# US 4,526,685 A · Waste water treatment plant > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,526,685 A - Document ID: US4526685A - Status: Granted - Kind: A - Application number: 06/599,251 - Filed: 1984-04-11 - Granted: 1985-07-02 - Earliest claimed: 1983-12-22 - Assignees: Klargester Environmental Engineering Ltd. - Inventors: Gerald Rowland - Web page: https://patentgrep.com/patent/US4526685A ## CPC - B01D 21/10: {Settling tanks with multiple outlets for the separated liquids} - B01D 21/00: Separation of suspended solid particles from liquids by sedimentation ({separation of ores or the like by sedimentation B03B5/48 - B03B5/60} ; differential sedimentation B03D3/00; {purification of water, waste water, sewage or sludge C02F, e.g.} devices for separating or removing fatty or oily substances or similar floating material from water, waste water or sewage C02F1/40) - B01D 21/0006: {Settling tanks provided with means for cleaning and maintenance} - C02F 3/082: {Rotating biological contactors} - Y02W 10/10: Biological treatment of water, waste water, or sewage - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) - C02F: TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE (separation in general B01D; special arrangements on waterborne vessels of installations for treating water, waste water or sewage, e.g. for producing fresh water, B63J; adding materials to water to prevent corrosion C23F; treating radioactively-contaminated liquids G21F9/04; regeneration of reactants for recirculation into processes, see the relevant places for the processes) - Y02W: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT ## Abstract To desludge the final settlement tank of a waste water treatment plant which includes a bio zone equipped with slowly rotating rotors on which biomass deposited from the waste water is digested by microorganisms as the biomass is periodically exposed to air, the level of liquid in the final settlement tank is raised above that in the bio zone so that gravity induced desludging can occur. One of the rotating rotors can be equipped with water lifting means to generate the required hydraulic head for desludging. Skimming off of scum from the surface of the water in the final settlement tank can also be effected using the hydraulic head between the tank and the bio zone. ## Claims ### Claim 1 In a waste water treatment plant including first tank means defining a bio zone, means to feed waste water to said bio zone tank means to generate a liquid level therein, at least one rotor means rotatable about an axis and dipping only partially below the liquid level in the bio zone tank means, drive means to turn said at least one rotor means about said axis to periodically convey an area of said rotor means through said waste water and then through the air above said liquid level, second tank means defining a settlement zone, means to feed liquid from said bio zone to said settlement zone, and duct means to feed purified liquid from the settlement zone away from the plant, and desludging means in said second tank means to suck sludge collected in the second tank means back into the bio zone, the improvement which includes arranging said means which feed liquid from said bio zone to said settlement zone to lift the liquid above the liquid level in the bio zone, whereby said desludging means operates on the head of water existing between the bio zone and the settlement zone. ### Claim 2 (depends on 1) Waste water treatment plant as claimed in claim 1, in which means is provided to use the said head of waste to remove surface scum from the settlement zone. ### Claim 3 (depends on 1) Waste water treatment plant as claimed in claim 1, in which the desludging means includes a timer controlled valve means and means to generate timed cycles of opening and closing of the valve means. ### Claim 4 (depends on 1) Waste water treatment plant as claimed in claim 1, in which the means to lift water above the liquid level in the bio zone include water lifting means on the at least one rotor means. ### Claim 5 A waste water treatment plant including first tank means defining a bio zone, means to feed waste water to said bio zone tank means to generate a first liquid level therein, a plurality of rotating members, each rotatable about an axis and each dipping only partially below the first liquid level in the bio zone tank means, drive means to turn said rotating members about said axis to periodically convey an area of each of said members through said waste water and then through the air above said liquid level, second tank means defining a final settlement zone, means to feed liquid from said bio zone to said final settlement zone to define a second liquid level therein, and duct means to feed purified liquid from the final settlement zone away from the plant, desludging means in said second tank means to suck sludge collected in the second tank means back into the bio zone, water lifting means on at least one of said rotating members arranged to lift water to a third level above that of the second liquid level, means to collect water from said lifting means and feed it to the final settlement zone, said desludging means including a sludge return pipe opening close to the bottom of the final settlement zone and leading to a stage in the plant upstream of the final settlement zone, and valve means in said sludge return pipe for controlling the flow therethrough. ### Claim 6 (depends on 5) A waste water treatment plant as claimed in claim 5, in which the valve means is timer controlled, the timed cycles of opening and closing of the valve means being chosen to prevent the sludge level in the bottom of the final settlement zone rising significantly. ### Claim 7 (depends on 6) A waste water treatment plant as claimed in claim 6, in which the water lifting means is arranged to make the second liquid level between 5 and 15 cms above the first liquid level. ### Claim 8 (depends on 5) A waste water treatment plant as claimed in claim 5, in which the sludge return pipe is also provided with an open ended flexible tube teed into it upstream of the valve means which flexible tube allows scum on the surface of the water in the final settlement zone to be also returned to the upstream stage. ### Claim 9 (depends on 5) A waste water treatment plant as claimed in claim 5, in which the first tank forms a housing located in an upper part of a primary settlement tank into which primary settlement tank the sludge pipe empties. ### Claim 10 (depends on 9) A waste water treatment plant as claimed in claim 9, in which the said housing is provided with baffles to force waste water to follow a serpentine path in flowing through the housing, the rotating members being coaxial discs formed in banks, each baffle being disposed between end discs in adjacent banks.