Consistently reliable solids measurement

Previously, two optical measuring systems had been used to monitor the solids content of digested sludge during sludge dewatering in the wastewater treatment plant. Deposits being left on the sensors led repeatedly to measuring deviations from the specified limit value of four percent solids content (TS). Dirty sensors also provided incorrect values, resulting in actual values below the limits going undetected in some cases. Regular cleaning, calibration, and manual checks were required to make sure measurements were accurate. Not only that, but changes in the sludge quality – such as color, particle size, or composition – had an impact on optical measurement methods, leading to additional work for operating staff and making process monitoring less reliable.

Key challenges:

• Maintenance-intensive optical measuring systems

• Measurement deviations due to dirty sensors

• Values below limits not identifiable

• Great amount of time spent on cleaning, calibration, and checks

• Measurements affected by fluctuating sludge quality

To increase process reliability and simultaneously reduce maintenance costs, Endress+Hauser has installed two Proline Teqwave MW 300 devices for continuously determining the solids content of sludge. The in-line meters use the principle of microwave transmission, which guides microwaves through the medium. The precise solids content of the sludge can be determined from a change in the signals. As this process is not based on optical properties, it is much less sensitive to changes in sludge quality, making it less prone to errors caused by contamination.
Measurements are taken consistently in the process itself, which means that operating staff always have access to the latest measured values. Changes in the solids content are instantly visible, making it possible to intervene in specific areas of the process if required, for example, to adjust the flocculant dosage.