This chapter explores innovative energy and environmental strategies in urban water systems to advance carbon neutrality. It highlights (i) the importance of integrating advanced water purification technologies such as riverbank filtration and reverse osmosis to remove emerging contaminants, (ii) the role of artificial intelligence and machine learning in optimizing wastewater treatment, (iii) the necessity of both engineering and non-engineering approaches to achieve greenhouse gas (GHG) emission reductions in urban water systems, (iv) the increasing relevance of circular economy principles for recovering useful resources from urban water systems, and (v) the role of life cycle assessments to ensure environmental sustainability in the pursuit of resource recovery. Case study cities illustrate the progress in decarbonizing urban water systems, with a focus on the potential and challenges of GHG emissions management. A systems thinking approach is advocated for identifying system-wide GHG mitigation opportunities in urban water systems and for leveraging GHG mitigation with environmental co-benefits and trade-offs.

This study presents the Pingjiang River Water Purification Project in Suzhou, a historic city facing water quality challenges due to urbanization. The project integrates advanced physical treatment techniques to restore water quality and ecological health while preserving the city's cultural heritage. The core component, the water purification plant, employs hollow-fibre ultrafiltration membrane technology to treat river water, achieving significant reductions in turbidity, suspended solids, total phosphorus, and chroma, along with improved transparency. Additionally, the plant's underground layout minimizes the land footprint, while sludge generated through the process is repurposed for brick manufacturing, supporting resource recovery. This study conducts a life cycle assessment to evaluate the environmental impacts of the plant's water purification process. Results show that electricity consumption, polyaluminium chloride, and sodium hypochlorite are the top contributors to environmental impacts, with a global warming potential of 0.207 kg CO2 eq/m(3). However, the plant also offsets impacts through phosphorus removal and sludge reuse. Recommendations include optimizing chemical inputs, improving energy efficiency, and integrating renewable energy. The findings highlight the project's role in balancing water quality improvement with environmental tradeoffs and co-benefits, providing insights for sustainable urban river restoration in culturally significant contexts. HIGHLIGHTS center dot The river water purification project significantly improves river water quality. center dot It employs hollow-fibre ultrafiltration membrane technology to treat river water. center dot Sludge is reused for brick manufacturing, thus promoting circular resource use. center dot Life cycle assessment identifies electricity, polyaluminum chloride, and NaOCl as major contributors. center dot Energy efficiency, reduced chemicals, and renewables lower environmental impacts.

Climate change, driven by unchecked greenhouse gas emissions, has become a pressing global concern. While large-scale anthropogenic activities are primary contributors, individual behaviours also play a significant role in carbon emissions. Carbon Footprint Calculators (CFCs) have emerged as tools to help individuals understand and mitigate their personal carbon footprints. This study presents a comprehensive evaluation of 24 publicly available CFCs, assessing their performance across five key dimensions: methodology, reference data, user inputs, output, and scientific standards. Each CFC has a score that indicates the level of performance, and our findings reveal significant variations in the performance of these CFCs. Notably, Carbon Independent, one of the CFCs, ranked the highest with an average score of 4.54, while the overall mean score for all calculators stood at 3.41, demonstrating its ability to more accurately and comprehensively assess human carbon footprint levels. A heatmap analysis further highlighted strengths and weaknesses across the evaluation dimensions. Additionally, using three hypothetical profiles (Average Household, Large Family, and Urban Single), we observed discrepancies in carbon footprint estimates among the CFCs (standard deviation equals 2.3 tons CO2 Emissions per capita), which means that the calculation design of the carbon footprint calculators is inconsistent. The Chuck Wright Calculator consistently produced the most conservative estimates across all three profiles, while the EPA CFC reported the highest emissions for the urban single profile. Our discussion underscores the potential of CFCs as tools for behavioral change, emphasizing their role in raising individual awareness and driving collective action. The study concludes with recommendations for enhancing the accuracy, transparency, and user-friendliness of CFCs, positioning them as pivotal instruments in the global fight against climate change.

