Water Flow Research Articles

Green Fabrication Methods and Performance Evaluation of Eco-Friendly Membranes for Enhanced Oil-Water Separation

A significant step toward sustainability in membrane technology has been made with the substitution of eco-friendly alternatives for conventional membrane fabrication techniques. A green fabrication process, which is derived from renewable and biodegradable materials, offers a promising solution to environmental concerns associated with conventional membrane fabrication. Additionally, by utilizing eco-friendly materials, the toxicity footprint of membrane fabrication techniques can be reduced considerably. This study aims to transform the non-solvent induced phase separation (NIPS) method into a green process, by utilizing a biodegradable polymeric base (polylactic acid; PLA), a green solvent (dimethyl sulfoxide; DMSO), and a green additive (deep eutectic solvents; DES). The membranes were thoroughly characterized to understand their structural transformations, and their performance was evaluated. Filtration experiments demonstrated a notable increase in the water flux using 20wt% PLA polymer, DMSO as a solvent, and 1wt% choline chloride: ethylene glycol (ChCl:EG) (1:2) as an additive. This resulted in a flux of 1138L/m2.h, a notable increase compared to 554L/m2.h achieved with 20wt% PLA using a conventional solvent (PLA-C). This increase in flux was also complemented by an increase in the membrane's oil rejection efficiency, (oil rejection of 96% for the modified membrane), as well as enhanced anti-fouling properties (maintained in interval flux recovery ratio; FRR of 80%). The findings suggest that creating environmentally friendly membranes through a sustainable process has the potential to improve both ecological impact and performance, hence progressing environmentally conscious industrial practices.

Spatial correlations and risk transmission of virtual water flow at city scale: A case study of the Yellow River Basin

By introducing virtual water (VW) flow correlation coefficients and risk indicators, this study examines the VW transmission relationship between urban agglomerations and cities in the Yellow River Basin (YRB) and its impact on regional water resources pressure. The results show that: except for the Shandong Peninsula Urban Agglomeration (SPUA) and Central Plains Urban Agglomeration (CPUA), the other urban agglomerations primarily act as VW exporting regions, while virtual water-importing cities are concentrated in the eastern regions. Notably, the Ningxia Urban Agglomeration (NUA) demonstrates significantly higher values in VW impact and sensitivity coefficients than the remaining six urban agglomerations. First-tier cities generally display lower virtual water impact and sensitivity coefficients, whereas emerging cities exhibit the opposite trend. Additionally, we observe uneven risk variations between VW importing and exporting regions. Taking NUA as an example, the risk increase resulting from VW exports significantly exceeds the risk reduction associated with VW imports in the corresponding regions. It's important to highlight that first-tier cities consistently decrease water resource risk through VW imports in both study years. However, among second and third-tier cities, only 38.9% experience reduced water resource risk through VW imports. Therefore, we recommend a focused examination of VW imports and exports in western region urban agglomerations, cities, and second and third-tier cities within the watershed. Leveraging virtual water's asymmetric and high-value transfer can alleviate water resource pressure and scarcity risks in high-pressure regions by shifting them to lower-pressure regions, thus mitigating water resource stress across regions.

The preparation technology and catalytic mechanism of PVDF/PVP/a-MoSx porous membrane for water flow driven piezoelectric PMS activation

Piezoelectric catalysis couples with peroxymonosulfate (PMS) activation technology can efficiently increase the yield of reactive oxygen species (ROS). Herein, a novel flexible polyvinylidene difluoride/polyvinyl pyrrolidone/amorphous molybdenum sulfide (PVDF/PVP/a-MoSx) membrane with finger-like pore structure was prepared by non-solvent induced phase separation (NIPS) method. As a result, a-MoSx nanosheets can be exposed out of the pores to provide multiple active sites. The PVDF/PVP/a-MoSx with large dipole moment can form enhanced polarization field under water flow to accelerate the charges separation and transfer, thereby promoting the breakage of the OO bond of PMS. The mechanism of piezo-photocatalytic activated PMS was confirmed by COMSOL multiphysics simulations, electrochemical experiments, contribution of active species and DFT calculations. Moreover, a self-cycling degradation reactor was proved more effective in generating piezoelectric potential and improving the degradation efficiency, supporting the practical potential of this strategy. This study provides a new platform to develop piezoelectric porous membrane for enhanced PMS activation under low density flow water energy.

