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バングラディシュで実証試験された砒素除去システムの実用化に関する研究
http://hdl.handle.net/10458/1685
http://hdl.handle.net/10458/1685e1fd9bf6-1759-43ca-8f69-2ddb9fdf39c1
| 名前 / ファイル | ライセンス | アクション |
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Miah,M,Hussainuzzaman.pdf (6.2 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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| 公開日 | 2008-12-08 | |||||
| タイトル | ||||||
| タイトル | Study on Implementation of Developed Arsenic Removal System in Bangladesh | |||||
| 言語 | en | |||||
| タイトル | ||||||
| タイトル | バングラディシュで実証試験された砒素除去システムの実用化に関する研究 | |||||
| 言語 | ja | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
| 資源タイプ | thesis | |||||
| 著者 |
Hussainuzzaman, Miah Mohammad
× Hussainuzzaman, Miah Mohammad |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | Background: Arsenic pollution of underground water in Bangladesh has become a national problem. Majority of the people in Bangladesh depends on groundwater for drinking water and about 29 million people are drinking from polluted wells for groundwater (concentration 50 ppb or more). This dissertation describes the development of arsenic removal unit (called GSF in short for Gravel Sand Filter), which is suitable in the rural socio-economic conditions of Bangladesh. The research was conducted with providing simultaneous water supply to the local people for more than three years; therefore, the research was not only to improve and develop the arsenic removal system but also on the implementation of the system. The research paper describes the arsenic removal mechanism of the GSF, as well as its maintenance technique, the ways to manage the arsenic waste, called sludge and also tried to develop design guidelines for such systems based on the implementation test results. Four such systems are operating at present. GSF Mechanism Groundwater is pumped by a hand pump and run through the gravel chambers. But before actually running through the gravels, an aeration arrangement provides oxygen for oxidation of the dissolved materials in the groundwater. The aeration oxidizes iron of groundwater to insoluble trivalent iron compounds; it also oxidizes the trivalent arsenic to pentavalent arsenic. The arsenic is adsorbed on the insoluble iron particles and being coprecipitated or being filtered out by the gravel roughing filters. The flow rate of water, controlling the residence/ reaction time, as well as the concentration of iron, arsenic and the competing phosphate ions are important considerations for successful operation of this kind of units. Maintenance ofthe unit Moreover, it is necessary to clean the accumulated arsenic containing iron particles, i.e. arsenic sludge, as they are accumulated in the inter-particular space of the gravels and thus block the flow. A regular maintenance operation has been developed to counter this problem. Slow sand filter (SSF) is used in GSF to remove microbial contamination from water. In SSF, algae are grown in the water and on the sand surface with the help of the nutrients of water and sunlight, which removes bacteria. The surface of the sand filter becomes clogged with the dead algae and small insects if not cleaned regularly. Besides blocking the flow, the dead bodies draw up all the oxygen leading to unhealthy condition to the living organisms. This situation can also cause leaching of arsenic, which might have accumulated in the sand. To overcome this problem, maintenance program has been developed. The maintenance of the gravel chambers includes checking the arsenic removal performance with field kit once in a month. The washout valves of the gravel chambers are opened once in every 10 days to let the accumulated sludge flow out with some water. In case of complete clogging, which may not be resolved by such draining, all the gravels are taken out of the chambers, wash/clean and then placed again inside the gravel chambers. In case of sand filter maintenance, the surface of the sand bed is scrapped or cut by a centimeter once in every month. Sludge management The removed sludge is flown to an underground collection chamber through drain channels to allow settling. The supernatant water flows to a lined control pond and then flows to the natural pond. Leaching of Arsenic from the precipitated sludge dose not exceed 10% and more than 90% is confined inside the sludge. Besides, addition of cement to the dried sludge makes the leaching less. But at present the sludge is opted to be stored in the site as long as no disposal facility is developed. Site selection, design and considerations Concentration of the competing ions and the necessary ions play the key role as design criterion. Besides aeration and the contact/reaction time should be sufficient to allow arsenic removal. Aeration method can be provided by placing the pump that delivers water at a higher elevation than the inlet. Water falls through the air and gets the oxygen. The falling energy will mix the bubbles to water to help further oxidation. Another method is to place a perforated tray well over the surface of water in the inlet chamber. Water will get aeration while showers down to this chamber. A third method would be arranging elevated channels over the side walls of the unit. Water from the pump flows through those shallow channels before falling into the inlet. Optimum gross flow velocity is kept between 75 ～100 cm/hr through the gravel chambers. The velocity is determined from the model tests in the laboratory by previous researches. This would decide the dimension of the chambers. To counter the negative impact of phosphorus on arsenic removal the following criteria are set. a) at low phosphate concentrations (0.0～0.7 mg/L) minimum Fe/As ratio of the raw water should be 15. In case of a lower ratio, scrap iron can be used to help increasing the Fe/As ratio by rusting. b) in case of high phosphate concentration (0.7～2.7 mgjL) the deciding Fe/As ratio is 30. Here also, in case of some shortage of iron, scrap metallic irons can be placed on the aeration tray to supply extra iron to the water. Advantages ofGSF The unit does not need any power and is made of locally available materials, which makes it the most feasible to the local conditions. Besides, it does not need any extra chemical which keeps the running cost to the minimal. The unit can be used as a part of hybrid water supply system as well as an independent water supply system. |
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| 言語 | en | |||||
| 内容記述 | ||||||
| 宮崎大学大学院工学研究科博士論文 | ||||||
| 内容記述 | ||||||
| ja | ||||||
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| 出版タイプ | VoR | |||||
| 出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||