Physicochemical methods, which are essential for treating highly toxic industrial wastewater, remain underexplored in terms of emissions reduction compared to biological methods. This work examines two electroplating wastewater treatment processes: an old process using sodium hydroxide as the hydroxide ion source and a new process that partially substitutes sodium hydroxide with low-cost calcium hydroxide. Life cycle assessment results demonstrate that the substitution improves environmental performance across all but one impact categories. Significant reductions in the categories of ammonia nitrogen (55.7%), chemical oxygen demand (54.6%), and volatile organic compounds (62.4%) are attributed to the use of key chemicals, offering a clear pathway for emissions reduction. However, reducing impacts in categories like global warming potential and primary energy demand is more challenging due to the balanced contribution of multiple inventory items. Field data highlight that calcium hydroxide not only reduces sodium hydroxide consumption but also decreases the use of other resources like sodium hypochlorite, activated carbon, and electricity, resulting in substantial environmental benefits. Among them, global warming potential is reduced from 15.3 kg CO2 eq/ton of water to 11.7 kg CO2 eq/ton of water, a decrease of 23.5%. This study demonstrates the multifunctionality of chemicals like calcium hydroxide in improving treatment efficiency and reducing life cycle environmental impacts. It provides insights into advancing and optimizing industrial wastewater treatment processes.

Urban water utilities are significant energy users and also key actors in decarbonisation. However, the integrated perspective of urban water supply and wastewater system emissions, the relevant driving forces, and the boundaries of inclusions or exclusions, are rarely discussed. This is due to widely disaggregated data, and complex issues regarding the boundary of the system being investigated. This work develops an innovative assessment approach to assess system-wide emissions. We investigate historical emissions from eight cities (representing 56 million people). This study answers the question: what are the emission trajectories of urban water supply and wastewater systems and influencing factors and the influence of system boundary inclusions? The results indicate that, in many systems, "additional" or "new" water sources such as desalination or long-distance water transfers can dominate the emissions trends. Inconsistent inclusion of infrastructure for these supplies complicates city comparisons. Additionally, clarity is needed on whether emissions from recycled water (potable and non-potable) is reported as water supply or wastewater emissions. The creation of water/wastewater-emission trajectories better illustrates trade-offs occurring with management - for example, water supply in Perth and Beijing. The trajectory also illustrates reductions achieved for 15 years, for example, water supply in San Diego (reducing 77 %) and wastewater in New York City, San Diego, Los Angeles and Tokyo (reducing 38, 44, 47, and 17 % respectively). Our integrated analysis method provides a new emphasis for more holistic management of the water cycle. By revealing system boundary issues in reporting and systematically assessing full water cycle emissions, we demonstrate how essential this is to enable comparison across complex systems and city and utility reporting schemes.

Wastewater has emerged as a potential bioenergy resource. Previous research has largely focused on assessing individual bioenergy supply pathways and products, limiting system boundaries to recovery processes, or considering only a limited range of environmental impacts. This study evaluated the life cycle environmental impacts of three forms of bioenergy products (i.e., bioelectricity, bioheat, and biohydrogen) recovered through 27 pathways from sewage sludges at wastewater treatment facilities and benchmarked them against their conventional energy counterparts across 311 pathways. The results indicate that bioelectricity and bioheat have substantial lower global warming and fossil resource scarcity impacts than conventional energy commodities. All bioenergy products involve trade-offs in specific environmental categories, such as toxicity, eutrophication, and mineral resource depletion. This study further compared the environmental impacts of both intermediate and final forms of bioenergy products-bioelectricity, bioheat, biomethane, and biohydrogen. Bioelectricity had the highest impacts per unit energy due to exergy-based allocation, while bioheat had the lowest. With similar environmental impacts and no end-use greenhouse gas emissions, biohydrogen could be preferable to biomethane. Accounting for the multifunctional nature of anaerobic digestion, beyond bioenergy production, can further improve the environmental performance of most bioenergy pathways.

Biochar offers a potential sustainable pathway for recovering phosphorus from wastewater to agriculture. Magnesium-modified biochar has demonstrated an enhanced phosphate adsorption capacity and excellent bioavailability. This study aims to identify the life cycle environmental hotspots in phosphorus recovery from wastewater using magnesium-modified biochars derived from bamboo, corn, and wood and compared them with common phosphate fertilizers. The results show that the biomass supply stage and the modification stage are the main environmental hotspots in most impact categories. As the phosphorus load of wastewater decreases, the phosphorus recovery stage could become the hotspot. Although phosphate-loaded magnesium-modified biochars in the base case do not have a better overall environmental performance than most phosphate fertilizers (especially those without nitrogen), they have significantly lower mineral resource scarcity and ecotoxicity. The sensitivity analysis suggests that the results are sensitive to the background inventory selected. The analysis indicates that the biochar yield, the phosphate adsorption capacity of the biochars, the source of modification chemical, and the source of biomass feedstock are key areas for technological and inventory improvement. In the future, a comprehensive field application inventory and a diverse set of background inventory are needed to better assess this sorption-based phosphorus recovery pathway.

