Background: Surfactants are one of the most important raw materials used in various industrial fields as emulsifiers, corrosion inhibitors, foaming agents, detergent products, and so on. However, commercial surfactant production is costly, and its demand is steadily increasing. This study aimed to evaluate the performance of typical strains of Bacillus sp. to produce biosurfactants through fermentation. It also included the investigation of the effect of initial glucose concentration and the carbon to nitrogen ratio. Results: The biosurfactant yield was in the range of 1–2.46 g/L at initial glucose concentrations of 10–70 g/L. The optimum fermentation condition was achieved at a carbon to nitrogen ratio of 12.4, with a decrease in surface tension of up to 27 mN/m. Conclusions: For further development and industrial applications, the modified Gompertz equation is proposed to predict the cell mass and biosurfactant production as a goodness of fit was obtained with this model. The modified Gompertz equation was also extended to enable the excellent prediction of the surface tension

Biodiesel is one of the potential alternative energies produced from a variety of vegetable oils. The utilization of a CaO/SiO₂ catalyst generated from eggshell and palm empty fruit bunch (PEFB) waste for biodiesel production from waste cooking oil was investigated. The optimum silica yield extracted from PEFB was 68.2% using 10% NaOH (w/v) at 80 °C for 1 h. Methanol with a mol ratio of 14 to waste cooking oil was used. The presence of a silica support in the CaO catalyst increased the yield of biodiesel from 78% to 96%. Three runs of the catalyst led to only a 1% reduction in biodiesel yield. The utilization of activated PEFB as a support showed a potential result with a biodiesel yield of 83%. The prospective heterogeneous catalysts were also characterized by using XRD, SEM, BET and FT-IR. The developed CaO/SiO₂ stands out as a promising catalyst for biodiesel production due to the utilization of abundant and cheap waste materials. Moreover, a significant yield of biodiesel was obtained using the catalyst; hence, it is feasible to be developed on a larger scale.