NITRINET: A nitrification predictive model for reclaimed water distribution networks

The present work consists of the development of a model (NITRINET) to simulate nitrification processes in reclaimed water distribution networks for agricultural irrigation. Due to water scarcity and climate change scenarios, irrigation with reclaimed water has gained interest worlwide, especially in arid and semi-arid regions, like the Mediterranean Basin. The Tintín Irrigation District distribution network (Montilla, southern Spain) was selected as case study. The importance of this model relies on the fact that the chemical composition of reclaimed water varies spatially along the distribution network. It has been observed that nitrate concentrations increase along the irrigation network in contrast to the reduction observed in the ammoniacal forms. It confirms that nitrification processes are occurring inside the pipes. To carry out precision fertigation strategies (fertilization and irrigation simultaneously) and optimize the amount of fertilizer applied it is necessary to determine the concentration of nutrients present in the water arriving at each farm. The nutrients that reclaimed water already carries must be considered when planning fertilization. This allows for a significant reduction in the amount of fertilizer applied to the soil, which has a positive impact both on the environment and on the farmer’s economy. Simulations performed with NITRINET have shown promising results, predicting water pH and the concentration of ammoniacal nitrogen (NH₄⁺-N) and nitric nitrogen (NO₃^--N) in irrigation water arriving at farms with a mean absolute error of 0.34, 1.46 mg·L^-1 and 1.23 mg·L^-1, respectively. The main purpose of NITRINET is that it can be used as a Decision Support System when planning fertilization at irrigation district level. The findings of this work suggest that spatio-temporal variability of water quality must be considered when reclaimed water is used for irrigation, especially in big irrigation districts with long pipe distances.