Suspended Solid Removal of Palm Oil Mill Effluent Using Horizontal Roughing Filter and Calcinated Limestone

Severe environmental pollution could occur in water bodies which serve as the discharge sites for improperly treated palm oil mill effluent (POME). This is because POME increases the chemical oxygen demand (COD) and suspended solids (SS) of the water body. This issue is addressed by investigating the use of raw and calcined limestone (800 °C) in a horizontal roughing filter to eliminate SS from POME in this work. The horizontal roughing filter was designed using various sizes of limestone (4 mm, 12 mm, and 20 mm) at various filtration rates (20, 60, and 100 mL/min). In order to model the experimental design, a method achieving ideal process conditions and optimum values of process variables, central composite design (CCD), and response surface methodology (RSM) were employed. From the column study conducted, a higher SS removal (75%) was obtained at a lower flow rate together with a smaller-sized (4 mm) calcined limestone (LS). The statistical analysis produced an SS removal model with considerable probability values (0.000). The Langmuir and Freundlich isotherms were also used to characterize the adsorption equilibrium during the removal of SS. However, the Langmuir isotherm proved to best fit the data.