Cyclic oxygenation of BOD-containing water

Abstract

BOD-containing water such as sewage is mixed with active biomass and a first quantity of oxygen feed gas in a first cycle for biochemical oxidation to produce oxygenated liquid-solid and unconsumed oxygen-containing gas of lower purity than the feed gas. The unconsumed oxygen is discharged and a second quantity of oxygen feed gas is introduced for mixing in a second biochemical oxygenation cycle.

What is claimed is: 
     
       1. A method for treatment of BOD-containing water by cyclic oxygenation in contact with biomass comprising: as a first oxygenation cycle.Iadd., introducing a first liquor of BOD-containing water and biomass into a chamber having a closed upper end and a lower end in fluid communication with a surrounding liquid storage enclosure and substantially filling said chamber with said first liquor, introducing into said chamber .Iaddend..[.mixing said BOD-containing water and biomass as liquor and.]. a first feed gas quantity comprising at least 50% oxygen (by volume) and having oxygen partial pressure of at least 7.3 p.s.i.a. .Iadd.to progressively downwardly displace said first liquor from an upper level in said chamber to a lower chamber level, mixing said first feed gas and first liquor in said chamber .Iaddend.while simultaneously continuously recirculating one of such fluids against the other .[.fluids in a chamber.]. .Iadd.fluid .Iaddend.for at least 10 minutes and with sufficient mixing and gas-liquor contact energy input to consume at least 60% (by volume) of the oxygen in said first feed gas to form .Iadd.a .Iaddend.first oxygenated liquid-solid and first unconsumed oxygen containing gas over said first oxygenated liquid-solid comprising 10-70% oxygen but of lower oxygen purity than said first feed gas and having oxygen partial pressure of at least 1.47 p.s.i.a. .[.;.]..Iadd., .Iaddend.discharging said first unconsumed oxygen-containing gas from said chamber .Iadd.by raising a hydrostatic head of a second liquor of second BOD-containing water and second biomass into said chamber until said chamber is substantially filled.Iaddend.; as a second oxygenation cycle, .[.mixing in.]. .Iadd.introducing into .Iaddend.said chamber a second feed gas quantity comprising at least 50% oxygen (by volume) and having oxygen partial pressure of at least 7.3 p.s.i.a. .Iadd.to progressively downwardly displace said second liquor from an upper level in said chamber to a lower chamber level, mixing said second feed gas and second liquor in said chamber .Iaddend..[., second BOD-containing water and second biomass.]. while simultaneously continuously recirculating one of such fluids against the other .[.fluids.].  .Iadd.fluid .Iaddend.for at least 10 minutes and with sufficient mixing and gas-liquid contact energy to consume at least 60% (by volume) of the oxygen in said second feed gas to form second oxygenated luqid-solid and second unconsumed oxygen-containing gas over said second oxygenated liquid-solid comprising 10-70% oxygen but of lower oxygen purity than said second feed gas and having oxygen partial pressure of at least 1.47 p.s.i.a., said second BOD-containing water and second biomass .Iadd.of said second liquor .Iaddend.being composed at least in part of said first oxygenated liquid-solid .[.;.]. .Iadd., .Iaddend.and discharging said second unconsumed oxygen-containing gas from said chamber .Iadd.by raising a hydrostatic head of liquor of BOD-containing water and biomass in said chamber until the chamber is substantially filled with said liquor. .Iaddend. 
     
     
       2. A method according to claim 1 wherein additional BOD-containing water and biomass are introduced to said chamber during each of said first and second oxygenation cycles. 
     
     
       3. A method according to claim 1 in which said biomass is concentrated from said oxygenated liquid-solid and recycled in sufficient quantity to provide volatile suspended solids content of at least 3000 p.p.m. in said first oxygenation cycle. 
     
     
       4. A method according to claim 1 in which .[.said chamber is substantially filled with liquor on discharging of unconsumed oxygen-containing gas therefrom at completion of an oxygenation cycle, said first feed gas is thereafter introduced and progressively downwardly displaces the liquor from the chamber upper portion, and.]. the mixing .Iadd.steps .Iaddend.of said first .Iadd.and second .Iaddend.oxygenation .[.cycle.]. .Iadd.cycles each .Iaddend.is initiated when the liquor is displaced to a predetermined chamber lower level. 
     
