Pilot-scale Study And Application Of Oxygenation-enhanced Activated Manganese Co-oxide Film For The Removal Of Ammonium From Water

Groundwater sources account for over 14.5%of urban drinking water,making it a crucial component of China’s drinking water sources,especially in the northwest region.Despite this,China’s rapidly growing economy has led to an increase in groundwater pollution,with high concentrations of ammonium（NH₄⁺-N）,manganese(Mn²⁺)and ferrous ions(Fe²⁺)being particularly typical.As a result,the primary objective of safe drinking water in China is to remove NH₄⁺-N,Mn²⁺and Fe²⁺from groundwater sources.Our research group previously developed an active manganese co-oxide film on the surface of quartz sand filter material to achieve simultaneous removal of these pollutants.However,due to the limitation of dissolved oxygen（DO）in the influent,the removal load of the oxide film was low,especially for NH₄⁺-N（DO in the influent was about 8.0 mg/L,and up to approximately 2.0 mg/L NH₄⁺-N at a filtration rate of 8 m/h）.In order to further improve the removal load for NH₄⁺-N in water by the co-oxide manganese oxide film,and solve the practical problem of increasing the concentration of NH₄⁺-N in groundwater year by year,the bottom layer（lower and bottom part of the sand filter）oxygenation method was used to study the NH₄⁺-N removal performance in a pilot-scale system.At the same time,the process conditions of the pilot system were optimized,and the kinetic process and microcosmic mechanism of NH₄⁺-N removal were ascertained,and the technology was applied in field engineering.The conclusions obtained are as follows:（1）The reverse flow oxygenation method was implemented in the pilot-scale system to improve the removal of NH₄⁺-N from water.By introducing air countercurrently at the bottom layer（bottom of sand filter）,the sufficient DO concentration in the filter column made the catalytic activity of the manganese co-oxide film in the middle and lower layers fully exerted.Consequently,the oxidation removal efficiency of NH₄⁺-N was significantly improved compared to natural conditions.Additionally,the use of reverse flow oxygenation,including air,oxygen and ozone,resulted in the removal of NH₄⁺-N at a maximum concentration of3.2-3.7 mg/L,meeting the standard concentration level.Furthermore,the NH₄⁺-N removal efficiency of oxygen was found to be better than that of air and ozone.（2）The study investigated the factors influencing the NH₄⁺-N removal rate under reverse flow oxygenation conditions.It was observed that the high concentration of Mn²⁺and Fe²⁺in the influent in the influent had a significant impact on the NH₄⁺-N removal performance.The filtration rate was also found to be an important factor that affected ammonium removal.In particular,when the NH₄⁺-N concentration in the influent was 3.0 mg/L,the NH₄⁺-N concentration in the effluent met the standard,and the maximum filtration rate was 10m/h.The minimum aeration and oxygenation volume required for counterflow oxygenation in three ways of air,oxygen and ozone was found to be 5.1～12.7L/（min·m²）when NH₄⁺-N concentration was 3.0 mg/L.The effective oxygen utilization rate of air,oxygen and ozone ranged from 5.8%to 23.0%,with ozone having the lowest effective utilization.Finally,oxygenation at the bottom of the system at 1/3 of the height of the filter column was found to be more effective in enhancing NH₄⁺-N removal compared to bottom oxygenation.（3）The study investigated changes in the surface properties of a manganese oxide film under varying oxygenation conditions,and discussed the kinetics and microscopic mechanisms involved in NH₄⁺-N removal.Results showed that filling oxygen in reverse flow using air and oxygen did not produce any significant changes in the oxide film’s surface.However,reverse flow oxygenation with ozone resulted in partial destruction of the surface of the oxide film.The study clarified that the catalytic oxidation process following adsorption was the more crucial step in the removal of NH₄⁺-N.The microscopic mechanism of NH₄⁺-N oxidation was discussed under different counterflow oxygenation conditions.The adsorption process of the manganese oxide film for NH₄⁺-N in water was found to follow a pseudo-first-order kinetic equation.Sufficient^·O on the surface of the oxide film after oxygen filling oxidized the NH₄⁺-N to nitrate.（4）The reverse flow counterflow oxygenation active manganese co-oxide film technology was successfully applied to the upgrade project of Xi’an W Water Plant（with a scale of 120,000 m³/d）.In order to solve the problem of seasonal excess of NH₄⁺-N found in the water source of W groundwater plant in Xi’an,the catalytic oxidation technology of bottom oxygenated co-oxide manganese oxide film was applied in the process of upgrading.Continuous monitoring of the effluent quality for half a year showed that the NH₄⁺-N had been continuously and stably reduced to safe levels,and it was suitable for the construction of new construction and upgrading of water supply plants polluted by NH₄⁺-N.