Post-treatment of Palm Oil Mill Effluent from a Polishing Pond Using a Limestone Horizontal Roughing Filter

This study aims to evaluate the removal of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), and turbidity by using three types of filter media with different size combinations with limestone media in a horizontal roughing filter (HRF). The optimum removal percentages of COD, NH3-N, and turbidity were 27.0 %, 51.3 %, and 31.5 %, respectively. The efficiencies of HRFs were found to depend on the size of the filter media and the applied filtration rates. The results indicate that the use of smaller filter media provided higher removal efficiency. Conversely, the use of larger filter media provided lower removal efficiency. One-way analysis of variance (ANOVA) was used to determine overall statistical significance. The values of COD, NH3-N, and turbidity were also simultaneously determined by using variances. A two-way ANOVA test was used to determine the significant interaction effect between the sizes of filter media and filtration rates. ANOVA outcomes were found to be statistically significant at p < 0.05.