Evaluating the Life Cycle Environmental Benefits and Trade-Offs of Water Reuse Systems for Net-Zero Buildings

Unequal exposure to heatwaves in Los Angeles: Impact of uneven green spaces

Cities worldwide are experiencing record-breaking summer temperatures. Urban environments exacerbate extreme heat, resulting in not only the urban heat island but also intracity variations in heat exposure. Understanding these disparities is crucial to support equitable climate mitigation and adaptation efforts. We found persistent negative correlations between daytime land surface temperature (LST) and median household income across the Los Angeles metropolitan area based on Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station observations from 2018 to 2021. Lower evapotranspiration resulting from the unequal distribution of vegetation cover is a major factor leading to higher LST in low-income neighborhoods. Disparities worsen with higher regional mean surface temperature, with a $10,000 decrease in income leading to ~0.2°C LST increase at 20°C and up to ~0.7°C at 45°C. With more frequent and intense heat waves projected in the future, equitable mitigation measures, such as increasing surface albedo and tree cover in low-income neighborhoods, are necessary to address these disparities.

Environmental synergies in decentralized wastewater treatment at a hotel resort

Climate change and water scarcity are clearly related environmental problems, making them global environmental issues. Accordingly, the water cycle management deserves a revision in its approach, integrating the concept of circular economy within an efficient and sustainable management of water resources and the design of wastewater facilities. In this sense, newly engineered decentralized facilities have emerged as a viable option for the treatment of segregated wastewater flows. The design has not only integrated the wastewater treatment function, but also resource recovery, such as water reclamation for agricultural and irrigation activities, fertigation, fertilization and energy sustainability. Based on these premises, the concept of decentralized wastewater management deserves the same degree of attention and development that has so far been reserved for conventional centralized management systems. Therefore, this paper proposes a progressive substitution of the business-as-usual scenario or centralized system by applying a small-scale wastewater management scheme performing a more efficient resource and water recovery in a medium-sized 4-5-star resort hotel. The spotlight was a membrane technology for the anaerobic digestion of the blackwater instead of the greywater treatment. A favorable environmental profile was found for the decentralized scenario under two circumstances: a large system boundary including the beneficial environmental impacts of the products and, based on the results obtained from a sensitivity analysis, an energy demand for the operation of the AnMBR lower than 2 kWh·m^-3. The global warming potential results (around 9%) were even for such high demand and much larger benefits were obtained for other impact categories (94% for SOD and 98% for LU). Nevertheless, the operation (gate-to-gate approach) of these on-site recovery facilities is far from being optimized and further research should follow to decrease the 39.8% difference in the global warming potential between decentralized and centralized systems.

Economic impact assessment indicators of circular economy in a decentralised circular water system - Case of eco-touristic facility

The transition from a linear make-use-dispose model to a Circular Economy (CE) model has gained momentum in recent years. To date, substantive efforts have been put by researchers and practitioners on environmental assessment of circular water systems (CWS). Yet, the economic aspect of CWS has not received the same attention. This research is an attempt to bridge this gap by evaluating the economic viability of a decentralised hybrid rainwater- wastewater-greywater (HRWG) system. For this purpose, a framework of Shadow Pricing- Life Cycle Cost-Benefit (SLCCB) to analyse a CWS is proposed. Shadow pricing could compliment the established Life Cycle Costing (LCC) methods. The main parameters (costs and benefits) of the proposed SLCCB framework are divided into two types: Internal and External. The Internal pricing covers the capital expenditure (CAPEX) and operational expenditure (OPEX), while the External pricing covers the environmental and social costs-benefits of implementing CWS. The proposed SLCCB added to the classical Net Present Value (NPV) and Payback Period (PP) calculations could provide a more realistic evaluation of the economic performance of CWS. To demonstrate the efficacy of the new CE model, a new CWS in Greece was studied. A sensitivity analysis was conducted to assess the impact of the reclaimed water tariffs, internal costs, life span of the project, and the annual discount rate on the SLCCB. The results of the study reveal that the SLCCB of CWS is highly sensitive to these parameters. The economic feasibility of CWS boost with increasing discount rate and reclaimed water tariffs, as well as with decreasing project's life span and internal costs. The conclusion of this research demonstrates that investment in CWS is economically viable if External parameters are taken into consideration.

