Biosolids and Residuals Processing & Energy Management Workshop
December 12, 2013
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
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
Program Agenda
• Regulatory Framework• Sludge Thickening• Sludge Dewatering• Sludge Conditioning• Sludge Stabilization• Side Stream Treatment• Post-Dewatering Advanced Stabilization
4
THERE WILL BE ACTIVE LEARNING COMPONENTS TO
THE SEMINAR
As my daughter says…
“If you snooze you lose”
5
REGULATORY FRAMEWORK &
CONSIDERATIONS
6
Residuals regulation is governed at the federal level under 40 CFR 503
• Major SectionsGeneral ProvisionsLand ApplicationSurface DisposalPathogen & Vector
Attraction ReductionIncineration
7
For land application sewage sludge must meet certain requirements
8
• Non-Hazardous
• Criteria Pollutants
• Pathogen Content
• Vector Attraction Reduction
“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
40 CFR 503 regulates specific heavy metals as “criteria” pollutants
• Ceiling Concentrations
• “Exceptional Quality” Thresholds
• Cumulative Pollutant Loading Rates
• Annual Pollutant Loading Rates
10
Exceed ceiling levels then land application is not permitted!
11
“Exceptional Quality” has lower criteria pollutant concentrations.
12
Cumulative loading rate tracking required for “non-EQ” biosolids.
13
Annual pollutant loading rate also applies for “non-EQ” biosolids.
14
DON’T’ BE “NON-EQ”
Save yourself a lot of regulatory headaches on cumulative and annual pollutant loading rates
tracking
15
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
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
“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
Class A pathogen reduction by “time and temperature”.
19
“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
20
“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)
21
Vector attraction reduction is regulated under 40 CFR 503.33.
22
Active learning exercise…
What federal regulation establishes the standards management of sewage sludges by land application, land disposal, and incineration?
23
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
Active learning exercise…
Discuss with a neighbor what FOUR criteria must be demonstrated in order to land apply biosolids:1.2.3.4.
25
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
• 9VAC25 – 20Fees
• 9VAC25 – 31RegulationsVPDES Permitting
• 9VAC25 – 32RegulationsVPA Permitting
27
In Virginia new biosolids management rules have recently been promulgated…
• 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.
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
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
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
An example of how regulatory changes can destabilize biosolids management.
32
The rules are changing for existing and new sewage sludge incinerators (SSI).
33
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)
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
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”
• 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
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.
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
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
Questions
41
C. Michael Bullard, P.E.Vice PresidentNational Residuals & Biosolids LeaderHazen and Sawyer – Raleigh Office(919) [email protected]
Biosolids and Residuals Processing & Energy Management Workshop
December 12, 2013
Biosolids 101 - Program Agenda
• Sludge Thickening• Sludge Dewatering• Sludge Conditioning for Thickening and
Dewatering
43
SLUDGE THICKENING
44
Dissolved Air Flotation Thickener
45Source: WEF, MOP-8.
Dissolved Air Floatation Thickener
46Image: Komline-Sanderson
Gravity Belt Thickener
47
Source: WEF, MOP-8.
Gravity Belt Thickener
48
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
Rotary drum thickener
50
Gravity Thickening
51
Source: WEF, MOP-8.
Gravity sludge thickener
52
Image: Madison (WI) MSD @ http://www.madsewer.org/SolidWasteTreatment.htm
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
Biosolids 101 - Program Agenda
• Sludge Thickening• Sludge Dewatering• Sludge Conditioning for Thickening and
Dewatering
54
SLUDGE DEWATERING
55
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
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
57
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
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
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
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
Biosolids 101 - Program Agenda
• Sludge Thickening• Sludge Dewatering• Sludge Conditioning for Thickening and
Dewatering
62
SLUDGE CONDITIONING FOR
THICKENING AND DEWATERING
63
Polymer Types
• Polymer is used for sludge conditioning and to enhance settling, thickening, and dewatering
• Electronic charge• Charge density• Molecular weight• Molecular structure
64
• Milky/cloudy liquid totes• Higher concentration of
active polymer• Shorter self life than dry
polymer• Usually 25% to 60%
active polymer
65
Emulsion Polymer
• Pellet or flake provided in large bulk bags
• Lower concentration of active polymer
• Longer shelf life than emulsion polymer
66
Dry Polymer
Dry Polymer
67
Questions?
