# US 9,039,897 B2 · Method and system for treating wastewater and sludges by optimizing sCO2 for anaerobic autotrophic microbes

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- Number: US 9,039,897 B2
- Document ID: US9039897B2
- Status: Granted
- Kind: B2
- Application number: 13/964,762
- Filed: 2013-08-12
- Published: 2013-12-12
- Granted: 2015-05-26
- Earliest claimed: 2011-02-15
- Assignees: University of South Florida
- Applicants: Peter George Stroot
- Inventors: Peter George Stroot
- Web page: https://patentgrep.com/patent/US9039897B2

## CPC

- C02F 3/2893: {with biogas recycling}
- C02F 3/006: {Regulation methods for biological treatment}
- C02F 3/307: {characterised by direct conversion of nitrite to molecular nitrogen, e.g. by using the Anammox process}
- C02F 3/308: {Biological phosphorus removal}
- C02F 11/04: Anaerobic treatment; Production of methane by such processes
- C02F 2209/001: Upstream control, i.e. monitoring for predictive control
- C02F 2209/006: comprising a software program or a logic diagram
- C02F 2209/24: CO2
- C02F 2209/245: in the gas phase
- C02F 2305/06: Nutrients for stimulating the growth of microorganisms
- Y02E 50/30: Fuel from waste, e.g. synthetic alcohol or diesel
- Y02W 10/20: Sludge processing
- Y10S 210/903: Nitrogenous
- Y10S 210/906: Phosphorus containing
- 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)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02W: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

The present invention describes a method of optimizing CO2 concentration to increase the specific growth rate of Anammox bacteria and methanogens in wastewater and sludge treatment, as well as novel systems and methods of treating wastewater and sludge. The specific growth rate or doubling time of the Anammox bacteria and methanogens were determined to be sensitive to dissolved CO2 concentration. Optimizing dissolved CO2 concentration increases the specific growth rate of the Anammox bacteria, which may be used as an alternative biological nitrogen removal process for the treatment of domestic wastewater. In the method and system of treating sludge, the CO2 stripper returns biogas with low CO2 concentration to the headspace of an anaerobic digester in order to lower the headspace CO2 concentration and therefore, the soluble CO2 concentration. The lower soluble CO2 concentration increases the specific growth rate of the methanogens for a more efficient anaerobic digestion process.

## Claims

### Claim 1

A method of increasing the specific growth rate of anaerobic, autotrophic microbes in a wastewater treatment system comprising:
optimizing dissolved CO2 further comprising:
establishing an optimal control value for the soluble CO2 concentration for wastewater;
measuring the concentration of soluble CO2 for the wastewater;
comparing the measured concentration of soluble CO2 in the wastewater against the optimal control value; and
adjusting the measured concentration of soluble CO2 to match the optimal soluble CO2 control value;
whereby optimizing the soluble CO2 increases the specific growth rate of the bacteria.

### Claim 2 (depends on 1)

The method of claim 1, wherein the microbes are Anammox bacteria.

### Claim 3 (depends on 1)

The method of claim 1, wherein the microbes are methanogens.

### Claim 4 (depends on 1)

The method of claim 1, wherein the optimal control value is established by Equation 1 below:
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
-
b
(
1
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; and b or kd is the decay coefficient.

### Claim 5 (depends on 1)

The method of claim 1, wherein the optimal control value is established by Equation 2 below:
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
×
1
(
1
+
[
H
+
]
K
⁢
⁢
1
+
K
⁢
⁢
2
[
H
+
]
)
-
b
(
2
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; b or kd is the decay coefficient; [H+] is the proton concentration; K1 is the lower pH limit; and K2 is the upper pH limit.

### Claim 6 (depends on 1)

The method of claim 1, wherein the soluble CO2 concentration of the wastewater in the aeration tank is adjusted by passing the wastewater through CO2 stripping equipment.

### Claim 7 (depends on 1)

The method of claim 1, wherein the soluble CO2 concentration of the wastewater in the aeration tank is adjusted by passing return activated sludge through CO2 stripping equipment.

### Claim 8

A method of treating wastewater for biochemical oxygen demand (BOD) and nitrogen removal comprising:
a. flowing wastewater effluent through a first aeration basin;
b. optimizing CO2 content of the effluent;
c. flowing at least a portion of the optimized CO2 effluent into a second aeration basin;
d. flowing the optimized CO2 effluent from steps (b) and (c) into an anaerobic reactor;
e. flowing the optimized CO2 effluent from the anaerobic reactor into a secondary clarifier; and
f. recycling at least a portion of wastewater in the secondary clarifier by channeling the wastewater into the first aeration basin.

