Water science and engineering最新文献

Local scour around pipelines crossing rivers or in marine environments is a significant concern. It can lead to failure of the pipelines resulting in environmental side effects and economic losses. This study developed an experimental method to reduce local scour around pipelines with a steady flow of clear water by installing cylindrical and cubical sacrificial piles. Three sizes of sacrificial piles were examined in a linear arrangement. Sacrificial piles were installed on the upstream side of the pipeline at three distances. Maximum scour depth reduction rates below the pipeline were computed. The results showed that sacrificial piles could protect a pipeline from local scour. A portion of scoured sediment around the sacrificial piles was deposited beneath the pipeline. This sediment accumulation reduced the scour depth beneath the pipeline. Analysis of the experimental results demonstrated that the size of piles (d), the spacing between piles, and the distance between the pipe and piles (X_p) were the variables that reduced the maximum scour beneath the pipeline with a diameter of D. For the piles with d = 0.40D and 0.64D, X_p = 40D was the optimal distance to install a group of piles, and cubical piles could mitigate scour more effectively than cylindrical piles under similar conditions. For the piles with d = D, the greatest reduction in scour depth was achieved at X_p = 50D with any desired spacings between piles, and cylindrical piles in this dimension could protect the pipeline against scour more effectively than cubical piles.

Sediment accumulation on the bed of open sewers and drains reduces hydraulic efficiency and can cause localized flooding. Slotted invert traps installed underneath the bed of open sewers and drains can eliminate sediment build-up by catching sediment load. Previous three-dimensional (3D) computational studies have examined the particle trapping performance of invert traps of different shapes and depths under varied sediment and flow conditions, considering particles as spheres. For two-dimensional and 3D numerical modeling, researchers assumed the lid geometry to be a thin line and a plane, respectively. In this 3D numerical study, the particle trapping efficiency of a slotted irregular hexagonal invert trap fitted at the flume bottom was examined by incorporating the particle shape factor of non-spherical sewage solid particles and the thicknesses of upstream and downstream lids over the trap in the discrete phase model of the ANSYS Fluent 2020 R1 software. The volume of fluid (VOF) and the realizable k–ε turbulence models were used to predict the velocity field. The two-dimensional particle image velocimetry (PIV) was used to measure the velocity field inside the invert trap. The results showed that the thicknesses of upstream and downstream lids affected the velocity field and turbulent kinetic energy at all flow depths. The joint impact of the particle shape factor and lid thickness on the trap efficiency was significant. When both the lid thickness and particle shape factor were considered in the numerical modeling, trap efficiencies were underestimated, with relative errors of −8.66% to −0.65% in comparison to the experimental values of Mohsin and Kaushal (2017). They were also lower than the values predicted by Mohsin and Kaushal (2017), which showed an overall overestimation with errors of −2.3% to 17.4%.

Considering that we still do not fully understand the behavior of air pockets trapped in rainstorm systems and water flow changes inside pipes, the study of actual geysers presents many challenges. In this study, three-dimensional numerical models were developed to investigate the mechanisms of geyser events triggered by rapid filling flows at different scales. The results showed that, in the first stage of the water–air mixture of the prototype model, a large amount of air was released quickly, and the subsequent overflow lasted for a more extended period. The transport capacity of the downstream pipe, as a critical factor, significantly influenced the water–air interaction of the geyser. Restricting the outlet area and increasing the outlet pressure simultaneously resulted in a stronger geyser. The equivalent density of the water–air mixture increased as the scale decreased during the geyser event.

Submerged vegetation commonly grows and plays a vital role in aquatic ecosystems, but it is also regarded as a barrier to the passing flow. Numerical simulations of flow through and over submerged vegetation were carried out to investigate the effect of vegetation density on flow field. Numerical simulations were computationally set up to replicate flume experiments, in which vegetation was mimicked with flexible plastic strips. The fluid–structure interaction between flow and flexible vegetation was solved by coupling the two modules of the COMSOL packages. Two cases with different vegetation densities were simulated, and the results were successfully validated against the experimental data. The contours of the simulated time-averaged streamwise velocity and Reynolds stress were extracted to highlight the differences in mean and turbulent flow statistics. The turbulence intensity was found to be more sensitive to vegetation density than the time-averaged velocity. The developing length increased with the spacing between plants. The snapshots of the bending vegetation under instantaneous velocity and vorticity revealed that flexible vegetation responded to the effects of eddies in the shear layer by swaying periodically. The first two rows of vegetation suffered stronger approaching flow and were prone to more streamlined postures. In addition, the origin of tip vortices was investigated via the distribution of vorticity. The results reveal the variation of flow properties with bending submerged vegetation and provide useful reference for optimization of restoration projects.

