Wastewater treatment

Abstract

Method and apparatus for upgrading the capability of existing activated sludge and trickling filter wastewater treatment plants to remove carbonaceous and oxidize nitrogenous pollutants. A single stage biological treatment unit utilizing partially submerged, rotating contactors for the growth of organisms utilizing the carbonaceous and nitrogenous components of wastewater is disclosed. The single stage unit is interposed between the biological treatment unit and final clarifier of the existing plant. Moreover, the existing biological unit is converted to use as a holding tank to absorb fluctuations in flow rate and pollutant concentration and thereby making possible the supply of a constant flow of wastewater to the single unit, while the existing final clarifier is used for the purpose of separating the suspended solids in the effluent from the single stage unit.

I claim: 
     
       1. A method for substantially upgrading the pollutant removal capability of wastewater treatment plants that include a primary treatment unit for the removal of settleable and floatable solids from said wastewater; an activated sludge processing tank, a clarifier disposed downstream from said processing tank and conduit means for recirculating solids from said clarifier to said processing tank, said method including the steps of, a. providing a .Iadd.single stage .Iaddend.biological treatment unit between said processing tank and said clarifier,   b. supplying wastewater containing carbonaceous pollutants measured as BOD 5  and ammonia nitrogen in a weight ratio of at least about 3.6:1 respectively to said processing tank from said primary treatment unit,   c. storing said wastewater in said processing tank,   d. supplying said wastewater at a substantially constant predetermined rate from said processing tank to said .Iadd.single stage .Iaddend.biological treatment unit,   e. said biological treatment unit including .[.not more than a single.]. .Iadd.at least one .Iaddend.rotatable shaft supporting a plurality of partially submerged biological contactors having surface area for the growth and maintenance of organisms,   f. creating a flow of said wastewater through said biological treatment unit in a direction generally perpendicular to said rotatable shaft .Iadd.so as to feed the organisms on said contactor surfaces substantially equally, .Iaddend.   g. rotating said shaft to impart a predetermined peripheral velocity to said biological contactors to alternately expose said surface area to wastewater and an oxygen containing atmosphere,   h. said predetermined rate and peripheral velocity being chosen to simultaneously oxidize at least about 83 weight percent of said BOD 5  and at least about 46 weight percent of said ammonia nitrogen on the same surface area of said biological .[.contacts,.]. .Iadd.contactors, .Iaddend.   i. said substantially constant predetermined rate being from about 0.4 to about 2.5 gallons/day/sq.ft. of said surface area, and   j. inactivating said conduit means to prevent recirculation of solids from said clarifier to said processing tank.   
     
     
       2. The method of claim 1 wherein said peripheral velocity is from about 0.25 to about 1.0 ft./sec. 
     
     
       3. The method according to claim 1 wherein up to about 95 percent by weight of said BOD 5  is removed from said wastewater and greater than 46 percent by weight of said nitrogenous pollutants are oxidized in said biological treatment .[.tank.]. .Iadd.unit. .Iaddend. 
     
     
       4. The method of claim 1 wherein said oxygen containing atmosphere comprises from 30 to 60 percent oxygen by volume and said predetermined rate is from about 1 to about 2.5 gallons per day per square foot of said surface area. 
     
     
       5. The method of claim 1 wherein said predetermined rate is from about 0.4 to about 1.5 gallons per day per square foot of said surface area and said peripheral velocity is from about 0.25 to about 1.0 ft./sec. 
     
     
       6. In the method for treating wastewater containing carbonaceous pollutants, expressed in terms of BOD 5 , and ammonia nitrogen in a weight ratio of at least 3.6:1 respectively to oxidize carbonaceous pollutants and ammonia nitrogen, said method including the steps of removing settleable and floatable solids from said wastewater, supplying said wastewater to a holding tank, storing said wastewater in said holding tank, supplying said wastewater at a predetermined rate from said holding tank to a .Iadd.single stage .Iaddend.biological treatment unit, and supplying the biologically treated wastewater to a final clarifier to remove suspended solids, the improvement comprising wherein said biological treatment includes .[.not more than a single.]. .Iadd.at least one .Iaddend.rotatable shaft supporting a plurality of partially submerged biological contactors having surface area for the growth and maintenance of organisms, creating a flow of said wastewater through said biological treatment unit in a direction generally perpendicular to said rotatable shaft .Iadd.so as to feed the organisms on said contactor surfaces substantially equally, .Iaddend.and rotating said shaft to impart a predetermined peripheral velocity to said biological contactors to alternately expose said surface area to said wastewater and an oxygen containing atmosphere, said predetermined rate and peripheral velocity being chosen to simultaneously oxidize at least about 83 weight percent of said BOD 5  and at least about 46 weight percent of said ammonia nitrogen, said predetermined rate being from about 0.4 to 1.5 gallons per day per square foot of said surface area.