Treatment of ammonia‑nitrogen wastewater by the ultrasonic strengthened break point chlorination method

Ammonia nitrogen wastewater has the potential to cause significant harm to the environment and human health and cannot be directly discharged, making it a problem in the wastewater industry. A novel ultrasonic strengthened break point chlorination method (USBM) was used to treat ammonia nitrogen wastewater produced by hot galvanized enterprises, and sodium hypochlorite was selected as the oxidizer. The effects of sodium hypochlorite (NaClO) dosage, initial pH, temperature, process time and ultrasonic power on the decomposition of ammonia nitrogen were studied. The experimental results show that under the optimal conditions of 4%, with a temperature of 308 K, an initial pH of 7.8, a process time of 15 min, and a ultrasonic power of 150 W, the ammonia nitrogen removal efficiency could reach more than 80.31% by USBM. Compared with the alone break point chlorination method (ABM), the ammonia nitrogen removal efficiency can increase by 29.86%. A kinetic difference analysis of ABM and USBM was conducted and the result indicated that both processes conform to the pseudo-second-order kinetic model, and the apparent rate constants of ABM and USBM were 0.00035 and 0.00119, respectively. To explore the removal mechanism of ammonia nitrogen, gas chromatography was used to analyze the gas produced in the process. The results show that the produced gas is nitrogen, which is a nontoxic and harmless gas for the environment. The USBM technique has the advantages of a simple process, a high ammonia nitrogen removal rate, low energy loss and is environmentally friendly.