Abstract: Although big data is publicly available on water quality parameters, virtual simulation has not yet been adequately adapted in environmental chemistry research. Digital twin is different from conventional geospatial modeling approaches and is particularly useful when systematic laboratory/field experiment is not realistic (e.g., climate impact and water-related environmental catastrophe) or difficult to design and monitor in a real time (e.g., pollutant and nutrient cycles in estuaries, soils, and sediments). Data-driven water research could realize early warning and disaster readiness simulations for diverse environmental scenarios, including drinking water contamination.
Abstract: Suzhou City, located in the Yangtze River Delta in China, is prone to flooding due to a complex combination of natural factors, including its monsoon climate, low elevation, and tidally influenced position, as well as intensive human activities. The Large Encirclement Flood Control Project (LEFCP) was launched to cope with serious floods in the urban area. This project changed the spatiotemporal pattern of flood processes and caused spatial diversion of floods from the urban area to the outskirts of the city. Therefore, this study developed a distributed flood simulation model in order to understand this transition of flood processes. The results revealed that the LEFCP effectively protected the urban areas from floods, but the present scheduling schemes resulted in the spatial diversion of floods to the outskirts of the city. With rainstorm frequencies of 10.0 % to 0.5 %, the water level differences between two representative water level stations (Miduqiao (MDQ) and Fengqiao (FQ)) located inside and outside the LEFCP area, ranged from 0.75 m to 0.24 m and from 1.80 m to 1.58 m, respectively. In addition, the flood safety margin at MDQ and the duration with the water level exceeding the warning water level at FQ ranged from 0.95 m to 0.43 m and from 4 h to 22 h, respectively. Rational scheduling schemes for the hydraulic facilities of the LEFCP in extreme precipitation cases were developed according to flood simulations under seven scheduling scenarios. This helps to regulate the spatial flood diversion caused by the LEFCP during extreme precipitation.
Abstract: Constructed wetlands (CW) are well known nature-based systems for water treatment. This study evaluated the efficiency and effectiveness of seven domestic wastewater treatment systems based on horizontal flow CWs in Jarabacoa, the Dominican Republic. The results showed that the CWs were efficient in reducing the degree of contamination of wastewater to levels below the Dominican wastewater discharge standards for parameters such as the 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand, but not for the removal of phosphorus and fecal coliforms. In addition, a horizontal flow subsurface wetland in the peri-urban area El Dorado was evaluated in terms of the performance of wastewater treatment in tropical climatic conditions. The concentrations of heavy metals, such as zinc, copper, chromium, and iron, were found to decrease in the effluent of the wetland, and the concentrations for nickel and manganese tended to increase. The levels of heavy metals in the effluent were lower than the limit values of the Dominican wastewater discharge standards. The construction cost of these facilities was around 200 USD per population equivalent, similar to the cost in other countries in the same region. This study suggested some solutions to the improved performance of CWs:selection of a microbial flora that guarantees the reduction of nitrates and nitrites to molecular nitrogen, use of endemic plants that bioaccumulate heavy metals, combination of constructed wetlands with filtration on activated carbon, and inclusion of water purification processes that allow to evaluate the reuse of treated water.
Abstract: Coastal wetlands are hotspots for nitrogen (N) cycling, and crab burrowing is known to transform N in intertidal marsh soils. However, the underlying mechanisms remain unclear. This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment-water interface in coastal tidal flat wetlands. The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth. Due to crab disturbance, nitrogen fluxes at the sediment-water interface were much greater in the box with crabs than in the box without crabs. In summer, NH4+-N showed a positive flux from the sediment to the overlying water, but NO2--N and NO3--N showed positive fluxes from the sediment to the overlying water only in early stages. In winter, NH4+-N showed a positive flux from the sediment to the overlying water, but NO2--N and NO3--N both exhibited positive and negative fluxes. These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8-15 cm in summer and directly promote nitrification at the sediment surface.
Abstract: Three-dimensional (3D) porous absorbents have attracted significant attention in the oily wastewater treatment technology due to their high porosity and elasticity. Given their amphiphilic surface, they have a propensity to simultaneously absorb water and oil, which restricts their range of applications. In this study, a reduced graphene oxide and titanium dioxide nanocomposite (rGO/TiO2) was used to fabricate an ultrahydrophobic melamine sponge (MS) through interfacial modification using a solution immersion technique. To further modify it, polydimethylsiloxane (PDMS) was grafted onto its surface to establish stronger covalent bonds with the composite. The water contact angle of the sponge (rGO/TiO2/PDMS/MS) was 164.2°, which satisfies the condition for ultrahydrophobicity. The evidence of its water repellency was demonstrated by the Cassie-Baxter theory and the lotus leaf effect. As a result of the increased density of rGO/TiO2/PDMS/MS, it recorded an initial capacity that was 2 g/g lower than the raw MS for crude oil absorption. The raw MS retained 53 % of its initial absorption capacity after 20 cycles of absorption, while rGO/TiO2/PDMS/MS retained 97 %, suggesting good recyclability. Excellent oil and organic solvent recovery (90 %-96 %) was demonstrated by rGO/TiO2/PDMS/MS in oil-water combinations. In a continuous separation system, it achieved a remarkable separation efficiency of 2.4×106 L/(m3·h), and in turbulent emulsion separation, it achieved a demulsification efficiency of 90 %-91 %. This study provides a practical substitute for massive oil spill cleaning.
