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