The aim of this work consists in a feasibility study to understand how arsenate ions could be removed from contaminated water by sorption onto chitosan, a biopolymer extracted from the wastes of the seafood industries. Firstly, a batch adsorption study investigates different models, namely Langmuir, Freundlich, Tempkin, and Redlich-Peterson. The sorption mechanism is shown to be sorption by an electrostatic attraction, with thermodynamic parameters indicating an exothermic and spontaneous reaction. The main influencing parameters are the temperature, the pH and the presence of other ions. Secondly, a semi-dynamic membrane process is proposed: a stirred batch reactor is coupled with a microfiltration immersed-membrane. A mass balance model is used to describe the adsorption process and the breakthrough curves are well simulated.