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Biosolids and Residuals Processing & Energy Management Workshop December 12, 2013

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Page 1: Biosolids and Residuals Processing & Energy Management

Biosolids and Residuals Processing & Energy Management Workshop

December 12, 2013

Page 2: Biosolids and Residuals Processing & Energy Management

Overall Program Agenda

Time Program Item

9:30 – 10:20 Biosolids Management / Regulatory Framework

10:20 – 10:30 Break

10:30 – 12:00 Biosolids Treatment Technologies

12:00 – 13:00 Lunch

13:00 – 13:30 Sidestream Treatment and Advanced Stabilization

13:30 – 14:30 Energy Management

14:30 Workshop Closure

2

Page 3: Biosolids and Residuals Processing & Energy Management

Biosolids Management SeminarExpected Learning Outcomes

• Discuss the regulatory framework for management of sewage sludge;

• Discuss major residuals thickening and dewatering unit processes;

• Discuss sludge conditioning for thickening and dewatering;

• Discuss major residuals stabilization unit processes;

• Discuss side-stream treatment and post-dewatering advanced stabilization

3

Page 4: Biosolids and Residuals Processing & Energy Management

Program Agenda

• Regulatory Framework• Sludge Thickening• Sludge Dewatering• Sludge Conditioning• Sludge Stabilization• Side Stream Treatment• Post-Dewatering Advanced Stabilization

4

Page 5: Biosolids and Residuals Processing & Energy Management

THERE WILL BE ACTIVE LEARNING COMPONENTS TO

THE SEMINAR

As my daughter says…

“If you snooze you lose”

5

Page 6: Biosolids and Residuals Processing & Energy Management

REGULATORY FRAMEWORK &

CONSIDERATIONS

6

Page 7: Biosolids and Residuals Processing & Energy Management

Residuals regulation is governed at the federal level under 40 CFR 503

• Major SectionsGeneral ProvisionsLand ApplicationSurface DisposalPathogen & Vector

Attraction ReductionIncineration

7

Page 8: Biosolids and Residuals Processing & Energy Management

For land application sewage sludge must meet certain requirements

8

• Non-Hazardous

• Criteria Pollutants

• Pathogen Content

• Vector Attraction Reduction

Page 9: Biosolids and Residuals Processing & Energy Management

“Non-hazardous” sludge must meet the requirements of 40 CFR 261

• Ignitable Flash Point < 140°F

• Reactive Explosive Reacts with water (fire, toxic

gas, etc.)

• Corrosive pH < 2.0 or pH > 12.5

• Toxic TCLP extractable toxics

9

Page 10: Biosolids and Residuals Processing & Energy Management

40 CFR 503 regulates specific heavy metals as “criteria” pollutants

• Ceiling Concentrations

• “Exceptional Quality” Thresholds

• Cumulative Pollutant Loading Rates

• Annual Pollutant Loading Rates

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Page 11: Biosolids and Residuals Processing & Energy Management

Exceed ceiling levels then land application is not permitted!

11

Page 12: Biosolids and Residuals Processing & Energy Management

“Exceptional Quality” has lower criteria pollutant concentrations.

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Page 13: Biosolids and Residuals Processing & Energy Management

Cumulative loading rate tracking required for “non-EQ” biosolids.

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Page 14: Biosolids and Residuals Processing & Energy Management

Annual pollutant loading rate also applies for “non-EQ” biosolids.

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Page 15: Biosolids and Residuals Processing & Energy Management

DON’T’ BE “NON-EQ”

Save yourself a lot of regulatory headaches on cumulative and annual pollutant loading rates

tracking

15

Page 16: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

What federal regulation establishes the standards for classification of materials as a hazardous or non-hazardous waste?

What are the four particular demonstrations that have to be made to show you are non-hazardous?

16

Page 17: Biosolids and Residuals Processing & Energy Management

Pathogen reduction requirements are regulated under 40 CFR 503.32

Pathogen Classifications• Class A• Class B

Class A• Lowest Pathogen Density• < 1,000 MPN/gram fecal

coliform density

Class B• Lower Pathogen Density• < 2*106 MPN/gram fecal

coliform density

Page 18: Biosolids and Residuals Processing & Energy Management

“Class B” pathogen reduction using PSRP unit processes

• Aerobic Digestion > 40-days MCRT @ 20°C or > 60-days MCRT @ 15°C

• Anaerobic Digestion > 15-days MCRT 35°C to 55°C or > 40-days MCRT @ 20°C

• Air Drying > 3-months at > 0°C (above freezing)

• Composting Windrow, aerated static pile, or in-vessel systems > 40°C for at least 5-days AND > 55°C for at least 4-hours

• Lime Stabilization pH > 12.0 standard units for > 2-hours

Page 19: Biosolids and Residuals Processing & Energy Management

Class A pathogen reduction by “time and temperature”.

19

Page 20: Biosolids and Residuals Processing & Energy Management

“Class A” pathogen reduction using PFRP unit processes.

• Composting Aerated Static Piles and in-vessel systems temperature

maintained at > 55°C for at least 3-daysWindrow systems temperature maintained at > 55°C for at

least 15-days with at least 5-turnings• Heat Drying

Dried to > 90% dry weight solids Particles Heated to > 80°C (indirect dryers) or Gas in contact with particles has a wet bulb gas

temperature > 80°C (direct dryers)• Heat Treatment

Liquid heated to > 180°C for > 30-minutes Zimpro, Porteous, and/or CAMBI thermal lysis

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Page 21: Biosolids and Residuals Processing & Energy Management

“Class A” pathogen reduction using PFRP unit processes

• Thermophilic Aerobic Digestion ATAD type systems Heat generated from aerobic degradation of volatile solids Sensitive to feed solids degradable VS content and %TS feed Temperature maintained at > 55°C for 10-day MCRT

• Irradiation Not commonly applied Beta or Gamma Rays > 1.0 megarad at > 20°C

• Pasteurization Sludge Temperature maintained at > 70°C for at least 30-

minutes Uncommon on “liquid” sludge due to heat demand Common on dewatered cakes (e.g., RDP lime stabilization)

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Page 22: Biosolids and Residuals Processing & Energy Management

Vector attraction reduction is regulated under 40 CFR 503.33.

22

Page 23: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

What federal regulation establishes the standards management of sewage sludges by land application, land disposal, and incineration?

23

Page 24: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

Class B pathogen reduction can be achieved using a “process to ___________ reduce pathogens” and Class A pathogen reduction can be achieved using a “process to ____________ reduce pathogens”

Discuss with a “neighbor” what process your utility uses for pathogen reduction.

24

Page 25: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

Discuss with a neighbor what FOUR criteria must be demonstrated in order to land apply biosolids:1.2.3.4.

25

Page 26: Biosolids and Residuals Processing & Energy Management

State and local regulations may result in more stringent regulatory constraints.

