Technical Aggregates - Filtration Media - Individual Packs

Filter Media - Fine "Slow" Sand
[20kg]

£29.80

Including delivery*

Price includes VAT and delivery:

Pack size: 20kg packs

Size: 0.1-0.3mm

A natural washed silica sand suitable for slow water filters.

Slow sand filters are used for treating surface or run off water. Whilst slow sand filters can provide water of drinking quality, throughout Europe they are frequently used for cleansing run-off from glass houses and industrial complexes. A slow bed filter is typically 1 –2 metres deep and the size of the containing tank is determined by the flow rate desired for the filter.
In the base of each tank is a series of herringbone drains that are covered with a layer of coarse support gravel ( Ref 2513) which in turn is covered with finer support gravel ( Ref 2641) . The active layer of filter sand ( Ref 3239) is then placed on top, this layering structure stops the top layer of fine sand from being washed away. The depth of support material may be in the order of 0.3 metre in depth, however, the majority of the filter comprises fine sand material, generally with a depth of 1 metre or more. On top of the filter sand bed sits a layer of raw, unfiltered water.
Slow sand filters work by the formation of a gelatinous layer, or biofilm in the top few millimetres of the fine sand. This layer consists of bacteria, fungi and protozoa together with a range of aquatic insect larvae. As a biofilm ages, more algae tend to develop and larger aquatic organisms may be present. It is this layer that provides the effective purification, the underlying sand providing the support medium for this biological layer. As water passes through the biofilm particles of foreign matter are trapped in the mucilaginous matrix and dissolved organic material is adsorbed. The water produced from a well-managed slow sand filter can be of exceptionally good quality with no detectable bacterial content.
Slow sand filters slowly lose their performance as the biofilm grows and thereby reduces the rate of flow through the filter. Eventually it is necessary to refurbish the filter. To do this. the top few millimetres of fine sand is carefully scraped off using to expose a new layer of clean sand. Water is then decanted back into the filter and re-circulated for a few hours to allow a new biofilm to develop. The filter is then filled to full depth and brought back into service.

Specify: Natural sand aggregate from Specialist Aggregates or similar approved.

Aggregate Type: Natural Sand

Product Code: 3239