Abstract Summary
Wastewater treatment plants (WWTPs) are shifting from pollution control facilities to increasingly recognized resource hubs, contributing to circular economy strategies through the recovering of water, nutrients and other valuable resources available on the wastewater inflows. But, in order to evaluate the potentialities of integrating new valorization stages on conventional WPPTs, it is needed to develop the appropriate assessments aiming at analyzing its economic viability, environmental loads and circularity enhancement. In this regard, this research delves into the evaluation of the sustainability and circularity performance of a WWTP located in Cyprus integrating additional process stages aiming at recovering sludge nutrients for fertilizer production, enabling the production of irrigation water for agricultural activities by the implementation of adequate pollutants removal units and chemicals recycling within the process for reducing the use of external resources. The environmental and economic analysis were made by following the Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) methodologies, standardized on ISO 14044 and ISO 15686, respectively. With respect to the circularity assessment, the guidelines provided by the ISO 59004 were followed, considering the scoring of both “resource flow indicators” (including resources, energy and economic flows) and “circular actions indicators” (based on process optimization, repurposing, cascading and regeneration actions). Once all the methodologies have been applied, the outcomes showed both benefits and trade-offs. While the alternative WWTP case study (ACS) improves circularity given the enhancement of the resources recovery and the production of high-added value products for the agricultural sector, it is also highly energy intensive, which implies significant environmental loads and economic costs compared to the already stablished WWTP (BCS). The integration of advanced treatment technologies, such as distillation, reverse osmosis and nanofiltration, are the responsible of the increases the environmental effects and operating costs, mostly because of energy demand and high-level maintenance requirements. In order to improve the environmental and economic sustainability potential of the ACS, sensitivity assessments were performed based on increasing the use of renewable energy, reducing process units (by eliminating those that require more energy), and optimizing the system. These adjustments improved the LCA and LCC results by reducing environmental impacts and costs, but not enough to improve the results obtained by the BCS. However, these optimizations also resulted in a decrease in circularity benefits due to lower recovery rates of resources. It is therefore necessary to consider a trade-off between greater resource recovery and the resulting impacts. However, it is important to keep in mind that the long-term benefits are assured when considering a prospective evaluation that shows the potential of a WWTP system to be considered as a cascading production system. But, in order to move towards the establishment of WWTPs as resource hubs, it is believed that more research is needed to optimize the valorization processes, as well as more incentives and economic support from policy makers.
