Comparison of extracellular polymeric substance (EPS) in nitrification and nitritation bioreactors

The production and composition of extracellular polymeric substances (EPS) are important parameters of bioreactor performance. This study compared the characteristics of EPS of nitritation- and nitrification-dominant processes in an integrated fixed-film activated sludge reactor. The results showed that the tightly bound-EPS (TB-EPS) were composed of polysaccharides and protein in variable ratios, while loosely bound-EPS (LB-EPS) contains almost no protein. Quartz crystal microbalance with dissipation studies demonstrated that the adsorption of TB-EPS to solid surface was stronger and less reversible as compared to the LB-EPS, which demonstrated the importance of protein in cell adhesion. Under nitritation condition, higher abundance of ammonia oxidizing bacteria was detected, and higher amide or amine like and aromatic and tryptophan protein like substances contents in TB-EPS was also observed. The other key finding is that when nitritaion was achieved, a decrease in the abundance of nitrite oxidizing bacteria and lower hydrocarbon-like substance and humic acid-like substances in the TB-EPS were observed.