Batch and automated SVI measurements based on short-term temperature variations

Abstract

Effects of short-term temperature variations on the sludge volume index (SVI) are evaluated with batch and automated mixed liquor suspended solids (MLSS) settling tests. The test-cylinder environment and meteorological conditions have a direct influence on the MLSS sample temperature (T δ). A Tδ. change of 4.3°C over the 30 min settling test duration results in an inverse SVI change of 63.0 ml/g, at an average SVI decrease of 14.8 ml/g per 1°C Tδ increase. Tδ compensation or control during routine SVI tests is not common practice, partially due to alack of temperature-controlled equipment and an absence of Tδ-based MLSS settling models. A practical solution is found to reduce Tδ variations experienced before and during batch MLSS settling tests. An automated MLSS settling meter is used to demonstrate a semi-continuous on-line method to determine SVI at the operational reactor temperature (Tτ) of a full-scale plant. Basic and best-fit SVI models are obtained from the SVI data generated over diurnal periods, based on MLSS concentration and Tτ fluctuations. These SVI models confirm the inverse dependence of SVI on temperature for the site-specific conditions. A diurnal Tτ fluctuation of 1.8°C results in an SVI change of 26.6 ml/g, at an average -14.8 ml/g SVI change per 1°C Tτ variation.