26

Wekiva Study Area

Anticipated Restricted Area Due to Everglades Protection

Anticipated Restricted Area Due to LOER Concerns

Restricted by Local Ordinance

Restricted by 100-Year Flood Zone

Page 27: Biosolids and Residuals Processing & Energy Management

• 9VAC25 – 20Fees

• 9VAC25 – 31RegulationsVPDES Permitting

• 9VAC25 – 32RegulationsVPA Permitting

27

In Virginia new biosolids management rules have recently been promulgated…

Page 28: Biosolids and Residuals Processing & Energy Management

• Statewide Programs Application Rates Slope Restrictions Buffer Restrictions Soil pH Management Nutrient Management Plans

• Local Government Programs Local Oversight Function Monitor Application at Sites Additional Residuals Testing Enforce State Regulations Fee Supported Program

State and local frameworks may raise the bar for management.

Page 29: Biosolids and Residuals Processing & Energy Management

Will land application be viable or vulnerableover the long term?

• Regulatory Challenges

Federal Rules

State Ordinances

Local Ordinances

• Legal Challenges

Toxic Tort Claims

Personal Property

Public Nuisance Claims

Page 30: Biosolids and Residuals Processing & Energy Management

Biosolids land application has been challenged in the trial courts.

Human Impact ClaimsVA - Wyatt et. al. vs. Sussex

Surry LLC and SynagroTN – Jones vs. Erwin Utility

DistrictFL – Bowen vs. American Water

Services Residuals Management

PA – Pennock vs. Lenzi

Animal Impact ClaimsGA – Boyce vs. Augusta-Richmond

CountyGA – McElmurray vs. Augusta-

Richmond County

Page 31: Biosolids and Residuals Processing & Energy Management

Pressure also exists for regulatory change on several fronts.

31

Emerging Contaminants

• Endocrine Disruptors• Pharmaceuticals• Personal Care Products• Flame Retardants• Dioxins

Pathogens

• Bacteria• Virus

Odors & Bio-aerosols

Page 32: Biosolids and Residuals Processing & Energy Management

An example of how regulatory changes can destabilize biosolids management.

32

Page 33: Biosolids and Residuals Processing & Energy Management

The rules are changing for existing and new sewage sludge incinerators (SSI).

33

Page 34: Biosolids and Residuals Processing & Energy Management

The former regulatory framework for sewage sludge incinerators.

• 40 CFR Standards of Performance for Sewage Treatment Plants Particulate Matter Opacity

• 40 CFR 61 National Emission Standards for Hazardous Air Pollutants (HAPS) Mercury (Hg) Beryllium (Be)

• Part 503 Regulations Incorporate 40 CFR 61 for Be, Hg Total Hydrocarbons/CO Lead, Arsenic, Cadmium, Chromium, Nickel

(Measured in Biosolids)

Page 35: Biosolids and Residuals Processing & Energy Management

Regulations have been evolving based on an expanded waste definition

• Clean Air Act Established Emission Standards for Specific Categories of Solid Waste Incineration Units (70 FR 74870)Municipal Waste > 250 TPDMunicipal Waste < 250 TPDHospital/Medical WasteCommercial or Industrial WasteOther Categories of Solid Waste

• EPA Established Emission Standards for otherSolid Waste Incinerator Units – 12/2005Did Not Include Emission Standards for SSI Units

Page 36: Biosolids and Residuals Processing & Energy Management

Regulations have been evolving based on an expanded waste definition

• Sierra Club Petitions EPA for SSI emission standards/litigates- Initial position of EPA – “no changes necessary to

70 FR 74870”

• EPA classifies sewage sludge as a solid waste and therefore regulated by CAA

• Rule promulgated to establish regulatory requirements for SSI units “new” and “existing”

Page 37: Biosolids and Residuals Processing & Energy Management

• Two Subcategories of SSI’s:- Multiple Hearth (163 units)- Fluidized Bed (55 units)

• Regulated Pollutants:- Cadmium (Cd)- Dioxins/Dibenzofurons (CDD/CDF)- Carbon Monoxide (CO)- Hydrogen Chloride (HCL)- Mercury (Hg)- Oxides of Nitrogen (NOx)- Opacity- Lead (Pb)- Particulate Matter (PM)- Sulfur Dioxide (SO₂)

Both FBTO and MHI will be regulated under the new rules

Page 38: Biosolids and Residuals Processing & Energy Management

Emission limits were developed based on the best performing units sampled.

• Section 129A-CAA –“Emission limits for existing units cannot be less stringent that the average emission limitation achieved by the best performing 12% of units in a source category” – MACT Standards

• EPA’s interpretation is that emission levels for each pollutant should be used to define “best performing”.

• Therefore the proposed limits represent the average of the lowest 12% of emission levels for each pollutant and not the best performing 12% of installations.

Page 39: Biosolids and Residuals Processing & Energy Management

What has been the response to a “sea change” in regulations…

Utility Response

Asheville, NCStay with IncinerationUpgrade APC System

Greensboro, NCStay with IncinerationUpgrade APC System

High Point, NCStay with IncinerationUpgrade APC System

Columbia, SCAbandon Incineration

Landfill / Class B Land Apply

North CharlestonAbandon Incineration

Landfill Disposal39

Page 40: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

Discuss the four potential challenges or regulatory changes which may impact biosolids and residuals management.

Discuss how your utility would respond to any one of these challenges if you lost the ability to manage biosolids as you do now.

40

Page 41: Biosolids and Residuals Processing & Energy Management

Questions

41

C. Michael Bullard, P.E.Vice PresidentNational Residuals & Biosolids LeaderHazen and Sawyer – Raleigh Office(919) [email protected]

Page 42: Biosolids and Residuals Processing & Energy Management

Biosolids and Residuals Processing & Energy Management Workshop

December 12, 2013

Page 43: Biosolids and Residuals Processing & Energy Management

Biosolids 101 - Program Agenda

• Sludge Thickening• Sludge Dewatering• Sludge Conditioning for Thickening and

Dewatering

43

Page 44: Biosolids and Residuals Processing & Energy Management

SLUDGE THICKENING

44

Page 45: Biosolids and Residuals Processing & Energy Management

Dissolved Air Flotation Thickener

45Source: WEF, MOP-8.

Page 46: Biosolids and Residuals Processing & Energy Management

Dissolved Air Floatation Thickener

46Image: Komline-Sanderson

Page 47: Biosolids and Residuals Processing & Energy Management

Gravity Belt Thickener

47

Source: WEF, MOP-8.

Page 48: Biosolids and Residuals Processing & Energy Management

Gravity Belt Thickener

48

Page 49: Biosolids and Residuals Processing & Energy Management

Some gravity belt thickener design characteristics for preliminary sizing.

Sludge Type PrimaryWaste

ActivatedBlended(50/50)

Feed Solids, %TS 2.0% - 4.0% 0.5% - 1.0% 1.0% - 2.0%

Thickened Solids, %TS 5.0% - 8.0% 4.5% - 5.5% 4.5% - 6.0%

Solids Loading Rate(lb/hr-meter)

750 – 1,000 600 - 750 750 - 900

Hydraulic Loading Rate(gallons/minute-meter)

75 – 100 200 – 250 150 - 200

49

Page 50: Biosolids and Residuals Processing & Energy Management

Rotary drum thickener

50

Page 51: Biosolids and Residuals Processing & Energy Management

Gravity Thickening

51

Source: WEF, MOP-8.

