An undivided electrochemical reactor with parallel plate Ti/Pt-Ir anode and stainless-steel cathode was used to treat tannery wastewater at constant current densities and different stirring rates. The pollutants were depleted by direct anodic oxidation and/or indirect electro-oxidation, mediated by active chlorine formed in situ, so that chemical oxygen demand, total organic carbon, tannin, sulfide, total Kjeldahl nitrogen and ammonium ion concentrations decayed with time. The results of the treatment, supported by data obtained with synthetic wastewater, showed that selectivity of the removal of different pollutants was affected by current density to a small extent. By contrast, hydrodynamic conditions strongly influenced the rates and the differential selectivity ratio of depletion of the pollutants, with the exception of tannins. The kinetics of elimination of ammonium ions, removed only via oxidation by "active chlorine", was diminished by agitation, contrary to its effect in enhancing the removal of the other pollutants, for which direct anodic oxidation was an additional process for their destruction.