A preliminary evaluation of the effects of aquatic environments on the recovery of fingermarks on porous substrates

Latent fingermark detection can become increasingly difficult in the weeks following deposition, due to chemical and physical changes influenced by environment. There has been increased research interest into ageing mechanisms of fingermark residue, however these studies have typically been conducted in dry, indoors conditions. Less information is available regarding degradation processes that may occur in scenarios involving water and the potential longevity of porous substrates under such conditions. A pilot study was conducted to investigate the performances of Oil Red O (ORO) and physical developer (PD) on samples submerged in different aquatic environments in a laboratory setting. Charged fingermarks from three donors were deposited on copy paper and immersed in either salt water or freshwater; still or with water flow. Samples were treated at multiple intervals (1, 12, 20 and 40 days) after submersion. Results showed that high quality of development could be achieved up to 40 days after immersion. The overall performances of ORO and PD were generally unaffected in the early stages of the study. Physical and chemical degradation of both latent residue and substrate were observed, which were increased by salt and water movement. While PD appeared to be less affected by potential chemical changes, it was less effective than ORO due to substrate degradation in moving salt water. These results present the first steps towards better understanding the practical effects of degradation processes specific to fingermarks on porous substrates underwater.

Off-Design Performance Optimization for Steam-Water Dual Heat Source ORC Systems

High-pressure steam and hot water often coexist as industrial waste heat. In this study, dual loop and single loop ORC systems are designed for 700 kPa, 4.1kg/s steam, and 90 ℃, 122.36kg/s hot water conditions to study the off-design performance when steam or hot water conditions change. To maximize net output power, we employ a particle swarm optimization algorithm to optimize the evaporation and condensation temperatures. The results show that within the specified hot water conditions, the evaporation and condensation temperatures of D-ORC's low-pressure loop and S-ORC increase with rising hot water inlet temperature and flow rate. The S-ORC demonstrates a higher net output power growth rate as hot water flow rate and temperature rise. Under specific steam conditions, when the steam outlet is in a gas-liquid two-phase state, D-ORC's maximum net output power is 1.7% higher than that of the S-ORC, with little variation in optimal evaporation and condensation temperatures with respect to steam inlet pressure. At a 3.5kg/s steam flow rate, the D-ORC's high-pressure loop becomes ineffective, whereas S-ORC efficiently adjusts heat exchange capacity under diverse steam-water conditions, Consequently, the D-ORC's average net output power is 34.2% lower than that of the S-ORC.

A generalized numerical model for clonal growth in scleractinian coral colonies.

Coral reefs, vital ecosystems supporting diverse marine life, are primarily shaped by the clonal expansion of coral colonies. Although the principles of coral clonal growth, involving polyp division for spatial extension, are well-understood, numerical modelling efforts are notably scarce in the literature. In this article, we present a parsimonious numerical model based on the cloning of polyps, using five key parameters to simulate a range of coral shapes. The model is agent-based, where each polyp represents an individual. The colony's surface expansion is dictated by the growth mode parameter (s), guiding the preferred growth direction. Varying s facilitates the emulation of diverse coral shapes, including massive, branching, cauliflower, columnar and tabular colonies. Additionally, we introduce a novel approach for self-regulatory branching, inspired by the intricate mesh-like canal system and internode regularity observed in Acropora species. Through a comprehensive sensitivity analysis, we demonstrate the robustness of our model, paving the way for future applications that incorporate environmental factors, such as light and water flow. Coral colonies are known for their high plasticity, and understanding how individual polyps interact with each other and their surroundings to create the reef structure has been a longstanding question in the field. This model offers a powerful framework for studying these interactions, enabling a future implementation of environmental factors and the possibility of identifying the key mechanisms influencing coral colonies' morphogenesis.

