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![Page 1: ANAEROBIC SLUDGE DIGESTION PROCESS Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit.](https://reader037.fdocuments.in/reader037/viewer/2022103005/56649dc95503460f94ac00d1/html5/thumbnails/1.jpg)
ANAEROBIC SLUDGE DIGESTION
PROCESS
Prepared ByMichigan Department of Environmental Quality
Operator Training and Certification Unit
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WASTEWATERWASTEWATERWASTEWATERWASTEWATER
Water used to carry waste products away from homes, schools, commercial
establishments, and industrial enterprises.
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Sources of Wastewater
Domestic
Industrial
Infiltration
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CHARACTERISTICS OF WASTEWATERCHARACTERISTICS OF WASTEWATER
Materials Toxic to BiotaMaterials Toxic to BiotaMetalsMetalsAmmoniaAmmoniaPesticidesPesticidesHerbicidesHerbicidesChlorineChlorineAcids/BasesAcids/Bases Human Health HazardsHuman Health Hazards
PathogensPathogensNitrateNitrateToxic MaterialsToxic Materials
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GOAL – PURPOSE – RESPONSIBILITYGOAL – PURPOSE – RESPONSIBILITYOfOf
“ “Treating” or Stabilizing WastewaterTreating” or Stabilizing Wastewater
GOAL – PURPOSE – RESPONSIBILITYGOAL – PURPOSE – RESPONSIBILITYOfOf
“ “Treating” or Stabilizing WastewaterTreating” or Stabilizing Wastewater
PROTECTION OF NATURAL RESOURCESPROTECTION OF NATURAL RESOURCES
PROTECTION OF PUBLIC HEALTHPROTECTION OF PUBLIC HEALTH
PROTECTION OF NATURAL RESOURCESPROTECTION OF NATURAL RESOURCES
PROTECTION OF PUBLIC HEALTHPROTECTION OF PUBLIC HEALTH
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Treatment Concerns
Solids
Oxygen Demand
Microorganisms
Nutrients
CHARACTERISTICS OF WASTEWATERCHARACTERISTICS OF WASTEWATER
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Wastewater “Treatment” Removes These “Pollutants”
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Wastewater Treatment Processes• Physical / Chemical– screening– sedimentation– filtration– precipitation– chemical destruct
• Biological– waste stabilization lagoon– trickling filter– rotating biological contactor– activated sludge
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Treatment EfficienciesTreatment Efficiencies
Primary (Physical) Treatment40 - 60 % Suspended Solids30 - 40 % BOD
Secondary (Biological) Treatment90+ % Suspended Solids90+ % BOD
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Secondary
OrganicInorganic
WastewaterPre
Treatment
RockGritPlasticEtc.
PrimaryClarifier
SettleableSuspendedDissolved
SuspendedDissolved
SecondaryClarifier
Effluent
Sludge Sludge
Removal of These “Pollutants” Produces “Residuals”Often called “Sludge”
Note: These residuals are sometimes called “Biosolids”, however that term is usually reserved for sludge that has been “stabilized” and meets specific requirements (pathogen reduction, vector attractions, metals concentration)
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SLUDGEThe SETTLEABLE solids
separated from liquidsduring processing.
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SLUDGECHARACTERISTICS
•Organic /Inorganic•Oxygen Demand
•Odors•Nutrients•Pathogens
•Mostly Water
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Purpose of ‘Treatment”
•Stabilize Organics•Eliminate Odors•Destroy Pathogens•Reduce Amount of Solids•Enhance De-watering
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Secondary
OrganicInorganic
Wastewater PreTreatment
RockGritPlasticEtc.
PrimaryClarifier
SettleableSuspendedDissolved
SuspendedDissolved
SecondaryClarifier
Effluent
Digester
SludgeSludge
Gas
Digested SludgeRecycled Water(Supernatant)
(Stabilized)
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TYPES of “TREATMENT”
Heat and Pressure Heat and Chemical Lime Stabilization Biological Digestion
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Types of Digestion
Biological
Bacteria
Aerobic
AnaerobicUse “Free” Oxygen
No “Free” Oxygen
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AEROBIC DIGESTION
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AEROBIC DIGESTIONAdvantages
Effective for “secondary” sludgeSimple operationNo hazardous gas production
DisadvantagesHigher operating costsHigh energy demandsNo burnable gasHigher organic content
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ANAEROBIC DIGESTION
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ANAEROBIC DIGESTION
AdvantagesLow operating costsProven effectivenessBurnable gas produced
DisadvantagesLong start-up timeAffected by changes in
loading and conditionsExplosive gas produced
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ANAEROBIC SLUDGE DIGESTION
DIGESTION PROCESS
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Anaerobic DigestionProcess
“TWO-STAGE” ProcessOR
“Two Phase” Process
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Anaerobic DigestionProcess
“TWO-STAGE” Process
This Does Not Mean Two Tanks
Process
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Anaerobic DigestionProcess
“TWO-STAGE” ProcessOR
“Two Phase” ProcessTwo Types of Bacteria
Each Relying On The Other
First Stage Second Stage
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Anaerobic DigestionProcess
First Organic Material Changed
By Acid Forming Bacteria
To Simple Organic Material
OrganicMatter Bacteria
OrganicAcids
First Stage
+
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Anaerobic DigestionProcess
First Organic Material Changed
By Acid Forming Bacteria
To Simple Organic Material
OrganicAcids
Also CalledVolatileAcids
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Anaerobic DigestionProcess
SecondMethane-Forming Bacteria
Use Organic Acids
Produce Carbon Dioxide and Methane
OrganicAcids + Bacteria
CH4
+CO2
Second Stage
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Anaerobic DigestionProcess
Continuous Process“TWO-STAGE” Process
StabilizationStabilization
OrganicMatter Bacteria
OrganicAcids
First Stage
Acid Forming
BacteriaCH4
+CO2
Methane Forming
Second Stage
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Type of FoodType of Food
Organic Inorganic
Soluble Insoluble
Anaerobic DigestionProcess
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Soluble Organics
CellMembrane
Acids
AdsorbedParticle
Enzymes
(Absorption)
Typical Acid Forming Bacteria
Liquid
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Not All Organic Material Broken Down
Type of FoodType of Food
Poor FoodInert Solids
- Not Readily Degradable- Plastics, etc.
