Study On Multi - Module Treatment Process Of Rare Earth Smelting High Concentration Ammonia Nitrogen Wastewater

In this study, a multi-module process was designed for treating high concentration of rare earth ammonia nitrogen wastewater. According to the different concentrations of ammonia nitrogen wastewater, struvite precipitation, adsorption and adsorption-dielectrophoresis, three process modules were established. Besides, the high concentration of rare earth ammonia nitrogen wastewater can be effectively treated by struvite precipitation reactor.This research was mainly divided into four aspects:(1) The effects of various factors on the treatment of high concentration ammonia nitrogen wastewater were explored by struvite precipitation and the optimum process conditions were determined. (2) The optimum reaction conditions on removal of ammonia nitrogen from the medium concentration wastewater by adsorption and struvite precipitation methods were investigated. (3) The operation condition and mechanism of the adsorption-dielectrophoresis(ADS-DEP) process on removal of ammonia nitrogen from low concentration of ammonia nitrogen wastewater were studied. (4) Multiple modules in continuous treatment of high concentration of NH4+-N wastewater were tested and the struvite precipitation reactor was applied on removal of the practical high concentration of ammonia nitrogen wastewater.In the study of NH4+removal from high concentration of ammonia nitrogen wastewater by struvite precipitation process, the main conclusions can be obtained:(1) In the orthogonal experiment, the factors of pH value, n(Mg):n(N), n(P):n(N) and reaction time were examined. The order was pH value> n(P):n(N)> n(Mg):n(N)>reaction time. By changing the chemical dosing method, it was found that the removal efficiency of high concentration ammonia nitrogen wastewater was better by liquid precipitation agent, and the residual ammonia nitrogen concentration decreased by 1149mg/L.(2) With the initial concentration of 30000 mg/L in ammonium chloride wastewater, the optimal process conditions were at pH 9.0, n (Mg):n (N):n (P)=1:1:1, reaction time=55 min, precipitation time=30min. The removal rate of NH4+-N was 96.46%, and the residual concentration of NH4+-N was 540mg/L. With the initial concentration of 8000 mg/L in ammonia sulfate wastewater, the optimal process conditions were at pH 9.0, n (Mg):n (N):n (P)=1:1:1, reaction time=50 min, precipitation time=30 min. The removal rate of NH4+-N was 95.76%. The residual concentration of NH4+-N was 180mg/L.In the study of the treatment of medium concentration ammonia nitrogen wastewater, the main conclusions can be obtained:(1) The removal rate of NH4+-N increased rapidly in 60 min. The adsoiption equilibrium achieved after 120 min. (2) In the study of effect on removal efficiency of NH4+-N by the struvite precipitation, the optimum conditions were that pH was at 9.0-10.0, reaction time was 60 min. When the initial concentration was 500 mg/L, the removal rate of NH4+-N was 96.53%. (3) With the same initial concentration of NH4+-N, struvite precipitation method showed the higher removal efficiency than the adsorption. After adsorption process, the removal rate of NH4+-N was only 75%. The removal rate of NH4+-N was increased by 21.5% by struvite precipitation.In the study of operation condition to remove the low concentration of ammonia nitrogen by ADS-DEP method, the main conclusions can be obtained: (1) The optimal dosage was 2 g/L and the removal rate of NH4+-N could be increased by 20%, the remainder concentration was only 4 mg/L. (2) The effect of applied voltage on the removal of ammonia nitrogen was investigated by ADS-DEP. The optimum voltage was 15V. The removal rate of NH4+-N was as high as 94%, the lowest residual concentrations of NH4+-N was 1.8 mg/L. (3) The effect of treatment time on the removal rate of ammonia nitrogen was investigated. The best DEP treatment time was 20 min, the removal rate of NH4+-N was increased by 24%.In the study of the treatment of high concentration actual ammonia nitrogen wastewater by multiple modules method, the main conclusions can be obtained:(1) In the study of the treatment of the actual ammonium chloride wastewater, the total removal rate of NH4+-N was 99.17% after two levels of struvite precipitation reactions. The residual concentration of NH4+-N was 50 mg/L after the adsorption process by zeolite. In the third module, the rest of the ammonia nitrogen concentration was 47.5 mg/L by the introduced dielectrophoresis method. With the initial concentration of 6640 mg/L of ammonium sulfate wastewater, the residual concentration of NH4+-N was 18.8 mg/L after two levels of struvite precipitation reactions. The residual concentration of NH4+-N was 17.8 mg/L after ADS-DEP process.In the treatment of ammonia nitrogen wastewater by the MAP reactor, the removal rate of NH4+-N was 96.73% when the pH value was 8. With the initial concentration of 23700 mg/L and 60000 mg/L of the actual ammonia nitrogen wastewater, the residual concentration of NH4+-N was 29.8 mg/L and 68 mg/L after two levels of struvite precipitation reactions, respectively. The total removal rate of NH4+-N was 99.87% and 99.87%, respectively. The generated precipitation product is a high quality of slow release fertilizer. The process combines control of pollution of wastewater and recovery of pollutants, and offers both environmental and economic benefits.