No abstract

Two problems still hamper the widespread industrial application of biotrickling ®lters (BTFs) for waste gas treatment in practice: clogging of the ®lters at higher carbon loads and a decrease in the elimination of a target compound when more than one compound is present in the waste gas. To investigate these phenomena three identical BTFs removing dichloromethane (DCM) from an arti®cial waste gas were operated counter-current wise for 12 months at a DCM load of 0.94 Cmole-DCM/(m 3 r á h). After ®ve months of operation methylmethacrylate (MMA) was added to the waste gas. Three different MMA loads were applied: 0.5, 1.0 and 1.5 Cmole-MMA/(m 3 r á h). Although the elimination of DCM in all three BTFs decreased after the introduction of MMA to the air stream, it stabilised at a lower steady-state value than before the MMA addition. MMA was completely degraded during the applied standard conditions. In all three ®lters biomass accumulation eventually caused clogging of the packing. In the ®lter with the lowest MMA load the ®rst signs of clogging were observed only after 7 months of stable operation, illustrating the need for long term studies to evaluate process stability. Short term experiments have provided information about the system's dynamics and showed that an accumulation of intermediates and a subsequent adaptation of the biomass in the BTF will occur upon a step increase in MMA load. To evaluate whether a stable BTF operation without clogging is possible, a novel process parameter (the rate of Carbon Conversion per unit void packing Volume) is introduced which possibilities and limitations are discussed.List of symbols EC dcm DCM elimination capacity (g/(m 3 r h)) EC max dcm

Measurement of the surface roughness and thickness of biological films is laborious and usually destructive, thus hampering research in this area. We developed a laser triangulation sensor (LTS) set‐up for the fast and nondestructive measurement of these biofilm parameters during growth. Using LTS measurements, the morphological development of a dichloromethane‐(DCM) degrading biofilm cultured on a wetted‐wall column was studied. The measurements show that the biofilm develops faster at the entrance of the reactor. The biofilm consisted of a base film in which microbial colonies were embedded. The biofilm‐surface area gradually increased by 23% compaerd to the bare surface due to the formation of a large number of these colonies. The number and shape of these colonies were followed in time. Using LTS measurements, biofilms distinctly different in surface roughness could be distinguished in a laboratory trickling filter removing DCM from a waste gas. The consequences of the observed surface characteristics for the reaction‐diffusion process in the biofilm and for the falling film hydrodynamics are discussed. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 619–629, 2000.