Biosolids Technology Overview · 2020. 2. 11. · Dewatering Comparison Belt Filter Press Screw...
Transcript of Biosolids Technology Overview · 2020. 2. 11. · Dewatering Comparison Belt Filter Press Screw...
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Biosolids Technology Overview
Solids Thickening
Solids Dewatering
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SOLIDS THICKENING
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Increasing solids concentration reduces the required digestion volume
0
10
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30
40
50
60
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80
90
0 2 4 6 8 10 12 14 16
GP
M
% Solids
Assumes 10,000 lbs/day
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Increasing solids concentration has an upper limit under conventional digestion
Percent Solids
Organic Loading @ 15 day HRT
(lbs VSS/cfDay) Limiting Criteria
1 0.03 Hydraulic
2 0.07 Hydraulic
3 0.10 Hydraulic
4 0.13 Hydraulic
5 0.17 Solids
6 0.20 Solids
7 0.23 Solids
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Facilities with digesters can benefit significantly
Digester No. 4(Primary)
Digester No. 1(Primary)
Digester No. 2(Secondary)
Digester No. 3(Secondary)
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Gravity thickeners are often overloaded
6” C.I. Secondary Sludge
8” C.I. Thickened Sludge
PS Thickener
WAS Thickener
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An example from Longview, Texas
1.21 MG
~15.0 days
Active Volume
HRT
3%
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HRT increases with thickened sludge
1.21 MG
24.9 days
Active Volume
HRT
5%
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Thickening should usually meet these goals
Maintenance friendly
Operations friendly
Capable of handling PS/WAS together
Ability to integrate odor control
Meet a 5% TS requirement
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Thickening options:
Gravity Belt Rotary Drum
Disk Membrane
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Gravity Belt Thickeners
Advantages• Low energy requirement• 90 – 98% capture rate• Can be odor controlled• Long term reliability• Ease of operation
Disadvantages• Larger footprint than other options
• Significant source of odor (if not enclosed)• Polymer dependent
• High wash water usage• Spray
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Rotary Drum Thickeners
Advantages• Fully enclosed
• Odors are contained• Smaller footprint
• Indoor/Outdoor use• Low wash water usage
Disadvantages• Higher capital costs
• Chance of shearing floc• Polymer dependent
• Can’t see thickening process
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Disk Thickeners
Advantages• Fully enclosed
• Odor is contained• Smallest footprint• Indoor/outdoor use
• Lower noise• Low power consumption
• Fully automated
Disadvantages• Newer technology
• Polymer dependent, high usage• Capacity of unit is relatively small
• Proprietary no competition
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Membrane Thickeners
Advantages• Use of existing infrastructure
• Treats sidestream to high quality• No return of ammonia• No return of phosphorus• No separate building
Disadvantages• High capital costs• Maintenance
• Need for pumps• Requires blowers
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Thickener Comparison
Gravity Belt Rotary Drum Disk Membrane
Hydraulic Capacity (GPD) 720,000 36,000-576,000 129,600-259,200 4-12 (g/d/ft^2)
Solids Capacity (lb/day) 54,741 2,400-48,000 10,560-21,120 varies
% Solids 4-8% 5-7% 4-8% 5%
Capture Rate 98% 93% 95% 99%
Footprint Large Medium Small Medium
Polymer need ( lbs/dry ton) 3 to 10 5 to 10 7 to 12 0
Capital Cost Low Medium Medium High
O&M Cost Low Low Low High
Comparing options…
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SOLIDS DEWATERING
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FILTER CLOTH
SLUDGE APPLIED SLUDGE OUT
WATER DRAWS OUT
What is mechanical dewatering?
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SLUDGE APPLIEDSLUDGE OUT
WATER DRAWS OUT
FILTER CLOTH
Dewatering units come in several forms
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Dewatering should usually meet these goals
Maintenance friendly
Operations friendly
Minimize O&M costs
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Hauling liquid sludge is not cheap
$0
$2,000
$4,000
$6,000
$8,000
$10,000
$12,000
$14,000
1-Sep 1-Oct 1-Nov 1-Dec 1-Jan 1-Feb
Monthly Liquid Sludge Hauling Cost
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A significant drop was immediately noticed
Solids,
lbs/day
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
$0
$2,000
$4,000
$6,000
$8,000
$10,000
$12,000
$14,000
Monthly
50% reduction
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The primary technology includes
Belt Filter Press
Centrifuge
Screw Presses
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Plate and Frame Press Drying Beds
Dewatering Boxes/Bags
Other dewatering options exist
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Belt Filter Press
Advantages• Low energy requirement• 90 – 98% capture rate• Long term reliability• Ease of operation
• Medium polymer usage
Disadvantages• Larger footprint than other options
• Polymer dependent• High wash water usage
• Spray• Regular O&M required
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BFP Options: How many belts do I want?
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The improved operation…
Clarifier Aerobic Digester
Pump
Polymer Belt Filter Press Belt Conveyor Dry Haul
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Dewatering Screw Press
Advantages• Fully enclosed
• Odors are contained• Smaller footprint
• Indoor/Outdoor use• Low wash water usage• Better cake percentage
Disadvantages• Polymer dependent• Can’t see process• More expensive
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Dewatering Screw Press
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Dewatering Screw Press
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General Process Flow
Digester 1
Digester 2
DayTank
PolymerTank
PolymerSkid
Screw Press
Stabilization
Pumps
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Advantages• “Cleaner” dewatering
process• Advanced technology • 20-26% dryness• 98% Solids Capture• Controls based operation• Compact footprint
Disadvantages• Highest power consumption• 20-25 lbs/tn polymer usage• Closed operation• Aggressive (shear) dewatering
process
Centrifuge
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Inside the centrifuge
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Advantages• Simple dewatering process• Advancing technology • Can achieve 85% dryness• Excellent water recovery• Very low polymer usage• Minimal labor during
dewatering
Disadvantages• Very large footprint• Labor intensive during
cleaning• Extended time for drying
Drying Bed
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Drying Bed
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Dewatering Comparison
Belt Filter Press Screw Press Centrifuge
% Solids 15-20% 17-25% 20-25%
Capture Rate 98% 95% 93%
Footprint Large Small Medium
Polymer need ( lbs/dry ton) 10 to 20 15 to 30 20 to 30
Capital Cost Low Medium High
O&M Cost Medium Low Medium
Comparing options…
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Sludge dewaterability comparison (BFP Example)
Expected Cake
Percentage %
Primary Sludge
Biological Sludge
Lime Sludge
Alum Sludge
Ferric Sludge
Carbon Sludge
0%
25%
5%
10%
15%
20%
Polymer Usage lbs/ton
15
0
5
10
20
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We need to condition the sludge with polymers for improved dewatering
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Polymer is plant and technology specific
Recommended Manufacturers
• Testing is required to determine appropriate polymer• Cationic (+)• Anionic (-)