This study assessed the evolution of wastewater systems during the rapid urbanization of Beijing, with special focuses on the carbon footprints and growing underground WWTPs (u-WWTPs). Specifically, the Bishui plant (in situ constructed u-WWTP) was assessed in detail regarding eco-environmental benefits. Our results showed that, the direct emission intensity of 65 WWTPs decreased from 0.47 to 0.24 kg CO_2eq/m³, when the electricity intensity increased from 0.22 to 0.39 kWh/m³ from 2010 to 2020. Bishui u-WWTP emitted 36.6 kt CO_2eq/year (0.09 kg CO_2eq/m³), with electricity intensity of 0.43 kg CO_2eq/m³. Additionally, compare to the hypothetical relocating scenario, it saved 6.67 × 10⁴ m² land and 33.0 kt CO_2eq/year, and the created urban river carries 6.5 × 10¹³ J/year heat outside town. The evaluation and balance of choice for conventional or underground WWTP should be made case by case. However, this study demonstrated that u-WWTP is not only a construction manner, but a sustainable management model with positive eco-environment effects, algin with future city expansion, and circular economy visions.

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Recovering phosphorus from wastewater in more concentrated forms has potential to sustainably recirculate phosphorus from cities to agriculture. The environmental sustainability of wastewater-based phosphorus recovery processes or wastewater-derived phosphorus products can be evaluated using life cycle assessment (LCA). Many LCA studies used a process perspective to account for the impacts of integrating phosphorus recovery processes at wastewater treatment plants, while some used a product perspective to assess the impacts of producing wastewater-derived phosphorus products. We demonstrated the application of an end-user perspective by assessing life cycle environmental impacts of substituting half of the conventional phosphorus rock-based fertilizers used in three crop production systems with wastewater-derived phosphorus products from six recovery pathways (RPs). The consequential LCA results show that the substitution reduces global warming potential, eutrophication potential, ecotoxicity potential, and acidification potential of the assessed crop production systems in most RPs and scenarios. The end-user perspective introduced in this study can (i) complement with the process perspective and the product perspective to give a more holistic picture of environmental impacts along the “circular economy value chains” of wastewater-based resource recovery, (ii) enable systemwide assessment of wide uptake of wastewater-derived products, and (iii) draw attention to understanding the long-term environmental impacts of using wastewater-derived products.@en

The authors would like to correct the value of water-related electricity consumption at utility as a percentage of total electricity consumption for Australia (2015). The correct value is 1.1% in Figure 2, and Table S1-2 and Figure S1-2 (Supplementary Information 1 of Appendix B). Associated with this error, the water-related electricity consumption at utility for Australia (2015) should be 10.2 PJ in Table S1-2. The authors would like to apologise for any inconvenience caused. There are no changes to conclusions or other sections of the paper. Please find below amended Figure 2, and Table S1-2 and Figure S1-2 (Supplementary Information 1) [Figure presented] Fig. 2 (amended). Electricity consumption by utilities as a percentage of total electricity consumption across countries and regions. (See Table S1-1 and Table S1-3 in the Supplementary Information 1 for references). Supplementary Information 1. [Table presented] A Based on total final consumption data from the International Energy Agency, if the referenced study/dataset does not provide. Figure S1-2 Utility electricity consumption as a percentage of total electricity consumption across each country or region. [Figure presented]@en

Historically, little consideration has been given to water performance of urban developments such as “hydrological naturalness” or “local water self-sufficiency”. This has led to problems with increased stormwater runoff, flooding, and lack of local contributions to urban water security. Architectural design, water servicing technologies and environmental conditions are each known to influence water performance. However, most existing models have overlooked the integration of these factors. In this work, we asked ‘how the water performance of urban developments at site-scale can be quantified, with joint consideration of architectural design, water servicing technologies, and environmental context (i.e. climate and soil)’. Answering this question led to the development of a new method and tool called Site-scale Urban Water Mass Balance Assessment (SUWMBA). It uses a daily urban water mass balance to simulate design-technology-environment configurations. Key features include: (i) a three-dimensional boundary focussed on the “entity” of development (ii) a comprehensive water balance accounting for all urban water flows, (iii) methods that include key variables capturing the interactions of natural, built-environment and socio-technological systems on water performance. SUWMBA's capabilities were demonstrated through an evaluation of a residential infill development case study with alternative design-technology-environment configurations, combining three dwelling designs, seven water technologies and three environmental contexts. The evaluation showed how a configuration can be identified that strikes a balance between the conflicting objectives of achieving the desired dwelling densities whilst simultaneously improving water performance. For two climate zones, the optimal configuration increases the total number of residents by 300% while reducing the imported water per capita and stormwater discharge by 45% and 15%, respectively. We infer that SUWMBA could have strong potential to contribute to performance-based urban design and planning by enabling the water performance of dwelling designs to be quantified, and by facilitating the setting of locally-specific water performance objectives and targets.

