emerging technologies for nutrient removal · 2020. 11. 3. · emerging technologies for nutrient...
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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
Return Activated Sludge
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
Return Activated Sludge
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
Return Activated Sludge
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
Return Activated Sludge
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
Return Activated Sludge
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
Return Activated Sludge
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
50
75
100
125
150
175
200
225
250
275
300
325
350
375
400
425
450
475
500
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)
Stereo microphotograph from 10/15/20Magnification approximately 15X.
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
Stereo microphotograph from 7/15/20Magnification approximately 15X.
Granule in the center is approximately 1 mm
Stereo microphotograph from 7/15/20Magnification approximately 15X.
Granule in the center is approximately 2 mm
0
10
20
30
40
50
60
70
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)
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Discussion
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