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 Citrobact er strain MCM B-181, a laboratory isolate, was characterized. Effects of en vironmental factors and growth conditions on metal uptake capacity were stu died. Pretreatment of biomass with chemical agents increased cadmium sorpti on efficiency; however, there was no significant enhancement in lead and zi nc sorption capacity. Metal sorption by Citrobacter strain MCM B-181 was fo und to be influenced by the pH of the solution, initial metal concentration , biomass concentration, and type of growth medium. The metal sorption proc ess was not affected by the age of the culture or change in temperature. Eq uilibrium metal sorption was found to fit the Langmuir adsorption model. Ki netic studies showed that metal uptake by Citrobacter strain MCM B-181 was a fast process, requiring <20 min to achieve >90% adsorption efficiency. Th e presence of cations reduced lead, zinc, and cadmium sorption to the exten t of 11.8%, 84.3%, and 33.4%, respectively. When biomass was exposed to mul timetal solutions, metals were adsorbed in the order Co2+ < Ni2+ < Cd2+ < C u2+ < Zn2+ < Pb2+. Among various anions tested, only phosphate and citrate were found to hamper metal sorption capacity of cells. Biosorbent beads pre pared by immobilizing the Citrobacter biomass in polysulfone matrix exhibit ed high metal loading capacities. A new mathematical model used for batch k inetic studies was found to be highly useful in prediction of experimentall y Obtained metal concentration profiles as a function of time. Metal desorp tion studies indicated that Citrobacter beads could, in principle, be regen erated and reused in adsorption-desorption cycles. In an expanded scale tri al, biosorbent beads were found to be useful in removal/recovery of metals such as lead from industrial wastewaters.