Biofilm Composition Changes and Degradation Characteristics During Gasoline Vapor Biofiltration

摘要

Degradation characteristics of aliphatic and aromatic components of unleaded gasoline vapor along the bed height were evaluated in a bench-scale biofilter with ID 100 mm and a bed height of 750 mm. Poraver media with a particle size of 8 - 16 mm was used as a packing material. An enrichment mixed culture was immobilized on the packing. Two different loading manners were applied: (1) with a constant OL = 0.4 g.m~(-3).h~(-1), the EBRT was changed in a range of 66.8 min to 6.7 min. and (2) changing the EBRT in a range of 26.7 min to 6.7 min at the constant gasoline concentration of 250 mg.m~(-3) in the inlet air. The results proved that aromatic components are preferentially degraded as long as their removal efficiency is maintained at 80 to 90 %. Below this aromatic removal threshold the aliphatic components begin to be efficiently degraded also.. Despite this phenomenon both the groups of hydrocarbon components can be degraded simultaneously in biofilters. Microbial analyses were used to characterize the strain and genera identification of the inoculum and of the biofilm after six, eighteen and thirty months of gasoline degradation. In addition, a quantitative comparison of the total cell number, the number of eukaryots, primary degraders and Pseudomonas cells, as CFM from the biofilms after six and thirty months of operation was carried out. The comparison shows that the loading manner caused a different selection of the microbial strains present. A microscopic observation of the biofilm structure using SEM was carried out 10 days and six months after the start of gasoline vapor degradation.