Evolution and functional analysis of extracellular polymeric substances during the granulation of aerobic sludge used to treat p-chloroaniline wastewater

Extracellular polymeric substances (EPS) are major high-molecular-weight secretions from microorganisms, binding with cells to form a vast net-like structure for protecting cells against external stress. In this study, the level and function of EPS during the granulation of aerobic sludge used to treat p-chloroaniline (p-ClA) wastewater were investigated. The content of extracellular proteins (PN) increased relative to the exopolysaccharides (PS) content during the sludge granulation (Stage I), implying that PN contributed significantly to the formation of aerobic granular sludge (AGS). Under the condition of high p-ClA shock loading (Stage II), the PS content increased from 122.7 ± 22.0 mg g−1 VSS to 482.6 ± 5.4 mg g−1 VSS, which might be a regulating mechanism of AGS to address high p-ClA loading. The results of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that PN bands increased with the development of sludge granulation, particularly the proteins with molecular weight located at 44.3-97.2 kDa. Fourier transform infrared (FTIR) spectra of inoculated activated sludge and matured granular sludge indicated that microorganisms appeared to aggregate in the presence of tyrosine protein, aspartic acid protein and proteins with secondary structures including 3-turn helix and β-sheets. Five types of proteins were identified by two-dimensional electrophoresis (2-DE), and these proteins were related to the granulation of aerobic sludge and EPS secretion. Furthermore, the analysis of sludge microbial community revealed that the enrichment of Zoogloea spp. and Thauera spp. as p-ClA degrading and EPS secreting microbes was conducive to the formation of granular sludge and degradation of p-ClA.