Metal sorption by algal biomass: From batch to continuous system

Algal biomass possesses tremendous metal binding ability and therefore has great potential for gleaning these pollutants from wastewaters. The algal cell wall and exopolymers contain diverse functional groups which confer negative charge to cell surface. Since metal ions in water are generally in cationic form, they are adsorbed onto the cell surface. Biosorption of metal ions from aqueous solution is influenced by various factors, such as, pH, charge density of metal ion, concentration of metal ion, concentration of interfering metal ions, nutrient availability, nature of biomass, culture age, temperature and contact time. Batch studies are very important for collecting information for subsequent application on a large scale. Continuous flow studies, like those conducted in packed bed column, seem more efficient and economically feasible than the batch operation for metal sorption. Various kinds of sorption isotherms have been used for the assessment of maximum sorption capacity. The data of metal sorption obtained from continuous system are generally expressed in the form of breakthrough curves. The shape and size of breakthrough curve is influenced by several factors, such as, metal concentration, flow rate, bed height, size of biosorbent particle, solution composition, and packing of column/density biosorbent in the column. Adam-Bohart, Thomas, mass transfer model, advection-dispersion-reaction equation and bed-depth-service-time model have been developed for elucidating breakthrough curve. However, new approaches, such as artificial neural networking and response surface methodology need adequate attention for modeling of breakthrough curves and metal sorption in multi-metal systems.