{"created":"2023-05-15T09:59:50.907944+00:00","id":4078,"links":{},"metadata":{"_buckets":{"deposit":"887441eb-6b94-4e83-b3b8-e378e53d5b13"},"_deposit":{"created_by":9,"id":"4078","owner":"9","owners":[9],"pid":{"revision_id":0,"type":"depid","value":"4078"},"status":"published"},"_oai":{"id":"oai:miyazaki-u.repo.nii.ac.jp:00004078","sets":["73","73:61"]},"author_link":["21421"],"item_10006_description_7":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"Background:\nArsenic pollution of underground water in Bangladesh has become a national problem.\nMajority of the people in Bangladesh depends on groundwater for drinking water and about\n29 million people are drinking from polluted wells for groundwater (concentration 50 ppb or\nmore). This dissertation describes the development of arsenic removal unit (called GSF in\nshort for Gravel Sand Filter), which is suitable in the rural socio-economic conditions of\nBangladesh. The research was conducted with providing simultaneous water supply to the\nlocal people for more than three years; therefore, the research was not only to improve and\ndevelop the arsenic removal system but also on the implementation of the system. The\nresearch paper describes the arsenic removal mechanism of the GSF, as well as its\nmaintenance technique, the ways to manage the arsenic waste, called sludge and also tried to\ndevelop design guidelines for such systems based on the implementation test results. Four\nsuch systems are operating at present.\nGSF Mechanism\nGroundwater is pumped by a hand pump and run through the gravel chambers. But before\nactually running through the gravels, an aeration arrangement provides oxygen for oxidation\nof the dissolved materials in the groundwater. The aeration oxidizes iron of groundwater to\ninsoluble trivalent iron compounds; it also oxidizes the trivalent arsenic to pentavalent arsenic.\nThe arsenic is adsorbed on the insoluble iron particles and being coprecipitated or being\nfiltered out by the gravel roughing filters. The flow rate of water, controlling the residence/\nreaction time, as well as the concentration of iron, arsenic and the competing phosphate ions\nare important considerations for successful operation of this kind of units.\nMaintenance ofthe unit\nMoreover, it is necessary to clean the accumulated arsenic containing iron particles, i.e.\narsenic sludge, as they are accumulated in the inter-particular space of the gravels and thus\nblock the flow. A regular maintenance operation has been developed to counter this problem.\nSlow sand filter (SSF) is used in GSF to remove microbial contamination from water. In SSF,\nalgae are grown in the water and on the sand surface with the help of the nutrients of water\nand sunlight, which removes bacteria. The surface of the sand filter becomes clogged with the\ndead algae and small insects if not cleaned regularly. Besides blocking the flow, the dead\nbodies draw up all the oxygen leading to unhealthy condition to the living organisms. This\nsituation can also cause leaching of arsenic, which might have accumulated in the sand. To\novercome this problem, maintenance program has been developed.\nThe maintenance of the gravel chambers includes checking the arsenic removal performance\nwith field kit once in a month. The washout valves of the gravel chambers are opened once in\nevery 10 days to let the accumulated sludge flow out with some water. In case of complete\nclogging, which may not be resolved by such draining, all the gravels are taken out of the\nchambers, wash/clean and then placed again inside the gravel chambers. In case of sand filter\nmaintenance, the surface of the sand bed is scrapped or cut by a centimeter once in every\nmonth.\nSludge management\nThe removed sludge is flown to an underground collection chamber through drain channels to\nallow settling. The supernatant water flows to a lined control pond and then flows to the\nnatural pond. Leaching of Arsenic from the precipitated sludge dose not exceed 10% and\nmore than 90% is confined inside the sludge. Besides, addition of cement to the dried sludge\nmakes the leaching less. But at present the sludge is opted to be stored in the site as long as no\ndisposal facility is developed.\nSite selection, design and considerations\nConcentration of the competing ions and the necessary ions play the key role as design\ncriterion. Besides aeration and the contact/reaction time should be sufficient to allow arsenic\nremoval.\nAeration method can be provided by placing the pump that delivers water at a higher\nelevation than the inlet. Water falls through the air and gets the oxygen. The falling energy\nwill mix the bubbles to water to help further oxidation. Another method is to place a\nperforated tray well over the surface of water in the inlet chamber. Water will get aeration\nwhile showers down to this chamber. A third method would be arranging elevated channels\nover the side walls of the unit. Water from the pump flows through those shallow channels\nbefore falling into the inlet.\nOptimum gross flow velocity is kept between 75 ～100 cm/hr through the gravel chambers.\nThe velocity is determined from the model tests in the laboratory by previous researches. This\nwould decide the dimension of the chambers.\nTo counter the negative impact of phosphorus on arsenic removal the following criteria are set.\na) at low phosphate concentrations (0.0～0.7 mg/L) minimum Fe/As ratio of the raw water\nshould be 15. In case of a lower ratio, scrap iron can be used to help increasing the Fe/As ratio\nby rusting. b) in case of high phosphate concentration (0.7～2.7 mgjL) the deciding Fe/As ratio\nis 30. Here also, in case of some shortage of iron, scrap metallic irons can be placed on the\naeration tray to supply extra iron to the water.\nAdvantages ofGSF\nThe unit does not need any power and is made of locally available materials, which makes it\nthe most feasible to the local conditions. Besides, it does not need any extra chemical which\nkeeps the running cost to the minimal. The unit can be used as a part of hybrid water supply\nsystem as well as an independent water supply system.","subitem_description_language":"en","subitem_description_type":"Abstract"}]},"item_10006_textarea_22":{"attribute_name":"内容記述","attribute_value_mlt":[{"subitem_textarea_value":"宮崎大学大学院工学研究科博士論文"},{"subitem_textarea_language":"ja"}]},"item_10006_version_type_18":{"attribute_name":"著者版フラグ","attribute_value_mlt":[{"subitem_version_resource":"http://purl.org/coar/version/c_970fb48d4fbd8a85","subitem_version_type":"VoR"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Hussainuzzaman, Miah Mohammad","creatorNameLang":"en"}],"nameIdentifiers":[{"nameIdentifier":"21421","nameIdentifierScheme":"WEKO"}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2020-06-21"}],"displaytype":"detail","filename":"miah_m_hussainuzzaman.pdf","filesize":[{"value":"6.2 MB"}],"format":"application/pdf","licensetype":"license_note","mimetype":"application/pdf","url":{"label":"Miah,M,Hussainuzzaman.pdf","url":"https://miyazaki-u.repo.nii.ac.jp/record/4078/files/miah_m_hussainuzzaman.pdf"},"version_id":"a0608ec0-7c5f-4336-9085-d230d42bdc98"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Study on Implementation of Developed Arsenic Removal System in Bangladesh","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Study on Implementation of Developed Arsenic Removal System in Bangladesh","subitem_title_language":"en"},{"subitem_title":"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","subitem_title_language":"ja"}]},"item_type_id":"10006","owner":"9","path":["73","61"],"pubdate":{"attribute_name":"PubDate","attribute_value":"2008-12-08"},"publish_date":"2008-12-08","publish_status":"0","recid":"4078","relation_version_is_last":true,"title":["Study on Implementation of Developed Arsenic Removal System in Bangladesh"],"weko_creator_id":"9","weko_shared_id":-1},"updated":"2023-07-30T03:44:28.724462+00:00"}