40 to 60 % of Organics are Reduced40 to 60 % of Organics are Reduced
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Anaerobic DigestionProcess
“TWO-STAGE” ProcessOR
“Two Phase” ProcessTwo Types of Bacteria
Each Relying On The Other
Must Be InMust Be InBalance !Balance !
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OrganicMatter Bacteria
OrganicAcids
First Stage
Acid Forming
BacteriaCH4
+CO2
Methane Forming
Second Stage
Anaerobic DigestionProcess
VolatileAcidsAcid PhaseAcid Phase
Acids Used at Rate Produced
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Start-upUpset
“Sour”“Stuck”
Anaerobic DigestionProcess
Acids Used at Rate ProducedIf Not Used - Drop in pH
Methane Formers Must Be Active
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Anaerobic DigestionProcess
Methane Formers:Slow GrowersVery Sensitive to Changes
LoadingpHTemperature
Digester Operation Depends On MaintainingProper Environment forMETHANE FORMERS
BALANCE !BALANCE !
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Anaerobic DigestionProcess
Products of Digestion1. Gases
Methane (CH4)Carbon Dioxide (CO2)
65 to 70 %30 to 35 %
7 to 12 cubic feet per pound of volatile destroyed
500 to 600 BTU per cubic foot
Can Be Utilized:Heating DigesterHeating BuildingsRunning EnginesElectrical Power
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Anaerobic DigestionProcess
Products of Digestion
2. ScumLighter Solids
Floating from Gas EntrapmentBuilds Up If MIXING Is Inadequate
Not Digested ( Separated from Bacteria)Reduces Digester CapacityPlugs PipingPlugs Vents and Flame Traps
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Anaerobic DigestionProcess
Products of Digestion3. Supernatant
Liquid That Leaves Digester
Two Sources of Water In Digester:Water Pumped InWater Formed During Digestion
Recycled Through Treatment PlantHigh In:
SolidsBODAmmonia
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Anaerobic DigestionProcess
Products of Digestion3. Supernatant
Liquid That Leaves Digester
Should Be RemovedFrequently
inSmall Quantities
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Anaerobic DigestionProcess
Products of Digestion4. Digested Sludge
“Stabilized”
Final Product
Inorganic SolidsVolatile (Organic) Solids - Not Easily Digested
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Well Digested SludgeCharacteristics
1. Less Solids
2. Lumpy Appearance
3. Black
4. Less Objectionable Odor
5. Volatile Content Reduced
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Anaerobic DigestionProcess
Products of Digestion
1. GasesMethane (CH4)Carbon Dioxide (CO2)
2. ScumLighter Solids
3. SupernatantLiquid Removed
4. Digested Sludge“Stabilized”
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TYPICAL “Two-Stage”ANAEROBIC DIGESTER SYSTEM
TransferPump
TransferPump
HeatExchanger
HeatExchanger
HotWaterHot
Water
Gas Gas
RecirculationPump
RecirculationPump
Note: Two-Stage System here refers to two separate tanks (One for the treatment process and one for water-solids separation)
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Digestion Factors
1.Bacteria2. Food3. Loading4. Contact5. Environment
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Digestion Factors
1. BACTERIA
Naturally OccurringMust Have EnoughLiving OrganismsTwo Different TypesBALANCE
The Other Factors –Important Because They Affect the Bacteria
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Digestion Factors
1. BACTERIABalance
2. FOODVolatile Solids
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Not All Organic Material Broken Down
Type of FoodType of Food
Poor FoodInert Solids
- Not Readily Degradable- Plastics, etc.
