Effect of Key Operating Parameters on NOx Removal in a Fungal Biofilter

摘要

Vapor-phase bioreactors containing the fungus Exophiala lecanii-corni have the potential to be a treatment alternative for nitrogen oxides (NOx) emissions from small-scale sources. In the current study, the NOx removal in a fungal bioreactor was evaluated as a function of NOx loading rates and EBCTs, and the effect of CO2 on NOx removal was examined under aerobic conditions. Also, the influence of NOx on toluene degradation and fungal respiration in the bioreactors was investigated. The NOx elimination capacity of the bioreactors increased as a function of NOx loading rate over the range of 14.9 to 151 g NOx/m3/hr. When the NOx loading rate exceeded 60 g NOx/m3/hr, the NOx removal efficiency in the bioreactors declined to less than 55 %. However, when the loading rate was decreased to 38 g NOx/m3/hr, the NOx removal efficiency increased to 76 %. For a given NOx loading rate, the NOx elimination capacity of the bioreactor declined at high gas flow rates corresponding to lower EBCTs as expected. At a 38 g NOx /m3/hr loading rate, NOx removal in the bioreactors was not influenced by the presence of high CO2 concentrations. In addition, the NOx removal process in the bioreactors is not directly affected by O2 concentrations in the range of 2.6 % to 15.6 %. Since lower toluene removal activity was observed in the presence of NOx, lower CO2 evolution from the bioreactors was expected. However, the CO2 evolution from the bioreactor increased substantially when NOx was present. The reason the pseudo-endogenous respiration rate of the fungal biofilm increased when exposed to NOx is unclear. However, it is postulated that the fungus may require additional energy to detoxify NO and nitrite species.