aerated anoxic principles

8/12/2019 Aerated Anoxic Principles

1/45

Page 1 Water Technologies

Aerated Anoxic Principles

Arkansas Water Environment Associations2012 Waters Worth It Specialty Conference


2/45


Getting Started

Define: Aerated Anoxic


3/45


The terms can be very confusing and aconsiderable number of definitions arrived at

Aerated-anoxic Anoxic-aeration Anaerobic-aeration Anammox bacteria

what in the world am I talkingabout!


4/45


Aerated-Anoxic is not limited to Siemensaeration systems but can be included inany activated sludge aeration processes,such as:

Multichannel Oxidation Ditch

Aeration tanks in series

Multi-pass plug flow systems


5/45


Aerobic

Reactor

Secondary

Clarifier

Internal Recycle

RAS

Influent

WAS

Effluent

Conventional plantdesigns use dedicatedanoxic and aerobic biological reactors

Anoxic

Reactor

No air added to the anoxic reactor

Nitrification achieved in the aerobic reactor

Nitrates brought back through internal recycle at 4Q

4Q


6/45


Aerated anoxicprocesses operate at constantoxygen deficit in the first part of the process

Aerobic Reactor Secondary

Clarifier

Internal Recycle

RAS

Influent

WAS

EffluentAerated

Anoxic

Reactor

Aerated

Anoxic

Reactor

O2suppl ied to aerated anoxic reactors is less than O2demand

No internal recycle required for total nitrogen removal


7/45Page 7 Water Technologies

A conventional oxidation ditch with aerobic and anoxic

zones is not the same as aerated anoxic reactors in series

Conventional Oxidation Ditch

O2supply must exceed demand for complete treatment

It is diffi cult to control aerobic and anoxic zones in a single reactor


8/45


9/45

Complete Mix

Plug Flow

Aeration Tanks

Complete Mix vs. Plug Flow

Influent

Influent

Effluent

Effluent



Aeration Tanks

Typical Oxidation Ditch



Aeration Tanks

Converting Plug flow to Complete Mix

Option 1: Add some pipes



Orris Albertson

Control of Sludge Bulking

Discussed the history of activatedsludge innovations used over 70years ago



Early Innovators

Wellington Donaldson 70 years ago

decided to compartmentalize plug flow

tanks



Orris Albertson

Control of Sludge Bulking

Phoenix 91st Avenue WWTP:Aerated-anoxic system

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.



Aerated Anoxic

Nitrification

Nitrification Requirements:

Adequate oxygen

Alkalinity

Adequate sludge age

Adequate ammonia

Advantages of Nitrification inAerated Anoxic Reactor:

Air did not hurt denitrification.

Immediate source of nitrates fordenitrification

Simultaneous nitrification-denitrification takes place

A short-cut nitrification/

denitrification pathway isavailable



Ive got a problem with what

youre saying

thats not the way I learned it!



Where does the nitrification occur?

Q: Does all the nitrificationoccur in the high DO zone?Y or N

A: Not in aerated anoxic systems the low DO reactors arethe BEST environment for thenitrifiers

0 0.5

2

Orbal DO profile in mg/l

The nitrification occurs wherethe majority of O2is delivered.


18/45


19/45


Carey, OH WWTP Case Study

Overview

Challenge: Five rectangular tanksoperating in parallel with nitrificationproblems. Ammonia level was notmeeting requirements

Solution: Switch operation from parallelto series.

Results:

Before (Two in parallel): eff. Ammonia

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

0.03 mg/l


20/45


Reactors in series improve nitr ification

Carey, OH WWTP case study

Challenge: 5 tanks in parallelwith nitrification problems

Ammonia not meeting limits

Solution: Switch parallel to series

Parallel Series

Results:

Before (parallel):eff. NH3 1.7 mg/l

After (series):

eff. NH3 0.03 mg/l

Explanation:

Switch to series eliminatedshort circuiting

Reactors in series created

aerated anoxic conditions thatpromote simultaneous N-D


21/45


Lower Oxygen Delivery Can Lead toSuperior Nitrification

Increasing Oxygen Delivery inAnoxic Tanks to ImproveDenitrification

Unusual Titles for Papers


22/45

INCREASING oxygen delivery in anoxic tanks to

IMPROVE Denitrif ication

Sounds backwards, huh?

