Sludge density is an important index for the control of sewage and sludge treatment processes. A new measuring method for sludge density, the microwave phase difference method, has been tested with a good correlation between density and phase difference. Comparison tests with conventional ultrasonic density meters have shown characteristics that are superior to the flow-through type and equivalent to the defoaming type.

We developed a sludge density meter that uses this method and made long-term field tests on the sludge pipelines in sewage treatment plants. Results demonstrated a good correlation with the values that were obtained by manual analysis, with excellent linearity from low density of less than 1% to high density of about 30%.

This new microwave measurement method is less affected by soil build-up and air bubbles, is able to measure a wide range of densities from low to high, and is capable of continuous measurement. It is a highly reliable measuring method for practical applications.

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