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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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Final Design

Final Design

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Installation

Installation

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Installation

Installation

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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?

THANK YOU!