How decentralized treatment can contribute to the symbiosis between environmental protection and resource recovery

Does resource recovery and utilization improve environmental and economic performance of rural wastewater treatment plants? A case study in Xiamen, China

Wastewater treatment (WWT) has been recognized as a major source of greenhouse gas emissions. Rural WWT often lags behind urban areas due to insufficient infrastructure construction and lack of funding to maintain operation. Selection of optimal WWT technologies in rural areas requires that environmental impacts and costs are traded-off across the entire lifecycle, including the construction, operation, and demolition phases. This study compared the lifecycle environmental impacts of different rural WWT technologies, incorporating both positive and negative externalities into the cost-benefit analysis (CBA). Results showed that the environmental and economic performance during the construction phase of small-scale rural WWT was critical, especially for the Source-separated Wastewater Treatment (SWWT), where construction contributed over 50 % of its environmental impacts and 70 % of its costs. SWWT exhibited the lowest carbon emissions, with wastewater reuse offsetting approximately 17 % of its emissions. However, its ranking of economic performance was worse due to high construction costs, meaning it is likely to be considered desirable only if a lower discount rate (<1.7 %) was used. Monetizing both positive and negative externalities can improve the economic performance of the SWWT. Notably, when positive externalities are included, its net present value remains non-negative (1.3 CNY/m³) even at discount rates as high as 10 %. Given its diverse revenues and low operation costs, SWWT is more suitable for low-income rural areas. This study proposed a framework in selecting rural WWT, considering both the construction and operation phases while integrating externalities into CBA. This can offer more informed policy insights (such as carbon price and tiered price) to support the development of sustainable rural WWT strategies.

Use of reclaimed municipal wastewater in agriculture: Comparison of present practice versus an emerging paradigm of anaerobic membrane bioreactor treatment coupled with hydroponic controlled environment agriculture

Advancements in anaerobic membrane bioreactor (AnMBR) technology have opened up exciting possibilities for sustaining precise water quality control in wastewater treatment and reuse. This approach not only presents an opportunity for energy generation and recovery but also produces an effluent that can serve as a valuable nutrient source for crop cultivation in hydroponic controlled environment agriculture (CEA). In this perspective article, we undertake a comparative analysis of two approaches to municipal wastewater utilization in agriculture. The conventional method, rooted in established practices of conventional activated sludge (CAS) wastewater treatment for soil/land-based agriculture, is contrasted with a new paradigm that integrates AnMBR technology with hydroponic (soilless) CEA. This work encompasses various facets, including wastewater treatment efficiency, effluent quality, resource recovery, and sustainability metrics. By juxtaposing the established methodologies with this emerging synergistic model, this work aims to shed light on the transformative potential of the integration of AnMBR and hydroponic-CEA for enhanced agricultural sustainability and resource utilization.

Review of linear and circular approaches to on-site domestic wastewater treatment: Analysis of research achievements, trends and distance to target

This comprehensive review critically assesses traditional and emerging technologies for domestic wastewater treatment and reuse, focusing on the transition from conventional centralised systems to innovative decentralised approaches. Through an extensive literature search on domestic wastewater systems serving a population equivalent of less than or equal to 10, the study juxtaposes linear and circular methods and highlights their impact on urban water management and the environment. The papers reviewed were classified into five categories: Environmental studies, economic studies, social studies, technological studies, and reviews and policy papers. The analysis was carried out separately for linear and circular approaches within each category. In addition, the maturity of the technology (lab/pilot or full-scale application) was taken into account in the analysis. The research landscape is shown to be evolving towards circular methods that promise sustainability through resource recovery, despite the dominance of linear perspectives. The lack of clear progress in decentralised technologies, the scarcity of circularity assessments and the challenges of urban integration are highlighted. Operational reliability, regulatory compliance and policy support are identified as key barriers to the adoption of decentralised systems. While conventional pollutants and their environmental impacts are well addressed for linear systems, the study of emerging pollutants is in its infancy. Conclusions on the impact of these hazardous pollutants are tentative and cautious. Social and economic studies are mainly based on virtual scenarios, which are useful research tools for achieving sustainability goals. The conceptual frameworks for assessing the social dimension need further refinement to be effective. The paper argues for a balanced integration of centralisation and decentralisation, proposing a dual strategy that emphasizes the development of interoperable technologies. It calls for further research, policy development and widespread implementation to promote decentralised solutions in urban water management and pave the way for sustainable urban ecosystems.

Wastewater recovery for sustainable agricultural systems in the circular economy - A systematic literature review of Life Cycle Assessments

Water availability and quality are known to affect agricultural production and nutrition. The aim of this study was to elaborate a systematic literature review of the most sustainable ways of wastewater treatment towards achieving circular economy (CE) in agro-industry activities. From the SLR, the authors selected twenty-seven papers that they classified into the three research themes of recovery of wastewater into irrigation water, extraction of sludge for production of bio-based compounds, and recovery of nutrients for soil amendment, including recovering of feeds for aquaculture, and recovery of nutrient biosolids for soil amendment. Results underlined that the recovery of nutrients biosolids for soil amendment can generate a GWP gain up to - 37 kg CO2-eq. So, the review highlighted that wastewater recovery for multiple purposes can be truly effective for the environmental sustainability of agricultural systems, and that LCA is a valid tool to assess and improve that sustainability. Under this perspective, this SLR's findings can stimulate public administrations at national and local scales in their planning and funding activities towards implementing circular bioeconomy paths based upon wastewater recovery for a sustainable, resilient agriculture. Overall, the authors believe that their article was effective in overviewing the current wastewater recovery paths in the CE context, and in highlighting key methodological aspects and findings of the reviewed LCAs, to advance the specialised literature and knowledge, and to guide practitioners for future LCA applications in the field. Finally, through its main findings, the article effectively contributes to the whole research project which it is part of and which the authors are deeply involved in. That research is performed under the Progetto GRINS "Growing Resilient, Inclusive and Sustainable" thanks to a PNRR M4C2- Investment 1.3 - GRINS with the aim of "Building a dataset for the circular economy of the main Italian production systems".

