Olive mill wastewater biodegradation for bacterial lipase production using a response surface methodology

Olive mill wastewater (OMW) represents the effluent generated during the olive oil extraction process. OMW, as an oil-rich residue, provides a source of lipase-producing microorganisms and a source of complex nutrients that is potentially suitable to be applied in bacterial lipase production. This study focused on isolating actinobacteria able to produce extracellular lipases with OMW as the sole carbon source. Thirteen isolates of actinobacteria have been obtained and screened for their lipase activity using rapid plate detection methods. Then, the extracellular lipolytic activity was monitored under shaking flask conditions, and the titrimetric method was applied for lipase activity determination. Maximum lipase activity was detected for the SC1 strain (5.33 U/mL), which was then identified as a Streptomyces species. To enhance lipase production using the SC1 strain, Box-Behnken design (BBD)-based response surface methodology (RSM) has been adopted, by varying incubation time (days), pH, temperature (°C), inoculum size (spores/mL), and initial OMW concentration (%, v/v). An accompanying analysis of variance (ANOVA) was carried out, and the production of lipase was reported by a mathematical equation according to the factors. Non linear regression equations with significant R2 and p-values were used to depict individual term, interaction, and square effects on lipase production. Individual term, interaction, and square effects on lipase production were shown using nonlinear regression equations with significant R2 and p-values. The optimization results obtained showed that the optimal lipase activity was achieved after a 9 days incubation time at pH 4, with an inoculum size of 1.7×107 (spores/mL), incubated at a temperature of 30°C using 6% (v/v) OMW as the sole carbon source.