| 31. | In most areas cartridge filters are less expensive than diatomaceous earth filters but cost more than sand filters.
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| 32. | *Due to the low filtration rate, slow sand filters require extensive land area for a large municipal system.
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| 33. | Between the late 1940s and the early 1960s, slow sand filters were replaced by more efficient rapid sand filters.
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| 34. | The water then goes through a sand filter which removes the coarse particles up to 30 micron in size.
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| 35. | In 1906 the first slow sand filter plant in Malaysia was built at the Ampang Intake for Kuala Lumpur.
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| 36. | Between the late 1940s and the early 1960s, slow sand filters were replaced by more efficient rapid sand filters.
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| 37. | The water produced from an exemplary slow sand filter is of excellent quality with 90-99 % bacterial cell count reduction.
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| 38. | Water for the beach is pumped through two large sand filters and chemically treated before being pumped back into the pools.
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| 39. | The United States also introduced the rapid sand filter which were a derivation of filters used in the paper making industry.
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| 40. | Slow sand filters slowly lose their performance as the biofilm thickens and thereby reduces the rate of flow through the filter.
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