Simulation of a real plant for the combined treatment of wastewaters and liquid wastes

This paper presents the upgrading of a full-scale domestic wastewater treatment plant, operating in Southern Italy, modified so as to process domestic wastewaters together with liquid wastes, such as leachate and digestate in an integrated manner. The two streams – domestic wastewaters and liquid wastes – are separately pre-treated and then sent into a conventional denitrification/nitrification section. The preliminary treatments consist in grinding, sand decantation, flocculation and sedimentation for wastewaters and in grinding, flocculation, biological pre-treatment and advanced oxidation (Fenton) for liquid wastes. Several scenarios were analyzed using a process simulator (SuperPro Designer®): the concentrations of the main parameters (Biochemical oxygen demand (BOD5); Chemical oxygen demand (COD); ammonium (NH4+), nitrate (NO3–), metals and total suspended solids (SST)) of the effluents were estimated as a function of BOD5/COD ratio, initial leachate volume and nitrate percentage in the recycle stream. In each case study, the parameter values were compared with the regulatory limits provided for by the Italian Legislative Decree 152/2006 for discharge in surface water bodies. The results obtained show the intervals of variation of the main process parameters that in some cases do not permit to achieve the established limits.