     
       5. A method according to claim .[.4.]. .Iadd.1 .Iaddend.in which part of .Iadd.each of .Iaddend.said first .Iadd.and second .Iaddend.feed gas is introduced during the mixing .Iadd.steps .Iaddend.of said first .Iadd.and second .Iaddend.oxygenation .[.cycle.]. .Iadd.cycles, respectively. .Iaddend. 
     
     
       6. A method according to claim .[.4.]. .Iadd.1 .Iaddend.in which part of .Iadd.each of .Iaddend.said first .Iadd.and second .Iaddend.feed gas is introduced during the mixing .Iadd.steps .Iaddend.of said first .Iadd.and second .Iaddend.oxygenation .[.cycle.]. .Iadd.cycles, respectively, .Iaddend.to maintain constant gas pressure and volume in said chamber. .[.7. A method according to claim 4 in which the lower end of said chamber is in fluid communication with a surrounding liquor storage enclosure and said first unconsumed oxygen-containing gas is discharged from said 
     
     
        chamber by a rising hydrostatic head of liquor in the chamber..]. 8. A method according to claim 1 wherein gas disengaging from the liquor during the mixing is continuously recirculated and reintroduced to said liquor. 
     
     
           A method according to claim 1 in which the oxygen feed gas is mechanically mixed with said liquor at average rate of 0.10-0.50 lb. moles O 2  per horsepower hour of mixing and gas-liquor contact energy input. 
     
     
        0. A method according to claim 1 in which the oxygen feed gas is mixed with said liquor at average rate of 0.08-2.0 cu. ft. O 2  per cu. ft. 
     
     
        liquor. 11. A method according to claim 1 wherein said feed gas comprises at least 90% oxygen, gas-liquor mixing is for at least 20 minutes, at least 75% of the oxygen is consumed and the unconsumed oxygen-containing 
     
     
        gas comprises 40-60% oxygen. 12. A method for cyclic treatment of sewage by oxygenation in contact with activated sludge comprising: (a) providing said sewage and activated sludge as liquor within and substantially filling a chamber having a closed upper end and a lower end in fluid communication with a surrounding liquor storage enclosure;   (b) introducing first feed gas comprising at least 50% oxygen (by volume) of said chamber in sufficient quantity to provide oxygen partial pressure of at least 7.3 p.s.i.a. and progressively downwardly displace the liquor from the chamber upper portion to a predetermined chamber lower level;   (c) as a first oxygenation cycle, mechanically mixing said first feed gas, sewage and activated sludge for at least 10 minutes while simultaneously continuously recirculating one of such fluids against the other fluids and also simultaneously introducing only sufficient additional first feed gas to maintain constant gas pressure in said chamber to form first oxygenated liquid-solid and first unconsumed oxygen-containing gas comprising 10-70% oxygen but of lower oxygen purity than said first feed gas and having oxygen partial pressure of at least 1.47 p.s.i.a., the mixing and gas-liquid contact energy input being sufficient to consume at least 60% (by volume) of the oxygen in said first feed gas;   (d) discharging said first unconsumed oxygen-containing gas from said chamber by a rising hydrostatic head of liquor in the chamber until the latter is substantially filled with liquor; and   (e) thereafter consecutively repeating steps (b), (c) and (d) as subsequent   
     
     
        oxygenation cycles. 13. Apparatus for cyclic oxygenation of BOD-containing water comprising: (a) a liquor storage enclosure;   (b) an oxygen gas source;   (c) an oxygenation chamber having a wall extending below the liquor level within said storage enclosure and its lower end in fluid communication with the enclosure, and a gas-tight cover;   (d) oxygen supply conduit means between said oxygen gas source and said oxygenation chamber;   (e) means for mechanically mixing said oxygen gas and said liquor in said oxygenation chamber;   (f) conduit means for discharging unconsumed oxygen-containing gas from the upper portion of said oxygenation chamber and having a vent valve therein; and   (g) gas flow control means comprising: a gas inlet flow control valve arranged to maintain a predetermined gas pressure in said oxygenation chamber, and a shut-off valve in said oxygen supply conduit; means for sensing gas pressure in said oxygenation chamber; signal transmitting means from the pressure sensing means to said gas inlet flow control valve; and cycle control means for simultaneously closing said shut-off valve and opening the gas vent valve, and thereafter simultaneously   
     
