Batch settling curve registration via image data modeling

•A new experimental method to register sludge blanket profiles is demonstrated.•Qualitative trend analysis is used for image analysis for the first time.•The applied qualitative trend analysis model is based on shape constrained splines.•The use of only inexpensive hardware and open software makes the method accessible.•The method is compared favorably against pre-existing methods.

To this day, obtaining reliable characterization of sludge settling properties remains a challenging and time-consuming task. Without such assessments however, optimal design and operation of secondary settling tanks is challenging and conservative approaches will remain necessary. With this study, we show that automated sludge blanket height registration and zone settling velocity estimation is possible thanks to analysis of images taken during batch settling experiments. The experimental setup is particularly interesting for practical applications as it consists of off-the-shelf components only, no moving parts are required, and the software is released publicly. Furthermore, the proposed multivariate shape constrained spline model for image analysis appears to be a promising method for reliable sludge blanket height profile registration.