Selecting the Best Dewatering Technology for a Challenging Ash SlurryPresented by: Elijah Williams, PE, City of GreensboroChristopher Crotwell, PE, HDR

NC AWWA-WEA Annual Conference 2013

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Background

Avai lab le Technologies

Test ing

Selected Equipment

Summary and Conclus ions

AGENDA

Background1

Click icon to add pictureT Z O s b o r n e W R F B A C K G R O U N D

Incinerator

• Rated for 40 mgd• In service since 1983• Major Processes:

• Preliminary Treatment• Primary Treatment• Secondary Treatment• Biosolids Treatment

Courtesy: Bing.com

Ash Clarifier

T Z O s b o r n e W R F B A C K G R O U N D

• Major Processes (continued):– Biosolids Treatment

• Thickening• Storage• Dewatering• Incineration• Disposal

• Incineration:– (2) incinerators– (3) centrifuges for dewatering of thickened

sludge before entering incinerator– Ash slurry is formed from quenching

process– Thickener/clarifier for ash slurry– Effluent to head of plant– Ash slurry feeds (1) belt filter press

T Z O s b o r n e W R F B A C K G R O U N D

• Existing Belt Filter Presses– Concerns:

• High maintenance• Low cake percent solids after switch in

type of incinerator sand• Nearing end of useful life• Low capture rate

– City developed dewatering screw to pilot• Operated for short period but would

clog and not allow water to drain back down the spiral conveyor

Schematic of Ash Slurry Dewatering Process

Existing Ash Dewatering Schematic

BFP (Klampress Circa 1980’s)

Fluidized Bed

IncineratorClarifier/ Thickener

Centrifuge

Cake

Cake

Cake

Scrubber

Belt Conveyor

Water

Cake

To Landfill

Primary Sludge

WAS

Drain to head of WWTP

Ash Slurry Characteristics

Ash Slurry CharacteristicsDate % Solids Flow (gpm) Wet lbs/hr Dry lbs/hr

3/25/20133.59% 46 23,018 8262.49% 46 23,018 573

3/26/20139.64% 40 20,016 1,9302.38% 47 23,519 560

3/27/20132.77% 38 19,015 5277.82% 37 18,515 1,448

3/28/2013 4.75% 49 24,520 1,1653/29/2013 4.58% 47 23,519 1,0773/30/2013 1.95% 46 23,018 4494/1/2013 3.27% 44 22,018 720

AVERAGE 4.23% 44 20,018 927

Ash Slurry Sieve Analysis

Available Technologies2

Potential Dewatering Technologies

• Centrifuge• Belt Filter Press• Filter Press (Plate and Frame)• Rotary Fan Press• Rotary Screw Press• Dewatering Bin• Vacuum Filters• Dewatering Screw

Belt Filter Press

BDP

Phoenix

Andritz

Recessed Chamber Filter Press (Plate and Frame Type)

Andritz MW Watermark

Rotary Fan Press

• Fournier

Rotary Fan Press

Rotary Fan Press

Screen (pressure side) Screen (drain side)

Screw Press

FKC

Screw Press

Comparison of Technologies

Alternative Advantages Disadvantages

Centrifuge • Becoming more common for medium to large WWTPs.

• Drier cake solids than most options. Small footprint. • Minimal wash water required and therefore smaller

recycle stream.

• Can not handle high grit sludge. • Slightly higher equipment costs. • Higher power costs. Can be more difficult to

maintain for local maintenance staff

Belt-filter Press • Most common option in existing plants. Easy to view solids during dewatering process.

• Can handle grit in sludge. • Lower power cost.

• Continuous wash water is required which generates recycle stream

• Dewatered solids not as dry as centrifuge• Maintenance intensive

Filter Press (Plate-and-Frame)

• Drier cake solids than most options. • Can handle grit in sludge.

• High equipment cost. • Labor intensive process with batch operation• High O&M cost

Rotary Fan Press • Minimal wash water required (intermittent)• Slow speed• Small footprint• Built in redundancy

• Cake solids generally not as high as centrifuge, but drier than belt filter press.

• High sand content in sludge can lead to premature wear of the screens inside channels.

Screw Press • Cake solids nearly as dry as centrifuge.• Minimal wash water. • Sturdy, reliable equipment.

