A pilot-scale reactor, consisting of a set of two-stage-in-series biotrickling filters, an influent gas supply system and a liquid recirculation system, was utilized to treat ammonia in an airstream. Each stage of the biotrickling filter was constructed from a 20 cm × 200 cm (inner diameter × height) acrylic column packed with cokes (average diameter = 3.0 cm, specific area = 150 m2/m3) of 125 cm height. Experimental results indicate that a time of 30 days is required for development of biofilms for nitrification of the absorbed ammonia from the gas. Long-term (187 days) experimental results show that, in the conditions of EBRT (empty bed gas retention time) = 7.25 s, "circulation liquid/gas" flow rate ratio = 7.7 L/m3, and liquid pH = 6.65, the level of ammonia in the influent gas was reduced from 230 to 4.0 ppm. With the volumetric ammonia loading of less than 7.37 g NH3–N/m3.h, the system could achieve ammonia removal and nitrification efficiencies of 98 and 94%, respectively, without supplementary glucose as a carbon source. However, with a loading of 13.1 g NH3–N/m3.h, both decreased gradually due to a lack of carbon source and an accumulation of ammonium and nitrite ions in the recirculation liquid.
Biofiltration is a process for removing contaminants in air using microorganisms immobilized on a solid support media surface. This technique is economically attractive, and has been adopted successfully to treat a number of air contaminants such as volatile organic compounds (VOCs) or odors. The performance of biofiltration for removal of ammonia from air streams was studied in a pilot-scale biofilter consisted of two columns [40 cm (w) × 40 cm (L) × 70 cm (H) acrylic column] arranged in a series. A medium consisting solely of fern chips, on which biofilms were cultivated, was used as a packing material. The biofilter was tested continuously for 110 days, measuring the removal efficiency, empty bed residence time (EBRT), removal capacity, pressure drop, moisture content, and pH. Most of ammonia was eliminated in the first biofiltration column, and the removal efficiency was increased with the increase in EBRT. Complete removal of the influent ammonia (20–120 ppm) was obtained with the ammonia loading as high as 5.4 g N kg−1 dry media day−1 during the experiment. The Michaelis-Menten equation was tested to be adequate for modeling the ammonia elimination kinetics in the biofilter and the maximum removal rate (Vm) and the half-saturation constant (Ks) were estimated to be 28.2 g N kg−1 dry media day−1 and 129 ppm, respectively.
This study reports a CMOS based optical focusing stage, which incorporates a binary phase-grating Fresnel-lens (PF-Lens). This PF-Lens is the first time implemented in CMOS micro stage. It exploits the superior fine line width and transparent dielectric thin film of CMOS process. Diffraction efficiency of PF-Lens is theoretically fourfold better than that of typical binary amplitude-grating Fresnel-lens (AF-Lens). In addition, by dispensing UV curable transparent polymer onto Fresnel-lens, the resulted compound lens can achieve a shorter focal length of 648 mum (HeNe laser). The integrated micro stage is thermally actuated. It provides 12 mum stroke alone optical-axis and 17.3 mum across optical-axis. It is sufficient to compensate optical alignment error and to speed up precision focus tracking.
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