Reclaimed water and irrigation: a cost-benefit analysis for desalination of WWTPs effluents

Abstract

The increase of salts both in soils and water for irrigation purposes is a growing problem for farmlands. Waster stress in arid and semi-arid regions encourages the use of non-conventional water sources, such as wastewater reuse. Current wastewater treatment plants (WWTPs) are unable to reduce salinity because they are designed to remove the organic fraction from the wastewater. Hence, effluent contains high amount of salts which adversely affect farmlands. This work addresses the desalination of the effluent from WWTPs with a dual purpose: irrigation and the leaching of salts in soils. The desalination of WWTPs effluent has an environmental impact (there will be environmental cost savings related to not spilling salts) and an economic impact (water will be available for irrigation of farmlands). This study assesses the feasibility of desalination in the effluent of a WWTP sample considering the internalization of environmental externalities. Using the shadow prices methodology, the environmental avoided cost of reducing the salinity of the effluent of WWTPs is quantified as 62 € per kg of salt which is reduced. The feasibility study of effluent desalination has been modelled for growing vegetables, taking into account the 272 hectares/year that can be irrigated with the available volume of desalinated effluents. This modelling confirms that the reduction in the effluent’s salinity makes it possible to reduce the environmental impact in soils with salinity problems, and also, from an economic point of view, allows farmers to generate an income.