Characteristics of sludge granulation and EPS production in development of stable partial nitrification

In this study, sequencing batch reactor (SBR) and aerobic upflow sludge bed reactor (AeUSB) were used to investigate the effects of sludge granulation on establishing partial nitrification (PN) process and explore the potential mechanism. The particle size was positively related to the NO₂^--N accumulating performance, satisfactory nitrite accumulation rate (NAR) of 96.4% and 77.3% were obtained with the appearance of micro-granules in SBR and AeUSB after day 105 and 83, respectively. To our knowledge, it is the first report describing the importance of extracellular polymeric substances (EPS) content and components, such as aromatic protein-like substances, by-product-like substances and special protein secondary structures (α-helices and 3-turn helices) for sludge granulation and even PN process. Quantitative microbial analysis suggested that ammonium oxidizing bacteria (AOB) predominated in nitrifying-bacterium in micro-granules system, guaranteeing a highly efficient PN process.