Influence of Type and Dose of Coagulants on Vehicle Wash Wastewater

Abstract

The study was conducted to investigate the effect of the type and dosage of coagulant on changes in phosphate and fatty oil levels in liquid waste from motor vehicle wash. The independent variables in this study were the type of coagulant (Al2(SO4)3 and FeCl3) and the dosage of coagulant (0 ml, 3 ml, 5 ml, and 7 ml), while the dependent variables were the content of phosphate and fatty oil. The experiment was conducted in 3 stages; fast stirring, slow stirring, and precipitation. From the preliminary test, it was found that the phosphate content before processing was 12.9 mg/lt and the content of fatty oil was 1.9 mg/lt. The most significant decrease in phosphate content was found when 7 ml of FeCl3 was used as coagulant; it dropped to 0.11 mg/lt (efficiency: 99.2%). Meanwhile, the most effective coagulant for fatty oil was 3 ml of Al2(SO4)3; the fatty oil content dropped to 1.4 mg/lt (efficiency: 30.7%). The addition of Al2(SO4)3 gave the opposite effect on phosphate and fatty oil, making the process ineffective. Meanwhile, the data showed that FeCl3 could be used as an effective coagulant for phosphate and fatty oil. To determine the significance of the differences between the results of the Randomized Complete Block Design analysis, the researcher used Least Significant Design test. The results showed that the variation of the type of coagulant affected the decrease in phosphate and fatty oil levels, while the variation in dosage gave no significant difference.