Abstract
Ammonia nitrogen wastewater (about 100 mg/L) was treated by two-stage ozone oxidation method. The effects of ozone flow rate and initial pH on ammonia removal were studied, and the mechanism of ammonia nitrogen removal by ozone oxidation was discussed. After the primary stage of ozone oxidation, the ammonia removal efficiency reached 59.32% and pH decreased to 6.63 under conditions of 1 L/min ozone flow rate and initial pH 11. Then, the removal efficiency could be over 85% (the left ammonia concentration was lower than 15 mg/L) after the second stage, which means the wastewater could have met the national discharge standards of China. Besides, the mechanism of ammonia removal by ozone oxidation was proposed by detecting the products of the oxidation: ozone oxidation directly and ·OH oxidation; ammonia was mainly transformed into NO3−-N, less into NO2−-N, not into N2.
Highlights
Wastewater generated during rare earth production is radioactive, ammonia-containing, fluoride-containing, acid or alkaline [1]
The reaction solution was sampled every 20 min to analyze the changes of pH values, concentrations of ammonia nitrogen (NH4+-N), nitrite nitrogen (NO2−-N), nitrate nitrogen (NO3−-N), and total nitrogen (TN). pH value was measured by pH meter, and the concentrations of chemicals above were measured by spectrophotometry methods as shown in where C0 is the initial concentration of ammonia nitrogen and C is the concentration at reaction time t
Ammonia removal efficiency in ozone oxidation system should be smaller than 12.8% because ozone flow rate would be set smaller than 3 L/min
Summary
Wastewater generated during rare earth production is radioactive, ammonia-containing, fluoride-containing, acid or alkaline [1]. Biological nitrification beds are subject to great fluctuations in efficiency, as nitrifying bacteria in biofilter beds are sensitive to environmental perturbations and changes in operating conditions, which often implicate color, odor and flavor problems and impair biofilter function [4]. All methods have their own characteristics, but each has its limitations, or has different levels of equipment investment, high operating costs, secondary pollution, and other shortcomings [5,6,7,8,9]. It is necessary and urgent to seek efficient, practical, low concentration ammonia removal methods
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