Water science and engineering最新文献

Nano zero-valent iron (nZVI) and sulfidation-modified nZVI (S-nZVI) were synthesized and used to remove hexavalent chromium (Cr(VI)) in wastewater. Characterization of the products showed that the sulfidation process significantly changed the morphology of nZVI, with enhanced crystallinity. The effects of S/Fe ratio, pH value, and reaction temperature on Cr(VI) removal were studied. A S/Fe ratio of 0.5 was the most appropriate parameter, with a removal efficiency of 98% in the condition of pH = 2. The effects of anions (Cl⁻, ${\text{NO}}_3^{-}$, ${\text{CO}}_3^{2-}$, and ${\text{SO}}_4^{2-}$) and cations (Ca²⁺ and Mg²⁺) on the Cr(VI) removal efficiency were investigated, and the relevant mechanisms were discussed. The Cr(VI) removal efficiency of S-nZVI was significantly greater than that of nZVI, mainly owing to the existence of FeS layers that could protect Fe⁰ cores and prompt electron transfer. The aging and cycling experiments showed that S-nZVI could maintain its reactivity when facing the corrosion of water, and showed cycling stability. Thus, S-nZVI is an effective and feasible agent for the remediation of Cr(VI)-contained wastewater.

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, ${\text{NH}}_4^{+}-N$ showed a positive flux from the sediment to the overlying water, but ${\text{NO}}_2^{-}\text{-}N$ and ${\text{NO}}_3^{-}\text{-}N$ showed positive fluxes from the sediment to the overlying water only in early stages. In winter, ${\text{NH}}_4^{+}\text{-}N$ showed a positive flux from the sediment to the overlying water, but ${\text{NO}}_2^{-}\text{-}N$ and ${\text{NO}}_3^{-}\text{-}N$ 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.

Deep storage tunnels (DSTs) are used in densely urbanized areas to relieve stormwater collection systems, thereby reducing urban floods and runoff pollution, due to their substantial storage capacity. The computation of the hydraulic characteristics and flow trajectories of DSTs under rapid filling scenarios can help to predict sediment deposition and pollutant accumulation associated with the stored runoff, as well as the likelihood of operational problems, such as excessive surging. However, such assessments are complicated by various inflow scenarios encountered in tunnel systems during their operation. In this study, the Suzhou River DST in China is selected as a study case. Particles were tracked, and hydraulic analysis was conducted with scaled model experiments and numerical models. The flow field, particle movement, air‒water phase, and pressure patterns in the DST were simulated under various one- and two-sided inflow scenarios. The results showed that with regards to the design conditions involving two-sided inflows, flow reversals occurred with stepwise increases in the water surface and pressure. In contrast, this phenomenon was not observed under the one-sided inflow scenario. Under the asymmetric two-sided inflow scenarios, water inflows led to particle accumulation near the shaft, reducing the received inflows. However, under the symmetric inflow conditions, particles were concentrated near the middle of the tunnel. Compared to those under the symmetric inflow scenario, asymmetric inflow caused surface wave and entrapped air reductions. This study could provide support for regulation of the inflow of the Suzhou River DST and for prediction of sediment and pollutant accumulation.

Globalization has led to a rapid rise in energy consumption, making climate change one of the world's most pressing issues. As wastewater treatment plants (WWTPs) contribute to climate change by emitting greenhouse gases (GHGs), this study estimated the total GHG emissions of WWTPs by classifying them as either direct or indirect carbon emissions. The effectiveness of the use of solar photovoltaic systems and biogas produced by WWTPs in increasing energy recovery and reducing GHG emissions was investigated. This study demonstrated that the use of an up-flow anaerobic sludge blanket (UASB) reactor with a biogas flow of 9 120.77 m³/d and an activated sludge processing system (ASPS) reactor with a biogas flow of 14 004 m³/d, in addition to the energy production from the UASB reactor (6 421.8 MW⸱h per year) and the ASPS reactor (9 860.0 MW⸱h per year), yielded a reduction of 3 316.85 and 5 092.69 t of CO₂ equivalent per year, respectively. Furthermore, the co-design of wastewater processes could be utilized to optimize biogas energy recovery. Moreover, the use of solar photovoltaic systems reduced GHG emissions from WWTPs. This is important to the transition to renewable energy because it resulted in a 10%–40% reduction in carbon emissions from WWTPs. Integrating renewable energy sources, biogas, and solar energy could provide up to 88% of the annual energy requirements of WWTPs. Recommendations are provided for further research considering the limited availability of integrated resources for studying the simultaneous utilization of photovoltaic and biogas systems.

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.

