| Summary: | 博士 === 國立暨南國際大學 === 土木工程學系 === 105 === Currently, the number of sewage treatment plants at home and abroad is increasing rapidly and the treatment rate is relatively increased, while a considerable amount of sludge produced on annual basis, which requires outsourcing treatment, leads to increased cost, constituting it as the most troublesome problem for the sewage treatment industry. Based on the principle of recycling waste, the PHA content in waste sludge was extracted by different methods to identify the optimal extraction condition and develop a system for recovery of waste sludge to reduce the production cost of biodegradable plastic. In addition, the waste sludge, which was originally useless and costly, could be recovered for its biodegradable plastic ingredients to become valuable materials that simultaneously solve the accumulation and reutilization of waste sludge. It reduced environmental pollution and established a sustainable development in the industry.
The result of waste sludge fermentation experiment showed that the concentration of VFA reached 1350±38 mg C/L at the fermentation temperature of 40℃ on day 5. The ADF domestication to increase PHA content showed that the PHA content in the sludge was increased by 70.6% after 1107 minutes (approximately 18 hours) of ADF domestication when the VFA inlet concentration was 400 mg/L at fermentation temperature of 25℃ and pH value of 9.
In the pure chemical extraction method, the optimal operating conditions were as follows: sodium hypochlorite concentration at 60 v/v%, sludge liquid to solid ratio of 1.00 mLmg-1 and sodium hypochlorite immerse time of 60 min. In the case of pressurized pulse and chemical compound extraction, the concentration of sodium hypochlorite and the time of immersion were reduced to 10 v/v and 5 min, respectively, before the sludge was subjected to chemical extraction, in which the process reduced the chemical usage. The optimal conditions of pressurized pulse and chemical compound extraction were 100 V, 30 sec reaction time, 500 Hz voltage frequency, PHA purity at 83.1±1.75wt% and PHA content of 705±1.22 wt%.
The cost per kilogram of PAH was estimated to be 421 NTD by cost analysis. The cost of ADF domestication was 23.4 NTD and the amount of sludge in the Dihua Sewage Treatment Plant was 2,700 metric tons per month, in which the commission fee was approximately 27,000,000 NTD per month. At an average water content of 80%, 1,512,000 metric tons of PHA could be monthly extracted from sludge. At a retail price of 450 NTD/kg, recovered sludge for extraction of PHA could save the treatment expense and the sales of raw materials to downstream manufacturers could be beneficial (commodity value of 680,400,000 NTD), yielding a monthly profit of 617,932,800 NTD.
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