Renewable biomass reinvigorates sustainable water-energy nexus

The water-energy nexus has garnered worldwide interest.Current dual-functional research aimed at coproducing freshwater and electricity faces significant challenges,including sub-optimal capacities("1+1<2"),poor inter-functional coordination,high carbon footprints,and large costs.Mainstream water-toelectricity conversions are often compromised owing to functionality separation and erratic gradients.Herein,we present a sustainable strategy based on renewable biomass that addresses these issues by jointly achieving competitive solar-evaporative desalination and robust clean electricity generation.Using hydrothermally activated basswood,our solar desalination exceeded the 100% efficiency bottleneck even under reduced solar illumination.Through simple size-tuning,we achieved a high evaporation rate of 3.56 kg h^(-1)m^(-2)and an efficiency of 149.1%,representing 128%-251% of recent values without sophisticated surface engineering.By incorporating an electron-ion nexus with interfacial Faradaic electron circulation and co-ion-predominated micro-tunnel hydrodynamic flow,we leveraged free energy from evaporation to generate long-term electricity(0.38 W m^(-3)for over 14 d),approximately 322% of peer performance levels.This inter-functional nexus strengthened dual functionalities and validated general engineering practices.Our presented strategy holds significant promise for global human–society–environment sustainability.

Numerical simulation and data assimilation of the water-energy cycle over semiarid northeastern China

The default fractional vegetation cover and terrain height were replaced by the estimated fractional vegetation cover, which was calculated by the Normalized Difference Vegetation Index （NDVI） of Earth Observing System Moderate-Resolution Im- aging Spectroradiometer （EOS-MODIS） and the Digital Elevation Model of the Shuttle Radar Topography Mission （SRTM） system. The near-surface meteorological elements over northeastern China were assimilated into the three-dimensional varia- tional data assimilation system （3DVar） module in the Weather Research and Forecasting （WRF） model. The structure and daily variations of air temperature, humidity, wind and energy fields over northeastern China were simulated using the WRF model. Four groups of numerical experiments were performed, and the simulation results were analyzed of latent heat flux, sensible heat flux, and their relationships with changes in the surface energy flux due to soil moisture and precipitation over different surfaces. The simulations were compared with observations of the stations Tongyu, Naiman, Jinzhou, and Miyun from June to August, 2009. The results showed that the WRF model achieves high-quality simulations of the diurnal charac- teristics of the surface layer temperature, wind direction, net radiation, sensible heat flux, and latent heat flux over semiarid northeastern China in the summer. The simulated near-surface temperature, relative humidity, and wind speed were improved in the data assimilation case （Case 2） compared with control case （Case 1）. The simulated sensible heat fluxes and surface heat fluxes were improved by the land surface parameterization case （Case 3） and the combined case （Case 4）. The simulated tem- poral variations in soil moisture over the northeastern arid areas agree well with observations in Case 4, but the simulated pre- cipitation should be improved in the WRF model. This study could improve the land surface parameters by utilizing remote sensing data and could further improve atmospheric elements with a data assimilation system. This work provides an effective attempt at combining multi-source data with different spatial and temporal scales into numerical simulations. The assimilation datasets generated by this work can be applied to research on climate change and environmental monitoring of add lands, as well as research on the formation and stability of climate over semiarid areas.

Moving Resources to the People or Moving the People to the Resources? A Hypothetical Consideration for Addressing Sustainability

Water and energy are rarely linked politically or technologically,yet both resources are intimately dependant upon each other.Energy is consumed by the extraction,distribution,and treatment of water.Water is consumed in the production and use of energy.Our study looks at this nexus,specifically,for resource islands—communities located considerable distances from their water and energy resources.Resource

Energy Consumption in the Municipal Water Supply Sector in the Kingdom of Bahrain

