REMOVAL OF NITROGEN-OXIDES FROM GAS STREAMS USING BIOFILTRATION

Nitrogen oxides (NOx) are primary air pollutants, and as such, there i s considerable interest in the development of efficient, cost effectiv e technologies to remediate NOx containing emissions, Biofiltration in volves the venting of contaminated gas streams through biologically ac tive material such as soil or compost. This technology has been used s uccessfully to control odors as well as volatile organic compounds fro m a variety of industrial and public sources. The purpose of this stud y was to evaluate the feasibility of using biofiltration as a means to remediate NOx containing gas streams. Biofiltration studies measuring nitric oxide (NO) removal by bacteria indigenous to wood compost were conducted. Vertical biofilters (2l volume) constructed from glass pro cess pipe (3 in i.d.xl2 in) were loaded with 1l of compost bed medium. Compaction of compost in the biofilters was minimized by the addition of wood chips (15% w/w). A nitrogen gas stream, containing various co ncentrations of NO (100-500 mu l/l), was purged (1lmin(-1)) through th e biofilter under single pass, continuous flow conditions. Adsorption studies comparing NO removal in autoclaved and non-autoclaved biofilte rs indicated that approximately 3% NO removal was attributed to abioti c uptake. Control of pH in the biofilter was a critical variable for m aximum nitric oxide removal. Optimum denitrifying activity occurred at pH levels ranging between 6 and 7. Nitric oxide removal rates increas ed in biofilters treated with an external carbon and energy source. Bi ofilters treated with phosphate buffer containing either lactate or de xtrose were capable of removing more than 90% of the NO from a 500 mu l/l NO gas stream flowing at 1lmin(-1).