Caracterização do lodo heterotrófico de sistemas de lodo ativado gerado a partir de esgoto bruto e digerido.

Abstract

Anaerobic pre treatment can reduce the investment and operational costs of activated sludge systems, particularly with respect to aeration and treatment of the produced sludge. Activated sludge systems receiving the effluent from an anaerobic digester can have different biological and settling properties from those observed with sludges generated in conventional activated sludge systems. In this context an experimental investigation was carried out in which two SBR (sequencing batch reactors) were operated at bench scale and fed with raw sewage (SBR system) and digested sewage (UASB-SBR system).The sludge age in the UASB-SBR and SBR systems was kept at 10 and 20 days, respectively. Standard methods were used to characterize the performance with respect to the removal efficiency of organic material, suspended solids and ammonium. The biological activity of the heterotrophic bacteria in the sludge was characterized by means of respirometric tests where the oxygen uptake rate (OUR) was determined. The result of these test allowed the determination of the maximum utilization rate of organic material (rmc) and the maximum specific growth rate Constant (pmC)- The settling properties of the sludges were evaluated by Volumetric Sludge Index (SVI) tests. Both systems were efficient in the removal of organic material and suspended solids. In the UASB-RBS nitrification did not develop, whereas in the SBR system nitrification was partial. The results of the experimental investigation show that the heterotrophic bacterial mass generated in the two aerobic reactors had very different metabolic capacities: The specific metabolic capacity of the heterotrophic bacteria generated in the SBR system was about three and half times as high as that of the bacteria generated in the UASB-SBR system. As for the settling properties, the sludge in the UASB-SBR system had a good settleability with an average SVI of 83 mL/g whereas the settleability in the RBS was fair with a SVI of 190 mL/g.