Performance Evaluation of Conventional Water Treatment Plants Using Turbidity and Disinfection Parameters

Conventional water treatment plants (WTPs) typically involve two primary processes: turbidity removal and disinfection. This study evaluates the turbidity removal efficiency and the effectiveness of chlorination using daily records collected over one year from two WTPs, Dokan-1 and Dokan-2, located in the Sulaymaniyah Governorate, Kurdistan Region of Iraq. Results of the study indicate mean turbidity removal efficiencies of 23.8% for Dokan-1 and 37.4% for Dokan-2. Although these values appear low, the performance of both plants is considered acceptable, as the 95th percentile of influent water turbidity during the study year was 9.46 NTU. The findings suggest that high turbidity removal efficiency is not expected when raw water turbidity is below 10 NTU. Therefore, assessing efficiency without considering influent turbidity is not a reliable approach. Throughout the study year of 2023, the average effluent turbidity values remained below the permissible limit of 5 NTU, with Dokan-1 and Dokan-2 recording averages of 3.27 NTU and 2.95 NTU, respectively. A one-sample t-test confirmed that effluent turbidity from both plants was significantly below the 5 NTU threshold. Turbidity removal efficiency can be calculated using two methods: (1) the mean of daily efficiencies which is the average of daily efficiencies, and (2) the efficiency based on average influent and effluent turbidity values. This study recommends the second method for evaluating conventional WTPs. Additionally, disinfection was successful in both plants, with average daily free chlorine concentrations of 1.41 mg/L for Dokan-1 and 2.26 mg/L for Dokan-2.