Weather Treatment While Meeting New Nutrient Requirements- Implications for CSO Communities Also Facing Nutrient Control Requirements

lameubiquityMécanique

21 févr. 2014 (il y a 3 années et 8 mois)

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Authors: A. Al
-
Omari, K. Kharkar, E. Locke, Metcalf & Eddy, Inc.


L. Benson, W. Bailey, R. DerMinassian, A. Tesfaye, S. Kharkar, District of
Columbia Water and Sewer Authority (DC WASA)

April 18, 2008 Chicago, Illinois

DC WASA’s Strategy to Maximize Wet
Weather Treatment While Meeting New
Nutrient Requirements
-

Implications for
CSO Communities Also Facing Nutrient
Control Requirements

Introduction


Background


Challenges for Enhanced Nitrogen Removal


Need for Integrated LTCP Plan and Total
Nitrogen Removal Planning


Addressing Hydraulic Limitations


Dynamic Modeling of Wet Weather Events


Summary

Background: Blue Plains Service Area

3

Blue Plains Wastewater
Treatment Plant

Background: Blue Plains Advanced
Wastewater Treatment Plant


Largest advanced
wastewater treatment
plant in the world


Serves over 2 million
people


Capacity:


370 mgd annual average


1076 mgd wet weather


740 mgd full treatment


336 mgd excess flow
treatment


Current average annual
flow is 330 mgd

Background: Blue Plains NPDES Permit


Outfall 001


CSO Related


Primary, disinfection, de
-
chlorination


Sampling required
-

No limits on pollutants


Outfall 002


“Complete Treatment”

Parameter

Annual
(lbs/year)

Monthly

(mg/l)

Weekly

(mg/l)

CBOD

5.0

7.5

TSS

7.0

10.5

TP

0.18

0.35

NH3 (5/1
-
10/31)

4.2

6.1

NH3 (11/1
-
2/14)

11.1

14.8

NH3 (2/15
-
4/30)

12.8

17.0

TN

8,467,000

4,689,000

Challenges for

Enhanced Nitrogen Removal

New Permit 4,689,000 lbs/yr

Challenges for

Enhanced Nutrient Removal


Primary Sedimentation Tanks

are overloaded during storm flows


Poor Primary Treatment performance

impacts biological processes


Nitrogen removal is impacted by:


Process aeration tank capacity


Secondary and BNR sedimentation basin capacity



Wet weather flows reduce ENR performance


1%

of total annual BNR volume (Flows >
555

mgd) causes ENR problems


Ratcheting TN to 3


no margin for error


Wet Weather Flows > 555
mgd equal 1% Annual BNR
Volume

Annual Volume

Need for Integrated

LTCP Plan and Total Nitrogen Removal
Planning



Final LTCP Report preceded Chesapeake Bay
Program TN Discharge Allocation


LTCP impacts to the Wastewater Treatment Plant


Primary Treatment of “Excess” Plant Influent Flows


Construction of 4 Additional Primary Sedimentation Tanks


Sustained Wet Weather Flows to the Blue Plains to Treat Wet
Weather Flows from the Storage Tunnels


A cost
-
effective way to achieve ENR is to reduce
wet weather flows through the treatment process


An Integrated Approach to Planning Addresses

Competing Needs for Treatment Processes

And Results in a More Reliable and Less Costly ENR
Program and Better Water Quality and Earlier CSO Control

Primary

Treatment

Secondary

Treatment

BNR

Disinfection

POTOMAC RIVER

001

002

Filtration

Peak Flow


740 MGD


4 hrs

Excess Flow

Peak Flow

336 MGD

Disinfection

Plant Influent

Peak 1,076 MGD

Blue Plains Process Flow Diagram

370 MGD Average Daily Flow


Complete Treatment

Excess Flow

CSO

Related

Bypass

Preliminary

Treatment


Testing of upgraded tanks showed limit of performance

0
10
20
30
40
50
60
70
80
90
100
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
Surface Overflow Rate (gpd/sf)
Percent Removal
TSS removal
BOD removal
Maximum SOR of 2000 (50% TSS removal) required for ENR

