Deep bed thickener/clarifiers with enhanced liquid removal

A method of operating a thickener/clarifier having an upper portion and a lower portion comprising;

• (a) feeding a slurry of a liquid and solid particles suspended in the liquid into a vessel;
• (b) separating said slurry by gravity into different zones having respective degrees of liquid-solids separation including, at a upper portion of said vessel, a free settling zone having a relatively low concentration of solid slurry particles and further including, at a lower portion of said vessel, a compaction zone having a relatively high concentration of solid slurry particles and a hindered settling zone between said free settling zone and said compaction zone, with said hindered zone and said compaction zone constituting lower settling zones;
• (c) discharging an overflow phase of the slurry that has been separated in said vessel into an overflow launder adjacent to an upper end of said vessel;
• (d) discharging, via an underflow discharge adjacent a bottom of said vessel, a thickened, underflow phase of the slurry that has been separated in said vessel;
• (e) directing free liquid released from at least one of said lower settling zones to flow up to said free settling zone via a flow path isolated from the flow of the slurry down in said vessel in said lower settling zones;
• and
• (f) forming generally upwardly extending channels in the slurry held in said lower portion of said vessel to release liquid in at least one of said lower settling zones to flow to said isolated flow path and then on to said free settling zone.

A thickener/clarifier, comprising:

• (a) a vessel having an inlet for receiving a slurry of a liquid and solid particles suspended in the liquid, said vessel having an upper portion surrounding a free settling zone having a relatively low concentration of solid slurry particles and having a lower portion surrounding a compaction zone having a relatively high concentration of solid slurry particles, and a hindered settling zone between said compaction zone and said free settling zone, with said compaction zone and said hindered settling zone constituting lower settling zones and having means for releasing liquid from at least one of said lower settling zones;
• (b) an overflow launder adjacent said upper end of said vessel for discharge of an overflow phase of the slurry that has been separated in said vessel;
• (c) an underflow discharge port adjacent said bottom of the vessel for discharge of a thickened, underflow phase of the slurry that has been separated in said vessel;
• (d) a deliquifying member in said vessel extending up from said lower portion of said vessel to said upper portion of said vessel for flow of free liquid to said free settling zone released from at least one of said lower settling zones while isolating said flow of liquid from the flow of slurry down in said lower settling zones;
• and
• (e) an injector for injecting flocculant into the flow of water to said free settling zone to facilitate settling of solid particles in the water.