Presented by: Ryan Hennessy Midwest Contract
Presented by: Ryan Hennessy Midwest Contract Operations
Phosphorous Limits Summary of Process Terminology Influences Volatile Fatty Acids Reactions in Anaerobic Zone Reactions in Aerobic Zone Hydraulic Retention Time and Sludge Age Sludge Hauling Considerations Effluent TSS Considerations Case Studies Questions
2
Wastewater plants typically remove phosphorous from wastewater due to environmental, public health, or economic concerns With increasingly stringent limits on phosphorous in wastewater discharge enhanced biological phosphorous removal (EBPR) is becoming increasingly common
3
In a conventional activated sludge system microorganisms take up soluble phosphorous as a nutrient to generate new biomass. ◦ These organisms contain about 2% of phosphorous on a dry weight basis.
Polyphosphate accumulating organisms (PAOs) consist of as high as up to 35% phosphorous
◦ By creating an environment to select PAOs more phosphorous can be taken up by the bacteria.
Sludges with high percentage of PAOs can contain up to 6% phosphorous on a dry weight basis
Aracheobacteria (we’ve known about these for a while) store energy as long polymers (up to 60 units) of phosphate Eubacteria (recently discovered) use AGP (Arabinogalactan-peptide) and their P content is a constant 2% (Dr. Michael Richard 2019)
5
Aerobic: a condition in which free and dissolved oxygen are available Anoxic: A condition in which oxygen is only available in combined forms. (nitrate, sulfate) Anaerobic: A condition in which no oxygen free or combined is available
6
PHAs- the intracellular energy storage of polyphosphate accumulating organisms
VFAs are taken up and stored internally as PHAs. PHAs are then used to uptake phosphorus in the aerobic zone
Secondary release: When phosphate is released when it isn’t supposed to be
May occur under anaerobic conditions such as the sludge blanket in the final clarifier
◦ May also occur when there is too much endogeny in the system and nutrients are released with cell lysis (starvation conditions)
7
Advantages ◦ ◦ ◦ ◦
Minimizes need for chemicals Reduces alkalinity loss from chemical addition Reduces extra sludge production from chemical addition Often provides superior settling characteristics due to the selection process which discourages many types of filaments
Disadvantages ◦ Higher capital cost (for baffles, mixers etc.) ◦ Sensitivity to nitrate or oxygen interference in anaerobic zone ◦ More complex operations
8
A two step process in which an anaerobic environment is followed by an aerobic process In the anaerobic selector PAOs release orthophosphate to obtain the energy to uptake readily biodegradable organics (soluble BOD) In the aerobic zone PAOs grow new biomass and take up phosphorus, typically more than they released in the anaerobic zone 9
An influent BOD: ratio of 25:1 or more is recommended An influent COD:P ratio of 45:1 or more is recommended ◦ Actual numbers needed are plant specific
If there is not enough readily available carbon present supplementation may be needed to maintain the desired ORPs in the selector zones ◦ Carbon supplements include high strength waste, acetate, methanol, glucose, and molasses
10
Septicity occurs when bacteria ferment organic matter (BOD) to “smaller pieces” in the absence of free dissolved oxygen ◦ These “smaller pieces” are known as organic acids (or volatile acids) Organic acids/ volatile acids are the needed form of BOD for the bacteria in the selector
12
Reviewing anaerobic treatment is helpful
13
1.Hydrolysis 2.Acidogenesis 3.Acetogenesis 4.Methanogenesis
Egg-shaped gas storage
Performed by bacteria, protozoa, and exocellular enzymes
Carbohydrates
Sugars
Fats
Fatty Acids
Proteins
Amino Acids
Done by Acid Forming Bacteria Sugars
Carbonic Acids Alcohols
Fatty Acids
Amino Acids
Hydrogen Carbon Dioxide Ammonia
Done by Acid Forming Bacteria Carbonic Acids Alcohols
Hydrogen Acetic Acid Carbon Dioxide Hydrogen Carbon Dioxide Ammonia
Done by Methanogens
Hydrogen Acetic Acid Carbon Dioxide
Methane Carbon Dioxide
19
Can occur ahead of the plant
◦ Lift stations ◦ Long retention time in collection system
Industrial wastes
◦ Dairy, pickling, textile dyeing operations
◦ Septage
Treatment Plant
◦ Equalization basins ◦ Primary clarifiers ◦ Sludge processing side-streams ◦ Co thickening WAS sludge can be a common cause 20
Every plant is a little different but in general good target selector ORPs are as follows:
Anaerobic Selector: ballpark -250 mV Anoxic Selector Ballpark -75 mV
21
RAS rate Internal recycle (some plants) D.O. Set-point Microscope
22
24
25
26
Picture from lenntech.com
Note: Discuss ORP control in selector
27
Depending on the amount of incoming VFAs a retention time of 1-3 hours in the anaerobic zone is needed High RAS rates and high influent flows caused by inflow and infiltration can interfere with the necessary retention time and dilute the wastewater where there isn’t the proper ratio of soluble carbon to P 28
Cycling Aeration on/off?
