High efficiency disinfection treatment for reuse by a combination of conventional and natural systems: an experimental investigation

In accordance with the current tendency to adopt soft treatments with the minimum use of chemical agents and of minimum environmental impact, an experimental investigation has been carried out on a combined disinfection system which treats the secondary effluent of the wastewater treatment plant of the town of Ferrara (Northern Italy). It includes a first low dosage conventional chemical disinfection stage, with sodium hypochlorite (NaClO), and a second stage of “natural” disinfection in a subsurface horizontal filter, with the aim to obtain a final effluent within the limits for “unrestricted” reuse in agriculture. The investigation has shown that the removal of E. Coli achieves 5 log units, with low dosages of NaClO (2 mg/L), a horizontal subsurface filter characterized by a specific area equal to 0.54 m2/AE and a low formation of byproducts, widely below the regulation limits