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 Screen entrance is sealed to channel Flow In Flow Out

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 or 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 1200 1000 800 600 400 200 0

Raw Sludge % Volatile 88.0 86.0 84.0 82.0 80.0 78.0 76.0 74.0 72.0 After Before 70.0

Grit Production 500 450 400 350 300 250 200 150 100 50 0

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??