With the paradigm shift in wastewater management from pollutant removal to resource recovery, more wastewater -derived products are emerging from different recovery pathways. It is becoming increasingly important to understand the potential environmental impacts of these products through life cycle assessment (LCA). This study aims to compile life cycle inventories of wastewater -derived products from the perspective of the product end users (e.g., agricultural sector, packaging industry), and to explore the challenges of their compilation. Using inventories from wastewater resource recovery LCA literature, we compiled an attributional inventory (88 sets) and a consequential inventory (33 sets) of three categories of wastewater -derived products - phosphorus compounds, nitrogen compounds, and biopolymers. The two inventories differ by the choices of system boundary, how foreground systems are being modelled, and how co -products are being handled. We found that while there is a large body of literature related to wastewater resource recovery LCA, very few studies (29 out of 174 for the three categories of products) are suitable for end users to successfully compile inventories of derived products. The inventories were assessed by the technology readiness level assessment, the data quality assessment, and the cumulative energy demand indicator. The inventories can be used directly by end users or served as "screening " inventories for end users to prioritize data collection effort. The identified challenges of inventory compilation include diverse recovery settings, the absence of baseline scenarios, the multifunctional nature of wastewater treatment plants, the lack of inventory transparency and completeness, and low technology readiness level for some recovery pathways. While established or emerging approaches exist to address most of these challenges for end users, wastewater resource recovery LCA practitioners can enhance their assessments to be more end -user -oriented. This can be achieved by including baseline non -recovery scenarios, disclosing detailed life cycle inventory by system components, and assessing a wide variety of operating scenarios. Addressing some of these compilation challenges would enhance the comprehensiveness and quality of wastewater -derived product inventories.

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 CO2eq/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 CO2eq/year (0.09 kg CO2eq/m3), with electricity intensity of 0.43 kg CO2eq/m3. Additionally, compare to the hypothetical relocating scenario, it saved 6.67 × 104 m2 land and 33.0 kt CO2eq/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.

The global water industry has a greater emphasis on energy management than ever before. The confluence of rising energy demand and costs, and net-zero greenhouse gas emission targets means the sector must rapidly transition to a new 'energy future'. Yet, few cities have assessed the long-term energy use of their water and wastewater systems. Here, we undertake a novel and integrated assessment of the historical trends of energy use for water and wastewater in three Australian and two US cities, collectively 17 million people. The key research question is what were the historical trends of energy use for water supply and wastewater treatment, and what can we understand about the drivers? The research contributes a first systematic time-series assessment of energy trajectories of both water and wastewater, across multiple cities. Uniquely, it integrates long-term (up to 20 years) energy dynamics in a comparative analysis. The work also contributes a qualitative analysis of driving factors behind the observed energy variations. The time-series analysis (2001-2020) identifies how energy use is evolving through time in widely differing climate, urban and water infrastructure conditions. The cities studied demonstrated downward trends in water use by 30-42% and wastewater collected by 5-30%, primarily due to water conservation and drought-related restrictions. Annual per-capita energy use for water supply reduced in Los Angeles (-58%, from 276 to 116.5 kWh/p/a), San Diego (-59%, from 503.7 to 204.2 kWh/p/a), Sydney (-26%, from 40.6 to 30.1 kWh/p/a) and increased in Melbourne (+859%, from 15.7 to 150.6 kWh/p/a) and Perth (+139%, from 118.1 to 281.9 kWh/p/a). Compared to water supply, energy use for wastewater was far more stable (it varied between 45 and 85 kWh/p/a), and not the crucial contributor to overall energy use dynamics. The significant increase in seawater desalination is identified as the primary driver of increased energy use in the three Australian cities. To offset this huge demand, developing renewable energy generation emerged as the key strategy. It causes high fluctuation of renewable energy use shares (Sydney: 317 GWh, accounting for 48.5% energy use for water and wastewater in 2011; compared to 19 GWh, accounting for only 2.5% in 2008). In contrast, both Los Angeles and San Diego managed to considerably reduce energy use by decreasing their imported water volume and energy intensity (the result of an adjusted supply portfolio). However, the absence of consistently comprehensive water/energy/renewable energy data remains a significant hurdle for a thorough quantitative analysis of drivers. Given these observations, it is evident that detailed quantitative analysis for influencing factors (e.g. water use, climate, infrastructure upgrading, sustainability targets), requires separately reported energy use for both water supply and wastewater, reported water from categorized sources and