A convection-diffusion-reaction system with discontinuous flux modelling biofilm growth in slow sand filters

A Slow Sand Filter (SSF) consists of biofilm attached to saturated packed sand with supernatant water on top, through which water flows by gravity. SSFs are used in the production of drinking water to improve water quality and remove pathogens, and, as they use biological filtration via the microbes present in the biofilm, they are simple and cheap to construct. A drawback of SSFs is that the difficult sampling and the complex dynamics associated with biofilm growth of microbes pose an obstacle for analysis and predictions. In order to overcome this issue, a mathematical model consisting of a non-linear convection-diffusion-reaction system with discontinuous flux is developed from first principles as a unified framework for the dynamics in time and depth of the biofilm and microbial community, where a variety of ecological models can be included in the reaction terms, which also contain attachment, detachment and transfer processes. The multi-phase approach considers three main physical volumes: a biofilm matrix, the water volume enclosed by it and the flowing suspension through the SSF surrounding the biofilm. The only input data needed are the inflow concentrations and rate, light irradiation and temperature. The model includes a Cahn–Hilliard-type equation for the biofilm velocity in the supernatant water. A numerical scheme that preserves physical properties of the solution is also presented. This is achieved with a time-splitting scheme using an upwind scheme with an adaptive time-step size that ensures positivity of the solution under a CFL condition and a reasonable assumption on the separate numerical solution of the Cahn–Hilliard-type equation. The latter is solved numerically with a semi-implicit finite-difference scheme using a mixed form of the equation. The flexible model framework with its numerical scheme allows for including a variety of ecological models, making the investigation and development of increasingly complex simulations possible. Simulations with different model parameters are shown to be qualitatively consistent with the literature.

Contraction of the radius of maximum symmetric rotational kinetic energy during the intensification of Tropical Cyclone Khanun (2017)

Tropical cyclone (TC) Khanun in 2017 was simulated in this study by the Weather Research and Forecasting (WRF) model. The observation-validated simulation data were used to examine how asymmetric rotational and environmental flows played the roles in determining the contraction of the radius of maximum kinetic energy of symmetric rotational flow (Kψs). The radius of maximum Kψs was contracted rapidly before rapid intensification (RI) and moved inward slowly, then barely moved, and moved inward slowly again during RI.The conversion from kinetic energy of asymmetric rotational flow (Kψa) to Kψs was induced by advection of asymmetric rotational tangential wind by asymmetric divergent radial wind. The conversion and convergence of inward flux of Kψs led to the rapid contraction before RI. During RI, in additional to horizontal and vertical flux convergence of Kψs, the conversion from environmental kinetic energy (Ke) to Kψs through the interaction between Kψs and symmetric radial environmental flow was important for the second slow contraction.

Rainwater shocks and economic growth: The role of the water cycle partition

This paper improves our understanding of how rainwater impacts economic growth by investigating the effects of overlooked properties of the water cycle. First, we consider the natural separation of rainwater into flows of blue water (i.e., the water that runs off towards rivers) and green water (i.e., that remaining in the soil). Second, we account for the presence of surface and groundwater stocks. These considerations allow us to comprehensively address the whole partition of rainwater, which, upon reaching the ground, splits into distinct water resources that determine water availability inland. Our analyses on a global panel coupling sub-national economic and hydrological data show that rainwater does increase growth, but do so differently depending on its partition. Specifically, blue water leads to more economic growth than green water at the margin, but, because two thirds of terrestrial water is green, the latter contributes more to growth in total. By missing this crucial partition, we find that commonly used rainwater measurements overstate rainwater’s contribution to growth (by about two). Our analyses further indicate that, although groundwater reserves always mitigate the impacts of rainwater reduction on growth, surface water reserves sometimes amplify regional dependence to rainwater (depending on sector, income and reserve types).

Modeling of Flood Wave Propagation Due to Hemren Dam Failure

The occurrence of dam failures and the consequent floods pose substantial risks to submerged regions, and their unpredictability increases the hazard of their impact. This research simulates the flood event scenario due to the dam failure of the Hemrem dam in Diyala Governorate, Iraq. HEC-RAC model jas been used to modeling the Hemren dam failure. The generated flood waves are routed downstream until the confluence of the Diyala and Tigris rivers, covering a large study area of 5,378.5 km². The configuration of the model's geometry is formulated using the Digital Elevation Model (DEM) that encompasses the geographical extent of the Diyala River study area, from Hemren Dam to the confluence with the Tigris River south of Baghdad. The length of this reach is approximately 210 km. Based on the inundation maps, the region's geography is classified as having catastrophic constraints due to the water depth and flow rate. The results demonstrate how to predict the magnitude of floods and highlight the severity if Hemren Dam were to fail. This underscores the need for effective risk management. Furthermore, the maps created by this study can be utilized to develop long-term flood control plans.