Excessive turbidity in water is aesthetically unappealing and severely malfunctions the photosynthesis process of aquatic ecosystems. This study aimed to evaluate the effectiveness of a nanocomposite adsorbent made of graphene oxide–keratin–chitosan for removing turbidity from tannery influent. The nanocomposite was fabricated with simple solution casting methods. Material dispersibility, bonding between composite materials (amide linkage), and the surface morphology of the nanocomposite were analyzed with the ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. At pH of 6, 2 g/L of adsorbent and a 25-min contact time resulted in about 88% of turbidity elimination. After the adsorption process, the total suspended solids, total dissolved solids, salinity, biochemical oxygen demand, and chemical oxygen demand of the tannery wastewater were reduced by 55%, 29%, 12%, 58%, and 75%, respectively. The optimum dosage of the nanocomposite with the maximum turbidity removal capacity was 12.62 mg/g. According the adsorption kinetic and isotherm models, the graphene oxide–keratin–chitosan nanocomposite played a key role in the turbidity removal process with chemisorption and electrostatic multilayer adsorption. This study provided methodological and mechanistic insights into the procedures of investigating the removal of turbidity from tannery wastewater with a novel composite material.

In this study, simultaneous nitrification and autotrophic denitrification (SNAD) with either elemental sulfur or pyrite were investigated in fluidized bed reactors in mesophilic conditions. The reactor performance was evaluated at different ammonium (12–40 mg/L of ${\text{NH}}_4^{+}-N$), nitrate (35–45 mg/L of ${\text{NO}}_3^{-}\text{-}N$), and dissolved oxygen (DO) (0.1–1.5 mg/L) concentrations, with a hydraulic retention time of 12 h. The pyrite reactor supported the SNAD process with a maximum nitrogen removal efficiency of 139.5 mg/(L⸱d) when the DO concentration was in the range of 0.8–1.5 mg/L. This range, however, limited the denitrification efficiency of the reactor, which decreased from 90.0% ± 5.3% in phases II–V to 67.9% ± 7.2% in phases VI and VII. Sulfate precipitated as iron sulfate (FeSO₄/Fe₂(SO₄)₃) and sodium sulfate (Na₂SO₄) minerals during the experiment. The sulfur reactor did not respond well to nitrification with a low and unstable ammonium removal efficiency, while denitrification occurred with a nitrate removal efficiency of 97.8%. In the pyrite system, the nitrifying bacterium Nitrosomonas sp. was present, and its relative abundance increased from 0.1% to 1.1%, while the autotrophic denitrifying genera Terrimonas, Ferruginibacter, and Denitratimonas dominated the community. Thiobacillus, Sulfurovum, and Trichlorobacter were the most abundant genera in the sulfur reactor during the entire experiment.

Jets caused by burst tubes erode the surrounding soil, eventually leading to issues such as ground collapse. It is therefore highly important to study the mechanisms of soil erosion caused by jets after pipeline leakage. To investigate the water–soil interaction mechanisms of pipe leakage, this study used transparent soil and developed a three-dimensional experimental device to observe the fluidization process. Changes in the boundary of the fluidization transition area were investigated, and a formula for calculating the soil damage area was derived. The results showed three different shapes of the fluidized cavity appearing in the fluidization process. The particles initially moved upward and then gradually transitioned into a state of backflow. The effects of particle size, upper load, and porosity on fluidization were also analyzed. It was found that soil with a large particle size and a lower porosity under a heavy upper load can effectively restrain fluidization. Therefore, large-diameter and dense soil can be used as pipe-covering material.