• Large footprint • No redundancy within unit

Dewatering Bin • Simple operation• Low maintenance

• Batch process• Finer particles are not collected• Experience with coal ash; limited experience with

municipal sludge incinerated ash

Notes:1. EPA Report on Emerging Management Technologies (2006)

2. Wastewater Treatment & Reuse (2004); WEFTEC 08 proceedings

3. Riedel, D: An Investigation into the Mechanisms of Sludge Reduction Technologies (2009)

Testing3

Sample Testing Results

Sample Manufacturer RecommendedModel

Total Solids (% by weight) pH Polymer

Used

Polymer Dose

(lb/Ton)

Cake Solids

(% by weight)Capture (%)

Belt Filter Press

1 BDP Industries 1.5m 3DP 9.5 4.6 Polymer name not provided 4 - 7 45% - 50% 95%

2 Andritz Power Press - - 8844FS 1.50 45% 95%

3 Phoenix WXG-6 9.5 6.0 Polydyne C-6257 1.98 48% 90%

Centrifuge

4 Centrisys CS18-4 11.8 - Not provided 0 - 0.5 60% - 70% 98% - 99.5%

Recessed Chamber Filter Press (Plate and Frame Type)

5 Andritz Model 1000/LP - - None n/a 48% 98%

6 M.W. Watermark 1500MM 9.4 4.9 None n/a 71% 99%

Screw Press

7 FKC SHX-800x4500L 6.24 7.0 Polydyne C-6257 5.2 55% 92%

Rotary Fan Press

8 Fournier 6-900/6000CVP 5.6 6.8 Ashland K274FLX 2.0 55% 95%

Pilot Testing

• Selected Rotary Fan Press and Screw Press for pilot testing– Rotary Fan Press (Fournier) in March 4 – 8, 2013– Screw Press (FKC) onsite twice, February 7-8, 2013 and

March 11, 2013

Pilot Location

Screw Press Pilot

• Results: – 50% solids, – 86% capture, – 6.48 lb/dry ton poly

(Greensboro’s polymer)

Rotary Fan Press Pilot

• Results: – 47% solids, – 86% capture, – 3 lb/dry ton poly

(Greensboro’s polymer)

EconomicsEconomic Assumptions

Parameter ValueHauling Cost (tipping fee) $38/tonPower Cost $0.066/kWhrNeat Polymer Cost (Polydyne) $0.90/lbDiscount Rate 4.5%Operation 24/7

Equipment DataAssumption Screw Press Rotary Fan Press

Total Hp 17.5 hp 4 hpPolymer Usage 8 3Capture Rate 86% 86%Cake %Total solids (TS) 50 47Annualized O&M Costs $3,000(1) $30,000(2)

Equipment Cost $425,000 $472,00020-year NPV $8.3 million(3) $8.6 millionNotes: (1) O&M costs include replacement of wear plates every 5 years, screens every 5 years and labor for these replacements.(2) O&M costs include replacement of blades and deflectors every 9 months and replacement of screens every 3 years.(3) Does not include costs associated with new polymer/polymer system (pumps, pipe, mixing equipment, polymer trials, cost of new

polymer)

Selected Equipment4

S e l e c t e d E q u i p m e n t

– Built in redundancy– Small footprint– Smaller overall weight– Quick results during

piloting

– Worked well with Greensboro’s polymer

– Ability to expand in the future

• Selected the Fournier Rotary Fan Press based on:

Conclusions and Summary5

S u m m a r y a n d C o n c l u s i o n s

• Ash slurry is uncharacteristic of other municipal sludges (fine particles)

• Sample testing not representative, pilot testing is preferred

• Project is currently in the Bid Phase• Rotary fan press is best for this unique

ash slurry and situation• Suggest investigating both the rotary fan

press and screw press for future projects• Rotary Fan press can have advantages

based on location and application including:– Small footprint– In place redundancy– Closed system

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Acknowledgements

• City of Greensboro– Lori Cooper– Don Howard– Mike Buck

• HDR– Will Shull– Mary Knosby

Questions?

Elijah Williams, PEElijah.Williams@greensboro-nc.gov

Christopher Crotwell, PEChristopher.Crotwell@hdrinc.com

THANKS!

Mass Balance