68
Laurissa Cubbage, PESenior Principal EngineerHazen and Sawyer – Richmond Office(919) [email protected]
Sludge Stabilization
69
Sludge Stabilization - Outline
• Aerobic Digestion• Anaerobic Digestion
70
AEROBIC DIGESTION
71
Aerobic Digestion – Overview
• Why Aerobic Digestion?Plant size (~< 5-mgd)ComplexityBiosolids constraintsEnergy
72
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
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+])
Aerobic Digestion – Overview
75
Highlights:
• Tank Sizing & Operation
• Alkalinity and pH
• Aeration for Oxygen Supply
• Process Monitoring and Control
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
Aerobic Digestion – Tank Sizing
• VSR as function of temperature and SRT:
U.S. EPA, 1979
38% minimum
VSR for Class B
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%
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
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
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
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
Aerobic Digestion – Process Monitoring and Control
• Performance considerations:VSRSRT
• Monitoring considerations:
83 Stege and Bailey, 2003
Sludge Stabilization - Outline
• Aerobic Digestion• Anaerobic Digestion
84
ANAEROBIC DIGESTION
85
Anaerobic Digestion – Overview
• Why Anaerobic Digestion?Plant sizeBiosolids constraintsEnergy
86
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
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
Anaerobic Digestion – Temperature Regime
• Temperature impacts anaerobic digestion VSR Methane formation
89
WEF, 2010
Grady, Daigger, Lim, 1999
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
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
Anaerobic Digestion – Heating and Temperature Control
92
Boiler
Digester Gas
HeatExchanger
Hot
Wat
er
WEF, 2010
Fuel Oil
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
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
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%
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.
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.
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
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
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
Anaerobic Digestion – Gas Storage
101
Floating
Fixed
Membrane
Metcalf & Eddy, 2003
Anaerobic Digestion – Biogas Handling and Safety
102
Example Diagram: Single Digester w/ Gas Mixing System
WEF, 2010
Anaerobic Digestion – Biogas Handling and Safety
103
Anaerobic Digestion – Biogas Utilization
104
Combined Heat and Power
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.
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
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
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.
Questions?
109
Evan C. Bowles, PE, ENV SPPrincipal EngineerHazen and Sawyer – Richmond Office(804) [email protected]
Side Stream Treatment andAdvanced Stabilization Technologies
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
SIDESTREAM TREATMENT
NITROGEN REMOVAL
3
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
• 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.
• 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
SIDESTREAM TREATMENT
PHOSPHORUS REMOVAL
7
Uncontrolled Struvite formation after anaerobic digestion can be a problem
8
OSTARA offers a “controlled” struvite recovery reactor system
9
Multiform Harvest offers a competing controlled struvite recovery reactor
10
OSTARA struvite recovery reactor system at the Nansemond WWTP.
11
OSTARA struvite recovery reactor system at the Nansemond WWTP.
12
Product quality can vary depending on the struvite recovery system installed.
13
OSTARA CrystalGreen Product Multiform Harvest Product
Active learning exercise…
The two major constituents of concern in side stream from dewatering anaerobically digested sludge are:
1. ___________________2. ___________________
14
Active learning exercise…
What are the five chemical elements found in struvite:
1. ___________________2. ___________________3. ___________________4. ___________________5. ___________________
15
POST-DEWATERING
TREATMENT TECHNOLOGIES
16
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
Basic process configuration for composting unit treatment process.