Abstract: Removal of uranium(VI) from nuclear wastewater is urgent due to the global nuclear energy exploitation. This study synthesized novel sponge-like 3D porous materials for enhanced uranium adsorption by combining electrospinning and fibrous freeze-shaping techniques. The materials possessed an organic-inorganic hybrid architecture based on the electrospun fibers of polyacrylonitrile (PAN) and SiO2. As a supporting material, the surface of fibrous SiO2 could be further functionalized by cyano groups via (3-cyanopropyl) triethoxysilane. All the cyano groups were turned into amidoxime (AO) groups to obtain a amidoxime-functionalized sponge (PAO/SiO2-AO) through the subsequent amidoximation process. The proposed sponge exhibited enhanced uranium adsorption performance with a high removal capacity of 367.12mg/g, a large adsorption coefficient of 4.0×104 mL/g, and a high removal efficiency of 97.59 %. The UO22+ adsorption kinetics perfectly conformed to the pseudo-second-order reaction. The sorbent also exhibited an excellent selectivity for UO22+ with other interfering metal ions.
Abstract: Bio-jarosite, an iron mineral synthesized biologically using bacteria, is a substitute for iron catalysts in the Fenton oxidation of organic pollutants. Iron nanocatalysts have been widely used as Fenton catalysts because they have a larger surface area than ordinary catalysts, are highly recyclable, and can be treated efficiently. This study aimed to explore the catalytic properties of bio-jarosite iron nanoparticles synthesized with green methods using two distinct plant species:Azadirachta indica and Eucalyptus gunni. The focus was on the degradation of dicamba via Fenton oxidation. The synthesized nanoparticles exhibited different particle size, shape, surface area, and chemical composition characteristics. Both particles were effective in removing dicamba, with removal efficiencies of 96.8 % for A. indica bio-jarosite iron nanoparticles (ABFeNPs) and 93.0 % for E. gunni bio-jarosite iron nanoparticles (EBFeNPs) within 120 min of treatment. Increasing the catalyst dosage by 0.1 g/L resulted in 7.6 % and 43.0 % increases in the dicamba removal efficiency for EBFeNPs and ABFeNPs with rate constants of 0.025 min-1 and 0.023 min-1, respectively, confirming their catalytic roles. Additionally, the high efficiency of both catalysts was demonstrated through five consecutive cycles of linear pseudo-first-order Fenton oxidation reactions.
Abstract: 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 %.
Abstract: Currently, more than ten ultrahigh arch dams have been constructed or are being constructed in China. Safety control is essential to long-term operation of these dams. This study employed the flexibility coefficient and plastic complementary energy norm to assess the structural safety of arch dams. A comprehensive analysis was conducted, focusing on differences among conventional methods in characterizing the structural behavior of the Xiaowan arch dam in China. Subsequently, the spatiotemporal characteristics of the measured performance of the Xiaowan dam were explored, including periodicity, convergence, and time-effect characteristics. These findings revealed the governing mechanism of main factors. Furthermore, a heterogeneous spatial panel vector model was developed, considering both common factors and specific factors affecting the safety and performance of arch dams. This model aims to comprehensively illustrate spatial heterogeneity between the entire structure and local regions, introducing a specific effect quantity to characterize local deformation differences. Ultimately, the proposed model was applied to the Xiaowan arch dam, accurately quantifying the spatiotemporal heterogeneity of dam performance. Additionally, the spatiotemporal distribution characteristics of environmental load effects on different parts of the dam were reasonably interpreted. Validation of the model prediction enhances its credibility, leading to the formulation of health diagnosis criteria for future long-term operation of the Xiaowan dam. The findings not only enhance the predictive ability and timely control of ultrahigh arch dams' performance but also provide a crucial basis for assessing the effectiveness of engineering treatment measures.
Abstract: 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 (Xp) 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, Xp=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 Xp=50D with any desired spacings between piles, and cylindrical piles in this dimension could protect the pipeline against scour more effectively than cubical piles.
Abstract: Lateral intakes are common in rivers. The pump efficiency and sediment deposition are determined by the local hydrodynamic characteristics and mainstream division width. The hydraulic characteristics of lateral withdrawal from inclined river slopes at different intake elevations should be investigated. Meanwhile, the division width exhibits significant vertical non-uniformity at an inclined river slope, which should be clarified. Hence, a three-dimensional (3-D) hydrodynamic and particle-tracking model was developed with the Open Source Field Operation and Manipulation (OpenFOAM), and the model was validated with physical model tests for 90° lateral withdrawal from an inclined side bank. The flow fields, withdrawal sources, and division widths were investigated with different intake bottom elevations, withdrawal discharges, and main channel velocities. This study showed that under inclined side bank conditions, water entered the intake at an oblique angle, causing significant 3-D spiral flows in the intake rather than two-dimensional closed recirculation. A lower withdrawal discharge, a lower bottom elevation of the intake, or a higher main channel velocity could further strengthen this phenomenon. The average division width and turbulent kinetic energy were smaller under inclined side bank conditions than under vertical bank conditions. With a low intake bottom elevation, a low withdrawal discharge, or a high main channel velocity, the sources of lateral withdrawal were in similar ranges near the local inclined bank in the vertical direction. Under inclined slope conditions, sediment deposition near the intake entrance could be reduced, compared to that under vertical slope conditions. The results provide hydrodynamic and sediment references for engineering designs for natural rivers with inclined terrains.
