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

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

1 Background

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

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

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

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

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

Ash Slurry Sieve Analysis

Available Technologies 2 Available Technologies

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 Andritz Phoenix

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. 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)

3 Testing

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- 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 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

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)

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)

4 Selected Equipment

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

Conclusions and Summary 5 Conclusions and Summary

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

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

Christopher Crotwell, PE Questions? Elijah Williams, PE Elijah.Williams@greensboro-nc.gov Christopher Crotwell, PE Christopher.Crotwell@hdrinc.com THANKS!

Mass Balance