Main and Interactive Effects of Polyaromatic Sulfur Heterocyclic Compounds on Growth and Biodegradation Efficiencies of Bacillus sphaericus HN1: Modeling and Statistical Analysis

Abstract

Bioremediation is an effective technique to remediate soil and water contaminated with a mixture of recalcitrant polyaromatic sulfur heterocyclic (PASH) compounds. Based on two levels of full factorial design, a statistical design of experiments was used in this study to investigate the interactive effects of three PASHs; thiophene (Th), benzothiophene (BT), and dibenzothiophene (DBT) on their biodegradation in multisubstrate batch process using Bacillus sphaericus HN1. Kinetic modeling was performed to estimate the rate of biodegradation of each PASH in single-, binary-, and tertiary-substrate systems. Biodegradation of BT, DBT, and total PASHs follows the first order kinetic reaction in the single- and multisubstrate batch systems, while biodegradation of Th follows the first-order kinetic reaction, in single-substrate system, but second-order kinetic reaction in multisubstrate batch system. Four linear interaction regression models were estimated and validated to describe the interactive effect of the three PASHs on their biodegradation. Statistical analysis of the results in the form of analysis of variance and Student t test indicated significant role played by the main effects of Th, BT and DBT on their biodegradation (p < 0.01). Th and the interactive effect between Th and DBT has statistically significant negative effect on DBT removal (p = 0.0665). However, DBT expresses higher statistically significant positive effect on total PASHs removal than that of Th (p = 0.0178 and p = 0.026, respectively), but their interaction has a significantly negative effect (p = 0.0143).