Inclined interfacial solar evaporator using polypyrrole/polydopamine composites for efficient desalination and salinity-driven electricity generation

Water-electricity cogeneration using solar energy is an innovative technology to address global freshwater shortages and energy demands. Here, we designed an inclined evaporator based on polypyrrole/polydopamine photothermal materials for efficient water evaporation and electricity cogeneration. Due to the ingenious inclined structure of the evaporator, the water transport was highly promoted by gravity and siphon effect. This process not only improves the evaporation flux of water, but also create a salinity gradient that can be used for further electricity generation. The designed inclined PPy/PDA@MF evaporator exhibits an evaporation flux of 3.02 kg m−2 h−1 under one sun irradiance and achieves an open-circuit voltage of 56 mV during the electricity generation.

Surface wettability and capillary flow of water in nanoslits of two-dimensional hexagonal-boron nitride

Surface wettability and capillary flow of water in nanoslits of two-dimensional hexagonal-boron nitride

Fugacity model covering abiotic and biotic matrices to investigate the transfer and fate of perfluoroalkyl acids in a large shallow lake of eastern China

Solving the challenges faced during the measurement of the cross-interface transfer of perfluoroalkyl acids (PFAAs) in lakes is crucial for clarifying environmental behaviours of these chemicals and their efficient governance. This study developed a multimedia fugacity model based on the quantitative water–air–sediment interaction (QWASI) covering abiotic/biotic matrices to investigate the cross-interface transfer and fate of PFAAs in Luoma Lake, a typical PFAA-contaminated shallow lake in eastern China. The accuracy and reliability of the established model were confirmed using Percent bias and Monte Carlo simulation, respectively. Using the QWASI model, the multimedia transfer of the PFAAs and their accumulation and persistence in different sub-compartments were described and measured, and the differences among individual PFAAs were explored. The simulation results showed that the sedimentation and resuspension of PFAAs were the most intense cross-interfacial transfers, and the sediments served as a chemical sink in the long term. A significant negative correlation of NC-F (the number of CF bonds) with the relative outflow flux (TW·out-ct) but a positive correlation with the relative net transfer across the interface between water and aquatic plants (Tp-ct) was detected, indicating that the PFAA migration capacity decreased but the bioaccumulation potential increased with the CF bond number. The persistence in water (Pw) of individual PFAAs ranged from 19.65d (PFOA) to 32.22d (PFOS), with an average of 26.15d; their persistence in sediment (Ps) ranged from 432d (PFBA) to 3216d (PFOS), with an average of 1524d, increasing linearly with an increase in NC-F. The water advection flows into and out of the lake (QW·in and QW·out), the PFAA concentration of water inflow (CW·in), and bioconcentration factor of aquatic plants (BCFp) were the primary parameters sensitive to PFAAs in all sub-compartments, which are essential indexes for exploring promising remediation pathways for lacustrine PFAA contamination based on the fugacity model simulation.

A framework for evaluating the combined effects of water transfer and storage strategies on water stress alleviation

Water transfer and storage are two effective anthropogenic management strategies to alleviate the contradictions between water supply and demand. However, the trade-off and synergistic impacts of management strategies in alleviating water stress remain unclear at the national level. Therefore, this study proposes a framework that integrates the fraction of runoff being withdrawn (scarcity coefficient) and the variation of runoff weighted by reservoir (variability coefficient) to evaluate the multifaceted impacts of management strategies on water stress mitigation. The proposed framework evaluates the changes in both the water supply–demand balance and the historical variability of runoff by considering physical water transfers, virtual water flows, and reservoir operations. This study applied the framework to evaluate the spatiotemporal patterns of water stress and used principal component analysis to estimate the relative contributions of management strategies across ten first-order basins in China for the period of 2014–2018. Results show that water-resource scarcity coefficient varied between −37.15% and 13.28% at the basin scale (the national average varied −5%) and water-resource variability coefficient varied between −100% and −19.26% at the basin scale (the national average varied −61.11%). Management strategies, incorporating water transfer and storage strategies, shifted the distribution patterns of national water stress. The attribution analysis revealed that reservoir storage capacity was the largest contributor to the first principal component representing infrastructure element, whereas the second component representing economic element was affected by the net virtual water inflows. Overall, through exploring the outcomes of combined effects among management strategies, this proposed framework provides a comprehensive perspective for investigating how human activity alleviates regional water stress.

