Study On Performance And Affecting Factors Of Integrated Simutaneous Removal Of Carbon, Nitrogen And Sulfur Process Under Micro-Aerobic Condition

Industry wastewater,such as pharmaceutical and chemical wastewater oftencontains high levels of sulfur, nitrogen, and carbon compounds. Under anaerobiccondition, the integrated carbon, nitrogen and sulfur removal process may obtained higheffective removal of sulfate, nitrate, and organic carbon in one system. However ,elemental sulfur conversion rate was much lower and produced sulfide in the effluentalso can cause an environmental problem. In allusion to existing problems of anaerobiccondition, this paper first proposed integrated simultaneous removal of carbon, nitrogenand sulfur process under micro-aerobic condition . It enhanced the performance of theintegrated simultaneous removal of carbon, nitrogen and sulfur process and increased theelemental sulfur conversion rate that was three times higher than that under anaerobiccondition.Expanded Granules Sludge Bank(EGSB) reactor was used in this study, through theoperation of integrated simultaneous removal of carbon, nitrogen and sulfur processunder different dissolved oxygen concentration as well as comparison on theperformance and elemental sulfur conversion rate, the most optimal dissolved oxygenconcentration was achieved. Besides, sulfide/nitrate (S/N) ratio were used to check theireffects on performance of the process under the optimum dissolved oxygen concentrationin order to optimize operations.The integrated simultaneous removal of carbon, nitrogen and sulfur process wassuccessfully started up under anaerobic condition. Then limited amount of air wasintroduced into the reactor, which brought different dissolved oxygen concentration. Themost appropriate dissolved oxygen concentration was 0.1~0.4 mg/L at loadings of 1.83kg S m ? 3 d ? 1 for sulfate, 0.67 kg N m ? 3 d ? 1 for nitrate and 6.7 kg organic-C m ? 3 d ? 1 . Duringthis period, sulfate, nitrate, organic removal rates were 96%, 99% and 58%, respectively.Especially, 87% of the elemental sulfur conversion rate was achieved. Undermicro-aerobic condition, the activity of sulfide– oxidizing bacterias in the integratedsimultaneous removal of carbon, nitrogen and sulfur process were stimulated, hencemitigating the inhibition of sulfide on denitrifiers and enhancing the performance andelemental sulfur conversion rate of the integrated carbon, nitrogen and sulfur removalprocess. The EGSB reactor was inoculated with granular sludge acclimated with sulfate andnitrate, so a very short period was needed for its start-up . The tests contained four stages:sulfur nitrogen ratio were 2/1,1/1,1/1.5 and 1/2, respectively. Sulfide-oxidizing processhad different biochemical reactions under different sulfur nitrogen ratios, in other words,final product s of sulfide-oxidizing were different. Sulfide-oxidizing proces s was notthorough and effluent contained abundant sulfide when the sulfur nitrogen ratio was 2/1;It converted sulfide to sulfate when the sulfur nitrogen ratio were 1/1.5 and 1/2; The mostappropriate S/N ratio was 1/1 at loadings of 0.98 kg SO 42--S m ? 3 d ? 1 , 0.62 kgNO 3--Nm ? 3 d ? 1 and 10.9 kgCODm ? 3 d ? 1 , During this period, sulfate, nitrate, COD removalrates were 91.4%, 97.7% and 41.2%, respectively as well as elemental sulfur conversionrate was 43.5%.