The completely autotrophic nitrogen removal over nitrite (CANON) is a new type of nitrogen removal process developed in recent years. The control of dissolved oxygen (DO) in this process is relatively stringent, especially in low-substrate wastewater treatment. However, the results of studies on the operation of the process in different aeration modes are still controversial, and investigations on biofilm type CANON reactors are limited. In this study, a pilot-scale CANON bioreactor filled with suspended carriers was investigated on the treatment of wastewater at low ammonium concentrations, and the effect of the aeration mode on autotrophic nitrogen removal was evaluated. Seven conditions with various aeration on/off times and DO levels were tested. The results showed that an intermittent aeration with a 20-min/20-min aeration on/off time and DO concentrations of 1.0–1.3 mg/L at the end of the aeration period was appropriate, potentially inhibiting nitrite oxidizing bacteria (NOB) and keeping the total nitrogen (TN) removal rate at a relatively high level of 76.7% ± 2.5%. In the optimal aeration mode, the reactor achieved effluent TN and ${\text{NH}}_4^{+}\text{-}N$ concentrations of (11.1 ± 3.3) mg/L and (3.6 ± 2.3) mg/L, respectively, with a hydraulic retention time of 12 h and an influent ${\text{NH}}_4^{+}\text{-}N$ concentration of (48.6 ± 9.4) mg/L at 30.1°C ± 2.2°C. The results of metagenomic sequencing for microorganisms on carriers indicated that the main nitrogen removal bacteria in the reactor were Proteobacteria, Planctomycetes, and Nitrospirae. The NOB genus Nitrospira was completely inhibited by intermittent aeration. Candidatus Kuenenia had strong adaptability to low-concentration wastewater.

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 367.12 mg/g, a large adsorption coefficient of 4.0 × 10⁴ mL/g, and a high removal efficiency of 97.59%. The ${\text{UO}}_2^{2+}$ adsorption kinetics perfectly conformed to the pseudo-second-order reaction. The sorbent also exhibited an excellent selectivity for ${\text{UO}}_2^{2+}$ with other interfering metal ions.

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.

The offshore renewable energy industry has been developing farms of floating offshore wind turbines in water depths up to 100 m. In Vietnam, floating offshore wind turbines have been developed to increase the production of clean and sustainable energy. The mooring system, which is used to keep the turbine stable and ensure the safety and economic efficiency of wind power production, is an important part of a floating offshore wind turbine. Appropriate selection of the mooring type and mooring line material can reduce the risks arising from the motion of wind turbines. Different types of mooring line material have been simulated and compared in order to determine the optimal type with the minimum motion risk for a floating wind turbine. This study focused on numerical modeling of semi-taut mooring systems using nonlinear materials for a semi-submersible wind turbine. Several modeling approaches common to current practice were applied. Hydrodynamic analysis was performed to investigate the motion of the response amplitude operators of the floating wind turbine. Dynamic analysis of mooring systems was performed using a time domain to obtain the tension responses of mooring lines under the ultimate limit states and fatigue limit states in Vietnamese sea conditions. The results showed that the use of nonlinear materials (polyester and/or nylon) for mooring systems can minimize the movement of the turbine and save costs. The use of synthetic fibers can reduce the maximum tension in mooring lines and the length of mooring lines. However, synthetic fiber ropes showed highly nonlinear load elongation properties, which were difficult to simulate using numerical software. The comparison of the characteristics of polyester and nylon mooring lines showed that the maximum and mean tensions of the nylon line were less than those of the polyester line. In addition, the un-stretched length of the polyester line was greater than that of the nylon line under the same mean tension load. Therefore, nylon material is recommended for the mooring lines of a floating offshore wind turbine.

Increasing bacteria levels in the Lower Neches River caused by Hurricane Harvey has been of a serious concern. This study is to analyze the historical water sampling measurements and real-time water quality data collected with wireless sensors to monitor and evaluate water quality under different hydrological and hydraulic conditions. The statistical and Pearson correlation analysis on historical water samples determines that alkalinity, chloride, hardness, conductivity, and pH are highly correlated, and they decrease with increasing flow rate due to dilution. The flow rate has positive correlations with Escherichia coli, total suspended solids, and turbidity, which demonstrates that runoff is one of the causes of the elevated bacteria and sediment loadings in the river. The correlation between E. coli and turbidity indicates that turbidity greater than 45 nephelometric turbidity units in the Neches River can serve as a proxy for E. coli to indicate the bacterial outbreak. A series of statistical tools and an innovative two-layer data smoothing filter are developed to detect outliers, fill missing values, and filter spikes of the sensor measurements. The correlation analysis on the sensor data illustrates that the elevated sediment/bacteria/algae in the river is either caused by the first flush rain and heavy rain events in December to March or practices of land use and land cover. Therefore, utilizing sensor measurements along with rainfall and discharge data is recommended to monitor and evaluate water quality, then in turn to provide early alerts on water resources management decisions.