Adsorption of aqueous Pb(II) using different metabolically inhibited bacterial cultures from industry

Sterilized reactors containing 100 ml of ultrapure water, 1 ml of 1.711 M 𝑁𝑎𝑁𝑂3 salt substitute with metabolically inhibited bacteria, and 100 ppm of Pb(II) were prepared. This will serve as the concentration for the basis of comparison with other microbial strains of the consortium. The reactor was triplicated to ensure repeatability and the Pb(II) removal over a 14 h period was investigated. Reactors were sampled at various time intervals and filtered (0.45 µm) and initial and final pH readings of the samples were measured. The Pb(II) concentration in samples was measured using atomic absorption spectroscopy (Perkin Elmer AAnalyst 400, Waltham, Massachusetts). The sampled adsorptions were fit to a pseudo-first order, two-phase pseudo-first order, pseudo-second order isotherms, and Crank's diffusion model.

Batch adsorption experiments were carried out to predict the equilibrium behaviour of the adsorbents. Serum bottles containing 1.352 g/L of adsorbate were prepared with 100 mL of Pb(II) solution in concentrations ranging from 0 - 600 mg/L Pb, and sealed with rubber stoppers. The serum bottles were agitated using a water-bath shaker (Labotec EcoBatch Model 207) at a constant agitation speed of 120 rpm maintained at temperatures of 25°C, 35°C, and 45°C. The pH, as well as lead concentrations, were measured well after equilibrium was reached (24-hrs) using atomic absorbance spectrophotometry (Perkin Elmer, Waltham, Massachusetts). Langmuir, two-surface Langmuir, and Freundlich, models was used in evaluating the relationship between the adsorbate concentration and the amount adsorbed in the aqueous phase at equilibrium.

Fourier-transform infrared (FTIR) spectra of the cultures were measured after four successive processes. The first measurement was taken after 24 h growth period of the bacteria. The second measurement was taken after 24 h oven drying of the bacteria at 74 °C. The third measurement was taken after the bacteria was exposed to 100 ppm of 𝑃𝑏(𝑁𝑂₃ )₂. The last measurement was taken 14 h after the addition of 100 ppm 𝑃𝑏(𝑁𝑂₃)₂ to the cultures. An attenuated total reflection (ATR) attachment was used in recording spectra on a Perkin Elmer Spectrum 100 FTIR spectrometer. All FTIR spectra were recorded on a wavenumber from 4000 to 500cm^-1 and represent an average of 30 scans.

An ultrahigh-resolution filed emission scanning electron microscope (HR FESEM Zeiss Ultra Plus 55, Carl Zeiss AG, Oberkochen, Germany) with an InLens detector was used in studying the particle morphologies of the adsorbents. The scanning electron microscope was also fitted with an energy dispersive Xray spectrophotometer (EDS) which was used in analyzing the elemental composition of the metabolically inhibited adsorbents.