Effect Of COD/N Ratio On The EPS And Characteristics Of Nitrifying Activated Sludge

Activated sludge process is one of the most widely used methods of sewagetreatment. The effectively remove of ammonia nitrogen in high-strength ammoniawastewater, carbon and nitrogen ratio has a significant influence on the growth ofactivated sludge. When the carbon source is adequate, heterotrophic microorganismsblooms and competes with nitrifying bacteria, causes the harm including sludge floatingand bulking. When the carbon source is inadequate, the autotrophic nitrifying bacteriacome up and activated sludge grows slowly. Two sequencing batch of reactor (SBR)reactor RA, RB are used in this test to culture activated sludge under conditions of highcarbon to nitrogen ratio and low carbon to nitrogen ratio respectively. Through themethod of adjusting the ratio of carbon and nitrogen (C/N) inlet to explore thediversification of activated sludge characteristics under different C/N conditions,including the shape, size, nitrification, settling, flocculation, dewatering, surface charge,relative hydrophobicity, oxygen breathing filamentous bacteria content and extracellularpolymeric composition. Furthermore, the nitrifying sludge loosely bound extracellularpolymeric substances (LB-EPS), closely extracellular polymeric component content(TB-EPS), the related relationships of sludge surface characteristics and flocculationsettlement performance were in-depth explored. The results showed that:(1) The performances of nitrification and biomass-liquid separation of the nitrifyingsludge flocs were significantly influenced by the high C/N in carbon-rich system, andthe poor performances were hard to recover even when decreasing the C/N. Thephysicochemical characteristics of sludge were relative stable in carbon-limited case,but improper low C/N would also lead to the inferior flocculation. (2) Sludge surfaces at higher C/N were more negatively charged and less hydrophobicthan those at lower C/N. The correlation analysis indicated that the hydrophobicity andzeta potential were crucial in controlling the flocculation, settleability anddewaterability of sludge in carbon-rich system, but no significant correlations wereobserved at the carbon-limited case.(3) The variations of C/N resulted in a similar total amount of TB-EPS, but differentcontents of LB-EPS. The change of EPS constituents under different C/N wascomplicated, but the ratio of PN/PS in the EPS had a negative correlation with the C/N.(4) Regardless of LB-EPS and TB-EPS in carbon-rich system, the PN and the ratio ofPN/PS were strongly correlated with the flocculation, settleability, dewaterability andsurface properties of sludge. When regarding to carbon-limited case, no significantcorrelations were observed between the sludge flocculation, settleability anddewaterability with the EPS, but the PN was also the most important factor indetermining the zeta potential and RH than any other constituents.