Other Water Treatment Plant Residuals Dewatering Equipment: An Investigation of Screw Press Technology

Lynn Williams, P.E. (WA)

• Discuss residual handling technologies

• Comparison of capital and O&M costs

• Pilot testing findings

• Water quality and piloting considerations

Presentation Roadmap

Brown and Caldwell 2

• Sedimentation sludge or spent filter backwash water• Removal of both organic and inorganic contaminants• Particulate and colloidal

• Chemical softening for removal of calcium and magnesium• Remove trace metals, radioactivity,

and particles (if surface water)

• Ion exchange processes • Remove cations or anions • Produce brine residual

• Membrane concentrate• Particulates and dissolved solids

Types of Residuals

Brown and Caldwell 3

4

• Non-mechanical dewatering

• Drying beds

• Geobags

• Mechanical dewatering

• Belt filter press

• Centrifuge

• Screw press

Residual Solids Handling Alternatives

Brown and Caldwell

Lake Oswego-Tigard Water Partnership

Brown and Caldwell 5

Lake Oswego-Tigard Water Partnership

Brown and Caldwell 6

Mechanical Dewatering Alternatives

• Combination of gravity draining and mechanical pressure

• Distribute uniformly across width of belt

• Finished Cake: typically 15-30%

Belt Filter Press

Brown and Caldwell 8

• High rotational speeds

• Require hearing protection when operators are in the vicinity

• Finished cake: typically 20 to 30%

Centrifuge

Brown and Caldwell 9

• Slow moving device

• Cake: 20 to 40%

Screw Press –Emerging Technology

Brown and Caldwell 10

Brown and Caldwell 11

Pros/ConsConsiderations Centrifuge Belt Filter Press Screw Press

Ease of Use Moderate Moderate Easy

Mechanical Complexity Moderate Moderate Low

Chemical Use Moderate Moderate Slightly higher

Energy Use High Moderate Low

Space Small Large Medium

Reliability Adequate Adequate Superior

Noise High Moderate Low

Brown and Caldwell 12

ParameterCentrifuge

(40 HP)Screw Press

(6.5 HP)

Construction Cost

Equipment Cost $470,000 $520,000

Building Construction & Installation

$700,000 $950,000

Total Constructive Cost $1,200,000 $1,500,000

O&M Cost

Electrical Cost $3,000 $1,000

Solids Disposal Cost $83,000 $68,000

Polymer Cost $6,000 $8,000

Annual Labor Costs $34,000 $22,000

Maintenance Costs $3,000 $1,000

Total O&M Cost $130,000 $100,000

Net Present Value $3,000,000 $2,900,000

Reference: Lake Oswego-Tigard Predesign Report (MWH)

Screw Press Pilot Study Setup and Findings

• Feed solids = 1 to 3 percent

• Willamette River Water Treatment Plant solids

• Utilized tanker

Comparison of Two Manufacturer’s Screw Presses

Brown and Caldwell 14

Video

Brown and Caldwell 15

Pilot Testing Results – Mfr 2

Brown and Caldwell 16

0

50

100

150

200

250

300

350

400

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12

solid loading [lbs / h] pressure at cone [PSI]ca

ke s

olid

s (%

TS)

scre

w s

peed

[% o

f max

imum

]

Test Runs

cake solidsscrew speedpressure at conesolid loading

Pilot Testing Results – Mfr 2

Brown and Caldwell 17

90

91

92

93

94

95

96

97

98

99

100

5

10

15

20

25

30

35

40

45

50

1 2 3 4 5 6 7 8 9 10 11 12

capture rate (%)

cake

sol

ids

(% D

S)po

lym

er (l

bs a

ctiv

e / t

onD

S)

Test Run

cake solids

polymer consumption

capture rate

Pilot Testing Results

Brown and Caldwell 18

Parameter Mfr 1 Mfr 2

Average Range Average Range

Inlet TS (%) 1 (1-2) 5 (2-6)Outlet/Cake TS (%) 37 (29-43) 37 (35-39)

Polymer Dose (lb/dry ton) 9 (7-11) 10 (6-19)

Speed (rpm) 0.45 (0.3 - 0.75) 0.9 (0.5-1.1)

Solids Loading Rate (kg/hr) 14 (12-16) 91 (70-140)

Water Quality and Piloting Considerations

• Consider what your facility is removing• Arsenic, identify type of residuals created when selecting arsenic removal

technologies• Residuals will be different for filter backwash water compared to membranes• Concentrate disposal with nanofiltration, RO, and desalination

• Dewatered liquid• Do you recycle liquid stream or waste it?

Water Quality Considerations for Residuals Disposal

• Certified cleaned tanks and mixing

• Identify solids align with future processes

• Work with equipment vendors to capture data appropriate for design

Pilot Study Considerations

Brown and Caldwell 21

Screw press technology is an emerging technology and viable alternative that should be considered when examining mechanical dewatering technologies.

Recommend bench or pilot scale study

The new Lake Oswego-Tigard WTP will have screw press technology.

Importance of water quality considerations when helping vendors transition to the water industry.

Conclusions and Findings

Brown and Caldwell 22

Lake Oswego-Tigard Water Partnership

City of Lake Oswego

City of Tigard

Brown and Caldwell Program Management Team

MWH Design Team

Willamette River Water Treatment Plant

Acknowledgements

Questions and Discussion

Thank You

Brown and Caldwell 25