Leveraging green infrastructure for efficient treatment of reclaimed water

Global water scarcity necessitates creative, yet practical, solutions to meet ever-growing demand. Green infrastructure is increasingly used in this context to provide water in environmentally friendly and sustainable ways. In this study, we focused on reclaimed wastewater from a joint gray and green infrastructure system employed by the Loxahatchee River District in Florida. The water system consists of a series of treatment stages for which we assessed 12 years of monitoring data. We measured water quality after secondary (gray) treatment, then in onsite lakes, offsite lakes, landscape irrigation (via sprinklers), and ultimately in downstream canals. Our findings show gray infrastructure designed for secondary treatment, integrated with green infrastructure, achieved nutrient concentrations nearly equivalent to advanced wastewater treatment systems. For example, we observed a dramatic decline in mean nitrogen concentration from 19.42 mg L^-1 after secondary treatment to 5.26 mg L^-1 after spending an average of 30 days in the onsite lakes. Nitrogen concentration continued to decline as reclaimed water moved from onsite lakes to offsite lakes (3.87 mg L^-1) and irrigation sprinklers (3.27 mg L^-1). Phosphorus concentrations exhibited a similar pattern. These decreasing nutrient concentrations led to relatively low nutrient loading rates and occurred while consuming substantially less energy and producing fewer greenhouse gas emissions than traditional gray infrastructure-at lower cost and higher efficiency. There was no evidence of eutrophication in canals downstream of the residential landscape whose sole source of irrigation water was reclaimed water. This study provides a long-term example of how circularity in water use can be used to work toward sustainable development goals.

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.

Life cycle and circularity metrics to measure the sustainability of closed-loop agri-food pathways

This work aims to present a methodological proposal based on Life Cycle (LC) methodologies, and circularity performance indicators, to assess closed-loop pathways by providing comprehensive results on economic and environmental impacts generated by agri-food production systems. The methodological approach will be tested on olive oil production systems, one of the most important agri-food chains for Mediterranean countries, whose import and export significance is set to grow in light of the shrinking market supply of seed oils. Some insights for the co-products valorization are provided through the evaluation of the reuse of by-products as a possible resource capable to improve the sustainability of the olive oil farms. The integrated application of three different methodologies, Life Cycle Assessment (LCA), Environmental Life Cycle Costing (ELCC) and Material Circularity Indicator (MCI), enabled comparative evaluation of Extra Virgin Olive Oil (EVOO) production under a linear production model with production under a circular model. The circular scenario was better in most environmental impact categories, registering an improvement in Global Warming Potential (GWP) of nearly 30%. In economic terms, there was a lower production cost for the circular scenario and a lower environmental cost by reducing the use of synthetic products through the reuse of waste products. The circular scenario recorded a higher degree of circularity due to a reduction in virgin raw materials used in the production process and a reduction in non-recoverable waste. The implementation of circular strategies represents one of the possible trajectories to guide the ecological transition, and the proposed methodological framework can support the decisions of both producers and public decision-makers toward more sustainable and efficient production patterns.

A customized multi-cycle model for measuring the sustainability of circular pathways in agri-food supply chains

Circular economy (CE) is claimed to be a promising pathway to achieve the Sustainable Development Goals (SDGs), but a reliable metric is needed to validate closed-loop strategies by measuring sustainability performances together with the degree of circularity. A significant contribution is offered by Life Cycle (LC) scholars in terms of methodological advances and operational tools for different sectors, also those more complex such as the agro-industrial systems that encompass biological and anthropogenic variables at different scales. However, to date, LC methodologies have not yet answered how to model the complexity of circular pathways. LC evaluations are often modelled for cradle-to-grave analyses, while a circularity evaluation would require an extension of the system boundaries to more interconnected life cycles, orienting towards a cradle-to-cradle perspective. This research gap led us to propose a multi-cycle approach with expanded assessment boundaries, including co-products, into a cradle-to-cradle perspective, in an attempt to internalize circularity impacts. The customized LC framework here proposed is based on the Life Cycle Assessment (LCA), the Environmental Life Cycle Costing (ELCC) in terms of internal and external costs, and the Social Life Cycle Assessment (SLCA) in terms of Psychosocial Risk Factor (PRF) impact pathway. The model is designed to be applied to the olive-oil sector, which commonly causes significant impacts by generating many by-products whose management is often problematic. Results are expected to show that the customized LC framework proposed can better highlight the environmental and socioeconomic performances of the system of cycles, allowing CE to deliver its promises of sustainability, as the circularity of materials per se is a means, not an end in itself.

Environmental synergies in decentralized wastewater treatment at a hotel resort

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