Catalytic Ozonation Of The Organic Wastewater

Ozonation is a promising alternative in water treatment for the removal of water pollutants, but ozone is also well known as a highly selective oxidant without the potential to further oxidize intermediates with refractory property. To overcome the disadvantage, catalytical ozonation are more and more focused on by many researchers. This study includes three parts: ozonation of phenol solution, catalytical ozonation of oxalic acid, and Mn(â…¡)-catalyzed degradation of phenol wastewater COD.In the third chapter, It was found that chemical oxidation of phenol by ozone is a very rapid process, whose absolute reaction rate is over 1000M^-1s_-1. So the rate of the whole process was contrlled by the mass trasfer of ozone from gas to liquid, which was proved by that the linear relationship of phenol degraded amount and the reaction time. Among of the parameters, some ones which changed the mass trasfer of ozone had the more effective behavior than the others which accelerate the reaction rate. The batch test showed that the stiochiometric factor is 2.2 in pH=3, the different value corresponds the relevant solution pH. Some intermediates were detected, such as benquenze, maliec acid and oxalic acid by HPLC. Oxalic acid was the main final product in the ozonation of phenol. The possible pathway of phenol oxidation by ozone was concluded.In the forth chapter, oxalic acid was oxidized through hydroxyl radical mechanism, different to ozonation of phenol, the chemical reaction was the bottle-neck step of the whole process. Three familiar transition metal ions (Mn²⁺, Fe²⁺, Cu²⁺) were introduced as catalyst into the degradation of oxalic acid by ozone, manganese ion behaved the best catalysis, Fe²⁺ took the second place, however Cu²⁺ did not enhance the oxidation of oxalic acid. Some experimental parameters, especially such as pH value and concentration of metal ions, effect strongly the reaction. pH is the key factor which whether determined the oxidation reaction take place, and the best efficiency of catalysis is gained at moderate concentration of catalyst. The final product, CO₂ being ionized into HCO₃^- and H⁺ in week acidic solution. Because HCO₃^- is a familiar scavenger of hydroxyl radical, the ionization of carbonic acid claged the conversion of oxalic acid.In the fifth chapter, it was found that the Mn(â…¡)-catalyzed degradation of organic wastewater COD took the similar characteristic as of the oxalic acid. The enhanced degradation of COD by Mn(â…¡) was devoted to by two reaction: (1) Mn(â…¡) accelerated the directed reaction of ozone and organic solutes, (2) Mn(â…¡) enhance the generation of hydroxyl radical to indirectly improve degradation of organic compounds. The experimental result indicated the Mn(â…¡) have the catalysis potential to oxidize organic wastewater with single component, but helpless to the industrial wastewater containing complicated components. In order to generalize the treatment technology, The further study was required.