Predicting THM Formation and Revealing Its Contributors in Drinking Water Treatment Using Machine Learning

Trihalomethanes (THMs) are disinfection byproducts (DBPs) that are formed during chemical disinfection of drinking water. However, a variety of factors, including water qualities and treatment conditions, can influence THM formation, making it challenging to predict and highlight the underlying mechanisms. Here, we used machine learning (ML) algorithms to analyze the complex relations between influent characteristics and operational parameters to predict THM formation. Five ML algorithms were used to create predictive models for THM formation using five input parameters (i.e., chlorine dose/DOC, reaction time, pH, bromide concentration, and temperature). The least-squares boosting (LSBoost) model demonstrated its superiority in predicting THM concentrations on the training and test sets with both R² values of 0.92. We also established a variant of the LSBoost model with an additional parameter, the specific ultraviolet absorbance (SUVA). Results showed that incorporating SUVA into model development gave a higher prediction accuracy on the training set with a reasonable R² value of 0.97. The partial dependence plots (PDPs) and Shapley additive explanation (SHAP) models were employed for in-depth analysis to identify key drivers for THM formation. Our results showed that chlorine dose/DOC was the major driver for THM formation and SUVA had the least impact on THM formation.