Addressing Hydraulic Limitations

Primary Sedimentation Tank Capacity

Addressing Hydraulic Limitations

Options to Improve Primary Treatment


50% TSS removal with existing 20 PST


Plant influent flow corresponds to 740 mgd


However, BP is required to treat up to 1,076 mgd


Build additional clarifiers


Space limited to 4 tanks


SOR is 2900 gpd/ft


~20% TSS removal


Build new high rate process for storm flows


“Enhanced Clarification Facility”


Hydraulically offload Primary Treatment


Provide higher quality storm flow effluent

POTOMAC RIVER

001

002

Peak Flow


740 MGD


4 hrs

Excess Flow

Disinfection

Primary

Treatment

Secondary

Treatment

BNR

Disinfection

Filtration

Plant Influent

Peak 1,076 MGD

Blue Plains Proposed Process Flow Diagram
to Reduce Hydraulic Load on Primary


Complete Treatment

Preliminary

Treatment

Enhanced

Clarification

Addressing Hydraulic Limitations

Comparison of Primary Effluent Quality

1. 4 Additional
PSTs

(per LTCP)

2. Enhanced Clarification
Facility

(Alternative)

To
Biological
Processes

To

Outfall 001

To
Biological
Processes

To

Outfall 001

TSS (mg/l)

112

112

70

14

BOD (mg/l)

84

84

64

37

TN (mg/l)

17

17

14

11

TP (mg/l)

2.1

2.1

1.7

0.2

ECF

Improves Disinfection Capability

Addressing Hydraulic Limitations

Secondary Treatment Clarifier Capacity

Plant Flow,
mgd

Flow to East

Basins, mgd

No. East Basins

In service

Surface Overflow,
gpd/sf

740

444

12

1,790

740

444

11

1,950

555

333

12

1,340

555

333

11

1,470


M&E Standard is 1,000
-
1,600 gpd/sf


10 States Standard is 1,000
-
1,200 gpd/sf


Solids Flux analysis shows a maximum flow of 340 mgd for East Secondary Basins

Secondary Treatment is Overloaded at Flows > 555 MGD

Normal Flows

Wet Weather Flows

Poor
effluent
quality

Very poor
effluent
quality

Sludge
blanket
washout

Sludge blanket in the
sedimentation tank builds
up


The wet weather flow shifts
the solids inventory from the
reactor to the sedimentation
tank


Wet
Weather
Flow
Event

Aeration Tank

Sedimentation


Tank

Returned Sludge

Effluent

Influent

Sludge
Blanket

Operations Response to Storm Event

to Prevent Washouts


Secondary process:


All reactors changed to step feed


24 hrs to return to plug flow after storm


Nitrification process:


6 reactors placed in wet weather mode


6 reactors placed in return only mode


5 days to return to normal mode after
storm

Operating Modes for BNR


Secondary
Effluen
t

1

2

3

4

5

RAS


3

4

5

RAS

1

2

Solids holding
t
ank

NO Secondary
Effluen
t

Normal
Operating
Mode

Wet Weather
Operating
Mode

Return
Only
Operating
Mode

POTOMAC RIVER

001

002

Complete

Treatment

Process Flow Diagrams for

Dynamic Modeling Options

Enhanced

Clarification

and

Disinfection

CS Tunnel to BP

Combined Sewer System

1076 MGD

Options 1 and 2

peak up to 740 mgd

Option 1

Option 2

001

002

Complete

Treatment

Enhanced

Clarification

and

Disinfection

CS Tunnel to BP

Options 3 and 4

peak up to 555 mgd

Combined Sewer System

1076 MGD

Option 3

Option 4


Option 1


Peak Flow Rate = 740 mgd PF=2


CSS tunnel pump out to Complete
Treatment


Option 2


Peak Flow Rate = 740 mgd PF=2


CSS tunnel pump out to Enhanced
Clarification


Option 3


Peak Flow Rate = 555 mgd PF=1.5


CSS tunnel pump out to Complete
Treatment


Option 4


Peak Flow Rate = 555 mgd PF=1.5


CSS tunnel pump out to Enhanced
Clarification


Dynamic Modeling Options


Wet Weather Dynamic Model

Storm Flow Simulation

Plant Influent hourly Flow
(WWO Model Input)
0
100
200
300
400
500
600
700
800
900
1000
0
2
4
6
8
10
Days
Flow, MGD

