The 20th Central Committee′s Third Plenary Session emphasized the comprehensive implementation of water conservancy reform tasks, with a focus on residential drinking water as a key livelihood task. The coagulation process is a critical step in drinking water treatment. Due to the significant time delay characteristic of the coagulation process, conventional PID control cannot achieve satisfactory results for control systems with frequent changes in raw water quality. Therefore, a linear active disturbance rejection controller (LADRC), which does not rely on an accurate system model, is applied to the system. An extended observer is used to estimate and compensate for disturbances in the coagulation control system. Additionally, an adaptive Smith controller, combining a Smith predictor with a fuzzy controller, is designed to mitigate the impact of large time delays on control effectiveness, leading to the proposed Fuzzy-Smith-LADRC controller. To address the difficulties in adjusting the controller parameters, an improved dung beetle optimization algorithm (MSIDBO) is introduced for parameter tuning. This improved algorithm optimizes issues such as uneven initial population distribution and the tendency to fall into local optima found in the DBO algorithm, enabling MSIDBO to converge quickly and better balance global exploration and local exploitation capabilities. When the system model is accurate, this control method reduces the settling time by 279 s and decreases overshoot by 8% compared to PID control, it also reduces settling time by 40 s compared to DMC control. When the system model changes, it demonstrates better anti-disturbance and robustness compared to LADRC.