degredation mechanism of the organic and inorganic compound yeild weakly organic acid and by increasing the time of oxidation or the adsorption the concentration of the compound decrease due to the degredation and yeild some organic fragments such as phenol or ketones or formic acid which still in solution and after long time you can achieve the full degredation or miniralizatiuon of organic compound which convert all organbc compound into CO2 and you will see agreat reduction of COD.