Electrodialysis (ED) is an electromembrane separation process in which ions are transported through ion permeable membranes from one solution to another under the influence of a potential gradient. ED is widely used today to reduce electrolyte content from solutions (desalination of brackish water, nitrate removal from drinking water), electrolytes recover (NaCl from seawater, Ni and Zn from electroplating rinse waters), salt splitting, methatesis, and ion substitution. This work aims to study the application of ED to the recovery of ammonium sulphate, a valuable fertilizer, from a biogas fermentation waste. A synthetic solution of analytical grade ammonium sulphate and deionised water (1.2 %) was used in this preliminary study. A 5 cell pair was assembled with AMX and CMS ion echange membranes, with an effective area of 200 cm2 each. Three different solution flow rates have been used in order to identify the a and b constants from the criterial equation of the limiting current:ilim/ Cdil = a vb (1)The values of the coefficient a were obtained from a double logarithmic diagram of ilim/ Cdil versus the linear liquid rate (v).These values have been between 0.42 and 0.50.The experimental values of ilim have been identified from the diagram of measured resistance versus current of the stack at constant flow rate. Additional experimental runs, with different ammonium sulphate and natrium sulphate concentrations have shown that the value of the constant a is strongly influenced by the nature and the concentration of the diluted solution but b is almost the same. Finally, the empirical limiting current has been compared to that calculated from the known theoratical equation: ilim = z F kL C dil / (tM- tS) (2)The mass transfer coefficient kL has been evaluated with the FroesslingMarshall criterial equation, taking into account the properties of the investigated system.The discrepancies between the calculated and determined values of ilim have been as high as 10- 20 %. Therefore, the empirical limiting current determining is recommended.