Centralised, decentralised or hybrid sanitation systems? Economic evaluation under urban development uncertainty and phased expansion

Comparative life-cycle sustainability assessment of centralized and decentralized remediation strategies at the city level

Remediation of contaminated soil at industrial sites has become a challenge and an opportunity for sustainable urban land use, considering the substantial secondary impacts resulting from remediation activities. The design of soil remediation strategies for multi-site remediation from a regional perspective is of great significance for cities with a large number of brownfields. Centralized and decentralized facilities have been studied in different environmental fields, yet limited research has focused on centralized soil remediation, specifically the treatment of contaminated soil from different sites through the construction of shared soil treatment facilities. This study proposes a framework for comparing centralized and decentralized strategies for contaminated soil remediation based on the integration of life-cycle sustainability assessment and multi-objective optimization. With Zhuzhou, an industrial city in China, serving as an example, results show that after optimization, the centralized scenario can reduce total environmental impacts by 25 %-41 %. In addition, the centralized scenario can reduce economic costs by 27 %-39 %, saving up to 176 million USD. The advantages of the centralized soil remediation strategy include: (1) increased use of soil washing, (2) reduced use of off-site disposal, and (3) reduced construction and efficient utilization of soil treatment facilities. In conclusion, the centralized strategy is relatively suitable for cities or areas with a large number of medium or small-sized contaminated sites. The built framework can quantitatively evaluate multiple sites soil remediation at both the city and individual site level, allowing for a straightforward and objective comparison with the optimal remediation design.

Wastewater reuse and energy saving require a more decentralized urban wastewater system? Evidence from multi-objective optimal design at the city scale

Decentralization is recognized as an emerging solution for a more sustainable urban wastewater system (UWS) for the future. However, the debate of centralization vs. decentralization at the system's planning stage remains unresolved, mainly due to the complexity of the system's spatial structure and the multiple design objectives, such as water reuse and energy conservation. This paper presents the Sustainable Urban Wastewater System Generator (SUWStor) as a tool to address this issue. Integrating a graph representation of the system structure and the ant colony algorithm, SUWStor can produce Pareto optimal solutions for system design under three objectives: minimizing the capital cost, minimizing the operational energy consumption, and maximizing the water reuse capacity. The model is used for system design in a 100-square-km new city, the Xiong'an New District in China. Compared to the solution based on human experience, the model can reduce the system's capital cost by 7% and the operational energy in the pipe network by 26%, while maintaining the water reuse capacity at 100%. With this model, the relation between the optimal system layout and the choice over different design objectives can be discussed for any given area. In our case study, the optimal capacity of WWTPs for the lowest-cost solution is 48,000 m³ per day, leading to a total number of WWTPs of 5. As the water reuse level increases to maximum, the optimal capacity reduces to 15,000 m³ per day, where the number of WWTPs is 16. The model is also able to perform significantly better than the locally optimized results, in which only the WWTP locations are fixed at their optimal values. This demonstrates the importance of a global optimization model in designing the integrated UWS.

Why are decentralised urban water solutions still rare given all the claimed benefits, and how could that be changed?

Numerous innovative decentralised urban water solutions have been described over many years, yet their application in practice is still not common at all. While many proposed solutions may have some techno-economic advantages over current systems, the real reasons for the slow uptake have more to do with system-wide inertia and technology 'lock-in' where existing solutions are preferred for simplicity and familiarity. A key factor is also the inadequate assessments in project decision making processes that should consider all relevant social, environmental and economic benefits and values. This paper highlights some key barriers and how to address them in a more holistic way. It also identifies opportunities where more integrated, hybrid solutions could offer significant benefits over current technologies. It calls on all key partners in this sector to foster broad and strong collaborations, and on water service providers to be empowered to take an inclusive leadership role in creating such innovative solutions that help address our growing challenges driven by rapid urbanisation and climate change.

The third route: A techno-economic evaluation of extreme water and wastewater decentralization

Water systems need to become more locally robust and sustainable in view of increased population demands and supply uncertainties. Decentralized treatment is often assumed to have the potential to improve the technical, environmental, and economic performance of current technologies. The techno-economic feasibility of implementing independent building-scale decentralized systems combining rainwater harvesting, potable water production, and wastewater treatment and recycling was assessed for six main types of buildings ranging from single-family dwellings to high-rise buildings. Five different treatment layouts were evaluated under five different climatic conditions for each type of building. The layouts considered varying levels of source separation (i.e., black, grey, yellow, brown, and combined wastewater) using the corresponding toilet types (vacuum, urine-diverting, and conventional) and the appropriate pipes and pumping requirements. Our results indicate that the proposed layouts could satisfy 100% of the water demand for the three smallest buildings in all but the aridest climate conditions. For the three larger buildings, rainwater would offset annual water needs by approximately 74 to 100%. A comprehensive economic analysis considering CapEx and OpEx indicated that the cost of installing on-site water harvesting and recycling systems would increase the overall construction cost of multi-family buildings by around 6% and single-family dwellings by about 12%, with relatively low space requirements. For buildings or combined water systems with more than 300 people, the estimated total price of on-site water provision (including harvesting, treatment, recycling, and monitoring) ranged from $1.5/m³ to $2.7/m,³ which is considerably less than the typical tariffs collected by utilities in the United States and Western Europe. Where buildings can avoid the need to connect to centralized supplies for potable water and sewage disposal, water costs could be even lower. Urine-diversion has the potential to yield the least expensive solution but is the least well developed and had higher uncertainty in the cost analysis. More mature layouts (e.g., membrane bioreactors) exhibited less cost uncertainty and were economically competitive. Our analysis indicates that existing technologies can be used to create economically viable systems that greatly reduce demands on centralized utilities and, under some conditions, eliminate the need for centralized water supply or sewage collection.