### Claim 9 (depends on 8)

The method of claim 8, wherein the step of optimizing CO2 content of the wastewater further comprises:
establishing an optimal control value for soluble CO2 concentration for the wastewater effluent in the first aeration basin wherein the optimal control value is established by Equation (1)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
-
b
(
1
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; and b or kd is the decay coefficient;
or Equation (2)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
×
1
(
1
+
[
H
+
]
K
⁢
⁢
1
+
K
⁢
⁢
2
[
H
+
]
)
-
b
(
2
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; b or kd is the decay coefficient; [H+] is the proton concentration; K1 is the lower pH limit; and K2 is the upper pH limit;
measuring a concentration of soluble CO2 for the wastewater effluent in the first aeration basin;
comparing the measured concentration of soluble CO2 in the waste water effluent in the first aeration basin against the optimal control value; and
adjusting the soluble CO2 concentration in the first aeration basin to match the optimal soluble CO2 control value.

### Claim 10 (depends on 9)

The method of claim 9, wherein the soluble CO2 concentration of the wastewater effluent in the first aeration basin is adjusted by passing the effluent through a CO2 stripping process.

### Claim 11 (depends on 9)

The method of claim 9, wherein the soluble CO2 concentration of the wastewater effluent in the first aeration basin is adjusted by passing return activated sludge through a CO2 stripping process.

### Claim 12 (depends on 8)

The method of claim 8, wherein the second aeration basin is an ammonium oxidizing bacteria (AOB) reactor.

### Claim 13 (depends on 12)

The method of claim 12, wherein the AOB reactor has a pH of at least about 8.

### Claim 14 (depends on 8)

The method of claim 8, wherein the anaerobic reactor is an Anammox reactor.

### Claim 15 (depends on 14)

The method of claim 14, wherein anaerobic conditions are maintained in the Anammox reactor by internally recycling Anammox effluent to Anammox influent.

### Claim 16 (depends on 14)

The method of claim 14, wherein anaerobic conditions are maintained in the Anammox reactor by flowing about 1% of primary solids or raw wastewater into the Anammox reactor.

### Claim 17

A method of treating wastewater for BOD, nitrogen and phosphorous removal comprising:
a. flowing a volume of wastewater through a primary clarifier;
b. optimizing CO2 content of primary effluent exiting the primary clarifier;
c. flowing the primary effluent having optimized CO2 into an anaerobic basin for phosphorous release;
d. flowing effluent from step (c) to an aerobic basin to remove BOD;
e. adding nitrite to the effluent from step (d);
f. flowing the effluent from step (e) into a second anaerobic basin;
g. flowing the effluent from step (f) into a secondary clarifier; and
h. recycling at least a portion of wastewater in the secondary clarifier to provide return activated sludge to the first anaerobic basin.

### Claim 18 (depends on 17)

The method of claim 17, wherein the step of optimizing CO2 content of the primary effluent further comprises:
establishing an optimal control value for soluble CO2 concentration for the primary effluent exiting the primary clarifier wherein the optimal control value is established by Equation (1)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
-
b
(
1
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; and b or kd is the decay coefficient;
or Equation (2)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
×
1
(
1
+
[
H
+
]
K
⁢
⁢
1
+
K
⁢
⁢
2
[
H
+
]
)
-
b
(
2
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; b or kd is the decay coefficient; [H+] is the proton concentration; K1 is the lower pH limit; and K2 is the upper pH limit;
measuring a concentration of soluble CO2 for the primary effluent exiting the primary clarifier;
comparing the measured concentration of soluble CO2 in the primary effluent exiting the primary clarifier against the optimal control value; and
adjusting the soluble CO2 concentration of the primary effluent to match the optimal soluble CO2 control value.

### Claim 19 (depends on 18)

The method of claim 18, wherein the soluble CO2 concentration of the primary effluent exiting the primary clarifier is adjusted by passing the wastewater through a CO2 stripping process.

### Claim 20 (depends on 18)

The method of claim 18, wherein the soluble CO2 concentration of the primary effluent exiting the primary clarifier is adjusted by passing return activated sludge through a CO2 stripping process.

