Combined chemical coagulation–flocculation/ultraviolet photolysis treatment for anionic surfactants in laundry wastewater

• Coagulation–flocculation/photolysis was used to treat the laundry wastewater.
• ZnCl2, ash and P-650 were used as precursor, coagulant and flocculant, respectively.
• Parameter optimization was achieved by response surface methodology (RSM).
• New mechanism of the present coagulation–flocculation process was proposed.

In this work, a combined chemical coagulation–flocculation/ultraviolet photolysis process was used to separate and oxidative degrade the linar alkylbenzene sulfonate (LAS), an anionic surfactant in laundry wastewater, aiming at making the effluent dischargeable with suitable characteristics. Mineral ash, ZnCl2, and Praestol-650 (P-650) were chosen as the coagulant-sorbent, the complex former and the cationic high-molecular flocculants, respectively. The dosages of three components were optimized through the response surface methodology (RSM). The optimum parameters values obtained from RSM were further proved by a successful parallel trial with the actual laundry wastewater. Results showed that the maximum LAS removal efficiency of 71.26% and 74.58% were achieved for the self-made LAS wastewater and the actual laundry wastewater when the dosages of ZnCl2, ash and P-650 was 29.54, 1936.35 and 196.38 mg/L, respectively. The effect of solution pH in LAS ultraviolet photolysis process was also investigated. Results indicated that the alkaline medium is beneficial to LAS photolysis removal. These results support the applicability of the combined chemical coagulation–flocculation/ultraviolet photolysis process for LAS removal due to its efficient and rapids treatment rate, high adsorption and extraction capacity, and acceptable catalytic oxidation ability using Zn2+ salts and mineral ash as specific coagulant and Praestol-650 as cationic high-molecular flocculant.