Biofiltration of volatile organic compounds by a fluidized bed of sawdust
Résumé
In this study, the use of a natural material, sawdust, in a fluidised biofiltrer has been considered. The performance of the biofiltration of ethanol and toluene was estimated in the presence of the native microorganisms of the material and also after the addition, and a period of acclimatization, of external microorganisms. Modifications of the physical and biological characteristics of the material were studied in order to better understand the process. The influence of biofilter shutdown periods was also considered to evaluate the effect of a period of inactivity on subsequent performances. This study shows that a significant degradation of the pollutants is obtainable provided that the following steps are performed: seeding with activated sludge, introduction of nutrients, and control of the changes in the material characteristics and the bed moisture. During the operation of the fluidized bed biofilter, the moisture of the bed had an important effect on the biofilter performance, but was rather difficult to control because of its dependence on the ambient and inlet air temperatures, which changed during the day and the seasons. During the tests with the batch of sawdust particles used as delivered without any sludge enrichment, a reduction in abatement performances was measured with time. In the case of ethanol alone, for a concentration of 0.02 g.m-3, abatement decreased from 24% to 18% then to 7%. The partial or complete addition of sawdust particles previously activated with sludge significantly enhanced the performance of the biofilter, both for ethanol and toluene pollution. Abatements of ethanol of 85% and 60% were achieved when the sawdust particles were activated by sludge. In contrast, a 5-week shutdown of the reactor produced a decrease in abatement, either by a loss of microorganism efficiency during their ''starvation'' or by their destruction.