Public Perceptions of Reuse of Faecal Sludge Co-Compost in Bhubaneswar, India

Although faecal sludge (FS) co-compost contains vital nutrients, there are several barriers limiting adoption and reuse of FS co-compost in agriculture. This study in Bhubaneswar found that health risk and bad odour were the two topmost negative perceptions of FS co-compost reuse. The main factors influencing farmers’ negative perceptions of FS co-compost were bad odour and fear of infection, whereas socio-cultural/religious beliefs and bad odour were the key factors influencing the negative perceptions of urban households practising kitchen gardening (UHPKG). Fear of infection and bad odour were the key factors influencing fertiliser retailers’ negative perceptions, while inadequate information, unavailability, and lack of government policy on FS co-compost reuse were the key factors influencing Farmer Producer Organisations’ negative perceptions. The majority of farmers (95%) and UHPKG (72%) were unwilling to consume food crops grown with FS co-compost, mainly because of feelings of disgust, fear of infection, and religious and socio-cultural beliefs.

Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems

In order to obviate the economic issues associated with pit latrine emptying and transport such as high water additions and rheologically difficult sludge properties, the implications of prompt solid/liquid separation were investigated. This was achieved through rheological characterisation of fresh human faeces and synthetic faeces, and comparison with aged faecal sludges. Shear yield stress, thixotropy and post-shear structural recovery were characterised for a total solids (TS) concentration range of 5-35% total solids (TS) and stickiness yield stress was determined for concentrations up to 100% TS. Fresh faeces rheology proved to be favourable when compared to aged matrices, evidenced by a lower shear yield stress and higher gel point solids concentration, suggesting that aging could alter the physico-chemical properties of faecal sludge. Fresh and synthetic faeces exhibited similar shear thinning, thixotropic behaviour with the majority of structural breakdown occurring at a low shear rate of 10 s^-1, and the extent increasing with higher solids concentrations. At 32% TS, fresh faeces shear yield stress was permanently reduced by 80%, suggesting that low shear pumping could reduce the energy demand required for faeces transport. The sticky phase, which represents the region to avoid faecal transport and mechanical drying processes, was identified to range from 30 to 50% TS, with 25% TS as ideal to commence dewatering processes. This also coincides with the average solids concentration of faeces, which is achievable by source separation. This study has identified that handling of fresh faeces as opposed to aged faecal sludges would result in economic and environmental benefits, with energy, water and labour savings.

To centralize or to decentralize? A systematic framework for optimizing rural wastewater treatment planning

Untreated rural sewage seriously affects the universal access to clean water of rural residents. The lack of decision-support tools in rural sewage treatment (RuST) planning makes it difficult for RuST system to achieve the expected results and is not conducive to the optimal allocation of limited funds. Hence, there is an urgent need to develop a decision-support framework for large-scale RuST planning. For the first time, RuST planning decision-support framework was developed using divide-and-conquer strategy based on rural residents' spatial pattern (RESP) and the optimal pattern of RuST. This framework can be transferred to other countries/regions easily by correcting RESP dataset according to the spatial and environmental characteristics. We confirmed that the variation of RESP made the ideal RuST pattern varied significantly under different topography. And community-based pattern could be the optimal pattern for large-scale RuST planning, when spatial obstacle and RESP were fully considered. The price of onsite sewage treatment facility is the most significant factor for RuST planning. In our selected case, requited onsite facility accounted for 65.51%. For the total investment, the cost of sewer systems accounted for 56.01%, and the average investment in plains, hills, platforms and mountains was 1401, 1803, 1903 and 1859 USD/household, respectively. We expect this research could provide reference for RuST planning in other developing countries/regions all around the world.

Environmental Concern Priming and Social Acceptance of Sustainable Technologies: The Case of Decentralized Wastewater Treatment Systems

According to a report by the World Economic Forum, the water crisis is the fourth most serious global risk to society. The apparent limitations of the hydraulic paradigm to solving this crisis are leading to a change in water management approaches. Recently, decentralized wastewater treatment systems have re-emerged as a partial solution to this problem. However, to implement these systems successfully, it is necessary not only to design this technology but also to have social support and willingness among citizens to use it. Previous studies have shown that these technologies are often perceived as being too costly, and people often do not consider the need for adopting them. However, it has also been pointed out that thinking about these technologies as a sustainable endeavor to reduce human impact on the environment can help to overcome the barriers to usage. Thus, we test whether priming environmental concerns before presenting information about decentralized wastewater treatment plants will increase acceptance of those technologies. In this study, we test whether priming environmental concerns can enhance the acceptance of decentralized wastewater treatment plants even when presenting disadvantages of the technology. In order to do so, we designed an experimental study with a sample of 287 people (85.7% women, M _age=20, 28). The experimental design was 2 (priming the environmental concern vs. no priming)×2 (type of information: only advantages vs. advantages and disadvantages). The results showed that those in the environmental concern priming condition had more positive attitudes and behavioral intentions toward decentralized wastewater treatment plants than those in the control condition group. Participants who received only advantages information had a more positive perception toward the decentralized wastewater systems than in the condition, where disadvantages were present, but in the priming condition this difference was not significant. This implies that priming environmental concern helps to overcome the possible disadvantages that act as barriers to acceptance.

