Freshwater Scarcity Research Articles

Can International Freshwater Trade Contribute to the SDG 6

Freshwater is fundamental for all aspects of human well-being and sustainable development. The supply of freshwater resource largely depends on the natural water cycle, leading to extremely unequal distribution over the world. This uneven distribution and increasing freshwater demand results in spatial and temporal physical freshwater shortage. By discussing the limitations of desalination techniques and the shortcomings of existing pathways for freshwater transfer including water transfer projects, bottled water market, and virtual water trade, we suggest that international freshwater trade as an additional pathway is necessary. The analysis of the cost structure of freshwater production and transportation and the hypothetical examples between potential exporting and importing countries show the feasibility of international freshwater trade. The establishment of a global freshwater market is confronted with six challenges, namely, natural sustainability, ecological safety, opinions of stakeholders, market access mechanism, pricing mechanism, and infrastructure system. We conclude that a global freshwater market is expected to make contributions to achieving SDG 6 by mitigating spatial and temporal freshwater scarcity and by resolving transboundary freshwater conflicts and managing local freshwater consumptions.

Multivariate Analysis of Clean Technologies in Agricultural and Livestock Companies in Castilla y León

Through multivariate data analysis, this research aims to study the current commitment of agricultural and livestock companies in Castilla y León to the mitigation of their negative environmental impacts and whether it is conditioned by their resources and capabilities, through the implementation of clean technologies. Agricultural and livestock production is vital for the subsistence of the world’s population, but the productive activities of this sector can have unfavorable consequences on the environment. These business projects are designed to mitigate the negative impacts on three essential environmental elements: air, freshwater and ecosystems (fauna and flora). The results were derived via the External Logistics Biplot methodology, whose purpose is to determine the influence of various factors or variables on a result, and which shows that 63% of the companies analyzed have invested in technological systems to optimize water use, 40% have invested in technologies and systems to avoid and control carbon dioxide (CO2) and Greenhouse Gases (GHG) emissions, and 24% of companies have implemented technologies for recycling and reusing waste, showing a hierarchical preference in mitigating risks related to freshwater scarcity, emitting polluting emissions into the air and the conservation of ecosystems.

The efficacy of hydrogen sulfide (H2S) tests for detecting microbial contamination in rooftop-harvested rainwater

As climate change strains the world’s freshwater resources, access to safe and clean water becomes limited. The use of alternative water sources, such as rooftop-harvested rainwater, has become one mechanism to address freshwater scarcity in the American Southwest, particularly when it comes to home gardening. The University of Arizona’s Project Harvest, in partnership with the Sonora Environmental Research Institute, Inc., is a multi-year, co-created citizen science project aimed at increasing current understanding of harvested rainwater quality. Citizens in four Arizona, USA, communities (Hayden/Winkelman, Globe/Miami, Dewey-Humboldt, and Tucson) submitted harvested rainwater samples over 3 years. The harvested rainwater samples were then analyzed using IDEXX Colilert® for total coliforms and E. coli and using Hach PathoScreen™ test for sulfate-reducing bacteria (SRB). This study design allows for the validation of a low-cost, at-home alternative methodology for testing rainwater for bacteria that may indicate fecal contamination. In total, 226 samples were tested using both methodologies, revealing a positive correlation (r=0.245; p<0.002) between total coliform MPN and SRB MPN, but no discernable correlation between E. coli MPN and SRB MPN. This work indicates a potential value of SRB testing for harvested rainwater if cost, laboratory access, and fecal contamination are of concern.

Partitioning blue and green water sources of evapotranspiration using the water evaluation and planning (WEAP) model

Abstract Understanding agricultural water use by sources such as rainwater (green water) or irrigation water (blue water) is vital to manage scarce freshwater resources. Tracing sources of evapotranspiration increases water management efficiency. This study proposes a two-bucket soil moisture water balance approach to trace sources of evapotranspiration over irrigated landscapes in the Awash Basin, Ethiopia, which is modeled in the water evaluation and planning model. Algorithms are devised to separate actual evapotranspiration into blue and green sources. The results showed annual basin renewable water of 15.78 BCM in the form of streamflow (4.65 BCM), stored water (3.54 BCM), and groundwater percolation (7.59 BCM). Annual actual evapotranspiration over irrigated landscapes was 805 MCM, which was separated as blue evapotranspiration (88.4%) and green evapotranspiration (11.6%). The findings also demonstrate that blue evapotranspiration predominantly occurs during dry months, indicating heavy reliance on stored water for irrigated landscapes. Subbasin-level analyses showed varying blue/green evapotranspiration patterns based on precipitation and irrigated agriculture. Irrigation accounted for less than 3% of the streamflow in upstream basins, while midstream and downstream basins utilized up to 30 and 70%, respectively. The complementary use of rainfall and irrigation in most parts of the basin is considered to be of interest to water managers.