     
        closing said gas vent valve and opening said shut-off valve. 14. Apparatus for cyclic oxygenation of BOD-containing liquor comprising: (a) a liquor storage enclosure;   (b) an oxygen gas source;   (c) an oxygenation chamber within said storage enclosure having its lower end in fluid communication with the enclosure, and a gas-tight cover;   (d) oxygen supply conduit means between said oxygen gas source and said oxygenation chamber and having a gas inlet flow control valve therein;   (e) an oxygen gas sparger positioned below the liquor level in said oxygenation chamber;   (f) gas-liquor mechanical mixing means positioned below the liquor level in said oxygenation chamber;   (g) a blower with the suction side in flow communication with the oxygenation chamber upper portion and the discharge side in flow communication with said sparger;   (h) conduit means for discharging unconsumed oxygen-containing gas from the oxygenation chamber upper portion and having a vent valve therein; and   (i) gas flow control means comprising: low liquor level sensing means associated with said oxygenation chamber; signal transmitting means from such low level sensing means arranged to close said gas inlet control valve when inflowing oxygen gas has downwardly forced the liquor level to a predetermined elevation; means for sensing the chamber gas content; signal transmitting means to open said vent valve when the sensed gas content descends to a predetermined value; high liquor level sensing means; signal transmitting means from such high level sensing means arranged to close said vent valve and open said gas inlet control valve when the rising liquor reaches a predetermined elevation. .Iadd. 15. A method for treatment of BOD-containing water by cyclic oxygenation in contact with biomass comprising: as a first oxygenation cycle, introducing a first liquor of BOD-containing water and biomass into a chamber having a closed upper end and a lower end in fluid common with a surrounding liquid storage enclosure and substantially filling said chamber with said first liquor, introducing into said chamber a first feed gas quantity comprising at least 50% oxygen (by volume) and having oxygen partial pressure of at least 7.3 p.s.i.a. to progressively downwardly displace said first liquor from an upper level in said chamber to a lower chamber level, mixing said first feed gas and first liquor in said chamber while simultaneously continuously recirculating one of such fluids against the other fluid for at least 10 minutes and with sufficient mixing and gas-liquor contact energy input to consume at least 60% (by volume) of the oxygen in said first feed gas to form a first oxygenated liquid-solid and first unconsumed oxygen containing gas over said first oxygenated liquid-solid comprising a 10-70% oxygen but of lower oxygen purity than said first feed gas and having oxygen partial pressure of at least 1.47 p.s.i.a., exhausting said first unconsumed oxygen-containing gas from said chamber and raising a hydrostatic head of a second liquor of second BOD-containing water and second biomass into said chamber until said chamber is substantially filled with said second liquor; as a second oxygenation cycle, introducing into said chamber a second feed gas quantity comprising at least 50% oxygen (by volume) and having oxygen partial pressure of at least 7.3 p.s.i.a. to progressively downwardly displace said second liquor from an upper level in said chamber to a lower chamber level, mixing said second feed gas and second liquor in said chamber while simultaneously continuously recirculating one of such fluids against the other fluid for at least 10 minutes and with sufficient mixing and gas-liquid contact energy to consume at least 60% (by volume) of the oxygen in said second feed gas to form second oxygenated liquid-solid and second unconsumed oxygen-containing gas over said second oxygenated liquid-solid comprising 10-70% oxygen but of lower oxygen purity than said second feed gas and having oxygen partial pressure of at least 1.47 p.s.i.a., said second BOD-containing water and second biomass of said second liquor being composed at least in part of said first oxygenated liquid-solid, and exhausting said second unconsumed oxygen-containing gas from said chamber and raising a hydrostatic head of liquor of BOD-containing water and biomass in said chamber until the chamber is substantially filled with said liquor.