Page 52: Biosolids and Residuals Processing & Energy Management

Gravity sludge thickener

52

Image: Madison (WI) MSD @ http://www.madsewer.org/SolidWasteTreatment.htm

Page 53: Biosolids and Residuals Processing & Energy Management

Some gravity sludge thickener design characteristics for preliminary sizing.

Sludge Type PrimaryWaste

ActivatedBlended(50/50)

Feed Solids, %TS 2.0% - 4.0% 0.5% - 1.5% 1.0% - 2.0%

Underflow Solids, %TS 5.0% -7.5% 2.0% - 3.0% 3.0% - 5.0%

Solids Loading Rate(lb/day-sft)

20-30 4-6 5-15

Hydraulic Loading Rate(gallons/day-sft)

400 – 750 100 – 200 250 - 450

53

Page 54: Biosolids and Residuals Processing & Energy Management

Biosolids 101 - Program Agenda

• Sludge Thickening• Sludge Dewatering• Sludge Conditioning for Thickening and

Dewatering

54

Page 55: Biosolids and Residuals Processing & Energy Management

SLUDGE DEWATERING

55

Page 56: Biosolids and Residuals Processing & Energy Management

Belt Filter Press Dewatering

56

• Good– Simpler than centrifuge

operation– Can be automated– High solids capture rate– Relatively low

maintenance costs• Not so Good

– Odor control– High water requirements– Difficult for large roller

and belt replacement– Large footprint

requirements

Page 57: Biosolids and Residuals Processing & Energy Management

Some belt filter press design loading characteristics for preliminary sizing.

Sludge TypeDigestedPrimary

DigestedWAS

DigestedBlend

(50/50)

Feed Solids, %TS 3.0% - 4.0% 2.0% - 3.0% 2.0% - 4.0%

Cake Solids, %TS 24% - 30% 12%-18% 20% - 25%

Solids Loading Rate(lb/hr-meter)

800-1,200 400 – 600 600-750

Hydraulic Loading Rate(gallons/minute-meter)

60-75 40-60 60-75

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Page 58: Biosolids and Residuals Processing & Energy Management

High Solids Centrifuge

58

• Good– Generally higher solids content

than belt press (1-2%?)– Compact footprint– Can generally be automated– High solids capture rate– Fully enclosed

• Not so Good– Specialized maintenance and

operation– High rotational speeds– Higher power consumption– Higher noise– Wear and tear

Page 59: Biosolids and Residuals Processing & Energy Management

Plate and Frame Filter Presses

59

• Good– High solids

• Not so Good– High pressure operation– Batch process– Difficult to automate– High operation and

maintenance requirements– Skilled / trained labor

requirements– High chemical costs

(typically lime and ferric)

Image: WesTechIndustries

Page 60: Biosolids and Residuals Processing & Energy Management

Rotary Screw Presses

60

• Slow rotating screw presses solids into smaller and smaller area toward discharge

• Two types – inclined and straight

• Good– Low speed, low power– High solids capture rate– Low water requirements– Automated operations– Ease of maintenance

• Not so Good– Recent technology– Lower performance without

primary solids

Image: Huber Industries

Page 61: Biosolids and Residuals Processing & Energy Management

Rotary Fan Presses

61

• Slow turning internal disc, pressure creates cake

• Good– Low speed, low power– High solids capture rate– Low water requirements– Automated operations– Ease of maintenance

• Not so Good– Better with primary solids– Performance with WAS

should be piloted

Page 62: Biosolids and Residuals Processing & Energy Management

Biosolids 101 - Program Agenda

• Sludge Thickening• Sludge Dewatering• Sludge Conditioning for Thickening and

Dewatering

62

Page 63: Biosolids and Residuals Processing & Energy Management

SLUDGE CONDITIONING FOR

THICKENING AND DEWATERING

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Page 64: Biosolids and Residuals Processing & Energy Management

Polymer Types

• Polymer is used for sludge conditioning and to enhance settling, thickening, and dewatering

• Electronic charge• Charge density• Molecular weight• Molecular structure

64

Page 65: Biosolids and Residuals Processing & Energy Management

• Milky/cloudy liquid totes• Higher concentration of

active polymer• Shorter self life than dry

polymer• Usually 25% to 60%

active polymer

65

Emulsion Polymer

Page 66: Biosolids and Residuals Processing & Energy Management

• Pellet or flake provided in large bulk bags

• Lower concentration of active polymer

• Longer shelf life than emulsion polymer

66

Dry Polymer

Page 67: Biosolids and Residuals Processing & Energy Management

Dry Polymer

67

Page 68: Biosolids and Residuals Processing & Energy Management

Questions?

68

Laurissa Cubbage, PESenior Principal EngineerHazen and Sawyer – Richmond Office(919) [email protected]

Page 69: Biosolids and Residuals Processing & Energy Management

Sludge Stabilization

69

Page 70: Biosolids and Residuals Processing & Energy Management

Sludge Stabilization - Outline

• Aerobic Digestion• Anaerobic Digestion

70

Page 71: Biosolids and Residuals Processing & Energy Management

AEROBIC DIGESTION

71

Page 72: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Overview

• Why Aerobic Digestion?Plant size (~< 5-mgd)ComplexityBiosolids constraintsEnergy

72

Page 73: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – OverviewGOAL

• Achieve desired volatile solids reduction (VSR) in an aerobic biological reactor.

INPUTS

• Primary sludge, WAS, or both (thickened or non-thickened)

• O2 (via diffused air, mechanical aerator, draft tube, etc.)

• Mixing (aeration, or aeration + mixing)

• Alkalinity (naturally occurring HCO3

-, or OH- or CO3-2 chemical

addition)OUTPUTS

• Red. sludge volume (e.g. VSR occurred)

• Supernatant

Grady, Daigger, and Lim, 1999

Page 74: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Overview

74

C5H7NO2 + 7O2 5CO2 + 3H2O + NO3- + H+

Biomass (input and food source)Dissolved Oxygen (D.O.) from aeration

Carbon oxidizes and causes pH to drop (CO2 + H2O H2CO3)

O2 (D.O.) oxidation state is reduced

NH3 is an intermediate product of WAS degradation, and it is nitrified into NO3

-

Due to conversion of organic N to NO3-, causing pH to drop

(consumption of alkalinity: H+ + HCO3- H2CO3; pH = -log[H+])

Page 75: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Overview

75

Highlights:

• Tank Sizing & Operation

• Alkalinity and pH

• Aeration for Oxygen Supply

• Process Monitoring and Control

Page 76: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Tank Sizing

• Tank volume governed by solids retention time (SRT) necessary to achieve required volatile solids reduction (VSR)

WEF, 1998

For Class B:

At 20°C 40 daysAt 15°C 60 days

Page 77: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Tank Sizing

• VSR as function of temperature and SRT:

U.S. EPA, 1979

38% minimum

VSR for Class B

Page 78: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Tank Sizing

• VSR considerations at variable temperatures:

Example:SRT = 30 daysSummer Temp = 25°CWinter Temp = 10°C

°C x

SR

T =

750

43%

°C x

SR

T =

30033%

Page 79: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Operation

• Typical single stage batch operation In-tank thickening

• 0.5% - 1.5% TS (typ.)