Pre-oxidized ultramicroporous carbon cloth with ultrahigh volumetric capacity and ultralong lifespan for capacitive desalination

Capacitive deionization is a promising desalination technique to tackle with freshwater scarcity, due to its facile, energy-efficient and eco-friendly operation. Carbon materials are primary electrode materials in capacitive deionization devices; however, their practical applications are limited by the low salt adsorption capacity and poor cycling stability. Here, we report a pre-oxidized strategy to significantly improve the salt adsorption capacity and cycling lifespan of carbon clothes. By the simple pre-oxidation treatment, it creates abundant ultramicropores and a superhydrophilic surface, which lead to a high salt adsorption capacity (31.5 mg g−1 and 13 mg cm−3) in 0.01 M NaCl aqueous solution. Moreover, the surface of each carbon fiber is oxidized, combined with a high mechanical strength, resulting in a stable surface during the cycling process. The retention rate is 74% even after 5000 adsorption/desorption cycles in diluted seawater. This work provides a new avenue to the design of high-performance, low-cost, and durable electrodes for capacitive deionization applications.

Facile fabrication of low-cost, degradable double-layer chitosan/MXene solar vapor generator for enhanced thermal localization efficiency

The interfacial solar vapor generator (ISVG) has emerged as a promising solution to address freshwater scarcity. The enhancement of thermal localization and suppression of salt crystallization are recognized as the design key factors for ISVG. In this study, we successfully fabricated a novel double-layer structure degradable interfacial solar vapor generator (DISVG) utilizing chitosan monolith (CM) with honeycomb porous morphology as carrier material, while employing MXene nano-sheets as solar absorber. The fabrication process involved facile chemical crosslinking and dip-coating methods. The incorporation of the double-layer structure in the DISVG plays a significant role in achieving effective thermal localization, thereby minimizing heat transfer to bulk water. Consequently, this feature results in a remarkable improvement in evaporation rate while simultaneously enhancing salt resistance. The DISVG demonstrated an outstanding evaporation rate of 3.88 kg m-2 h-1 under 1 sun (1 kW m-2) irradiation and effectively removed more than 99% of salt and dyes in water. Interestingly, even without the presence of MXene, the DISVG still achieved efficient evaporation at a rate of 2.63 kg m-2 h-1 under 1 sun irradiation. Moreover, both DISVGs exhibited stability over extended period of operation without any rate decay. This study not only presents a novel approach for the progress of environmentally friendly and cost-efficient ISVG but also offers valuable insights into overcoming the trade-off between thermal localization and salt resistance in such systems.

Revolutionary solar evaporation system: Harnessing the power of bacterial cellulose/Ag NPs/polypyrrole with its promoted antibacterial applications

Extensive research is being conducted on a promising technology that utilizes solar energy and photothermal materials to address the global challenges of freshwater scarcity and energy shortage. Real-world applications of this technology require materials with specific properties such as mechanical flexibility and antimicrobial characteristics. Herein, a self-supporting membrane for interfacial photothermal water evaporation is developed, incorporating bacterial cellulose (BC) as a resilient and hydrophilic backbone material, along with Polypyrrole（PPy）loading and silver nanoparticles (Ag NPs) doping. The addition of Ag NPs not only enhances the antibacterial properties of the material, but also improves light absorption through plasma resonance, resulting in enhanced photothermal conversion efficiency. Experimental results demonstrate that the BC/Ag/PPy hybridized membrane exhibits an outstanding photothermal evaporation efficiency of 91%. Additionally, the membrane maintains a stable evaporation rate and favorable mechanical properties. With its exceptional performance, this BC/Ag/PPy membrane offers a practical solution for long-term seawater desalination applications.

