Method and apparatus for nitrogen removal in wastewater

Abstract

A reactor and control method thereof for nitrogen removal in wastewater treatment achieves a measured control of maintaining high ammonia oxidizing bacteria (AOB) oxidation rates while achieving nitrite oxidizing bacteria (NOB) repression, using various control strategies, including: 1) ammonia and the use of ammonia setpoints, 2) operational DO and the proper use of DO setpoints, 3) bioaugmentation of a lighter flocculant AOB fraction, and 4) proper implementation of transient anoxia within a wide range of reactor configurations and operating conditions.

1 ) A reactor for biological nitrogen removal from wastewaters comprising a nitrite-shunt which targets repression of the nitrite oxidizing bacteria (NOB) under controlled transient anoxia conditions, the conditions being controlled either along the flow-path or along the process time-line, wherein a dissolved oxygen (DO) profile switches between a lower DO-setpoint of less than 0.1 mg/L and a upper DO-setpoint of greater than 1.0 mg/L, and wherein at least one of an aeration system activation interval or the upper DO setpoint are set such that an on-line measured ammonia concentration is higher than an ammonia setpoint of 1.5 mg NH 4 —N/L in more than 75% of the transiently aerated reactor volume (in space or time). 
     
     
         2 ) The reactor of  claim 1 , wherein said reactor has a limited aerobic sludge retention time just sufficient to reach the ammonia setpoint by controlled extension of anoxic periods or volume and by operating a high sludge wasting rate, wherein the sludge wasting rate is controlled to maintain high DO setpoints (>1 mg/L) in the case of ammonia concentration control of aeration. 
     
     
         3 ) The reactor of  claim 1 , wherein said reactor further includes a bioaugmentation of aerobic ammonia oxidizing bacteria (AOB) produced from a high-strength ammonia sidestream reactor, wherein the less dense and more compressible or unattached sludge fraction is selected from the high-strength ammonia sidestream reactor for the bioaugmentation by an appropriate device and fed to the reactor at a maximum rate leading to a retention time of the bioaugmentation fraction of less than 10 days in the sidestream system. 
     
     
         4 ) The reactor of  claim 3 , wherein the appropriate device for selecting the biomass for Bioaugmentation from the high-strength ammonia sidestream reactor for the bioaugmentation comprises one of the following devices: a cyclone, centrifuge, lamella settler, sieve, or integrated biofilm process. 
     
     
         5 ) The reactor of  claim 1 , wherein said reactor includes a bioaugmentation of anammox organisms from a sidestream reactor to the mainstream reactor in order to provide microbial competitors for nitrite which help to repress NOB. 
     
     
         6 ) The reactor of  claim 1 , wherein a mixed liquor solids (MLSS) concentration is higher than 2 g/L, or equivalent biomass quantities in a biofilm system, in order to enhance oxygen uptake rate (OUR) to facilitate rapid transitions from aerobic to anoxic conditions. 
     
     
         7 ) The reactor of  claim 1 , further comprising an aeration control system which is configured to maximize the frequency of transitions between aerobic and anoxic conditions. 
     
     
         8 ) The reactor of  claim 1 , further comprising an aeration control system which is configured to increase the upper DO-setpoint in correspondence with load increase. 
     
     
         9 ) The reactor of  claim 1 , wherein said reactor can be any one of a sequencing batch reactor, a completely mixed reactor, an oxidation ditch or a plug flow process, wherein at least one of the oxic and anoxic steps or DO setpoints is controlled either in time or in space. 
     
     
         10 ) The reactor of  claim 1 , wherein said reactor includes one of a suspended growth process, a granular process or a biofilm process or a hybrid combination of these processes. 
     
     
         11 ) The reactor of  claim 1 , wherein the separation process can occur using a settler, a dissolved air flotation device, a filter or a membrane. 
     
     
         12 ) The reactor of  claim 1 , wherein said reactor maintains a high oxygen uptake rate to allow for a rapid transition to anoxia from an aerated state. 
     
     
         13 ) The reactor of  claim 12 , wherein said reactor feeds a minimum mass-flow of organic carbon to the reactor to enhance heterotrophic growth for more rapid transition to anoxia from an aerated state and for additional competition for nitrite for improved NOB-repression. 
     
     
         14 ) A method of controlling a reactor for biological nitrogen removal from wastewaters comprising a nitrite-shunt which targets repression of the nitrite oxidizing bacteria (NOB) under controlled transient anoxia conditions, the conditions being controlled either along a flow-path or along a process time-line, wherein a dissolved oxygen (DO) profile switches between a lower DO-setpoint of less than 0.1 mg/L and an upper DO-setpoint of greater than 1.0 mg/L, and wherein at least one of an activation of an aeration system of the reactor or the upper DO setpoint is dependent on an on-line measured ammonia concentration being higher than an ammonia setpoint of 1.5 mg NH 4 —N/L in more than 75% of transiently aerated reactor volume (in space or time). 
     
     
         15 ) The method of  claim 14 , further comprising controlling said reactor to have a limited aerobic sludge retention time just sufficient to reach the ammonia setpoint by controlled extension of anoxic periods or volume and by operating a high sludge wasting rate, wherein the wasting rate is controlled to maintain high DO setpoints (>1 mg/L) in the case of ammonia concentration control of aeration. 
     
     
         16 ) The method of  claim 14 , further comprising said reactor receiving a bioaugmentation of aerobic ammonia oxidizing bacteria (AOB) produced from a high-strength ammonia sidestream reactor, wherein the less dense and more compressible or unattached sludge fraction is selected from the high-strength ammonia sidestream reactor for the bioaugmentation by an appropriate device and fed to the main reactor system at a maximum rate leading to a retention time of the bioaugmentation fraction of less than 10 days in the sidestream system. 
     
     
         17 ) The method of  claim 16 , wherein the appropriate device is one of a cyclone, centrifuge, lamella settler, sieve, or integrated biofilm process. 
     
     
         18 ) The method of  claim 14 , wherein a bioaugmentation of anammox organisms from a sidestream reactor to the mainstream reactor is provided in order to provide microbial competitors for nitrite which help to repress NOB. 
     
     
         19 ) The method of  claim 14 , wherein the reactor is controlled to achieve a mixed liquor solids (MLSS) concentration of higher than 2 g/L, or equivalent biomass quantities in a biofilm system, in order to enhance oxygen uptake rate (OUR) to facilitate rapid transitions from aerobic- to anoxic conditions. 
     
     
         20 ) The method of  claim 14 , wherein controlling said reactor further comprises controlling an aeration control system to maximize the frequency of transitions between aerobic and anoxic conditions. 
     
     
         21 ) The method of  claim 14 , wherein controlling said reactor further comprises controlling an aeration control system to increase the higher DO-setpoint in correspondence with load increase. 
     
     
         22 ) The method of  claim 14 , wherein said reactor controlled by the method can be any one of a sequencing batch reactor, a completely mixed reactor, an oxidation ditch or a plug flow process, and wherein at least one of the oxic and anoxic steps or DO setpoints are controlled in time or in space.