The Hydraulic and Efficiency Study of Ji-Ji Sedimentation Weir

• Main Authors: Chih-Li Lin, 林致立
• Other Authors: Paris Honglay Chen
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/81219336931427835971

碩士 === 國立中興大學 === 水土保持學系 === 92 === There are four major parts of researches in this study, as following: (I) The overall grit chambers study: We investigated the best measuring parameters of water quality in practice and theory, water quality of effluent, the treatment efficiency, field flow pattern, sludge volumes, etc. by sampling, lab experiment, statistical analysis, removal & theoretical calculations. (II) The settling channel study: We studied the field measurements, field flow data, field water quality data, detention time and removal efficiency, the contents and removal differences of organic and inorganic solids, etc.. In addition, the on-site operation and management as well as effects from upstream power-station operation were explored. Also, (III) The design parameters study: We searched the related literatures & reports, the original design maps & plans, and on-site data to calculate, analyze and compare the design parameters including (A) efficiency criteria (detention time, settling velocity, mean velocity, design length, theoretical removal efficiency, etc.), (B) capacity criteria (water flow volume and sediment storage), as well as (C) inlet and outlet of subsidiary design. Finally, (IV) The mathematical simulation model study: The numerical model, SSIIM, was adopted and built with the original design data. After the boundary conditions were established by on-site design and field measuring data, this model was used not only to simulate the grit chamber, settling channel, particles motion routes, and overflow wall flow pattern, but also to verify the conclusion of result findings. And, these four part studies results will be summarized as following: (I) Overall grit chambers study: linear regression analysis of suspended solids against turbidity, yielded values of R20.991. The regression analysis ANOVA showed a P-value (5.041024) was smaller than 5%, this result indicated both turbidity and suspended solids were strongly correlated. The regression equation, y1.2486x125.32, presented that turbidity can be practically measured instead of suspended solids, i.e., its possible to proceed on-line monitoring with turbidity measurement for quick data. The removals of grit chamber for turbidity and suspended solids were 69.12~91.15% (mean 81.18%) and 74.11~91.32% (mean 83.09%), respectively. Simultaneously, sedimentation weir only removed turbidity 5.56~8.32% (mean 6.94%) and suspended solids, 0.62~8.44% (mean 4.53%). The results also showed that the removal efficiency in the back of overflow wall were obviously lower than that in the front of overflow wall. This phenomenon is due to turbulent flow occurred from overflow wall. Apparently, to improve the outlet design is the only way to ensure the function of grit chamber. According to Taiwan water body classification of water quality, the water quality of the grit chamber effluent is the fifth category of water body, which only fits the use of environmental conservation. If we hope the grit chamber effluent to be used as irrigable or industrial water sources, the water quality of outlet must be promoted to the fourth category of water body. If the effluent want to be used as public water supply, the water quality must at least meet the requirements of third category of water body. This means, that the effluent of grit chamber needs to be further treated. (II) Settling channel study: The measurement of flow rates for every settling channel showed that the detention time was similar, and surface flow rates increased toward left side. In the treatment efficiency, the removals of turbidity and suspended solids were 46.72~80.33% (mean 66.92%) and 61.88~81.94% (mean 73.94%), respectively. In order to understand the situations of removing organic and inorganic solids from grit chamber, the t-test analysis indicated t1.982 > critical value 1.691, and P-value (one way)0.028 < 0.05, i.e., these two settling efficiencies are different. This is because turbulent flow possibly caused organic and inorganic solids to separate, and the removals varied with their specific gravity. Comparing with the results also exhibited the operation and management from upstream power-station affect the treatment efficiency of grit chamber. By comparison of the study, the results of settling channel study were consistent with the conclusions from the treatment efficiency of the overall grit chamber study. (III) Design parameters study: After analyzing the parameters of design (detention time, settling velocity, horizontal velocity, and length, etc.) for grit chamber, we found its function lay between traditional grit chamber and sedimentation tank, and this facility had the ability to remove particles in size more than 0.2 mm. In settlable solids test, it was predicted that the potential, efficient, and current sediment volumes were about 238,810, 174,960 and 10,022 CMD respectively. In addition, the data showed that the diffusing angle of 36 degrees for the inlet front slope of grit chamber in this study was much larger than 20 degrees which was recommended in Japan. This parameter caused an unbalanced distribution for the flow rate of inlet and sedimentary concentrations. Again, owing to improper parameters of design in outlet, the turbulent flow occurred from overflow wall will carry sludge out of grit chamber. (IV) Mathematical simulation model study: the results of math model simulation verified the field measurement. Among them, the distribution of velocity in grit chamber also was verified. This result significantly proved that two flow direction changes in influent channel caused the flow rate increasing toward left side. Furthermore, the simulation of settling channels showed 100% removal efficiency can be achieved for the particle size of 2 mm, no matter what the overflow wall was installed or not. The removals for the particle size of 0.2 mm were near to 100%, and the influence of overflow wall could be neglected. For the particle size of 0.1 and 0.05 mm, the overflow wall would reduce significantly their removals. Unfortunately there is no influent particle size distribution measurement to verify this simulation finding this time. It needs further study. The simulation of overflow wall presented the same results as the first three parts of studies. The extra finding is that the influence for overflow wall was put more effect to smaller particles than the bigger was also not verified because of same above-mentioned reason.. The simulation for the flow direction change of settling channels showed that different particle size would cause different turbulence. By the F-test analysis (5%) between simulation data and field measurement for the removals of settling channel, the results showed that F1.945 was smaller than critical value 2.717, and P-value 0.134 was more than 0.05, i.e., we can not prove both variance were different. Consequently, the SSIIM model can provide a reasonably good simulation for the removal efficiency of grit chamber.