Energy Efficiency Opportunities at Wastewater Treatment Facilities UW – Madison Class November 3, 2010 Focus on Energy Joseph Cantwell, P.E.

Energy Efficiency Opportunitiesat Wastewater Treatment

Facilities

UW – Madison Class

November 3, 2010

Focus on Energy

Joseph Cantwell, P.E.

Economic Benefits of Efficiency

• Reduces the need for new power plants

New power plant cost >$3,000/kW

Efficiency program cost <$500/kW

• Reduced environmental impacts,

including $$

Why?

• Why energy?

– Limited resource– Costs are

increasing– Major component

of facility budgets– Can be managed

• Why Water & Wastewater?

– Facilities consume 35% of energy used by municipalities

– Operation is 24/7

– W/WW energy costs are $9 billion/yr

– W/WW consume 70 billion kWh/yr

Energy Baseline

Find out where you’re at (baseline)...

…so you can figure out where you want to go (benchmark).

Implementation Value

Single shift

– (8 hrs/day) (5 days/wk) (52 wks/yr)

= 2,080 hrs/yr Continuous

– (24 hrs/day) (365 days/yr) = 8,760 hrs/yr

8,760 hrs/yr / 2,080 hrs/yr = 4.2

Electricity Requirement for Typical Activated Sludge Facilities (WEF)

Grit1%

Screens1%

Clarifiers3%

Wastewater Pumping

12%

Lighting and Buildings

6%

Chlorination1%

Belt Press3%Anaerobic

Digestion11%

Gravity Thickening1%

Return Sludge Pumping

1%

Aeration60%

Water/Wastewater Approach

• Site surveys—How performed

• Data requested• Discussions with

operators• Assessment

approach• Assessment report

Assessment Approach

• Explore major energy uses

• Address facility operations

• Modify/adjust operations

• Level of interest of operator

• Acceptance of assessment

• Cooperation to implement

Data to Gather

• Energy bills• Demand consumption• Size of treatment units• Design memorandum• Existing loading information• Effluent limits• Site input• Equipment data

Basic Assessments

• Plot energy consumption and demand• Percent loading – components and systems• Variability of process equipment• Variation in loading hourly/daily/weekly• Distribution of energy consumption• Obtain Amp, Watt or DO readings• Meet and review operations with site

personnel

Identified Energy Saving Opportunities

Wastewater Aeration Pumping Variable Speed

Drives Automatic Controls Solids Management Operation Equipment Selection

Water Pressure Throttled Valves Drives Controls Pumps Operation

Electric Energy Bill Basics

• Kilowatt (kW) = Power or Electric Demand ─ kW is measured over 15-minute periods

(averaged kW)─ Equals KWH measured over 15 minutes * 4

• KWH (Kilowatt hour) = Energy Used─ KWH = kW * hours─ On-peak kWh = kWh used during weekday─ Off-peak kWh = kWh used during weeknight

and weekends

Demand-side management

Demand

Learn when “on-peak” demand is

Review when changes in equipment occur

Schedule maintenance/equipment tests

Maintenance operations (welding, pump station cleaning, filter backwashing)

Treating hauled in wastes

Impact on demand

Demand

Change in blowers

Change in pumps

Utilize standby generator

Interior and exterior lighting

Exercising equipment

Stagger large energy processes

Daily DemandAugust 15, 2001

1600

1620

1640

1660

1680

1700

1720

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00

Time of Day

kWUnderstand Electric Demand

Understand Electric Demand

WWTP - November 2008 Demand Data

0

10

20

30

40

50

60

70

80

90

100

11/1

/200

8  0

0:15

11/1

1/20

08  1

4:45

11/1

4/20

08  0

5:15

11/1

6/20

08  1

9:45

11/1

9/20

08  1

0:15

11/2

0/20

08  2

3:45

11/2

3/20

08  1

4:15

11/2

6/20

08  0

4:45

11/2

8/20

08  1

9:15

11/3

0/20

08  0

9:45

11/6

/200

8  0

1:00

11/8

/200

8  1

5:30

Dem

and

(kW

)

Understand Electric Demand

Aeration

Aeration

Aeration

Organic loading• Biochemical oxygen demand (BOD)• Ammonia

Mixing• 0.125 cfm/SF• 0.25 cfm/SF

Aeration “capability” to meet code Diffuser density Flexibility of blower selection Existing and design loading

Must assess:

Effect of bubble size

The smaller the bubbles, the larger the area-to-volume ratio

The smaller the bubbles, the slower the bubble rise rate

Smaller bubbles have more surface area and longer residence time in the liquid.

Both increase the clean water oxygen transfer.

Aeration

Bubble size comparison

One hundred seventy-five golf balls fit into the volume of a basketball. So, with the same volume, you increase the surface area for O2 transfer by about 5.6 times.434.9/2.5 = 175175 X 8.9 = 1557.5/277.6 = 5.6

Diameter (in)

Surface area (in2)

Volume (in3)

Golf ball 1.7 8.9 2.5

Baseball 2.9 25.8 12.3

Basketball 9.4 277.6 434.9

Aeration

Energy Savings from DO Management

Actual Setpoint SavingsDO DO Fraction %2 2 - -3 2 1/8 12.54 2 2/8 255 2 3/8 37.56 2 4/8 507 2 5/8 67.58 2 6/8 75

