advances in nitrogen and phosphorus removal at low do

Advances in Nitrogen and Phosphorus Removal at Low DO Conditions

Pusker RegmiVail Operator Training Seminar

13 October, 2016

• The water quality industry is currently facing dramatic changes

• It is shifting away from energy intensive wastewater treatment towards low-energy, sustainable technologies

• The future needs to focus on how one could extract energy captured from the wastewater rather than just treating it.

Wastewater Treatment and Energy

2

• The potential energy available in the wastewater exceeds the electricity requirements of the treatment process significantly.

• Energy required for secondary wastewater treatment1,200 to 2,400 MJ/1000 m3

• Energy available in wastewater for treatment, using previous data

5,850 MJ/1000 m3 (@ COD = 500 mg/L)

• Energy available in wastewater is 2 to 4 times the amount required for treatment

Energy Content of Wastewater

3

Energy Balance of WRRF

4

ET - thermal energy ES - syntheses energy EE - electricity

Wett et al. (2007)

• The conundrum of aerobic treatment is that electrical energy is needed to destroy chemical energy

Energy Balance of WRRF

5

Primary

Clarification

Secondary

Clarification

Q = 20 MGD

COD = 500 mg/L

TSS = 240 mg/L

Energy = 610,000 MJ/d

Q = 0.15 MGD

TSS = 1.5%

Energy = 215,000 MJ/d Q = 0.6 MGD

TSS = 0.5%


COD = 30 mg/L

TSS = 10 mg/L


Energy Lost

226,000 MJ/dEnergy Input

110,000 MJ/d

Total Energy Needed ~ 250,000 MJ/d

Energy Generated thru CHP ~ 70,000 to 100,000 MJ/d

Energy Usage in WRRF

6

Energy Usage in WRRF Based on the WERF Report ENER1C12

Major Electricity Using Processes Units Typical Best Energy Practice

Influent and Effluent Pumping kWh/MG 420 296

Screening and Grit Removal kWh/MG 61 10

Odor Control kWh/MG 300 300

Nitrifying Activated Sludge kWh/MG 944 519

BNR Biological Reactor kWh/MG 1454 690

Final Clarifiers and RAS Pumping kWh/MG 106 77

Anaerobic Digestion kWh/MG 122 11

Tertiary Filtration kWh/MG 102 89

Other kWh/MG 273 87

Energy Usage in Activated Sludge Plants

7

Carbonaceous

RemovalNitrification

Enhanced

Nitrogen Removal

Low Energy technology:

Simultaneous

nitrification

denitrification

• N and P removal generally are carried out with physically separated anaerobic, anoxic and aerobic zones

• N removal relies primarily on autotrophic nitrification and heterotrophic denitrification

Conventional Biological Nutrient Removal

• Biological process where nitrification and denitrification occur concurrently in the same aerobic reactor (or in the same floc)

• SND relies on achieving a dynamic balance between nitrification and denitrification

• SND depends on:• Micro environment that affects oxygen

diffusivity inside the flocs [floc size]

• Macro environment that is related to mixing [bioreactor configuration]

• Bulk DO concentration

• Carbon availability

• Presence of novel microorganisms

Simultaneous Nitrification-Denitrification

10

NH3-N

DO

NO3-N

Carbon

Diffusion Layer

Aerobic Zone

Anoxic Zone


11

COD,

Potential Advantages

• Elimination of separate

tanks and internal recycle

systems for denitrification

• Simpler process design

• Reduction of carbon,

oxygen, energy and

alkalinity consumption


Potential Disadvantages

• Limited controlled aspects

of the process such as:

• floc sizes

• internal storage of COD

• DO profile within the flocs

• Sludge bulking; primarily

because of the excessive

growth of filamentous

bacteria

12

Factors affecting SND

for N removal

• To accomplish denitrification in any process, the availability of readily biodegradable organic carbon is essential

Effect of Influent Carbon on SND

14

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12

Eff

luen

t N

O3-N

(m

g/L

)

Influent BOD:TKN Ratio (mg BOD5/mg TKN as N)

Jimenez et al. (2010) Jimenez et al. (2011)