40 to 60 % of Organics are Reduced40 to 60 % of Organics are Reduced
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Digestion Factors
1. BACTERIABalance
2. FOOD
Not All Volatile MaterialNone of the Inorganic
Volatile Solids
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Digestion Factors
1. BACTERIABalance
2. FOOD
3. LOADING
Volatile Solids
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Digestion Factors
3. LOADING
AMOUNTAMOUNTApplied to the Treatment Process
Related to the SIZE of the System
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Digestion Factors
1. BACTERIABalance
2. FOOD
3. LOADING
Volatile Solids
Amount and Type Concentration of Sludge (% Total Solids) Amount Usable in Sludge (%Volatile) Amount (pounds) of Volatile per Volume Available Volume (gallons) of Sludge per Volume Available
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Digestion Factors
1. BACTERIABalance
2. FOOD
3. LOADING
4. CONTACT
Volatile Solids
Amount and Type
Mixing
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Digestion Factors
1. CONTACTBacteria and Food
2. HEAT DISTRIBUTION
3. MINIMIZE SETTLING
4. MINIMIZE SCUM
Even Throughout
Reduces Available Volume
Operational Problems
MIXING
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Digestion Factors
1. CONTACT2. HEAT DISTRIBUTION3. MINIMIZE SETTLING4. MINIMIZE SCUM
Maximize Digestion Efficiency
MIXING
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Digestion Factors
1. BACTERIABalance
2. FOOD
3. LOADING
4. CONTACT
5. ENVIRONMENT
Volatile Solids
Amount and Type
Mixing
Happy Bugs
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Digestion FactorsENVIRONMENT
Methane Forming BacteriaAre
Very Sensitive to ConditionsIn the
Digester
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Digestion Factors
1. ANAEROBIC
2. TEMPERTURE
ENVIRONMENT
No Oxygen
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Temperature controls activity of bacteria.Temperature controls activity of bacteria.
Psychrophilic50 F to 68 F
Mesophilic68 F to 113 FBest 85 F to 100 F
ThermophilicAbove 113 F Best 120 F to 135 F
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Temperature controls activity of bacteria.Temperature controls activity of bacteria.
Mesophilic68 F to 113 FBest 85 F to 100 F
Mesophilic68 F to 113 FBest 85 F to 100 F
Within the Range, the Bacteria areWithin the Range, the Bacteria areVery Sensitive to Temperature CHANGEVery Sensitive to Temperature CHANGE
Most Anaerobic Digesters Are Operated in the Mesophilic Range
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Temperature controls activity of bacteria.Temperature controls activity of bacteria.
Mesophilic68 F to 113 FBest 85 F to 100 F
Mesophilic68 F to 113 FBest 85 F to 100 F
Temperature Should Not Be Allowed toTemperature Should Not Be Allowed toCHANGECHANGE
by More Than 1 Degree per Dayby More Than 1 Degree per Day
(After Start-up)
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Digestion Factors
1. ANAEROBIC
2. TEMPERTURE
3. pH
4. VOLATILE ACIDS
Mesophilic - Constant
Best - 6.8 to 7.2
ENVIRONMENT
5. BUFFERS (Alkalinity)Incoming Sludge and Created
No Oxygen
Not Excessive
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Digestion Factors
1. ANAEROBIC
2. TEMPERTURE
3. pH
4. VOLATILE ACIDS
Mesophilic - Constant
Best - 6.8 to 7.2
ENVIRONMENT
5. BUFFERS (Alkalinity)Incoming Sludge and Created
No Oxygen
Not Excessive
ACID Production INCREASEDOR
ALKALINITY DECREASED
Sudden ChangesToxic Materials
Start-up
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Digestion Factors
1. ANAEROBIC
2. TEMPERTURE
3. pH
4. VOLATILE ACIDS
Mesophilic - Constant
Best - 6.8 to 7.2
ENVIRONMENT
5. BUFFERS (Alkalinity)
6. TOXIC MATERIALS
Incoming Sludge and Created
No Oxygen
Not Excessive
Inhibit Biological Activity
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OPERATION AND CONTROL
BALANCE !Maintaining Suitable Conditions
Maintaining Definite Ranges and Ratios
Organic (Solids) LoadingAlkalinity
Volatile AcidsTemperature
Mixing
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Digestion Factors
1. BACTERIA
2. FOOD
3. LOADING
4. CONTACT
5. ENVIRONMENT
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OPERATION AND CONTROL
1. BACTERIAMaintain Adequate Quantity
Don’t Remove Too MuchDon’t Displace Too MuchPlan For Re-Start
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OPERATION AND CONTROL
2. FOODMinimize Amount of Inorganics Entering
Eliminate Toxic Material
Industrial DischargesGrit Systems
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OPERATION AND CONTROL
3. LOADING
AMOUNTAMOUNTApplied to the Treatment Process
Related to the SIZE of the System
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3. LOADINGAMOUNTAMOUNT
Applied to the Treatment Process
Related to the SIZE of the System
For An Anaerobic Digestion System – The SIZE Is The VOLUME
Available for Digestion
(Volume - Cubic Feet OR Gallons)
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Calculationof
DigesterVolume
?
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h1
Volumecylinder =
r2h1
h2
Volumecone =
⅓ r2h2
r
r
Cylinder
Cone
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Digester Volume Example Problem
The diameter of a digester is 54 feet.The side water depth (SWD) is 22 feet.The cone depth is 12 feet.Calculate the volume in cubic feet and gallons.
Volumecylinder = r2h1
= 3.14 X 27 ft X 27 ft 22 ftX
= 50,360 ft3
Volumecone = ⅓ r2h2
= ⅓ X 3.14 X 27 ft X 27 ft X 12 ft
= 9,156 ft3
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Digester Volume Example Problem
Total Volume
= 50,360 ft3 + 9,156 ft3
= 59,516 ft3
Total Volume (gallons) =
cubic feet X 7.48 gal/ft3
= 59,516 ft3 X 7.48 gal/ft3
= 445,180 gallons
= Volumecylinder + Volumecone
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Digester Volume Practice Problems
The diameter of a digester is 50 feet.The side water depth (SWD) is 20 feet.The cone depth is 10 feet.Calculate the volume in cubic feet and gallons.
Work Calculations on Separate PaperAnswers Given on Next Slides
1.
