The impact of a storage facility on optimality conditions of wastewater reuse in land application: A case study in Lebanon

Although land application (or reuse of treated wastewater for irrigation) is a potentially successful alternative to the disposal of treated wastewater into fresh water streams, its economic feasibility has not been adequately examined. The focus of this paper is to investigate the economic feasibility of land application in the presence of a reservoir with different capacities and to compare the outcome to the application without a storage reservoir. A 5-year dynamic linear programming model was developed to determine the optimal cropping pattern that will consume all or most of the effluent throughout the optimization horizon, utilize all the effluent's nitrogen (being the most limiting constituent) and bring in the highest revenues. A case study in Tyre region, South Lebanon, was used for model application. Three scenarios were developed and then compared to no-storage scenario. The first scenario represents the current existing cropping pattern, while in the second and third new crops were added in addition to the current ones. Supplementary irrigation was allowed in the first and the third scenarios. The three scenarios were tested for different reservoir capacities. The results indicate that the presence of a reservoir enhances the efficiency of the wastewater usage and the flexibility of the associated cropping pattern. The results also indicate that there is a trade-off between the storage capacity and the presence of supplementary irrigation of fresh water. As the storage capacity increases, less land and fresh water are needed, more effluent volume is consumed and higher net returns are achieved as compared to no reservoir situation.