• Control of bulk DO concentration in the system is essential for achieving a high degree of SND

Effect of DO on SND

15Jimenez et al. (2010)

DO constraints – nitrification kineticsNitrification fundamentals

16

Effect of DO on SND – Constant Aeration

17

Bulk DO Controlled to 0.5 mg/L

Effect of DO on SND – Cyclical Aeration

18

• Low DO required for SND is considered more susceptible to sludge bulking

• This has been considered one of the main disadvantages for SND processes

• Many facilities being operated in SND mode produce mixed liquor with marginal settling characteristics

• BNR facilities with AN or AX selectors often produce SVI values (90 percentile) of less than 120 and 150 mL/g (Parker et al., 2004)

Low DO Bulking in Plants Performing SND

19

Plant ProcessSVI

(mL/g)

Iron Bridge Bardenpho 115/165

Eastern Reg. Bardenpho 120/160

Snapfinger Single-Stage 200/300

Central Single-Stage 140/180

Winter Haven Bardenpho 130/190

Mandarin MLE 150/180

Marlay Taylor Single-Stage 170/280

Stuart Single-Stage 212/350

Smith Creek A2O 200/245

• Bulking in SND plants has driven some plants to convert to more conventional BNR processes

Low DO Bulking in Plants Performing SND

20

0

50

100

150

200

250

300

350

400

450

1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2008 1/1/2009

SV

I (m

L/g

)

Date

Construction

Period

A/O Process - Anaerobic Selector

and New Fine-bubble aeration

SND Process - Extended Aeration with

Mechanical Aerators

Evaluation of SND Plants Performance at Selected Treatment Facilities

21

Plant LocationCapacity

(m3/hr)Process

SRT

(days)

Effluent TN

(mg/L)

N Removal

(%)

SVI

(mL/g)

Iron Bridge Orlando, FL 6,420 Bardenpho 15 2.0 96 115/165

Eastern Reg. Orange Co., FL 4,010 Bardenpho 12 2.6 89 120/160

Snapfinger DeKalb Co., GA 2,410 Single-Stage 20 3.8 80 200/300

Central Ft. Myers, FL 1,765 Single-Stage NA 5.5 84 140/180

Winter Haven Winter Haven, FL 1,205 Bardenpho 25 2.4 93 130/190

Mandarin Jacksonville, FL 1,205 MLE 18 4.0 90 150/180

Marlay Taylor St. Mary’s Co., MD 965 Single-Stage 25 4.5 86 170/280

Northwest Reg. Hillsborough Co., FL 805 Bardenpho 12 2.7 93 NA

Tarpon Springs Tarpon Springs, FL 645 Bardenpho NA 2.2 92 NA

Stuart Stuart, FL 645 Single-Stage 18 5.5 86 212/350

Smith Creek Raleigh, NC 545 A2O 25 4.5 90 200/245

• Facilities with BNR configurations exhibited TN removal efficiencies of 89 to 96 percent

• Facilities using a single-reactor configurations (without explicitly defined anoxic zones) realized TN removal efficiencies in the order of 80 to 86 percent

Evaluation of SND Plants Performance at Selected Treatment Facilities

22

Iron Bridge WWTP, City of Orlando FL

23

Anaerobic Anoxic Oxidation Ditch operated in SND

Influent and

RAS

Post

Anoxic

Post

Aerobic

Mixed Liquor Recycle

To FST

0 0 0.3 0

1

15.5

7.1

0.2 0.5 0.140 00.95

0.35 0.4

0

2

4

6

8

10

12

14

16

18

Anaerobic Anoxic Oxidation

Ditch

Post-Anoxic Post-Aerobic

Con

cen

tra

tion

(m

g/L

)

DO NH3-N NO3-N

Iron Bridge WWTP, City of Orlando FLN Removal

WERF, 2011 24

0.10

1.00

10.00

Nov-04 May-05 Dec-05 Jul-06 Jan-07 Aug-07 Feb-08

N S

pe

cie

s (m

g N

/L)

TKN

NOx-N

TN

• The application of SND processes may be based and limited by:• Influent C:N ratio

• Optimum bulk DO from 0.3 mg/L to 0.7 mg/L

• Sludge bulking issues due to the excessive growth of filamentous bacteria

• The operator has limited control over important parameters impacting SND

Conclusions

25

Intr

od

uct

ion

Acetate and

propionate

Wate

r phase

NO2-, or NO3

-

Enhanced Biological Phosphorus Removal (EBPR)

• EBPR is favorable with an COD:P ratio > 15

• PAOs tend to dominate at COD:P ratios of 10-20 whereas GAOs tend to dominate at COD:P ratios >50 mg-COD/mg-P.