An integrated assessment of environmental, economic, social and technological parameters of source separated and conventional sanitation concepts: A contribution to sustainability analysis

Resource recovery and reuse from domestic wastewater has become an important subject for the current development of sanitation technologies and infrastructures. Different technologies are available and combined into sanitation concepts, with different performances. This study provides a methodological approach to evaluate the sustainability of these sanitation concepts with focus on resource recovery and reuse. St. Eustatius, a small tropical island in the Caribbean, was used as a case study for the evaluation. Three source separation-community-on-site and two combined sewerage island-scale concepts were selected and compared in terms of environmental (net energy use, nutrient recovery/reuse, BOD/COD, pathogens, and GHG emission, land use), economic (CAPEX and OPEX), social cultural (acceptance, required competences and education), and technological (flexibility/adaptability, reliability/continuity of service) indicators. The best performing concept, is the application of Upflow Anaerobic Sludge Bed (UASB) and Trickling Filter (TF) at island level for combined domestic wastewater treatment with subsequent reuse in agriculture. Its overall average normalised score across the four categories (i.e., average of average per category) is about 15% (0.85) higher than the values of the remaining systems and with a score of 0.73 (conventional activated sludge - centralised level), 0.77 (UASB-septic tank (ST)), 0.76 (UASB-TF - community level), and 0.75 (ST - household level). The higher score of the UASB-TF at community level is mainly due to much better performance in the environmental and economic categories. In conclusion, the case study provides a methodological approach that can support urban planning and decision-making in selecting more sustainable sanitation concepts, allowing resource recovery and reuse in small island context or in other contexts.

Wastewater treatment decentralization: Is this the right direction for megacities in the Global South?

The centralization-decentralization dichotomy in wastewater treatment management has been a recurrent topic of discussion in the urban context. The escalation of environmental hazards linked to increasing mismanaged wastewater flows in emerging or developing cities has vivified this conundrum. It is argued that there is a wide range of parameters to identify the optimal level of centralization-decentralization that must be implemented. In many cases, this prevents decision-makers from having a clear picture of the most appropriate management choices that must be undertaken. Hence, the main objective of the current discussion consists of an in-depth comparison between centralized wastewater treatment systems and decentralized systems with source separation in urban environments of the Global South. Moreover, a set of actions that should be considered in order to upgrade wastewater treatment systems amidst the existence of numerous economic, social and environmental constraints are analyzed. Considering the constraints of megacentralization as a preferred option, we argue that decision-makers should restrain from entering a centralization-decentralization dichotomy, seeing the process as a gradient between the two concepts. In fact, we advocate combining the benefits of each of the two perspectives to generate an adaptive management, site-specific solution for urban environments. For this, the inclusion of quantitative management tools, such as life-cycle environmental or cost management methodologies, in multi-objective optimization models, constitutes an interesting path forward towards fostering comprehensive policy support.

Energy Self-Sufficiency Aiming for Sustainable Wastewater Systems: Are All Options Being Explored?

In upcoming years, water demand is expected to boost worldwide, and with that, wastewater generation and the required energy for treatment. Provided that efficiency measures should be implemented at first instance, developments of renewable energy technologies are needed to improve sustainability at wastewater treatment plants (WWTPs). Based on theoretical analyses of literature data, this article presents a novel perspective of the role that hydropower could play in that energy framework. This research applied a new approach compared to previous studies, considering the introduction of sustainability aspects in the decision-making process, other than economic feasibility. With that aim, a broad search of real case studies was conducted, and suitable Key Performance Indicators based on the energy self-sufficiency concept were selected and applied to the identified cases. The findings suggest that there is not a rule of thumb to determine feasibility for hydropower installation and this technology might deserve more attention. This new perspective can help to raise awareness among policy makers, decision managers, or plant operators, of the possibilities hydropower could offer to the wastewater industry in the pathway towards more sustainable systems.

What factors affect the selection of industrial wastewater treatment configuration?

