Kinetics and fundamental mechanisms of protein removal by activated sludge: hydrolysis of peptone to amino acids is the rate-determining step

Abstract

Most ninhydrin reactants in primary effluent are proteins (polymers), and activated sludge (AS) bacteria can only directly take up monomers such as amino acids (AAs) which are produced from proteins by hydrolysis. Whether the hydrolysis of protein to amino acids by AS is the rate-determining step in the removal of protein was examined by comparing not only the removal rate of peptone and a mixture of free AAs but also the oxygen uptake rates of AS during the removal of these substrates, as well as analyzing the time courses of the concentration of each AA during the removal of these substrates. The removal rates of the AA mixture by AS were higher than those of peptone, and the oxygen uptake rates of AS during AA mixture removal were higher than those during peptone removal. The composition ratios of AAs during peptone removal were almost constant, whereas those of AAs markedly changed during AA mixture removal. The important difference between the two substrates used in this study (peptone and an AA mixture) is whether or not peptide bonds exist in the substrates. It was therefore verified that the hydrolysis of protein to AAs by AS was the rate-determining step in the removal of protein from municipal sewage.