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 s). A Ts 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 T s increase. Ts compensation or control during routine SVI tests is not common practice, partially due to a lack of temperature-controlled equipment and an absence of Ts-based MLSS settling models. A practical solution is found to reduce T s 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 deter mine SVI at the operational reactor temperature (T r) 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 T r fluctuations.

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