Industrial wastewater treatment is gaining significance in literature due to stricter environmental policies and increased environmental awareness. The selection of the wastewater configuration encompasses both the treatment as well as several decisions around wastewater collection and disposal pertaining industrial decision-making sphere. However, so far in the wastewater literature, research has mostly discussed either technical features of wastewater technologies, or wastewater policy issues at broader level, without focusing on the industrial decision-making issues and driving factors leading to the selection of a specific configuration. Starting from a literature review, the present study provides an innovative framework of the possible options for wastewater system configuration, as well as major adoption factors by industrial decision-makers. The factors have been classified according to 7 categories, namely: influent-related, technological, economic/financial, internal socio-cultural, external socio-cultural, regulation, site characteristics. The framework, validated with acknowledgeable experts, policy makers and firms, has been preliminarily applied to Italian and Australian food firms. Our investigation reveals that the framework was able to include all relevant problems faced by industries in the selection of a treatment system configuration; besides, the relative importance of factors has been assessed: legal requirements emerge as the most critical factors, followed by volume and discharge fee, the latter particularly interesting for policy makers purposes, since it may guide the decision-making process. Further, the wastewater volume seems to play a key role in our exploratory investigation, with smaller firms preferring a complete off-site treatment to reduce the complexity, whilst larger firms preferring instead more partial or complete on-site treatment configurations for compliance costs reduction. In conclusion, we have provided policy and managerial implications stemming from the study as well as sketched interesting future research avenues.

Energy recovery potential in coupling of sanitation and agriculture: Techno-economic analysis on resource-oriented sanitation

The coupling of sanitation system and agriculture production is essential to mitigate the environmental burden and offset unsustainable fertilizer utilization by employing resource-oriented sanitation. Yet, the economic feasibility and energy recovery potential from domestic waste have rarely been investigated. To assess four scenarios (whether with kitchen waste separation; whether with energy recovery) in the resource-oriented sanitation system, an integrated assessment framework based on energy analysis and techno-economic analysis is employed to investigate the comprehensive sanitation system including both wastewater treatment and solid waste disposal. The results show that energy recovery from human excreta and kitchen waste can offset the energy consumption of the sanitation system and the energy surplus can even be 1067.70 kJ·PE^-1·day^-1. The optimum covering range of the regional recovery center was quantified from the balance between scale effect and spatial distribution, and the serving inhabitants need to be more than 2800.

Key criteria for considering decentralization in municipal wastewater management

Wastewater pollution problems are associated with population growth and the concentration of population in large urban centers. According to United Nations projections for 2050, the world population will reach 9 billion people, increasing the pressures on water resources due to their demand and pollution. Based on UNICEF and World Health Organization estimates, 2.4 billion people worldwide currently lack access to improved sanitation facilities, with 946 million practicing open defecation. Decentralized wastewater treatment systems are a viable and necessary alternative for wastewater management, thus, minimizing environmental impacts, facilitating resource recovery, and providing rural and peri-urban inhabitants with access to basic sanitation. This literature review article uses the multicriteria analysis tool to present the key economic, institutional, social, environmental, and technological aspects, criteria, and indicators that must be considered for successful decentralized system implementation planning to strengthen basic sanitation service coverage in the rural and peri-urban areas where it does not exist.

Treatment and Effective Utilization of Greywater: A Preliminary Case Study

Greywater has been identified as a valuable alternative water source over recent years. Few practices (i.e., recycling and reuse) of greywater have attracted global attention in meeting the future water demand. However, essential parameters should be analyzed for reliable reuse and treatment. The present study addresses the possibilities of the alternative source with the treated greywater. Gravity—governed flow methods through a column containing gravel, sand, and activated carbon was applied. The quality of treated greywater from the university campus, which included physical, chemical, and biological parameters, was assessed to check non-potable reuse suitability. The reduction percentage of organics in biological oxygen demand and chemical oxygen demand was 64% and 42%, respectively. Similarly, the reduction percentage was obtained at 74% and 66% for turbidity and electrical conductivity. The removal efficiency was 57%, 77%, 48%, and 44% for total dissolved solids, alkalinity, chlorides, and total hardness. The pH of treated water samples was found in the neutral range suggesting its suitability for reuse. Hence, the proposed greywater treatment method is a cost-effective and straightforward approach to reuse greywater for irrigation, watering the lawns, and car washing. The greywater collected can be disinfected immediately and reused with minimal possibility of regrowth of microorganisms.

Real-world sustainability analysis of an innovative decentralized water system with rainwater harvesting and wastewater reclamation

This study investigated an innovative decentralized water system which combined rainwater harvesting with wastewater reclamation to generate 39% of the water resources needed for a higher education institution with student and staff accommodation in India. We collected performance data to critically appraise the current water system, design alternatives and water management optimization opportunities. The campus was recently built in a hot, semi-arid region of India with a summer, monsoon and winter season. It represented in a microcosm the vision of leading Indian engineers for a more sustainable urban systems future. We collated the water infrastructure costs, blue and recycled water demands, chemical demands, electricity demands and operational costs over a calendar year. The annual institutional water demand was 379,768 m³, of which 32% was sourced from reclaimed wastewater, and 7% from roof-collected rainwater. Electricity consumption was 0.40 kWh/m³ for drinking water treatment, and 0.62 kWh/m³ for wastewater treatment, in line with median values reported for centralized systems. Rainwater harvesting and wastewater reclamation accounted for 42% of the water infrastructure costs, with a predicted payback period of >250 years through reduced operational costs. Scenario analysis recommended a water system design alternative with wastewater reclamation for ground maintenance only, which was predicted to yield similar environmental benefits, with an infrastructure cost payback period of only 15 years. Scenario analysis also revealed how better water management to address leakage, and more drought-tolerant landscaping, could improve environmental metrics of the current system by up to 52% and reduce operational costs by up to 23%. Reducing high domestic water usage was found to be essential to secure gains achieved with water infrastructure innovations. Rainwater harvesting had high infrastructure costs, and water policy in low- and middle-income countries should instead support wastewater reclamation and best practice in water management.

