Biofiltration of butyric acid: Monitoring odor abatement and microbial communities

The objective of this study is to evaluate comparatively the odor removal efficacy of two biofilters operated under different conditions and to identify taxonomically the microbial communities responsible for butyric acid degradation. Both biofiltration systems, which were filled with non-inoculated wood chips and exposed to gas streams containing butyric acid, were evaluated under different operational conditions (gas airflow and temperature) from the physical-chemical, microbiological and olfactometric points of view. The physical-chemical characterization showed the acidification of the packing material and the accumulation of butyric acid during the biofiltration process (<60 days). The removal efficacy was found to be 98–100% during the first 20 days of operation, even at high odor concentration. Changes in the operational temperature increased the odor load factor from 400 to 1400 ouE/m2·s, which led to the reduction of microbiota in the packing material, and a drastic drop of the odor removal efficacy. However, the progressive increase in gas airflow improved the biodegradation efficacy of butyric acid up to 88% with odor loadings as high as 33,000 ouE/m3, while a linear relationship between odor inlet load and removal capacity was also found. The analysis of the microbial community showed that Proteobacteria was the most abundant phylum along the biofiltration time (58–92%) and regardless of the operational conditions. Finally, principal component analysis applied to the physical-chemical and microbiological data set revealed significant differences between the two biofilters under study.