Open gravity backwash filter and method

An open gravity backwash filter comprising:

• a filter basin defined by a first floor and a plurality of walls of about the same height that extend vertically upwardly from said floor,
• a filter compartment located within said filter basin defined along one side by a first vertical partition of less height than said walls and on the remaining sides by some of said walls of said filter basin,
• a gullet located within said filter basin juxtaposed to said filter compartment defined along one side by said vertical partition and on the remaining sides by some of said walls of said filter basin,
• a filter bed of particulate material supported in said filter compartment above said first floor on a perforate horizontal web,
• a drainage space between said first floor and said horizontal web,
• distribution means extending above said filter bed into said filter compartment from said gullet to distribute liquid to said filter compartment from said gullet,
• an effluent channel,
• a conduit connecting said drainage space to said effluent channel for flow of liquid between them,
• flow limiting means associated with said conduit to regulate the volume of liquid flowing through said conduit,
• a weir in said effluent channel having a vertical height greater than the height of said distribution means and less than the height of said walls,
• an influent channel defined by a floor and sidewalls,
• a vertical transverse partition in said influent channel of less height than said influent channel sidewalls creating in said influent channel an inlet water seal chamber,
• a waste channel defined by a third floor and sidewalls,
• a vertical overflow baffle in said waste channel that creates in said waste channel an exit water seal chamber,
• a first siphon that extends above the height of said enclosure wall of said filter basin, one end of said first siphon extending into said inlet water seal chamber and its other end extending into said gullet,
• a second siphon that extends above the height of said enclosure wall of said filter basin, one end of said second siphon extending into said exit water seal chamber and its other end extending into said gullet,
• a third siphon that extends above the height of said weir, one end of said third siphon extending into said effluent channel and its other end being connected for flow of liquid from it into said drainage space,
• ports in each of said siphons at approximately the highest point of each siphon by which the siphons may be primed by application of vacuum to said ports or deactivated by opening of said ports.

In a method of removing suspended material from a aqueous suspension thereof by flowing in a filter mode said suspension from a gullet on to and through a filter bed of particulate material contained in a filter chamber to produce filtered effluent and in a backwash mode regeneration of said bed by backwashing said bed thereby producing waste effluent that is passed to a waste channel, the improvement which comprises:

• flowing said filtered effluent in said filter mode into an effulent channel,
• controlling the height of said filtered effluent in said effluent channel so that it is higher at the completion of said filter mode than the top of said filter bed,
• providing aqueous suspension to be filtered via an influent channel at a level above the top of said filter bed,
• siphoning during said filter mode aqueous suspension from said influent channel into said gullet,
• siphoning during said backwash mode filtered effluent from said effluent channel into said filter chamber beneath said filter bed, and
• siphoning during said backwash mode waste effluent from said gullet into said waste channel.