• COD must have a sufficient VFAs, or COD that ferments into VFAs (5 mgVFA/L per 1 mg/L of P to be removed)

• Seasonal variations in COD ratios and VFA content must be closely investigated preceding EBPR design.

Effect of Carbon Source on EBPR Performance

Traditional Flow Diagrams for N and P Removal

Barnard (2011)

Estimate of VFA and rbCOD Requirements for EBPR

Effect of MCRT & Temperature on EBPR

0

2

4

6

8

10

12

10 12 14 16 18 20 22 24 26 28 30

Temperature, º C

SR

T, d

ay

s

Nitrification in Conventional AS

Note: Incipient Washout Conditions with No Design “Safety Factor” on SRT

BPR only,No Nitrification

No BPR, No Nitrification

MCES Metro WWTP, St. Paul MN

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Eff

lue

nt

TP

, m

g/L

Daily

Daily 30-DMA Annual Moving

• EBPR becomes less stable when applied in conjunction with N removal processes due:

• competition with GAOs

• introduction of nitrate/nitrite to anaerobic zone

• competition for carbon

• N removal via denitrification becomes carbon limited due to EBPR

• Supplemental carbon is added for denitrification and/or EBPR

Issues with Simultaneous EBPR and N Removal

Integration of EBPR and N Removal

Anaerobic-Oxic Process

Anaerobic-Anoxic-Oxic Process

• Competition for carbon between heterotrophs and polyphosphate accumulating organisms (PAOs)

• Introduction of nitrate/nitrite to anaerobic zone, thereby disrupting anaerobic carbon uptake

• Competition with glycogen accumulating organisms (GAOs)

Challenges Combined Nitrogen Removal and Phosphorus removal

Brown and Caldwell 34

Carbon limited conditions makes

it even more difficult!!

Is low carbon combined shortcut nitrogen removal and BioP possible?

35

City of St. Petersburg Southwest WRF

37

No Primaries

Anaerobic digestion

• A/O Process

• Rated Capacity = 20 MGD

• Total SRT = 5 days

• Aerobic SRT = 3.5 days

• HRT = 6 hrs

• COD:TKN = 6.0 – 8.0

• Minimum Temp. = 22 degree C

• Maximum Temp. = 30 degree C

• Effluent nutrient limits (Florida Water Reuse requirements)• Total N = 10 mg/L

• Total P = 1.0 mg/L


38


39

GBT

BFP

Screening Grit Removal

Biological ReactorsSecondary

ClarificationTertiary

Filtration

Anaerobic DigestionSidestream Return

DO and SRT Control Strategy

40

DO and SRT Control Strategy

41

Control Parameter Condition Action

NH4+ Control

NH4+ lower than 1.0 mg N/L

Reduce SRT to limit NH4+ removal and

keep the average DO to a minimum value

of 0.1 mg/L.

NH4+ higher than 3.0 mg N/L

Increase SRT to improve NH4+ removal

and keep DO to a minimum value of 0.1

mg/L. If SRT approaches 5 days,

increase the DO to a maximum value of

0.3 mg/L until NH4+ is reduced

NO3- Control

NO3- higher than 1.0 mg N/L

Decrease the DO to a minimum value of

0.1 mg/L and monitor NO2- accumulation

(profile) in the aeration basin

NO3- lower than 1.0 mgN/L No action required

NO2- Control Monitor effluent NO2

- as surrogate measurement of shunt performance

Summary of Influent Characteristics

42

Parameters (mg/L) Value (Standard Deviation)

COD 300 (±65)