2. Calculate the volume in gallons of a digester 35 feet in diameter, 12 feet SWD and a cone depth of 6 feet.
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Digester Volume Practice Problem
The diameter of a digester is 50 feet.The side water depth (SWD) is 20 feet.The cone depth is 10 feet.Calculate the volume in cubic feet and gallons.
Volumecylinder = r2h1
= 3.14 X 25 ft X 25 ft 20 ftX
= 39,250 ft3
Volumecone = ⅓ r2h2
= ⅓ X 3.14 X 25 ft X 25 ft X 10 ft
= 6,542 ft3
1.
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Digester Volume Practice Problems
The diameter of a digester is 50 feet.The side water depth (SWD) is 20 feet.The cone depth is 10 feet.Calculate the volume in cubic feet and gallons.
1.
Total Volume = Volumecylinder + Volumecone
= 39,250 ft3 + 6,542 ft3
= 45,792 ft3
Total Volume (gallons) = cubic feet X 7.48 gal/ft3
= 45,792 ft3 X 7.48 gal/ft3
= 342,524 gallons
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Digester Volume Practice Problems
2. Calculate the volume in gallons of a digester 35 feet in diameter, 12 feet SWD and a cone depth of 6 feet.
Volumecylinder = r2h1
= 3.14 X 17.5 ftX 17.5 ft 12 ftX
= 11,539.5 ft3
Volumecone = ⅓ r2h2
= ⅓X 3.14 X 17.5 ft X 17.5 ft X 6 ft
= 1,923 ft3
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Digester Volume Practice Problems
Total Volume = Volumecyl + Volumecone
= 11,539.5 ft3 +1,923 ft3
= 13,462.5 ft3
Total Volume (gallons) = cubic feet X 7.48 gal/ft3
= 13,462.5 ft3 X 7.48 gal/ft3
= 100,700 gallons
2. Calculate the volume in gallons of a digester 35 feet in diameter, 12 feet SWD and a cone depth of 6 feet.
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“LOADING” Amount Applied to the Treatment
ProcessRelated to the SIZE of the System
Hydraulic LoadingAmount of Sludge Added
Volume (gallons)
Organic LoadingAmount of VOLATILE Solids added
Weight (pounds)
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Digester Hydraulic Loading
AVERAGE TIME(in Days)
that the liquid stays in the digester
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Digester Hydraulic Loading
AVERAGE TIME (in Days) that the liquid stays in the digester
Proper DigestionConvert SolidsAcids to Gas
Minimum Time Required:
VariesDigester EfficiencyType of Waste
Holding Time Increased by Thickening
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Digester Hydraulic Loading
Digester VolumeFeed Volume
Gallons
Hydraulic Loading =
Hydraulic Loading =Gallons/Day
AVERAGE TIME(in Days)
that the liquid stays in the digester
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Detention TimeDetention Time
EXAMPLEAt an average pumping rate of 4,000 gallons per day into a
140,000 gallon digester, the detention time would be:
Detention Time
GallonsGallons / Day)
=140,000 gallons
4,000 gallons/day
= 35 Days
DET. TIME (Days) =
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Detention Time Practice Problems
1. Calculate the Detention Time for a 120,000 gallon digester that receives 3,200 gallons of sludge per day.
2. Calculate the Detention Time for a 260,000 gallon digester that receives 7,200 gallons of sludge per day.
3. Calculate the Detention Time for a 12,000 cubic foot digester that receives 2,500 gallons of sludge per day.
Work Calculations on Separate PaperAnswers Given on Next Slides
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Detention Time Practice Problems
1. Calculate the Detention Time for a 120,000 gallon digester that receives 3,200 gallons of sludge per day.
Detention Time =Digester Volume (Gal)
Pumping Rate (Gal/Day)
=120,000 gallons
3,200 gallons/day
= 37.5 Days
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Detention Time Practice Problems
2. Calculate the Detention Time for a 260,000 gallon digester that receives 7,200 gallons of sludge per day.
Detention Time =Digester Volume (Gal)
Pumping Rate (Gal/Day)
=260,000 gallons
7,200 gallons/day
= 36.1 Days
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Detention Time Practice Problems
Detention Time =Digester Volume (Gal)
Pumping Rate (Gal/Day)
