| Summary: | 碩士 === 國立屏東科技大學 === 水土保持系所 === 97 === Constructed Wetland（CW） is a kind of natural ecological system which can be used to purify wastewater. It has advantages of low cost and low operation cost. It may be the best way to recycle wastewater if we apply the water which is purified by CW to farm irrigation. The purpose of this study is to evaluate the effectiveness of Linlou Wetland Park（LWP） via monitoring changes of water quality and assessing its effectiveness on treatment of wastewater. This study also explored the possibility of using the purified water to farm irrigation and compared the operation and construction costs between wetlands and second effluent plant.
Results from this study shown that Hydraulic Loading Rates (HLR) were 0.1 and 0.08 m/day, Hydraulic Retention Time (HRT) were 7.81 and 9.01 day during wet season and dry season. The average removal efficiencies were 12.4% for Electrical Conductivity (EC), 9.3% for salinity, 76.9% for turbidity, and 42.4% for Suspended Solids（SS）. Effects on reduction in Dissolved Oxygen（DO）were not obvious. Through the analyses of the Effluent Probability Method (EPM) and box-and-whisker plot, when SS influent concentration ＞30 mg/L, the outfluent concentration can be maintained at ＜20 mg/L. During wet season, EC influent concentration ＜550μs/cm, the removal efficiency of up to 150～200 μs/cm. When turbidity influent concentration ＞10 NTU, the outfluent concentration can be maintained at ＜10 NTU. DO reduce 0.5～1.5 mg/L. During dry season, EC influent concentration ＞700 μs/cm, the removal efficiency of up to 100 μs/cm. DO influent concentration ＞6 mg/L, the outfluent concentration can add to 1～2 mg/L.
Regarding to Pollutant Load (PLR) and removal rate, there was high positive correlation on them for turbidity and SS. There was moderate positive correlation on them for salinity. There was low positive correlation on them for DO. There was no correlation on them for EC. Concerning about PLR and the effluent, there was moderate positive correlation on them for EC,DO and SS. There was low positive correlation on them for salinity and turbidity.
For the quality of effluent used to irrigation, the study results indicated that if we lower the pH of the effluent, it would meet the standard for irrigation water. In the wet season, except for the PH, the effluent more met the Class Ⅳ surface water body quality standard and irrigation water standard. In the dry season, the effluent usually more meet the Class Ⅱ surface water body quality standard and irrigation water standard.
Without consideration to the costs of land, the construction cost for CW is $944/ m2, which is about 30% off from the construction cost for the secondary effluent plant. The maintenance cost is $47/m2 per year, which is about 7% off from the construction cost for the secondary effluent plant. After 25 years, the maintenance cost for CW is 50% off from that for the secondary effluent plant. The benefits generated by the agricultural irrigation are $594,300/ m2 per year. In addition, after 20 years, the economic benefits of LWP are $507.84 million, the maintenance cost is $33,648 million, and the benefit is 1.18 times. It indicated that LWP is a kind of construction that is worth investing.
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