Ammonia Gas Removal Using a Biotrickling Filter Coupled with an Anammox Reactor
Ammonia is an odorous gaseous compound emitted by a variety of industrial facilities. This study aimed to address the feasibility of ammonia gas removal using a biotrickling filter (BTF) coupled with an anammox bioreactor. In the BTF, the influent ammonia gas partitioned into the trickling water and was converted to nitrite via partial nitrification. The effluent liquid from the BTF, containing nitrite and ammonium concentrations, was fed into the anammox reactor where autotrophic denitrifying bacteria converted the ammonium and nitrite to dinitrogen gas. For the anammox reactor to operate efficiently, the influent ammonium and nitrite concentrations must be in a 1 to 1 molar ratio. To evaluate the feasibility of this system, a lab scale BTF and anammox reactor were constructed and operated and a conceptual model for this system was developed. To obtain a nitrite to ammonium ratio close to 1, it was found that the effluent pH from the BTF must be maintained below 7, and the loading rate could not exceed 8.7 g N/m3h. At this loading rate, complete ammonia gas removal occurred. A recycle rate of 1.4 times that of the influent was implemented in the BTF to increase performance and improve the nitrite to ammonium ratio. The addition of the recycle line achieved a nitrite of ammonium ratio of 0.97 at a pH value of 7.67. The anammox reactor achieved 88% removal of ammonium and nitrite at a loading rate of 10.5 g N /m3h. The fact that the BTF was able to achieve a 1 to 1 nitrite to ammonium ratio indicated that coupling of a BTF with the anammox reactor should be feasible. The mathematical model underpredicted effluent ammonium and nitrite concentrations in the BTF and greatly overpredicted the effluent concentrations from the anammox reactor. To improve the BTF model inhibition factors and oxygen supply need to be accounted for. Further development of the growth kinetics in the annamox model are necessary as well.
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