Supernatant• Telescoping valve or

floating decanter

Reynolds & Richards, 1996

Page 80: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Operation

• Typical single stage continuous operation Upstream thickening

• As discussed earlier in presentation• If thickened upstream, < ~3.5% - 4% TS for adequate tank mixing

Downstream thickening• As discussed earlier in presentation

Dewatered liquid from thickening

Reynolds & Richards, 1996

Page 81: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Alkalinity and pH

• Reactions during aerobic digestion (nitrif.)

• Reactions during aerobic/anoxic digestion (nitrif. and denit.)

• If pH < ~5.5, supplemental alkalinity addition required

Daigger et al. 1997

• Due to oxidation of ammonia

• 7 lb alkalinity cons. per lb ammonia conv.

• Up to 50% recovery of alkalinity

• No aeration 25% -50% of time

• Req. mech. mixing• Will decrease VSR

Page 82: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Aeration for Oxygen Supply

• Maintain D.O. ≥ 1.0 mg/L during aeration

• ~2.3 lb O2 per lb BOD oxidized

• Oxygen transfer efficiency will also dictate blower req.

Typical for aerobic digestion

Hammer & Hammer, 2008

Page 83: Biosolids and Residuals Processing & Energy Management

Aerobic Digestion – Process Monitoring and Control

• Performance considerations:VSRSRT

• Monitoring considerations:

83 Stege and Bailey, 2003

Page 84: Biosolids and Residuals Processing & Energy Management

Sludge Stabilization - Outline

• Aerobic Digestion• Anaerobic Digestion

84

Page 85: Biosolids and Residuals Processing & Energy Management

ANAEROBIC DIGESTION

85

Page 86: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Overview

• Why Anaerobic Digestion?Plant sizeBiosolids constraintsEnergy

86

Page 87: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Overview

87

GOAL

• Achieve desired VSR in an anaerobic biological reactor, and recover byproducts of process as valuable resources

INPUTS

• Primary sludge, WAS, or both (thickened)

• Heat (via heat exchanger)• Mixing (biogas or mech.

mixing)

OUTPUTS

• Digested sludge w/ red. volume (e.g. VSR occurred)

• Dewatered liquid• Methane rich biogas• Nutrient rich biosolids

WEF, 2010

Page 88: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Overview

88

Complex biodegradableparticulates (raw sludge)

Soluble organics (amino acids, simple sugars, &

long chain fatty acids)

Hydrolysis

Acidogenesis

Volatile fatty acids(propionic, butyric,

valeric, etc.)

Acetate H2Acetogenesis

CH4CO2 MethanogenesisMethanogenesis

Hydrolysis:

• Hydrolytic bacteria convert complex organics into smaller molecules, and solubilized to amino acids, simple sugars, and LCFAAcidogenesis:

• Acidogenic bacteria convert products of hydrolysis into VFAs, acetate, and H2

Methanogenesis:

• Methanogenic Archae generate CH4• Aceticlastic (acetate CH4 + CO2)• Hydrogenotrophic (H2 + CO2 CH4)

Acetogenesis:

• Acetogenic bacteria convert products of acidogenesis into acetate & H2

Page 89: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Temperature Regime

• Temperature impacts anaerobic digestion VSR Methane formation

89

WEF, 2010

Grady, Daigger, Lim, 1999

Page 90: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – SRT and Tank Sizing

• REMINDER CFR 503 mandates: Class B biosolids: SRT = 15-days Class A biosolids:

• If feed sludge < 7% TS: SRT (days) = 50,070,000/100.14T

• If feed sludge ≥ 7% TS: SRT (days) = 131,700,000/100.14T

• SRT = HRT = Tank Volume / Q

Tank Volume = SRT x Q

90

Page 91: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Mixing

91

Digester mixing is vital for some of the following reasons:• Reduction of thermal stratification• Dispersion of “food”

Primary methods:1. Mechanical

• Pumped• Impeller,

propeller, and turbine wheels

3. Gas recirculation• Tubes,

lances, and diffusion

Metcalf & Eddy, 2003

Page 92: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Heating and Temperature Control

92

Boiler

Digester Gas

HeatExchanger

Hot

Wat

er

WEF, 2010

Fuel Oil

Page 93: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Heating and Temperature Control

93

Depending on desired operation, digester contents are heated to:• Mesophilic temperatures (~35°C, ~95°F)• Thermophilic temperatures (~55°C, ~131°F)

Heat is imparted to sludge via Heat Exchanger:

www.hrs-heatexchangers.com

Concentric Pipe

www.tranter.com

Spiral PlateTyp. heat sources for Heat Exchangers from biogas combustion:• Fired boilers (steam or

hot water) from biogas or fuel oil combustion

• Cogeneration (AKA “CHP”, or combined heat and power)

• Water-source heat pump

Page 94: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Monitoring and Control

94

• Temperature Maintain mesophilic or thermophilic temperature range Daily temperature deviation ≤ 0.6 °C (1 °F)

• pH Desired operating range is 6.8 to 7.2, ideal for methanogens

• At pH < 6, un-ionized volatile acids are toxic to methanogens• At pH > 8, un-ionized ammonia is toxic to methanogens

• Alkalinity Ammonium bicarbonate (NH4HCO3), calcium, and magnesium Desirable range: 1,500 – 5,000 mg/L and CaCO3

• Volatile Acids VA: ALK ratio = volatile acids (mg/L) / alkalinity as CaCO3 (mg/L)

• 0.3 – 0.4 corrective action needed; > 0.8 methane inhibition

Page 95: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Implications of Sludge Feed Type

95

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Vo

lati

le S

olid

s R

ed

uct

ion

(%

VSR

)

Digester Residence Time (days)

Volatile Solids Reduction at Selected Degradation Rate Constants

WAS - Low Range WAS - High Range

PS - Low Range PS - High Range

VSR(t) = VSR(max) * (1-e-rt)Where:PS VSR(max) = 65.0% PS Rate Constant = 0.125-0.150 per day WAS VSR(max) = 32.5%

Page 96: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Implications of Sludge Feed Type on Overall Mass Red.

96

Plant TypeNo Primary

Clarifiers

With Primary Clarifiers

Primary Secondary

Feed Solids Rate(Ibs/MG Treated)

1,7800.77 VS/TS

1,2500.80 VS/TS

9700.82 VS/TS

Digester MCRT(days)

20 20 20

Volatile Solids Reduction(% VSR)

22.5% 62.5% 22.5%

Volatile Solids Destroyed(lbs VSR/MG Treated)

310 625 180

Post Digestion Solids(lb/MG Treated)

1,470 1,415

Note: Sludge production estimate based on 250 mg/L influent BOD and TSS concentration, 10-day MCRT activated sludge process, 30% BOD removal and 60% TSS removal in primary clarifiers (where applicable), influent VS/TS fraction 0.80, 20% influent volatile solids un-degradable particulate solids.

Page 97: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Implications of Sludge Feed Type on Digester Gas Yield

97

Plant TypeNo Primary

Clarifiers

With Primary Clarifiers

Primary Secondary

Feed Solids Rate(Ibs/MG Treated)

1,7800.77 VS/TS

1,2500.80 VS/TS

9700.82 VS/TS

Digester MCRT(days)

20 20 20

Volatile Solids Reduction(% VSR)

22.5% 62.5% 22.5%

Volatile Solids Destroyed(lbs VSR/MG Treated)

310 625 180

Gas Production(SCF/MG Treated)

4,700 12,100

Note: Sludge production estimate based on 250 mg/L influent BOD and TSS concentration, 10-day MCRT activated sludge process, 30% BOD removal and 60% TSS removal in primary clarifiers (where applicable), influent VS/TS fraction 0.80, 20% influent volatile solids un-degradable particulate solids, gas production rate of 15 SCF/lb VSR.

