Denitrification Process And Dynamics Research In Step Feeding Aerobic Rotating Biological Contactor

Biological nutrient removal processes were introduced into wastewater treatment because nitrogen and phosphorus induced eutrophication of closed water bodies. However conventional rotating biological contactor biological nutrient removal processes exists some problems such as system complex, large footprint, high investment, etc. In this paper, biological nutrient removal was studied in the RBC system. When the inlet ammonia nitrogen concentration was adequate, by changing feeding method, adjusting the running environment of the system, the system was more effective on nitrification and denitrification, as well as to remove COD are summarized. The main conclusions obtained as follows.(1) RBC system is effective to remove COD, organic nitrogen and ammonia nitrogen. When the influent COD load is F=8.60g/(m~2d), influent ammonia nitrogen is 25 mg / L, 15 mg / L, 40 mg / L, through step feed in the first, second stages of the RBC, ammonia conversion rate can increase to more than 90%. Influent ammonia nitrogen concentration is higher, the increase is clearer.(2) Step feeding make the whole system run at a low loading, nitration bacteria grow better and this can speed up nitration reaction. But, if there is not obvious anoxic reaction section in the system, anoxic layer is hard to remove nitrogen and hard to control.(3) By adding a cover on the bottom stage of the RBC to create good survival environment for denitrification bacteria, nitrogen removal rate can increase more. When the influent ammonia nitrogen is 15 mg / L, 30 mg / L, 45 mg / L, influent ratio adjusted to 3:0:2, the denitrification efficiency of the system can increase from 45%, 20%, 15% to 70%, 75%, 75%. The higher ammonia nitrogen concentration is, the clearer improvement of the denitrification effiency is.(4) The volumetric ratio of the inlet among the three stages has great influence on the denitrification, as the organic matters in the inlet of the third stage is provided as the carbon source for denitrification as well as DO consumer, which created anoxicenvironment for the thorough denitrification in the third stage. If the volumetric ratio is properly designed, the DO in the third stage can be remained below lmg/L, which is helpful for denitrification.(5) Analyze and detect the main indexes of COD. The dynamics of the decomposition reaction of COD was conducted. The reaction speed parameters and the dynamic formula of COD were determined, the degradation reaction kinetic equation of the first stage is Ct =312.7e"05333t, the second stage is Ct =312.7e"00759t;COD degradation rate of the first stage is larger than the second stage.(6) The degradation dynamics of ammonia nitrogen in the first stage is Ct =27.4e"°1546t of single point feeding compared with Ct =27.4e"°I657t of step feeding, between which there is little difference. Meanwhile the degradation dynamics of ammonia nitrogen in the second stage is correspondingly Q =27.4e"01232t and Ct =27.4e"03435t, with the latter is much greater than the former;and in the third stage is correspondingly Ct =27.4e-° 0542t and C,=27.4e"° 0709t, with the latter is a little bit greater than the former.(7) The degrading velocity of ammonia nitrogen in the second and third stage when step feeding is much higher than that of single stage-point feeding, on condition of fixed HRT and concentration of ammonia nitrogen. Therefore, the degrading of ammonia nitrogen is more thoroughly when step feeding.