Use of a filter material of sand comprising specific particle size distribution in a filter having a thickness < 30 cm

摘要

The filter material comprises a symmetrical grading curve (2) and sand with fractions of different particle sizes, particularly crushed sand in cubic shape. The crushed sand is mixed with the fluviatile sand or the river sand for attaining a symmetric grading curve. The particle size is provided less than 4 millimeters, particularly less than 2 millimeters.