Water-energy nexus is an emerging issue that receives considerable attention in the world in general and in the Gulf Cooperation Council (GCC) countries in particular. The GCC countries depend mainly on energy generated from fossil fuels to produce drinking water. Yet, the amount of water-related energy use in Bahrain remains unexplored. This study aims to quantify the amount of energy used in the water supply cycle for the first time in Bahrain using quantitative methods. A bottom-up approach for data collection was adopted where data for the three main stages of the water supply in Bahrain: water production, water transmission, and water distribution were collected. Results show that the water production stage consumes about 97% of the total energy consumption in the water supply sector, followed by water transmission (2.9%) and water distribution (0.1%). Comparisons conducted with best practices in the world show that water desalination plants in Bahrain consume relatively high amounts of energy to produce water based on the desalination technology used. This study calls for focusing on the production stage in achieving energy efficiency since it is the largest consumer and where losses are occurring based on the benchmarking. This study also recommends investigating the share of electricity and thermal energy consumed in the water supply cycle in Bahrain in addition to the wastewater treatment sector. This is imperative to provide a holistic overview of the water-related energy use in Bahrain.

A REVIEW OF THE SUSTAINABILITY OF RESIDENTIAL HOT WATER INFRASTRUCTURE:PUBLIC HEALTH,ENVIRONMENTAL IMPACTS,AND CONSUMER DRIVERS

Residential water heating is linked to the primary source of waterborne disease outbreaks in the United States,and accounts for greater energy demand than the combined water/wastewater utility sector.Furthermore,home water heating is the second largest energy consumer in the home and thus represents an integral part of the water-energy nexus.To date,there has been little practical research that can guide decision-making by consumers,public health officials and regulators with regards to water heater selection and operation to minimize energy costs and the likelihood of waterborne disease.Scientific uncertainties associated with existing“green”advice have potentially created misguided policy with long-term negative repercussions.This review is aimed at defining the current state of knowledge related to hot water infrastructure and in highlighting current gaps in the research.While there are many sustainability claims of certain water heater types(i.e.,hot water recirculation systems and instantaneous water heaters)these claims have not been substantiated in head-to-head testing of the interplay between water temperature,energy,microbial growth,and scaling,all measures that need to be better defined.

WATER AND ENERGY SAVINGS FROM ON-DEMAND AND HOT WATER RECIRCULATING SYSTEMS

Electric hot water recirculation and on-demand instant hot water systems have been identified as“green”water systems due to purported energy and water savings,and some municipalities and districts even require green systems in residences.The performance of these devices have never been rigorously tested and evaluated.This work aims to address that gap by conducting a comparative,head-to-head study evaluating energy efficiency,temperature profiles and consumer issues such as cost and quality of system for two“green”water heating systems as compared to a standard water heater.Not only did the standard system outperform the hot water recirculation system with respect to temperature profile during flushing,but the standard system also operated with 32-36%more energy efficiency.Although the recirculation system did in fact save some water at the tap,when factoring in the energy efficiency reductions and associated water demand,recirculation systems actually consumed up to 7 gallons more water per day and cost consumers more money.On-demand systems operate with virtually 100%energy efficiency,but cannot be used in many circumstances dependent on scaling and incoming water temperature,and may require expensive upgrades to home electrical systems and use of low/ultra low flow showerheads.Although additional research is necessary to better understand nuances of electric water heating in the context of the water-energy nexus,this research provides a first step for rational decision making by regulators,public health officials,manufacturers and consumers.