Soluble COD 120 (±20)

Readily Biodegradable COD 65 (±15)

Unbiodegradable COD 20 (±8.5)

VFAs 13 (±5)

TSS 140 (±35)

TKN 42 (±5.6)

NH3-N 30 (±4.5)

TP 3.9 (±0.75)

PO4-P 2.4 (±0.30)

Alkalinity (mg/L CaCO3) 210 (±20)

pH (SU) 7.1 (±0.22)

Inorganic Nitrogen Profile

0.8

Unaerated

DO = 0.02 ±

0.01 mg/L

Aerobic 1

DO = 0.22 ±

0.15 mg/L

Aerobic 2

DO = 0.12 ±

0.08 mg/L

Aerobic 3

DO = 0.08 ±

0.05 mg/L

Final Effluent Inorganic Nitrogen

Reason for excellent N removal?

45

1 mole Ammonia

(NH3 / NH4 +)

½ mol Nitrogen Gas

(N2 )

1 mole Nitrite

(NO2-)

1 mole Nitrite

(NO2-)

1 mole Nitrate

(NO3-)

Autotrophic Bacteria

Aerobic Environment

Heterotrophic Bacteria

Anoxic Environment

75% O2 (energy)

~100% Alkalinity

25% O2 (energy)

40% Carbon (COD)

60% Carbon (COD)

Ammonia Oxidizing Bacteria (AOB)

Nitrite Oxidizing .Bacteria (NOB)

Advantages:

• 25% reduction in oxygen demand (energy)

• 40% reduction in carbon (e- donor) demand

• 40% reduction in biomass production

NitritationDenitritation

Maximum Nitrification Rate Tests

46

SNR # DO

(mg/L)

Batch Test

MLVSS (mg/L)

SNH3RR

(mgN/gVSS/h)

SNOXPR

(mgN/gVSS/h)

SNO3PR

(mgN/gVSS/h)

SNO3PR/

SNOXPR

1 5 2443 0.96 0.94 0.25 0.27

2 5 2280 0.98 1.04 0.30 0.29

3 0.30 2217 0.91 0.51 0.21 -

4 0.10 2300 0 0 0 -

• Residual effluent ammonia >1 mg/L (Maximize AOB activity)

• Heterotrophs out-competing NOB for NO2-N at low DO conditions

• Maintaining aggressive SRT based on AOB activity

Mechanism of NOB out-selection


What about Bio-P?

48

Soluble PO4-P Profile

49

Unaerated

DO = 0.02 ±

0.01 mg/L

Aerobic 1

DO = 0.22 ±

0.15 mg/L

Aerobic 2

DO = 0.12 ±

0.08 mg/L

Aerobic 3

DO = 0.08 ±

0.05 mg/L

Stable High Temperature Bio-P

P Removal with NO2 Under Low DO/ Anoxic Conditions

Denitrifying PAOs???

What about settling??

• N removal is via nitrite-shunt - The low DO and short SRT operation resulted in significant NOB out-selection

• Effective SND was achieved in a simple AO process

• High temperature and low DO operation didn't adversely affect biological phosphate uptake (Large anaerobic volume and low NOx-N recycle could be helpful)

• Excellent settling at low DO operation

• Simple manual control strategy for DO and SRT was effective

• Low DO ammonia oxidation was key to this process

Final Thoughts

53

• Molecular work – Who is doing what?

• Modeling – Simultaneous N and P removal at low DO

• And the ultimate goal would be to replicate this process elsewhere with better process understanding

• WERF Project: Understanding the Impacts of Low-Energy and Low-Carbon Nitrogen Removal Technologies on Bio-P and Nutrient Recovery Processes (Started this week)

Future Work


Granules/flocs system

Carbon efficient WRRFCarbon efficient WRRF

Advanced aeration control

for SND

Low DO shortcut nitrogen

removal

GoalGoal BenefitsBenefits

Improved bio-P with

DPAOs

Process intensification

Increased C and P recovery

potential

Reduced energy and

chemical input

Pusker RegmiPh.D.

Email: [email protected]

Presenter contact information

55

advances in nitrogen and phosphorus removal at low do

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