Energy and resource consumptions required to treat and transport wastewater have led to efforts to improve the environmental sustainability of wastewater treatment plants (WWTPs). Resource recovery can reduce the environmental impact of these systems; however, limited research has considered how the scale of implementation impacts the sustainability of WWTPs integrated with resource recovery. Accordingly, this research uses life cycle assessment (LCA) to evaluate how the scale of implementation impacts the environmental sustainability of wastewater treatment integrated with water reuse, energy recovery, and nutrient recycling. Three systems were selected: a septic tank with aerobic treatment at the household scale, an advanced water reclamation facility at the community scale, and an advanced water reclamation facility at the city scale. Three sustainability indicators were considered: embodied energy, carbon footprint, and eutrophication potential. This study determined that as with economies of scale, there are benefits to centralization of WWTPs with resource recovery in terms of embodied energy and carbon footprint; however, the community scale was shown to have the lowest eutrophication potential. Additionally, technology selection, nutrient control practices, system layout, and topographical conditions may have a larger impact on environmental sustainability than the implementation scale in some cases.

This Feature examines significant challenges and opportunities to spur innovation and accelerate adoption of reliable technologies that enhance integrated resource recovery in the wastewater sector through the creation of a national testbed network. The network is a virtual entity that connects appropriate physical testing facilities, and other components needed for a testbed network, with researchers, investors, technology providers, utilities, regulators, and other stakeholders to accelerate the adoption of innovative technologies and processes that are needed for the water resource recovery facility of the future. Here we summarize and extract key issues and developments, to provide a strategy for the wastewater sector to accelerate a path forward that leads to new sustainable water infrastructures.

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As population and water demand increase, there is a growing need for alternative water supplies from water reuse and desalination systems. These systems are beneficial to water augmentation; however, there are concerns related to their carbon footprint. This study compiles the reported carbon footprint of these systems from existing literature, recognizes general trends of carbon footprint of water reuse and desalination, and identifies challenges associated with comparing the carbon footprint. Furthermore, limitations, challenges, knowledge gaps, and recommendations associated with carbon footprint estimation tools are presented. Reverse osmosis (RO) technologies were found to have lower CO 2 emissions than thermal desalination technologies and the estimated carbon footprint of seawater RO desalination (0.4-6.7 kg CO 2 eq/m 3 ) is generally larger than brackish water RO desalination (0.4-2.5 kg CO 2 eq/m 3 ) and water reuse systems (0.1-2.4 kg CO 2 eq/m 3 ). The large range of reported values is due to variability in location, technologies, life cycle stages, parameters considered, and estimation tools, which were identified as major challenges to making accurate comparisons. Carbon footprint estimation tools could be improved by separating emissions by unit process, direct and indirect emissions, and considering the offset potential of various resource recovery strategies.

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