PERFORMANCE EVALUATION OF A CONVENTIONAL DRINKING-WATER TREATMENT PLANT: A 12-MONTH CASE STUDY OF THE AL-DHULUIYA WATER PROJECT, SALAH AL-DIN, IRAQ

Abstract

The Al-Dhuluiya conventional water treatment plant (WTP), in Salah Al-Din Governorate, Iraq, receives raw water from the Tigris River, and this paper presents the results of a 12-month (2024-2025) physicochemical study of the plant. Paired grab samples were taken once a month at the plant inlet (before coagulation) and at the final outlet (after chlorination) through a full hydrological year (November–October) and analysed for twelve parameters including colour, turbidity, pH, total dissolved solids (TDS), total hardness (as CaCO₃), sulfate, nitrite, chloride, nitrate, calcium, magnesium and free residual chlorine. Removal percentage was determined for each parameter and paired samples t-tests were used to identify if differences between the influent and effluent were statistically different. A weighted arithmetic water quality index (WAWQI) was calculated for each month's sample at all sampling sites and compared with four standard norms: Iraqi standard (IQS 417), WHO (2017), US EPA drinking water (2017), and EU Directive (2020/2184). The overall average turbidity removal was 92.8 per cent (inlet turbidity: 31.8 ± 32.1 NTU; outlet turbidity: 2.3 ± 1.3 NTU); and all nine chemical parameters were reduced statistically significantly (p < 0.05). At the inlet, the median WAWQI was 158.4 ("Unsuitable"), while it was 23.2 ("Good") at the outlet; and none of the effluent samples exceeded the IQS 417 or WHO limits. A few months reached a marginal exceedance of the operational turbidity limit set by US EPA/EU of 1 NTU, but the recorded turbidity values were all below the Iraqi/WHO limit of 5 NTU.