Aeration

1. Aeration Tank Volume: 50 ft x 250 ft x 18 ft = 225,000 ft3

2. Floor Area: 50 ft x 250 ft x 0.125 cfm/ft2 = 1,563 cfm (Mixing)

3. Code (air rate capability)@ 20 cfm/1000 ft3 = 4,500 cfm (Mixing)

4. Organic Loading: (3.5 MGD) BOD = 4,500 lb/day & NH3 = 625 lb/day (4,500 lb/day x 1.1lbO2/BOD x ft3/0.0172 lbO2/ft3air x day/1440 min)/0.20eff = 1,000 cfm (625 lb/day x 4.6 lbO2/lbNH3 x ft3/0.0172 lbO2/ft3air x day/1440 min)/0.20eff = 580 cfm

1,000 cfm + 580 cfm = 1,580 cfm

EXAMPLE – AERATION CONTROL PARAMETER

Aeration

Organic Loading Controlled @ 1,580 cfm: 1,580cfm @8.5 psi = 75 hp x (0.746 kWh/hp/0.90eff ) x 8,760 hr/yr x $0.08/kWh =

$43,570/yr

Mixing (use 20 cfm/1000 ft3) 4,500cfm @8.5 psi = 200hp x (0.746 kWh/hp/0.90eff) x 8,760 hr/yr x $0.08/kWh =

$104,240/yr

SAVINGS = $60,670/yr

EXAMPLE – AERATION CONTROL PARAMETER

Electricity Requirements for Activated Sludge Wastewater

Lighting & Buildings8.1%

Anaerobic Digestion14.2%

Aeration54.1%

Return Sludge Pumping0.5%

Gravity Thickening0.1%

Screens0.0% Grit

1.4%Clarifiers

3.2%

Belt Press3.9%

Chlorination0.3%

Wastewater Pumping

14.3%

Derived from data from the Water Environm ent Energy Conservation Task Force Energy Conservation in Wastewater Treatm ent

Energy Intensive Processes - Pumping

• Pump performance curve• Drive (if applicable)• Motor specifications• Design information• Amp draw (field-measured)• Existing flow conditions• Discussion with operations personnel• System components

– Static– Dynamic – conveyance

configuration

Pumping Assessment

Pumping System Efficiency

Rangeof Eff.

Low Ave High

Motor 85-95 .85 .9 .95

Drive 20-98 .20 .6 .98

Pump 30-85 .30 .6 .85

Eff. of System .05 .32 .80

5 to 80%

Variable speed pump selection

Energy-Intensive Processes - Pumping

Energy Savings Obtained Through Installed Projects

• Oxidation DitchMonthly Average Energy Savings

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthly Average kWh BEFORE Monthly Average kWh AFTER

Energy Savings Obtained Through Installed Projects

• Package PlantMonthly Average Energy Savings

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Monthly Average kWh BEFORE Monthly Average kWh AFTER

Energy Savings Obtained Through Installed Projects

• Activated SludgeMonthly Average Energy Savings

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Monthly Average kWh BEFORE Monthly Average kWh AFTER

Ensuring a Sustainable Future:An Energy Management Guidebook for Wastewater and Water Utilities

http://www.epa.gov/waterinfrastructure/bettermanagement_energy.html

Energy Benchmarking

MGD = million gallons per day

Source: Focus on Energy," Water and Wastewater Energy Best Practice Guidebook”

Energy Savings Identified

What We Learned with Focus

• Energy Awareness – Management

• Knowledge of energy use is critical

• Energy efficiency w/o impact to effluent limits

• Significant savings available

• System assessment necessary

• Savings are long-term

• Publicize the need for energy efficiency

What We “Also” Learned with Focus

• Must overcome barriers

• Designers need to become aware of value

• Need to address electric charge rates

• Need to develop more training in energy efficiency

• Require energy efficiency/education for certification

• Agencies need to address energy efficiency

Design

Design development needs to be energy efficient from start up through design life of system

Operation

Does all equipment need to be in operation?

Flexibility in equipment selection

Range of operation

Energy efficient throughout range

Aerated Lagoons

Wastewater Treatment Facility• An aerated lagoon wastewater treatment facility

consisting of three lagoons (two aerated and one settling).

• The two aerated lagoons work by using helixor aerators with three 40 hp blowers.

• The annual electric consumption was 494,710 kWh/yr, relating to 7,340 kWh/million gallons.

• The village installed a new fine-bubble diffusion system and reduced the speed of the existing blowers.

• Resulting in energy savings of 264,000 kWh/yr

Installed Projects ….

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Oct-05

Nov-0

5

Dec-0

5

Jan-

06

Feb-0

6

Mar

-06

Apr-0

6

May

-06

Jun-

06

Jul-0

6

Aug-0

6

Sep-0

6

Oct-06

Nov-0

6

Dec-0

6

Jan-

07

Feb-0

7

Mar

-07

Apr-0

7

May

-07

Jun-

07

Jul-0

7

Aug-0

7

Sep-0

7

Oct-07

Nov-0

7

Dec-0

7

Date

kWh

per

mo

nth

Coarse Bubble DiffusersAvg. Monthly Power Consumption = 45,660 kWh

Fine Bubble DiffusersAvg. Monthly Power Consumption = 21,047 kWh

Assessed Project…

Assessed Project…

Municipal Wastewater Treatment Facility

• An activated sludge facility, oxidation ditch• The WWTF is not loaded at design • The annual electric consumption reduction

potential was forecasted to be 200,000 kWh for aeration and 250,000 for mixing

• The Municipality changed operations to reduce on – peak electric consumption

• The Municipality has additional opportunities to reduce energy through more awareness of operational impact on energy consumption

Assessed Project …

IF YOU HAVE QUESTIONS, PLEASE CONTACT:

Joseph Cantwell, P.E.Focus on Energy/SAIC

1845 Derrin LaneBrookfield, WI 53045Tel: (262) 786-8221Fax: (262) [email protected]