An Innovative Approach to Retrofitting for Nitrogen Removal...Nitrate Recycle Rate Anoxic Volume...
Transcript of An Innovative Approach to Retrofitting for Nitrogen Removal...Nitrate Recycle Rate Anoxic Volume...
An Innovative Approach to Retrofitting for Nitrogen Removal OWEA 2017 TECHNICAL CONFERENCE & EXPO
June 29, 2017
Innovation
From Wikipedia:
“The application of better solutions that meet new requirements.”
2
Today’s Topics
Nitrogen Removal from Wastewater
• Principles
• Case Studies
- A: Stabilizing Nitrification in HPO system
- B: Creating an Anoxic zone
- C: Denitrifying STEP ww
All case studies presented include an
(online) process monitoring component
3
Why Nitrogen Removal?
Required by Discharge Permit
Improve Water Quality (avoid future limit)
Increase Revenue (water quality trading)
Stabilize Process
Save Energy
4
Energy Intensity Benchmarking
5
Joint WEF/WERF Webcast: Net‐Zero Energy Solutions for Water Resource Recovery Facilities
Wednesday, October 29th, 2014
1,412
1,934 1,853
1,955
973
1,249 1,118
1,202
0
500
1,000
1,500
2,000
2,500
BasicSecondary
Nitrification BNR ENR
kW
h / M
G
Typical
Best Practice
The Microbiological Nitrogen Cycle
AOB NOB
OHO NO2-
The Microbiological Nitrogen Cycle
AOB NOB
OHO NO2-
3 Requirements for Biological N Removal
Stable nitrification to generate nitrate (NH3 NO3)
Anoxic (low DO, low/negative ORP) conditions
Carbon (BOD) for a source of energy
8
Case Study A – HPO Activated Sludge
Short retention time – conditions change fast
Caustic added to effluent to meet pH requirements
Summer limit: 1.9 mg NH3-N / L
Winter limit: 5.0 mg NH3-N / L
(30-day average)
Problems maintaining adequate nitrification, especially in Spring
9
Nitrification
Aeration to provide DO > 1.0
Solids Retention Time > 8 days (depends on temperature)
pH – 6.5 to 8.5 (peak rate is around 7.5)
Usually relatively easy to achieve provided DO, SRT, and pH
conditions are maintained within acceptable ranges
10
Measuring Nitrification
11
Good
Better
Best
Case Study A – Innovations
12
Relocated caustic dosing point to upstream from aeration tanks.
Redirected 2nd stage solids to 1st stage.
Installed monitoring system for ammonium, nitrate, and pH.
6
0
12
7
10
0 0
5
10
15
Ammonia Exceedances
CAU
arrives Online process monitoring installed
Case Study B – Extended Aeration Activated Sludge
2 x 1-pass aerated tanks (212 kgal. ea.) –
1 in service for daily flow of 260 kgpd
EQ, Sand filters, chlorine disinfection,
post aeration, aerobic sludge storage
tanks
New discharge limits: 10 mg TIN / L
Fully aerobic (oxic)
Stable nitrification but not designed for
denitrification – no anoxic zones or nitrate
recirculation
13
Clarifier
Typical Denitrification Flow Sheet
14
Anoxic Oxic
RAS
WW
NO3-N
NO3-N NO3-N
NH3 NO3 NO3 N2
3-4 Q NO3-N
Nitrate recycle
Clarifier
Typical Denitrification Flow Sheet
15
Anoxic Oxic
RAS
WW
NO3-N
NO3-N NO3-N
NH3 NO3 NO3 N2
3-4 Q NO3-N
Nitrate recycle
Case Study B – Innovations
16
Convert EQ tank to anoxic zone?
Convert 1 of 2 aerated tanks to anoxic zone?
Build anoxic zone into existing online aeration tank?
Case Study B – Innovations
17
Convert EQ tank to anoxic zone?
Convert 1 of 2 aerated tanks to anoxic zone?
Build anoxic zone into existing online aeration tank?
6.0
6.2
6.4
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
0123456789
101112
pH
NO
3-N
(m
g N
/L)
NO3-N pH
Case Study B – Nitrate Recirculation?
18
No nitrate recirculation
Instead: Intermittent aeration of oxic zone for increased denitrification Lead blower “off” 3 x / day
2 blowers operated continuously for nitrification of peak morning load
Case Study B - Process Monitoring System
Anoxic Oxic
A N A N O H O H
Case Study C: STEP system
20
WWTP on new housing development / early in build-out
Nitrate recycle system but no external carbon
Nitrates in effluent exceed limits / nitrification stable
Troubleshooting Denitrification
Oxic /
effluent Anoxic Condition Remedy
Low NO3 Low NO3 DN not limited None as long as
nitrification is stable
High NO3 Low NO3 Nitrate limited Increase nitrate recycle
High NO3 High NO3 Carbon limited Increase carbon dosing
21
Case Study C
22
Oxic
NO 3
Anoxic
NO 3
Nitrate
Recycle
Rate
Anoxic
Volume Carbon
Initial 16.4 15.6 100% 1 x N/A
Stop nitrate recycle pump 10.6 5.1 0% 1 x N/A
Resume nitrate recycle /
add anoxic volume 7.0 3.9? 15 / 75 2x N/A
New nitrate method 14.1 7.3
Add mixer to 2 nd anoxic zone 22.2 10.8
Case Study C: Optical Nitrate Probe
23
8
9
10
11
12
13
14
15
16
2:3
3 P
M
10
:33
PM
6:3
3 A
M
2:3
3 P
M
10
:33
PM
6:3
3 A
M
2:3
3 P
M
10
:33
PM
2:1
1 P
M
10
:11
PM
6:1
1 A
M
2:1
1 P
M
10
:11
PM
6:1
1 A
M
3:4
0 P
M
Eff
luen
t N
O3-N
(m
g/L
)
Case Study C – Simple Carbon Dosing System
24
Peristaltic pump – off the shelf
Gycerin – safe alternative to methanol
Case Study C
25
Oxic
NO 3
Anoxic
NO 3
Nitrate
Recycle
Rate
Anoxic
Volume Carbon
Initial 16.4 15.6 100% 1 x N/A
Stop nitrate recycle pump 10.6 5.1 0% 1 x N/A
Resume nitrate recycle /
add anoxic volume 7.0 3.9? 15 / 75 2x N/A
New nitrate method 14.1 7.3
Add mixer to 2 nd anoxic zone 22.2 10.8
Add carbon dosing system 10.1 0.7
Case Study C – Effluent Monthly Total Inorganic Nitrogen (TIN)
26
Summary
Innovation to provide N removal requires an understanding of the biology to cultivate and enrich critical populations.
Innovation includes modifications to existing equipment, developing new ways to operate, or creating new systems from off-the-shelf materials and equipment.
Online process monitoring is valuable for understanding what is limiting treatment performance and quickly evaluating viability of solutions.
Case Study A: HPO system – modified chemical dosing point and implemented new solids recirculation to stabilize nitrification.
Case Study B: Extended Aeration – constructed new zone, operational modification to aeration to create anoxic conditions.
Case Study C: STEP system influent – optimized nitrate recirculation, added carbon dosing system to stabilize denitrification.
27
Acknowledgments
Jon van Dommelen, Ohio EPA Compliance Assistance Unit
Delaware County RSD Wastewater Facility Operations Department
28
Questions?
29