Page 98: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Tank Types

98

WEF, 2010

• Most common configuration• Easier & cheaper to construct• Geometry permits operational flexibility• Prone to dead zones, lower VSR, and

grit deposition (frequent cleaning)• Reinforced conc. w/ sloped bottom

Cylindrical (“Pancake”) Digester

Page 99: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Tank Types

99

Egg-Shaped Digester• Optimal shape for digestion

(excellent mixing, higher active tank volume, low grit deposition)

• Specialty (expensive) construction

• Limited integral gas volume• Reinforced conc. or steel

WEF, 2010

WEF, 2010

Page 100: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Gas Production

100

• Biogas yield = 12 – 18 ft3/lb volatile solids destroyed

• Biogas Constituents 65% - 70% CH4 (by volume) 25% - 30% CO2 (by volume) Remainder: N2, H2, H2S, water vapor, other gases

• Lower heating values: Methane = 960 Btu/ft3

Biogas = 600 Btu/ft3

By comparison Natural Gas = 1,000 960 Btu/ft3

Page 101: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Gas Storage

101

Floating

Fixed

Membrane

Metcalf & Eddy, 2003

Page 102: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Handling and Safety

102

Example Diagram: Single Digester w/ Gas Mixing System

WEF, 2010

Page 103: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Handling and Safety

103

Page 104: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Utilization

104

Combined Heat and Power

Page 105: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Nuisance Issues and Treatment

105

Hydrogen Sulfide

How is it primarily generated?1. Presence of sulfate (SO4

-2) in sludge

SO4-2 S-2 HS- H2S

2. Degradation of proteins in sludge

Proteins Cysteine S-2 HS- H2S

What sorts of problems does H2S cause?• Diminished methane production (due to bacterial competition and

sulfide toxicity to methanogens)• Corrosion & acidification• Criteria pollutant (SOX) when combusted

sulfate reducing

bacteria

H+ conc. dep. on

pH and temp.

enz.

hyd.

bac.

deg.

H+ conc. dep. on

pH and temp.

Page 106: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Nuisance Issues and Treatment

106

Hydrogen Sulfide Removal

Iron Sponge

• Iron oxide impregnated wood chips

• Converts H2S to elemental iron & sulfur, and water

Chemical Scrubber

• Uses high pH liquid (e.g. caustic) for H2S absorption to packed media

• Requires oxidant (e.g. sodium hypochlorite) to manage adsorbent disposal issues & extend media life

Page 107: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Nuisance Issues and Treatment

107

Siloxanes and SiO2 (Sand) DepositionHow is it primarily generated?

• Siloxane compounds volatilize from sludge during digestion• Enters WWTP influent due to heavy use

in commercial cosmetic and hygienic products (e.g. shampoo, deodorant)

• Siloxane compounds are combusted with biogas, become SiO2

What sorts of problems does SiO2 cause?• Decreased efficiency of energy recovery

equipment• Voiding of equipment warranties• Catastrophic failure of energy recovery

systems

WERF, 2011

WERF, 2011

Page 108: Biosolids and Residuals Processing & Energy Management

Anaerobic Digestion – Biogas Nuisance Issues and Treatment

108

Siloxane Removal

Carbon Adsorption

• Gas-phase siloxane compounds adsorbed onto activated carbon

• Requires upstream H2S and moisture removal

Cryogenic Condensation

• Most biogas chilled to -25°C (or lower), gas-phase siloxanescondensed and removed.

• Developing technology, mixed successes

Gastreatment Services B.V.

Page 109: Biosolids and Residuals Processing & Energy Management

Questions?

109

Evan C. Bowles, PE, ENV SPPrincipal EngineerHazen and Sawyer – Richmond Office(804) [email protected]

Page 110: Biosolids and Residuals Processing & Energy Management

Side Stream Treatment andAdvanced Stabilization Technologies

Page 111: Biosolids and Residuals Processing & Energy Management

Overall Program Agenda

Time Program Item

9:30 – 10:20 Biosolids Management / Regulatory Framework

10:20 – 10:30 Break

10:30 – 12:00 Biosolids Treatment Technologies

12:00 – 13:00 Lunch

13:00 – 13:30 Sidestream Treatment and Advanced Stabilization

13:30 – 14:30 Energy Management

14:30 Workshop Closure

2

Page 112: Biosolids and Residuals Processing & Energy Management

SIDESTREAM TREATMENT

NITROGEN REMOVAL

3

Page 113: Biosolids and Residuals Processing & Energy Management

Conventional nitrogen removal pathway is energy and carbon “intensive”

4

12834-031

NO -N3

NO -N2NO -N2

25% O2

75% O2

40% BOD/COD

60% BOD/COD

Nitratation

Nitritation

Denitratation

Denitritation

NH -N3 N -gas2

Page 114: Biosolids and Residuals Processing & Energy Management

• Shortcuts traditional nitrification and /denitrification

• Stopping at nitrite rather than nitrate.

• Uses 25% less oxygen (theoretical)

• Uses 40% less carbon (theoretical)

5

There are more energy and carbon efficient pathways for nitrogen removal.

Page 115: Biosolids and Residuals Processing & Energy Management

• The most energy-efficient and low cost way to remove nitrogen

• Uses 62.5% less oxygen

• Does not require any supplemental carbon

• Utilizes annamoxbacteria

Nitritation and Deammonification is an even more efficient N removal pathway.

6

Page 116: Biosolids and Residuals Processing & Energy Management

SIDESTREAM TREATMENT

PHOSPHORUS REMOVAL

7

Page 117: Biosolids and Residuals Processing & Energy Management

Uncontrolled Struvite formation after anaerobic digestion can be a problem

8

Page 118: Biosolids and Residuals Processing & Energy Management

OSTARA offers a “controlled” struvite recovery reactor system

9

Page 119: Biosolids and Residuals Processing & Energy Management

Multiform Harvest offers a competing controlled struvite recovery reactor

10

Page 120: Biosolids and Residuals Processing & Energy Management

OSTARA struvite recovery reactor system at the Nansemond WWTP.

11

Page 121: Biosolids and Residuals Processing & Energy Management

OSTARA struvite recovery reactor system at the Nansemond WWTP.

12

Page 122: Biosolids and Residuals Processing & Energy Management

Product quality can vary depending on the struvite recovery system installed.

13

OSTARA CrystalGreen Product Multiform Harvest Product

Page 123: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

The two major constituents of concern in side stream from dewatering anaerobically digested sludge are:

1. ___________________2. ___________________

14

Page 124: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

What are the five chemical elements found in struvite:

1. ___________________2. ___________________3. ___________________4. ___________________5. ___________________

15

Page 125: Biosolids and Residuals Processing & Energy Management

POST-DEWATERING

TREATMENT TECHNOLOGIES

16

Page 126: Biosolids and Residuals Processing & Energy Management

Composting can be utilized to achieve 40 CFR 503 “Class A” standards.