29
• Organic Acids (VFA’s) are needed for enhanced biological nutrient removal • Denitrification • Biological Phosphorus Removal
• To obtain enhanced biological nutrient removal plant must be designed with selector • If VFAs are too high and pass through selector can grow filamentous bacteria and zooglea • >100 mg/L of organic acids is a recognized cause for filamentous bulking
If Overloaded
Selectors
Filamentous Bulking
• Selector should remove 6080% of soluble BOD
32
Nitrate-nitrogen entering the anaerobic zone should be minimal or true anaerobic conditions aren’t possible ◦ Some plants have had success running a lower RAS rate to limit nitrate interference but this is not without risk of creating septic conditions in the clarifier and increased effluent TSS due to maintaining higher sludge blankets ◦ Best are designs that include a zone for denitrification (anoxic) and a separate zone for anaerobic conditions
33
No man’s land
Enough carbon to Create VFAs, but not enough for the PAOs to compete
34
For the PAOs to utilize stored PHA for uptake of phosphorus they need to be able to outcompete other bacteria for food in the aeration basin
Thiothrix II outcompeting PAOs 35
36
PAOs grow slowly but faster than nitrifying bacteria A minimum sludge age of 5 days is recommended. Successful performance has been seen in sludge ages between 5-30 days or more
37
Also decanting aerobic digesters can introduce high P concentrations lowering BOD:P ratio 38
39
Mg/L TSS
10
15
20
25
30
3%P
0.30
0.45
0.60
0.75
0.90
4%P
0.40
0.60
0.80
1.00
1.20
5%P
0.50
0.75
1.00
1.25
1.50
6% P
0.60
0.90
1.20
1.50
1.80
41
42
Phosphorous Limits Summary of Process Terminology Influences Volatile Fatty Acids Reactions in Anaerobic Zone Reactions in Aerobic Zone Hydraulic Retention Time and Sludge Age Sludge Hauling Considerations Effluent TSS Considerations Case Studies Questions
2
Wastewater plants typically remove phosphorous from wastewater due to environmental, public health, or economic concerns With increasingly stringent limits on phosphorous in wastewater discharge enhanced biological phosphorous removal (EBPR) is becoming increasingly common
3
In a conventional activated sludge system microorganisms take up soluble phosphorous as a nutrient to generate new biomass. ◦ These organisms contain about 2% of phosphorous on a dry weight basis.
Polyphosphate accumulating organisms (PAOs) consist of as high as up to 35% phosphorous
◦ By creating an environment to select PAOs more phosphorous can be taken up by the bacteria.
