emerging technologies for nutrient removal · 2020. 11. 3. · emerging technologies for nutrient...

Emerging Technologies for Nutrient Removal

Presenters:Tom Coleman, PE, RH2 Engineering, Inc.H. David Stensel, PhD, PE, University of Washington Civil and Environmental EngineeringApril Gu, PhD, Cornell University Civil and Environmental Engineering

Puget Sound Nutrient ForumNovember 3, 2020

Introduction• The results of the first phase of the Salish Sea modeling work

indicate that human sources of nutrients are having a significant impact on dissolved oxygen in Puget Sound

• The model has also shown that reducing nutrient loads from municipal wastewater treatment plants would provide significant progress toward meeting the dissolved oxygen water quality standards in the Sound.

• Innovative and sustainable nutrient reduction technologies and strategies will be needed to meet water quality standards and accommodate projected population growth in the region while at the same time being affordable and limiting or reducing adverse impacts on climate change.

Overview of Biological Nitrogen Removal using Conventional Activated Sludge Treatment

• Activated Sludge for Secondary Treatment without Nitrification (typical of many WWTPs discharging to Puget Sound)

• Activated Sludge with Nitrification reduces effluent ammonia but not Total Inorganic Nitrogen (TIN)

• Activated Sludge with Nitrification and Denitrification

Activated Sludge Secondary Treatment (for BOD and TSS)

Aeration BasinClarifier

• Influent contains BOD, NH3, and organic nitrogen. • Solids retention time (SRT) in Aeration Basin is not long enough to support nitrification.• Most of the inorganic nitrogen in the effluent will be in the form of NH3.

Influent

Return Activate Sludge

Effluent

Activated Sludge with Nitrification

Aeration BasinClarifier

• Influent contains BOD, NH3, and organic nitrogen.• Aeration Basin is larger than for Secondary Treatment to provide longer SRT.• Most of the inorganic nitrogen in the effluent will be in the form of nitrate (NO3

-).• TIN in the effluent is similar to the TIN in secondary effluent without nitrification.

Influent

Return Activated Sludge

Effluent

Activated Sludge with Nitrification and Denitrification

Aerated ZoneClarifier

• Influent contains BOD, NH3, and organic nitrogen.• Aerated Zone is large enough to support nitrification• Internal recycle brings nitrate into the Anoxic where it is denitrified using influent BOD.• Effluent contains reduced levels of total inorganic nitrogen (TIN)

Influent


Effluent

AnoxicZone

Internal Recycle

Activate Sludge with Advanced Nitrification and Denitrification

Aerated ZoneClarifier

Additional tanks and carbon addition may be needed to meet low TIN limits (e.g. <3mg/L)

Influent

Return Activate Sludge

Effluent

Pre-Anoxic

Zone

Internal Recycle

Post-Anoxic

Zone

Post-Aerobic

Zone

Carbon Addition

Aerobic solids retention time (SRT) and volume is controlled by NITRIFICATION needs

• Lower temperatures

requires longer SRT

• Lower NH4+ requires longer

SRT

• Longer SRT increases

aerobic volume needed

• Higher influent BOD –

greater volume

• Higher MLSS – less volume

Settleability of the activated sludge mixed liquor is a limiting factor in determining WWTP capacity

• Upgrades to flocculant activated sludge plants designed for only secondary treatment will in most cases require substantial increases in aeration basin volumes and clarifier capacity to enable them to achieve needed reductions in TIN.

• Settleability of mixed liquor is expressed as Sludge Volume Index (SVI) where a lower SVI value indicates better settling.

• Typical design for flocculant activated sludge assumes an SVI of 150 mL/gram.

• SVIs lower than 150 are possible with flocculant activated sludge but difficult to maintain consistently.

• SVIs of 200 or higher commonly occur due to sludge bulking caused by filamentous bacteria.

• Upgrades using conventional flocculant activated process will therefore be costly to construct and in many cases insufficient space is available at existing sites to install the additional tankage and related equipment which would be needed.

Benefits of increasing the density of active biomass

Clarifier

For an existing activated sludge system designed around an SVI of 150, the capacity can be approximately doubled if the SVI can be reliably maintained at 75.

Aeration basin capacity in terms of BOD and NH3 loading is roughly proportional to the mass of mixed liquor suspended solids (MLSS) in the reactors

Aerated ZoneAnoxicZone


Options for increasing the density of active biomass

• Membrane bioreactors (MBRs) - can be used to increase mixed liquor concentrations and reduce reactors volumes since membrane separation does not rely on gravity settling. Disadvantages include high capital cost, high life cycle costs, and high energy consumption.

• Integrated fixed film activated sludge (IFAS) - the addition of plastic or other media to aeration basins to support fixed film growth in addition to suspended growth. The benefits of IFAS must be weighed against the cost of the media, the associated media handling systems, and other considerations.

• Membrane aerated bioreactors (MABRs) - a new technology which may be promising for some applications, but it is a technology which is still at the pilot testing and demonstration project stage.

• Modify the bacterial selection processes to fundamentally change the structure and function of the microbial communities from those that predominate in conventional flocculant activated sludge systems.

An Ax Ox

Anaerobic Selectors and Phosphorus Accumulating Organism (PAOs)

Aeration Basin

Clarifier

In the 1980s James Barnard observed what would later be termed enhanced biological phosphorus removal (EBPR). A typical EBPR flow diagram is shown below.

Influent Effluent

Internal Recycle


The PAOs are ‘selected’ for in the EBPR process which achieves both nitrogen removal and phosphorus removal. The PAOs are key to the development of microbial communities with extremely good settling properties which is important even where only nitrogen removal is required.

