energy conservation using aerated anoxic technology

8/12/2019 Energy Conservation Using Aerated Anoxic Technology

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Page 1 Water Technologies

Energy Conservation usingAerated Anoxic TreatmentTechnology


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Aerated Anoxic is an activatedSludge Process!

Aerated Anoxic can be applied anywheresecondary biological treatment is required.

BOD removal only (30/30 effluent)

Nutrient removal (TN and TP limits)

New construction

Plant retrofits/upgrades High peak/storm flows

Application of Aerated Anoxic Processes


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Advantages of Aerated Anoxic Processes

Provides the environment for simultaneousnitrification / denitrification

Reduced power requirements (>30% vs.Conv.)

Reactors in series eliminates impact of shortcircuiting. It is compete mix technology

Anoxic and aerobic zones confined indefined volumes so environmentalconditions of each zone can be controlledexactly.


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The terms can be very confusing

Aerated-anoxic

Anoxic-aeration

Anaerobic-aeration

what in the world am I talking

about!


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Recognition of Aerobic / Anoxic Science

Aerobic / Anoxic Discussion is Found in

Environmental Engineering Text Books.

Grady, Daiger & LimBiological wastewater Treatment;2ndEdition; Marcell Dekker; New York; 1999

Design of Municipal Wastewater Treatment Plants; WaterEnvironment Federation Manual of Practice No. 8; 2ndEdition;Book Press; Brattleboro;1991


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Key Oxygen Level Definitions

AnaerobicDevoid of all sources of O. Bacteria function in thecomplete absence of oxygen.

AnoxicNo DO; Chemically combined O used by micro-organisms. Bacteria function by metabolizing constituentscontaining oxygen like nitrate and nitrite.

Aerobic/AnoxicDO available but not measurable; Both DOand chemically combined O used by micro-organisms in a highfood environment

AerobicDO Plentiful.Bacteria function in the presence of freedissolved oxygen.



Typical designs use dedicated Anoxic and Aerobic

reactors

AerobicZonew/ Aeration

Secondary

Clarifier

Internal recycle

RAS

Anoxic Zone

w/o Aeration

Dedicated zones for nitrification and denitrification Mixing is achieved by a mechanical mixer

No air added to the anoxic reactor

Nitrates are brought back through internal recycle

4Q required to achieve 80% denitrification

Influent

WAS

Effluent



An Aerated Anoxic Reactor is not the same as a

reactor with Aerobic and Anoxic zones

Non carbon driven denitrification (lower rate) Oxygen supply has to be greater than demand to complete treatment

Difficult to control aerobic and anoxic zones in a single stage

Load variations cause zone variations

Anoxic

AnoxicAerobic

Aerobic



Aerated/anoxic is a biological process which operates

at constant oxygen deficit in the first part of the process

Oxygen is supplied the anoxic zone but it is less than the O2demand inthat zone.

Supplied oxygen includes oxygen recovered through denitrification

Internal recycle not required for the same level of denitrification as plantwith dedicated anoxic and aerobic zones

Aerobic Zone

RAS WAS

Anoxic Zone

w/ Aeration

Secondary

ClarifierInfluent Effluent



DO Deficit Condition

Demand Supplied

Deficit

Result = 0 DO

O2Supplied = 25 to 75% of O2Demand



An oxygen deficit is when the O2supplied to a reactor

is less than



-800 mV +200 mV

Anaerobic

Anoxic

Aerobic

Methanogenesis

Sulfur

Reduction

Acid

Formation

Phosphorus

Release

Denite

Nitrification

Aerobic Oxidation

What really is aerobic, anoxic and anaerobic?

ORP gives the answer



Advantages of Reactors in Series

Eliminates impact of short circuitingExample

Single Stage Reactor = 5%

3 stage Series Complete Mix Reactor with higherdegree of short circuiting perstage = 10% x 10% x 10% = 0.1%

Reduces sludge bulking

Less than 0.2 mg/l DO with high F:M upfrontreactors

Positive DO with low FM in later reactors

Wellington Donaldson compartmentalized plugflow tanks to reduce bulking over 70 years ago

Orris Albertson Control of Sludge Bulking

Inf. Eff.

