Mathematical Modelling on the effect of Mercury on the Growth Rate of Serratia marcescens strain DRY6 on Sodium Dodecyl Sulphate

Abstract

Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS) is a common anionic surfactant found in various cleaning and personal hygiene products. It has both a polar "headgroup" and a hydrocarbon tail, giving it amphiphilic properties that make it effective as a detergent. However, this also makes it a major pollutant in aquatic environments. Researchers have studied the biodegradation of SDS by microorganisms, particularly bacteria, as a potential cleanup method. It has been found that mercury can significantly inhibit the degradation of SDS by the Serratia marcescens strain DRY6 bacteria. At different mercury concentrations, the bacteria exhibited sigmoidal growth with lag times of 7 to 10 hours, but overall growth was decreased with higher mercury concentrations, with a concentration of 1.0 g/L virtually stopping all growth. A modified Gompertz model was used to calculate growth rates at various mercury concentrations, and these rates were then modeled using five different models: modified Han-Levenspiel, Wang, Liu, modified Andrews, and Amor. Only three of the models (Wang, modified Han-Levenspiel, and Liu) were able to accurately fit the curve, with the Wang model performing the best statistically. The Wang model yielded estimates of 0.216 (95% confidence interval: 0.193 to 0.239) for the critical heavy metal ion concentration, 1.05 (95% confidence interval: 0.938 to 1.167) for the maximum growth rate, and 0.389 (95% confidence interval: 0.148 to 0.636) for the empirical constant , represented by Ccrit, max and m, respectively.