Innovative system for BWRO desalination powered by PV and pumped hydro storage – Economic and GHG emissions analysis

Brackish water reverse osmosis (BWRO) desalination driven by photovoltaic (PV) system as a primary energy source and pumped hydro storage (PHS) as an intermediate storage offers an energy-efficient and competitive solution to overcome freshwater scarcity. This innovative system for drinking water production from brackish groundwater was developed and technically analyzed in a prior work. In this paper, the entire system with two power supply scenarios: scenario 1 (PV, PHS and battery storage) and scenario 2 (PV, PHS and grid) is economically assessed and its greenhouse gas (GHG) emissions are analyzed. Thereafter, this system is compared with the state-of-the-art and BWRO systems powered by a conventional energy source (grid or diesel generator) to discuss and evaluate the future role of this innovative system in the BWRO desalination market. For off-grid operation, the innovative system with scenario 1 is the most economical system for drinking water production from brackish groundwater compared to the other examined systems as long as the diesel fuel price is equal to or more expensive than 0.58 US$/L. Moreover, the minimum specific GHG emissions produced per unit of drinking water production in scenario 1 is 46.8 % less than in the current system (PV and battery storage).

Impact of Water Management on Methane Emission Dynamics in Sri Lankan Paddy Ecosystems

Paddy ecosystems constitute a dominant source of greenhouse gases, particularly of methane (CH4), due to the continuous flooding (CF) practiced under conventional paddy cultivation. A new management method, namely alternative wetting and draining (AWD) (i.e., flooding whenever surface water levels decline to 15 cm below the soil surface), is an emerging practice developed to mitigate CH4 emissions while providing an optimal solution for freshwater scarcity. Despite extensive paddy cultivation in Sri Lanka, no systematic research study has been conducted to investigate CH4 emissions under different water management practices. Thus, field experiments were conducted in Sri Lanka to investigate the feedback of controlled water management on seasonal and diel variation of CH4 emission, water consumption, and crop productivity. Adopting the same rice variety, two water management methods, continuous flooding (CF) and alternative wetting and draining (AWD), were compared with plants (W/P) and without plants (N/P) present. The emission of CH4 was measured using the static closed chamber method. The results show a 32% reduction in cumulative CH4 emission, on average, under AWD when compared to CF. The yield under the AWD was slightly higher than that of CF. Although it was not statistically significant (p &gt; 0.05) there was not any reduction in yield in AWD than in CF. The total water saving under AWD ranged between 27–35% when compared to CF. Thus, the results support (without considering the effect of nitrous oxide) AWD as a promising method for mitigating CH4 emissions while preserving freshwater and maintaining grain yield in paddy systems.

Application of solid phase adsorption toxin tracking technology (SPATT) for monitoring microcystins in farm dams in Levubu farming area, South Africa

South Africa has scarce freshwater resources most of which are being affected by eutrophication and the resultant harmful algal blooms (HABs). Irrigation of edible plants with cyanobacteria-infested water poses an indirect threat to humans since cyanotoxins can be bioaccumulated in the irrigated plant tissues. The study assessed the applicability of the solid phase adsorption toxin tracking technology (SPATT) as an early warning tool for the passive sampling of microcystins (MCs) in farm dams around Levubu area and determine the physicochemical parameters that correlate to toxin loads in the farm dams.Three farm dams were selected and sampled monthly from June to November 2021. Physicochemical parameters monitored included electrical conductivity (EC), pH, Temperature, total dissolved solids (TDS), turbidity, chlorophyll-a and total dissolved nitrates and phosphates.Findings showed that the water temperature, pH, EC and TDS were all within optimal range for the growth of cyanobacteria. Nutrients (phosphates and nitrates) were below the detection limit. Chlorophyll-a ranged from 0.355 to 14.07 μg L−1, indicating oligotrophic to mesotrophic eutrophic status of the rivers. Among cyanoHABs identified were the Microcystis and Lyngbya genus.Both grab and SPATT samplers detected MCs in all the farm dams throughout the sampling period but there was no correlation between the MCs detected by the two methods. None of the physicochemical parameters correlated with phytoplankton biomass nor with MC levels in the water. The use of SPATT increased the likelihood of detecting MCs thus indicating the applicability of SPATT as a useful early warning tool for the presence of MCs to the water users.