17

• Space intensive

• High odor potential

• Labor and equipment intensive for material handling

• Seasonal product demand

• Unique marketing and distribution challenges

Page 127: Biosolids and Residuals Processing & Energy Management

Basic process configuration for composting unit treatment process.

18

Image: Inland Empire Regional Composting Authority (http://www.ierca.org/process/compostprocess.html)

Page 128: Biosolids and Residuals Processing & Energy Management

Alkaline stabilization can meet both “Class A” or “Class B” standards

19

• Calcium Oxide (Lime) is blended with dewatered cake

• Elevated pH can result in high ammonia odors release

• “Class A” achieved by:– pH + Temperature– Time + Temperature

• Finish Product used as Soil Conditioner

Page 129: Biosolids and Residuals Processing & Energy Management

Fluid bed thermal oxidation is the current “standard” in incineration

20Image Courtesy IDI Technologies

Page 130: Biosolids and Residuals Processing & Energy Management

Thermal drying systems are “rated” by evaporation rate capacity

21

Page 131: Biosolids and Residuals Processing & Energy Management

Rotary drum thermal drying is the most prominent technology for “large” systems.

22

Source: Andritz-Ruthner

Page 132: Biosolids and Residuals Processing & Energy Management

South Cary WRF thermal drying facility 8,800 lb/hour evaporation rate capacity.

23

Page 133: Biosolids and Residuals Processing & Energy Management

Compact rotary drum drying systems are available for “smaller” size systems.

24

Photo Courtesy: Andritz-Ruthner

Page 134: Biosolids and Residuals Processing & Energy Management

Belt drying systems are a more recent addition to the sludge drying market.

25

Source: Andritz-Ruthner

Page 135: Biosolids and Residuals Processing & Energy Management

Belt dryer installation in Biel, Switzerland with an evaporation rate 2,900 lb/hour.

26

Image: Andrtiz-Ruthner

Page 136: Biosolids and Residuals Processing & Energy Management

Paddle dryers are the most common of the “indirect” dryer systems.

27

Source: Komline-Sanderson

Page 137: Biosolids and Residuals Processing & Energy Management

Paddle drying system in Mason, OH with 6,500 lb/hour evaporation rate capacity.

28

Page 138: Biosolids and Residuals Processing & Energy Management

Fluid bed dryers are not common in the North American market.

29

Source: Andritz-Ruthner

Page 139: Biosolids and Residuals Processing & Energy Management

Fluid bed dryer in Houthalen, Belgium with evaporative capacity 8,000 lb/hour.

30

Image: Andritz-Ruthner

Page 140: Biosolids and Residuals Processing & Energy Management

Biosolids gasification is an emerging technology for energy recovery.

31

Page 141: Biosolids and Residuals Processing & Energy Management

Solar sludge drying beds can be covered to reduce seasonal impacts

32

Source: Veolia-Water / Kruger

Page 142: Biosolids and Residuals Processing & Energy Management

Automation can be applied to increase solids loading rates to reduce footprint.

33Source: Veolia-Water / Kruger

Page 143: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

What are three major types of processes used for producing a Class A biosolids after dewatering:

1. ___________________2. ___________________3. ___________________

34

Page 144: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

What is the primary criteria used for sizing an thermal drying system?

35

Page 145: Biosolids and Residuals Processing & Energy Management

Active learning exercise…

What are the five major types of thermal drying systems on the market:

1. ___________________2. ___________________3. ___________________4. ___________________5. ___________________

36

Page 146: Biosolids and Residuals Processing & Energy Management

The big picture take away items…

• The “on-site” residuals stabilization and handling requirements are largely governed by the needs of the “off-site” residuals management program.

• Thickening, stabilization, dewatering, and post-dewatering treatment must work together as a system to effectively achieve residuals processing objectives.

37

Page 147: Biosolids and Residuals Processing & Energy Management

Reference Materials

38

Page 148: Biosolids and Residuals Processing & Energy Management

Reference Materials

39

Page 149: Biosolids and Residuals Processing & Energy Management

Reference Materials

40

Page 150: Biosolids and Residuals Processing & Energy Management

Questions?

C. Michael Bullard, P.E.Vice PresidentNational Residuals & Biosolids LeaderHazen and Sawyer – Raleigh Office(919) [email protected]

41

Page 151: Biosolids and Residuals Processing & Energy Management

Biosolids and Residuals Processing & Energy Management Workshop

December 12, 2013

Energy Management

Page 152: Biosolids and Residuals Processing & Energy Management

Agenda

• Electric Utilities Overview• Electric Billing• Demand Management• Resource Recovery• Power Monitoring• Typical Energy Efficiency Opportunities

Page 153: Biosolids and Residuals Processing & Energy Management

Energy management is more than energy efficiency

EnergyManagement

Energy Procurement

Energy Efficiency

Resource Recovery

Demand Management

Energy Awareness

Energy Monitoring

Energy Modeling

and Planning

Page 154: Biosolids and Residuals Processing & Energy Management

Energy Management has potential savings of 10-40%

45

Biogas

Process

Optimization

Renewables

Energy Procurement

Page 155: Biosolids and Residuals Processing & Energy Management

Energy Management is a Continuous Process

46

Energy Management Program

Energy Auditing

Implement

Monitor & Verify

Education & Training

Page 156: Biosolids and Residuals Processing & Energy Management

Managing energy begins with an energy management program

Energy Modeling and BenchmarkingPower Monitoring and Plant Control Capabilities

Understand Utility Billing Rates and Configuration

Understand Current and Future Energy Costs

Demand ManagementProcess Optimization

LightingHVAC/Building Improvements

Alternative Energy UtilizationProcess Upgrades

Energy Efficient Equipment

Energy management program

High Benefit PotentialLow Capital Costs

High Benefit PotentialModerate to High Capital Costs

Moderate to Low Benefit PotentialLow Capital Costs

Page 157: Biosolids and Residuals Processing & Energy Management

Electrical Utilities

Page 158: Biosolids and Residuals Processing & Energy Management

United States Electric Grid

• ..

Page 159: Biosolids and Residuals Processing & Energy Management

Utility Distribution Systems

Electric Utility Customers

Electric Utility

Electric Cooperative

Utility Grid

Page 160: Biosolids and Residuals Processing & Energy Management

Electrical Utility Billing

“How” you are charged for energy is just as important as “how much” energy you use.

Page 161: Biosolids and Residuals Processing & Energy Management

Utility Bill Example

Page 162: Biosolids and Residuals Processing & Energy Management

Electrical utility bills are typically comprised of several “charges”.

• Energy Usage Charge (kWh)

Energy consumed during the billing period.Typically “Flat Rate” or “Time of Use”.

• Demand Charge (kW)

Typically 15-30 minute peak power demand during a billing period

• Fixed Charges

Independent of demand or usage.Facility chargesMinimum demand/energy charges

Page 163: Biosolids and Residuals Processing & Energy Management

The demand profile establishes both “demand” and “energy usage”.

Page 164: Biosolids and Residuals Processing & Energy Management

Demand ratchets can significantly impact electrical utility cost.

