Sand filters are used as a step in the water treatment process of water purification.
There are three main types; rapid (gravity) sand filters, upward flow sand filters and slow sand filters. All three methods are used extensively in the water industry throughout the world. The first two require the use of flocculant chemicals to work effectively while slow sand filters can produce very high quality water free from pathogens, taste and odour without the need for chemical aids.
Sand filters are used in various sectors and processes, where far-reaching removal of suspended matter from water or wastewater is required.
Below are some implementation examples:
- Iron-removal from groundwater using aeration and sand filtration.
- Final purification of wastewater, follow-up to metal precipitation and sedimentation, to remove residual traces of metal-based sludge.
- Final purification of wastewater produced in the production of iron, steel and non-ferro alloys. Sand filtration can be preceded by processes like precipitation/sedimentation, coagulation/flocculation/sedimentation and flotation.
- Purification of wastewater containing sand-blasting grit and paint particles, at shipyards for example.
- Final purification (or prior to active carbon filtration) to permit re-use.
AKTIFPAK® Sand Filters can be designed as either Vertical or Horizontal. Some basic design data are as follows ;
| Characteristics | Rapid Sand Filter | Slow Sand Filter |
| Filtration rate [m/h] | 5 – 15 | 0.08 – 0.25 |
| Media effective size [mm] | 0.5 – 1.2 | 0.15 – 0.30 |
| Bed depth [m] | 0.6 – 1.8 | 0.9 – 1.5 |
| Run length | 1 – 4 days | 1 – 6 months |
| Ripening period | 15 min – 2 h | Several days |
| Regeneration method | Backwashing | Scraping |
| Maximum raw-water turbidity | Unlimited with proper pretreatment | 10 NTU |