Settling characterisation using on-line sensors at a full-scale wastewater treatment plant

Abstract

An on-line settlometer is presented which automatically records sludge settling curves. From these curves the sensor deduces the initial hindered zone settling velocity (Vs). In order to evaluate the information gathered by the sensor, the instrument was used at an information-rich full-scale wastewater treatment plant (Klagshamn, Sweden). This plant is operated as a single sludge postdenitrification activated sludge system with an external carbon source. With the sensor a diurnal pattern of Vs could be detected. This pattern was mainly caused by the diurnal change of the sludge concentration. Using the Vesilind equation it was possible to standardise Vs to the sludge concentration (Vs’). The variation in the standardised Vs’ was less compared to the experimental Vs. Still, it was possible to detect a sudden drop in Vs’ on nearly daily basis. At two of these instances rising sludge was even detected in the settlometer during the 35 min lasting sedimentation period.

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