Protection layers for the extension of slow sand filter running times in wastewater reuse

The running time of slow sand filters in wastewater reuse is usually limited by the increase of pressure drop which is mainly caused by surface filtration effects of suspended solids. Surface filtration mechanisms on the top of filter sand layer can be avoided e.g. by so-called protection layers. By choosing suitable materials for protection layers a considerable extension of slow sand filter running times can be achieved.