The drinking water production process naturally consists of a variety of filtration steps, which frequently involve the use of sand and gravel as a filter medium. At many water treatment plants, such sand/gravel filters are used to remove ferric (hydr)oxide from the water, and are periodically replaced.
The grain size of the filter medium ranges from the sand fraction to gravel. The sand/gravel frequently keeps its original colour, but at some locations it turns red-brown as a result of the attachment of ferric (hydr)oxide.
The sand/gravel is used, within the framework of the Soil Quality Regulations, in noise barriers or golf courses. The material is also finding its way to higher-value applications, such as in helophyte filters, nutrient weirs and tree soil.
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