18
Image: Inland Empire Regional Composting Authority (http://www.ierca.org/process/compostprocess.html)
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
Fluid bed thermal oxidation is the current “standard” in incineration
20Image Courtesy IDI Technologies
Thermal drying systems are “rated” by evaporation rate capacity
21
Rotary drum thermal drying is the most prominent technology for “large” systems.
22
Source: Andritz-Ruthner
South Cary WRF thermal drying facility 8,800 lb/hour evaporation rate capacity.
23
Compact rotary drum drying systems are available for “smaller” size systems.
24
Photo Courtesy: Andritz-Ruthner
Belt drying systems are a more recent addition to the sludge drying market.
25
Source: Andritz-Ruthner
Belt dryer installation in Biel, Switzerland with an evaporation rate 2,900 lb/hour.
26
Image: Andrtiz-Ruthner
Paddle dryers are the most common of the “indirect” dryer systems.
27
Source: Komline-Sanderson
Paddle drying system in Mason, OH with 6,500 lb/hour evaporation rate capacity.
28
Fluid bed dryers are not common in the North American market.
29
Source: Andritz-Ruthner
Fluid bed dryer in Houthalen, Belgium with evaporative capacity 8,000 lb/hour.
30
Image: Andritz-Ruthner
Biosolids gasification is an emerging technology for energy recovery.
31
Solar sludge drying beds can be covered to reduce seasonal impacts
32
Source: Veolia-Water / Kruger
Automation can be applied to increase solids loading rates to reduce footprint.
33Source: Veolia-Water / Kruger
Active learning exercise…
What are three major types of processes used for producing a Class A biosolids after dewatering:
1. ___________________2. ___________________3. ___________________
34
Active learning exercise…
What is the primary criteria used for sizing an thermal drying system?
35
Active learning exercise…
What are the five major types of thermal drying systems on the market:
1. ___________________2. ___________________3. ___________________4. ___________________5. ___________________
36
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
Reference Materials
38
Reference Materials
39
Reference Materials
40
Questions?
C. Michael Bullard, P.E.Vice PresidentNational Residuals & Biosolids LeaderHazen and Sawyer – Raleigh Office(919) [email protected]
41
Biosolids and Residuals Processing & Energy Management Workshop
December 12, 2013
Energy Management
Agenda
• Electric Utilities Overview• Electric Billing• Demand Management• Resource Recovery• Power Monitoring• Typical Energy Efficiency Opportunities
Energy management is more than energy efficiency
EnergyManagement
Energy Procurement
Energy Efficiency
Resource Recovery
Demand Management
Energy Awareness
Energy Monitoring
Energy Modeling
and Planning
Energy Management has potential savings of 10-40%
45
Biogas
Process
Optimization
Renewables
Energy Procurement
Energy Management is a Continuous Process
46
Energy Management Program
Energy Auditing
Implement
Monitor & Verify
Education & Training
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
Electrical Utilities
United States Electric Grid
• ..
Utility Distribution Systems
Electric Utility Customers
Electric Utility
Electric Cooperative
Utility Grid
Electrical Utility Billing
“How” you are charged for energy is just as important as “how much” energy you use.
Utility Bill Example
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
The demand profile establishes both “demand” and “energy usage”.
Demand ratchets can significantly impact electrical utility cost.
Dem
and
(K
W)
80% Annual Demand Ratchet Example
Demand ratchets can significantly impact electrical utility cost.
“Time of Use” energy and demand billing is very common
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
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
Energy efficiency benefit example:LED Lighting
So…..
175,000KWH X 8.5₵/KWH = ~$15,000/yr. of savings right?
Maybe not!.......
60
0
200
400
600
800
1000
1200
1400
0:0
0
2:0
0
4:0
0
6:0
0
8:0
0
10
:00
12
:00
14
:00
16
:00
18
:00
20
:00
22
:00
0:0
0
De
man
d (
KW
)
Time
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
0
200
400
600
800
1000
1200
0:0
0
2:0
0
4:0
0
6:0
0
8:0
0
10
:00
12
:00
14
:00
16
:00
18
:00
20
:00
22
:00
0:0
0
De
man
d (
KW
)
Time
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)
Key Point.