### Claim 21 (depends on 17)

The method of claim 17, wherein the second anaerobic basin is an Anammox reactor.

### Claim 22 (depends on 21)

The method of claim 21, wherein anaerobic conditions are maintained in the Anammox reactor by internally recycling Anammox effluent to Anammox influent.

### Claim 23 (depends on 21)

The method of claim 21, wherein anaerobic conditions are maintained in the Anammox reactor by flowing about 1% of primary solids or raw wastewater into the Anammox reactor.

### Claim 24

A method of treating wastewater for BOD, nitrogen and phosphorous removal comprising:
a. flowing a volume of wastewater through a primary clarifier wherein phosphorous is removed by allowing the wastewater to occupy the primary clarifier for a sufficient hydraulic residence time (HRT);
b. optimizing CO2 content of at least a portion of primary effluent exiting the primary clarifier;
c. flowing effluent from steps (a) and (b) to an aerobic basin to remove BOD;
d. adding nitrite to the effluent from step (c);
e. flowing the effluent from step (d) into an anaerobic basin;
f. flowing the effluent from step (e) into a secondary clarifier; and
g. recycling at least a portion of wastewater in the secondary clarifier to provide return activated sludge to the primary clarifier.

### Claim 25 (depends on 24)

The method of claim 24, wherein the step of optimizing CO2 content of the primary effluent further comprises:
establishing an optimal control value for soluble CO2 concentration for the primary effluent exiting the primary clarifier wherein the optimal control value is established by Equation (1)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
-
b
(
1
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; and b or kd is the decay coefficient;
or Equation (2)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
×
1
(
1
+
[
H
+
]
K
⁢
⁢
1
+
K
⁢
⁢
2
[
H
+
]
)
-
b
(
2
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; b or kd is the decay coefficient; [H+] is the proton concentration; K1 is the lower pH limit; and K2 is the upper pH limit;
measuring a concentration of soluble CO2 for the primary effluent exiting the primary clarifier;
comparing the measured concentration of soluble CO2 in the primary effluent exiting the primary clarifier against the optimal control value; and
adjusting the soluble CO2 concentration in the primary effluent to match the optimal soluble CO2 control value.

### Claim 26 (depends on 25)

The method of claim 25, wherein the soluble CO2 concentration of the primary effluent exiting the primary clarifier is adjusted by passing the wastewater through a CO2 stripping process.

### Claim 27 (depends on 25)

The method of claim 25, wherein the soluble CO2 concentration of the primary effluent exiting the primary clarifier is adjusted by passing return activated sludge through a CO2 stripping process.

### Claim 28 (depends on 24)

The method of claim 24, wherein the anaerobic basin is an Anammox reactor.

### Claim 29 (depends on 28)

The method of claim 28, wherein anaerobic conditions are maintained in the Anammox reactor by internally recycling Anammox effluent to Anammox influent.

### Claim 30 (depends on 28)

The method of claim 28, wherein anaerobic conditions are maintained in the Anammox reactor by flowing about 1% of primary solids or raw wastewater into the Anammox reactor.

### Claim 31

A wastewater treatment system comprising:
an aerobic treatment zone;
an anaerobic treatment zone wherein the anaerobic treatment zone is positioned downstream from the aerobic treatment zone; and
a CO2 stripping zone wherein the CO2 stripping zone is positioned between the aerobic and anaerobic treatment zones.

### Claim 32 (depends on 31)

The system of claim 31, further comprising a recycling zone wherein at least a portion of wastewater in the anaerobic treatment zone is recycled to re-enter the aerobic treatment zone.

### Claim 33

A wastewater treatment system comprising:
a CO2 stripping zone;
at least one anaerobic treatment zone wherein the anaerobic treatment zone is positioned downstream from the CO2 stripping zone; and
an aerobic treatment zone wherein the aerobic treatment zone is positioned between the CO2 stripping zone and the at least one anaerobic treatment zone.

### Claim 34 (depends on 33)

The system of claim 33, further comprising a recycling zone wherein at least a portion of wastewater in the anaerobic treatment zone is recycled to re-enter the anaerobic treatment zone.

### Claim 35 (depends on 33)

The system of claim 33, further comprising a recycling zone wherein at least a portion of wastewater in the anaerobic treatment zone is recycled to re-enter the CO2 stripping zone.

