||Adsorption, an effective separation technology based on the affinity of adsorbates and adsorbents, is widely used in water and wastewater treatment in most natural systems as well as in industrial applications. This research project aims at studying the sorption capacity, uptake kinetics and mechanism of arsenic removal, including arsenate and arsenite onto chitosan and nanochitosan, a biopolymer from the natural polysaccharide of chitin. Firstly, the equilibrium sorption of arsenic on chitosan with varying pH, adsorbent particle sizes, adsorbate concentrations and the presence of competitive anions are studied and simulated with four conventional single-component isotherms. A novel pH correlation for the equilibrium isotherms has been developed to predict the pH influence on the adsorption of arsenic on chitosan. Three multicomponent isotherms and the ideal adsorbed solution theory are employed to predict the adsorption capacities of arsenate and competitive anions on chitosan. The sorption kinetics of arsenate on chitosan are studied using batch agitated contacting system with varying pH, adsorbent particle sizes, adsorbate concentration, agitation speed, adsorbent mass and the presence of competitive anions and correlated with two conventional kinetic models. A series of novel pseudo reversible kinetic models are developed to describe the sorption and desorption properties, mechanism and reaction order of arsenate on chitosan. A correlation of solution pH against contact time is incorporated to the rate constants in the pseudo first order reversible model. To enhance the adsorption performance of arsenic on chitosan, the nanochitosan emulsions with crosslinking, having higher contacting surface area, are developed. In order to investigate the adsorption mechanism, the fresh chitosan and adsorbed chitosans are characterized to study the physiochemical properties of the adsorbent and adsorbed species. Two batch adsorber design models have been developed in the single-stage batch and the two-stage batch reactors result in a saving in adsorbent mass and the turnaround time.