Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten
During the last few years the presence of high arsenic (As) concentrations in ground water has been of major concern both internationally and in Sweden. Much evidence has been reported about toxic effects caused by arsenic. The carcinogenic effects and the possibility to measure the toxic impacts at...
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| Formato: | Otro |
| Lenguaje: | sueco sueco |
| Publicado: |
2008
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| Materias: | |
| Acceso en línea: | https://stud.epsilon.slu.se/11778/ |
| _version_ | 1855571937391017984 |
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| author | Tjernberg, Beatrice |
| author_browse | Tjernberg, Beatrice |
| author_facet | Tjernberg, Beatrice |
| author_sort | Tjernberg, Beatrice |
| collection | Epsilon Archive for Student Projects |
| description | During the last few years the presence of high arsenic (As) concentrations in ground water has been of major concern both internationally and in Sweden. Much evidence has been reported about toxic effects caused by arsenic. The carcinogenic effects and the possibility to measure the toxic impacts at low concentrations made the World Health Organisation (WHO) to reduce the guideline value from 50 to 10 μg l-1 in 1993. In Sweden the corresponding reduction was implemented in 2003.
Several surveys in Sweden have shown that high arsenic concentrations may occur in ground water. The National Board of Health and Welfare is responsible for guidance and supervision of health protection. This responsibility covers privately owned wells and drinking water facilities that produce less than 10 m3 drinking water per day or support less than 50 people. In 2006 the National Board published a report in which they stated that the existing knowledge was limited concerning As removal from ground water. The objective of this master's thesis is to test some of the current commercially available filter techniques that are used to remove As from ground water. In addition, the national geographic distribution of arsenic and factors governing that distribution are discussed.
Experiments regarding As removal by different filter techniques were carried out in a small water purification plant in the village of Lästringe, located 40 km NE of the city of Nyköping. Only ground water is used in the purification plant. In the experiments, As(III) was added to the water as NaAsO2. Seven different filters of varying size were tested, three of which were based on adsorption to titanium oxide or iron hydroxide, while another two were based on a strong base ion exchanger (SBA) combined with iron or aluminium (hydr)oxide. Finally, two filters were based on reversed osmosis.
The filter experiment was set up in two rounds of 30 days each, and no firm conclusions can therefore be made about the endurance of the filters. The incoming water contained 26-40,5 μg As l-1 during the first round and 125-142 μg As l-1during the second round. After the first round the five most efficient filters were selected for the second round. Magnetic valves and timers were used to adjust the daily volume of water put through the filters in order to simulate the water consumption pattern of a household during 24 hours. A chemical analysis of existing As species revealed that almost all As(III) had been oxidized to As(V). The oxidation could have been catalyzed by manganese oxides together with bacteria. Consequently the filters were supplied with water containing both As(III) and As(V).
The filters containing TiO2 and Fe(OH)3 granulates and the Fe(OH)3 impregnated anion exchanger had the highest As removal efficiency (³ 97,3 %), resulting in As concentrations well below the guideline value of 10 ug As l-1. The rather large reverse osmosis filter showed a smaller percentage of As removal and the As concentration in the water that had passed the filter was mostly higher than the guideline value whenever the incoming water had an As concentration ³ 125 μg l-1. However, the reverse osmosis filter removed many other substances to a large extent. The lower extent of As removal can probably be explained by a high fraction of As (III) occurring as arsenite.