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This study reviewed nexus researches, synthesize and discuss insights, methodological practices, and future outlook of water-related energy consumption assessment of the food system. For the first time, the study assessed: (i) the trends and drivers of water-related energy research in different countries, (ii) how water-related energy in the food system is being evaluated (objectives & scale, study dimension & analysis focus, and methods) and (iii) the significance of food-system water-related energy in comparison with other sectors. Of 686 nexus studies undertaken since 1990, 104 studies (15%) quantified water-related energy. Studies have generally broadened in scope through time. The USA, China, and Australia have conducted most studies representing 23%, 17%, 15% of total respectively. A few of the identified major drivers in these countries leading water-related energy assessment are: providing optimal solutions and avoiding problem-shifting, analyzing the challenges and opportunities to reduce water-related energy, and exploring the energy-saving benefits by saving water. Of the 104 water-related energy studies, 65 articles (∼60%) related to the food system, focussed on the agriculture phase for irrigation energy consumption. Existing nexus studies often ignored other phases such as food processing and cooking, which are more energy-intensive. Over 50% of studies used material flow analysis to evaluate water-related energy in the food system. Few of the nexus studies evaluated inter-regional flows or changes through time. Absence of a comprehensive study of the entire food system, and wide variations in study system boundary and definitions, make it difficult to compare sectoral significance. However, the order of sectoral water-related energy consumption (from highest to lowest) identified as industrial, residential, agriculture, and water and wastewater service. Our review demonstrates a tremendous opportunity and need for an overarching framework to enable systematic evaluation and benchmarking of water-related energy consumption of the food system.

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This study focused on understanding what sector-region combinations could be targeted to reduce total city water footprints? We used multi-regional input-output analysis of direct and virtual water, across five Australian capital cities and their supporting regions. The key novelty of this study is the high spatial resolution policy-relevant sub-sectoral analysis to identify sector-region combinations to reduce city water footprints. Virtual water footprints were 8-10 times higher than direct water consumption (per capita) in all studied cities. Virtual water from outside the city boundary is almost 20 times higher than the virtual water sourced from within the city boundary in all studied cities. Water-efficiency programs can significantly reduce the virtual water footprints of the studied cities. This includes water-efficiency and recycling on farm, and in food processing (e.g. livestock feed growing, dairy cattle farming, vegetable growing and processing) in rural regions of New South Wales, Queensland, and Victoria. The results are relevant to strategic city water footprints reduction, sustainable sourcing and planning for future disturbance of product supply, and water-sensitive city developments considering both direct and virtual water flows.

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Recovering resources from wastewater systems is increasingly being emphasised. Many technologies exist or are under development for recycling nutrients such as nitrogen and phosphorus from wastewater to agriculture. Planning and design methodologies are needed to identify and deploy the most sustainable solutions in given contexts. For the environmental sustainability dimension, life cycle assessment (LCA) can be used to assess environmental impact potentials of wastewater-based nutrient recycling alternatives, especially nitrogen and phosphorus recycling. This review aims to evaluate how well the LCA methodology has been adapted and applied for assessing opportunities of wastewater-based nutrient recycling in the form of monomineral, multimineral, nutrient solution and organic solid. We reviewed 65 LCA studies that considered nutrient recycling from wastewater for agricultural land application. We synthesised some of their insights and methodological practices, and discussed the future outlook of using LCA for wastewater-based nutrient recycling. In general, more studies suggested positive environmental outcomes from wastewater-based nutrient recycling, especially when chemical inputs are minimised, and source separation of human excreta is achieved. The review shows the need to improve methodological consistency (e.g., multifunctionality, fertiliser offset accounting, contaminant accounting), ensure transparency of inventory and methods, consider uncertainty in comparative LCA context, integrate up-to-date cross-disciplinary knowledge (e.g., agriculture science, soil science) into LCA models, and consider the localised impacts of recycled nutrient products. Many opportunities exist for applying LCA at various scales to support decisions on wastewater-based nutrient recycling – for instance, performing “product perspective” LCA on recycled nutrient products, integrating “process perspective” LCA with other systems approaches for selecting and optimising individual recovery processes, assessing emerging nutrient recovery technologies and integrated resource recovery systems, and conducting systems analysis at city, national and global level.

