Recent absorbents, activated carbon cloths (ACCs) are used to absorb dyes. First, adsorption is carried out in batch reactors; initial kinetic coefficients and adsorption capacities are determined, thanks to adsorption kinetics and isotherms. Twenty-two dyes are tested and two ACCs are used, one exclusively microporous, the other being partially mesoporous. With the view to understanding the absorption process of dyes onto ACCs, quantitative structure–activity relationships are developed using molecular connectivity indices as dyes descriptions. The statistical tool introduced is the multiple linear regression. Then, the ability of ACC to treat coloured wastewater is assessed by coupling adsorption with ultrafiltration. First, both processes are operated step after step. The membrane filtration step (3000 Da molecular weight cut-off) allows a great removal of turbidity (>98%), whereas adsorption onto ACC provides the decolourization of the stream with an adsorption capacity in continuous flow reactor of 180 mgg−1 of the acid orange 7. Secondly, ultrafiltration and adsorption onto ACC are operated continuously. When the breakthrough is reached, a total volume of 101 l is successfully discoloured, with a permeate flow rate higher than 20 lm−2h−1.