Novel Measurements in Primary Settling Tanks of Large Municipal Wastewater Treatment Plants

This paper shows the in situ analysis of a primary settling tank (PST) at the Graz Municipal Wastewater Treatment Plant (500 000 PE). The study aims at the deeper understanding of primary settling tanks behaviour by measurement of flow pattern within the tank and suspended solids (SS) separation.

Measurement campaigns were carried out at different surface overflow rates (a main measure of PST load), that ranged from low to even higher values than recommended ones by design guidelines. During the measurements the inflowing and outflowing SS concentrations and loads were registered on-line. The flow pattern (3D velocity measurements, turbulence characteristics) was measured by using Acoustic - Doppler - Velocimetry (ADV) in raster [1]. The settling function was carried out by laboratory test at Budapest Central Wastewater Treatment Plant, which was investigated at representative concentration of PST.

The measurements provided detailed insight into the flow and mass transport processes within the PST and valuable calibration and verification data for further CFD modelling.