Single Stage Reactor

Inf. Eff.

Reactors in Series


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Advantages and Disadvantages of Complete Mix

and Plug Flow Reactors

Inf. Eff.

Quick dispersionhandles short-term high loads

Short circuitingsmall amount of influent will exitprematurely

Slower reaction rates

No short circuiting: flow will travel slowly from one end to

the other

Faster reaction rates

Shock loads are not buffered and could upset the process

Inf. Eff.

Reactors in Series combines the best of both!

Complete Mix

Plug Flow



Aerated Anoxic processes are all designed as

complete mix reactors operated in series

Complete mix tank ensures quick dispersionhandles short-term high loads

Reactors in series eliminates impact of short circuiting

Reactors in series improves kinetics by moving closer to plug flow kinetics

Complete mix is accomplished automatically in an oxidation ditch

At an average velocity of 1 ft/s a completes circuit occurs in less than 5 minutes for a length of300 ft

Inf. Eff.

Complete Mix Reactors in Series



OrbalDesigns using Reactors in SeriesTake Advantage of Aerated AnoxicEnvironments

OuterMiddle

Inner

RASWAS

EffluentInfluent

Aerobic

Anoxic

At average load, 50% ofvolume is an anoxic first tank

Second and thirdtanks are aerobic


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Reactors in Series Improves Nitrification

Carey, OH WWTP Case Study

Challenge: 5 tanks in parallelwith nitrification problems.

Ammonia not meeting limits

Solution: Switch from parallel to

series.

Results:

Before (Two in parallel): eff.Ammonia 1.7 mg/l

After (Three in Series): eff.Ammonia 0.03 mg/l

Parallel Series


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Simultaneous Biological Nitrification and

Denitrification

Nitrification, Denitrification, and Bio-Pprocesses can occur simultaneouslyin thesame vessel given the appropriate conditions

Essential to simultaneousnutrient removalis creation of an aerated-anoxic treatmentenvironment


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Advantages of Simultaneous Nitrification/Denitrification

Aerated Anoxic the environment for simultaneousnitrification/denitrification

Immediate production of nitrites in 1sttank

Results in a shorter pathway for simultaneousnitrification / denitrification, Lowering operatingcosts

Increased safety factor for nitrification vs. samevolume of a conventional design

Better denitrification without internal recycle andIncreased Total Nitrogen reduction rates

Increased operating stability


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Denitrification

Shortcut Pathway

5-step pathway:

Ammonianitritenitrate

nitritenitrogen gas

3-step Shortcut pathway (in

aerated anoxic tanks):

Ammonianitritenitrogen gas

Requires 33% lesscarbon

Explains lack of nitrite oxidizers inOrris Albertsons Phoenix study


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Lower Little Miami, Ohio WWTP

VLR Process

Four VLR tanks in series

First two tanks operate at zero DO andconstant air input year around

Additional O2is added to the later tanks toadjust for seasonal load variations.

Ammonia is 5 times higher in the summer

Super anoxic during summer

Mildly anoxic during winter

Q: Denitrification is better during winter.Why?

A: More air is available for simultaneous

nitrification/denitrification

21 SWD

110

30

20 hp

2 mg/l

20 hp

20 hp 20 hp 20 hp

20 hp 20 hp

0 mg/l 0 mg/l 4 mg/l

20 hp


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Errors in the Science of Nitrification

For efficient nitrification, DO at a concentration of 1.5 to 2 mg/L isrecommended (Wanner 1997).

DO concentrations greater than 2 mg/L may be required in practice

(EPA, 1993).

Nitrification is not expected to occur below 0.3 mg/L of DO (Stenstrom

and Poduska, 1980).