=12,000 ft3
2,500 gallons/day
= 35.9 Days
X 7.48 gal/ft3
= 89,760 gallons2,500 gal/day
3. Calculate the Detention Time for a 12,000 cubic foot digester that receives 2,500 gallons of sludge per day.
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“LOADING” Amount Applied to the Treatment
ProcessRelated to the SIZE of the System
Hydraulic LoadingAmount of Sludge Added
Volume (gallons)
Detention TimeDetention Time
Digester VolumeFeed Volume
GallonsGallons/Day
OROR
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“LOADING” Amount Applied to the Treatment
ProcessRelated to the SIZE of the System
Hydraulic LoadingAmount of Sludge Added
Volume (gallons)
Organic LoadingAmount of VOLATILE Solids added
Weight (pounds)
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PERCENT TOTAL SOLIDS
Outline of Solids Analysis Procedure
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SLUDGE SOLIDS PROCEDUREEvaporating Dish Preparation
Ignite Cool Weigh
WeighAdd
Sample
Total Solids Analysis
CoolWeigh
DryEvaporate
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Percent Total SolidsPercent Total Solids
% = Amount in Question Total Amount Possible
X 100%
% Total Solids = Wt. Of (Dry) SolidsWt. Of (Wet) Sample
X 100%
% Total Solids = Dry Wet
X 100%
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SLUDGE SOLIDS PROCEDUREEvaporating Dish Preparation
Ignite Cool Weigh
WeighAdd
Sample
Total Solids Analysis
CoolWeigh
DryEvaporate
Volatile Solids Analysis
Ignite Cool Weigh
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Percent Volatile SolidsPercent Volatile Solids
% = Amount in Question Total Amount Possible
X 100%
% Volatile Solids = Wt. Of Volatile SolidsWt. Of Dry Solids
X 100%
% Volatile Solids = Dry - Ash X 100%Dry
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SLUDGE SOLIDS DIAGRAM
Sludge
Solids6%
94%Water
100 #
6 #
94 #
TOTALSOLIDS
6 #
ASH
VOLATILE70 %
30 %
4.2 #
1.8 #
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TYPICAL RESULTS OF THE DIGESTION PROCESS
BEFORE DIGESTION100,000 Lbs. RAW SLUDGE
75%VOLATILE
25%FIXED
50%VOLATILE
50%FIXED
75,000 Lbs.
25,000 Lbs.
25,000 Lbs.
50,000 Lbs.
DIGESTION CONVERTSVOLATILES TO
CH4, CO2, AND H2O
REMAININGDIGESTED SLUDGE
25,000 Lbs.
AFTER DIGESTIONCH4, CO2, H2O
(Dry Weight)
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“LOADING” Amount Applied to the Treatment
ProcessRelated to the SIZE of the System
Organic LoadingAmount of VOLATILE Solids added
Weight (pounds)
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SLUDGESLUDGEPOUNDSPOUNDS
CALCULATIONSCALCULATIONS
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SLUDGE POUNDS CALCULATIONS
Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 8,000 GALLONSSOLIDS CONCENTRATION 4.2%VOLATILE SOLIDS 82%
LBS DRY SOLIDS =
GALS WET X 8.34 LBSGAL X % SOLIDS
= 8,000 GAL X 8.34 LBSGAL X 4.2
100
= 8,000 X 8.34 X 0.042
= 2,802 POUNDS DRY SOLIDS
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SLUDGE POUNDS CALCULATIONS
Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 8,000 GALLONSSOLIDS CONCENTRATION 4.2%VOLATILE SOLIDS 82%
LBS VOLATILE SOLIDS =
LBS DRY SOLIDS X % VOLATILE SOLIDS
= 2,802 LBS DRY SOLIDS X 82100
= 2,802 X 0.82
= 2,298 POUNDS VOLATILE SOLIDS
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SLUDGE POUNDS CALCULATIONS
1. Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 7,500 GALLONSSOLIDS CONCENTRATION 3.6%VOLATILE SOLIDS 78%
2. Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 6,000 GALLONSSOLIDS CONCENTRATION 3.0%VOLATILE SOLIDS 73%
Work Calculations on Separate PaperAnswers Given on Next Slides
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SLUDGE POUNDS CALCULATIONS
1. Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 7,500 GALLONSSOLIDS CONCENTRATION 3.6%VOLATILE SOLIDS 78%
LBS DRY SOLIDS =
GALS WET X 8.34 LBSGAL X % SOLIDS
= 7,500 GAL X 8.34 LBSGAL X 3.6
100
= 7,500 X 8.34 X 0.036
= 2,252 POUNDS DRY SOLIDS
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SLUDGE POUNDS CALCULATIONS
1. Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 7,500 GALLONSSOLIDS CONCENTRATION 3.6%VOLATILE SOLIDS 78%
LBS VOLATILE SOLIDS =
LBS DRY SOLIDS X % VOLATILE SOLIDS
= 2,252 LBS DRY SOLIDS X 78100
= 2,252 X 0.78
= 1,756.6 POUNDS VOLATILE SOLIDS
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SLUDGE POUNDS CALCULATIONS2. Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 6,000 GALLONSSOLIDS CONCENTRATION 3.0%VOLATILE SOLIDS 73%
LBS DRY SOLIDS =
GALS WET X 8.34 LBSGAL X % SOLIDS
= 6,000 GAL X 8.34 LBSGAL X 3.0
100
= 6,000 X 8.34 X 0.030
= 1501 POUNDS DRY SOLIDS
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SLUDGE POUNDS CALCULATIONS2. Given the following information, calculate the pounds of dry solids and the pounds of volatile solids:
VOLUME OF SLUDGE 6,000 GALLONSSOLIDS CONCENTRATION 3.0%VOLATILE SOLIDS 73%
LBS VOLATILE SOLIDS =
LBS DRY SOLIDS X % VOLATILE SOLIDS
= 1,501 LBS DRY SOLIDS X 73100
= 1,501 X 0.73
= 1,095.7 POUNDS VOLATILE SOLIDS
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ORGANICORGANICLOADINGLOADING
CALCULATIONSCALCULATIONS
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Organic (Solids) Loading Rate
Amount of Volatile Solids Added per DayCompared to the Size (volume) of the Digester
Pounds of Volatile Solids per Day per Cubic Foot0.02 to 0.10 # Vol. Solids/Day/Ft3
Sometimes asPounds of Volatile Solids per Day per 1000 Cubic Feet
20 to 100 # Vol. Solids/Day/1000Ft3
Organic Loading Rate Amount of V.S.Volume of Digester=
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Digester Organic Loading
AMOUNT of Organic Solids added to a digester
related to the SIZE
of the digester.