Machine learning-based investigation of forest evapotranspiration, net ecosystem productivity, water use efficiency and their climate controls at meteorological station level

Evapotranspiration (ET), net ecosystem productivity (NEP), and ecosystem water use efficiency (EWUE) of forests are changing due to climate change. Traditional models using coarse-scale climate reanalysis data fail to capture local meteorological and hydrological conditions accurately. This study combines in situ meteorological observations, remote sensing, and advanced datasets (forest age, rooting depth, soil moisture) to estimate ET, NEP, and EWUE at forest meteorological stations via machine learning. About 60.6 % of stations showed a decrease in NEP from 2003 to 2010 to 2011–2019, while 63.9 % showed an increase in ET, and 58.9 % showed a decrease in EWUE. NEP and EWUE significantly declined in forests older than 60 years, with younger forests exhibiting higher NEP. EWUE in different forest types is driven by varying mechanisms, with DBF sites influenced by VPD and ENF sites by RSDN. EWUE of regions with inconsistent VPD data between site and reanalysis, such as northwestern North America, showed divergences from previous reanalysis-based studies but aligned more with atmospheric inversion findings. Slight summer VPD increases boosted NEP, especially in high-latitude areas, while early spring phenology and increased spring VPD reduced summer water availability. Incorporating more site-specific observations, such as plant traits, could enhance understanding of climate-plant-ecosystem relationships. This study underscores the potential of meteorological station-level data to improve forest carbon and water flux dynamics understanding, aiding forest management for carbon neutrality and climate adaptation.

Can temperature be a low-cost tracer for modelling water age distributions in a karst catchment?

To investigate the feasibility of using temperature for tracking rainfall-runoff processes in karst catchments, this study developed a tracer-aided conceptual model using temperature as a tracer by coupling water and heat transport processes at the catchment scale. The model was calibrated and validated using hourly hydrometeorological and temperature data from a 1.25 km2 karst catchment in south-western China. The results showed that the model was able to capture the water flux and temperature dynamics of different landscape units in the karst catchment. Utilizing this framework, the model delineated the flux age distribution within different landscape units, as well as the overall water transit times through the catchment. The average flux ages were determined to be approximately 80 days for the hillslope unit, 452 days for the slow flow system, and 260 days for the fast flow regime within the depression areas. These estimations align broadly with those acquired using stable isotopes as tracers. Comparative analysis revealed that the flux age distributions derived from both temperature and isotopic tracers exhibited analogous patterns at the catchment outlet and across the hillslope compartments. However, the simulations based on temperature hinted at a heightened proportion of exceedingly young and decidedly old water in the outflow, alluding to a potential overestimation of these extreme age classes by the temperature-tracer model. From the temperature-simulated transit time distribution, about 31 % of the precipitation entering during the study period have left the catchment within 3 years, and a notable proportion of rain water was either stored in the aquifer or lost through evapotranspiration. The general characteristics of the transit time distribution simulated using temperature was similar with that simulated using isotopes, though a higher proportion of precipitation being drained by fast flows was inferred from the transit time distribution simulated using temperature. Collectively, our study demonstrated that temperature can serve as a cost-effective tracer for modelling of water age distributions and associated hydrological processes in karst catchments.

CuO-Fe3C-C modified PVDF membrane for catalysis and antifouling

Modification of membranes is an effective method for degrading organic pollutants and alleviating membrane fouling. In this study, CuO-Fe3C-C catalyst was prepared by high-temperature pyrolysis. The membrane modified by CuO- Fe3C-C was prepared by vacuum filtration. The bacteriostatic rate of the modified membrane can reach to 96.8 %. Compared to the pristine membrane, the pure water flux of the modified membrane increased from 223.43 L m−2h−1 bar−1 to 422.27 L m−2h−1 bar−1, the flux recovery ratio (FRR) of modified membranes increased from 39.7 % to 79.25 %. Removal rate of TC (Tetracycline) by modified membrane activated PMS can reach to 90.75 %. After 5 cycles, the degradation efficiency of modified membranes was still 83.77 %, which was only 6.39 % lower than that of the first cycle. Free radical quenching experiments and ESR tests explored the possible catalysis and antifouling mechanisms of the modified membrane system, the results showed main active species were SO4−•, OH•, O2−• and 1O2. This study prepared membranes with excellent antifouling properties, providing a theoretical reference for alleviating membrane fouling in membrane-based water treatment.

