Much waste cooking oil (WCO) is still discarded even though it can be processed into more valuable products, such as dishwashing liquid soap. The quality of dishwashing liquid soap made from WCO is influenced by the method used, the concentration of potassium hydroxide (KOH) and the adsorption material used. Variations of these three variables produce different qualities. Soap quality is measured based on PH, free alkalis and fatty acids produced. This study uses an experimental design to produce the best combination. The results of the combination will be checked for conformity with the quality standards of SNI 06-2048-1990. The best treatment combination is the cold method, 22.5% KOH concentration, activated carbon purification material with a pH value of 9.00, 0.05 free alkalis, and 0.32 free fatty acids. The soap products produced are in accordance with Indonesian quality standards and generate profits economically.
Keywords: dishwashing liquid soap; waste cooking oil; experiment design