Rapid and real-time detection of municipal sludge moisture content based on microwave reflection principle

The moisture content (MC) of municipal sludge is the key factor affecting sludge treatment and disposal technologies, while the vast majority of existing measurement methods are off-line and time-consuming. To realize rapid online detection for the MC of sludge, a detection method based on the microwave reflection principle is proposed: experiments are carried out and the MC computation model of the sludge is derived using the resonant frequency and the permittivity ( \(\varepsilon^{\prime}\) ${\epsilon }^{\prime }$ ). The results reveal that the detection accuracy of granular sludge with a thickness of 10 mm is higher. The theoretical model between the MC and the real part of \(\varepsilon^{\prime}\) ${\epsilon }^{\prime }$ is developed, and the relationship between the resonant frequency and \(\varepsilon^{\prime}\) ${\epsilon }^{\prime }$ is expressed by a cubic polynomial. The average error and the root mean square error (RMSE) of sludge are 2.06% and 2.49%, respectively. The prediction model for the MC of sludge is also given, and the determination coefficient and RMSE are 0.981 and 2.06%, respectively.