Nitrous oxide (N2O) gas is emitted as an intermediate in the biological nitrogen removal process. A track study was performed to investigate the characteristics of N2O emission depending on the cyclic mode of a sequencing batch reactor (SBR). A major emission of N2O took place at the aerobic phase, while N2O emission at the anoxic phase was insignificant. Especially, the highest N2O emission rate was observed at the initial stage of aerobic phase under the limited dissolved oxygen (DO) condition. Under such a condition, nitrite (NO2-) was transiently accumulated along with significant N2O emission due to incomplete nitrification. In addition, N2O production at the aerobic phase was strongly related with incomplete denitrification by nitrifiers. N2O emission could be reduced by change in fill modes in the SBR. A significant conversion to N2O took place in the SBR with the anoxic fill mode, while only small amount of N2O was conversed in the SBR with the aerobic fill mode. Relatively high concentration of ammonia nitrogen (NH4+) accelerated N2O production at the aerobic phase in the SBR with the anoxic fill compared to the aerobic fill. For control of N2O emission in the SBR, the aerobic fill mode could be an effective method even if denitrification efficiency may be reduced at the anoxic phase.

We present the results of Ti/Ni/Ti/Au multilayer ohmic contacts on n-type 6H-SiC and their interface analysis. The as-deposited contacts show rectifying behavior and, with the increase in annealing temperature, they gradually transform to high-quality ohmic contacts exhibiting linear current-voltage characteristics. The interface evolution was analyzed through glancing angle X-ray diffraction, Auger electron spectroscopy, and atomic force microscopy. The TiSi 2 and Ni 2 Si formed at the interfaces during the low-temperature annealing initiate the conversion from Schottky to ohmic behavior, while the increased Ni 2 Si formation at high-temperature annealing makes the perfect ohmic contacts. The results were interpreted through the thermodynamic reaction mechanisms.

Injecting acetate into the sludge layer during the settling and decanting periods was adopted to enhance phosphorus release inside the sludge layer during those periods and phosphorus uptake during the subsequent aeration period in a KIST Intermittently Decanted Extended Aeration (KIDEA) process. The relationship among nitrification, denitrification and phosphorus removal was investigated in detail and analyzed with a qualitative floc model. Dependencies of nitrification on the maximum DO level during the aerobic phase and phosphorus release on residual nitrate concentration during the settling phase were significant. High degree of nitrification resulted that phosphorus release inside the sludge layer was significantly interfered with nitrate due to the limitation of available acetate and the carbon sources from influent. Such limitation was related to the primary utilization of organic substance for denitrification in the outer layer of the floc and the retarded mass transfer into the inner layer of the floc. Nevertheless, effects of acetate injection on both denitrification and phosphorus release during the settling phase were significant. Denitrification rate after acetate injection was two times as high as that before acetate injection, and phosphorus release reached about 14 mg PO4(3-)-P/g MLVSS/hr during the decanting phase after the termination of denitrification inside the sludge layer. Extremely low level of maximum DO (around 0.5 mg/L) during the aerobic phase may inhibited nitrification, considerably, and thus nearly no nitrate was present. However, the absence of nitrate increased when the phosphorus release rate was reached up to 33 mg PO4(3-)-P/g MLVSS/hr during the settling and decanting phase, and nearly all phosphorus was taken up during subsequent aerobic phase. Since the sludge layer could function as a blocking layer, phosphorus concentrations in the supernatant was not influenced by the released phosphorus inside the sludge layer during the settling and decanting period. Phosphorus removal was directly (for uptake) and indirectly (for release) dependent on the median and maximum DO concentration during the aerobic phase, and those optimal values may exist within the range from 0.2 to 0.6 mg/L and 0.4 to 1.2 mg/L, respectively.