A Market-Based Payment Study for Forest Water Purification Service in Loess Plateau of Yellow River Basin, China

Freshwater scarcity is increasingly threatening social development and human survival, and more effective watershed environmental management measures are yet to be developed. Market-based payment is an innovative tool to coordinate the relationship between ecosystem services’ supply and demand sides in watersheds, emphasizing the market (rather than government intervention) as the main means to regulate and control the behavior of interest-related subjects. We proposed a marked-based plan for forestry water purification service and stimulate the potential benefits of this plan under the zero transaction cost assumption. We applied and demonstrated the approach in the Loess Plateau of the Yellow River Basin (LPB) in China. By constructing the relationship between the higher reaches of annual forestry investment and the corresponding lower reaches of sediment concentration, we established forestry water purification service supply function (R2 = 0.956). Then, connecting the agents’ cost function of water treatment plants in the lower reaches with the forest water purification service, we obtained the forestry water purification service demand function (R2 = 0.943). Combining both the service supply and demand functions, we stimulated the market equilibrium state. The results show that higher reaches will provide 13.164 kg/m3 of water purification service by afforestation, and lower reaches can save RMB 2.131 billion annually via this service. This study suggests that marked-based payment between areas is feasible for a watershed ecosystem service, and promoting the establishment of watershed compensation market is a rewarding development direction. All of these insights provide a valuable reference point for Chinese horizontal ecological compensation practice.

Carbonized Sweet Potato‐Based Evaporator for Highly Efficient Solar Vapor Generation

Solar vapor generation has been considered an appealing way to solve freshwater scarcity issues. Although several natural materials have been developed, the exploration of biomass materials with stable evaporation, simple processes, and low energy consumption is still necessary. Herein, sweet potato, a high‐yield natural plant, is explored to prepare a solar evaporator with a cross‐linked porous structure. Carbonized sweet potato exhibits a high evaporation rate of 1.7 kg m−2 h−1 and an excellent solar–thermal conversion efficiency of 76% under 1 sun. This demonstrates excellent photothermal ability and enhanced water evaporation performance. Thanks to the unobstructed cross‐linking structure and fast water transport, the salt does not accumulate on the evaporator's surface in high‐salinity brine (10–20 wt% NaCl) and the evaporation rate is 1.35 kg m−2 h−1. This suggests superior evaporative stability and self‐desalting capability. The purpose of this study is to provide an eco‐friendly, stable, and efficient evaporator, with salt resistance by simple processes, and to demonstrate the potential application of biomass materials in solar vapor generation.

Bio‐Inspired Sandwich‐Structured All‐Day‐Round Solar Evaporator for Synergistic Clean Water and Electricity Generation

AbstractThe integration of solar‐driven interfacial evaporation and electricity co‐generation is considered a promising approach to simultaneously alleviate freshwater scarcity and the energy crisis. However, affected by intermittent solar irradiation/uncontrollable weather, the overall performance of solar‐driven evaporation in the real world is greatly reduced. Herein, inspired by antifreeze proteins in beetles that survive in extreme climates, all‐weather solar‐driven interfacial evaporators with a sandwich structure are designed. The top and bottom layers composed of MnO2‐modified cotton cloth are used for photothermal conversion and water transport, meanwhile, the middle layer made of a phase change microcapsule/hydrogel composite serves for heat storage and release. Under 1 kW m−2 irradiation, the evaporator exhibits a high evaporation rate of 2.67 kg m−2 h−1 and an efficiency of 89.5%. In the dark, the heat released from the phase change layer supports an evaporation rate of 0.43 kg m−2 h−1, 3.6 times that of pure water. Additionally, assembled with a thermoelectric module, the hybrid device achieves a stable output electricity power of 0.42 W m−2 under 1‐sun illumination and a prolonged output for 30 min in the dark. This work provides a novel approach for full‐time solar‐powered steam‐electricity co‐generation and a proof of concept for biomimetic steam generation/heat management integration.