For efficient nitrification in an aerated anoxic process,most of the process should operate at less than 0.3 mg/l

DO or negative ORP.


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Oxygen delivery is not harmful to denitrifcation

Phoenix 91st Avenue WWTP Aerated-anoxic study*:

Established that anoxic tank could be mixed with

course bubble air instead of conventional mixers

Anoxic tank equaled 25% of total volume

Air did not hurt denitrification.

Study did not specifically address:

Where was the nitrification occurring?

Why was it assumed that oxygen delivery might hurtdenitrification?

Why was there a reduced number of nitrite oxidizers?

*Orris Albertson Evaluation of Anoxic-Aerobic

Treatment at th e Phoenix 91stAvenue Plant


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Aerated Anoxic

Nitrification

Nitrification Requirements:

Adequate oxygen

Alkalinity

Adequate sludge age for

appropriate temperatures Adequate ammonia

Advantages of Nitrifying in theAerated Anoxic Reactor:

Complete nitrification in smallerfootprint

Single system SRT

Better denitrification withoutinternal recycle

Immediate source of nitrates fordenitrification

A short-cut nitrification/denitrification pathway is available(nitrite to nitrogen gas)


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Where does the nitrification occur?

Q: Does all the nitrificationoccur in the high DO zones?

A: Not in Siemens BNRsystems The low DO

reactors are the BESTenvironment for thenitrifiers.

The nitrification occurswhere the majority of O2isdelivered

0 1

2

DO Profile in Orbal


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Channel O2Demand,

lb/Hr

O2Supplied, lb/Hr

Before After

Outer 160 45 90

Middle 90 120 120

Inner 25 66 66

Total 275

Effect of Increasing O2Delivery in Outer Channel

INCREASING oxygen delivery in anoxic tanks to

IMPROVE DenitrificationHammonton, NJ WWTP

Effluent NO3-N, mg/L went from 2.8 mg/l to 1.6 mg/l by increasing O2

delivery to the Aerated Anoxic part of the process!

Sounds backwards?

Wouldnt denitrification be better with no

oxygen delivery in anoxic tanks?


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Hammonton, NJ WWTP

Nitrogen Balance

Q: With 0.3 mg/l nitrate, how muchdenitrification is due to recycle?

Influent N to be nitrified @ 200 lbs/day

N denitrified @ 197 lbs/day

N in recycle @ 13 lbs/day

N denitrified due to simultaneous N-D@ 184 lbs/day

A: More than 93% is denitrified due to

simultaneous N-D!

Similar results achieved at Elkton, MD


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Research discovers nitrifiers will adapt and thrive

in Aerated Anoxic Processes

University of Wisconsin Studies

Molecular probes to identify NH3oxidizingpopulation diversity

Compare Orbal population to modified

UCT Process - Glenn Tranowski(complete MS thesis)

Isolate as many different NH3 oxidizingbacteria a possible - Scott Cheng, MSstudent

Determine differences in microbialpopulations in various BNR plants,Hee Dung Park, PH.D student


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FISH Analysis of Ammonia Oxidizing Activity


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Research validates benefits simultaneous

nitrification/denitrifcation processes

Max kinetic rate similar between high and low DO AOB

At low DO the kinetic rate for aerated anoxic AOB is significantly higher thanhigh DO nitrifiers.

