Olpas demonstrates state-of-the-art activated sludge concentration measurements with wireless datalogging by Crodeon Reporter

Activated sludge concentration measurements in the Aquafin Diest WWTP

Mixed Liquor Suspended Solids (MLSS) is a key parameter in wastewater treatment plants. It refers to the activated sludge concentration in the aeration basin of biological wastewater treatment plant.

The MLSS concentration needs to be controlled: too low means too little sludge to process the incoming load of wastewater, too high means that there is a limited oxygen transfer and potential settling issues. Also, knowing the MLSS concentration allows to calculate the sludge age or Sludge Rentention Time (SRT) of treatment plant: another key operational parameter.

Currently, the majority of WWTP’s monitor MLSS concentration with optical concentration sensors based on light scattering or transmittance. Turbidity or light scattering is correlated to the sludge concentration. Alltough a very precise method, the reliability of optical sensors is strongly tied to the cleanliness of the sensor surface.

The majority of turbidimeters employ one or more cleaning methods in-situ to postpone cumbersome manual maintenance. For the wastewater treatment plant of Diest, the optical concentration sensor is equipped with a wiper and weekly operator cleaning is required. This need for manual maintenance and the dependency on optical sludge characteristics are considered to be the key limiting factors of the well-known optical concentration sensors.

Olpas technology removes fouling issues

The Olpas MLSS concentration sensor is based on ultrasound backscattering as measurement principle. Hence, it is not affected by changes in sludge particle appearance or optical properties at all. The Olpas Technology is temperature independent, not sensitive to sludge particle size and not affected by the aeration cycles in the treatment plant. Furthermore, the ultrasound wave passes through any buildup of fouling layer up to 2 mm allowing maintenance to be postponed to monthly intervals or even longer.

The Olpas MLSS concentration sensor is installed in the wastewater treatment plant of Diest, operated by Aquafin, to demonstrate this superior accuracy with zero maintenance efforts. The sensor is installed with a factory calibration and connected to the Crodeon Reporter datalogger.

MLSS concentration measured by the Olpas MLSS probe. No maintenance was needed during the measurement campaign.

The sensor is installed during a prolonged dry period (little to no rainfall for more than one month). Therefore it is expected to see MLSS concentration increases during the first heavy rain events with a large inrush of wastewater with high (solids) loading. These events allow to validate the sensor performance in a dynamic environment with large concentration swings.

Olpas MLSS concentration sensor after approx. 6 weeks of measuring without maintenance or cleaning. The orange ultrasound measurement window is clear visible in the center of the probe. No measurement issues were reported even-though some biofouling formation can be observed.

Pilots made easy with the Reporter

The Olpas Tentacle MLSS concentration sensor can directly be connected to the Crodeon Reporter, allowing data capture with minimal installation requirements. The flexible installation with the Reporter, allows for WWTP operators to quickly test and evaluate sensor location and depth in the aeration basin. With up to four sensors connected, users can monitor MLSS at different depths or aeration zones or add additional measurement parameters.

Olpas Tentacle MLSS concentration sensor next to the Crodeon Reporter. The Reporter supplies power for up to 4 Olpas sensors and ensures reliable datalogging.

The Olpas Tentacle sensor connected to the Reporter provides the MLSS concentration, sludge temperature and sensor serial number - allowing to fully track local concentrations and sensor calibrations and traceability.

Plug and play measurements require easy datalogging

The combination of Olpas concentration sensors and the Crodeon Reporter changes the way measurements can be performed. Olpas sensors can be operated with minimal maintenance for prolonged duration, an industry first. Combined with the remote logging made easy with the Reporter mobile wastewater treatment units or water treatment pilots can be tracked more accurately and operated with more certainty. As the Reporter provides power and datalogging for up to four Olpas sensors, it can be employed to quickly monitor and control wastewater treatment processes or combining MLSS concentration sensors with auxiliary flow or level measurements.