Recent Progress, Challenges, and Future Prospects in Solar H2 Evolution via Pure/Sea Water Splitting Using Nanocomposites as Photocatalysts under Solar Light

AbstractPhotocatalytic pure/sea water splitting driven by solar light, emerges as the most promising strategy to address both the global energy crisis and environmental degradation. Research efforts have mainly resulted in the development of artificial photocatalytic solar hydrogen generation systems applicable to both freshwater and sea water. During long‐term testing, sea water demonstrated enhanced stability compared to pure water, offering experimental advantages in designing novel techniques aimed at reducing hydrogen generation costs, alleviating freshwater scarcity, and optimizing the utilization of natural water resources. Moreover, sea water splitting proves to be more effective in producing solar hydrogen due to the potential sacrificial action of salt ions, which promote hydrogen evolution within the photocatalytic system. This review comprehensively outlines the fundamental principles of photocatalytic H2 production, examines the efficiencies and recent progress in hydrogen generation, explores the challenges faced, and envisions the future prospects of enhancing hydrogen production efficiency and reactivity through photocatalytic pure/sea water splitting.

Enhancing solar steam generation in hydrogel evaporator by bio-based microfluidic component

The hydrogel-based evaporator exhibits exceptional water activation capabilities, enabling it to surpass the previously established upper limits of evaporation rates in interfacial solar steam generation (ISSG). Although hydrogels possess a pronounced affinity for water, this characteristic could result in temporary expansion and heat loss, which hinder their capacity to sustain rapid and efficient evaporation over prolonged durations. Herein, polyacrylamide-based photothermal hydrogel with customized microfluidic components achieved long-term operation. The photothermal hydrogel showed high sunlight absorbance (∼95.5%) and its surface temperature spontaneously could reach 44.1 °C under one sun simulated irradiation (1.0 kW/m2). The efficient regulation of water transport was accomplished by Nafion-modified corn straw, i.e., a microfluidic component. This hydrogel-based evaporator demonstrated an increasing evaporation rate from 2.03 to 2.42 kg/m2/h during 12 h of continuous solar illumination. Notably, the microfluidic component resulted in controlled water transport enabling programmable adjustment of the hydrogel evaporator, allowing it to be reused multiple times in practical applications around the clock. The daily potable freshwater production amount reached 7.84 kg/m2/h in outdoor seawater desalination experiments. This research provides a paradigm approach to address freshwater scarcity on a global scale by using waste biomass to fully compensate for the shortcomings of hydrogels in ISSG systems.

Facile fabrication of functionalized wood evaporator through deep eutectic solvent delignification for efficient solar-driven water purification

Solar-driven sewage purification was considered to be a promising technique for the alleviation of freshwater scarcity issues globally. However, most steam generation devices focused on ultrahigh photothermal conversion and also neglected to develop the potential functions of natural creatures. Here, a deep eutectic solvent (DES) functionalized wood was designed as the supported substrate decorated with black polypyrrole (PPy) to construct low-cost and efficient solar interfacial evaporator. DES modification selectively removed most of the lignin, which enhanced the hydrophilic wetness of wood for the efficient transportation of water from the bottom to the solar interface. The lignin selective removal lowered the thermal conductivity of the evaporator, facilitating the heat location on the gas-liquid interface for efficient steam generation. Most importantly, more cellulose hydroxyl was exposed on the wood surface by the DES process, which was conducive to the in-situ polymerization of pyrrole on the wood surface by hydrogen bond interaction. The prepared PPy-DES wood evaporator achieved a considerable water evaporation rate of about 1.94 kg m−2 h−1 with a corresponding photothermal conversion efficiency of about 83.4% in one sun, arising from the functionalized design of DES wood and efficient photothermal conversion. For seawater desalination and sewage purification, the prepared evaporator exhibited excellent salt self-cleaning ability and stable wastewater purification performance. It was envisioned that the strategy of functionalized design of natural evaporators would motivate a large-scale application of biomaterials for efficient wastewater purification.

Evolution of Morphology and Distribution of Salt Crystals on a Photothermal Layer during Solar Interfacial Evaporation.

Solar interfacial evaporation (SIE) by leveraging photothermal conversion could be a clean and sustainable solution to the scarcity of fresh water, decontamination of wastewater, and steam sterilization. However, the process of salt crystallization on photothermal materials used in SIE, especially from saltwater evaporation, has not been completely understood. We report the temporal and spatial evolution of salt crystals on the photothermal layer during SIE. By using a typical oil lamp evaporator, we found that salt crystallization always initiates from the edge of the evaporation surface of the photothermal layer due to the local fast flux of the vapor to the surroundings. Interestingly, the salt crystals exhibit either compact or loose morphology, depending on the location and evaporation duration. By employing a suite of complementary analytical techniques of Raman and infrared spectroscopy and temperature mapping, we followed the evolution and spatial distribution of salt crystals, interfacial water, and surface temperature during evaporation. Our results suggested that the compact crystal structure may emerge from the recrystallization of salt in an initially porous structure, driven by continuous water evaporation from the porous and loose crystals. The holistic view provided in this study may lay the foundation for effective strategies for mitigation of the negative impact of salt crystallization in solar evaporation.

