Effect of oxygen on thermophilic denitrifying 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 NO{sub x} control strategies must be developed. Compost biofilters operated at 55 C at an empty bed contact time (EBCT) of 13 seconds have been shown to be feasible for removal of nitric oxide (NO) from synthetic flue gas. Denitrifying microbial populations in these biofilters have been shown to reduce influent NO feeds by 90 to 95% at inlet NO concentrations of 500 ppmv. Oxygen has been shown to have a significant effect on the NO removal efficiency demonstrated by 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. Understanding changes in the microbial population will allow for determination of 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. Both biofilters showed NO removal efficiency greater than 50% once steady anaerobic operation was achieved. One biofilter was supplied with 2% oxygen after 22 days of anaerobic operation. NO removal dropped to between 10 and 20% when oxygen was present in the influent stream. Incomplete conversion of lactate to carbon dioxide was hypothesized to be the cause for the decreased NO removal efficiency in the anaerobic biofilter compared to previous biofiltration experiments. Bed medium microbes converted the bulk of the lactate to acetate, not fully utilizing reducing equivalents present in the carbon source. The inactive compost used to pack the biofilters may have also caused the decreased NO removal efficiency compared to previous biofiltration experiments.
- Research Organization:
- Idaho National Engineering and Environmental Lab., Idaho Falls, ID (US)
- OSTI ID:
- 20002192
- Report Number(s):
- CONF-990608--
- Country of Publication:
- United States
- Language:
- English
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