Many opportunities are available to reduce greenhouse gas (GHG) emissions associated with municipal wastewater management. The vision of low-carbon or carbon-neutral operation of wastewater treatment plants is emerging. Is the vision of low-carbon wastewater management consistent with improving environmental performances? Here, we explored this question using wastewater management life cycle assessment studies that had scenarios with GHG emissions reduction through alternative wastewater treatment options, sludge treatment options, and resource recovery options. Among these options that contribute to GHG emissions reduction, integrating resource recovery (i.e., water, biogas, phosphorus) appears to have greater chances of co-benefits (especially on acidification, eutrophication, and photochemical oxidant formation). In contrast, shifting sludge disposal practices require more attention to their potential trade-offs (especially on eutrophication and toxicity). It is evident that achieving GHG emissions reduction oftentimes involves compromising on other environmental performances. While more GHG emissions reduction and environmental co-benefits can be seen in most of the scenarios and impact categories (over 75% combining), achieving GHG emissions reduction can still lead to deteriorating of at least one of the environmental impact categories in over half of all the scenarios. Instead of exclusively focusing only on GHG emissions mitigation, abatement strategies from municipal wastewater management systems should also consider harnessing environmental co-benefits and alleviating unintended environmental trade-offs. Identifying the potential contributing factors behind environmental trade-offs can also represent opportunities for optimizing the design and operation of these GHG emissions reduction options. Into the future, wastewater management needs to adopt a broader systems perspective considering the wider system boundary and environmental scope.

ABSTRACT Anthropogenic nitrogen fluxes are profoundly altering the global biogeochemical nitrogen cycle. Better management of these nitrogen fluxes is essential. Recovering nitrogen from urban wastewater reduces both the energy and resources required to produce nitrogen-based fertilizer and to remove nitrogen from wastewater collected. Nitrogen can be recovered from wastewater in the form of ammonium sulfate, a common nitrogen-based fertilizer. In the urban setting, the technology can be applied to target source-separated urine or municipal wastewater. To assess the environmental sustainability of this approach, this study compared the life cycle environmental impacts of ammonium sulfate recovered from urban wastewater (through eight different recovery technology trains) and ammonium sulfate produced by six different industrial processes. The results show that wastewater-derived ammonium sulfate generally has lower potential environmental impacts than industrially produced ammonium sulfate in most of the impact categories assessed. The impact for the source-separated urine centralized recovery train is the smallest. The contribution analysis shows that energy, sulfuric acid and sodium hydroxide use are the major contributors, while the background inventory analysis shows that the results can be sensitive to the choice of region-specific background inventory. In the future, nitrogen recovery from urban wastewater is promising for the circular economy in cities.

AbstractRadical changes are needed in metropolitan-scale strategic planning to better integrate land use, transport planning, and urban water planning, as well as new models for water-sensitive urban design at building and precinct scales that deliver liveability and ecosystem benefits. This is a mission-scale challenge. Transition pathways involve combinations of new technology, innovative urban design, enabling policies and regulations, novel planning processes and urban development, and demand-side changes in consumers’ attitudes regarding urban lifestyles related to water and energy use. The chapter draws on 10 years of applied research undertaken collaboratively with government and industry to illustrate how integrated plans and designs can be established and tested. Examples of good design spanning the architectural and technological realms supported by quantified performance analysis and institutional change across the entire water cycle including natural and anthropogenic systems are provided. They address urban water transitions that need to be accelerated across scales, including site, precinct, and city to achieve more sustainable water-sensitive urban regions.

Urban sprawl, excessive rainfall, and resource limitations have challenged the performance of conventional water-sensitive urban designs (WSUD). To address these issues, there is a growing interest in adopting site real-time adaptive control (SRAC) for integrated and real-time water management. This research evaluates the effectiveness of SRAC technology in reducing stormwater pollutants in a highly developed urban area, comparing it with conventional WSUD methods. The study focuses on examining the impact of the SRAC-WSUD method on stormwater quality. Findings indicate that the SRAC-WSUD method reliably reduces stormwater pollutants under varying rainfall conditions. Moreover, it enhances the resilience and performance of existing stormwater systems without the need for additional infrastructure upgrades. For the whole year scenario, the SRAC-WSUD method resulted in reductions in total pollutant loads. Notably, there was a 196.72 kg/year decrease in total suspended solids (TSS), a 0.07 kg/year decrease in total phosphorus (TP), and a 0.78 kg/year decrease in total nitrogen (TN). These findings highlight the potential of SRAC-WSUD in improving stormwater quality and its implications for sustainable urban water management. Overall, this research contributes to advancing the understanding and practical implementation of SRAC technology in stormwater management, offering valuable insights for urban planning and water resource preservation.

