Assessment of the effect of digestion technology on the dewaterability of waste activated sludge

Politecnico di Torino - Laurea Magistrale in Ingegneria per l’Ambiente e il Territorio Assessment of the effect of digestion technology on the dewaterability of waste activated sludge Relatore: Prof.ssa Silvia Fiore??????????????Candidata: Chiara Marchi Co-relatore: Prof Pavel Jenicek, VSCHT University of Prague Over 11 M tons of waste activated sludge (WAS) are produced every year by wastewater treatment plants in Europe, often with a dry substance content below 20-25 % w/w. It is crucial to find the best solution to treat WAS in order to reduce its amount, and thus the disposal costs, and to explore reuse perspectives that could imply the lowest possible costs and environmental impacts. WAS management is a common topic nowadays and its disposal usually involves landfilling, incineration, composting and other applications related to agricultural use. The main goal of the optimization of WAS management should be to reduce the amounts landfilled and/or destined to agricultural applications and to increase the fraction sent to thermal valorization. There are many techniques that can be used to reduce water content in WAS and one of these, that is getting improved these last years, is the dewatering process. It helps to separate the water from the solid particles and it plays a key role within any sludge disposal perspective. This thesis is aimed at the investigation of the optimization of dewaterability through the analysis of different types of WAS obtained from different digestion processes (mesophilic and thermophilic). The considered WAS samples were obtained from Central Prague wastewater treatment plant and from pilot-scale reactors. For each type of WAS different process parameters (applied pressure, dose and type of flocculant) have been investigated in order to assess the performances of the dewatering process through the amount of residual total solids after press-filtering at lab scale. The most challenging phase of the study was related to the optimization of the coagulation phase, particularly because the efficiency of the flocculant is highly unstable because of several factors that can change during the process and affect flocs structure and amount of water that could be extracted. The results of the experimental activity showed that different WAS samples exhibited different behaviors towards the overall dewaterability process. An economic preliminar assessment of the scale-up of the dewaterability process concluded the study. The experimental activity of this thesis was performed at VSCHT University in Prague along 5 months in the period February – June 2019. I gratefully acknowledge ERASMUS+ program for the economic support of a 10 months stay at VSCHT University in Prague in the period September 2018-June 2019.