Performance of aluminum sulphate and polyaluminium choloride in biodiesel wastewater

The production of biodiesel through the transesterification method produces a large amount of wastewater that contains a high level of chemical oxygen demand (COD) and oil and grease (O&G). In this study, coagulation was adopted to treat the biodiesel wastewater. Two types of coagulation were examined using a standard jar test apparatus, i.e. polyaluminium chloride (PAC) and aluminium sulphate. The effects of pH and coagulant dosage were examined at 150 rpm of rapid mixing and 20 rpm slow mixing and 30 min settling time. Higher removal of suspended solids (SS), colour, oil and grease (over 90%), and COD (over 80%) were achieved at pH 6. PAC was found to be superior to aluminium sulphate, yielding a lower amount of coagulation, i.e., 300 mg/L. The result indicated that the coagulation and flocculation process played bigger roles in the integrated treatment system