SHIFT FROM GROWTH TO NUTRIENT-LIMITED MAINTENANCE KINETICS DURING BIOFILTER ACCLIMATION

During long-term operation of a biofilter, the mandatory absence of ne t cell growth forces the cells into maintenance metabolism, which is o f relatively low rate compared to substrate consumption during the act ive growth of the acclimation phase. A model based on this shift in me tabolism can explain the postacclimation decrease in activity sometime s reported for biofilters. The cessation of growth can be caused by nu trient depletion in the bed. Postacclimation nutrient addition increas es activity primarily by allowing a return to the high substrate consu mption rate of active growth, and only secondarily helps raise bed act ivity because of the ultimately higher amount of biomass in the bed. S imulations incorporating the acclimation period and the role of mainte nance metabolism predict about 4 logarithms of growth during acclimati on of a hexane biofilter, which was confirmed experimentally. Changes in a biofilter's biomass during the acclimation phase can be estimated from substrate conversion data using two approximate methods. The fir st follows the cumulative amount of substrate converted and uses the e stimated yield of cells from substrate during active growth to estimat e the total biomass created. The second method follows a rate constant for conversion of substrate in the bed. (C) 1997 John Wiley & Sons, I nc.