Avaliação da influência das condições operacionais e da configuração de sistemas de lodo ativado sobre a sedimentabilidade do lodo.

Abstract

The objective of this study was to evaluate the settleability of sludge generated in different sludge activated systems and methodological aspects of the settling tests for determining settleability constants of the Vesilind equation. Three different types of activated sludge system were operated, consisting of two Sequential Batch Systems (SBR), one with a Single reactor and the other with the Dedicated reactors for nitrification and denitrification, and one continuous flow system UCT (University of Cape Town). The operation of the activated sludge systems occurred in two stages and varied in function of the applied organic load, where in the 1st step was used only influent of municipal sewerage and in the 2nd step sewage mixed with material rich in organic matter and the flow rate was increased. Static tests were performed to obtain the Vesilind constants k and v0 for evaluate the settling of the sludges. Tests with the static and dynamic methods was performed to evaluate if they led to the same numerical results. The influence of two operational aspects of static method was evaluated: the settling column diameter and stirring velocity applied to the sludge during the tests. The experimental settleability of the sludges in terms of the compression constant (k) was worse than expected, when comparing with research of the literature, with values between 0,32 to 0,46 L/g. For the unhindered settling constant (v0), the found values were between regular to good, with values above of 8,5 m/h. There was no significant difference between the static and the dynamic method. Also no significant influence was found for the influence of the diameter of the settle column between 0,5 and 10 cm. Under the operational conditions, the stirrer intensity influenced positively in determination of the results of k constant (2 and 4 rpm), however, it became negative from of 6rpm onwards. In case of the v0 constant, the stirrer intensity affected negatively an initial sedimentation velocity of the sludge – v0 (11 and 12 m/h) when compared with test without stirring (17 m/h).