NC AWWA-WEA 93rd Annual Conference November 12, 2013 Tim Woody Resource Recovery Division Director,...

NC AWWA-WEA 93rd Annual Conference

November 12, 2013

Tim WoodyResource Recovery Division Director, City of Raleigh

Jonathan TreadwayP.E, BCEE, CDM Smith

TAKE 2 – BIOSOLIDS STRATEGY MODIFICATIONS FOR THE CITY OF RALEIGH TO TAKE ADVANTAGE OF

TECHNOLOGY ADVANCEMENTS

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Presentation Outline

1. Project Background and Objectives2. Biosolids Management Alternatives3. Selected Project Direction4. Implementation Plan5. Conclusion

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City of Raleigh provides wastewater service to nearly 500,000 people

• Neuse River WWTP– 44 mgd average

• Smith Creek WWTP– 1.2 mgd

• Little Creek WWTP– 0.7 mgd average

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Goals for Master Plan Update

• Identify financially feasible management strategy• Demonstrate cost-effectiveness compared to the

“base case”• Update 2008 Biosolids Master Plan with new

technologies• Account for changing conditions• Advance the goals of the City’s EMS program for

biosolids

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Changing Conditions Driving Update

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Changing Conditions Driving Update

2008

2012

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Overview of Management Strategies Considered

Alternative Management Strategy1 Base Case*

2 Anaerobic Digestion + Solar Drying3 Thermal Hydrolysis + Anaerobic

Digestion + Solar Drying

* Base case includes diversified outlets:• Alkaline stabilized Class A product (Raleigh-Plus)• Third party composting• Aerobically digested Class B product• Landfill

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Management StrategiesAlt. 1 - Base Case (Aerobic Digestion)

7 DT/day

57 DT/day

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Management StrategiesAlt. 2 - Anaerobic Digestion + Solar Drying

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40 DT/day

New Facilities Include:• New GBT Building• Three An. Digesters (2.75 MG each)• Biogas Storage• Upgraded Dewatering• 16 Solar Dryers

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Management StrategiesAlt. 3- Thermal Hydrolysis + Anaerobic Digestion + Solar Drying

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New Facilities Include:• Pre-screening and Pre-dewatering• Thermal Hydrolysis Equipment• Two An. Digesters (1.6 MG each)• Upgraded Dewatering • Biogas Storage• 8 Solar Dryers

32 DT/day

NC AWWA-WEA 93rd Annual Conference11JT


Comparison of Alternatives - 20 year net present worth

Alt. No.

Description Capital Cost($M)

O&M Cost($M)

Total Cost($M)

2008 An. Digestion + Thermal Drying $153.4 $43.6 $197.0

1 Base Case $ 28.3 $82.1 $110.4

2 An. Digestion + Solar Drying $ 97.5 $ 34.1 $131.6

3Thermal Hydrolysis + An. Digestion + Solar Drying

$ 81.2 $ 27.6 $ 108.8

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Evaluation Criteria and Summary of Results

Alt. No.

Description Net Present Value of

Costs($M)

O&M Cost per Dry Ton

Non-Cost

Criteria

Greenhouse Gas Off-

Set (metric ton

CO2/yr)

1 Base Case $110.4 $237 58% 1,000

2 An. Digestion + Solar Drying $131.6 $144 83% 5,000

3 Thermal Hydrolysis + An. Digestion + Solar Drying $ 108.8 $140 82% 14,000

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Non-cost factors include: 1) regulatory requirements, 2) public health and environmental impacts, 3) outlet diversification, 4) operator friendliness, 5) ease of maintenance, plus 6 others.


Recommended ImprovementsPre-Screening Platform

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• Free-standing outdoor structure

• Two mechanical screens for co-settled sludge on top

• Screening drop to dumpster below

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Recommended ImprovementsPre-Dewatering Facility

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• Pre-Dewatering (2-Story Bldg.) • Cake Bins Storage (Outdoors)

– Screened solids are pre-dewatered by centrifuges – Discharged to outdoor cake bins using screw conveyors

THP FEED PUMPS

TO THPCAKE BINS

CENTRIFUGES

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Recommended ImprovementsThermal Hydrolysis Process

PulperFlashTank

Reactors (3)Digester

Feed Pumps


Recommended ImprovementsAnaerobic Digesters

• Prestressed concrete tanks• 64-ft diameter• Cone bottom• Draft tube mixers mounted

to concrete cover• Digester gas flare• Adjacent digester building

for pumps, etc.• Outdoor heat exchangers for

cooling sludge from THP


Recommended ImprovementsFinal Dewatering Building

• Option A: Reuse Existing Facilities– Refurbish or replace 3 BFPs– Continue to operate centrifuge– Ventilation and other improvements to

mitigate corrosion problems– Can continue to use truck loading

station• Option B: New Final Dewatering

Building and Truck loading Station


Recommended ImprovementsSolar Dryers

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• Eight modules, 42-ft x 435-ft• Fans, louvers, controls to optimize

temperature and humidity for drying


Recommended ImprovementsNutrient Recovery

• Optional addition for enhanced sustainability

• Reduce sidestream loading on liquid treatment process

• Recover phosphorous• Third-party responsible for

product marketing• Can be added at any time

Photo Courtesy of Ostara

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Recommended ImprovementsCombined Heat and Power (CHP) Engine Generator

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– Single 1.75 MW generator – Containerized units available– Optional, but recommended for

sustainability when THP is implemented– Generate electricity and heat– Requires biogas conditioning system– Engine can be purchased, leased, or

procured via 3rd-party Energy Services Co. (ESCO)

Photos Courtesy of GE

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Recommended ImprovementsImplementation Schedule

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Phase Year Description Cost

Phase I 2016

Pre-screening, pre-dewatering, thermal hydrolysis, anaerobic digesters, CHP engine, additional cake storage

$59.3 M

Phase II 2021 Eight solar drying modules, BFP replacement and

final dewatering building improvements $26.2 M

Phase III 2028 Replace existing conveyance equipment and truck

loading station $4.3 M

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Recommended Improvement Planvs. 2008 Master Plan

2016-2020 2021-2025 2026-2030$0

$20

$40

$60

$80

$100

$1202008 MP ($151 M) 2012 Update ($90 M)

(mill

ions

)

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THANK YOU

NC AWWA-WEA 93rd Annual Conference November 12, 2013 Tim Woody Resource Recovery Division Director,...

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