"Who Cares?": The Acceptance of Decentralized Wastewater Systems in Regions without Water Problems

There is a growing interest in decentralized wastewater treatment systems, especially in regions with water scarcity problems or water management issues. This study aims to determine whether the perceived advantages and disadvantages (leading to acceptance) of decentralized wastewater plants in such regions are the same in regions where the population is not aware of these water issues. Firstly, this study systematically reviews previous findings on public perceptions of the acceptance of decentralized wastewater treatment systems. Then, the study details the results of a focus group study to determine whether the elements identified in the literature are also relevant in a region where people are unaware of water problems. The results show that a lack of awareness of water issues seems to be a critical factor influencing acceptance. Reframing the usefulness of these systems by focusing on other aspects, such as environmental sustainability, is key.

Influence of rain events on the efficiency of a compact wastewater treatment plant: a case study on a university campus aiming water reuse for agriculture

In this study, the efficiency of contaminant removal from a compact wastewater treatment plant (CWTP) in a university campus under different rain conditions was evaluated. Wastewater samples were collected weekly for 1 year and the physicochemical parameters were monitored. Removal efficiency higher than 77%, reaching values above 95% for samples with lower wastewater flow rates, was found for biological oxygen demand (BOD) and total and fecal coliforms. The pH values remained in the range of 6.0-8.0. However, pH values below 6.8 impaired the nitrification rate and, therefore, the removal of total Kjeldahl nitrogen (TKN) and ammonia was lower than the expected, with concentration values above those set by the Brazilian regulation for wastewater discharge. The results show that the flow rate of wastewater at the entrance of the CWTP is directly related to the rain events, thus affecting its efficiency, mainly in the removal of total solids, turbidity, and organic matter. The assessment of the treated wastewater reuse on site for agricultural purposes showed to be a prominent and more sustainable alternative regarding the discharge of wastewater into water bodies.

Seasonal influences on the use of genetic markers as performance indicators for small wastewater treatment plants

The development of microbial source tracking methods has resulted in an array of genetic faecal markers for assessing human health risks posed from surface water pollution. However, their use as performance metrics at wastewater treatment plants (WWTPs) has not been explored extensively. Here we compared three Bacteroides (HF183, HumM2, AllBac) and two E. coli (H8, RodA) genetic markers for summer and winter performance monitoring at twelve small rural (<250 PE) and three larger WWTPs in NE England. Small WWTPs are of interest because they are poorly understood and their impact on surface water quality may be underestimated. Overall, genetic marker data showed significant differences in treatment performance at smaller versus larger WWTPs. For example, effluent abundances of HF183 and HumM2 were significantly higher in smaller systems (p = 0.003 for HumM2; p = 0.02 for HF183). Genetic markers also showed significant differences in performance between seasons (p < 0.01, n = 120), with human-specific markers (i.e., HF183, HumM2, H8) being generally better for summer WWTP monitoring. In contrast, Bacteroides markers were much more suitable for winter monitoring, possibly because the E. coli markers are less sensitive to differences in temperature and sunlight conditions. Overall, Bacteroides markers best described WWTP treatment performance across all samples, although seasonal differences suggest caution is needed when markers are used for performance monitoring. Genetic markers definitely provide rapid and new information about WWTP performance, but more spatially diverse studies are needed to refine their use for routine WWTP monitoring.

Conventional Sewer Systems Are Too Time-Consuming, Costly and Inflexible to Meet the Challenges of the 21st Century

There is an urgent need for innovation in the sanitation sector because the conventional model (toilet-to-sewer-to-treatment) is too time-consuming and costly, and alternatives are lacking. We estimate the challenge ahead by developing scenarios for 60 of the fastest-growing urban conglomerates in the World. We find that the majority would need to build out their sewer systems at a rate that is ten to 50 times higher than the highest rate for any project in the World Bank’s database, which is unrealistic. We also carry out a case study of Lagos, Nigeria, which suggests that, in any given year, 14–37% of Lagos State’s budget would need to be invested to provide sanitation to the presently underserviced population while keeping up with population growth, which also is unrealistic. Our study provides clear evidence that the conventional model for sanitation is unworkable for rapidly growing urban areas. We conclude there is an urgent need to encourage and fund projects that promote innovations that can tackle the three core challenges: can be built sufficiently quickly, are flexible, and affordable. This is not likely to happen unless the future generation is systematically trained and educated to creatively support innovation in sustainable sanitation.

