The kinetics of metal uptake by microbial biomass: implications for the design of a biosorption reactor

Abstract

The kinetics of copper ion biosorption by free cell suspensions of inactivated Penicillium biomass was investigated. During the first 15 seconds of the metal uptake reaction copper biosorption was extremely rapid, becoming progressively slower until equilibrium was achieved. At a biomass concentration of 5.48 g dry weight/l, the copper biosorption reaction reached approximately 90% of the equilibrium position in one minute. This is in contrast with biosorption onto immobilised biomass which is known to take up to 24 hours or longer to reach equilibrium. However, the conventional reactor design for free cell suspensions, the stirred tank, may make inefficient use of the equipment and process due to the extended retention time. A plug-flow biosorption reactor with a limited retention time has been developed and demonstrated in the laboratory. The biomass and metal solution were mixed together using static in-line mixers and pumped along a length of pipe before discharging the mixed liquor into a settling tank to achieve phase separation. Desorption of the bound copper ions was achieved by drawing an eluant solution through metal-loaded biomass immobilised as a filter cake. The combination of metal uptake using free cells, and desorption using immobilised cells, optimises the kinetic and mass transfer effects for both processes and minimises the equipment requirements.