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Mainly marketed in North America, this compact unit includes a metal Pulsatube (see sludge blanket settling tanks) combined with two dual media gravity filters (anthracite + sand). There are six standard sizes, ranging from 23 to 135 m3·h–1. When the raw water is moderately contaminated, PAC can be injected to capitalise on the advantages offered by the sludge blanket as a contact medium.