Wet Weather Planning for Wastewater Treatment Plants

June 23, 2017

Peak Flow Management: Collection vs. Treatment Collection System Peak Flow

Management Single 24 hour design storm I/I reduction SSO elimination by increasing system

capacity

WWTP Peak Flow Management All flows go to the WWTP Increased peak flows to the WWTP Single storm event is not indicative of wet

weather event Wet weather periods of longer duration

5 YR, 24 Hour Peak Flow Hydrograph

0 4 8 12 16 20 24

1.0

0

3.5

1.5

2.5

2.0

3.0

4.0

Time (Hrs)

Peak

Flo

w M

ultip

lier x

Qav

g

Collection System Hydrograph

SSO

sFl

ows M

eter

ed

Peak

at W

WTP

Pre I/I and SSO Reduction Program

Base Flow

Inflow

Infiltration

InflowInflow

Inflow

Infiltration

Infiltration

Infiltration

ManholeManhole

Manhole

Wastewater Treatment Plant

OverflowOverflow

Infiltration / Inflow

Base Flow

Plant Influent Flow

System Outflows

Flow Profile, Pre SSO Reduction

Overflow

2.5 x Qavg

1.5 x Qavg

Sanitary Sewer Overflows (SSOs)

5 YR, 24 Hour Peak Flow System Hydrograph

0 4 8 12 16 20 24

1.0

0

3.5

1.5

2.5

2.0

3.0

4.0

Time (Hrs)

Peak

Flo

w M

ultip

lier x

Qav

g

I/I Reduction & SSO Elimination

Proj

ecte

d Pe

ak F

low

s to

WW

TP

15% I/I Reduction

Post I/I and SSO Reduction Program

Base Flow

Infiltration

InflowInflow

InfiltrationManhole

Manhole

Manhole

Wastewater Treatment Plant

Surcharge

Inflow

Flow Profile Post SSO Reduction

I/I Reduction and SSO Elimination

Plant Influent Flow

System Outflows Eliminated

Infiltration / Inflow

Base Flow

3.25 x Qavg

Reality of I/I and SSO Reduction at the WWTP

Infiltration / Inflow

Base FlowPlant Influent

Flows

Collection System Outflows

Pre I/I and SSO Reduction

Infiltration / Inflow

Base Flow

Post I/I and SSO Reduction

Increased Peak Flow

3.25

x Q

avg

2.5

x Q

avg

Wet Weather Event Duration Peak wet weather flows to WWTPs are not

representative of a single 5-yr. 24 hr. Storm event Typical wet weather events last 7 to 10 days Events may not or may not contain a 5-yr. 24 storm event Daily rainfall totals are key to designing a representative

Wet Weather Event

Rainfall Hydrographs

Building Representative WWE Flow 7Q

4Q

3Q

2Q

1Q

0

5Q

6Q

24 168 192 2161441209672480

Time (Hrs)

Flow

(MG

D)

240 48

Coupling SS Modeling Results w/ Measured Flows

WWE Recorded Influent Flow (Q)Modeled Hydrographs for WWE Daily Rainfall

Representative WWE Design Flows

7Q

4Q

3Q

2Q

1Q

0

5Q

6Q

24 168 192 2161441209672480

Time (Hrs)

Flow

(MG

D)

Recorded Flow Data Coupled w/ SS Modeling Results

Design WWE (Q)Recorded Influent Flow (Q)Historical Diurnal Flow Pattern (Q)

2 hr. Peaks

Average Sustained Peak Flow

Historic Peak Rainfall Intensity

Peak TSS Loadings “Pollutographs”

Developing Peak Solids (TSS) Loading

Requires data sets; Peak TSS concentration for increasing antecedent dry

weather conditions. Peak TSS loadings during measured peak influent flows.

