A Comparative Techno-Economic Analysis of Waste Cooking Oils and Chlorella Microalgae for Sustainable Biodiesel Production

This research work presents a techno-economic assessment of biodiesel production with non-standard waste cooking oil (WCO) (brown grease of small restaurants, yellow grease of households) and semi-open Chlorella sp. microalgal cultivation, which covers the problematic areas of scale and cost-efficiency in sustainable biodiesel production. Cost-effective biodiesel feedstock research has been motivated by the urgency of finding sustainable sources of energy. With base-catalyzed transesterification optimized by ANOVA and response surface methodology (RSM), the present study recorded biodiesel yields of up to 99.08% in household WCO (at optimum conditions; 55 °C, 3.3 mg/g NaOH, ethanol) and 96.61% in restaurant WCO (at optimum conditions; 54 °C, 1.5 mg/g NaOH, methanol) compared to 28.6% in Chlorella sp. (semi-open photobioreactors). Concerning the two types of WCO feedstocks, the obtained equations are able to compute the biodiesel viscosity and yield, in good correlation with the experimental values, in relation to the temperature and ratio of catalyst to oil/alcohol solution. The assessed household WCO has better yield and quality as it contains fewer impurities, whereas the restaurant WCO needed to be further purified, driving up the prices. Although Chlorella biodiesel is carbon neutral, its production and extraction costs are higher, making it less economically feasible for biodiesel production. Economic analysis showed that the capital costs of household WCO, restaurant WCO, and Chlorella sp. are USD 190,000, USD 220,000, and USD 720,000, respectively, based on 1,000,000 L/year as biodiesel production rate. Low capital costs as well as byproduct glycerol income of the two investigated types of WCO play a role in their low payback periods (0.23–0.91 years) and high ROI (110–444.4%). The analysis highlights the economic and environmental benefits of WCO, especially household WCO, as a scalable biodiesel feedstock, which provides new insights into process optimization and sustainable biodiesel strategies. To enhance its sustainability and cost-effectiveness and contribute to the transition to renewable biofuels globally, future studies need to emphasize energy reduction in microalgae production and purification of restaurant WCO.