Employing a Central Composite Rotatable Design to Define and Determine Significant Toxic Levels of Heavy Metals on Shewanella putrefaciens in Microbial Fuel Cell

Abstract

Microbial fuel cells (MFCs) are a unique technology that takes advantage of bacterial metabolism to generate electricity and remove chemical oxygen demand (COD) from organic pollutants. Existence of heavy metals in fuel affects vitally bacterial activity in MFC. Present study aimed to define the negative effect of three most toxic heavy metals, namely mercury (HgCl2), lead (Pb(NO3)2), and cadmium (CdCl2), on the activity of bacterium Shewanella putrefaciens with respect to electricity generation and COD removal in MFC from food industry wastewater. A central composite rotatable design was employed to determine the significant toxic levels of used heavy metals. The results indicted that the main effect of HgCl2, Pb(NO3)2, and CdCl2 was −62.17, −58.55, and −31.65 %, respectively, with respect to electricity generation, as well as −34.32, −32.25, and −18.95 %, respectively, with respect to COD removal, at 95 % confidence. The statistical design determined the significant toxic levels for each factor of heavy metals alone as (mg/100 mL) HgCl2 23.45, Pb(NO3)2 34.38, and CdCl2 48.31, with respect to electricity generation, as well as 26.34, 31.84, and 52.56, respectively, with regard to COD removal at 95 % confidence. The coefficient of determination (R2) was found to be 0.93 and 0.98 for electricity generation and COD removal, respectively. The confirmatory experiments showed closeness of predicted and observed values.