Analysis and optimization of the processes in a physical-chemical wastewater treatment plant serving a Waste-to-Energy plant

The present thesis is the result of the internship done at the Waste-to-Energy plant “San Lazzaro” of Padova. The aim of the activity was to produce a technical document regarding the wastewater treatment plant present inside the Waste-to-Energy plant, that can be used from the company managing the plant or published on its website. It describes in detail the devices and the sections from which it is composed, and it reports their technical data, the connections among the different components and a graphical representation of the entire system. In a second phase, the chemical-physical reactor of the plant has been analyzed together with the chemical reactions that take place inside it. It has been found that the main parameters that influence the processes are the reagent concentrations to add, the pH inside the reactor and the mixing of the same one. The optimal quantity of the reagents needed have been calculated on the base of the stoichiometric reactions, also considering introducing excess of reagent to move the equilibrium towards the products. The optimal pH to maintain in the tank has been determined through a literature review and we have derived the concentrations of reagents to add in the system to get that condition. The effect of the mixing has been studied and we have obtained that the velocity of stirring into the reactor under analysis stays inside the optimal range of velocity given by literature. Regarding the residence time of the water, for one of the processes, the coagulation of colloidal solids, the optimal range is 1-10 minutes while in our case study the residence time is 18 minutes, so it does not follow what we have found as optimal residence time.