Dem

and

(K

W)

80% Annual Demand Ratchet Example

Page 165: Biosolids and Residuals Processing & Energy Management

Demand ratchets can significantly impact electrical utility cost.

Page 166: Biosolids and Residuals Processing & Energy Management

“Time of Use” energy and demand billing is very common

Page 167: Biosolids and Residuals Processing & Energy Management

0

1

2

3

4

5

6

7

8

9

10A

vera

ge E

lect

ric

Uti

lity

Co

st ₵

/KW

H

Utility billing structures will vary significantly

Demand Charges

Energy Charges

Fixed Charges

Plant A Plant B

Page 168: Biosolids and Residuals Processing & Energy Management

Energy efficiency benefit example:LED Lighting

• LED outdoor lighting reduces plant’s outdoor lighting demand by 50kW

• Annual Energy Savings - 175,000 kWh per year.

59

Page 169: Biosolids and Residuals Processing & Energy Management

Energy efficiency benefit example:LED Lighting

So…..

175,000KWH X 8.5₵/KWH = ~$15,000/yr. of savings right?

Maybe not!.......

60

Page 170: Biosolids and Residuals Processing & Energy Management

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KW

)

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LED Lighting Evaluation – Water Treatment Plant

Plant Demand Profile

Energy efficiency benefit example:LED Lighting

SVEC Rate LP-10 - $17/kW any time, $0.041/KWH any time LED light demand offset - $10,400/yr, LED light energy usage offset - $7,100/year

61

50kW Peak Demand Reduction

Page 171: Biosolids and Residuals Processing & Energy Management

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LED Lighting Evaluation – Wastewater Treatment Plant

Plant Demand Profile

Energy efficiency benefit example:LED Lighting

SVEC Rate LP-10 - $17/kW any time, $0.041/KWH any time LED light demand offset - $0

LED light energy usage offset - $7,100/year

62

Peak Demand(No Demand Reduction)

Page 172: Biosolids and Residuals Processing & Energy Management

Key Point.

“When” energy is used and “how much” energy is used determines the overall cost.

63

Page 173: Biosolids and Residuals Processing & Energy Management

Demand Management

“Using Energy More Efficiently”

64

Page 174: Biosolids and Residuals Processing & Energy Management

Common Demand Management Strategies

Manage plant operations to reduce demand during on-peak hours

Defer non-critical operations to off-peak hours

Interlock intermittent loadsUtilize on-site power generation

capacity to manage plant demandElectric utility load response programs

65

Page 175: Biosolids and Residuals Processing & Energy Management

DEMAND MANAGEMENT

STRATEGY

Electric Utility Billing Rate

Demand Profile

Process Flexibility

Demand Management Strategies Will Depend on Multiple Elements

Page 176: Biosolids and Residuals Processing & Energy Management

Plant demand profile impacts energy costs

Page 177: Biosolids and Residuals Processing & Energy Management

Plant demand profile impacts energy costs

• Evaluate the energy costs for two demand profilesEnergy Charge – 3.0¢/KWHMonthly Demand Charge - $10.00/kW

Energy Usage

Energy Charge @ 3.0¢/KWH

Metered Demand

Demand Charge @ $10.00/KW

Total Charges

AverageCost per/KWH

High Peaking Scenario

2330400 KWH

$69,912 6500kW $65,000 $134,912 5.8¢/KWH

Low Peaking Scenario

2330400 KWH

$69,912 3700kW $37,000 $106,912 4.6¢/KWH

Page 178: Biosolids and Residuals Processing & Energy Management

Case Study – Managing plant loads to reduce demand charges – HRRSA

• Electric Utility RateDemand charges - $17.33/KW (any 15 min

period)Energy Charges $0.041/KWH

• Opportunity – Stop non-critical mixing loads during each 20 min filter backwash cycle.Filter backwash loads (~100hp)Digester mixing loads (~85hp).

• Annual benefit - ~$10,000/year (@ 80% load factor) in demand savings

Page 179: Biosolids and Residuals Processing & Energy Management

Case Study – Reduced demand charges through filter backwash timing

Daily Demands, June 2011

The Cause: Automatic Deep-bed

filter backwash process during on-

peak periods - ~150kW

The Response: Move timing to

lower demand periods. Potential

to save ~$1500 per month

Filter Backwashing

causing high demand

charges

On-Peak$15/KW

5.7₵/KWH

Off-Peak$1/KW

3.4₵/KWH

Page 180: Biosolids and Residuals Processing & Energy Management

Case Study – Managing demand during on-peak periods

0

100

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De

man

d (

KW

)

Average Weekday ( kW )

Average On-Peak Demand – 437kW

On-Peak$15/KW

5.7₵/KWH

Stop Electric Blowers and Start Engine Blowers

Problem: Stopping electric blowers 10 minutes

after On-Peak period began. ~$20,000/Year in

excess demand charges

Off-Peak$1/KW

3.4₵/KWH

Optimum On-Peak Demand – 265kW

Page 181: Biosolids and Residuals Processing & Energy Management

Demand Management Key Points

• Demand Management primary objective is to lower energy costs.

• Demand Management strategies can be implement at a low or zero cost.

• Power monitoring and an understanding of the utility billing structure are key components to developing demand management strategies

72

Page 182: Biosolids and Residuals Processing & Energy Management

Onsite power generation systems can be used to manage demand

Standby Power Generator Systems Biogas Fueled CHP Systems

Page 183: Biosolids and Residuals Processing & Energy Management

* 2.0₵/KWH O&M costs included** Does not include fixed charges

Average Fuel and Energy Costs

On average, generating electric energy costs more than purchased electric energy

Fuel SourceAverage Fuel Cost

($/MMBTU)

Electric Energy Conversion

Efficiency (%)Cost of Electric Energy

Generated ($/KWH)

No.2 Non-Road Diesel @ $3/Gal

$21.43 37.5% $0.23*

Natural Gas $7.70 37.5% $0.088*

Electric Utility $17.88 100% $0.071**

Page 184: Biosolids and Residuals Processing & Energy Management

Onsite Power Generation Systems –Peak Shaving

Operate generators to reduce demand charges This strategy can be risky!

EPA emission restrictions Better to defer load

Page 185: Biosolids and Residuals Processing & Energy Management

Load management is valuable to electric utilities

Electric Utility Customers

Electric Utility

Electric Cooperative

Utility Grid

Page 186: Biosolids and Residuals Processing & Energy Management

Demand Response Programs

End user’s ability to shed load is valuable to electric utilities

Many electric utilities will pay end users for “capacity”.

Plant owner is compensated by the utility to have the standby power generators available in the event of an utility emergency

Generally less than 100 hours/year of operation

Page 187: Biosolids and Residuals Processing & Energy Management

EPA Emission Requirements

• EPA National Emission Standards for Hazardous Air Pollutants (NESHAP)Regulates the Carbon Monoxide emissions for

existing non-emergency enginesRegulations not applicable to emergency use

application and biogas fueled CHP systems.

