A new tannin-based coagulant and flocculant agent has been tested on the removal of sodium dodecyl benzene sulfonate (SDBS), a dangerous and pollutant anionic surfactant. It is called Tanfloc and consists of a chemically modified tannin extract from Acacia mearnsii de Wild. In order to study the interaction between pH and initial surfactant concentration (ISC), a design of experiments procedure has been carried out. The influence of these two variables has been evaluated. Increasing pH level leads to a loss of efficiency in surfactant removal, while increasing ISC allows the system to enhance the efficiency of the removal process. ANOVA test reported significativity for four of the five involved variables and the influence of pH was similar to the influence of ISC. An optimum q of 0.96 mg mg(-1) was found at pH 4.9 and ISC equal to 103.2 mg L-1. (C) 2009 Elsevier B.V. All rights reserved.