Biosorption of lead, cadmium, and zinc by Citrobacter strain MCM B-181: characterization studies.

The biosorption process for removal of lead, cadmium, and zinc by Citrobacter strain MCM B-181, a laboratory isolate, was characterized. Effects of environmental factors and growth conditions on metal uptake capacity were studied. Pretreatment of biomass with chemical agents increased cadmium sorption efficiency; however, there was no significant enhancement in lead and zinc sorption capacity. Metal sorption by Citrobacter strain MCM B-181 was found to be influenced by the pH of the solution, initial metal concentration, biomass concentration, and type of growth medium. The metal sorption process was not affected by the age of the culture or change in temperature. Equilibrium metal sorption was found to fit the Langmuir adsorption model. Kinetic studies showed that metal uptake by Citrobacter strain MCM B-181 was a fast process, requiring <20 min to achieve >90% adsorption efficiency. The presence of cations reduced lead, zinc, and cadmium sorption to the extent of 11. 8%, 84.3%, and 33.4%, respectively. When biomass was exposed to multimetal solutions, metals were adsorbed in the order Co2+ < Ni2+ < Cd2+ < Cu2+ < Zn2+ < Pb2+. Among various anions tested, only phosphate and citrate were found to hamper metal sorption capacity of cells. Biosorbent beads prepared by immobilizing the Citrobacter biomass in polysulfone matrix exhibited high metal loading capacities. A new mathematical model used for batch kinetic studies was found to be highly useful in prediction of experimentally obtained metal concentration profiles as a function of time. Metal desorption studies indicated that Citrobacter beads could, in principle, be regenerated and reused in adsorption-desorption cycles. In an expanded scale trial, biosorbent beads were found to be useful in removal/recovery of metals such as lead from industrial wastewaters.

Biosorption of lead and zinc from solutions using Streptoverticillium cinnamoneum waste biomass.

Mycelial wastes of microbial origin from fermentation industries have been recognized as potential biosorbents for decontamination of waste waters containing heavy metals. Dried, nonliving, granulated biomass of Streptoverticillium cinnamoneum was used for the recovery of lead and zinc from solutions. It was found that pretreatment of the biomass with boiling water for 15 min increased the biosorption of lead and zinc by 52 and 41%, respectively. The optimum pH range for lead uptake was 3.5-4.5 while for zinc it was 5.0-6.0. The lead and zinc adsorption data when applied to Freundlich and Langmuir isotherm equations showed good correlation (r2 = 0.97) and hence equal conformity to both models. The Scatchard plots indicated clearly that more than one type of binding sites were involved in the adsorption of lead and zinc by the biomass. The maximum loading capacity of S. cinnamoneum biomass was found to be 57.7 mg/g for lead and 21.3 mg/g for zinc with boiling water pretreatment. The loaded metals could be desorbed effectively with dilute hydrochloric acid, nitric acid and 0.1 M EDTA. Treatment with 0.1 M sodium carbonate permitted reuse of the desorbed biomass although the metal loading capacity in the subsequent cycles decreased by 14-37%. The metal biosorbent granules prepared are a value-added product that has the potential for removal/recovery of lead and zinc from dilute solutions on a commercial scale.