• EPA New Source Performance Standards (NSPS)New non-emergency generators must meet stringent

emission limits. Most applications require emissions after treatment for non-emergency applications

• Air Permitting

Page 188: Biosolids and Residuals Processing & Energy Management

Resource Recovery

79

Page 189: Biosolids and Residuals Processing & Energy Management

Energy Sources Available

• Biogas• Thermal Energy• Chemical Energy• Hydraulic Energy• Renewable Energy

80

Page 190: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

Typical WW plant will support 15-30kW of generation capacity per MGD

Page 191: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

35%40%

Page 192: Biosolids and Residuals Processing & Energy Management

Biogas to energy systems have been around a while!

Popular Science1922

Boy haven’t we come a long way in the last 90 years….

Page 193: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

“Free” fuel source

Generate an average of 20% to 40% of the electric energy usage.

Considered renewable energy source.

Generally feasible where energy costs are above 7.5₵/KWH

Page 194: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

Image Courtesy GE/Jenbacher Engines

Reciprocating Internal Combustion EngineMicroturbine

Page 195: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

Prime Mover Technology

Common Size Range

(kW)

Typical Electrical

Efficiency (%)

Typical Thermal

Efficiency (%)

Installed Cost ($/kW)

Gas Conditioning

Requirements

Spark Ignited Reciprocating Engines

150-5000kW

35%-40% 25%45% with

exhaust heat recovery

1500 - 2000$/kW with

Heat Recovery

Moderate

Microturbines 30 –250kW

30% 45% 2000-2500 $/kW with

Heat Recovery

High

Fuel Cells 100 –250kW

50% $5000+ Very High

Stirling Engines(New Technology)

~50kW 25% 45% $2500+ Low

Page 196: Biosolids and Residuals Processing & Energy Management

Waste Heat Recovery Systems

• Beneficial Uses of Thermal EnergyDigester Heating (Most Common)Building Heat and Cooling (Absorption

Chillers)Sludge Drying

Absorption Chiller Process Diagram

Page 197: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

CHP systems can be used to drive process equipment Offset plants purchased power with

mechanical energy Common applications are process pumping

and aeration Benefit is

dependent on the process demand.

Page 198: Biosolids and Residuals Processing & Energy Management

Combined Heat and Power Generation Systems - CHP

CHP systems can be used to generate electricity

Offset plant’s purchased power with electricityBenefit is not dependent on process

demands.Possible to

increase benefit by selling energy directly the utility.

Page 199: Biosolids and Residuals Processing & Energy Management

Energy generated from biogas can be sold directly to the utility

TREATMENT FACILITY

Utility Meter

Utility Service

CHP System

Offset Purchased Utility Power Source

OR

Sell Energy Directly To Electric Utility

Page 200: Biosolids and Residuals Processing & Energy Management

0

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Plant Demand Profile with and without 1000kW CHP System

Demand kWW/O CHP

Demand kWW/ CHP

Utility rates have a significant impact on CHP system benefit

~1000kW demand loss with 1 day of CHP system downtime

Peak Demand with 1 day of CHP system downtime

Peak Demand with continuous CHP system operation

CHP Downtime

Page 201: Biosolids and Residuals Processing & Energy Management

CHP System Benefit AnalysisSVEC – Rate LP10

• 3 day CHP peak period downtime resulted in a 40% loss of the CHP system benefit for the billing period.

• Demand ratchets can extend the loss for up to 12 months! – 80% 12 month ratchet could result in a loss of ~$170,000/year

ElectricUtility Cost

CHP Demand [email protected]/KW

CHP Energy Offset @ $0.041/KWH

CHPSystem Benefit

CHP System Operation % Savings

No CHP $164,000 N/A N/A N/A N/A

1000kW Base Load –Continuous Operation

$119,200 $17,300 $27,500 $44,800 27%

1000kW Base Load – 1 day CHP Down Time

$133,000 $0 $26,000 $26,000 10%

Page 202: Biosolids and Residuals Processing & Energy Management

Some utilities purchase renewable energy on a energy charge only rate.

$0.00

$0.02

$0.04

$0.06

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$0.10

$0.12

$0.14

12:0

1am

1:00

am

2:00

am

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am

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am

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am

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am

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am

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am

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am

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0am

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0am

12:0

0pm

1:00

pm

2:00

pm

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pm

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pm

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pm

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0pm

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0pm

Ener

gy C

ost

$/K

WH

Time of Day

Duke Energy (NC) Rate PP-N Rate Option A

On-PeakMonday-Friday

(9.05¢/kWH)Off-Peak

Weekends and Holidays (5.18¢/kWH)

No Demand Ratcheting!!!!

Page 203: Biosolids and Residuals Processing & Energy Management

Benefit may depend on renewable energy portfolio standards and goals.www.dsireusa.org

Source:dsireusa.org

Page 204: Biosolids and Residuals Processing & Energy Management

Power Monitoring

Page 205: Biosolids and Residuals Processing & Energy Management

Power monitoring is key to energy management and optimization

Page 206: Biosolids and Residuals Processing & Energy Management

Benefits from incorporating energy usage data into process operations

Page 207: Biosolids and Residuals Processing & Energy Management

Monitor individual loads as well as overall distribution equipment loads

Page 208: Biosolids and Residuals Processing & Energy Management

Power monitoring dashboard example

99

Page 209: Biosolids and Residuals Processing & Energy Management

Typical Energy Management Opportunities

Page 210: Biosolids and Residuals Processing & Energy Management

The treatment process typically consumes 90% of the energy usage

101

Grit

1%

Screens

1%

Clarifiers

3%

Wastewater

Pumping

12%

Lighting and

Buildings

6%

Chlorination

1%

Belt Press

3%Anaerobic

Digestion

11%

Gravity Thickening

1%

Return Sludge

Pumping

1%

Aeration

60%

Page 211: Biosolids and Residuals Processing & Energy Management

Secondary TreatmentActivated Sludge with Advanced Treatment and Nitrification

Activated Sludge with Advanced Treatment, No Nitrification

Activated Sludge with No Advanced Treatment or Nitrification

No Activated Sludge, Trickling Filter

kWh/MG

1,000

1,400

1,900

1,600

National Energy Benchmark Data

Source: WEF MOP-32

Page 212: Biosolids and Residuals Processing & Energy Management

Energy Optimization – Secondary Treatment Considerations

• Excessive operating units (too many tanks online)

• DO control (excessively high DO)

• Blower turndown limitations

• Over mixing• Diffuser fouling• Inefficient aeration

equipment• Primary clarifier efficiency

Page 213: Biosolids and Residuals Processing & Energy Management

Damaged equipment

Damaged Diffuser

Page 214: Biosolids and Residuals Processing & Energy Management

Aeration equipment can impact energy efficiency

• Conversion to fine bubble is not always cost effective.• Have to make an economic case to change to fine

bubble from surface aerators• Cost of energy impacts economic case

Aerator Type

SAE

lbO2/hp-hr

AE

at 2 mg/L DO

lbO2/hp-hr

Surface Aerators 1.5 – 3.2 0.7 – 2.5

Coarse Bubble 1 - 2.5 0.5 – 1.6

Fine Bubble 6 – 8 2.0 - 4.0

Aerator technologies oxygen transfer efficiencies

Page 215: Biosolids and Residuals Processing & Energy Management

Questions?

Bryan R. Lisk, PE, CEMSenior AssociateHazen and Sawyer – Raleigh Office(919) [email protected]