Abstract

Biosurfactants have several industrial, environmental, agricultural, and medical applications because they can emulsify oils, enhance the removal of contaminants, and improve the interaction between different substances. The production of biosurfactants from agricultural wastes provides an eco-friendly and sustainable alternative to synthetic surfactants. This study evaluated the use of cassava mill effluent (CME), palm oil mill effluent (POME), and spoilt fruits extract (SFE) as substrates for biosurfactant production using Bacillus thuringiensis and Yarrowia lipolytica. Soil and river water samples used for microbial isolation were obtained from the Rivers State University farm, while agricultural waste substrates were collected from a fruit garden market in Rivers State, Nigeria. Standard microbiological and analytical methods were employed for isolation, screening, identification, and biosurfactant production studies. Biosurfactant activity was assessed using surface tension, oil spread, and drop collapse tests. Results showed high microbial loads in the agricultural wastes. Total heterotrophic bacterial counts ranged from 1.84 ± 0.02 × 10⁷ CFU/ml in POME to 2.31 ± 0.41 × 10⁷ CFU/ml in SFE, while total fungal counts ranged from 4.6 ± 0.12 × 10⁵ CFU/ml in SFE to 8.3 ± 0.17 × 10⁵ CFU/ml in CME. Bacillus thuringiensis and Yarrowia lipolytica were successfully isolated, identified, and screened for biosurfactant production. Nutrient analysis revealed that SFE contained the highest nitrate and phosphorus concentrations, whereas POME had the lowest nitrate level. Surface tension analysis showed that Bacillus with  CME produced the lowest surface tension, 31.6 N/m, followed closely by Bacillus grown with  POME at 32.1 mN/m. Yarrowia recorded relatively similar values of 33.1 mN/m, 33.6 mN/m, and 33.7 mN/mwhen grown with CME, POME, and SFE, respectively. Conversely, the highest surface tension, 60 N/m, was recorded for Bacillus with SFE, indicating poor biosurfactant activity under these conditions. Oil spread results showed that SFE with Bacillus thuringiensis produced a 20 mm clearing zone, while SFE with Yarrowia lipolytica produced the least (15 mm). The drop collapse test further confirmed that Yarrowia lipolytica produced more biosurfactant in CME. Overall, the findings revealed that, among the tested substrates, sterilized Cassava Mill Effluent has potential for biosurfactant production using Bacillus thuringiensis, while Spoilt Fruit Extract has potential for biosurfactant production using Yarrowia lipolytica.