Aerobic Granular Sludge (AGS)

Sidestream Fermentation

An Ax Ox

Aeration Basin

ClarifierInfluent Effluent

Internal Recycle


An

Dave Stensel – Aerobic Granular Sludge

April Gu - Sidestream Fermentation

Case studies: Cashmere and Peshastin WWTPs

Cashmere WWTP – EBPR and Fermentation Case Study

AnAx2 Ax3

(Swing)Ax

Ax1

Ox1 Ox2 Ox3

Aeration Basin


Internal Recycle Waste Activated Sludge to Digestion

Effluent to UV disinfection

Influent

Clarifier

LegendAn – AnaerobicAx – AnoxicOx - Aerobic

Cashmere WWTP – Process Flow Schematic

Photo from 10/15/1930-MIN Settle: 440MLSS: 7,400 MG/L

SVI: 59 mL/G

Cashmere WWTP – Settleability and Granule formation

Stereo microphotograph from 11/15/19Magnification approximately 35X.

Granules ranging in size from 200 to 600 microns

AnAx2 Ax3

(Swing)Ax

Ax1

Ox1 Ox2 Ox3

Aeration Basin


Internal Recycle Waste Activated Sludge to Digestion

Effluent to UV disinfection

Influent

Clarifier

LegendAn – AnaerobicAx – AnoxicOx - Aerobic

Cashmere WWTP – Mixed Liquor Fermentation Pilot Test

Fermentation pilot test – turn off mixers in An, Ax1 and Ax2 during the low flow period of the early morning hours (initially 4 AM to 7 AM).

Cashmere WWTP – Fermentation Pilot Test SVI data

0

25

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75

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150

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475

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0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

SVI (

mL/

g)

MLS

S (m

g/L

)

MLSS SVI Industry Loading Decrease Due to Pandemic (approx 3-18-20) Fermentation Started (8-10-20)


Granules ranging in size from about 200 to 700 microns

Cashmere WWTP – Fermentation Pilot Test observations

Peshastin WWTP – Sequencing Batch Reactor Upgrade

Peshastin WWTP – Sequencing Batch Reactor Cycles

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

12

:24

:43

AM

12

:49

:33

AM

1:1

4:2

3 A

M1

:39

:13

AM

2:0

4:0

3 A

M2

:28

:53

AM

2:5

3:4

3 A

M3

:18

:33

AM

3:4

3:2

3 A

M4

:08

:13

AM

4:3

3:0

3 A

M4

:57

:53

AM

5:2

2:4

3 A

M5

:47

:33

AM

6:1

2:2

3 A

M6

:37

:13

AM

7:0

2:0

3 A

M7

:26

:53

AM

7:5

1:4

3 A

M8

:16

:33

AM

8:4

1:2

3 A

M9

:06

:13

AM

9:3

1:0

3 A

M9

:55

:53

AM

10

:20

:43

AM

10

:45

:33

AM

11

:10

:23

AM

11

:35

:13

AM

12

:00

:03

PM

12

:24

:53

PM

12

:49

:43

PM

1:1

4:3

3 P

M1

:39

:23

PM

2:0

4:1

3 P

M2

:29

:03

PM

2:5

3:5

3 P

M3

:18

:43

PM

3:4

3:3

3 P

M4

:08

:23

PM

4:3

3:1

3 P

M4

:58

:03

PM

5:2

2:5

3 P

M5

:47

:43

PM

6:1

2:3

3 P

M6

:37

:23

PM

7:0

2:1

3 P

M7

:27

:03

PM

7:5

1:5

3 P

M8

:16

:43

PM

8:4

1:3

3 P

M9

:06

:23

PM

9:3

1:1

3 P

M9

:56

:03

PM

10

:20

:53

PM

10

:45

:43

PM

11

:10

:33

PM

11

:35

:23

PM

Peshastin WWTP - Typical 24-hour chart of ORP vs. time in SBR 1 and SBR 2

SBR 1 [mV]

SBR 2 [mV]

Begin Fill (Typical of each cycle)

Begin React (Typical of each cycle)

Begin Settle (Typical of each cycle)

Depletion of nitrate (Typical of most cycles)

ORP measurement are taken approximately 1 ft from the floor of the reactor tank which is within the settled activate sludge bed during the Settle, Decant, and Ferment Cycles.

Peshastin WWTP – Surface Wasting System

Peshastin WWTP – stereo photomicrographs of granules


Granule in the center is approximately 1 mm


Granule in the center is approximately 2 mm

0

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80

SVI30 Trends June through October 15 2020

SBR1 SVI30 mL/g

SBR2 SVI30 mL/g

Peshastin WWTP SVI trends June – October 2020

Striking a Balance Between Nutrient Removal in Point Sources and Sustainability

Greenhouse GasEnvironmental

Stewardship

Adapted from Water Environment Research Foundation Report

(December 2010)

Algae Production Potential vs GHG

0

5,000

10,000

15,000

20,000

25,000

Level 1 Level 2 Level 3 Level 4 Level 5

Alg

ae

Pro

du

cti

on

(lb

alg

ae

/d)

Algae

Production

0

2,000

4,000

6,000

8,000

10,000

GH

G E

mis

sio

ns

(C

O2

eq

mt

ton

s/y

r)

GHG

Emissions

Note: Assumes Algae Comprised of 10% N and 1% P

Level TN(mg/L)

TP(mg/L)

1 - -

2 8 1

3 4-8 0.1-0.3

4 3 <0.1

5 1 <0.01

Adapted from Water Environment Research

Foundation Report (December 2010)

Questions

Discussion

Next Steps?

emerging technologies for nutrient removal · 2020. 11. 3. · emerging technologies for nutrient...

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