Wouldnt denitrification be better with no oxygen

delivery in anoxic tanks?


23/45


Case Study: Hammonton, NJ WWTP

Increasing O2delivery in aerated anoxic tanks improves denitr ification

175

150

125

100

75

50

25

0

Outer Middle Inner

O2Demand,

lbs/hr

Channel

By increasing O2delivery in outer channel NO3-N dropped from 2.8 mg/l to 1.6 mg/l!

O2Supply Before

O2Supply After

O2Demand


24/45


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!


25/45


Compared nitrifiers from:

1. Orbal plants with aerated anoxicreactors

2. Nitrification plants with conventional

upfront non-aerated anoxic tanks

University of Wisconsin F.I.S.H. Study

Found different types of nitrifiersfor two different types of plant:

NITROSOMONAS typical ammonia oxidizer for most nitrification

plants, including those with non-aerated anoxic reactors NITROSPIREA dominant ammonia oxidizer for plants with aerated-

anoxic reactors

NITROBACTER dominant nitrite oxidizer


26/45


University of Wisconsin F.I.S.H. Study

NITROSPIREA:

The dominant ammoniaoxidizer in systems wherethere is simultaneousnitrifcation-denitrification

A nitrifier that is very good

at going dormant There are a lot of

dormant nitrifiers in ourBNR designs

Staging with aerated anoxic reactors infront is a good way to increase (evendouble) the nitrifier population.

Nitrifier population does not exclusively

depend upon the amount of ammoniaentering the plant.

Under typical conditions:

10,000 units

50% active 50% inactive

With increased dormant population:

25,000 units

20% active 80% inactive

Dormant Nitr ifiers


27/45


Nine Springs WWTP: Madison, WI

Conventional FB plant with upfront anaerobic tank

Operates at a 10 day SRT side by side test with one side beingaerated anoxic

Loading MLSS eTN eP CFM/lb of BODConventional: 14 2800 15 0.4 1100Aerated Anoxic: 26 4100 11 0.2 673

Anaerobic Aerobic (fine bubble)


28/45


Denitrification

Shortcut Pathway

5-step pathway:

Ammonia nitrite nitrate

nitrite nitrogen gas

3-step Shortcut pathway (in

aerated anoxic tanks):

Ammonia nitrite nitrogen gas

Requires 33% lesscarbon

Explains lack of nitrite oxidizers inOrris Albertsons Phoenix study


29/45


Aerated Anaerobic

It sounds too odd

But works in designs with LARGEaerated anoxic tanks and limited

oxygen


30/45


McMinnvil le, Oregon WWTP

Two 3-channel Orbal Basins

1stchannel operates asaerated anaerobic channel

2ndchannel operates as

aerated anoxic channel 1.52 m.gal. Aeration Volume per

basin

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


31/45


McMinnvil le, Oregon WWTP

P-removal Performance

Typical Municipal Plant

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

Second channel operates with70% of the air and 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


32/45


System A SAE @ 3 lbs/hp-hr

DO levels 0 - 2 - 4

alpha @ 0.9

power draw @ 544 hp

System B

SAE @ 3 lbs/hp-hr

DO levels 0 - 2 - 4

alpha @ 0.9

power draw @ 444 hp

Comparison of Two Identical Aeration Systems


33/45


Case Study @ Lit tle Lower Miami, OH

Adding more O2at Zero DO saves power DO

Operating Condi tions: DO levels and alpha/FCF same

Aerobic Zone 12mg/l DO0.7 FCF

Aerated Anoxic Zone0 mg/l DO0.9 FCF

Aerobic Zone 24mg/l DO0.5 FCF

Add more O2where absorption rateis greatest

Add less O2 where absorption rateis less

Add less O2where absorption rateis less

Actual Optimized

800

700

600

500

400

300

200

100

0

Aerated Anoxic Opt imizat ion Recommendations

OxygenDelive

red,

lbs/d

Actual Optimized Actual Optimized

O2absorbedfrom aerators(AOR)

