The design and development of a novel biofilter is described in this paper. Moisture control is a key aspect of the design. Moisture from the gas stream leaving the biofilter is condensed and returned to the top of biofilter as reflux of pure water. The refluxed water maintains a moist environment for the bacteria throughout the total biofilter column. It also washes down microbial product/s (nitrite and nitrate in the case of ammonia oxidation) that may be toxic to microorganism at a high concentration. This allows microbial activity to be maintained at its most favorable level in the top section of the biofilter. Optimization of moisture balance between evaporation and condensation can result in a system whereby water level on the media surface is sufficient for microbes to thrive while no leachate is produced.
In a proof-of-concept study, a laboratory-scale computer controlled biofilter system employing the reflux process was operated to remove ammonia from an air stream (2.05 μmol /L= 50 ppmv) at a volume load of 1 L/L/min. Inoculated zeolite (clinoptilolite) was used as filter media. Depth profile analysis of the filter bed showed the development of a steep gradient of ammonia, nitrite and nitrate from the top layer to the bottom layer of filter media in the biofilter. Aside from the well-known ammonium adsorption on zeolite, consistent microbial nitrification continued to take place. Nitrite and nitrate level at the bottom of the biofilter continued to increase over 180 day period of experiment. As a result, ammonia removal efficiency remained close to 100% in the leachate-free biofilter
