Rheology of sludge from double phase anaerobic digestion of organic fraction of municipal solid waste

In this paper experimental results on the anaerobic digestion of sewage slu dge and organic fraction of municipal solid waste (OFMSW) by using a double phase process are reported. The long-term experiment has been carried out on a pilot scale plant, performed in different sets of operative conditions , during which granulometric distributions of particles in sludges and rheo logical properties of sludges were monitored. A significant fiuidification of sludge was evidenced in the meso-thermo process, especially taking into account the variation in sludge behaviour from the first to the second phas e. In the thermo-thermo process a fiuidification higher than that shown in meso-thermo conditions is not observed. this suggesting that better results in terms of sludge conditioning can be obtained in a long time spent in th ermophilic anaerobic digestion. Total volatile solids (TVS) and total fixed solids (TFS) become the most important parameters when mathematical modell ing is applied to these processes. In the acidogenic phase, hydraulic reten tion time (HRT) and temperature are used to determine rigidity coefficient (RC), while only temperature is needed for yield stress (YC). Organic loadi ng rate (OLR) and specific gas production (SGP) exert an important role in methanogenic phase description.