5 YR, 24 Hour Peak Flow System Hydrograph

0 4 8 12 16 20 24

1.0

0

3.5

1.5

2.5

2.0

3.0

4.0

1.0

6.0

2.0

4.0

3.0

5.0

7.0

Time (Hrs)

Peak

Flo

w M

ultip

lier x

Qav

g

Resulting Pollutograph

Flow to WWTP

TSS Concentration

Peak TSS Multiplier x TSS

avg

3 hour

Design WWE Solids Loading Profile:“First Flush Pollutograph”

7Q

4Q

3Q

2Q

1Q

0

5Q

6Q

24 168 192 2161441209672480

Time (Hrs)

Flow

(Q)

1,400

1,200

1,000

800

600

400

200

0

TSS

( mg/

L)

Design WWE (Q)Historical Diurnal Flow Pattern (Q)TSS Concentration (mg/L)

15 hour1,380 mg/L

2.2 Q

Optimizing Peak Wet Management at the WWTP

Peak Flow Process

Addition

Peak Flow Storage Addition

Maximize Sustained Treatment Capacity

Primary Objective is to “Protect” the Biological Process

$$$COMPLEXITY

7Q

4Q

3Q

2Q

1Q

0

5Q

6Q

24 168 192 2161441209672480

Time (Hrs)

Flow

(Q)

1,400

1,200

1,000

800

600

400

200

0

TSS

( mg/

L)

Design WWE (Q)Historical Diurnal Flow Pattern (Q)Total Mass Loading (mg/L)Sustained Treatment Capacity

Excess Flow

Sustained Treatment

Sustained Treatment Capacity & Remaining Excess Flow

3.8 Q

Step Feed Addition Maximizes Sustained Peak Flow Treatment

Primary Clarifier

Aeration Basin

Secondary Clarifier Effluent FiltersVortex Grit

Disinfection

Step Feed Arrangement

RAS

Step Feed

Cost effective, no permitting required, and slightly increases complexity.

Primary Clarifier Aeration Basin Secondary Clarifier Effluent FiltersVortex Grit

DisinfectionMLSS Storage Basin

Offline MLSS Storage Arrangement

RAS Storage Addition Maximizes Sustained Peak Flow Treatment

RAS

Less cost effective and more complex, but no permitting required, and provides better protection of RAS.

Addition of Offline Storage Increases Peak Flow Capacity

Primary Clarifier Aeration Basin Secondary Clarifier Effluent FiltersVortex Grit

Disinfection

Raw Offline Influent Storage

EQ Basins

Cost effective, easily permitted, but increases complexity, and isn’t as aesthetically acceptable.

Addition of Partially Treated Peak Flow Storage Increases Capacity

Primary Clarifier Aeration Basin Secondary Clarifier Effluent FiltersVortex Grit

Disinfection

High Rate Clarification Storage

EQ BasinsHigh Rate Clarification

Less cost effective, increased complexity, but easily permitted, and more aesthetically acceptable

Addition of Parallel Phys./Chem. Process Increases Treatment Capacity

Primary Clarifier Aeration Basin Secondary Clarifier Effluent FiltersVortex Grit

High Rate Clarification Disinfection

Enhanced High Rate Clarification

Cost effective, but difficult to permit, and complex to operate intermittently.

Addition of Parallel Peak Flow Biological Process Increases Treatment Capacity

Primary Clarifier Aeration Basin Secondary Clarifier Effluent FiltersVortex Grit

High Rate Biological Process

High Rate Biological Treatment Arrangement

Disinfection

Less cost effective and more complex to operate intermittently, but easily permitted.

Analyze Conventional/High Rate Treatment vs. Storage

7Q

4Q

3Q

2Q

1Q

0

5Q

6Q

24 168 192 2161441209672480

Time (Hrs)

Flow

(Q)

1,400

1,200

1,000

800

600

400

0

TSS

( mg/

L)

Design WWE (Q)Peak Flow Treatment Capacity (Q)Total Mass Loading (mg/L)Sustained Treatment Capacity (Q)

Storage Volume

200

Peak Flow Treatment

Sustained Conventional Treatment

Optimization & Cost Savings

Treatment and storage options must be balanced based on total associated costs

Site ConstraintsAesthetics

Question & Answers