Characteristics and Mechanism of Biological Nitrogen and Phosphorus Removal Granular Sludge Under Carbon Source Stress

Abstract

In SBR reactor, the mature granular sludge fed with sodium acetate was gradually cultivated with different carbon sources (sodium acetate/glucose ratio was 1:0, 3:1, 1:1, 1:3 and 0:1, in terms of COD, respectively). During the five stages, the physical, biochemical properties, extracellular polymeric substances (EPS), phosphorus fractions and nitrogen and phosphorus removal efficiency of granular sludge were studied. 705 days' experimental results were showed as follows. At stage Ⅳ, the granular sludge had the smallest diameter of 0.5 mm; moreover the phosphorus release/uptake rate, denitrification rate and the total phosphorus (TP) content were the lowest. While at stages Ⅰ and Ⅱ, the phosphorus release/uptake and denitrification rates were the highest, meanwhile, the TP content reached up to 72.36 mg·g-1, and the EPS content was about 350 mg·g-1, as a result, the nitrogen and phosphorus removal efficiencies were both over 94%. Nevertheless at stage Ⅴ, the biochemical rates were slightly slower than values of stages Ⅰ and Ⅱ, simultaneously the TP, glycogen and EPS contents in sludge were maintained at 69.60 mg·g-1, 224.18 mg·g-1 and 200 mg·g-1, respectively, while high nitrogen and phosphorus removal efficiency was obtained. During all stages, Ca-P was the main phosphorus fraction, and inorganic phosphorus(IP) was closely related to phosphorus removal of granular sludge.