A novel methodological approach for the assessment of drinking water treatment plant robustness under challenging turbidity scenarios

Abstract

The “ALERT” method, allows to handle management criticalities related to high-turbidity levels in a drinking water treatment plant, is a stepwise procedure based on the 95th percentile-based turbidity robustness index (TRI95B). The method is novel compared to existing literature and identifies the existing relationship between the TRI and the raw water turbidity, allowing setting up critical operational thresholds above which a noticeable plant robustness loss takes place. Additionally, ALERT also proposes two novel turbidity load indicators, the turbidity load index (TLI) and the turbidity event (TE). TLI provides a qualitative indication of the quantity of suspended solids potentially associated with the raw water, whereas TE indicates the occurrence of extreme and short-duration turbidity peaks in the influent. ALERT method has been applied to a full-scale drinking water treatment plant. Results showed that ALERT identified TLI thresholds above which the case study DWTP exhibited a lower robustness and frequent deviations from the regulation turbidity goal. Specifically, sand filter FS3 shows a notable weakness when the TLI exceeds 50, whereas sand filters FS1 and FS2 consistently fall within the very stable class across all TLI levels. Therefore, during events where the TLI surpasses 50, it is advisable to reduce the inlet flow rate to FS3 until its specific TLI drops below 50. The proposed method allows the early detection of plants performance degradation. Indeed, it can support operators at implementing corrective measures to maintain high water quality safeguarding the integrity of the treatment processes under high turbidity load.