Kinetics of methanogens in an expanded-bed reactor

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_a, K_sa, and a microbial biofilm density, X_af. BBest estimates of k_a, K_sa, and X_af were obtained by observing the lowest value of the minimum sum of squared deviations between the modelpredicted biomass and measured biomass. The biofilm kinetics were characterized as fully penetrated, with no significant external mass transport resistance.