Low-DO environment supports stable nitrification

Different DO conditions select for phylogenetically different AOB

Lab enriched AOB are different from full-scale AOB (N. europaealineage vs.Nitrosospiria)

0.0

0.4

0.8

1.2

0 2 4 6 8 10

DO (mg DO/L)

(day-1)

Measured Values (High DO)Non-linear Regression (H)

Measured Values (Low DO)

Non-linear Regression (L)

Kinetic Parameters

0.0

0.4

0.8

1.2

0 2 4 6 8 10

DO (mg DO/L)

(day-1)

Measured Values (High DO)Non-linear Regression (H)

Measured Values (Low DO)

Non-linear Regression (L)

Kinetic Parameters

0.1

MarshallClones

MarshallClones

MarshallClones

MarshallClones

H-DO Reactor

Clones

L-DO ReactorClones

L-DO Reactor

Clones

N. europaea

lineage

Nitrosospira

lineage

N. oligotropha

lineage

N. marina

lineage

N. communis

lineage

N. cryotolerans

lineage

Phylogenetic Locations

Nine SpringsClones

Nine SpringsClones

Nine SpringsClones

NineSpringsClones

0.1

MarshallClones

MarshallClones

MarshallClones

MarshallClonesMarshall

Clones

MarshallClones

MarshallClones

MarshallClones

H-DO Reactor

Clones

H-DO Reactor

Clones

L-DO ReactorClones

L-DO Reactor

Clones

L-DO ReactorClones

L-DO Reactor

Clones

N. europaea

lineage

Nitrosospira

lineage

N. oligotropha

lineage

N. marina

lineage

N. communis

lineage

N. cryotolerans

lineage

Phylogenetic Locations

Nine SpringsClones

Nine SpringsClones

Nine SpringsClones

NineSpringsClones

Nine SpringsClones

Nine SpringsClones

Nine SpringsClones

NineSpringsClones


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Nitrifiers Denitrifiers

Nitrosomonas Achromobacter

europaea Aerobacter

oligotropha Bacillus

cryotolerans Micrococcus

marina Pseudomonas

communis Flavobacterium

Nitrobacter Proteus

Nitrospira Alcaligenes

Research Results


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Aerated Anoxic Processes Provide Power Savings

Better oxygen transfer by deliveringthe majority the oxygen underaerated anoxic conditions.

Oxygen transfer is dependent upon:

(CsC)

Alpha () = O2transfer in MLSS/clean water

(CsC) = difference between saturation DO(Cs) and the mixed liquor DO (C)

20 - 30% power savings possible

Orbal Disc


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Aerated Anoxic Saves 20 to 30% in power vs.

conventional textbook designs

MLE with Fine

Bubble Bionutre VertiCel

Anoxic Aerobic VLRFine

Bubble

Flow, MGD 18 18 18

Net AOR*,lb/hr

2025 2025 890 1135

Alpha - 0.5 0.5 0.95 0.68

DO, mg/l 0 2 0,1,2 0 1, 2

SOR, lb/hr 5220 973 2012

Aerator bHp - 816 650 322 298

Mixer/PumpbhP

70 - - - -

Total bHp886 650 620

* Includes Denitrification Credit

$0.0 M

$2.0 M

$4.0 M

$6.0 M

$8.0 M

VertiCel Bionutre MLE

Total Annualized Present Value

Energy Cost

Discount Rate = 5%Life Cycle Duration = 20 yearsPower Costs = 0.069 $/kwh (2009 US Average)

Power Cost Inflation Rate = 5% (rate from 2000-2009 for US)


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Enhanced Bio-Phosphorus Removal

Requires staged reactors in series that expose the mixed liquor to anaerobicconditions followed by aerobic conditions

BOD5 uptake and PO4 release from cells occur under anaerobic conditions.

Aerobic conditions support the luxury uptake of PO4.

Non-enhanced treatment systems will contain from 1 to 2 % phosphorus in itssludge.

Enhanced treatment systems can contain from 4 to 6 % phosphorus in its sludge


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PAO Behavior

CellPOLY-P

PHB

Short

Chain

Fatty

Acids

PO4

CellPOLY-P

PHB

PO4

O2 CO2

CellPOLY-P

PHB

PO4

NO3 N2

Anaerobic AerobicAnoxic


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Aerated Anaerobic ?

It sounds too odd

But it works in designs with LARGEaerated anoxic tanks and limited oxygensupplied. (The outer channel of the

Orbal is 50% of the volume!)

