Two-stage dispersed-growth treatment of halogenated aliphatic compounds by cometabolism

Abstract

A two-stage bioreactor that utilizes cometabolic biotransformations for the treatment of halogenated aliphatics is proposed. Methanotrophic cells are grown in a dispersed-growth reactor in which they are contacted with the waste stream and transformation occurs. A model describing cometabolic biotransformation is used together with basic equations for design of the growth and treatment reactors to predict treatment efficiencies and to evaluate the effects of the finite transformation capacity of resting cells, electron donor supply, and product toxicity on process design. For an example treatment scenario targeting trichloroethylene (TCE), methane transfer and growth reactor size are found to dominate the system design at high contaminant concentrations, while at low concentrations, the treatment reactor size becomes more important. The results of this analysis for a two-stage suspended-growth reactor system suggest that increasing methane and oxygen mass-transfer rates, cell yield, and transformation capacity may have a greater impact on reducing overall size than would an increase in trichloroethylene transformation rate.