<![CDATA[The Tabalong River is a raw water source for PT Air Minum Tabalong Bersinar and experiences substantial fluctuations in quality, especially during the rainy season. This study evaluated the technical effectiveness and cost-efficiency of polyaluminium chloride (PAC), alum, and their combinations during the coagulation–flocculation stage. A laboratory experiment was conducted using the jar test method in two stages. In the first stage, optimal operational doses of PAC and alum were determined by varying doses from 0–25 mg/L and setting a turbidity target of ≤5 NTU. In the second stage, five PAC:alum formulations, namely 100:0, 75:25, 50:50, 25:75, and 0:100, were tested. PAC and alum stock solutions were prepared at 2% w/v (20 mg/mL) and dosed into 1-L raw-water samples. Based on optimum doses of 10 mg/L PAC and 15 mg/L alum, the 75:25 formulation contained 7.50 mg/L PAC and 3.75 mg/L alum, corresponding to 0.375 mL/L PAC stock and 0.188 mL/L alum stock. The 75:25 formulation produced the best performance, reducing turbidity by 98.2%, colour by 100%, TSS by 90.3%, Fe by 90.8%, Mn by 88.9%, and E. coli by at least 97.8%, while maintaining pH at 7.18. Its final values were 2.27 NTU, 0 TCU, 15.40 mg/L TSS, 0.06 mg/L Fe, 0.06 mg/L Mn, and 22 MPN/100 mL E. coli. The coagulant cost was IDR 144/m³. This formulation provided the best balance between technical performance and coagulant cost; however, the treated water still required sedimentation, filtration, and disinfection to meet final drinking-water requirements under the tested conditions.]]>