Before choosing the filter technique, it is important to analyse the groundwater with respect to existing As species, total concentration of As and other elements forming oxyanions, dissolved organic carbon (DOC) and pH. Silica (H2SiO40) can compete with arsenic for adsorption sites in filters based on metal (hydr)oxides. Sulphate (SO42-) can be a competitor through anion exchange in filters based on SBA. |
| format | Otro |
| id | RepoSLU11778 |
| institution | Swedish University of Agricultural Sciences |
| language | Swedish swe |
| publishDate | 2008 |
| publishDateSort | 2008 |
| record_format | eprints |
| spelling | RepoSLU117782017-10-17T10:37:53Z https://stud.epsilon.slu.se/11778/ Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten Tjernberg, Beatrice Dept. of Soil Sciences Water resources and management During the last few years the presence of high arsenic (As) concentrations in ground water has been of major concern both internationally and in Sweden. Much evidence has been reported about toxic effects caused by arsenic. The carcinogenic effects and the possibility to measure the toxic impacts at low concentrations made the World Health Organisation (WHO) to reduce the guideline value from 50 to 10 μg l-1 in 1993. In Sweden the corresponding reduction was implemented in 2003. Several surveys in Sweden have shown that high arsenic concentrations may occur in ground water. The National Board of Health and Welfare is responsible for guidance and supervision of health protection. This responsibility covers privately owned wells and drinking water facilities that produce less than 10 m3 drinking water per day or support less than 50 people. In 2006 the National Board published a report in which they stated that the existing knowledge was limited concerning As removal from ground water. The objective of this master's thesis is to test some of the current commercially available filter techniques that are used to remove As from ground water. In addition, the national geographic distribution of arsenic and factors governing that distribution are discussed. Experiments regarding As removal by different filter techniques were carried out in a small water purification plant in the village of Lästringe, located 40 km NE of the city of Nyköping. Only ground water is used in the purification plant. In the experiments, As(III) was added to the water as NaAsO2. Seven different filters of varying size were tested, three of which were based on adsorption to titanium oxide or iron hydroxide, while another two were based on a strong base ion exchanger (SBA) combined with iron or aluminium (hydr)oxide. Finally, two filters were based on reversed osmosis. The filter experiment was set up in two rounds of 30 days each, and no firm conclusions can therefore be made about the endurance of the filters. The incoming water contained 26-40,5 μg As l-1 during the first round and 125-142 μg As l-1during the second round. After the first round the five most efficient filters were selected for the second round. Magnetic valves and timers were used to adjust the daily volume of water put through the filters in order to simulate the water consumption pattern of a household during 24 hours. A chemical analysis of existing As species revealed that almost all As(III) had been oxidized to As(V). The oxidation could have been catalyzed by manganese oxides together with bacteria. Consequently the filters were supplied with water containing both As(III) and As(V). The filters containing TiO2 and Fe(OH)3 granulates and the Fe(OH)3 impregnated anion exchanger had the highest As removal efficiency (³ 97,3 %), resulting in As concentrations well below the guideline value of 10 ug As l-1. The rather large reverse osmosis filter showed a smaller percentage of As removal and the As concentration in the water that had passed the filter was mostly higher than the guideline value whenever the incoming water had an As concentration ³ 125 μg l-1. However, the reverse osmosis filter removed many other substances to a large extent. The lower extent of As removal can probably be explained by a high fraction of As (III) occurring as arsenite. Before choosing the filter technique, it is important to analyse the groundwater with respect to existing As species, total concentration of As and other elements forming oxyanions, dissolved organic carbon (DOC) and pH. Silica (H2SiO40) can compete with arsenic for adsorption sites in filters based on metal (hydr)oxides. Sulphate (SO42-) can be a competitor through anion exchange in filters based on SBA. Under senare år har naturlig förekomst av höga halter