Design of a high-performance polyaniline coated niobium dicarbide MXene nanostructure based electro-membrane system for improved nanoplastic separation

This study explores the development of advanced electro-membrane filtration by incorporating Nb-based MXene (Nb2CTx) to enhance nanoplastic (NP) separation and fouling mitigation. The presence of NPs in water results in less effective filtration, hence increasing cost, highlighting the urgent need for advanced removal technologies. Nb2CTx was incorporated at varying loadings, revealing significant alterations in their morphological, structural, and physiochemical properties. The performance evaluation using NP-rich suspensions demonstrated that the membrane with 5 % Nb2CTx loading (MS5) achieved a NP removal efficiency of 97.4 % and a water flux of 90.5 L.m−2.h−1, which was significantly higher than the pristine sulfonated polyether sulfone (SPES) membrane (18.9 L.m−2.h−1 with 94 % removal efficiency). The membrane was developed for an electro-membrane system using a sacrificial anode. The sacrificial anode allowed for multiple complex process to occur simultaneously, including electrocoagulation and membrane filtration. Polyaniline (PANI) coating was added to further increase the conductivity to allow for a more energy efficient process. The study underscores the importance of Nb2CTx loading and PANI modification in improving the filtration efficiency and fouling resistance. Furthermore, applied electric field resulted in enhanced operational sustainability of SPES membranes, offering a novel approach for water treatment applications.

Enhanced water purification performance of composite PVA–ZnO–Al2O3 hollow fiber membrane: A breakthrough approach for high-temperature stability, low-pressure water separation

This work describes the development of a composite Al2O3 hollow fiber combined with multiple-layer ZnO nanoparticles and PVA polymer as the active side for low-pressure saltwater purification. The composite membrane was evaluated with an active layer-facing salt solution, and slight suction condition was applied to the permeate inside the membrane lumen. Results show that varying nanoparticle layers to tune the porosity of the composite membrane influenced its morphology, porosity, and hydrophilicity. The effect of porosity tuning on the membrane characteristics and desalination performance was investigated. A salt rejection rate of >90 % was recorded for all 5 % PVA–ZnO–Al2O3 hollow fiber membranes with the highest salt rejection of 96.34 % and the water flux of 15.49 kg·m−2·h−1. The membrane was further tested with untreated natural seawater to demonstrate its ability to withstand continuous operation. The membrane has acceptable chemical stability when exposed to untreated natural seawater. The optimal PVA–ZnO–Al2O3 hollow fiber membrane exhibited efficient water phase change transfer and high salt rejection, making it a promising candidate for seawater purification.

A first assessment of airborne HyTES-based land surface temperature and evapotranspiration

The Hyperspectral Thermal Emission Spectrometer (HyTES) offers high spatial and spectral resolution thermal infrared (TIR) airborne measurements, which are crucial for deriving land surface temperature and emissivity (LST&E). These measurements have wide-ranging applications, particularly in understanding water stress and plant water use. One critical application of TIR satellite-sensor systems is the estimation of evapotranspiration (ET), which can be derived from LST. ET is essential for modeling water fluxes from the land surface, and various algorithms leverage LST as a key boundary condition for this purpose. In this study, we apply an ET algorithm to HyTES LST data for the first time, using an analytical surface energy balance model, the Surface Temperature Initiated Closure (STIC) version 1.3. We provide an overview of the STIC model, detailing its application to HyTES data, including the integration of ancillary datasets. We demonstrate the practicality of this approach by presenting ET and LST calculations for HyTES flightlines from three field campaigns conducted in 2019, 2021, and 2023. To validate our results, we compare the derived ET and LST against available in situ measurements, including eddy covariance-derived latent heat flux and radiometer-derived LST. While this study focuses on HyTES data, the same methodology is applicable to any instantaneous LST dataset. Advancing TIR mapping of ET is crucial for applications in agriculture, water management and for understanding the evolving water cycle.