Rapid sand filter


A sand or anthracite filter applied for the reduction of turbidity. Grain size ~0.4-2mm. Suspended solids (sand, clay and flocks) are retained after treatment. It is applied subsequently to a coagulation and flocculation stage or as a stand-alone treatment. The filtrate is collected via nozzles at the filter floor.


Both construction costs and O&M costs are medium. For construction local materials can be used. Energy is required for backwashing.


Can be applied at local or centralized level. Simple to construct, only limited labor is required for management. Since rapid filtration is used in combination with other processes (e.g. flocculation and aeration), caretakers of other processes can do cleaning and maintenance jointly.


Risk of contamination of the partly treated water if the installation is open (not covered). Heavy rains might flush filter material. Large flows of highly contaminated backwash water occur, requiring proper handling and disposal.


Easy to construct. Local materials, manpower and equipment can be used. Water flows downward with 5-15 m3.m-2.h-1 through the filter. Low-tech solution, only backwashing requires additional expertise. Because of cleaning periods, two parallel units required. Regular water quality checks required.


Does not require specific actions from users. Since the method is widely known and applied acceptance will be good. Rapid filtration does not give guarantee of safe water, it should always be used in combination with other (e.g. disinfection) processes.

Relevant remarks:

No relevant remarks for Rapid sand filter.