ORP conditions of -200 to -400


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Phosphorus Accumulating Organisms

AcinetobacterCandidatus AccumulobacterRhodocyclus Sp.Thauera selenatis

Propionibacter pelophilusDechlorimonas Sp.


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McMinnville, Oregon WWTP

Two 3-channel Orbal Basins

1stchannel operates asaerated anaerobic channel

2ndchannel operates asaerated anoxic channel

1.52 m.gal. Aeration Volume perbasin

Four 50 hp Drives

0.07 mg/l eff. P required

Designed for 8 day sludge age

0.5 mg/l eff. ammonia required

Only 18% of total basin volume isaerobic


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McMinnville, Oregon WWTP

P-removal Performance

Typical Municipal Plant

Operates first channel with discsat 29 rpmless than 10% of thetotal oxygen (aerated anaerobic)

Second channel operates with70% of the airand a zero DO(aerated anoxic)

Effluent ammonia at 0.2 mg/l (with 8 day sludge age)

Sol. P from Orbal/FC is 0.03 mg/l

Total P from Orbal/FC is 0.1 mg/l

A t ti t l f BNR E i t


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Automatic control of BNR Environment

using DO and ORP


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Conclusion

Aerated Anoxic operation is essential in the design of highly efficientBNR systems.

Tanks in series operation allows for complete isolation of aeratedanaerobic, aerated anoxic, and aerobic zones.

These new environments have been found to contain their ownbiological populations.

Research is on-going.

IT WORKS!


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Contact

John E. Olson P.E.Technical Sales Manager, Biological ProcessesSiemens Water Technologies2607 North Grandview BlvdWaukesha, WI 53188

Phone: 262-521-8495Cell: 262-488-5996Fax: 262-521-8287

E-mail: [email protected]


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Thank you for your attention!


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Activated Sludge

Operation &

Control Strategies

John E. Olson P.E.

Siemens Water Technologies

Bi l i l M h i i A t d A i


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Biological Mechanisms in Aerated-Anoxic

Treatment

Bio-reactor macro environment DO, Temp, MLSS, Mixing velocity, F/M, etc.

Floc micro environment

Anaerobic, anoxic, aerobic

Novel micro-organisms

Nitrosospira Sp., Rhodocyclus Sp.

Current studies at Rutgers University and The University ofWisconsin are investigating the biological mechanismsinvolved.


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Activated Sludge

Developed 18801920 in Europe & US

Batch treatment first developed

Officially named activated sludge on Jan 12,1915

Use naturally occurring aerobic microbiology tostabilize WW before discharge to environment


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Activated Sludge Systems

Conventional with course or fine bubble aeration

(plug, complete mix, step feed, contact stabilization)

Oxidation ditches

Sequencing Batch Reactors

Vertical Loop Reactors

All are environments that contain adispersed microbiological growth

suspended in a mixture of raw wastewaterand recycled settled sludge from clarifiers


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Floc, Filaments & Critters


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Sphaerotilus natans = Low DO

Type 1701Sphaerotilus natans

Haliscomenobacter hydrossis

Cause

Inadequate Dissolved O2throughout basin

Cure

Increase DO

False Branching identifies SN


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Design & Control Parameters for Activated Sludge

Dissolved Oxygen

Flows (Hydraulics)

Food / Micro-organism Ratio (F/M)

MCRT - Mean Cell Residence Time (Sludge age)

Yield (Solids Production)

Loading Rates (BOD, Ammonia, Phosphorus, etc.)


