Removal of volatile organic compound (VOC) vapors in biotrickling filters: Process modeling and validation with chlorinated aromatic compounds

This study dealt with the removal of vapors of volatile organic compounds from airstreams in biotrickling filters (BTFs). A detailed general model was developed for describing the process under steady-state conditions. The model accounts for mass transfer between phases (air, liquid, biofilm) and biodegradation of pollutants in the biofilm. It also accounts for potential kinetic interactions among pollutants as well as potential process limitations by oxygen availability.; The general model was experimentally validated using mono-chlorobenzene (m-CB) and ortho-dichlorobenzene (o-DCB) as model compounds either alone or in mixture with each other. Before BTF experiments were undertaken, a systematic kinetic study was performed with suspended cultures. Two microbial consortia, called m-CB and o-DCB consortium, were used. In all cases it was found that self-inhibition (Andrews kinetics) takes place. When the two compounds are present in a mixture they are simultaneously used but are involved in a competitive cross-inhibition which is stronger from m-CB presence on o-DCB removal than vice versa. Studies on the effect of pH showed that a value of 6.8 is optimal.; Experiments in a BTF with the m-CB consortium and m-CB as model compound were performed. The percent m-CB removal observed ranged from 79 to 96% and the maximum removal rate was 60 gm{dollar}sp{lcub}-3{rcub}{dollar}-packing h{dollar}sp{lcub}-1{rcub}.{dollar} Removal of o-DCB vapor was found to be more difficult. In fact, using a BTF with the o-DCB consortium percent o-DCB removal ranged from 57 to 76% and the removal rate never exceed 30 gm{dollar}sp{lcub}-3{rcub}{dollar}-packing h{dollar}sp{lcub}-1{rcub}.{dollar} Experiments in a BTF with the o-DCB consortium and airstreams laden by both m-CB and o-DCB validated the proposed model for the case of mixtures. In all cases, a very good agreement between data and model predictions was found. Co-current operation was found to be slightly superior to the counter-current mode; this is also predicted by the model.; Regarding oxygen, it was found that an oxygen-controlled zone exists in the BTF (close to the inlet of the polluted air) when the total VOC concentration is relatively high. For the hydrophobic compounds used in this study oxygen availability does not seem to play a crucial role. Model sensitivity studies have shown that at least two kinetic constants are important and thus, zero or first-order kinetic approximations cannot and should not be made.; The model developed in this study along with the computer code generated for solving the equations can be used in (at least preliminary) scale-up calculations for the design of BTFs.