Kinetics of assimilation of multiple substrates in dispersed growth systems

Abstract

1. (1) Equations predicting substrate removal and sludge production could be derived by including a substrate utilization factor, maintenance coefficient and a specific death rate constant. 2. (2) In mixed substrate metabolism, growth yield and specific growth rates were controlled by the concentration of that component substrate which allows the minimum generation time and maximum biomass yield in comparison to the other substrates. 3. (3) The assimilation and effluent concentration of non-growth controlling substrates of the mixture could be described by equations incorporating uptake parameters analogous to the constants of the Michaelis-Menten equation. 4. (4) The introduction of a less efficient substrate like galactose into processes treating highly biodegradable substrates like glucose caused deterioration of effluent quality of high rate activated sludge processes. However, no such adverse effect was observed when the reactor was operated at detention times higher than 4 h as employed in conventional practice. 5. (5) Due to higher maintenance energy requirements in mixed substrate metabolism, a larger fraction of the assimilated substrate is completely oxidized. Consequently, sludge productions per unit mass of mixed substrate COD removed were less at all detention times than those obtained for single substrate metabolism.