1. Selecting the Best Dewatering Technology for a Challenging Ash Slurry
Presented by:
Elijah Williams, PE, City of Greensboro
Christopher Crotwell, PE, HDR
NC AWWA-WEA Annual Conference 2013

2. 1 2 3 4 5 AGENDA Background Available Technologies Testing
Selected Equipment 5
Summary and Conclusions

3. 1
Background

4. TZ Osborne WRF BACKGROUND
Rated for 40 mgd
In service since 1983
Major Processes:
Preliminary Treatment
Primary Treatment
Secondary Treatment
Biosolids Treatment
Incinerator
Ash Clarifier
Courtesy: Bing.com

5. Major Processes (continued):
TZ Osborne WRF BACKGROUND
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

6. Existing Belt Filter Presses
TZ Osborne WRF BACKGROUND
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

7. Schematic of Ash Slurry Dewatering Process
Existing Ash Dewatering Schematic
BFP (Klampress Circa 1980’s)
Fluidized Bed Incinerator
Clarifier/ Thickener
Centrifuge
Cake
Scrubber
Belt Conveyor
Water
To Landfill
Primary Sludge
WAS
Drain to head of WWTP

8. Ash Slurry Characteristics
Date
% Solids
Flow (gpm)
Wet lbs/hr
Dry lbs/hr
3/25/2013
3.59% 46
23,018
826
2.49%
573
3/26/2013
9.64% 40
20,016
1,930
2.38% 47
23,519
560
3/27/2013
2.77% 38
19,015
527
7.82% 37
18,515
1,448
3/28/2013
4.75% 49
24,520
1,165
3/29/2013
4.58%
1,077
3/30/2013
1.95%
449
4/1/2013
3.27% 44
22,018
720
AVERAGE
4.23%
20,018
927

9. Ash Slurry Sieve Analysis

10. Available Technologies2
Available Technologies

11. Potential Dewatering Technologies
Centrifuge
Belt Filter Press
Filter Press (Plate and Frame)
Rotary Fan Press
Rotary Screw Press
Dewatering Bin
Vacuum Filters
Dewatering Screw

12. Belt Filter Press
BDP
Andritz
Phoenix

13. Recessed Chamber Filter Press (Plate and Frame Type)
Andritz
MW Watermark

14. Rotary Fan Press
Fournier

15. Rotary Fan Press

16. Rotary Fan Press
Screen (pressure side)
Screen (drain side)

17. Screw Press
FKC

18. Screw Press

19. 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.
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)

20. 3
Testing

21. Sample Testing Results
Manufacturer
Recommended Model
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% 3
Phoenix
WXG-6
6.0
Polydyne C
1.98
48%
90%
Centrifuge 4
Centrisys
CS18-4
11.8
Not provided
60% - 70%
98% %
Recessed Chamber Filter Press (Plate and Frame Type) 5
Model 1000/LP
None
n/a
98% 6
M.W. Watermark
1500MM
9.4
4.9
71%
99%
Screw Press 7
FKC
SHX-800x4500L
6.24
7.0
5.2
55%
92%
Rotary Fan Press 8
Fournier
6-900/6000CVP
5.6
6.8
Ashland K274FLX
2.0

22. 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

23. Screw Press Pilot Results: 50% solids, 86% capture,
6.48 lb/dry ton poly (Greensboro’s polymer)

24. Rotary Fan Press Pilot Results: 47% solids, 86% capture,
3 lb/dry ton poly (Greensboro’s polymer)

25. Economics Parameter Value Hauling Cost (tipping fee) $38/ton
Economic Assumptions
Parameter
Value
Hauling Cost (tipping fee)
$38/ton
Power Cost
$0.066/kWhr
Neat Polymer Cost (Polydyne)
$0.90/lb
Discount Rate
4.5%
Operation
24/7
Equipment Data
Assumption
Screw Press
Rotary Fan Press
Total Hp
17.5 hp
4 hp
Polymer Usage 8 3
Capture Rate
86%
Cake %Total solids (TS) 50 47
Annualized O&M Costs
$3,000(1)
$30,000(2)
Equipment Cost
$425,000
$472,000
20-year NPV
$8.3 million(3)
$8.6 million
Notes:
(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)

26. 4
Selected Equipment

27. Selected the Fournier Rotary Fan Press based on:
Selected Equipment
Selected the Fournier Rotary Fan Press based on:
Built in redundancy
Worked well with Greensboro’s polymer
Small footprint
Smaller overall weight
Ability to expand in the future
Quick results during piloting

28. Conclusions and Summary5
Conclusions and Summary

29. Sample testing not representative, pilot testing is preferred
Summary and Conclusions
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

30. Acknowledgements City of Greensboro Lori Cooper Don Howard Mike Buck
HDR
Will Shull
Mary Knosby

31. Christopher Crotwell, PE
Questions?
Elijah Williams, PE
Christopher Crotwell, PE
THANKS!

32. Mass Balance