Production of Liquid Soap from Lye and Used Vegetable Oil Recovered from Restaurants in Abuja, FCT

Used cooking oil from food service establishments in Abuja, Federal Capital Territory, is frequently disposed of through drains and solid waste streams, contributing to water pollution and grease blockages in municipal sewers. This study formulates liquid soap from potassium hydroxide lye and used vegetable oil recovered from restaurants in Wuse and Garki districts of Abuja, as a waste valorisation and circular economy demonstration. Used oil samples were characterised for moisture, free fatty acid content, peroxide value, and colour before and after purification by filtration and acid treatment. Saponification was carried out using the cold process method with potassium hydroxide solution at 80 degrees Celsius, with coconut oil co-substrate at 20% of total oil content to improve lathering. Three formulations with varying glycerine and preservative concentrations were produced and evaluated for pH, viscosity, total fatty matter, free alkali, foam height, stability under temperature cycling, and bacterial contamination. Results indicated that all three formulations achieved pH values between 9.1 and 9.8 and total fatty matter exceeding the NIS 543 minimum of 25% for liquid soap. Foam height and stability were consistent with commercially available general-purpose liquid soaps. Bacterial contamination tests confirmed absence of Staphylococcus aureus and Pseudomonas aeruginosa after addition of a phenoxyethanol preservative. The study supports restaurant-scale used oil recovery programmes in Abuja as a feedstock supply strategy for small-scale liquid soap enterprises. Keywords: liquid soap, used vegetable oil, waste valorisation, saponification, Abuja FCT