Coldwater WWTP - mi-wea.org 3 - Nitrofication with IFAS.pdf · Speed Turbocompressors at Coldwater...
Transcript of Coldwater WWTP - mi-wea.org 3 - Nitrofication with IFAS.pdf · Speed Turbocompressors at Coldwater...
11/2/2011
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Fishbeck, Thompson, Carr & Huber, Inc.
2011 MWEA Process Seminar
Ammonia Polishing with IFAS and High Speed Turbocompressors at Coldwater WWTP
Jim Flamming, P.E., Senior Process Engineer, FTC&H
Coldwater WWTP
� Coldwater, Michigan, USA
� Owned by Coldwater BPU
� Average flow: 3.2 mgd
Peak flow: 8 mgd
� BOD, TSS, ammonia,
phosphorus, and
pathogen removal
� Surface water discharge
� Treats residential, commercial,
some industrial, plus septage
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Coldwater WWTP
Background
� New discharge permit issued August 2007
� Included seasonal ammonia limits
� 2 mg/l from May through November
� Previously was report only
� Routine violations through spring and summer 2008
� CBPU hired FTC&H to investigate possible solutions
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Combined Biological Treatment Processes
� Pair fixed film and conventional activated sludge
� Done for decades in municipal WWTPs
� Offers advantages of both processes, minimizes
disadvantages
� Fixed Film – energy efficient, stable, resistant to shock loads
� Activated Sludge – improved settling characteristics, higher effluent quality
� Systems can be combined in several different ways
Trickling Filter Solids Contact Process
� TF/SC
� Combines trickling filter with relatively small activated sludge basin
� Majority of BOD removal done in trickling filter – low to moderate loading rates
� Activated sludge has low HRT, used for polishing
Trickling
Filter
Aeration Basin Secondary Clarifier
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TF/SC Design Criteria
� Design manuals list typical design criteria*� Trickling filters:
� BOD loading rates: 20-75 lb/day/1,000 cu ft of filter media/day
� Aeration Basins:� HRTs: 0.5 – 2.0 hrs (10-15% of strictly AS alone)� MCRTs: 0.2 – 2.0 days� F/Ms vary widely: 1.5 – 30
� At low TF loading rates, process is capable of nitrification, though achieving consistent results can be difficult due to the nature of the TF process
* - WEF, 2000; WEF/ASCE, 1998; Metcalf & Eddy, 2003
Nitrification in TF/SC Process
� To achieve higher levels of nitrification, add:
� Intermediate clarifiers downstream of TFs to reduce organic loads on SCs
� Solids reaeration basins to increase MCRT and inventory of nitrifiers; called TF/SC-R process
� Regardless of configuration, nitrifying in TFs can significantly reduce volume and aeration required for nitrification in subsequent aeration basins
� IFAS media could also be used to increase nitrification capacity in SC basins of TF/SCs if other modifications are not feasible; creating a TF/SC-IFAS system
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Engineering Review
and Problem Solving
� Coldwater TF/SC process
� Three, 115 ft dia TFs filled with 7 ft of cross flow plastic media
� Followed by two parallel 152,000 gallon solids contact aeration basins (each 70’ X 20’ X 14.5’ deep)
� Low TF BOD loading rates:� Average 10.5 lb/day/1,000 cu ft
� Maximum 44.8 lb/day/1,000 cu ft
� Minimum 1.1 lb/day/1,000 cu ft
� Significant but inconsistent nitrification observed in TFs
Engineering Review
and Problem Solving
� Expansion of aeration basins difficult due to high groundwater level at the site.
� Evaluated expanding the trickling filters
� Discussed options with Brentwood Industries
� Concrete tanks with aluminum domes
� 4th trickling filter would be expensive
� Investigated potential for upgrading aeration basins with IFAS media
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IFAS Systems
� Suspended media
� Poured into aeration basin
� Moves freely in mixed liquor
� Retained in basin typically
with in-basin screens
� Various manufacturers
IFAS Systems
� AccuFAS IFAS (Brentwood Industries)
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BioWin Modeling
� Used to size aeration requirements and predict effluent quality under various flow scenarios.
� Both basins in operation
� One aeration grid out of service
� One basin in operation, one out of service
� Modeling showed aeration expansion required
Aeration BasinTF Effluent Effluent
Sludge
Types of Aeration Blowers
� Aeration consumes 40-70% of energy used in activated sludge plants (WEF MOP OM-9)
� For supplying diffused aeration grids, 2 types:
� Positive Displacement
� Approx. 60% efficient
� Typically smaller (<100 hp)
� Output varies with speed,
not pressure
� Factory or OEM packages available
� Widely applied, low capital costs
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Types of Aeration Blowers
� Multistage Centrifugal:
� Approx. 65-75% efficient
� Wide range of sizes, typ. >50 hp
� Output varies with pressure
� Widely applied for over 100 yrs.
� Can be more expensive initially
than positive displacement
� PD and multistage blowers are the workhorses of the industry.
Times Are Changing!
� With renewed emphasis on energy efficiency, new styles of blowers are starting to be applied.
� High speed turbocompressors offer several potential advantages over traditional blowers:
� Higher efficiencies
� Lower maintenance costs
� Variable output
� Quiet operation
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High Speed Turbocompressors
� Operate at very high speeds:25,000 to 45,000 rpm
� No contact bearing surface: magnetic or airfoil bearings
� No contact = no friction = no wear parts
� Oil free operation; no lubrication requiredor bearings to service
� Very low maintenance
High Speed Turbocompressors
� 10-20% improvement in efficiency
� Operate on VFDs; maintaining best efficiency at turndowns of up to 50% of max output
� No contact – very low
vibrations – low noise
(<70 dB at op. speed)
� Factory supplied
pkg units w/ controls
� Typ. small footprints
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High Speed Turbocompressors
� Different styles from different manufacturers
� Magnetic Bearings – ABS/HST, Hoffman Revolution, Atlas Copco ZB-VSD; Spencer AyrJet
� Air Foil Bearings – HIS HT; APG-Neuros; Turblex; Aerzen; Howden
� Magnetic bearings prevent any contact during operation, but typically cost more upfront
� Most are direct drive units; Turblex also providesa separately geared unit with additional control capability
ABS/HST
� Five models
� 93-536 HP
� 600-10,400 scfm
� 5.5 – 18.2 psig
discharge pressure
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Coldwater WWTP
� Existing plant had two 75-hp, 900-scfm blowers
� Biowin model showed system required a firm
capacity of 3,260 scfm.
� Installed two 93-hp ABS/HST S2500-2-A-5; each 1,257
scfm at 8 psig
� Placed in new building; existing blowers remain as
backup units
� City doesn’t have historical flow and hp draw data for
blowers; difficult to compare
Final Design
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Results
Secondary effluent >
discharge limit 60 times
before IFAS
Secondary effluent >
discharge limit 43 times
after IFAS startup …
… 41 of those times were
as a result of industrial
plant failure
Results
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Summary
� IFAS can be applied to existing TF/SCs and other plants to increase sludge age and total inventory of nitrifiers, without increasing loads to secondary clafifiers, and reduce effluent ammonia concentrations.
� High-speed turbocompressors offer improved efficiency over other aeration blowers.
Fishbeck, Thompson, Carr & Huber, Inc.
Any Questions?
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