Sludges with high percentage of PAOs can contain up to 6% phosphorous on a dry weight basis
Aracheobacteria (we’ve known about these for a while) store energy as long polymers (up to 60 units) of phosphate Eubacteria (recently discovered) use AGP (Arabinogalactan-peptide) and their P content is a constant 2% (Dr. Michael Richard 2019)
5
Aerobic: a condition in which free and dissolved oxygen are available Anoxic: A condition in which oxygen is only available in combined forms. (nitrate, sulfate) Anaerobic: A condition in which no oxygen free or combined is available
6
PHAs- the intracellular energy storage of polyphosphate accumulating organisms
VFAs are taken up and stored internally as PHAs. PHAs are then used to uptake phosphorus in the aerobic zone
Secondary release: When phosphate is released when it isn’t supposed to be
May occur under anaerobic conditions such as the sludge blanket in the final clarifier
◦ May also occur when there is too much endogeny in the system and nutrients are released with cell lysis (starvation conditions)
7
Advantages ◦ ◦ ◦ ◦
Minimizes need for chemicals Reduces alkalinity loss from chemical addition Reduces extra sludge production from chemical addition Often provides superior settling characteristics due to the selection process which discourages many types of filaments
Disadvantages ◦ Higher capital cost (for baffles, mixers etc.) ◦ Sensitivity to nitrate or oxygen interference in anaerobic zone ◦ More complex operations
8
A two step process in which an anaerobic environment is followed by an aerobic process In the anaerobic selector PAOs release orthophosphate to obtain the energy to uptake readily biodegradable organics (soluble BOD) In the aerobic zone PAOs grow new biomass and take up phosphorus, typically more than they released in the anaerobic zone 9
An influent BOD: ratio of 25:1 or more is recommended An influent COD:P ratio of 45:1 or more is recommended ◦ Actual numbers needed are plant specific
If there is not enough readily available carbon present supplementation may be needed to maintain the desired ORPs in the selector zones ◦ Carbon supplements include high strength waste, acetate, methanol, glucose, and molasses
10
Septicity occurs when bacteria ferment organic matter (BOD) to “smaller pieces” in the absence of free dissolved oxygen ◦ These “smaller pieces” are known as organic acids (or volatile acids) Organic acids/ volatile acids are the needed form of BOD for the bacteria in the selector
12
Reviewing anaerobic treatment is helpful
13
1.Hydrolysis 2.Acidogenesis 3.Acetogenesis 4.Methanogenesis
Egg-shaped gas storage
Performed by bacteria, protozoa, and exocellular enzymes
Carbohydrates
Sugars
Fats
Fatty Acids
Proteins
Amino Acids
Done by Acid Forming Bacteria Sugars
Carbonic Acids Alcohols
Fatty Acids
Amino Acids
Hydrogen Carbon Dioxide Ammonia
Done by Acid Forming Bacteria Carbonic Acids Alcohols
Hydrogen Acetic Acid Carbon Dioxide Hydrogen Carbon Dioxide Ammonia
Done by Methanogens
Hydrogen Acetic Acid Carbon Dioxide
Methane Carbon Dioxide
19
Can occur ahead of the plant
◦ Lift stations ◦ Long retention time in collection system
Industrial wastes
◦ Dairy, pickling, textile dyeing operations
◦ Septage
Treatment Plant
◦ Equalization basins ◦ Primary clarifiers ◦ Sludge processing side-streams ◦ Co thickening WAS sludge can be a common cause 20
Every plant is a little different but in general good target selector ORPs are as follows:
Anaerobic Selector: ballpark -250 mV Anoxic Selector Ballpark -75 mV
21
RAS rate Internal recycle (some plants) D.O. Set-point Microscope
22
24
25
26
Picture from lenntech.com
Note: Discuss ORP control in selector
27
Depending on the amount of incoming VFAs a retention time of 1-3 hours in the anaerobic zone is needed High RAS rates and high influent flows caused by inflow and infiltration can interfere with the necessary retention time and dilute the wastewater where there isn’t the proper ratio of soluble carbon to P 28
Cycling Aeration on/off?
29
• Organic Acids (VFA’s) are needed for enhanced biological nutrient removal • Denitrification • Biological Phosphorus Removal
• To obtain enhanced biological nutrient removal plant must be designed with selector • If VFAs are too high and pass through selector can grow filamentous bacteria and zooglea • >100 mg/L of organic acids is a recognized cause for filamentous bulking
If Overloaded
Selectors
Filamentous Bulking
• Selector should remove 6080% of soluble BOD
32
Nitrate-nitrogen entering the anaerobic zone should be minimal or true anaerobic conditions aren’t possible ◦ Some plants have had success running a lower RAS rate to limit nitrate interference but this is not without risk of creating septic conditions in the clarifier and increased effluent TSS due to maintaining higher sludge blankets ◦ Best are designs that include a zone for denitrification (anoxic) and a separate zone for anaerobic conditions
33
No man’s land
Enough carbon to Create VFAs, but not enough for the PAOs to compete
34
For the PAOs to utilize stored PHA for uptake of phosphorus they need to be able to outcompete other bacteria for food in the aeration basin
Thiothrix II outcompeting PAOs 35
36
PAOs grow slowly but faster than nitrifying bacteria A minimum sludge age of 5 days is recommended. Successful performance has been seen in sludge ages between 5-30 days or more
37
Also decanting aerobic digesters can introduce high P concentrations lowering BOD:P ratio 38
39
Mg/L TSS
10
15
20
25
30
3%P
0.30
0.45
0.60
0.75
0.90
4%P
0.40
0.60
0.80
1.00
1.20
5%P
0.50
0.75
1.00
1.25
1.50
6% P
0.60
0.90
1.20
1.50
1.80
41
42
