| Summary: | 碩士 === 臺灣大學 === 生物環境系統工程學研究所 === 98 === Aerator is widely used in aquaculture today. It improves dissolved oxygen increasing, promotes water body flowing, eliminates the stratification, lets oxygen down into the bottom and makes sediments become aerobic in order to reduce the noxious gas production. However, using aerator will consume massive energy. If we can use green energy such like wind power as one kind of usable power, it will be beneficial to energy conservation and carbon reduction.
In the field, I used multi-paddle wheel aerators and horizontal sprayer aerators at Ming-Hua treatment wetland in Chiayi County to understand the promoting purification efficiency of aerators on wastewater treatment wetlands in Taiwan. Consider the wetland as a process unit, sampled inflow and outflow once per hour continuing 24 hours and measured dissolved oxygen, temperature, biochemical oxygen demand, total Kjeldahl nitrogen. The results showed that there are no significant differences of standard oxygen transfer rate (SOTR) whether the aerator is working or not, but dissolved oxygen had more diurnal variation when the aerator closed. Biochemical oxygen demand removal efficiency was better when the aerator operates then closed, but the total Kjeldahl nitrogen removal efficiency was contrary. The standard aeration efficiency (SAE) of Ming-Hua treatment wetland was about 0.090 kg O2/kWh.
Consider the model of multi-blade windmills and paddle wheel aerators, I designed a small wind power paddle wheel aerator. Performed the aerator in laboratory, and lay it in a tank which water depth is 0.1 m and total volume is 0.0227 m3. Using deferent wind speed (2.0-4.5 m/s) and two paddle depths (0.025m, 0.045m) to test dissolved oxygen change. The results showed that no matter what depth the paddle is, when the paddle wheel rotational speed enhanced, the volumetric mass transfer coefficient (KLa) increased. However, when the paddle depth is 0.045m had higher KLa then the paddle depth is 0.025m in equal slowly rotational speed. The SAE of wind power paddle wheel aerator was 1.21 kg O2/kWh when paddle depth was 0.025m and 4.54 kg O2/kWh when 0.045m. Compared with previous aerators, the wind power paddle wheel aerator had higher SAE. Used multi factor linear regression methods to analyze the variance and use T test to estimate the affected degree of KLa of paddle depth and rotational speed. It showed that rotational speed affected KLa significantly more than paddle depth.
This study showed that the wind power paddle wheel could eliminate energy consume and keep a certain concentration of dissolved oxygen, so that water body could become better habitats. It is possible to set up at treatment wetlands on floodplains or costal aquaculture ponds where the wind condition is stable and continued.
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