INTEGRATING RAINWATER HARVESTING AND GREYWATER RECYCLING TO INCREASE WATER EFFICIENCY IN OFFICE BUILDINGS

Water is an essential component of existence. It is one of the primary resources for maintaining a daily presence. Due to high demand, freshwater becomes limited; therefore, rainwater harvesting and greywater recycling should be implemented as an alternative to substituting freshwater consumption for non-potable activities. This study discusses the implementation of rainwater harvesting and greywater recycling and the contribution to water efficiency and the environment. The main objectives of this paper are to explicate the potential benefits of integrating rainwater harvesting and greywater recycling in office buildings and to elucidate the impact of water conservation from office buildings on the environment. The result shows that implementing both systems in buildings can reduce freshwater consumption, water saving, and the discharge of wastewater to the environment, which is an essential point for water efficiency. The findings can serve as a reference for stakeholders, as they can reduce the freshwater consumption for non-potable activities and increase the water efficiency of buildings, thereby alleviating freshwater scarcity in the future.

Distribution of Heavy Metals in Water and Bottom Sediments in the Basin of Lake Gusinoe (Russia): Ecological Risk Assessment

Fresh water scarcity is considered a significant component, and potentially one of the most critical, of global climate change. With the rapid development of industry, there is an increasing risk of freshwater contamination by heavy metals (HMs). The danger of HM pollution is also attributed to their accumulation, which can subsequently become a source of secondary pollution in aquatic environments. In the Lake Gusinoe basin, located in Russia, concentrations of HMs were measured in both water and bottom sediments within the lake area, as well as in inflowing and outflowing watercourses. Ecological risk indices were also calculated for the Gusinoe basin. Our results showed that the average concentrations of Fe, Zn, Cr, Ni, Cd, and Pb in the water did not exceed the maximum allowable concentrations (MACs) set by Russian national standards and WHO standards, while the concentrations of Mn and Cu exceeded the corresponding MACs during winter, spring, and autumn possibly due to decomposition of aquatic vegetation and influx from groundwater sources. The average concentrations of the investigated HMs in the BSs did not exceed the background values. The water hazard index indicated a low risk for all samples in the lake water area. For all BS samples, the geoaccumulation index (Igeo) and the Pollution Load Index (PLI) indicated low pollution levels, while the values of the Enrichment Factor (EF) and the Contamination Factor (CF) indicated moderate pollution in the central part of the lake. The Ecological Risk Factor (Er) for Cu in BSs at points near major settlements and in the Tel River indicated moderate pollution. The Potential Ecological Risk Index (RI) in all investigated BS samples indicated a low risk of contamination.

The energy efficiency of multistage interfacial desalination: Comprehensive analysis and further improvement strategy

Multistage interfacial desalination is a promising strategy to address global freshwater scarcity due to its ultra-high energy conversion efficiency. While numerous researches focus on materials improvement and system design, the underlying mechanisms of energy efficiency improvement are less explored. In this work, we establish a theoretical framework based on energy conservation and heat and mass transfer to comprehensively analyze the energy efficiency of multistage interfacial desalination. We demonstrate that there is an efficiency upper limit of 894 % under ideal conditions, which is mainly limited by the unavoidable sensible heat loss from the fresh water. Furthermore, we show that a typical ten-stage desalination system with a lab scale (10 cm × 10 cm) can reach a calculated efficiency of 232 %. An energy loss analysis allows us to identify another important heat transfer term, the wick where the evaporator takes seawater, which also causes significant heat loss. Experiments are conducted to show that better thermal insulation on wick can enhance energy efficiency. Moreover, we found that the system efficiency can be improved by enhancing the internal convective heat and mass transfer. This work provides insights into physical processes involved in multistage interfacial desalination and offers important guidance for further performance improvement towards its application.