Study On The Combined Technique Of Catalytic Oxidation And Biologic Contact Oxidation Process For Spent Caustic Treatment

Spent caustic is a kind of high toxic and alkaline industrial waste water discharged from the petroleum and chemical plant, and it contains high content of COD, large quantity of sulfide and little phenol. The aim of this paper is to find an effective and economic method to treat the spent caustic in the condition of normal temperature and normal pressure.First, we chose the ferrous sulfate (FeSO₄) as to be a catalyst to oxidize the spent caustic by air. Almost all the sulfide were oxidized to be thiosulfate, sulfite, and sulfate, and the concentration of COD and phenol were reduced a few at the mean time. The experimental results show that the raw water didn't need to be dilute and it could react with oxygen directly, and the adding of sodium hydroxide (NaOH) would promote the reaction velocity. When we added 30% (the real adding amount proportion colonize the theoretical amount) agential into the water on the temperature of 60℃, controlled the reaction time to be 32 hours the removal effect was best. The removing rate of sulfide, COD, and phenol was 95.15%, 17.05% and 15.65% respectively, and the spent caustic's color became pale, faint yellow from brown, the turbidity value was lower, the odor was erased wholly.After eliminated the toxic action on microorganisms of the spent caustic , we used the biologic contact oxidation process to degrade the spent caustic discharged from the catalytic oxidation tank The experimental results show that the spent caustic oxidized need to be diluted by 1/100 , and the biochemical system should to be acclimated about 50⁶0 days before regular operation . And the results also show that when the concentration of COD , sulfide and phenol in the inlet water is among 2000mg/L-3000mg/L, 30mg/L-150mg/L , 0-4.5mg/L respectively , we controlled the hydraulic residence time to be 48 hours , aerated sufficiently , the COD , sulfide and phenol in the effluent water could be reduced to 70 mg/L-300mg/L , 0-5.6mg/L and <1.0mg/L respectively , and we could get the removing rate of COD , sulfide and phenol of spent caustic as 80%-97%, 94%-100%, and 98%-99 % . Besides, when the biologic contact oxidation system was subjected to attack load, it would recover rapidly, about within 3-5 periodicities.In addition, this paper analyzed the mechanism of the removing course of sulfide , COD and phenol by catalytic oxidation means preliminarily , we also researched the mechanism of the removing course of sulfide , phenol and hydrocarbon by the biologic contact oxidationprocess , and got the reaction mode of the degradation of organisms as : U=(?)...