Amount of Organic SolidsDigester Volume
Volatile Solids, pounds /day
O.L. =
O.L. =Digester Volume, cubic feet
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Digester Organic LoadingData:
Digester Volume = 30,000 ft3
Raw sludge pumped = 9,000 gal/dayRaw sludge solids concentration = 4.0 %Raw sludge volatile solids = 70.0 %
Calculate the organic loading into the digester in lbs of volatile solids per day per ft3.
LBS VOLATILE SOLIDS =
GAL PUMPED X 8.34 lbs/gal X % Solids (decimal) X % Volatile (decimal)
= 9,000 gal/day X 8.34 lbs/gal X 0.04 x 0.70
= 2,102 lbs/day
ORGANIC LOADING =2,102 lbs/day
30,000 ft3
= 0.07 lbs/day/ft3
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Digester Organic Loading
1. Data:Digester Volume = 21,500 ft3
Raw sludge pumped = 5,500 gal/dayRaw sludge solids concentration = 3.1 %Raw sludge volatile solids = 76 %
Calculate the organic loading into the digester in lbs of volatile solid per day per ft3.
Practice Problems
2. Data:Digester Volume = 11,000 ft3
Raw sludge pumped = 4,600 gal/dayRaw sludge solids concentration = 3.5 %Raw sludge volatile solids = 74 %
Calculate the organic loading into the digester in lbs of volatile solid per day per ft3.
Work Calculations on Separate PaperAnswers Given on Next Slides
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Digester Organic Loading
1. Data:Digester Volume = 21,500 ft3
Raw sludge pumped = 5,500 gal/dayRaw sludge solids concentration = 3.1 %Raw sludge volatile solids = 76 %
Calculate the organic loading into the digester in lbs of volatile solid per day per ft3.
LBS VOLATILE SOLIDS =
GAL PUMPED X 8.34 lbs/gal X % Solids (decimal) X % Volatile (decimal)
= 5,500 gal/day X 8.34 lbs/gal X 0.031 x 0.76
= 1,080.7 lbs/day
ORGANIC LOADING =1,080.7 lbs/day
21,500 ft3
= 0.050 lbs/day/ft3
Practice Problems
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Digester Organic Loading
2. Data:Digester Volume = 11,000 ft3
Raw sludge pumped = 4,600 gal/dayRaw sludge solids concentration = 3.5 %Raw sludge volatile solids = 74 %
Calculate the organic loading into the digester in lbs of volatile solid per day per ft3.
LBS VOLATILE SOLIDS =
GAL PUMPED X 8.34 lbs/gal X % Solids (decimal) X % Volatile (decimal)
= 4,600 gal/day X 8.34 lbs/gal X 0.035 x 0.74
= 993.6 lbs/day
ORGANIC LOADING =993.6 lbs/day
11,000 ft3
= 0.090 lbs/day/ft3
Practice Problems
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Organic (Solids) Loading Rate
Amount of Volatile Solids Added per DayCompared to the Size (volume) of the Digester
Pounds of Volatile Solids per Day per Cubic Foot0.02 to 0.10 # Vol. Solids/Day/Ft3
Sometimes asPounds of Volatile Solids per Day per 1000 Cubic Feet
20 to 100 # Vol. Solids/Day/1000Ft3
Organic Loading Rate Amount of V.S.Volume of Digester
(page 28)
=
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OPERATION AND CONTROL
3. LOADINGPump Thick Sludge
(High % Total Solids)
Pump Several Times per DayUniform Digester LoadingUniform Plant Operations
Excess Water Requires More HeatExcess Water Reduces Holding TimeExcess Water Removes Bacteria and Buffers
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OPERATION AND CONTROL
3. LOADING% Total Solids
% Total Volatile SolidsOrganic (Solids) Loading
Hydraulic Loading
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OPERATION AND CONTROL
1. BACTERIA
2. FOOD
3. LOADING4. CONTACT
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1. CONTACTBacteria and Food
2. HEAT DISTRIBUTION
3. MINIMIZE SETTLING
4. MINIMIZE SCUM
Even Throughout
Reduces Available Volume
Operational Problems
CONTACT (MIXING)
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OPERATION AND CONTROL
1. BACTERIA
2. FOOD
3. LOADING4. CONTACT
5. ENVIRONMENT
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Temperature controls activity of bacteria.Temperature controls activity of bacteria.
