Competition of Reactive red 4 (RR4), Reactive orange 16 (RO16) and Basic blue 3 (BB3) during biosorption of Reactive blue 4 (RB4) by polysulfone-immobilized protonated Corynebacterium glutamicum (PIPC) was investigated in batch and column mode of operations. Through potentiometric titrations, and with the aid of proton-binding model, carboxyl, phosphonate and amine were identified as functional groups of PIPC, with apparent pKa values of 3.47 +/- 0.05, 7.08 +/- 0.07 and 9.90 +/- 0.05 mmol/g, respectively. Since reactive dyes release dye anions (ROSO3-) in solutions, the positively charged amine groups were responsible for biosorption. PIPC favored biosorption at pH 3 when RB4 was studied/used as single-solute; while the presence of RR4 and RO16 severely affected the RB4 biosorption. When present as a single-solute, PEPC recorded 184.5 mg RB4/g; while PIPC exhibited 126.9,120.9 and 169.6 mg RB4/g in the presence of RR4, RO16 and BB3, respectively. In general, the accessibility of amine group depends on the molecular size, number of sulfonate groups and reactivity of each reactive dye. Single and multicomponent Freundlich equations successfully described the biosorption isotherms. With 0.1 M NaOH, it is possible to reuse PIPC for RB4 biosorption in 10 repeated cycles. Column experiments in an up-flow packed column coincided with batch results, that is PIPC showed strong preference towards highly reactive and relatively small RB4 anions; however, the presence of competing dyes hinder the RB4 column biosorption performance. (c) 2007 Elsevier B.V. All rights reserved.