| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 96 === At present, the construction of public sewarage sewer systems is accelerated. In the near future, the operation and maintenance (O&M) of sewage treatment plants becomes more important. Because the influent sewage has low concentration of organics and nutrient, the operation of anaerobic digestion tanks is not easily to reach the normal state. Therefore, the produced biogas has not been properly reused. In the developed countries, the anaerobic sludge digestion process in the municipal wastewater treatment plant has been modified to have codigestion with various sources of organic wastes, such as food-processing waste, food residuals, and poultry and livestock excrements. A typical application is the codigestion of sludge associated with nightsoil.
Due to the insufficient of treatment facilities, the nightsoil in many counties cannot be effectively treated. The most efficient way to solve this problem is to construct the nightsoil treatment facilities. However, the construction and the O&M cost would be a large financial encumbrance for the local government. An alternative is the combination with the existed facilities, such as wastewater treatment plant in the industrial park, landfill leachate treatment plants, municipal wastewater treatment plants, landfill and waste incinerators. With a proper performance elevation of these facilities, the nightsoil can be treated by minimum investment.
In this study we investigated the feasibility of codigestion with waste sludges and nightsoil, in order to solve the insufficient treatment facilities of nightsoil, as well as to elevate the performance of anaerobic digester in the municipal wastewater treatment plant. On the other hands, the feasibility of power cogeneration using biogas and the optimal management of digested sludge is also studied. The results of this study showed that after the digestion of sewage sludges and the nightsoil (200 CMD), the digested sludge could be used as fertilizer to the fertility of green belt in the city. Also the power cogenerated from this system could bring the income around NT$10,700,000/year. This would be the optimal alternative for operating the digestion facility.
In conclusion, we suggest that the anaerobic sludge digester can be operated more efficiently. The short-term target can be set as codigestion with sludge and nightsoil, not only to recover the energy but also avoid the illegal disposal of nightsoils. The codigestion of the sludge with other source of organic waste will be the trend and the long-term target.
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