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Basic Formulas

Pounds (lbs) = Flow (MGD) x Concentration (mg/l) x 8.34

Area (ft) = length x width or 3.14(radius)

Volume (ft) = Area x Depth

Gallons = Cubic Feet (ft) x 7.48


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Flow

Influent

Storm

Side-streams

RAS

WAS

Types of Flow Measurement

Flumes

Mag Meters

Fill & Draw

Pump capacity

Q = A*V


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Dissolved Oxygen Measurement

Manual DO measurement of basins

Must always be done in-situ with portable meter

Oxygen Uptake RateOUR

Measure the rate of Oxygen utilization in thebasin which correlates to the strength of

wastewater in the basin


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Flow Control

Storage & Equalization

Pumps & Pumping Capacities

Variable Frequencies Drives

PLC-based Control Systems

Control the Hydraulic and Organic Loading on ProcessesWithin the Plant


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Clarifier operation / RAS control

A clarifier is designed to remove solids from the wastewater.

It is not a sludge holding basin!

Target: 0.5 to 1.5 foot sludge blanket

RAS flow range: 50% to 150% Q range (60 to 80% Q typical)

Automatic Flow Control Helps Maintain Constant Sludge BlanketLevel


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Detention Time (hrs)

DT = Tank Volume (gallons) X 24 (hrs/day)Total all Flows (gallons / day)

Example:

WW Influent = 450,000 GPD VLR Tank #1 Volume

RAS = 100% of Influent = 240,000 gallons

Digester Supernate = 20,000 GPD

Septage Hauler = 8,000 GPD

DT VLR Tank 1 = ???


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Sludge Quality Management

Four Questions

How many micro-organisms are in my WW treatment process?(Inventory)

Where are they? (basins, clarifiers, etc)

How long have they been there? (MCRT)

Where are they going? (WAS or Effluent)


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A + B

MCRT =C + D


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A + B = Sludge Inventory

A = Lbs MLSS in Aeration Basins

MLSS (mg/l) x Basin Volume (MG) x 8.34


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A + B = Sludge Inventory

B = Lbs TSS in Clarifier

[RAS (mg/l) + MLSS (mg/l)] = AVG Conc.

2

(3.14 x Radius x Sludge bed (ft) x 7.48) = Sludge Volume

1,000,000

AVG Conc. x Sludge Volume x 8.34 = Clarifier Solids


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C + D = Sludge Wasted

C = Lbs Solids Intentionally Wasted

RAS (mg/l) x Daily Waste Sludge Flow x 8.341,000,000


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Calculate MCRT

Influent Flow = 1,225,000 GPDMLSS = 2500 mg/l

RAS = 7500 mg/l

Eff TSS = 12 mg/l3 VLR Tanks = 25 W x 80 L x 20 D

2 Clarifiers = 50 diameter x 12 D

Average sludge bed depth = 9

Waste Sludge Flow = 75,000 gallons

Supernate Return from digester = 50,000 GPD


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Loading Rates

Organic loading = lbs BOD1000 ft Tank Volume

Nitrogen Loading = lbs BODlbs TKN (NH3 +Org N

Phosphorus Loading = lbs BOD

lbs Phosphorus


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Food / Micro-organism Ratio

Food = lbs BOD coming into process(mg/l influent BOD x MG Flow x 8.34)

Micro-organisms = lbs MLSS in Basin

(mg/l MLSS x Basin volume (MG) x 8.34)

F/M ultimately controls the population of micro-organisms that inhabit the WW system


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Yield

Yield = The Amount of Sludge ProducedThe Amount of BOD Removed

Y = RAS mg/l x Waste Sludge Flow x 8.34[BOD InfBOD eff] (mg/l) x Influent Flow (MG) x 8.34


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Settleability

Most Important Operational GoalGood Settleability!

Problems

Pin floc

Ashing

Filaments

Solution

Manage the MCRT in the plant!


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30 Minute Settling Test

Fill Beaker to 100%

Stir

Set timer for 30 Min.

Allow to settle

Read level of settled sludge inbeaker

Record every minute for rate

Record final result after 30 min.


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Monitoring Settleability

SVISludge Volume Index (mL/Gram)

SVI = Settled Volume (mL/L) x 1000 (mG/Gram)

MLSS (mG/L)

energy conservation using aerated anoxic technology

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