Experimental study on supercritical water oxidation of azo dye wastewater

For exploring the transformation mechanism of azo group during the oxidation reaction,the supercritical water oxidation of the azo dye C.I.Reactive Orange 7 was investigated in a batch reactor.Temperature,oxidant coefficient,initial COD mass concentration,reaction time and solution pH value were selected as process parameters and the total nitrogen removal rate and ammonia-nitrogen mass concentration as the responses.Central Composite Design(CCD)method was employed for the experimental design,of which an experimental matrix of five-factorial,five-level CCD consisting of 22 experimental runs was obtained.The experimental results were simulated and analyzed by response surface methodology.A quadratic polynomial equation was established for describing the relationship between the total nitrogen removal rate and five process parameters.The analysis of individual and interactive effects of the five variables on responses was conducted in accordance with the simulated equation.The experimental results demonstrate that during the supercritical water oxidation for C.I.Reactive Orange 7,total nitrogen degrades obviously,which can reach 20.10%-64.16%,but NH3-N mass concentration is rarely produced.Moreover,the five variables all made a positive one-order contribution on total nitrogen removal rate.