High oxygen utilization in BOD-containing water treatment

Abstract

BOD-containing water such as municipal waste is mixed with at least 60% oxygen gas and active biomass in accordance with specified relationships of oxygen feed gas quantity/energy supplied ratio, oxygen concentration range in the aeration gas, and degree of oxygen saturation in the mixing liquor.

What is claimed is: 
     
       1. In a method for treating BOD-containing water by oxygenation in contact with active biomass, the improvement comprising: mixing BOD-containing water, biomass and feed gas comprising at least 60% oxygen (by volume) in an aeration zone .Iadd.of a reactor .Iaddend.to form .[.a.]. .Iadd.an oxygenated .Iaddend.liquor body and .[.continuing said mixing while.]. .Iadd.a body of aeration gas isolated from the atmosphere above said liquor and continuously recirculating one of the aeration gas and liquor fluids in intimate contact with the other of said fluids in said aeration zone while venting a portion of the aeration gas to the atmosphere; and .Iaddend. simultaneously maintaining: (a) the oxygen feed gas to mixing plus gas-liquor contact energy ratio of 0.03-0.4 lb. moles oxygen per horsepower hour of energy supplied, (b) the aeration gas above said liquor at oxygen partial pressure of at least 300 mm. Hg but below 80% oxygen while consuming at least 50% of the feed gas oxygen in said liquor, (c) the dissolved oxygen concentration of said liquor at below 70% of saturation with respect to the oxygen in said aeration gas but above about 2 p.p.m. and .[.(d) continuously recirculating one of the aeration gas and liquor fluids in intimate contact with the other of said fluids in said aeration zone; and thereafter.]. withdrawing oxygenated liquor from said aeration zone. 
     
     
       2. A method according to claim 1 in which said aeration gas is continuously withdrawn from said aeration zone and reintroduced to the body of said liquor. 
     
     
       3. A method according to claim 1 in which said feed gas comprises at least 90% oxygen. 
     
     
       4. A method according to claim 1 in which the dissolved oxygen concentration of said liquor is maintained at below 35% of saturation. 
     
     
       5. A method according to claim 1 in which the oxygen partial pressure of said aeration gas is maintained above 380 mm. Hg. 
     
     
       6. A method according to claim 1 in which said oxygen feed gas to mixing plus gas-liquor contact energy ratio is maintained at 0.1-0.3 lb. moles oxygen per horsepower hour of energy supplied. 
     
     
       7. A method according to claim 1 in which the aeration gas is maintained below 65% oxygen. 
     
     
       8. A method according to claim 1 in which the volatile suspended solids content (MLVSS) of the liquor is at least 3000 p.p.m. 
     
     
       9. A method according to claim 1 in which municipal waste comprises said BOD-containing feed water, said oxygenated liquor is separated into sludge and clean effluent, and at least part of said sludge is recycled to said aeration zone as said active biomass. 
     
     
       10. In a method for treating municipal waste water by oxygenation in contact with sludge, the improvement comprising.Iadd.: .Iaddend.mechanically mixing waste water, sludge and feed gas comprising at least 90% oxygen (by volume) in an aeration zone .Iadd.of a reactor .Iaddend.to form .[.a.]. .Iadd.an oxygenated .Iaddend.liquor body having volatile suspended solids content (MLVSS) of at least 3000 p.p.m. .[.and continuing said mixing while.]..Iadd., and a body of aeration gas isolated from the atmosphere above said liquor and continuously recirculating aeration gas in intimate contact with liquor in said zone while venting a portion of the aeration gas of the atmosphere; and .Iaddend.simultaneously maintaining: (a) the oxygen feed gas to mixing plus gas-liquor contact energy ratio at 0.1-0.2 lb. moles oxygen per horsepower hour of energy supplied, (b) the aeration gas above said liquor at oxygen partial pressure of at least 380 mm. Hg but below 65% oxygen while consuming at least 70% of the feed gas oxygen in said liquor, (c) the dissolved oxygen concentration of said liquor at below 35% of saturation with respect to the oxygen in said aeration gas but above about 2 p.p.m..[., and (e) continuously recirculating aeration gas in intimate contact with said liquor in said aeration zone.].; withdrawing oxygenated liquor from said aeration zone and separating said oxygenated liquor into sludge and clean effluent; and recycling at least part of said sludge to said aeration zone.