Analysis of the Optimum Dosage of Poly Aluminum Chloride (PAC) Coagulant to Reduce Turbidity and TDS in the Raw Water of the Bengawan Solo River During Morning and Afternoon at Semanggi Water Treatment Plant, Perumda Surakarta

The Bengawan Solo River serves as a surface water source utilized by the PDAM Kota Surakarta for clean water treatment. In the process of water treatment, one of the most critical steps is coagulation-flocculation. Through this process, colloidal particles responsible for turbidity are destabilized, leading to their agglomeration and subsequent autonomous settling. Given the fluctuating turbidity of water during the rainy and dry seasons, it becomes imperative to conduct research to determine the optimal dosage of Poly Aluminium Chloride (PAC) coagulant during morning and afternoon periods. The primary objective of this study is twofold: firstly, to ascertain the average percentage reduction of turbidity and total dissolved solids (TDS) in raw water at the Semanggi Water Treatment Plant; secondly, to establish the requisite dosage of PAC coagulant necessary to achieve the turbidity and TDS quality standards mandated for drinking water. The research method employed in this study involved a scale-down approach utilizing the jar test apparatus, which served as a means of coagulation-flocculation and sedimentation processes.

The research findings indicate that, on average, the efficiency of turbidity reduction during the morning was 96.74% and TDS reduction was 50.80%. In the afternoon, the efficiency of turbidity reduction was 98.01%, and TDS reduction was 53.76%. The optimum dosage of PAC coagulant required to achieve the Turbidity Standard in the Indonesian Ministry of Health Regulation No. 492/MENKES/ PER/ IV/ 2010 for both morning and afternoon periods was found to be 15.71 mg/l and 15.28 mg/l, respectively.