“When” energy is used and “how much” energy is used determines the overall cost.
63
Demand Management
“Using Energy More Efficiently”
64
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
DEMAND MANAGEMENT
STRATEGY
Electric Utility Billing Rate
Demand Profile
Process Flexibility
Demand Management Strategies Will Depend on Multiple Elements
Plant demand profile impacts energy costs
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
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
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
Case Study – Managing demand during on-peak periods
0
100
200
300
400
500
600
700
0:3
0
1:3
0
2:3
0
3:3
0
4:3
0
5:3
0
6:3
0
7:3
0
8:3
0
9:3
0
10
:30
11
:30
12
:30
13
:30
14
:30
15
:30
16
:30
17
:30
18
:30
19
:30
20
:30
21
:30
22
:30
23
:30
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$1/KW
3.4₵/KWH
Optimum On-Peak Demand – 265kW
Demand Management Key Points
• Demand Management primary objective is to lower energy costs.
• Demand Management strategies can be implement at a low or zero cost.
• Power monitoring and an understanding of the utility billing structure are key components to developing demand management strategies
72
Onsite power generation systems can be used to manage demand
Standby Power Generator Systems Biogas Fueled CHP Systems
* 2.0₵/KWH O&M costs included** Does not include fixed charges
Average Fuel and Energy Costs
On average, generating electric energy costs more than purchased electric energy
Fuel SourceAverage Fuel Cost
($/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**
Onsite Power Generation Systems –Peak Shaving
Operate generators to reduce demand charges This strategy can be risky!
EPA emission restrictions Better to defer load
Load management is valuable to electric utilities
Electric Utility Customers
Electric Utility
Electric Cooperative
Utility Grid
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
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
Resource Recovery
79
Energy Sources Available
• Biogas• Thermal Energy• Chemical Energy• Hydraulic Energy• Renewable Energy
80
Combined Heat and Power Generation Systems - CHP
Typical WW plant will support 15-30kW of generation capacity per MGD
Combined Heat and Power Generation Systems - CHP
35%40%
Biogas to energy systems have been around a while!
Popular Science1922
Boy haven’t we come a long way in the last 90 years….
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
Combined Heat and Power Generation Systems - CHP
Image Courtesy GE/Jenbacher Engines
Reciprocating Internal Combustion EngineMicroturbine
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
Waste Heat Recovery Systems
• Beneficial Uses of Thermal EnergyDigester Heating (Most Common)Building Heat and Cooling (Absorption
Chillers)Sludge Drying
Absorption Chiller Process Diagram
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.
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.
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
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
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
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%
Some utilities purchase renewable energy on a energy charge only rate.
$0.00
$0.02
$0.04
$0.06
$0.08
$0.10
$0.12
$0.14
12:0
1am
1:00
am
2:00
am
3:00
am
4:00
am
5:00
am
6:00
am
7:00
am
8:00
am
9:00
am
10:0
0am
11:0
0am
12:0
0pm
1:00
pm
2:00
pm
3:00
pm
4:00
pm
5:00
pm
6:00
pm
7:00
pm
8:00
pm
9:00
pm
10:0
0pm
11:0
0pm
12:0
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!!!!
Benefit may depend on renewable energy portfolio standards and goals.www.dsireusa.org
Source:dsireusa.org
Power Monitoring
Power monitoring is key to energy management and optimization
Benefits from incorporating energy usage data into process operations
Monitor individual loads as well as overall distribution equipment loads
Power monitoring dashboard example
99
Typical Energy Management Opportunities
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%
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
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
Damaged equipment
Damaged Diffuser
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
Questions?
Bryan R. Lisk, PE, CEMSenior AssociateHazen and Sawyer – Raleigh Office(919) [email protected]