the factors of rainfall, soil type, land use, catchment slope, elevation, and upslope accumulated area (UAA). The AHP method was used to select the optimal sites using the site-specific criteria. 30.3% of the catchment area in the Australian Water Resources Assessment Landscape (AWRA-L) Grid_DC2 can be considered acceptable as representative area with the MIF method. Four potential sites were evaluated for each AWRA-L grid using the relative weights of the site-specific criteria with the AHP method. The Grid_DC2 required two sites that had the highest overall weight chosen with the AHP analysis. The procedure was repeated for the remaining four AWRA-L grids within the study area to select the required SMM sites.
Aquatic Environment
Abstract:
Fe3O4 magnetic xerogel composites were prepared by polycondensation of resorcinol (R)-formaldehyde reaction via a sol-gel process in an aqueous solution through varying the molar ratio of Fe3O4 nanoparticles (MNPs), catalyst (C), and water (W) content. MNPs were obtained by co-precipitation (MC), oxidation of iron salts (MO), or solvothermal synthesis (MS). Both MNPs and magnetic xerogels were examined regarding the performance of arsenic and fluoride removal in a batch system. The MC-based MNPs had higher adsorption capacities for both fluoride (202.9 mg/g) and arsenic (3.2 mg/g) than other MNPs in optimum conditions. The X-ray diffraction, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy confirmed that Fe was composed into the polymeric matrix of magnetic xerogels that contained 0.59%-4.42% of Fe with a molar ratio of MNPs (M) to R between 0.01 and 0.10. With low R/C and optimum M/R ratios, an increase in the surface area of magnetic xerogels affected the fluoride and arsenic adsorption capacities. The magnetic xerogel composites with the MCbased MNPs prepared at a fixed R/C ratio (100) and at different R/W (0.05-0.06) and M/R (0.07-0.10) ratios had a high arsenic removal efficiency of 100% at an As(V) concentration of 0.1 mg/L and pH of 3.0. The maximum adsorption capacities of magnetic xerogels were approximately five times higher than those of the xerogels without MNP composites. Therefore, Fe3O4 nanoparticles enhanced the adsorption of arsenate and fluoride. The variations of alkaline catalyst and water content significantly affected the resulting properties of textural and surface chemistry of magnetic xerogel composites.
Abstract:
Antibiotics and antibiotic resistance genes (ARGs) pose health risks in aquatic environments because of their persistence and mobility. River networks can provide a perfect opportunity for exploring the occurrence and enrichment of ARGs and antibiotics in freshwater environments. On this basis, the abundances of four types of antibiotics (sulfonamides, quinolones, tetracyclines, and macrolides) and 13 ARGs (sulⅠ, sulⅡ, tetA, tetB, tetO, tetW, qnrA, qnrS, qnrD, ermB, ermF, ermC, and ereA) were measured in the river networks of the west bank of the Wangyu River in China. The spatial distribution and temporal variation of these antibiotics and ARGs were characterized, and their controlling factors were analyzed. All four types of antibiotics were detected with high frequencies between 41% and 100%. Quinolone antibiotics exhibited the highest average concentration (286.53 ng/L). The concentrations of quinolones, tetracyclines, and macrolides were significantly higher in the winter than in the summer, whereas the concentration of sulfonamides was higher in wet periods than in dry periods. Of the 13 ARGs, sulI was the most abundant (1.28 ×105 copies per milliliter), followed by sulII and tetO (5.41×104 and 4.45×104 copies per milliliter, respectively). The canonical correspondence analysis showed that environmental factors, including dissolved oxygen, water temperature, total nitrogen, pH, and total phosphorus, had significant effects on the abundance of ARGs. sulⅠ, sulⅡ, tetA, and tetB were significantly correlated with 16S ribosomal RNA sequences, indicating that the bacterioplankton community might affect the distribution of ARGs. The correlation heat map analysis showed that the spread of ARGs was influenced by specific bacterial groups, such as Acidobacteria and Cyanobacteria, indicating that these bacterioplankton may be the hosts of environmental ARGs.
