Study On Circulation Process Of Ammonium Removal By Map Synergistic Decomposed By Ultrasound And Stripping

Ammonia nitrogen removal in the wastewater containing high concentration ammonia has been urgent problem. MAP(Magnesium ammonium phosphate) chemical precipitation techinique can efficiently and quickly remove ammonia of high concentrations in wastewater. However, it is always restricted in the application because of agents’cost. The united technologies of ultrasound and air stripping were applied in this article to remove the ammonia in MAP and then recycle it.In this article, it is studied on the performance and mechanism of the united process of ultrasound and air stripping treating ammonia wastewater and MAP-containing mixture. The MAP treated by ultrasound and air stripping was recycled to remove ammonia in wastewater and the recycling efficiencies were studied.The study results showed the existence of obvious synergies between the ultrasound and air stripping treating ammonia wastewater, the enhancement factor reached up to1.49. Ammonia removal rate reached97%at the optimum process condition:pH9.4～10、reaction time40 min、reaction temperature45℃and air flow600L/h. Ultrasound can enhance the gas-liquid mass transfer and stripping air can enhance the ultrasonic oxidation. At pH<8.2, ultrasonic oxidation played a major role for the united process and the highest oxidation efficiency reached12.1%, but air stripping played the major role at pH>8.2.With the united process treating the MAP-containing mixture, ultrasound could enhance the dissolution of ammonia from MAP and then promote ammonia removal. The dissolution effect decided ammonia removal efficiency. When the pH was relatively higher, more insoluble magnesium phosphate would be produced and it would be beneficial to the dissolution of ammonia from MAP. The efficiencies of dissolution and removal increased with the increase of pH、reaction time、reaction temperature and air flow. Ammonia in MAP removal rate could reach94.9%at the optimum process condition:pH11、reaction time60min、 reaction temperature60℃、ultrasonic power200W and air flow of150L/h.The MAP treated by the ultrasound and air stripping was recycled to treat ammonia wastewater. When the number of cycles less than6times, ammonia removal efficiency more than80%could be obtained at pH9.5and reaction time30min. Ammonia removal effiency decreased with the increase of the cycle times. The reasons might be related to the losses of precipitant in the recycle.