Water Consumption and Environmental Impact of Multifamily Residential Buildings: A Life Cycle Assessment Study

Water use in buildings accounts for a large share in global freshwater consumption where research on the impacts of life cycle water use receive little or no attention. Moreover, there is very limited knowledge regarding such impacts that focus on the life cycle emissions from water consumption in building environments in the world’s most water-stressed countries. Hence, this study attempted to quantify the environmental impacts of operational water use in a multi-family residential building through a life cycle assessment (LCA). A small part of a Middle Eastern country, Doha (Qatar), has been selected for the primary assessment, while water-use impact in Miami (Florida) was chosen as a second case study, as both locations fall into similar climate zone according to ASHRAE Climate Zone Map. The LCA score indicated much higher impacts in the Doha case study compared to Miami. The variation in the result is mainly attributed to the raw water treatment stage in Doha, which involves energy-intensive thermal desalination. Again, relative comparison of the annual water and electricity use impacts for the modeled building was performed at the final stage for both locations. Water use was attributable for 18% of the environmental impacts in Miami, while this value increased to 35% in Doha. This initial assembled LCA result will be beneficial to both water authorities and building research communities in establishing more sustainable water use policies for specific regions/countries that will ultimately benefit the overall building environment.

The role of climate change and decentralization in urban water services: A dynamic energy-water nexus analysis

Urban water services, including drinking water supply and wastewater treatment, are highly energy dependent, contributing to the challenges described under the water-energy nexus. Both future climate change and decentralized water system adoptions can potentially influence the energy use of the urban water services. However, the trend and the extent of such influences have not been well understood. In this study, a modeling framework was developed to quantify both the separate and the combined influences of climate change and decentralization on the life cycle energy use of the urban water cycle, using the City of Boston, MA as a testbed. Two types of household decentralized systems were considered, the greywater recycling (GWR) systems and the rainwater harvesting (RWH) systems. This modeling framework integrates empirical models based on multilinear regression analysis, hydrologic modeling, water balance models, and life cycle assessment to capture the complex interactions among centralized water services, decentralized water system adoptions, and climate parameters for cumulative energy demand (CED) assessment, considering all residential buildings in Boston. It was found that climate change alone will slightly increase the energy use of the centralized systems towards the end of the century, due to the cancelation effect amongst changes in water quality, flow rate, and space and water heating demand. When decentralization is considered alone, we found economically viable decentralized systems may not necessarily produce energy savings. In fact, RWH adoptions may increase energy use. When climate change and decentralization are combined, they will increase the water yield and cost savings of the decentralized systems, while reducing the energy use from the centralized systems. When the centralized systems are further added into the picture, the CED of the entire urban water cycle is projected to increase by 0.9% or 2.3% towards the end of the century under climate change if GWR or RWH systems are adopted by respective cost saving positive buildings.

Onsite Non-potable Reuse for Large Buildings: Environmental and Economic Suitability as a Function of Building Characteristics and Location

Onsite non-potable reuse (NPR) is a way for buildings to conserve water using onsite sources for uses like toilet flushing, laundry and irrigation. Although early case study results are promising, aspects like system suitability, cost and environmental performance remain difficult to quantify and compare across broad geographic contexts and variable system configurations. In this study, we evaluate four NPR system types - rainwater harvesting (RWH), air-conditioning condensate harvesting (ACH), and source-separated graywater and mixed wastewater membrane bioreactors (GWMBR, WWMBR) - in terms of their ability to satisfy onsite non-potable demand, their environmental impacts and their economic cost. As part of the analysis, we developed the Non-potable Environmental and Economic Water Reuse Calculator (NEWR), a publicly available U.S. EPA web application that allows users to generate planning-level estimates of system cost and environmental performance using location and basic building characteristics as inputs. By running NEWR for a range of scenarios, we find that, across the U.S., rainfall and air-conditioner condensate are only able to satisfy a fraction of the non-potable demand typical of large buildings even under favorable climate conditions. Environmental impacts of RWH and ACH systems depend on local climate and were comparable to the ones of MBR systems where annual rainfall exceeds approximately 10 in/yr or annual condensate potential exceeds approximately 3 gal/cfm. MBR systems can meet all non-potable demands but their environmental impacts depend more on the composition of the local energy grid, owing to their greater reliance on electricity inputs. Incorporation of thermal recovery to offset building hot water heating requirements amplifies the influence of the local grid mix on environmental impacts, with mixed results depending on grid composition and whether thermal recovery offsets natural gas or electricity consumption. Additional environmental benefits are realized when NPR systems are implemented in water scarce regions with diverse topography and regions relying on groundwater sources, which increases the benefits of reducing reliance on centralized drinking water services. In terms of cost, WWMBRs were found to have the lowest cost under the largest range of building characteristics and locations, achieving cost parity with local drinking water rates when those rates were more than $7 per 1000 gallons, which occurred in 19% of surveyed cities.