A composite indicator approach to assess the sustainability and resilience of wastewater management alternatives

Evaluating the sustainability of wastewater management alternatives is a challenging task. This paper proposes an innovative methodology to assess and compare the sustainability of four wastewater management alternatives: a) centralised water resource recovery facility (WRRF) based on activated sludge (AS); b) centralised WRRF with membrane bioreactors (MBR); c) decentralised WRRFs with upflow anaerobic sludge blanket reactors and trickling filters; d) centralised-decentralised hybrid system. In doing so, a composite indicator embracing total annual equivalent costs, carbon emission intensity, eutrophication and resilience (based on robustness and rapidity metrics) was developed using the analytic hierarchy process (AHP) method. The results show that decentralised and hybrid systems contribute less to carbon emission and eutrophication because of energy and fertilizer harvest and with a trade-off of higher costs of 7-17% than the ones of AS and MBR. In addition, decentralised and hybrid systems are more resilient, contributing to lower environmental impacts facing natural disasters. Based on the weights obtained by AHP, the decentralised alternative appears to be the most sustainable option due to its best performance in terms of carbon emission intensity and resilience. By contrast, the MBR alternative appeared the least sustainable evaluated wastewater management alternative. However, this alternative is sustainable option when the eutrophication criterion is heavily prioritized. The proposed approach contributes to the selection of the most sustainable wastewater management alternative from a holistic perspective.

Does China's Urban Development Satisfy Zipf's Law? A Multiscale Perspective from the NPP-VIIRS Nighttime Light Data

Currently, whether the urban development in China satisfies Zipf's law across different scales is still unclear. Thus, this study attempted to explore whether China's urban development satisfies Zipf's law across different scales from the National Polar-Orbiting Partnership's Visible Infrared Imaging Radiometer Suite (NPP-VIIRS) nighttime light data. First, the NPP-VIIRS data were corrected. Then, based on the Zipf law model, the corrected NPP-VIIRS data were used to evaluate China's urban development at multiple scales. The results showed that the corrected NPP-VIIRS data could effectively reflect the state of urban development in China. Additionally, the Zipf index (q) values, which could express the degree of urban development, decreased from 2012 to 2018 overall in all provinces, prefectures, and counties. Since the value of q was relatively close to 1 with an R2 value > 0.70, the development of the provinces and prefectures was close to the ideal Zipf's law state. In all counties, q > 1 with an R2 value > 0.70, which showed that the primate county had a relatively stronger monopoly capacity. When the value of q < 1 with a continuous declination in the top 2000 counties, the top 250 prefectures, and the top 20 provinces in equilibrium, there was little difference in the scale of development at the multiscale level with an R2 > 0.90. The results enriched our understanding of urban development in terms of Zipf's law and had valuable implications for relevant decision-makers and stakeholders.

Techno-economic analysis of combining forward osmosis-reverse osmosis and anaerobic membrane bioreactor technologies for municipal wastewater treatment and water production

The economic feasibility of combining forward osmosis (FO), reverse osmosis (RO) and anaerobic membrane bioreactor (AnMBR) technologies for municipal wastewater treatment with energy and water production was analysed. FO was used to pre-concentrate the AnMBR influent, RO for draw solution regeneration and water production, and AnMBR for wastewater treatment and energy production. The minimum wastewater treatment cost was estimated at 0.81 € m^-3, achieved when limiting the FO recovery to 50% in a closed-loop scheme. However, the cost increased to 1.01 and 1.27 € m^-3 for FO recoveries of 80% and 90%, respectively. The fresh water production cost was estimated at 0.80 and 1.16 € m^-3 for an open-loop scheme maximising water production and a closed-loop scheme, respectively. The low FO membrane fluxes were identified as a limiting factor and a sensitivity analysis revealed that FO membrane fluxes of 10 LMH would significantly improve the competitiveness of FO-RO + AnMBR technology.

A metastochastic frontier analysis for technical efficiency comparison of water companies in England and Wales

Evaluating the performance of water companies is of great importance for both water utilities and water regulators. This paper explores comparative levels of technical efficiencies and technology gap ratios with the metafrontier concept by estimating an input distance function using stochastic frontier techniques. The metafrontier framework is employed in the water services of water and sewerage companies (WaSCs) and water-only companies (WoCs) in England and Wales. The results show that the English and Welsh water industry is an efficient industry, with WaSCs more efficient than WoCs. On average, a water company can increase its technical efficiency by operating in more densely populated areas and by investing in technology to reduce bursts in water mains. We also link the efficiency results with the regulatory cycle to assess the impact of regulation on the efficiency levels of water companies.

How Urban Storm- and Wastewater Management Prepares for Emerging Opportunities and Threats: Digital Transformation, Ubiquitous Sensing, New Data Sources, and Beyond - A Horizon Scan

Ubiquitous sensing will create many opportunities and threats for urban water management, which are only poorly understood today. To identify the most relevant trends, we conducted a horizon scan regarding how ubiquitous sensing will shape the future of urban drainage and wastewater management. Our survey of the international urban water community received an active response from both the academics and the professionals from the water industry. The analysis of the responses demonstrates that emerging topics for urban water will often involve experts from different communities, including aquatic ecologists, urban water system engineers and managers, as well as information and communications technology professionals and computer scientists. Activities in topics that are identified as novel will either require (i) cross-disciplinary training, such as importing new developments from the IT sector, or (ii) research in new areas for urban water specialists, for example, to help solve open questions in aquatic ecology. These results are, therefore, a call for interdisciplinary research beyond our own discipline. They also demonstrate that the water management community is not yet prepared for the digital transformation, where we will experience a data demand, i.e. a "pull" of urban water data into external services. The results suggest that a lot remains to be done to harvest the upcoming opportunities. Horizon scanning should be repeated on a routine basis, under the umbrella of an experienced polling organization.

