| Summary: | 碩士 === 國立高雄海洋科技大學 === 海洋環境工程研究所 === 95 === Currently in Taiwan, agitation-based natural compositing is the main composting method for food waste. However, the release of bad odors has always been a trouble for staff and nearby residents during agitation. Besides, in batched agitation, the compost has the highest oxygen content during turning and heaping. It will gradually turn into an anaerobic state and not turn into an aerobic state until the next agitation. The instable aerobic environment is also the major problem in the optimization design. Based on the above weaknesses, this study applied the principle of passive aeration to design a passive aeration tank for food waste composting. The advantages of the proposed design included: (1) The bad odors could be treated at the terminal exit; (2) aeration could be optimized to get the optimal air extraction rate for food waste compositing. In the experiment, the moisture of raw compost was adjusted to 60~65% and added with 20% (w/w) mature compost as composting strains. After evenly blended, the experimental compost was moved into a fermentation tank with various air extraction rates. The temperature rising speed and the optimal air extraction rate for high-temperature fermentation were observed. The experiment was conducted over 60 days. During this period, the physical, chemical, aerial, and biological parameters were monitored to stabilize the composting process. Besides, the quality check of the finished product was performed to assure the compost quality.
The study showed that the optimal air extraction rate for food waste composting in passive aeration fermentation tank was 1.8L air/kg dry solid min. The temperature rose to 65℃ above in one day and maintained for 30 days. The temperature started to decline and maintained at 35℃ on the 60th day. In this period, the pH value decreased first and increased later. The initial pH value was 5.2. On the first day, it dropped to 4.3 and slowly climbed to 7.2 by the 60th day. The electro-conductivity increased first, decreased later, and finally maintained at 2.87 dS/m. After 60 days of composting, C/N ratio was reduced from 32 to 20. The concentration of NH3 generated by the passive aeration fermentation tank reached 7ppm. It decreased to lower than 1ppm after passing biological filter, indicating the proposed system is effective in odor control. The quality analysis of compost products showed that the contents of nitrogen, phosphorous, and potassium were 1.6%, 0.6%, and 1.4%, respectively. The contents of harmful heavy metals, Cu, Zn, As, Hg, Cd, Pb, Ni, and Cr were 0.00011%, 0.00093%, ND, 0.0000023%, ND, 0.00023%, 0.0000033%, and ND, respectively. In terms of E-coliform bacillus, after acidification and high-temperature sterilization, the content of E-coliform bacillus was reduced to below 3 MPN/100ml. Besides, the germination rate of seeds planted in mature compost was 90%. All of the above results were compliant with the regulations of Fertilizer Management Act on miscellaneous composts. Moreover, this study also used organic acidic substances to alleviate the pH value of compost and reduce the release of ammonium. The test result showed that tea leaf has the effects of slowing the acceleration of pH value, reducing the release of NH3, and also increasing the concentration of nitrogen in composts.
Based on the above findings, it could be proved that the proposed passive aeration fermentation tank was a feasible approach for food waste compositing. It has advantages of simple operations, low failure rate, low pollution, and high compost quality.
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