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The provision of urban water and wastewater services contributes to greenhouse gas (GHG) emissions. Urban water supply and wastewater utilities can potentially achieve low-carbon or carbon-neutral operation through many “utility opportunities”. Outside the jurisdiction of water utilities, many water-related “wider opportunities” can also contribute to GHG emissions abatement for cities. This study aims to explore the GHG emissions abatement potential, cost effectiveness, and enabling factors of implementing wider opportunities in cities. Using Amsterdam as a case study, we developed a marginal abatement cost curve to compare the abatement potential and cost effectiveness of both utility and wider opportunities. The results show that many wider opportunities related to thermal energy, water end use, and life cycle are cost-effective with significant abatement potential, compared to utility opportunities. This case study and emerging worldwide examples show that the water industry has a role to play to support wider water-related opportunities in cities. This vision can be supported by developing mechanisms to credit utilities for wider opportunity initiatives, building inter- and intrasectoral partnerships for utilities, accounting for scope 3 emissions of utilities, and being open to extend utilities’ role beyond water and wastewater services providers.@en

The wastewater chain of Amsterdam offers an opportunity to recover up to 100% of phosphorus per year, versus 47% currently recovered. However, for the stakeholders of Amsterdam (e.g. citizens, business) it remains difficult to scale-up existing solutions for resource recovery. Mainly, due to the limitations of the widelyused methods (e.g. mass flow, life-cycle analysis) to provide holistic assessment of the solutions and the changes they will propagate outside the wastewater chain (e.g. solid waste). In the current study, three existing phosphorus recovery Solutions applied at three scales of Amsterdam (city, neighborhood, house) were analyzed. The study showed that the house scale closed-loop solution has higher positive influence on resilience of the city. Moreover, the DSM indicators could be used to measure resilience of the city and constituent parts, given an influence of a specific Solution. The developed toolkit is applicable for analysis of other resources in the wastewater of Amsterdam.@en

Life cycle assessment (LCA) is an established methodology to assess the potential environmental impacts of products and processes. We reviewed 49 recent LCA studies (2010-2019) on wastewater nutrient recovery to synthesise some current methodological practices. Their scopes, variations, nutrient recovery accounting, uncertainty and sensitivity management, and future opportunities are discussed. There are many opportunities to improve the current practice such as assessing a broader scope of environmental impacts, improving model and inventory transparency, communicating uncertainties and understanding model sensitivities. While this study focuses on nutrient recovery from wastewater, a lot of the insights are also relevant to other water-related LCA. @en

Water plays a central role in creating sustainable cities. Past focus has been on centralised potable water supplies, wastewater treatment and drainage. However, focus is shifting towards localised fit-for purpose supplies, restoring natural water flows, minimising water-related energy, and achieving liveability through water. New conceptual frameworks help us understand this broader context. The urban water metabolism framework gives a big-picture perspective and comprehensive account of all water flows to generate water performance indicators. Quantification of the energy- and carbon-intensity of urban water (life cycle assessment and marginal abatement cost curves) helps identify the role of water management in decarbonising cities. Frameworks for understanding water-related liveability help us consider water efficiency in terms of the broader functions water delivers, instead of just per unit supplied.@en

The need for energy in water provision and use is obvious, however the drivers are often complex, difficult to assess, and often inconsistently presented. Here we build a clearer definition and conceptual framework of “water-related energy”. We apply this framework to harmonise data and results across disparate studies so that regional estimates of water-related energy can be compared in a consistent way for the first time. We show how widely different boundaries have been used for analysis including or excluding: water and wastewater utilities, as well as residential, commercial, industrial, and agricultural water users. Consequently, understanding of what constitutes “water-related energy” is widely divergent. We demonstrate how up to 12.6% of total national primary energy use can be influenced by water, when (i) water-related energy of water users, and (ii) energy use by water utilities, are all included. Water heating for residential, commercial, and industrial purposes is the dominant fraction. Water and wastewater utilities use 0.4–2.3% of primary energy or 0.6–6.2% of regional electricity, mostly for water pumping. This is substantial, but lower than frequent claims in the media and reports. To answer how is miscommunication influencing policy? we undertake a novel systematic tracking of communication to demonstrate distortion between research and its application in government reports, media and policy. We show that significant confusion is caused by (i) unclear or inconsistent boundaries (ii) widely differing use of terms for water “system”, “sector”, and “supply”, (iii) frequent failure to distinguish ‘energy’ from ‘electricity’ and (iv) wide use of non-standard units. While acknowledging that media is often less accurate than government reports, and that peer-reviewed articles generally have highest overall quality, we observe miscommunication and inconsistency in all publication forms. We argue a global protocol is needed to improve consistency of analysis and sharpen policy towards sustainable water end use because this is where most water-related energy occurs. We establish a foundational framework and definitions for this protocol while recognising much more needs to be done. The strong practical and theoretical implications of the work for sustainable cleaner production are elucidated. This is timely, as global quantification of water-related energy has yet to occur particularly for water end-use which is the dominant component.

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