Christopher HillDecember 6, 2006

CE 679

Application of Ballast Flocculation for Sanitary

Sewer Overflow Management

North Dakota State University

Outline• Problem Overview

• Introduction

• Application

• Design

• Conclusion

Problem Overview

• What are SSOs?

• What is the cause of SSOs?

• Why are SSOs a problem?

• What is the frequency of SSOs?

• How are SSOs managed?

Ballasted Flocculation

• What is ballasted flocculation?

• Why ballasted flocculation?

• Actiflo®, DensaDeg®, Sirofloc®

Actiflo® System

Application – Satellite

Basin

Interceptor Sewer

WWTP

River

Actiflo

Disinfection

Sludge

Actiflo®

Screen

• Located in the collection system

• Does not meet EPA secondary treatment standards

• Cost effective

Application – WWTP Bypass

Headworks

River

Disinfection

Actiflo®

• Located at WWTP

• Mixing with the WWTP effluent to comply with permitting limits

• Cost effective

Secondary Treatment

Design – Flow MonitoringBasin 8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00

Time (hr)

Flo

w (

mg

d)

0.0

1.0

06/11/20010.92 inches/hr

Ra

in F

all

(in

)

Wet-Day Flow Dry-Day Flow Rain Fall

Inflow

Infiltration

• Base on flow monitoring, develop model for sewer system.

• Typically designed for 5 year return period storm

• Design peak wet weather flow = 15 MGD

Design - Pretreatment

• Design Flow– Ramp-up 150% Q– Ramp-down 50% Q– Hydraulically 200%

Q

• Pretreatment– Screening

(3 – 6 mm)– 2 x 10 MGD

Q = 10 MGD

2 x 5 MGD

Design – Coagulation

• Coagulation– Chemical Coagulant – HRT 1 – 2 minutes– Rapid Mixing

(G = 500-1500 s-1)

V

PG

Jar Test/Pilot Study

Sizing TankV = (HRT) x Q = 1 min x 3472.5 gal/min = 3472.5 gal or 464.2 ft3

Mixing

Theoretical Power Requirement

P = G2 V = 12002(1.307x10-3 N*s/m2)13.2m3

= 24,844 W or 25 kW

Design – Flocculation

• Flocculation– Polymer– Sand (2 – 4 g/L)– HRT 1 – 2 minutes– Rapid Mixing

(G = 500-1500 s-1)

V

PG

Jar Test/Pilot Study

Sizing TankV = (HRT) x Q = 1 min x 3472.5 gal/min = 3472.5 gal or 464.2 ft3

Mixing

Theoretical Power Requirement

P = G2 V = 12002(1.307x10-3 N*s/m2)13.2m3

= 24,844 W or 25 kW

Design – Maturation

• Maturation– HRT 3 – 5 minutes – Slow Mixing

(G = 160 – 200 s-1)

Sizing TankV = (HRT) x Q = 3 min x 3472.5 gal/min

= 10,417 gal or 1,393 ft3

Mixing

Theoretical Power Requirement

P = G2 V

= 2002(1.307x10-3 N*s/m2)52.6m3

= 2,750 W or 2.8 kW

Design - Settler• Settler

– Overflow Rate 20 to 80 gal/ft2*min

– Typically 30 gal/ft2*min– Length: Width = 1:1 – Lamellar Tubes

Tank AreaA = Q / Vo

= 3472.5 gal/min / 30 gal/ft2*min = 115.75 ft2

Tank DimensionsL = W = A1/2

= 115.751/2

= 10.75 ft Use 11 ft

Design Criteria Between 45o and 60o InclineNominal Spacing 2 inIncline Length 3 to 6 ft

Design – Actiflo® System

• Assume Depth of 12 ft

Design - Microsand

4.8% of Q Sludge

Actiflo®

Influent Q

Hydrocyclone

1.2% of QRecycled

Sand

River

Clarified Water 6% of Q

Sludge Handling

WWTP

• 2 – 4 g/L of Microsand• Total Volume – Coagulation = 3,375 ft3 or 95,600 L• The system requires 191.2 - 382.4 kg (421.5 - 843 lb)• Sludge = 10 MGD x 0.048 = 480,000 gal/day

Actiflo® Design

Actiflo® Design

Conclusions• Evaluation of Alternatives• Design• Pilot Study• Disadvantages

Questions?