Analysis of the Water–Energy Nexus of Treated Wastewater Reuse at a Municipal Scale

Cristina Santos,Francisco Taveira-Pinto,Cristina Matos,David Pereira

doi:10.3390/w13141911

Cristina Santos, Francisco Taveira-Pinto + Show 2 more

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https://doi.org/10.3390/w13141911

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Abstract

Treated wastewater has the potential to be a feasible alternative to supply non-potable uses and avoid water scarcity in urban areas, but it is important to understand and compare the associated energy consumption and CO2 emissions. This study presents a comparative analysis of the water–energy nexus associated with the traditional water supply and to the alternative reuse of treated wastewater, both for non-potable purposes. A case study of a Portuguese municipality was considered, regarding golf course irrigation and municipal gardens irrigation. A balance between production and demand was established, and the energy consumption and CO2 emissions were calculated considering the supply with drinking water and with treated wastewater. Three scenarios were defined to analyze the water–energy nexus for different configurations of the potential end-uses: (1) golf course supply, (2) municipal irrigation supply and (3) simultaneous supply to the golf course and to municipal irrigation. A quality analysis was also carried out by comparing the records from discharged wastewater quality parameters with the limits presented in the legislation for each proposed non-potable use. The results show that all scenarios present significant annual savings from using treated wastewater instead of drinking water from the public network, especially scenarios 1 and 3, that consider the golf course irrigation (water costs decrease by about 60,000.00 EUR/year). Regarding the water–energy nexus, this study reveals that treated wastewater spends less energy on its production and supply and produces fewer CO2 emissions. The energy savings can reach an average value of about kWh/year, with 5300 fewer kg of CO2 emitted in the best scenario.

Highlights

According to the European Environmental Agency [1], about 80% of Europe’s freshwater use comes from rivers and groundwater, which makes these sources extremely vulnerable to threats stood by over-exploitation, pollution and climate change
The reuse of treated wastewater is strategic for Portugal to relieve the pressure on water resources and make the country more resilient to climate change
This interest is demonstrated by the recent publication of a specific regulation in the European Union and a decree-law in Portugal concerning this practice, covering all the aspects needed to a safe and reliable reuse

Summary

Introduction

According to the European Environmental Agency [1], about 80% of Europe’s freshwater use (drinking and other uses) comes from rivers and groundwater, which makes these sources extremely vulnerable to threats stood by over-exploitation, pollution and climate change. For the Mediterranean region, climate change projections anticipate more extreme heat events and less water [1]. To improve the resilience of the cities and prepare them to this new climate reality, it is essential to provide alternative water sources, such as wastewater reuse. When the reuse systems are correctly designed and operated, the development of the plants can be enhanced by the high content of nutrients in the reused water, improving productivity and allowing the replacement of chemical fertigation with the supply of nutrients contained in the irrigation water [3,4]

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