Abstract:
In a beamhouse, liming plays a key role in the removal of hair/wool and epidermis, but problems are created when waste liming sludge is discharged to the environment. The treatment of tannery wastewater is another major challenge to the industry. In this study, thermally-activated biochars derived from liming sludge were studied for their effective adsorption of chromium (Cr) from the tannery wastewater. The thermally activated biochars (B500, B550, B600, and B650) were prepared at different temperatures from the liming sludge. Their characteristics before and after the treatment were investigated using Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, BrunauereEmmetteTeller, and scanning electron microscopy analyses. The related functional groups (C-H, O-H, C-N, and =C-O) and chromium adsorption capacity were determined according to the surface morphology, element contents (C, O, Ca, Na, Al, Mg, and Si), surface area (5.8-9.2 m2/g), pore size (5.22-5.53 nm), and particle size (652-1 034 nm) of the experimental biochars. The biochar originated at 600 C from the tannery liming sludge (B600) had a greater surface area with a chromium adsorption capacity of 99.8% in comparison to B500, B550, and B650 biochars. This study developed an innovative way of utilizing liming sludge waste to minimize the pollution load and wastewater treatment cost in the tannery industry.
Water Engineering
Abstract:
Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling. This leads to a high computational cost for mesoscale modeling and thus slows the development of multiscale modeling of hydraulic mass concrete structures. To overcome this obstacle, an efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete was developed based on the concept of the governing mesostructure. The mesostructure was characterized by a critical aggregate size. Coarse aggregates smaller than the critical size were homogenized into mortar matrices. Key issues in mesostructure generation of fully-graded hydraulic concrete are discussed, as is the development of mesoscale finite element modeling methodology. The basic concept and implementation procedures of the proposed approach are also described in detail. The numerical results indicated that the proposed approach not only significantly improves the computational efficiency of mesoscale modeling but also captures the dominant fracturing mechanism at the mesoscale and reproduces reasonable fracture properties at the macroscale. Therefore, the proposed approach can serve as a basis for multiscale fracture modeling of hydraulic mass concrete structures.
Abstract:
Sediment deposition problems have attracted the interest of engineers and researchers. Several experimental studies have been conducted on scour depth using turbulent jets. However, field observation and monitoring have rarely been reported. This study aimed to eliminate sediments on a tidal riverbed using a prototype device, which consisted of a set of submerged vertical water nozzles and submerged horizontal air nozzles. The effectiveness of the water jet in sediment removal during spring and neap tides was evaluated. The quantitative relationships of dimensionless parameters, such as (1) the relative sediment scour volume versus the number of flows from the jet exit, (2) the relative sediment scour volume versus the relative scour depth, and (3) the relative scour size versus the relative jet intensity, were analyzed. The results showed that the freshwater flowing to the sea affected the sediment scour volume during the falling cycle of spring tides. In contrast, the rising cycle of spring tides retarded the freshwater flow, resulting in a decrease in the sediment scour volume. A steep water surface slope accelerated the river flow and further influenced the cross-flow current around the study area. As a result, a highly diffusive turbulent flow was produced, causing suspended sediments to be rapidly removed from the scour hole center. An increase in the number of flows from the jets led to intensified diffusion of turbulent energy into the flow. The rapidly varying water depth caused jet energy to be dissipated before approaching the riverbed, and it significantly affected the scour process during the spring-tide period. The proposed equations can be used to estimate the scour volume, scour size, and re-suspended sediments in tidal rivers within defined ranges of parameters.
Abstract:
In rockfill dam engineering, particle breakage of rockfill materials is one of the major factors resulting in dam settlement. In this study, onedimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions (PSDs) were carried out. The tests focused on understanding the role of initial PSDs in the dense packing density, compressibility and crushability of coarse granular materials. The effects of fractal dimension (D) and size polydispersity (θ) of PSDs were quantitatively analyzed. Two different loading stages were identified from the logarithms of the stressestrain relationships, with the turning point marked as the yield stress. A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials. The packing density and low-pressure modulus increased monotonically with θ, and their peak values were attained at a D value of approximately 2.2. However, there was no unique correspondence between the dense packing density and low-pressure modulus. The particle breakage was influenced differently by the initial PSDs, and it decreased with the values of D and θ. The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests. The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.