The deterioration of the surface water environment has become a serious challenge for water resources management due to increasing anthropogenic disturbance. Water resources protection requires control of potential pollution sources. In this study, 99 water samples were collected from a river in a typical agricultural city of Anhui Province in eastern China, and these samples were analyzed in terms of pH, electrical conductivity, and the concentrations of F⁻, Cl⁻, ${\text{SO}}_4^{2-}$, Na⁺, K⁺, Mg²⁺, Ca²⁺, As, Cr, Cu, Zn, and Pb. Cluster analysis, co-occurrence network analysis, and principal component analysis/factor analysis were conducted to qualitatively identify the potential sources of river water pollution in the study area. An absolute principal component score–multiple linear regression receptor model was used to quantitatively evaluate the contribution of each source to water quality parameters. The results showed that all observed water quality indices met the quality criteria specified in the Chinese drinking water standards, except for pH, ρ(F⁻), ρ(${\text{SO}}_4^{2-}$), and ρ(As). The heat map showed that the frequent recharge of pollutants from the tributaries during the wet season was the main reason for the deterioration of water quality. Five sources of river water pollution were identified, and their contribution ratios in a descending order were as follows: the geogenic process (24%) > agricultural activities (21%) > poultry farming sources (17%) > domestic pollution (9%) > transportation pollution (5%). Therefore, controlling pollution from agricultural activities, strengthening the regulation of livestock farming, and improving the sewage network are the recommended strategies for improving the quality of surface water resources in this area.

Water pollution caused by industrial dyes has become a severe problem in the modern world. Biosorbents can be used in an eco-friendly manner to remove industrial dyes. In this study, five biosorbents were selected: palmyrah sprout casing (PSC), manioc peel, lime peel, king coconut husk, and coconut kernel. Batch adsorption experiments were conducted to identify the best biosorbent with the highest ability to adsorb methylene blue (MB) from wastewater. The detailed mechanisms of PSC used in the adsorptive removal of MB in aqueous phase were investigated. Of the five biosorbents, PSC exhibited the best removal performance with an adsorption capacity at equilibrium (q_e) of 27.67 mg/g. The q_e values of lime peel, king coconut husk, manioc peel, and coconut kernel were 24.25 mg/g, 15.29 mg/g, 10.84 mg/g, and 7.06 mg/g, respectively. To explain the mechanisms of MB adsorption with the selected biosorbents, the Fourier transform infrared (FTIR) spectrometry and X-ray diffraction (XRD) analyses were performed to characterize functional properties, and isotherm, kinetic, rate-limiting, and thermodynamic analyses were conducted. The FTIR analysis revealed that different biosorbents had different functional properties on their adsorptive surfaces. The FTIR and XRD results obtained before and after MB adsorption with PSC indicated that the surface functional groups of carbonyl and hydroxyl actively participated in the removal process. According to the isotherm analysis, monolayer adsorption was observed with the Langmuir model with a determination coefficient of 0.998. The duration to reach the maximum adsorption capacity for MB adsorption with PSC was 120 min, and the adsorption process was exothermic due to the negative enthalpy change (−9.950 kJ/mol). Moreover, the boundary layer thickness and intraparticle diffusion were the rate-limiting factors in the adsorption process. As a new biosorbent for MB adsorption, PSC could be used in activated carbon production to enhance the performance of dye removal.

For a water supply system with long-distance diversion pipelines, in addition to the water hammer problems that occur beyond pumps, the safety of the water diversion pipeline in front of pumps also deserves attention. In this study, a water hammer protection scheme combined with an overflow surge tank and a regulating valve was developed. A mathematical model of the overflow surge tank was developed, and an analytical formula for the height of the overflow surge tank was derived. Furthermore, a practical water supply project was used to evaluate the feasibility of the combined protection scheme and analyze the sensitivity of valve regulation rules. The results showed that the combined protection scheme effectively reduced the height of the surge tank, lessened the difficulties related to construction, and reduced the necessary financial investment for the project. The two-stage closing rule articulated as fast first and then slow could minimize the overflow volume of the surge tank when the power failure occurred, while the two-stage opening rule articulated as slow first and then fast could be more conducive to the safety of the water supply system when the pump started up.