Identification of Obstacles to Implementing Sustainability in the Civil Construction Industry Using Bow-Tie Tool

The construction industry is responsible for causing a large adverse impact on the environment. To minimize these impacts, sustainable practices are being sought mainly in the area of the wastage of and the waste from raw materials. Many obstacles and difficulties are encountered when trying to implement sustainable practices in civil construction. Thus, a study to identify what the obstacles are to implementing such practices is necessary. Therefore, the objective of this study is to present an assessment of the main obstacles to implementing sustainability in civil construction for which the bow-tie tool is used. Three cases were analyzed: construction material waste, the wastage of plaster and planning a sustainable construction project. Results showed that the lack of planning for sustainable construction projects, the lack of compliance with technical standards and the lack of technical knowledge of the workforce and of standardization are among the main obstacles to implementing sustainability in civil construction. This study offers a structured methodology to identify causes, consequences and obstacles related to events that affect the implementation of sustainable practices. It provides a visualization of the scenario investigated through the diagram generated, facilitating its understanding and analysis.

Environmental performance of building integrated grey water reuse systems based on Life-Cycle Assessment: A systematic and bibliographic analysis

The increasing demand for fresh water has been a global concern for decades. Desalination and water transportation systems consume an ample amount of energy, which also adds to the environmental pollution. This has led to a constant look-out for more viable options to conserve freshwater resources without compromising the environmental quality. The building sectors are remarkably the largest consumers of fresh water in the world; thus, the reclamation and reuse of greywater for non-potable purposes helps to reduce a significant amount of water consumed within a building. This study critically reviews the environmental performance of building-integrated greywater treatment systems compared to the conventional treatment systems deployed. Life-Cycle Assessment (LCA) is the method used to identify the environmental impacts associated with both the systems during their entire life span. The greywater treatment techniques and the guidelines for its reuse are also investigated. The bibliographic analysis was systematic, and the resources for this study were chosen after three stages of quality assessment. The study found physical and biological treatment techniques to be beneficial as they produce excellent quality of treated greywater for reuse. The environmental assessment by various studies prefers the reuse of greywater over its disposal. Guidelines for the reuse of treated greywater have recently been proposed by various countries and building rating systems. This study aims to address the policymakers, governmental and environmental organizations, mainly situated in the water-stressed areas such as the Middle East and North Africa (MENA) region, to raise awareness and initiate greywater reuse techniques within residential and commercial building sectors.

Characterization of implementation limits and identification of optimization strategies for sustainable water resource recovery through life cycle impact analysis

How we manage alternative freshwater resources to close the gap between water supply and demand is pivotal to the future of the environment and human well-being. Increased scarcity of water for agricultural irrigation in semi-arid and arid regions has resulted in a growing interest in water reuse practices. However, insight into the life cycle impacts and potential trade-offs of these emerging practices are still limited by the paucity of systematic evaluations of different water reuse implementations. In this study, a host of environmental and human health impacts at three implementation levels of allowing water reclamation for crop irrigation was comparatively evaluated across the operational landscape via a combination of scenario modelling, life-cycle impact analyses and Monte Carlo simulations. Net harvesting of reclaimed water for irrigation was found to be dependent upon the sophistication of the treatment processes, since multistage and complex configurations can cause greater direct water consumption during processing. Further, the direct benefits of water resource recovery can be essentially offset by indirect adverse impacts, such as mineral depletion, global warming, ozone depletion, ecotoxicity, and human health risks, which are associated with increased usage of energy and chemicals for rigorous removal of contaminants, such as heavy metals and contaminants of emerging concern. Nonetheless, expanded simulations suggest the significance of concurrently implementing energy recovery, nutrient recycling, and/or nature-based, chemical-free water technologies to reduce the magnitude of negative impacts from engineered water reclamation processes.

Dynamic Life Cycle Assessments of a Conventional Green Building and a Net Zero Energy Building: Exploration of Static, Dynamic, Attributional, and Consequential Electricity Grid Models

Our study assesses the differences between regional average- and marginal-electricity generation mixes as well as the variability between predicted and observed energy consumption of a "conventional green" Leadership in Energy and Environmental Design (LEED) building and a Net-Zero Energy Living Building (NZEB). The aim of our study was to evaluate the importance of using temporally resolved building-level data while capturing the dynamic effects a changing electrical grid has on the life cycle impacts of buildings. Two static and four dynamic life cycle assessment (LCA) models were evaluated for both buildings. Both buildings' results show that the most appropriate models ( hybrid consequential for the LEED Gold building, hourly consequential for the NZEB) significantly modified the use-phase global warming potential (GWP) impacts relative to the design static LCA (49% greater impact for the LEED Gold building; 45% greater reduction for the NZEB). In other words, a "standard" LCA would underestimate the use phase impacts of the LEED Gold building and the benefits of the NZEB in the GWP category. Although the results in this paper are specific to two case study buildings, the methods developed are scalable and can be implemented more widely to improve building life cycle impact estimates.