RESEARCH ON ENDOGENOUS PARTIAL DENITRIFICATION GRANULAR SLUDGE CULTIVATION AND KEY INFLUENCING FACTORS
To facilitate the green transition of biological nitrogen removal,it is imperative to address the challenge of stable nitrite nitrogen(NO2--N)acquisition for mainstream anammox application.In this study,aerobic granular sludge(AGS)was acclimatized for endogenous partial denitrification(EPD)to accomplish stable NO2--N accumulation with limited carbon sources.This research provides theoretical support for the application of mainstream anammox.When the influent chemical oxygen demand/nitrate nitrogen(COD/NO3--N)was 3,the enrichment and stability of EPD granular sludge could be achieved under anaerobic/anoxic/micro-oxygen condition,and nitrate-to-nitrite transformation ratio(NTR)reached 72.73％.During the anaerobic stage,carbon source and glycogen(Gly)were consumed to synthesize polyhydroxyalkanoic acid(PHA),and the ΔPHA/ΔGly of the anaerobic stage(1.30 mol C/mol C)was close to the glycogen accumulating organisms(GAOs)model value,indicating that the intracellular carbon source storage was mainly completed by GAOs.NO2-N was accumulated with the reduction of PHA and the synthesis of Gly during the anoxic phase.The activity of nitrate reductase remarkably exceeded nitrite reductase,confirming the successful implementation of EPD.The NTR was improved to 80.01％under a COD/NO3--N of 4.2 by optimizing the operating parameters.The results of batch tests found that NTR rose to 89.15％as the pH varied from 6.0 to 9.0,and the NTR reached a peak of 91.16％with the temperature reduced from 40 ℃ to 5 ℃.The results suggested that the alkaline condition and lower temperature were more conducive to NO2--N accumulation.Therefore,appropriate COD/NO3--N,pH and temperature can effectively reinforce the NO2--N accumulation of EPD.
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