Kinetics of Methanogens in an Expanded‐Bed Reactor

Abstract

A biofilm mathematical model for single-stage substrate utilization was developed for an expanded-bed, activated-carbon anaerobic reactor. The concepts of liquid-layer mass transport, biofilm molecular diffusion, and Monod kinetics were incorporated into the model. During 849 days of continuous operation, four steady state operating conditions were obtained, covering a wide range of feed acetate concentration. Steady state data collected when the feed acetate concentrations were 1,600 mg/L and 3,200 mg/L and weekly data obtained when the feed acetate concentration was 6,400 mg/L were used to estimate biokinetic parameters. The model input for each data set consisted of the acetate flux and the log-mean bulk acetate concentration within the reactor. The model was solved for attached biomass using each data set and various trial values of the two Monod constants, k\da, K\ds\da, and a microbial biofilm density, X\da\df. Best estimates of k\da, and X\da\df were obtained by observing the lowest value of the minimum sum of squared deviations between the model-predicted biomass and measured biomass. The biofilm kinetics were characterized as fully penetrated, with no significant external mass transport resistance.