Psychrophilic50 F to 68 F
Mesophilic68 F to 113 FBest 85 F to 100 F
Mesophilic68 F to 113 FBest 85 F to 100 F
ThermophilicAbove 113 F Best 120 F to 135 F
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OPERATION AND CONTROL
ENVIRONMENTTemperature Control
90 to 950 F
Methane Formers Very Sensitive to ChangesChanges
Good Mixing Essential
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SUMMARYSUMMARY
First Stage Second Stage
BalanceBalance
Poor MixingPoor MixingOver LoadingOver LoadingExcess WaterExcess WaterTemperatureTemperature
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SUMMARYSUMMARY
First Stage Second Stage
BalanceBalance
Poor MixingPoor MixingOver LoadingOver LoadingExcess WaterExcess WaterTemperatureTemperature
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OPERATION AND CONTROL
ENVIRONMENTVolatile Acid/Alkalinity Relationship
RatioVolatile Acids, mg/L
Alkalinity, mg/L
140 mg/L2,800 mg/L
= 0.05
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I. Relationship of Volatile Acids to Alkalinity
TimeTime
AlkalinityAlkalinity
Volatile AcidsVolatile Acids
mg/L
2000
1000600200
Graph of Digester With Good Buffering Capacity ( Low V.A. at 200 mg/L Compared to Alk. of 2000 mg/L)
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I. Relationship of Volatile Acids to Alkalinity
TimeTime
AlkalinityAlkalinity
Volatile AcidsVolatile Acids
mg/L
2000
1000600200
A B C
At Time A Something has Happened to Cause the Volatile Acids to Increase
Followed by a Decrease in Alkalinity at Time B
At Time C the Digester has Become Sour
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II. Volatile Acids / Alkalinity Ratio
VA/ALK RATIOVA/ALK RATIO
1.41.21.00.80.60.40.2
0
TimeTime
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Comparing Graph I to Graph II
TimeTime
AlkalinityAlkalinity
Volatile AcidsVolatile Acids
mg/L
2000
1000600200
A B C
VA/ALK RATIOVA/ALK RATIO
1.41.21.00.80.60.40.2
0
BRatioRatio0.30.3RatioRatio
0.10.1 At Time B Measurable
Change in Ratio
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%100 90 80 70 60 50 40 30 20
III. Relationship of Methane and Carbon Dioxide
TimeTime
CHCH44
COCO22
SludgeFeed
At 44% COAt 44% CO22
Will Not BurnWill Not Burn
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TimeTime
AlkalinityAlkalinity
Volatile AcidsVolatile Acids
mg/L
2000
1000600200
A B C
B
%100 90 80 70 60 50 40 30 20
CHCH44
COCO22
At Time BNo Change
Comparing Graph I to Graph III
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VA/ALK RATIOVA/ALK RATIO
1.41.21.00.80.60.40.2
0
%100 90 80 70 60 50 40 30 20
CHCH44
COCO22
Change At0.5
TimeTime
BNo Change
At 0.3
Comparing Graph II to Graph III
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IV. Relationship of pH Change
7.0
6.8
6.4
TimeTime
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TimeTime
AlkalinityAlkalinity
Volatile AcidsVolatile Acids
mg/L
2000
1000600200
A B C
At Time BNo Change7.0
6.8
6.4 pH
Comparing Graph I to Graph IV
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VA/ALK RATIOVA/ALK RATIO
1.41.21.00.80.60.40.2
0 Change At0.8
TimeTime
BNo Change
At 0.3
7.0
6.8
6.4
No ChangeAt 0.5
pH
Comparing Graph II to Graph IV
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OPERATION AND CONTROL
ENVIRONMENTOrder of Measurable Changes When A
Digester is BECOMING Upset
1. An Increase in VA/Alk. Ratio
2. An Increase in % CO2
3. Inability of Digester Gas to Burn
4. A Decrease in pH
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Volatile Acid/Alkalinity Ratio
First Measurable Change
Volatile Acids - Low Compared to Alkalinity
Best Operation - Ratio Below 0.4
OPERATION AND CONTROL
ENVIRONMENT
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Response To Increase
Extend Mixing TimeHeat More Evenly
Decrease Sludge Withdrawal RateReturn Sludge From Secondary Digester
*Add Alkalinity (Bicarbonate)
Volatile Acid/Alkalinity Ratio
OPERATION AND CONTROL
ENVIRONMENT
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VOLATILE ACIDS AND TOTAL ALKALINITY
Outline of Procedure
1. SeparateSolids
2. Measure50 mL
3. Titrate to pH 4.0
4. Record mL used, Then Titrate to pH 3.3
5. Lightly Boil Sample 3 Min. 6. Cool in
Water Bath
7. Titrate from pH 4.0 to 7.0
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Digester Efficiency
ReductionOf
Volatile Solids
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% Reduction of Volatile Solids
% Reduction of Volatile Solids =
%Volatiles In - % Volatiles Out X 100%% Volatile In - ( % Volatile In X % Volatile Out)
NOTE: % Must be as Decimals
72% = 72/100 = .72
% Reduction of Volatile Solids =
In - OutIn - OutIn - (In X Out)In - (In X Out) X 100 %X 100 %
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% Reduction of Volatile Solids
% Reduction of Volatile Solids =
%Volatiles In - % Volatiles Out X 100%% Volatile In - ( % Volatile In X % Volatile Out)
EXAMPLE:
Volatile Solids in Raw Sludge = 68%Volatile Solids in Digested Sludge = 45%
% Reduction of Volatile Solids =
0.68 – 0.450.68 – (0.68 X 0.45) X 100%
0.68 – 0.450.68 – 0.31 X 100% = 0.23
0.37X 100%
= 62%
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1. Calculate the percent reduction of volatile solids in a digester withthe following data:
73%Vol. Solids in the raw sludge51%Vol. Solids in the digested sludge
