Development and Characterization of a Powder Detergent Based on Waste-Derived Soap and Eco-Friendly Builders

Growing interest in waste valorization and sustainable cleaning products motivated the development and characterization of an eco-friendly powder detergent based on soap derived from waste cooking oil and enriched with juniper essential oil. Waste sunflower oil was pretreated and, together with coconut oil, subjected to cold saponification; the resulting soap base was incorporated at 30% into a detergent formulated with sodium carbonate, sodium bicarbonate, sodium percarbonate and natural zeolite. The raw materials—waste sunflower oil, coconut oil, clinoptilolite and juniper essential oil—were characterized using physicochemical analyses: DSC for coconut oil and Raman spectroscopy for oils, XRF for zeolite, and physicochemical analysis and GC-FID for the essential oil. The soap exhibited pH 9.93, 14.8% moisture, 24 cm foam capacity, and a 3.0 g/min dissolution rate, versus pH 9.33, 10.5% moisture, 12 cm foam capacity, and 1.0 g/min dissolution rate for the detergent. In vitro antibacterial activity was assessed against Escherichia coli and Staphylococcus aureus by agar well diffusion. At 500 mg/mL, inhibition zones reached 8.53 and 17.00 mm for the soap and 7.47 and 15.03 mm for the detergent. Two-way ANOVA confirmed significant effects of sample type and concentration (p < 0.001), with the strain being the dominant source of variation (η2p = 0.983); both products reached 71.0–87.7% of a commercial reference and were more effective against S. aureus. Antibacterial activity decreased significantly with decreasing concentration (p < 0.001 for all pairwise comparisons), while both formulations showed greater efficacy against S. aureus than against E. coli. The results demonstrate the potential for valorizing waste cooking oil into functional cleaning products and highlight the possibility of contribution of juniper essential oil to the antimicrobial performance of the formulations, supporting the development of sustainable and environmentally compatible detergent products within a circular economy approach.