UnabsorbedO2fromaerators(FCF)

Total O2Supplied (lb/hr)

Actual Optimized DifferenceFor AOR 1050 1000

For FCF 583 322

Total 1633 1322 22.5% less

Power Use 544 HP 444 HP 22.5% less


34/45


Anammox Bacteria

Nitrogen Removal Efficiency at Centralized Domestic

Wastewater Treatment Plant in Bangkok, Thailand

VLR @ Nongkhaem: BOD NI 32.8 11.8E 3.8 6.7

Of the several plants (8) in the study, Anammox type

bacteria was only present at the Nongkhaem plant


35/45


Anammox Bacteria

2.5 mgd Orbal plant with primaries

Ratio of BOD:N@ 3.5:1 (105 mg/l BOD 30 mg/l TKN)

Effluent ammonia @ 0.1 mg/l Effluent nitrate @ 2 mg/l

AnammoxPathway:

50% of the ammonia oxidized to NO2-N

50% of the ammonia uses NO2-N for oxygen supplier


36/45


Where do we go from here?

Blending erobic With naerobic


37/45


50,000 gpd Pilot Study in Singapore

Roof Installation Roof with Canvas

Gas Holder Installation Digester with Gas Holder


38/45


With DAFT and Anaerobic Digestion


39/45


BOD Extraction and Digester Recycle

Plant main gate

ConstructionTemporaryAccess


40/45


Prime Float Normal Loading Conditions


41/45


Prime Float High Solids Loading Conditions

(Simulate Captivator)


42/45


Test Plans and Summary for High Solids Loading Condit ions

High Solids LoadingConditions

Biosolids TSS Loading/Influent BOD Loading

DAF performance,Removal Efficiencies, %

Targeted Actual TSS BOD CODBase Case 2.7 3.5 98 93 96

Base Case +10 ppm FeCl3 2.7 3.1 99 95 96Base Case + 5 ppm FeCl3 2.7 3.1 97 97 96

DAF

System

DAF Influent

Biosolids Flow, TSS Source

Q Inf = 30 gpm,

BOD = 400 mg/L

TSS = 375 mg/L

Q R = 6 gpm, TSS = 6000 mg/L

DAF Float Sludge, 3.5%

DAF Effluent, to Aeration Tanks

BOD = 50 mg/L, TSS = 35 mg/L

FeCl3,

0 - 10 ppm

Primary

Clarifier

Contact

Tank

Influent Flow

QDAF = 18 gpm,

Directly To Aeration Tanks

Q= 18 gpm

BOD = 320 mg/L

TSS = 210 mg/L

Half of raw influent was treated by combined primary clarifier and contact tank (CT) + DAF:

DAF effluent BOD = 50 mg/L with total removal of 88%: 20% removed by clari fier and 68% removed by CT + DAF

DAF effluent TSS = 35 mg/L with to tal removal of 91%: 44% removed by clari fier and 47% removed by CT + DAF

Estimated reduction in aeration requ ired = 0.5*Q*(320-50)/(Q*320) = 42% based on BOD balance


43/45


Sand Island WWTP, Hawaii

Currently no secondary treatment

Upgrade cost estimate: $1.2 Billion

Power Cost: $0.21/kW

Limited land area for upgrade


44/45


Aeration Energy Reduction/Biogas Production

Conventional Mode BE/DR

2700 kW Energy used 1300 kW1800 kW Energy recovered 4800 kW

Total revenue gain of $8M/year

Total surplus of $6M/year


45/45

Remembering Wellington Donaldson

He had great ideas.

But for the most part they were:

ignored

neglectedforgottennot used

Maybe now we are finally back on the right

course

aerated anoxic principles

Documents