Urban Wastewater Reuse for Citrus Irrigation in Algarve, Portugal—Environmental Benefits and Carbon Fluxes

Abstract

Water scarcity is increasing in the Mediterranean and alternative sources of water are needed to meet food production needs, protect the environment and reduce the effects of climate change. Currently, many urban wastewater treatment plants (WWTP) produce high volumes of treated effluents which can be an alternative source of water for agriculture irrigation, since they fulfill the quality requirements for crops and the environment. This work analyzed the quantity and quality of a treated effluent produced by an urban WWTP in Algarve, and the environmental benefits of its use on the irrigation of a citrus orchard, as an alternative to groundwater. Carbon dioxide emissions related to orange production were quantified and the orchard’s potential to sequester CO2 was estimated. The reuse of this urban wastewater is revealed to be technologically feasible and environmentally advantageous, avoiding the overexploitation of the local aquifer and preventing the eutrophication of aquatic ecosystems, contributing to the improvement of soil characteristics and decreasing the carbon emissions in orange production. Furthermore, it was found that during the five-month experimental period, the citrus orchard sequestered 87.5% of the CO2e emitted by WWTP in the effluent treatment, converting 72,623 kg of sequestered CO2 into orange biomass.