Multiparametric investigation of competitive and noncompetitive sorption characteristics of SMP fractions (carbohydrate and protein) on activated carbon.

Sorption characteristics of soluble microbial products (SMPs) as carbohydrate and protein on activated carbon were investigated. Batch experiments were conducted to evaluate the sorption kinetics and the equilibrium conditions. The parameters studied included initial SMP concentration (50-200mg/L), activated carbon dosage (0.25-50 g/L), contact time (0.02-4h), particle size of activated carbon used (5-75 μm, 75-850 μm, and 850-1000 μm), and presence of one or both SMP fractions. The equilibrium sorption of carbohydrate and protein were significantly affected by the presence of the second SMP fraction in the solutions. Adsorption isotherms were expressed by the Langmuir and Freundlich models. The adsorption rates under noncompetitive and competitive conditions were analyzed with kinetics-based Lagergren pseudo-first order and pseudo-second order models; and diffusion-based external diffusion and Weber-Morris intraparticle models. Both SMP fractions were removed effectively, however, sorption of protein was significantly better than that of carbohydrate in all cases. The relatively significant effect of particle size on sorption of protein indicates that protein is most likely adsorbed as a single layer on the carbon surface. For the carbohydrate, the increase in particle size did not decrease the sorption significantly indicating that carbohydrate may be adsorbed in multiple layers or may diffuse into the porous matrix more effectively.