The water sector could play a major role towards a Net Zero greenhouse gas (GHG) future if Scope 3 emissions were embraced and operationalised. Significant opportunities and challenges exist in tackling Scope 3 emissions including those associated with customer hot water use. Present GHG emission reduction practices predominantly focus on Scope 1 "within utility" and Scope 2 "purchased energy" emissions. In the urban water cycle, Scope 3 "indirect" emissions dominate, and water use is only one example of Scope 3 emissions. Over 90% of all water cycle GHG emissions can be attributed to water use in residential, industrial and commercial premises, collectively some 7% of global GHG emissions. One possibility is for water utilities to actively support efficient hot water use such as new ultra-low flow shower heads. Scope 3 opportunities also offer a range of cost-effective emissions-reduction opportunities, particularly when the wider perspective of "community value" is considered and not just a "business financial perspective". Hot water efficiency is additionally essential to Net Zero carbon futures, even with decarbonised grids, because most major Net Zero roadmaps require energy efficiency gains. Scientific and management advance needed includes: accounting methodologies, clear roles, collaboration, new business models, and clear definitions. The water sector has the opportunity to play a significant role in achieving Net Zero cities. The decision how much is yet to be made.

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.

This book aims to provide an overview of how photocatalysis can be employed in water and wastewater treatment. Each chapter will attend to a different area of interest, starting with an introduction on the fundamentals of photocatalysis. The covered topics include metal organic frameworks (MOFs), photocatalytic reactor types and configurations, landfill leachate treatment, and life cycle assessment (LCA) of solar photocatalytic wastewater treatment. In addition, the final two chapters provide fresh new insight, by analyzing international patents on photocatalytic materials, solar photocatalysis, and nanotechnology.ISBN: 9781789061925 (Paperback)ISBN: 9781789061932 (eBook)ISBN: 9781789061949 (ePUB)

Accounting for carbon should be undertaken at multiple scales to create awareness of the negative environmental impacts of consumption. We undertake a comprehensive consumption-based supply-chain assessment of a community's emissions for a selected council area in the Greater Sydney region of Australia using multi-regional input-output analysis, by constructing a customised input-output table with data from the Australian Household Expenditure Survey on items related to food, beverages, housing, transport, energy, clothing & footwear, household appliances & furniture, medical services, communication, recreation and education. We quantify the Scope-1, -2, and -3 emissions of households in the council area, and put the results in the context of voting preferences of the Council community. Our results suggest that despite left-wing voter preferences, the consumption habits of green voters carry high carbon footprints – the per-capita carbon footprint of Inner West residents is about 1.3 times more than the footprint of residents in the Rest of Greater Sydney. Furthermore, about two-thirds of the footprint is embodied in upstream supply chains for satisfying consumption. This result is significant in that it means that if policy addressed only energy-related direct emissions, it would be missing a majority of the population's CO2e footprint.

Many cities have pledged to achieve carbon neutrality. The urban water industry can also contribute its share to a carbon-neutral future. Using a multi-city time-series analysis approach, this study aims to assess the progress and lessons learned from the greenhouse gas (GHG) emissions management of urban water systems in four global cities: Amsterdam, Melbourne, New York City, and Tokyo. These cities are advanced in setting GHG emissions reduction targets and reporting GHG emissions in their water industries. All four cities have reduced the GHG emissions in their water industries, compared with those from more than a decade ago (i.e., the latest three-year moving averages are 13%–32% lower), although the emissions have “rebounded” multiple times over the years. The emissions reductions were mainly due to various engineering opportunities such as solar and mini-hydro power generation, biogas valorization, sludge digestion and incineration optimization, and aeration system optimization. These cities have recognized the many challenges in reaching carbon-neutrality goals, which include fluctuating water demand and rainfall, more carbon-intensive flood-prevention and water-supply strategies, meeting new air and water quality standards, and revising GHG emissions accounting methods. This study has also shown that it is difficult for the water industry to achieve carbon neutrality on its own. A collaborative approach with other sectors is needed when aiming toward the city’s carbon-neutrality goal. Such an approach involves expanding the usual system boundary of the water industry to externally tap into both engineering and non-engineering opportunities.