Modelling reactive CAH transport using batch experiment degradation kinetics

Models describing transport of degradable organic substances in a porous medium require parameters of the biodegradation kinetics that can be obtained from batch degradation assays. It is rarely assessed if liquid batch biodegradation rates allow extrapolation to reactive transport in a porous medium, i.e. if the cell specific activity in a porous medium with flow-through is identical to that of pelagic cells in liquid cultures. Failure of model predictions can be used to identify the rate-limiting processes in the reactive transport. Column data of anaerobic trichloroethene (TCE) transport and degradation at three flow rates were predicted with a model using biodegradation kinetics derived from a liquid culture. The extent of dechlorination at the column outlet was very well predicted within a factor 1.4 if the specific microbial biomass in the columns was used as an input parameter. This suggests that potential mass transfer limitations in biofilms or differences in microbial ecology between batch and column had minor effects on dechlorination. The model was subsequently extended with Monod kinetics to predict both biomass growth and chlorinated aliphatic hydrocarbon (CAH) degradation in the columns using liquid batch data. These models largely overestimated CAH dechlorination unless microbial transport with cell elution was included and unless a slight batch to column adjustment was made to better predict microbial biomass. With 4 adjustable parameters the model succeeded in predicting the microbial numbers within a factor 4.3 and the extent of dechlorination within a factor 1.2. Our analysis validates the batch to column extrapolation for this dedicated set-up provided that the microbial biomass in columns is well predicted. The sensitivity analysis shows that the extent of dechlorination in the reactive transport is most sensitive to the parameters of TCE degradation kinetics, including microbial growth followed by the residence time.