OPTIMIZATION OF ELECTRIC HOT WATER RECIRCULATION SYSTEMS FOR COMFORT,ENERGY AND PUBLIC HEALTH

Hot water recirculation systems(RECIRC)are labeled green and are sometimes mandated in local plumbing codes.Previous work conducted under non-optimized operation schemes demonstrated that these systems actually waste energy and water versus standard(STAND)water heater counterparts.Optimization of RECIRC system operation by minimizing pump operation did improve energy efficiency 6-60%,saving consumers 5-140%annually in associated utility costs.However,STAND systems were still more energy efficient than any of the RECIRC systems.With respect to factors that might influence pathogen growth,reducing RECIRC pump operations increased disinfectant residual by as much as 560%as compared to the baseline RECIRC system;however,STAND systems still had 25-250%more total chlorine residual than any of the RECIRC systems.At 60℃operating temperature,STAND systems have 30-230%more volume at risk for pathogen growth(e.g.,volume with temp 37-46℃)than any of the RECIRC systems.Thus,in the context of“green”design,RECIRC systems provide a convenience to consumers in the form of nearly instant hot water,at a cost of higher capital,operating and overall energy costs.RECIRC systems have distinct advantages in controlling pathogens via thermal disinfection but disadvantages in control via secondary disinfection residual.

The effects of urban water cycle on energy consumption in Beijing, China

Energy is consumed at every stage of the cycle of water production, distribution, end use, and recycled water treatment. Understanding the nexus of energy and water may help to minimize energy and water consumption and reduce environmental emissions. However, the interlinkages between water and energy have not received adequate attention. To address this gap, this paper disaggregates and quantifies the energy consumption of the entire water cycle process in Beijing. The results of this study show that total energy consumption by water production, treatment and distribution, end use, and recycled water reuse amounts to 55.6 billion kWh of electricity in 2015, or about 33% of the total urban energy usage. While water supply amount increased by only 10% from 2005 to 2015, the related energy consumption increased by 215% due to water supply structural change. The Beijing municipal government plans to implement many water saving measures in the area from 2016 to 2020, however, these policies will increase energy consumption by 74 million kWh in Beijing. This study responds to the urgent need for research on the synergies between energy and water. In order to achieve the goal of low-energy water utilization in the future, water and energy should be integrated in planning and management.

Water, energy and food interactions --Challenges and opportunities

Water and energy are inextricably linked, and as a consequence both have to be addressed together. This is called the water-energy nexus. When access to either is limited, it becomes obvious that it is necessary to consider their interdependence. Population growth, climate change, urbanization, increasing living standards and food con- sumption will require an integrated approach where food, water and energy security are considered together. In this paper we examine water, energy and food security and their couplings. The nexus also creates conflicts between water use, energy extraction and generation as well as food production. Some of these conflicts are illustrated. It is argued that there is an urgent need for integrated planning and operation. Not only will better technology be needed, but also better integration of policies, organizations and political decisions.

Grey water footprint for global energy demands

With a Multi-Regional Input-Output model,this study quantifies global final energy demands’grey water footprint(GWF)based on the latest available data.In 2009,9.10 km^3 of freshwater was required to dilute the pollutants generated along the life-cycle supply chain of global energy final demands to concentrations permitted by relevant environmental regulations.On a national level,final energy demands in China,USA,India,Japan,and Brazil required the largest GWF of 1.45,1.19,0.79,0.51,and 0.45 km^3 respectively,while European countries have the highest energy demands GWF per capita.From the producer perspective,the largest GWF was generated in BRIC countries,i.e.5 Russia(1.54 km^3),China(1.35 km^3),India(0.92 km^3)and Brazil(0.56 km^3)to support global final energy demands.Because of global trading activities,a country or region’s final energy demands also give rise to water pollutants beyond its territorial boundaries.Cyprus,Greece,Luxembourg,and Malta almost entirely rely on foreign water resources to dilute water pollutants generated to meet their final energy demands.Energy demands in BRIC countries have the least dependency on external water resources.On a global average,56.9%of GWF for energy demands was generated beyond national boundaries.Energy demands in the global north are inducing water pollutions in the global south.

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales.However,annual catchment water balance can also be easily and simply predicted using lumped conceptual model.Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales.In this paper,a distributed physically-based hydrological model(i.e.,bottom-up approach)and a simple water-energy balance model(i.e.,top-down approach)are used to predict actual evapotranspiration in nine sub-catchments,and the whole basin of the Luan River in northern China.Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale.From the analysis at different time scales through comparison of the top-down and the bottom-up methods,it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration,and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas.It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales,which is commonly used in the physicallybased hydrological models.