Dynamic Simulation Results
-

TN Effluent

TN Discharge Loadings
PF = 2.0/TPO to 002
0
10000
20000
30000
40000
50000
60000
0
1
2
3
4
5
6
7
8
9
10
Time, days
lb/d
002, TN = 247,000 lb
001, TN = 16,000 lb

TN Discharge Loadings
PF = 2.0/TPO to 001
0
10000
20000
30000
40000
50000
60000
0
1
2
3
4
5
6
7
8
9
10
Time, days
lb/d
002, TN = 222,000 lb
001, TN = 18,000 lb
TN Discharge Loadings
PF = 1.5/TPO to 001
0
10000
20000
30000
40000
50000
60000
0
1
2
3
4
5
6
7
8
9
10
Time, days
lb/d
002, TN = 172,000 lb
001, TN = 21,000 lb
TN Discharge Loadings
PF = 1.5/TPO to 002
0
10000
20000
30000
40000
50000
60000
0
1
2
3
4
5
6
7
8
9
10
Time, days
lb/d
002, TN = 195,000 lb
001, TN = 19,000 lb
Predicted TN Discharge

for the Selected Wet Weather Event

Option
Total
001
002
Load To
River
TN, lb
TN, lb
TN, lb
Option 1
PF = 2.0, TPO to 002
16,000
247,000
263,000
Option 2
PF = 2.0, TPO to 001
18,000
222,000
240,000
Option 3
PF = 1.5, TPO to 002
19,000
195,000
214,000
Option 4
PF = 1.5, TPO to 001
21,000
172,000
193,000
Outfall
Impact of ECF on Potomac River Water Quality

Potomac River Segment 129

# days
D.O.<5

No. of Days
FC>200/100 ml

No. of Days
EC>126/100ml

WQS

30 day


geo
-
mean

None yet

4 new PST

7

18

21

ECF

336 MGD

PF=2.0


1


3


3







Impact of Reducing Peak Flows through
the Plant on Receiving Water Quality


ECF

521 MGD

1

3

3


PF=1.5

Wet Weather Event Dynamic Modeling
Summary


Steady state modeling predicted 116,000 lbs
of TN for the 10
-
day simulation period


Dynamic modeling predicted 263,000 lbs of
TN, an increase of 127%, for the same period


Forcing peak flows through biological
treatment may not result in least effluent load


When planning ENR, account for wet weather
flows and impact on predicted performance


Operating changes to prevent washouts
will impact TN performance


Impacts of storm events can last days


POTOMAC RIVER

001

002

Peak Flow


740 MGD


4 hrs

Excess Flow

Disinfection

Primary

Treatment

Secondary

Treatment

BNR

Disinfection

Filtration

Plant Influent

Peak 1,076 MGD

Blue Plains Proposed Process Flow Diagram
to Meet TN Removal and LTCP Requirements


Complete Treatment

Preliminary

Treatment

Enhanced

Clarification

CS Tunnel to BP

555

555

Overflow to tunnel

Benefits of Integrating LTCP
and TN Removal Planning


Better water quality compared to LTCP


LTCP meets WQS


Better effluent quality from Outfall 001


Lower TN and other Loads to the Potomac River


More Cost Effective


Earlier CSO reduction vs. LTCP consent
decree


More Reliable Flow Management


ECF treatment system is Expandable
Supports revitalization of Poplar Point