Chemical precipitation of palm oil mill effluent

Abstract

Many palm oil mills failed to comply with the standard discharge limits especially BOD and TSS concentration although they have applied biological treatment system. Hence, it is suggested that coagulation and flocculation process will enhance the BOD and TSS removal so that the final discharge will meet the Department of Environment (DOE) standards besides curtailing the large land area required by the aerobic pond. A study using coagulation–flocculation method as a pre-treatment for palm oil mill effluent (POME) has been carried out. The efficiency of chitosan, polyacrylamide (PAM) and polyaluminum chloride (PACl) as coagulants were explored in this study. Jar test method has been used to identify the best coagulant in removing the organic matter. The reduction of turbidity, BOD, and TSS were the main evaluating parameters. In coagulation–flocculation process, coagulant dosage and pH played an important role in determining the coagulation efficiency. Chemical cost estimation was done to determine the applicability of the type of coagulant and its dosage. At the optimum chitosan dosage (250 mg/L) and pH 5.0, turbidity reduction was found to be 94%, TSS removal was 97% and BOD reduction was 61%. The optimum dosage and pH for PAM were 500 mg/L and 5.0, respectively, at which it gave 44% reduction of turbidity, 94.8% of TSS removal and 63% of BOD reduction. At the optimum PACl dosage (500 mg/L) and pH 6.0, turbidity reduction was found to be 76.3%, TSS removal was 96% and BOD reduction was 59%. For PAM and PACl to obtain a comparable percentage of BOD removal as performed by chitosan, the optimum dosages were 500 mg/L, respectively, employing the same mixing speed and sedimentation time, and a pH value of 5.0 and 6.0, respectively. Amongst the three types of sole coagulant, the total chemical cost of PACl needed per tonne of crude palm oil produced was the cheapest (RM0.85), followed by PAM (RM23.88) and chitosan (RM39.13).