Effect of initial ratio of heavy metal to biomass on growth yield in batch culture of activated sludge

Abstract

The effect of heavy metal on the observed growth yield (yobs) was observed in batch culture of activated sludge. However, no attention has been paid to quantitatively describe the relationship between heavy metal concentration and yobs so far. In this study, a growth yield model in relation to the ratio of initial heavy metal concentration (Cm) to initial biomass concentration (X 0) was proposed for batch culture of activated sludge, and was verified with experimental and literature data. A significant decline in Yobs was found with the increase of the Cm/X0 ratio. It was clearly demonstrated that for a given initial heavy metal concentration, real strength of heavy metal exerted on unit biomass would be reduced with the increase of initial biomass concentration. This study for the first time revealed that the toxicity of heavy metal to microbial growth should be correlated with the Cm/X0 ratio rather than to Cm only. A concept of effective Cm/X0 ratio, namely (Cm/X0 )50 was then developed for more reasonably and reliably assessing toxicity of heavy metal to microorganisms.