| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 100 === Food processing waste and wastewater from small factories are the potential energy resource distributed widely. Utilizing the food processing waste and wastewater can reduce pressures on environment and public health in developing regions by achieving 1) better access to energy for factories, 2) less reliance on construction of infrastructure, and 3) reduction of environmental loads associated with conventional food processing waste and wastewater treatment. However, its wide implementation is hindered because those small factories have its specific food processing waste and wastewater characteristics, constraints, and allowance for initial investment, while available technologies are diverse.
Here, reductions in life cycle greenhouse gas emission and cost potentially achieved by an integrated food processing waste and wastewater treatment and energy recovery system optimized over various budget allowances are assessed.
A case study on a small tofu factory located in residential area of Tainan city is conducted to demonstrate the developed design and evaluation schemes that propose a process which minimizes chemical oxygen demand (COD) with the given budget allowance. The process would meet the local conditions such as amount and characteristics of waste and wastewater generated, heat and electricity demand in the factory and regulations. For the tofu factory producing 4,900kg of tofu per day, a reduction of 54 kg CO2-eq. per day is potentially achieved with the minimum investment for meeting the local wastewater standard. A combination of dark fermentation (H2 production) and anaerobic digestion (CH4 production) was chosen, reducing COD from 14,793 to 100 mg/L. The product gas is used for cogeneration of 20 kWh electricity (22.5%) and 12 kWh heat (0.8%) used within the factory. Dreg is used as pig feed or compost in Taiwan. By introducing dreg as additional substrate, more energy is exploited (33.3 and 1.4% of total demand for electricity and heat, respectively). Our calculation shows that GHG emission reduction is also enhanced (1,348 kg CO2-eq. day-1) with this option, considering the deficit in the compost that is produced otherwise. Without energy recovery, treatment by advanced oxidization process would be needed if a tighter regulation were introduced. It is shown in this study that the payback time can be significantly different under varied regulations and promotion strategies.
The synthesis, optimization and evaluation schemes used in this study serves as a framework for designing similar systems tailored to other small factories thereby expected to promote food processing waste and wastewater utilization. To discuss the cost and payback time more in depth, further study on a more specific design (scheduling of reactor operations, introduction of storage tanks, etc.) is needed to consider shortcomings in capability to provide as much energy as needed at any time.
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