Evaluation of Filtration Technologies and Upgrade

Report
Presenter: Walid Al-Ani, P.Eng, P.E., BCEE, LEED® AP
Project Manager for Stantec Consulting Michigan Inc.

Overview of the Cadillac WWTP

Background Information

Filtration Technologies Evaluation &
Selection

Design Highlights

Construction Highlights

Post-Construction Performance

Questions and Answers
2

Plant Rated for 3.2 MGD Average Daily Flow and 4.5 MGD Maximum Daily
Flow

Influent Pump Station – Screw Pumps

Equalization Basin

Preliminary Treatment

Primary Treatment

Secondary Treatment – Activated Sludge/Chemical Addition for Phosphorous
Removal

Rotating Biological Contactors

Tertiary Filters

UV Disinfection

Anaerobic Digestion

Biosolids Land Application
3
4


Project plan prepared in 2006 to address overall plant needs –
Requirement for seeking State Revolving Funds (SRF)
Tertiary Treatment major needs identified:
◦ Replacement of the sand filters that were nearing the end of their useful life
◦ Replacement of the sampling pumps
◦ Replacement of the samplers

Design completed in the summer of 2007

Construction completed in the early spring of 2008

Overall construction cost approximately $3,800,000


Construction cost for Tertiary Treatment Improvements approximately
$1,000,000
Construction cost for the installed filters approximately $620,000
5

Three sand filters (Hydroclear)
commissioned in 1977

Some rehabilitation work performed over
the years including replacement of filter
media, valves, and control system

Deteriorating performance and extensive
backwashing necessary
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Traveling Bridge Filters

Traveling Hood Filters

Disc Cloth Media Filters

Synthetic Media Filters

Deep Sand Filters

Membrane Biological Reactors (MBRs)
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
Continuous downflows, automatic backwash, low head,
granular medium depth filter.

Filter bed is divided into independent filter cells.


Treated wastewater flows through the medium by gravity and
exits to the clearwell plenum via a porous-plate, polyethylene
underdrain.
Each filter cell is backwashed individually by an overhead
traveling – bridge assembly, while the other cells remain in
service.

During the backwash cycle, wastewater is filtered continuously
through the cells that are not being backwashed.

Example is the US Filter Davco Products – Gravisand.
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Source Aqua-Aerobics Systems, Inc.
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


Similar to the Traveling Bridge Sand Filter.
Uses a pneumatically driven self – propelled hood
instead of a conventional rail-mounted traveling
bridge.
Simpler, more compact installation, lower equipment
cost compared to the Traveling Bridge Sand Filter.
Example is EIMCO Water Technologies.
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Source Water Online
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




Filter tank contains a series of circular disk elements
covered with a specialized cloth media.
The cloth media traps particulates within its interior as
well as forming a particulate layer upon its outer
surface.
Backwash cycle begins at a predetermined water level.
During the backwash cycle, the center tube rotates while
a centrifugal pump draws filtered water through a
suction header from the clean side of the filter cloth.
Examples are the Aqua-Aerobic Aqua Disks and the
Kruger Hydrotech Disc Filter.
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Source Aqua-Aerobic Systems, Inc.
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
Filters use highly porous synthetic medium.

Porosity modified by compressing the filter medium.