### Claim 36

An anaerobic digestion system comprising:
at least one anaerobic digester having a biogas headspace; and
CO2 stripping equipment positioned adjacent the biogas headspace of the at least one anaerobic digester;
whereby biogas contained in the biogas headspace is cycled through the CO2 stripping equipment and re-enters the biogas headspace with lower CO2 concentration.

### Claim 37

A method of treating sludge comprising:
flowing sludge through at least one anaerobic digester having a biogas headspace;
cycling headspace biogas from the biogas headspace through CO2 stripping equipment to lower CO2 levels in the headspace biogas; and
flowing the lower CO2 biogas back into the biogas headspace of the at least one anaerobic digester;
whereby the lower CO2 headspace biogas encourages the growth of autotrophic anaerobic microbes.

### Claim 38 (depends on 37)

The method of claim 37, wherein the step of optimizing CO2 content of the biogas further comprises:
establishing an optimal control value for gaseous CO2 concentration in the headspace of the at least one anaerobic digester wherein the optimal control value is established by Equation (1)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
-
b
(
1
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; and b or kd is the decay coefficient;
or Equation (2)
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
×
1
(
1
+
[
H
+
]
K
⁢
⁢
1
+
K
⁢
⁢
2
[
H
+
]
)
-
b
(
2
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; b or kd is the decay coefficient; [H+] is the proton concentration; K1 is the lower pH limit; and K2 is the upper pH limit;
measuring a concentration of gaseous CO2 for the biogas in the headspace;
comparing the measured concentration of gaseous CO2 in the biogas in the headspace against the optimal control value; and
adjusting the gaseous CO2 concentration in the headspace to match the optimal gaseous CO2 control value.

### Claim 39 (depends on 38)

The method of claim 38, wherein the gaseous CO2 concentration in the headspace is adjusted by stripping CO2 from the biogas.

### Claim 40 (depends on 38)

The method of claim 38, further comprising gas-mixing the contents of the at least one anaerobic digester using the lower CO2 biogas.

### Claim 41

A method of increasing the specific growth rate of anaerobic, autotrophic microbes in a wastewater treatment system comprising:
optimizing soluble CO2 further comprising:
establishing an optimal control value for the soluble CO2 concentration for wastewater;
measuring the concentration of gaseous CO2 for the wastewater wherein the gaseous CO2 concentration is in equilibrium with reactor contents;
comparing the measured concentration of gaseous CO2 against the optimal control value; and
adjusting the measured concentration of gaseous CO2 to match the optimal soluble CO2 control value;
whereby optimizing the soluble CO2 increases the specific growth rate of the bacteria.

### Claim 42 (depends on 41)

The method of claim 41, wherein the microbes are Anammox bacteria.

### Claim 43 (depends on 41)

The method of claim 41, wherein the microbes are methanogens.

### Claim 44 (depends on 41)

The method of claim 41, wherein the optimal control value is established by Equation 1 below:
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
-
b
(
1
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; and b or kd is the decay coefficient.

### Claim 45 (depends on 41)

The method of claim 41, wherein the optimal control value is established by Equation 2 below:
μ
⁢
⁢
obs
=
μ
⁢
⁢
max
×
[
CO
⁢
⁢
2
]
[
CO
⁢
⁢
2
]
+
Ks
,
CO
⁢
⁢
2
+
[
CO
⁢
⁢
2
]
2
Ki
,
CO
⁢
⁢
2
×
1
(
1
+
[
H
+
]
K
⁢
⁢
1
+
K
⁢
⁢
2
[
H
+
]
)
-
b
(
2
)
wherein μobs is the specific growth rate; μmax is the maximum specific growth rate, h−1; Ks,CO2 is the saturation constant for CO2, mg/L; Ki,CO2 is the inhibition constant for CO2, mg/L; [CO2] is the concentration of CO2; b or kd is the decay coefficient; [H+] is the proton concentration; K1 is the lower pH limit; and K2 is the upper pH limit.

### Claim 46 (depends on 41)

The method of claim 41, wherein the soluble CO2 concentration of the wastewater in the aeration tank is adjusted by passing the wastewater through CO2 stripping equipment.

### Claim 47 (depends on 41)

The method of claim 41, wherein the soluble CO2 concentration of the wastewater in the aeration tank is adjusted by passing return activated sludge through CO2 stripping equipment.