Grain displacement during backwash of drinking water filters
Backwashing rapid sand filters causes inadvertent displacement of filter media grains from their previous depths. This displacement can affect the hydraulic function of filters by mixing or segregating media grains, and the function of biofilters through displacement of active biomass and coatings f...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IWA Publishing
2021-02-01
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| Series: | Water Supply |
| Subjects: | |
| Online Access: | http://ws.iwaponline.com/content/21/1/356 |
| _version_ | 1818982028821921792 |
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| author | Loren Ramsay Feng Du Majbritt Lund Haiyan He Ditte A. Søborg |
| author_facet | Loren Ramsay Feng Du Majbritt Lund Haiyan He Ditte A. Søborg |
| author_sort | Loren Ramsay |
| collection | DOAJ |
| description | Backwashing rapid sand filters causes inadvertent displacement of filter media grains from their previous depths. This displacement can affect the hydraulic function of filters by mixing or segregating media grains, and the function of biofilters through displacement of active biomass and coatings from proper depths. This study quantifies grain displacement in a pilot-scale filter using tracer grains of colored sand, glass beads, anthracite and garnet to determine the effect of grain size, density and shape on grain displacement. Statistical moments are used to describe the depth distributions resulting from displacement during backwashing. Results show that significant grain displacement occurs during backwash consisting of air scour, air-and-water wash and sub-fluidization water-only wash. Here, displacement is largely independent of grain size, density and shape. When fluidization backwash is used, greater displacement and more dependence on grain characteristics is seen. A variety of grain movement phenomena can be observed during the backwashing steps, indicating that grain movement and therefore the resulting displacement is highly inhomogeneous in four dimensions. These results have direct practical implications for the design of rapid sand filters and the optimization of backwashing procedures, while suggesting that the current widespread backwashing practice used in the case study country (Denmark) should be abandoned. |
| first_indexed | 2024-12-20T17:40:42Z |
| format | Article |
| id | doaj.art-568ab13a323c4a02b8acd275a25433c6 |
| institution | Directory Open Access Journal |
| issn | 1606-9749 1607-0798 |
| language | English |
| last_indexed | 2024-12-20T17:40:42Z |
| publishDate | 2021-02-01 |
| publisher | IWA Publishing |
| record_format | Article |
| series | Water Supply |
| spelling | doaj.art-568ab13a323c4a02b8acd275a25433c62022-12-21T19:31:07ZengIWA PublishingWater Supply1606-97491607-07982021-02-0121135636710.2166/ws.2020.300300Grain displacement during backwash of drinking water filtersLoren Ramsay0Feng Du1Majbritt Lund2Haiyan He3Ditte A. Søborg4 Research Centre for Built Environment, Energy, Water and Climate, VIA University College, Chr. M Østergaardsvej 4, 8700 Horsens, Denmark Research Centre for Built Environment, Energy, Water and Climate, VIA University College, Chr. M Østergaardsvej 4, 8700 Horsens, Denmark Research Centre for Built Environment, Energy, Water and Climate, VIA University College, Chr. M Østergaardsvej 4, 8700 Horsens, Denmark Research Centre for Built Environment, Energy, Water and Climate, VIA University College, Chr. M Østergaardsvej 4, 8700 Horsens, Denmark Research Centre for Built Environment, Energy, Water and Climate, VIA University College, Chr. M Østergaardsvej 4, 8700 Horsens, Denmark Backwashing rapid sand filters causes inadvertent displacement of filter media grains from their previous depths. This displacement can affect the hydraulic function of filters by mixing or segregating media grains, and the function of biofilters through displacement of active biomass and coatings from proper depths. This study quantifies grain displacement in a pilot-scale filter using tracer grains of colored sand, glass beads, anthracite and garnet to determine the effect of grain size, density and shape on grain displacement. Statistical moments are used to describe the depth distributions resulting from displacement during backwashing. Results show that significant grain displacement occurs during backwash consisting of air scour, air-and-water wash and sub-fluidization water-only wash. Here, displacement is largely independent of grain size, density and shape. When fluidization backwash is used, greater displacement and more dependence on grain characteristics is seen. A variety of grain movement phenomena can be observed during the backwashing steps, indicating that grain movement and therefore the resulting displacement is highly inhomogeneous in four dimensions. These results have direct practical implications for the design of rapid sand filters and the optimization of backwashing procedures, while suggesting that the current widespread backwashing practice used in the case study country (Denmark) should be abandoned.http://ws.iwaponline.com/content/21/1/356backwashbiofiltrationdrinking watergrain displacementrapid sand filtration |
| spellingShingle | Loren Ramsay Feng Du Majbritt Lund Haiyan He Ditte A. Søborg Grain displacement during backwash of drinking water filters Water Supply backwash biofiltration drinking water grain displacement rapid sand filtration |
| title | Grain displacement during backwash of drinking water filters |
| title_full | Grain displacement during backwash of drinking water filters |
| title_fullStr | Grain displacement during backwash of drinking water filters |
| title_full_unstemmed | Grain displacement during backwash of drinking water filters |
| title_short | Grain displacement during backwash of drinking water filters |
| title_sort | grain displacement during backwash of drinking water filters |
| topic | backwash biofiltration drinking water grain displacement rapid sand filtration |
| url | http://ws.iwaponline.com/content/21/1/356 |
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