Need for Project Class A Sludge Anaerobic Digestion System Heat - - PowerPoint PPT Presentation

Presentation for MWEA Process Committee Seminar November 6, 2013

SCREENING AND CONSEQUENCES

Tom Grant, Hubbell Roth and Clark Sandra Diorka, Delhi Charter Township

Need for Project

• Class A Sludge Anaerobic Digestion System Heat

Exchangers Plugging

Plugging Heat Exchangers

• All raw sludge is macerated such that fibers, plastics,
• etc. are relatively small, about ¼” wide x 3” to 6”

long

• During sludge recirculation and pumping through 1

1/4” and 3” diameter heat exchanger tubes, small pieces become entwined and form ropes that plug the heat exchangers

• Heat exchangers required cleaning every other day

Plugging Heat Exchangers

Existing Not Effective

• Existing headworks grinding with capture was not

effectively removing screenable materials from wastewater

• Requires seasonal cleaning of primary clarifiers and

disposal of wet settlings to drying beds

• Causing early wear on POTW equipment
• Excessive labor spent removing rags from all process

equipment

• Wasting pumps
• Telescopic valves
• Decant valves
• Digester heat exchangers

Existing Not Effective

Existing Not Effective

• Removal of about 40 pounds wet material per day

New Screen Selection: Site Visits, Round 1

• Traditional bar screens
• Visited Michigan WWTPs to view their headworks

screens:

• South Lyon, ¼” bar
• Grand Rapids, ¼” bar

Bar Screen Observations

• During site visits noticed:
• Bar screens had excessive pass through
• Equipment had grease balls and strings hanging
• Resulting screenings were very dirty
• Bar screen room and environment was gross
• Primaries, aeration tanks, and secondaries had floaters
• Conclusion: Bar screens are not so good. What else

can we get?

Pilot Testing at POTW

• How do we pick between round holes and slots (bar

screen)? How big should the holes be?

• Devised an in house experiment
• Fabricated a slide gate with four different “screens”

built in

• 1/8 inch round hole (perforated plate)
• 1/4 inch round hole
• 1/4 inch “bar” hole
• Window screen (around 1mm hole size)

Pilot Testing at POTW

• Placed each gate in the influent channel for a

specified time

• Weighed the material collected
• Window screen was considered “100%” capture
• Roughly 8000 pounds per day
• Round holes collected roughly 4 times the amount of

material as the bar or slot shaped openings

• Conclusion: We want round holes!!

New Screen Selection: Site Visits, Round 2

• North Kent, 1 to 3 mm drum screen

New Screen Selection: Site Visits, Round 2

• Kalamazoo, 6 mm

bandscreen

Flow Out

Screen entrance is sealed to channel

Flow In

Discovered and Purchased U.K. Study

• Purchased “National Screen Evaluation Facility, Inlet

Screen Comparative Report” performed between 1999 and 2011 by the UK Water Industry Research

• Installed and compared the performance of 27 different

headworks treatment products

• Finescreen
• Stepscreen
• Combined screen (bar or round with processing)
• Bandscreen
• Reported % capture of material
• Maintenance frequency

Finescreen

• Screen rotates

around to carry stuff to the top

• Can have round
• r bar openings

Stepscreen

• Like a fine screen
• Steps move and

transport stuff to the top – body of the screen holds still

Discovered and Purchased U.K. Study

• Bandscreens showed the best performance
• Highest screen capture rate
• Lowest risk of “pass through” or “carry over” because of

seal between opening and the channel

• Study showed two brands had the highest screen capture

rate

• Screens incorporating slots or bar spacing showed the

lowest performance

• Conclusion: We want one of the bandscreens with

the highest capture rate!

Site Visits Round 3

• Made a three day trip to visit four additional screens
• Ishpeming, MI – Jones and Atwood band, 6 mm holes
• Sheboygan, WI – Brackett Green band, 6 mm holes
• Madison, WI – Brackett Green band, 6 mm holes
• Fond du Lac, WI – JWC Fine Screen, 3 mm holes

Site Visits

• Ishpeming

Site Visits

• Sheboygan

The Final Decision

• How did we decide?
• The cleanest end product
• 3mm because
• Madison had 6mm hole size with the same type of heat

exchanger

• Heat exchangers still plugged
• Fond du Lac had 3mm hole size with the same type of

heat exchanger

• Heat exchangers did NOT plug!!

What Happened After ?

• Heat exchangers no longer routinely cleaned
• Primaries have no rags or floating “salad”
• Grease hauled less often (contains only grease)
• Aeration tanks do not have to be “skimmed”
• No more condoms
• Wasting pumps no longer need to be routinely

cleaned

• Sludge storage decant valves have remained clean
• Telescopic valves no longer have to be cleaned

Screenings Production

200 400 600 800 1000 1200

70.0 72.0 74.0 76.0 78.0 80.0 82.0 84.0 86.0 88.0

Before After Raw Sludge % Volatile

50 100 150 200 250 300 350 400 450 500

Grit Production

Before – NOT Gritty

After – Actually Grit

Engineering and Construction Design Engineering

• 2 screens, each handle 6 mgd, bypass/overflow

manually cleaned channel 5 mgd

• Tight site – fit between existing influent screw

pumps, grit tank and primary clarifiers

• Existing hydraulic grade line is fixed
• Poor soils for building & channels foundation

Tight Site

Poor Soils Helical Screw Piles Foundation

Construction

• Extended schedule due to piles, originally June 2012

completion, first screen started in October 2012

• Alternate bypass

Construction Gravity Bypass

Construction

Construction

Construction

Construction

Results

Results

Questions??