2. Calculate the percent reduction of volatile solids in a digester withthe following data:
73.4%Vol. Solids in the raw sludge50.5%Vol. Solids in the digested sludge
Work Calculations on Separate PaperAnswers Given on Next Slides
% Reduction of Volatile Solids
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1. Calculate the percent reduction of volatile solids in a digester withthe following data:
73%Vol. Solids in the raw sludge51%Vol. Solids in the digested sludge
% Reduction of Volatile Solids =
In - OutIn - (In X Out) X 100 %
=.73 - .51
.73 - ( .73 X .51)
=.73 - .51
.73 - .372
X 100 %
X 100 %
=.22
.358X 100 % = 61.5 %
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2. Calculate the percent reduction of volatile solids in a digester withthe following data:
73.4%Vol. Solids in the raw sludge50.5%Vol. Solids in the digested sludge
% Reduction of Volatile Solids =
In - OutIn - (In X Out) X 100 %
=.734 - .505
.734 - ( .734 X .505)
=.734 - .505
.734 - .371
X 100 %
X 100 %
=.229.363
X 100 % = 63.1 %
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Gas Production
Digesters ProduceMethane and Carbon Dioxide
Normal: 25% to 35% CO2 by Volume
As the Bacteria Break Downthe Volatile Organics
CHANGE - Indicator of Conditions
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Gas Production
Digesters ProduceMethane and Carbon Dioxide
Normal: 65% to 70% Methane by Volume
Burns: > 56% Methane
Usable as Fuel: > 62% Methane
Can Be Used To:Heat the DigesterPower EnginesHeat Buildings
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Gas Production
Digesters ProduceMethane and Carbon Dioxide
Digesters ProduceMethane and Carbon Dioxide
Normal: 65% to 70% Methane by Volume
Burns: > 56% Methane
Usable as Fuel: > 62% Methane
Healthy Digester Should Produce:7 to 12 cubic feet/pound vol. solids Destroyed
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GAS PRODUCTION CALCULATIONData:
Raw sludge pumped in per day = 9,000 gallons Raw sludge solids concentration = 4%Raw sludge volatile solids = 65%% Volatile Solids Reduction = 48%Gas production per day = 8,000 ft3
LBS VOLATILE SOLIDS =
GAL PUMPED X 8.34 lbs/gal X % Solids (decimal) X % Volatile (decimal)
= 9,000 gal/day X 8.34 lbs/gal X 0.04 x 0.65
= 1,951.6 lbs/day
1,951.6 lbs X .48 = 937 lbs Vol. Solids Destroyed
48% of the Volatile Solids were Destroyed
What is the gas production in terms of cubic feet per pound of volatile solids destroyed?
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GAS PRODUCTION CALCULATIONData:
Raw sludge pumped in per day = 9,000 gallons Raw sludge solids concentration = 4%Raw sludge volatile solids = 65%% Volatile Solids Reduction = 48%Gas production per day = 8,000 ft3
What is the gas production in terms of cubic feet per pound of volatile solids destroyed?
937 lbs Vol. Solids Destroyed
Gas Production, cu.ft. / lb vol. solids Destroyed =
8,000 cu. ft.
= 8.5 cu ft / lb vol. solids destroyed
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GAS PRODUCTION 1. Data:
Raw sludge pumped in per day = 7,200 gallons Raw sludge solids concentration = 4%Raw sludge volatile solids = 67%% Volatile Solids Reduction = 53%Gas production per day = 7,850 ft3
What is the gas production in terms of cubic feet per pound of volatile solids destroyed?
2. Data:Raw sludge pumped in per day = 2,300 gallons Raw sludge solids concentration = 3.4%Raw sludge volatile solids = 72.6%% Volatile Solids Reduction = 49.3%Gas production per day = 2,800 ft3
What is the gas production in terms of cubic feet per pound of volatile solids destroyed?
Work Calculations on Separate PaperAnswers Given on Next Slides
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GAS PRODUCTION
1. Data:Raw sludge pumped in per day = 7,200 gallons Raw sludge solids concentration = 4%Raw sludge volatile solids = 67%% Volatile Solids Reduction = 53%Gas production per day = 7,850 ft3
What is the gas production in terms of cubic feet per pound of volatile solids destroyed?
Gas Production, cu.ft. / lb vol. solids Destroyed =Cubic Feet Gas
% Vol. Slds. Destroyed (decimal) X Lbs. Vol. Slds. InLbs. Vol. Solids Destroyed
=7,850 ft3
7,200 gal/day X 8.34 lbs/gal X 0.04 x 0.67.53 X Lbs. Vol. Solids In
=7,850 ft3
852.9 # Vol. Slds. Destroyed= 9.2 ft3/Lb. Vol. Slds. Destroyed
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GAS PRODUCTION
2. Data:Raw sludge pumped in per day = 2,300 gallons Raw sludge solids concentration = 3.4%Raw sludge volatile solids = 72.6%% Volatile Solids Reduction = 49.3%Gas production per day = 2,800 ft3
What is the gas production in terms of cubic feet per pound of volatile solids destroyed?
Gas Production, cu.ft. / lb vol. solids Destroyed =Cubic Feet Gas
% Vol. Slds. Destroyed (decimal) X Lbs. Vol. Slds. In
=2,800 ft3
.493 X 2,300 gal/day X 8.34 lbs/gal X 0.034 x 0.726
=2,800 ft3
233.4 # Vol. Slds. Destroyed= 12.0 ft3/Lb. Vol. Slds. Destroyed
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Anaerobic DigestionProcess
Methane Formers:Slow GrowersVery Sensitive to Changes
LoadingpHTemperature
Digester Operation Depends On MaintainingProper Environment forMETHANE FORMERS
BALANCE !BALANCE !
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ANAEROBIC SLUDGE DIGESTION
PROCESS
Prepared ByMichigan Department of Environmental Quality
Operator Training and Certification Unit