Oxygen effects on thermophilic microbial populations in biofilters treating nitric oxide containing off-gas streams

Electricity generation from coal has increased by an average of 51 billion kWh per year over the past 3 years. For this reason cost-effective strategies to control nitrogen oxides (NO)from coal-fired power plant combustion gases must be developed. Compost biofilters operated at 55 degreesC at an empty bed contact time (EBCT) of 13 seconds were shown to be feasible for removal of nitric oxide (NO) from synthetic flue gas. Denitrifying microbial populations in these biofilters were shown to reduce influent NO feeds by 90 to 95% at inlet NO concentrations of 500ppmv. Oxygen was shown to have a significant effect on the NO removal efficiency demonstrated ki, these biofilters. Two biofilters were set up under identical conditions for the purpose of monitoring NO removal as well as changes in the microbial population in the bed medium under anaerobic and aerobic conditions, Changes in the microbial population were monitored to determine the maximum oxygen tolerance of a denitrifying biofilter as well as methods of optimizing microbial populations capable of denitrification in the presence of low oxygen concentrations. Nitric oxide removal dropped to between 10 and 20% when oxygen tvas present in the influent stream. The inactive compost used to pack the biofilters may have also caused the decreased NO removal efficiency compared to previous biofiltration experiments. Analysis of the bed medium microbial population using environmental scanning electron microscopy indicated significant increases in biomass populating the surface of the compost when compared to unacclimated Compost.