CHARACTERIZATION OF AUTOTROPHIC SLUDGE IN ACTIVATED SLUDGE SYSTEMS GENERATED FROM DIFFERENT SUBSTRATES

Abstract

The association of anaerobic pre-treatment, for example in a UASB reactor with activated sludge systems has been an object of several studies and has been applied in practice of waste water treatment systems. Activated sludge systems with different substrates (for example raw or digested sewage) tend to produce sludges with different mechanical and biological characteristics. In order to evaluate the characteristics of the autotrophic fraction of sludge generated from different substrates an experimental investigation was carried out, where three activated sludge systems of the sequencing batch reactor (SBR) type, were operated with raw sewage, digested sewage an ammonium solution as substrates. The systems were evaluated with respect to the suspended solids, organic material and ammonium, settleability and activity of the sludges. The Volumetric Sludge Index (VSI) and the Oxygen Uptake Rate (OUR) were used for the assessment of the mechanical and biological characteristics. The obtained results during the experimental investigation showed that the systems were equally efficient in the removal of organic material and suspended solids with efficiencies of 83% for COD and 91% for TSS. The settleability of the sludge was considered good and median for systems fed with raw sewage and digested sewage, respectively. However, the autotrophic sludge did not exhibit high biological activity having values of the specific growth rate constant for Nitrosomonas (m) in the range of 0.31 d-1 and 0.21 d-1 respectively for systems fed with raw sewage and ammonium substrate and, whereas no activity was detected in the system fed with digested sewage.

Key Words: wastewater treatment, activated sludge, respirometry, sludge autotrophic.