Modelling of the ultrasonic disintegration of activated sludge

Ultrasonic treatment of waste activated sludge is one of the possibilities to reduce excess sludge production through the mechanism of sludge disintegration and cell lysis. In the past, several attempts have been made to model the process of solubilisation of the particulate volatile suspended solid part of the activated sludge (VSS) into soluble COD (sCOD). However, the focus of these models was predominantly on predicting an efficiency factor for the release of sCOD (Disintegration Degree, DDCOD) and provided no information on the release of nutrients and the instantaneous reduction of VSS. Moreover, often insufficient influential variables were included in the model equations, making the models only applicable on the training dataset of their own experimental research. This paper, therefore, seeks to build a simple model, which contains all influential input variables, that can predict not only the sCOD release but also the nutrients release (ortho-PO4-P and soluble Kjeldahl nitrogen) and VSS reduction simultaneously. Therefore, in first instance, a Principal Component Analysis (PCA) is carried out on the input and output data matrix of obtained experimental observations that will be used as training data. In this way, certain correlated input variables and independent output variables can be removed from the model, in order to increase its simplicity and predictive nature. Then, the model is built on the basis of Partial Least Squares Regression (PLS-R) and a part of the observations is used to validate the predictive strength of the model.