Life cycle assessment of wastewater treatment in developing countries: A review

Within developing countries, wastewater treatment (WWT) has improved in recent years but remains a high priority sustainability challenge. Accordingly, life cycle assessment (LCA) studies have recently started to analyse the environmental impacts of WWT technologies on the specific context of less developed countries, mainly in China and India. This work presents a comprehensive review of this knowledge with the aim of critically analysing the main conclusions, gaps and challenges for future WWT-related LCAs in developing countries. The most commonly assessed technologies in the 43 reviewed articles are different variations of activated sludge and extensive treatments applied in decentralized systems; however, studies focused on advanced technologies or new sources of pollution (e.g. micropollutants) are still lacking. Goal and system boundaries are normally clearly defined, but significant stages for some technologies such as the construction and sludge management are frequently not included and functional units should be defined accordingly to specific conditions in developing countries. At the inventory level, a more concise description of sources and technical parameters would greatly improve the quality of the LCAs along with accountability of direct greenhouse gas emissions. Eutrophication and global warming are the two most commonly assessed impacts; however, the calculation of terrestrial ecotoxicity when the sludge is used for agricultural purposes, of water use and of the land use change impacts associated to extensive technologies should be encouraged. The estimation of more site-specific databases, characterization factors (especially for eutrophication) or normalization and weighting values combined with more affordable access to background databases and LCA software, would deeply increase the accuracy of WWT-related LCAs in developing countries. An increased usage of the uncertainty analysis should be encouraged to assess the influence of these gaps in the final interpretation of the results. The review finishes with a summary of the main challenges and research gaps identified and with specific guidelines for future researchers to avoid the most common shortcomings found in the reviewed studies.

Strategic Approach for Prioritising Local and Regional Sanitation Interventions for Reducing Global Antibiotic Resistance

Globally increasing antibiotic resistance (AR) will only be reversed through a suite of multidisciplinary actions (One Health), including more prudent antibiotic use and improved sanitation on international scales. Relative to sanitation, advanced technologies exist that reduce AR in waste releases, but such technologies are expensive, and a strategic approach is needed to prioritize more affordable mitigation options, especially for Low- and Middle-Income Countries (LMICs). Such an approach is proposed here, which overlays the incremental cost of different sanitation options and their relative benefit in reducing AR, ultimately suggesting the “next-most-economic” options for different locations. When considering AR gene fate versus intervention costs, reducing open defecation (OD) and increasing decentralized secondary wastewater treatment, with condominial sewers, will probably have the greatest impact on reducing AR, for the least expense. However, the best option for a given country depends on the existing sewerage infrastructure. Using Southeast Asia as a case study and World Bank/WHO/UNICEF data, the approach suggests that Cambodia and East Timor should target reducing OD as a national priority. In contrast, increasing decentralized secondary treatment is well suited to Thailand, Vietnam and rural Malaysia. Our approach provides a science-informed starting point for decision-makers, for prioritising AR mitigation interventions; an approach that will evolve and refine as more data become available.

Shifting Infrastructure Landscapes in a Circular Economy: An Institutional Work Analysis of the Water and Energy Sector

Under pressure by the transition towards a circular economy, the infrastructure landscape is changing. Using Institutional Work as an analytical lens, this article analyses the work actors do to change and adapt institutional structures. In this process of restructuring, the research shows that there are four dominant types of institutional work: Enabling, Constructing Identities, Constructing Normative Networks, and Changing Normative Associations. The increasing fragmentation of infrastructure as well as the increasing connections made between different flows forces organisations to readjust their internal institutions as well as those that guide their interactions with their surroundings such as other organisational actors as well as citizens. Circularity requires a restructuring of infrastructure governance in order to adapt to the increasing flux caused by decentralised technologies and the need for integration of different systems. Additionally, the actors associated with energy and water infrastructure are responding accordingly.

The Economics of Wastewater Treatment Decentralization: A Techno-economic Evaluation

The existing wastewater treatment infrastructure has not adequately established an efficient and sustainable use of energy, water, and nutrients. A proposed scheme based on source separation and water-efficient use is compared to the current wastewater management paradigm (one largely based on activated sludge) using techno-economic terms. This paper explores the economic viability of adopting more sustainable management alternatives and expands the understanding of the economics of decentralization and source-separation. The feasibility of three different potential types of source-separation (with different levels of decentralization) are compared to the conventional centralized activated sludge process by using recognized economic assessment methodologies together with widely accepted modeling tools. The alternatives were evaluated for two common scenarios: new developments and retrofit due to the aging of existing infrastructures. The results prove that source-separated alternatives can be competitive options despite existing drawbacks (only when countable incomes are included), while the hybrid approach resulted in the least cost-effective solution. A detailed techno-economic evaluation of the costs of decentralization provides insight into the current constraints concerning the paradigm shift and the cost of existing technologic inertia.

