Activated Sludge and Suspended Growth Bioreactors

Abstract

Of the number of alternative designs for biological treatment of contaminated air streams, activated sludge reactors are often overlooked. The concept behind activated sludge treatment is simple: in a single reactor the contaminant transfers from gas into bulk liquid where it is degraded by a suspension of bacteria. The gas is generally introduced into the bottom of the liquid in the reactor in the form of dispersed bubbles. Using this most simplistic definition, a number of terms have been used to describe these systems with subtle differences implied. In true activated sludge treatment, the primary function is to biologically treat dissolved contaminants such as the organic carbon in conventional municipal waste water. The air contaminants, such as odours or volatile organic compounds, are co-degraded with the contaminants dissolved in the inlet waste water. In general these reactors are not specifically designed for optimal gas treatment. Slight variations where the reactor is specifically designed for gas treatment and is not co-degrading waste water contaminants have been termed sparged suspended growth bioreactors (Bielefeldt and Stensel, 1998), suspended growth reactors (Neal and Loehr, 2000), and bubble columns (Andrews and Noah, 1995). More specialised designs of these simple systems are airlift bioreactors which are most widely used in chemical engineering applications (Chisti, 1989; Cesario et al., 1995).