Wastewater Storage Basins for Irrigation Reuse and P/N Removal: Finishing Lagoons in Imola, Bologna, Italy

Water scarcity has become more prominent in the last decades so since the ’70 many studies focused on the use of natural basins both for treatment and storage of wastewater for irrigation. Afterwards, interesting projects of lagoons for reuse have been implemented in all Mediterranean countries. The irrigation water requirements depend on different factors as crops typology, soil structure, environmental features, seasonal variations etc. Consequently, the key point for a correct irrigation management is the possibility to store the proper water volume in storage basins where it is always available on demand. In this contest the aim of the present paper is to study the natural finishing processes occurring in lagoon basins in order to optimize the management policies. Those policies must take into account three main features: 1) respect of the legal thresholds for wastewater reuse, 2) satisfy the irrigation needs with an appropriate water volume 3) set the finishing capacity of the basin to regulate the best ratio Phosphorus/Nitrogen (P/N) in output in relationship with the amount requested by the different crops for their growth. The study focuses on the data collected in the first basin of the natural finishing part of the Santerno wastewater treatment plant. The plant is located in Imola (Bologna, Italy) and can be divided in two main parts: primary/secondary treatment and natural finishing treatment. The second part of the plant consists of five natural treatment basins. The monitoring campaigns focuses on the first basin called Basin 1 as the plant management company, HERA S.p.A., intends to destine the outlet of this basin to irrigation reuse. The Hydraulic Retention Time and wet surface area of Basin 1 are 2 days and 14000 m2 respectively.