Coagulation–flocculation process as an efficient, cost-effective and scalable methodology was used to treat an industrial wastewater of detergent manufacturing plant. The jar test apparatus, ferric chloride (FeCl3), polyaluminum chloride, aluminum sulfate and a hybrid coagulant as the coagulants (at concentration of 1,000 and 3,000 mg/L), and three cationic, anionic and neutral polyelectrolytes as the flocculants were used. The effects of the coagulant dosage and type as well as the flocculant type on the chemical oxygen demand (COD) and turbidity removal efficiencies and also on the final pH and total dissolved solids (TDS) of five detergent wastewaters with different production sources as well as their mixture were investigated. The obtained results showed that for the combined wastewater, the use of 3,000 mg/L FeCl3 with anionic flocculant had the highest COD removal efficiency (80.8%±0.0%) and high turbidity removal efficiency, but resulted a high increase in the effluent TDS, as well as a sharp decrease in the effluent pH (≤ 2). Finally, FeCl3 at a concentration of 1,000 mg/L along with anionic flocculant is considered as the optimum condition. Under these conditions, the wastewater biodegradability increased by enhancing biological oxygen demand (BOD5)/COD ratio. Furthermore, sweep-floc coagulation, adsorption and bridging were mainly responsible for coagulation–flocculation processes.