arsenik (As) i grundvatten upp-märksammats både internationellt och i Sverige. Flera bevis har lagts fram för arsenikens toxiska effekter i dricksvatten. Den cancerogena effekten och nya möjligheter att mäta låga halter gjorde att WHO 1993 sänkte det rekommenderade gränsvärdet från 50 till 10 μg As l-1. I Sverige genomfördes motsvarande sänkning 2003. Flera undersökningar har visat att höga As-halter kan förekomma i grundvatten. I Sverige har Socialstyrelsen ansvaret för tillsynsvägledning rörande hälsoskydd. Det innebär bland annat ett ansvar för dricksvatten producerat i enskilda brunnar samt dricksvattenanläggningar och vattenverk som i genomsnitt använder mindre än 10 m3 dricksvatten per dygn eller försörjer mindre än 50 personer. Socialstyrelsen publicerade 2006 en rapport där man bland annat redogör för befintlig kunskap om rening av arsenikhaltigt grundvatten och drar slutsatsen att kunskapen är begränsad. Detta examensarbete syftade till att genomföra en undersökning av avskiljningsgraden hos de på marknaden existerande filtertyperna för rening av arsenikhaltigt grundvatten och dricksvatten. Dessutom har arsenikens geografiska fördelning i Sverige samt de faktorer som är viktiga för dess förekomst och spridning sammanfattats i en litteratur-studie. Undersökningen av arsenikavskiljning genomfördes i Lästringe vattenverk cirka 4 mil NO om Nyköping. Råvattnet ifrån vattenverket var ett naturligt grundvatten som genomgick viss förbehandling innan uttag till testet utfördes. As (III) tillsattes därefter i form av en nyberedd NaAsO2-lösning. Sju olika filter med varierande storlek testades. Tre filter var baserade på adsorption till titanoxid eller järnhydroxid och ytterligare två filter hade en starkt basisk jonbytarmassa (SBA) i kombination med järn- eller aluminiumoxid. De återstående två filtren byggde på omvänd osmos. Filtertestet lades upp i två omgångar om vardera 30 dagar. Inga säkra slutsatser kan därför dras om deras uthållighet. Ingående As-halt var 26-40,5 μg As l-1 under den första omgången och 125-142 μg As l-1 under den andra omgången. Efter första omgången valdes de fem mest effektiva filtren ut till andra omgången. Med hjälp av magnet-ventiler och tidur reglerades volymen vatten genom filtren per dygn så att flödet skulle efterlikna ett hushålls konsumtionsmönster över dygnet. En analys av vilka As-former som förekom i ingående vatten visade att i princip all As (III) hade oxiderats till As (V). Oxidationen kan ha påskyndats av förekommande Mn-oxider och mikroorganismer. Därmed antas att filtren försågs med ett vatten innehållande både As (III) och As (V). Filtren med TiO2 - och Fe(OH)3 -granulat, samt Fe(OH)3 -impregnerad anjonbytare visade tillfredställande avskiljning av As (³ 97,3 %) med halter väl under riktvärdet (10 ug l-1). Det stora filtret med omvänd osmos visade en lägre reningsgrad av As. Utgående As-halt var i flertalet fall högre än riktvärdet då den ingående As-halten var ³125 μg l-1. Detta filter av-skiljde däremot flera andra ämnen i hög grad. Det sämre resultatet berodde sannolikt på att As tillsattes i trevärd form. Det är viktigt att analysera grundvatten eller råvatten som ska användas som dricksvatten med avseende på förekommande As-former, total As-halt, halter av andra ämnen i anjonform, såsom DOC samt pH värdet inför valet av filterteknik. Kisel kan vara en konkurrent till As i filter baserade på adsorption till (hydr)oxider, och sulfat kan utgöra en konkurrent i anjonbytesfilter som bygger på SBA. 2008-06-27 Other NonPeerReviewed application/pdf sv https://stud.epsilon.slu.se/11778/1/tjernberg_b_171017.pdf Tjernberg, Beatrice, 2008. Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten : test av olika filtertekniker avsedda för enskilda brunnar. UNSPECIFIED, Uppsala. Uppsala: (NL, NJ) > Dept. of Soil Sciences <https://stud.epsilon.slu.se/view/divisions/4023.html> urn:nbn:se:slu:epsilon-s-7911 swe |
| spellingShingle | Dept. of Soil Sciences Water resources and management Tjernberg, Beatrice Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| title | Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| title_full | Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| title_fullStr | Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| title_full_unstemmed | Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| title_short | Naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| title_sort | naturlig förekomst av arsenik och avskiljning av arsenik från grundvatten |
| topic | Dept. of Soil Sciences Water resources and management |
| url | https://stud.epsilon.slu.se/11778/ https://stud.epsilon.slu.se/11778/ |