Most of the organic compounds in primary effluent are polymers such as proteins and polysaccharides. However the bacteria present in activated sludge (AS) can only directly take up monomers such as amino acids and glucose which are produced from polymers by hydrolysis. Therefore, it is assumed that the hydrolysis of polymers to monomers by the bacteria is the rate-determining step in polymer removal. In this study, AS was acclimated to dextrin or peptone, and polymers (dextrin or peptone) and monomers (glucose or a mixture of free amino acids) were used as substrates for kinetic tests. The removal of monomers and polymers by the AS followed zero- and pseudo first-order reaction kinetics, respectively. The removal rate of monomers was higher than that of polymers, and the oxygen uptake rate of the AS during monomer removal was higher than that during polymer removal. One of the important differences between the polymers and monomers used in this study is whether glycosidic linkages or peptide bonds exist in the material. It was therefore verified that the hydrolysis of polymers to monomers by AS was the rate-determining step in polymer removal. The removal of polymers apparently followed first-order reaction kinetics at high F/M ratios, but nth-order reaction kinetics at low F/M ratios (n>1), which are commonly used in municipal sewage treatment.

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