Estabilização de lodo de sistemas aeróbios em reatores tipo UASB.

Abstract

In this thesis the performance of a UASB reactor is evaluated, when it is used as a pre treatment reactor for raw sewage digestion and at the same time as a unit for stabilization of aerobic sludge. Aerobic sludge enters in decomposition after a short time without presence of dissolved .oxygen, due to the presence oft a high concentration of biodegradable organic material, so that it must be stabilized. The alternative of using the UASB reactor as a unit for digestion and thickening of aerobic sludge is attractive because the conventional processes for sludge treatment are costly. Four pilot scale UASB reactors (R1, R2, R3 e R4) were operated at a retention time of 6 h and an organic loading rate of 2,8 kgCODm"3d"1 from raw municipal sewage. In addition the reactors R2, R3 and R4 received additional COD loads in the form of aerobic sludge in proportions of 20, 40 and 60% respectively of the organic sewage load. The results showed that even in the reactor with the largest additional load the COD removal efficiency of the sewage was more than 70%, so that efficient pre treatment was guaranteed. Anaerobic sludge samples from the UASB reactors when incubated during 40 days showed a reduction of less than 17 % of its volatile mass, which is within the limits set by EPA (1992), and hence indicates sludges with a fair stability. The metabolic capacity of the anaerobic sludges, as quantified by their specific methanogenic activity (SMA) increased as the load of aerobic sludge on the reactor increased. Important mechanic properties of the sludges like settleability and filterability were not affected by aerobic sludge additions. The sludge expelled from the UASB reactors requires attention as it was observed that in these sludges the reduction of volatile matter exceeded 17%, which indicates that these sludge may not yet have the degree of stabilization that is compatible with a secure final disposal.