Energy intensity modeling for wastewater treatment technologies

Wastewater treatment plants (WWTPs) are energy intensive facilities; therefore increased pressure has been placed on managers and policy makers to reduce the facilities' energy use. Several studies were conducted to compare the energy intensity (EI) of WWTPs, which showed large dispersion in EI among the facilities. In the present study, the degree EI influenced WWTPs was tested using a set of technical variables by modeling the EI of a 305 WWTP sample grouped into five secondary treatment technologies. Results indicated the following two major findings: i) WWTPs using conventional activated sludge, extended aeration, trickling biofilters, and biodisks exhibited significant economies of scale in energy use; and ii) pollutant removal efficiency demonstrated low impacts on WWTP EI. The methodology and results of this study are of value to policy makers in planning new WWTPs and developing management plans to improve energy efficiency of wastewater treatment.

Capture-Ferment-Upgrade: A Three-Step Approach for the Valorization of Sewage Organics as Commodities

This critical review outlines a roadmap for the conversion of chemical oxygen demand (COD) contained in sewage to commodities based on three-steps: capture COD as sludge, ferment it to volatile fatty acids (VFA), and upgrade VFA to products. The article analyzes the state-of-the-art of this three-step approach and discusses the bottlenecks and challenges. The potential of this approach is illustrated for the European Union's 28 member states (EU-28) through Monte Carlo simulations. High-rate contact stabilization captures the highest amount of COD (66-86 g COD person equivalent^-1 day^-1 in 60% of the iterations). Combined with thermal hydrolysis, this would lead to a VFA-yield of 23-44 g COD person equivalent^-1 day^-1. Upgrading VFA generated by the EU-28 would allow, in 60% of the simulations, for a yearly production of 0.2-2.0 megatonnes of esters, 0.7-1.4 megatonnes of polyhydroxyalkanoates or 0.6-2.2 megatonnes of microbial protein substituting, respectively, 20-273%, 70-140% or 21-72% of their global counterparts (i.e., petrochemical-based esters, bioplastics or fishmeal). From these flows, we conclude that sewage has a strong potential as biorefinery feedstock, although research is needed to enhance capture, fermentation and upgrading efficiencies. These developments need to be supported by economic/environmental analyses and policies that incentivize a more sustainable management of our resources.

Measuring adaptive capacity of urban wastewater infrastructure - Change impact and change propagation

The ability of urban wastewater systems to adapt and transform as a response to change is an integral part of sustainable development. This requires technology and infrastructure that can be adapted to new operational challenges. In this study the adaptive capacity of urban wastewater systems is evaluated by assessing the interdependencies between system components. In interdependent and therefore tightly coupled systems, changes to one systems component will require alteration elsewhere in the system, therefore impairing the capacity of these systems to be changed. The aim of this paper is to develop a methodology to evaluate the adaptive capacity of urban wastewater systems by assessing how change drivers and innovation affect existing wastewater technology and infrastructure. The methodology comprises 7 steps and applies a change impact table and a design structure matrix that are completed by experts during workshops. Change impact tables quantify where change drivers, such as energy neutrality and resource recovery, require innovation in a system. The design structure matrix is a tool to quantify "emerging changes" that are a result of the innovation. The method is applied for the change driver of energy neutrality and shown for two innovations: a decentralised upflow anaerobic sludge blanket reactor followed by an anammox process and a conventional activated sludge treatment with enhanced chemical precipitation and high temperature-high pressure hydrolysis. The results show that the energy neutrality of wastewater systems can be address by either innovation in the decentralised or centralised treatment. The quantification of the emerging changes for both innovations indicates that the decentralised treatment is more disruptive, or in other words, the system needs to undergo more adaptation. It is concluded that the change impact and change propagation method can be used to characterise and quantify the technological or infrastructural transformations. In addition, it provides insight into the stakeholders affected by change.

Expert opinion on risks to the long-term viability of residential recycled water schemes: An Australian study

The water sector needs to make efficient and prudent investment decisions by carefully considering the long-term viability of water infrastructure projects. To support the assessment and planning of residential recycled water schemes in Australia, we have sought to clarify scheme objectives and to further define the array of critical risks that can impact the long-term viability of schemes. Building on historical information, we conducted a national survey which elicited responses from 88 Australian expert practitioners, of which 64% have over 10 years of industry experience and 42% have experience with more than five residential recycled water schemes. On the basis of expert opinion, residential recycled water schemes are considered to be highly relevant for diversifying and improving water supply security, reducing wastewater effluent discharge and pollutant load to waterways and contributing to sustainable urban development. At present however, the inability to demonstrate an incontestable business case is posing a significant risk to the long-term viability of residential recycled water schemes. Political, regulatory, organisational and financial factors were also rated as critical risks, in addition to community risk perception and fall in demand. The survey results shed further light on the regulatory environment of residential recycled water schemes, with regulatory participants rating the level and impact of risk factors higher than other survey participants in most cases. The research outcomes provide a comprehensive understanding of the critical risks to the long-term viability of residential recycled water schemes, thereby enabling the specification of targeted risk management measures at the assessment and planning stage of a scheme.