Fenton oxidation of primary municipal wastewater treatment plant sludge: Process modelling and reactor scale-up

Abstract

The aim of this work was to propose a mass-transfer model and scale-up procedure of the Fenton process of organic pollutants present in sludge produced in a municipal wastewater treatment plant. The sludge was collected at the end of anaerobic stabilization, sedimentation and filter press thickening and was firstly characterized by measuring the Total Organic Carbon on the whole sludge and on the liquid phase, the Chemical Oxygen Demand on the liquid phase, the viscosity, the pH, the Cu and Fe concentration and the water content. The optimal water content for the subsequent Fenton process was assessed basing on preliminary pumpability tests, and on Fenton process performances. The analysis of Fenton process was performed by evaluating, at 24 h, the optimal Fe(II) and hydrogen peroxide concentration with respect to the initial total organic content of whole sludge and of sludge liquid phase, as well as to the chemical oxygen demand of sludge liquid phase: the optimal parameters were H2O2/total organic carbon = 1.6 g/g, added Fe(II)/H2O2 = 0.1 g/g, water content = 75 %, through which a chemical oxygen demand and total organic carbon removal efficiency of 72 and 52 %, respectively, was achieved. Kinetic tests were carried out in a batch stirred tank reactor and the results were interpreted in light of a comprehensive mass transfer model to obtain suitable kinetic parameters necessary for reactor design and scale-up. Finally, a simplified process flow diagram was also proposed. Basing on the obtained results, a first real scale-up of the lab-scale reactors could be performed adopting optimal operating parameter values found in the present study, using axial-flow impeller and maintaining constant the Re number.