Biosorption of Pb and Cu using fixed and suspended bacteria

To compare heavy metal (HM) adsorption capabilities between fixed and suspended morphologies of bacteria, batch adsorption tests of Cu(II) and Pb(II) were performed. Adsorption experiments were performed at 22 °C, neutral pH (7–7.5), and low concentrations of HMs (2.5–25 mg/l). A mixed bed bioreactor (MBBR) and a batch reactor were used to develop the fixed and suspended bacteria, respectively. The dominant bacteria were identified by 16s RNA sequencing as Enterobacter ludwigii, Zoogloea ramigerais and Comamonas testosteroni. The two morphologies exhibited significant differences in percent dry weight and in extracellular polymeric substances (EPS) content. The fixed bacteria displayed 29% EPS content by weight compared to 9.5% EPS found on the suspended bacteria.The adsorption data fit the Freundlich isotherm for all trials, while data fit the Langmuir isotherm for Cu(II) only. The Langmuir adsorption data for Cu(II) revealed that the qmax was greater for fixed bacteria, at 9.80 mg/g compared to 6.52 mg/g for suspended bacteria. Maximum HMs removal was greater by fixed bacteria with 83.7% and 97.5% removal of Pb(II) and Cu(II), respectively, while suspended bacteria removed 72.6% and 83.8% of Pb(II) and Cu(II), respectively.