Real-time measurement of the moisture contents of dewatered sewage sludge during thermal drying using a low-cost ECH₂O EC-5 soil moisture sensor

Abstract

Real-time measurement of sewage sludge moisture content renders it possible to optimize the consumption of auxiliary fuel and the thermal treatment. Thus, we explored whether a dielectric soil moisture sensor could be used to measure real-time changes in sludge moisture content. This was possible with the aid of a unified calibration curve. The explanatory variable was the third-order sensor output voltage. The calibration curve well-fitted the data; the mean measurement error was 6.14 wt.%. The use of individual calibration curves for each sludge batch reduced the mean measurement error to 3.09 wt.%. The mean measurement error improves when multiple sensors are simultaneously used. The sensor operates very well when the moisture content is low; the results are minimally affected by the bulk density and Fe level. Considering feed-back to the process, it is ideal to measure sludge moisture content near the outlet of the thermal treatment.

Keywords:

• Dewatered sewage sludge
• thermal drying
• real-time measurement
• moisture content
• dielectric soil moisture sensor
• calibration

Disclosure of interest statement

The authors used a bench kneader PNV-5H (Irie Shokai Co. Ltd., Japan) that was rented from TAKUMA Co., Ltd., Japan.