| Summary: | 博士 === 國立中山大學 === 環境工程研究所 === 98 === The Wu-Luo River, located in the Ping-Tong County of southern Taiwan, has long been polluted by untreated domestic and partially treated swine wastewaters and is among the most polluted rivers in Taiwan. The main objective of this study was to find a practical and effective way to improve water qualities of seriously polluted rivers with a natural technology. The Wu-Luo River was taken as an illustration of the approach in the first subject of this study. The second subject used mixed sewage and a partially-treated swine waster as a simulated polluted river water to test if an UASB (upflow anaerobic sludge blanket) reactor followed by a constructed wetland (CW) system could be used for clarification of the water. For verification of the performance results achieved by the second subject, the third subject used a pilot UASB-CWs system to test the performances by using the water sampled from the Wu-Luo River.
A full-scale constructed wetland system (CWs) has been in operation for cleaning a portion of polluted Wu-Luo River water since January 2005. The first section of study investigated the efficiency and treatment capacity of this full-scale CWs on the river shore, and the operation parameters of CWs could be improved to enhance the treatment.
Due to the limited efficiency and capacity of the full-scale CWs treatment, the second section of this study use a pilot-scale system to treat wastewater mixed in laboratory to simulate the polluted water treatment of the Wu-Luo River. This system was equipped with an UASB reactor in front of the CWs, which is expected to raise the efficiency and capacity of the CWs.
Since the system of UASB-CWs in the second section showed good performance, the actual Wu-Luo River water was introduced to 2 pilot-scale systems which only the experimental one had UASB reactor before CWs in the third section of study. The removal efficiency of pollutants including heavy metals between the experimental and control systems was compared.
In the first section, the Wu-Luo River CWs occupied a total area of 18 hectares in which approximately 9 hectares were wetted by the introduced river water. Close to 4.7 hectares of the CWs was flooded by the river water with 1.9 hectares occupied by emergent and floating plants. A total water volume of about 9,930 m3 was estimated. During the investigation period, 10,000-20,000 m3/d (CMD) (average 10,800 CMD) of the polluted river water was introduced to the CWs with a hydraulic retention time (HRT) of 0.92 day. It was concluded that water sampled from near the midpoint of the CWs got better clarification results than those from the effluent end. Pollutant removal efficiencies were 60, 60, and 67%, respectively, for TCOD, BOD, and SS at the midpoint, and 56, 54, and 45%, respectively, for TCOD, BOD, and SS at the effluent end. Organics, N, and P released from decayed plants were responsible for the poor water qualities at the end. The CWs had only a TN removal efficacy of approximately 18% with no TP removal effect.
In the second section, a pilot system with an UASB reactor combined with two CW reactors was used to evaluate the feasibility of treating wastewater samples (mixture of sewage and partially-treated swine wastewater). To observe the influence of HRT on the removal efficiency of various pollutants in the wastewater in the UASB reactor, 2 phases of experiments with HRTs of 6 and 2 hours were conducted. The UASB reactor responded well in removing most of the pollutants observed except for AN and TP. The average removal efficiency could reach the levels of 93, 91, 86, 89, and 78% for SS, SCOD, SBOD, AN, and TP with the UASB-CWs systems, which have potentials to be used to improve the water quality in river in practice. To observe the influence of HRT on the removal efficiency of various pollutants in the wastewater in the UASB reactor, 2 phases of experiments with HRTs of 6 and 2 hours were conducted.
In the third section, the experimental system was composed of UASB-CW1-CW2 in seris, whereas that of control system was only CW1-CW2 in series. Water samples were taken from Wu-Luo River water. To observe the influence of HRT on the removal efficiency of various pollutants in the river water in the UASB reactor, 3 phases of experiments with HRTs of 6, 4, and 2 hours were conducted. Heavy metals were easily settled in the first section of treatment, the concentrations of them were found higher in the sediments in UASB of experimental system than those in CW1 of control system. UASB can be used for primary sedimentation to prevent the CW1 blocking especially when the river quality changes dramatically on SS. With 4 hrs of HRT in UASB and 32 hrs in CW1 and CW2 each, the removal efficiency is the highest for all pollutants observed in this study. In the effluent of both of the whole systems, more than 96% of SS, NH3, and TN were removed, while more than 70% of COD and TP, more than 60% of BOD were also removed. When HRT in CW1 and CW2 is decreased to be lower than 16 hrs, the ability of CWs to remove TN and TP is also lowered.
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