| Summary: | 碩士 === 長榮大學 === 職業安全與衛生研究所 === 95 === Due to the improper drainages of wastewaters from factories, households and livestock husbandries, the mid- and downstream river segments in Taiwan have suffered various degrees of water pollution. Considering the high expenses for land requisition, construction and maintenance for river cleanup facilities, it becomes an urge to develop a low land-demanding, easy-operating treatment technology. The present study tested the effectiveness of the foam-free oxygen dissolution apparatus (®Green Harmony T.H.A. system, Daiei Inc., Japan), an on-channel treatment technology, to river restoration. The apparatus was designed to achieve low land demanding, low noise, easy operation, no hindering problem for flood control, improvement of sediment quality, and potentially, cost-effectiveness.
In order to test its effectiveness and application, the foam-free oxygen dissolution apparatus was tested on site, in the laboratory-scale tanks, and simulated with a water quality dynamic model by this study. For the on site testing, the apparatus was installed in the Ming-Sheng interception station of the Tainan Canal, where most of the discharged municipal wastewaters were intercepted and treated by the An-Ping Wastewater Treatment Plant. Water stagnation, caused by the bi-direction tidal motion, and accumulation of sedimentary organics are the main reasons resulting in the deteriorating water quality of this river reach. The 8-month trial was from May, 2006 to January, 2007. The routine water quality monitoring indicated that the dissolved oxygen in water was raised at the outlet of the apparatus. After 8 months of operation, water BOD and COD were dropped 91% and 76%, respectively. Sedimentary sulfur was dropped 70%. Sedimentary ORP was increased from -200mV to -125mV. A cross-sectional, detail investigation was conducted to examine the water quality, sediment quality, and community structures of benthos and fishes on the 25-meter radius of the treatment area. The results showed that the sampling spot most close to the outlet of the treatment apparatus had the highest DO than other ones. Sediment oxygen consumption rate was 0.5g/m2/day lower in the outlet of apparatus, comparing with the inlet. Large-scale mullet, Mugil cephalus, grey mullet fishes that had never present in this river reach were appeared after 8 months of treatment.
For the laboratory-scale study, water and sediment from Erhjen River were filled in three replicated tanks and treated by the foam-free oxygen dissolution apparatus for 28 days. The tanks were operated at completely mixed, no-flow, and semi-environmental control conditions. After 28 days of treatment, DO was increased from 5.8 to 40mg/L; BOD was dropped from 8.6 to 0.8mg/L; SOD was dropped from 4.68 to 4.24 g/m2/day.
Water quality dynamic model, based on the chemical parameters collected in the laboratory-scale study, was established. The model with the first order BOD degradation rate of 1.6hr-1 offered the best correlation (r2 =0.986) between simulation and real BOD values. The model further simulated and compared the effectiveness of the foam-free oxygen dissolution apparatus (DO = 40mg/L) and of traditional aeration device (DO = 8mg/L). At the same BOD loading, the foam-free oxygen dissolution apparatus is more effective in terms of the amount of O2 demand and of the time requirement to achieve a BOD level of the non-polluted criteria. The comparison of different BOD loadings from 10 to 200 mg/L suggested the foam-free oxygen dissolution apparatus performs better at higher loadings for its relative less oxygen waste to the atmosphere. The study has concluded that the foam-free oxygen dissolution apparatus is an effective technology to improve water quality on channel and its effectiveness is more eminent upon applying to mitigate heavily polluted conditions.
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