Wastewater flows through medium; not around filtering
medium as in conventional sand and anthracite filters.
Wastewater introduced in bottom of filter and flows
upward through filter medium, which is retained by two
porous plates.
Upper porous plate raised mechanically in backwash.
Flow to filter continues and air introduced below lower
porous plate causing medium to move in a rolling
motion.
Example is Schreiber’s Fuzzy Filter.
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Source Schreiber
Source:
Schreiber
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• Wastewater introduced into bottom of filter where it
flows upward through a series of riser tubes.
• Wastewater then flows upward through downward
moving sand and exits filter.
• Sand particles and trapped solids are drawn downward
into the suction of an airlift pipe. A small volume of
compressed air draws sand, solids, and water upward.
• At the top of the airlift, the dirty slurry spills over into a
central reject compartment. Sand settles and is cleaned
further as it moves down through a washer.
• Example is Parkson’s DynaSand Filter.
16
Source: DynaSand
Source DynaSand
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• MBRs combine secondary & tertiary treatment into one
process.
• Integrated bioreactor uses membranes immersed in
bioreactor; re-circulated MBR in which mixed liquid circulates
through a membrane module located outside the bioreactor.
• In the integrated bioreactor wastewater is drawn through the
membranes using vacuum. Compressed air is used to scour
the membrane surfaces.
• In the re-circulated MBR wastewater is pumped into the
membranes where solids are retained inside the membranes
and wastewater passes through to the outside. The
membranes are backwashed systematically to remove solids.
• Examples are MBRs manufactured by Zenon, US Filter
Memcor, and Envirogroup.
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Source: Memcor
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
Required performance based on NPDES effluent
limitations for the summer months listed in the
Cadillac WWTP permit:
◦ 30-Day Average BOD5
7 mg/L
◦ 30-Day Average TSS
20 mg/L
◦ 30-Day Average Ammonia Nitrogen (N) 0.9 mg/L
◦ 30-Day Average Phosphorous
0.5 mg/L
• Evaluation of all technologies indicated that the
effluent limitation for TSS could be met.
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Filter Type
Budgetary Price *
Traveling Bridge Sand Filter
$200,000
Traveling Hood Sand Filter
$300,000
Disc Cloth Media Filter
$500,000
Synthetic Media Filter
$700,000
Deep Bed Sand Filter
$800,000
Membrane Biological Reactor
$2,400,000
* 2006 Prices – Based on equipment cost from manufacturers
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Filter Type
Remarks
Traveling Bridge Sand Filter
Does not fit into the existing building.
Traveling Hood Sand Filter
Does not fit into the existing filter
footprint but may fit into existing
building with structural modifications.
Disc Cloth Media Filter
Fits into the existing filter footprint
but requires removal of the mud well.
Synthetic Media Filter
Fits into the existing filter footprint
but requires removal of the mud well.
Deep Bed Sand Filter
Does not fit into the existing building.
Membrane Biological Reactor
Does not fit into the existing filter
footprint but may fit into existing
building with structural modifications.
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Filter Type
Remarks
Warrants Further
Consideration
Traveling Bridge Sand
Filter
Does not fit into existing
building
No
Traveling Hood Sand
Filter
Does fit into existing filters
footprint
No
Disc Cloth Media Filter
Fits into existing filters
footprint
Yes
Synthetic Media Filter
Fits into existing filters
footprint
Yes
Deep Bed Sand Filter
Does not fit into existing
building
No
Membrane Biological
Reactor
Does not fit into existing
building and is too costly
No
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Filter Type
Installations in MI
and other
Surrounding States
as of early 2007
Remarks
Warrants
Further
Consideration
Disc Cloth
Filter
Media
(Aqua –
Aerobic)
Several nationwide
including MI
•Will not require pilot testing due
to sufficient experience in MI
•Site visit to Sutton Bay WWTP, MI
•Conference call with
Superintendent of Champagne
Sanitary District WWTP
Yes
Disc Cloth
Filter
Media
(Kruger)
One in MI one in
Ravenna, OH
•May require pilot testing due to
limited experience in MI
•Site visit to Ravenna WWTP, OH
Yes
Synthetic
Media
Filter
(Schreiber)
One in MI
•Likely to require pilot testing
due to limited experience in MI
and high loading rates due to
small footprint
No
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Item of
Comparison
Cloth Media Disc Filter
(Aqua-Aerobic)
Cloth Media Disc Filter
(Kruger)
Equipment Cost
$547,000
$500,000
Structural
Modifications
•Demolition of Mud Well
•Columns and beams remain
•Partial demolition of mud well
•Columns and beams remain
•Significant concrete work required
to accommodate open channel
flows
Access Into Existing
Building
•Requires demolition of building exterior
wall
•Requires demolition of building
exterior wall
Experience in
Michigan
•Several Installations
•Pilot testing not required
•One installation only as of early
2007
•Pilot testing likely required
Experience at Similar
Installations
Sutton Bay WWTP
•In Operation since 2006
•No Mechanical Problems
•Good Workmanship
Ravenna WWTP
•Difficulty meeting the 2 MGD
peak flow with one filter out of
service
•Belt supporting the discs has
failed
•Major rigging required for belt
replacement
Urbana-Champagne Sanitary District WWTP
•In Operation since 2005
•Good responsiveness during construction,
start-up, and post construction
•Decision to install same type of filters at
the larger District’s WWTP
•Peak flows of 17 MGD were handled with
no reported problems
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Decision was to adopt the cloth media filter
technology (Aqua-Aerobic) based on the
following:




Established experience nationwide including
Michigan
Ease of Maintenance
Demonstrated ability to handle peak flows
Ability to meet the project’s strict milestones
since no pilot testing would be required
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

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Limitations on when construction could occur
had to be established, due to the NPDES
Limitations
Higher SS discharge limits allowed December
1 through April 30 (30 lbs/day on a monthly
basis compared to 20 lbs/day for rest of the
year)
Therefore, taking the existing filters off-line
and completing installation of the new filters
was allowed for December 1 through April 1
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


Structural integrity had
to be confirmed to
allow partial
demolition of the walls
and slab
Existing piping
arrangement had to be
confirmed to allow
bypass of the filters to
the disinfection
process
Demolition of existing
exterior walls had to
be addressed to verify
access issues
28


Hydraulic
calculations had to
be performed to
ensure new filters
would not be a
bottleneck
Filters, piping,
platforms, and
controls had to be
fitted into the
existing space
29

Entire work (demolition, installation, start-up, on-line) had to be
completed in three months
30

Access limited through existing building wall
31

Filters demolished and removed
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All piping in gallery removed
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“Mud Well” slab demolished
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New Floor
35
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Filter concrete support pads
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New filter piping
37
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Filters installed on concrete pads
38
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New piping in gallery
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Filters in operation
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Filter Control Panels
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Backwash and Sludge Valves
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Back Wash Cycle
 Back Wash Initiation:
◦
◦
◦
◦

Sludge Cycle
 Sludge Removal Initiation:
Water level exceeds specified level
Time interval elapses
Manual back wash cycle
High level float switch activates
Back Wash Set Points:
◦ Back Wash interval, time between
automatic backwash cycles
◦ Back Wash duration, wash time for
each collection manifold
◦ Back Wash level, water level that
triggers a back wash cycle
◦ Time interval elapses
◦ Back wash counts elapse
◦ Manual sludge cycle

Sludge Cycle Set Points:
◦ Sludge interval, time between
automatic sludge cycles
◦ Backwash count, number of back
washes between automatic sludge
cycles
◦ Sludge duration, duration of the
sludge cycle
43

Filters are operating successfully and meeting the NPDES requirements
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