A system for reducing head against which air blowers must operate in a filter

摘要

A waste liquid filter comprises a vessel 10 having a base arranged to support a particulate media column 12 in the vessel. Means are provided to supply gas and liquid to flow along the column during normal and backwashing operation of the filter. The vessel has a first outlet 14 arranged to maintain a liquid head at a first level in the vessel during normal operation and a second outlet 17 arranged to maintain a liquid head at a second level in the vessel during backwashing operation. The head at the second level may be greater to contain the media in the column during backwashing.