Experimental Study On The Effect Of Carbon And Nitrogen Ratio On Biological Denitrification

Based on the analysis of the influence of carbon nitrogen ratio(COD/N)on the removal and denitrification of COD and nitrogen in the nitrification process,the effect of C/N on biological nitrogen removal was studied.Four different C/N systems(C/N is 0,5,10,15,respectively,denoted as R0,R5,R10 and R15)nitrification process nitrogen conversion rules were investigated using a sequential batch reactor(SBR)based on simulated domestic sewage and using ethanol as carbon source.In addition,denitrification characteristics of domesticated microorganisms under different C/N conditions were studied by adding three different electron receptors(NO3--N,NO2--N,NO3--N+NO2--N).Under different C/N conditions,the wastewater has a relatively consistent nitrogen transformation during SBR operation.In the nitrification stage,the NH4+-N concentration is reduced from 20 mg/L to 0.6 mg/L,NO;-N and NO3--N concentration accumulation amount reaches the maximum,and the larger the C/N,the more significant the TN loss in the nitrification stage.When C/N is 0 and 5 in the nitrification process,the nitrification time is 150 min when the concentration of NH 4+-N drops to 0 mg/L;when C/N is 10,the concentration of NH4+-N decreases to 0 mg/L,which takes 120 min.When C/N is 15,the NH 4+-N concentration is reduced to 0 mg/L,and it takes 90 minutes,that is,when C/N is equal to 15,the degradation rate of NH4+-N is the highest.In addition,under different C/N conditions,the COD degradation rate was basically the same,and the COD effluent concentration was maintained at about 30 mg/L,indicating that the effect of C/N on effluent COD was not significant.In the denitrification stage,NO;-N and NO3--N basically reacted completely.With the increase of C/N,the increase of organic carbon source in the system provided a suitable growth environment for denitrifying bacteria,which promoted NO2--N The removal rate of N,but C/N is too high(C/N is equal to 15),but inhibits the growth and reproduction of the Nitrobactcr sp.,making the heterotrophic bacteria that degrade COD become the dominant bacteria,weakening the system's denitrification capacity.At C/N is equal to 0,the direct entry of microorganisms into the endogenous respiration phase in the system results in lower denitrification efficiency.Therefore,autotrophic bacteria using inorganic carbon sources will grow,and this kind of flora also has a certain denitrification function,but its denitrification effect is not obvious due to its slow growth process.When NO;-N is used as an electron acceptor,when C/N is low(C/N is below to 10),the Rs system has the best denitrification effect compared to the R0 and R10 systems.When C/N is high(C/N is equal to 15),since the carbon source at this time is very sufficient,the denitrification effect is also good.In addition,after 20 min of denitrification,whether NO3--N or NO2--N,the removal rate of R5 and R10 is the highest,indicating that the sludge denitrification ability is stronger when the C/N ratio is 5 or 10 in the water environment.When C/N is too high(C/N is equal to 15),the heterotrophic bacteria that degrade COD in water gradually become the dominant species,and the nitrifying bacteria are thus inhibited,and the denitrification ability of the system is weakened.Therefore,the higher the C/N,the higher the denitrification rate and the better the denitrification effect,but the higher the C/N,the better,and the C/N imbalance will also be detrimental to the growth of heterotrophic bacteria.