Variations in extracellular polymeric substances (EPS) during adaptation of activated sludges to new feeding conditions

•EPS production was studied in activated sludges operated at different COD/TKN.•In contrast to substrate removal, stabilization of EPS lasted much longer.•Following the start-up of the nitrifying reactor, EPS stabilized very rapidly.•Tightly bound EPS and protein-EPS were dominant in all sludges.•This study identified for the first time a very loosely bound fraction in EPS.

The study examined the dynamics of EPS production in activated sludges. Semi-continuously fed batch activated sludge reactors were operated at different feeding conditions, namely at COD/TKN ratios of 10, 5 and 0, respectively. Parallel to this operation, EPS production and fractionation were evaluated. The study identified for the first time a very loosely bound fraction in EPS, the VLB-EPS. Bound EPS were divided into many fractions as Very Loosely Bound-EPS (VLB-EPS), Loosely Bound-EPS (LB-EPS) and Tightly Bound-EPS (TB-EPS) while the carbohydrate and protein content of each fraction was measured. Regardless of the COD/TKN ratio, tightly bound EPS and protein-EPS were dominant in all sludges. As determined by HPSEC analyses, in all EPS fractions, a great portion of protein-EPS had a molecular weight (MW) ≤12.5 kDa. Although all substrates were very effectively removed after start-up of reactors, a long operation time was required for stabilization of EPS. The only exception was the nitrifying sludge in which EPS were soon stabilized.

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