Planning a New WTP? Use UV to Save Cost

Paul D. Swaim, P.E. – Jacobs/CH2M

Denver, Colorado

IUVA Americas Conference

February 27, 2018

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Acknowledgments:• Jason Curl, Bill Carter, Larry Schimmoller – CH2M/Jacobs Denver

• Joseph Zalla – CH2M/Jacobs Salt Lake City

• Todd Elliott – CH2M/Jacobs Minneapolis

• Denver Water

• Park City Municipal Corporation

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Denver Water Northwater Treatment Plant

– 150 mgd greenfield Northwater Treatment Plant

– CH2M performing process design of conventional filtration WTP

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Best Approach is Planning for UV at the Start of the Project

Lakeview 2

• Planning for UV means that UV can be readily accommodated:− overall hydraulic

gradeline− filter driving head − space planning− Electrical system

capacity−O&M access

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Disinfection Alternatives

1. Disinfection contact basin only with Free Chlorine (sized for Giardia)

2. Individual filter effluent (IFE) UV (Giardia) and DCB (virus)

3. Combined filter effluent (CFE) UV (Giardia) and DCB (virus)

3/2/2018

FLOCCULATION/SEDIMENTATION(6 DUTY, 0 STANDBY)

FILTERS + IFE UV(12 DUTY, 2 STANDBY)

DISINFECTION CONTACT BASINS(2 DUTY, 0 STANDBY)

RAPID MIX(6 DUTY, 0 STANDBY)

M

M

M

M

M

M

PRV/HYDRO

FLOCCULATION/SEDIMENTATION(6 DUTY, 0 STANDBY)

FILTERS(12 DUTY, 2 STANDBY)

DISINFECTION CONTACT BASINS(2 DUTY, 0 STANDBY)

UV REACTORS(3 DUTY, 1 STANDBY)

RAPID MIX(6 DUTY, 0 STANDBY)

M

M

M

M

M

M

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Some Filter Gallery Layouts

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A New Filter Gallery Does Not Have to Follow 20th

Century Filter Gallery Layouts

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Pros and Cons of IFE vs. CFE for the DW NTP• IFE Pros

– lower construction cost

– uses existing flowmeters, valves, and FCVs

– disinfects FTW

• IFE Cons– higher O&M cost

– more reactors

– cannot install after future GAC

– couple operation with filters (if UV shuts down, so does filter)

– expand with more filters/more UV

3/2/2018

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• CFE Pros – lower O&M cost– UV independent of filter operation– fewer reactors– could expand in same bldg– could modify to UV-AOP in future

• CFE Cons – higher construction cost– does not disinfect FTW– adds another building

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UV Disinfection Design Criteria

3/2/2018

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UV dose to provide >> 0.5 log Giardia inactivation– Provide 1.0 log Giardia (and Crypto) inactivation with similar system

150 mgd, 90% UVT

Number of trains (for CFE) dictated by flow range for reactor models, as determined by UV vendors

Redundancy– Match # of filters (N+2) for IFE

– N+1 for CFE

Considered both LPHO and MP options

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Chlorine Disinfection Design Criteria

3/2/2018

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150 mgd, in 2 equally sized DCBs (i.e., 75 mgd each)

Water quality assumptions

– Water temperature = 5 °C

– pH = 7.0

– Chlorine residual concentration = 1.6 mg/L

– Hydraulic efficiency/baffle factor = 0.7

– CT safety factor = 20%

If no UV disinfection, DCB provides 0.5-log Giardia inactivation with free chlorine

– DCB volume (total) = 3.2 MG

If UV disinfection, DCB provides 2.0-log virus inactivation with free chlorine

– DCB volume (total) = 0.5 MG

Assume rectangular DCB

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Updated Cost Summary

3/2/2018

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ChlorineOnly

IFE UV (MP)

CFE UV (MP)

DCB Facility Cost $4.7M $0.98M $0.98M

UV Facility Cost N/A $2.0M $4.2M

UV O&M Cost N/A $0.08M $0.03M

NPV $4.7M $4.5M $5.9M

O&M cost basis:

– UV power at $0.075/kW-hr

– UV lamp, ballast, sensor, and sleeve replacement at manufacturer’s guaranteed lifetime and replacement cost

Selected Option

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Pros and Cons of Chlorine vs. UV+Cl2 for NTP

3/2/2018

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• Chlorine Only Pros– Traditional disinfection

approach– Consistent with other DW

facilities– Minimal O&M– Need to utilize chlorine no

matter what (virus and distribution system residual)

• Chlorine Only Cons– Higher facility and NPV costs– Larger footprint– Potentially higher DBP

formation

• UV+Cl2 Pros – Recognized disinfection

approach– Lower facility and NPV costs– Additional disinfection barrier

(higher Giardia and Crypto)– Lower DBP formation

• UV+ Cl2 Cons – Still requires a DCB (but

smaller than chlorine only option)

– Requires more equipment (O&M) and new type of equipment requiring additional O&M considerations

– New issues (power quality, mercury release potential)

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Key process decision for Denver Water: implement UV disinfection now

• UV is the most effective disinfectant for Giardia and Cryptosporidium

• UV allows the Disinfection Contact Basin (DCB) to shrink in size significantly

• Implementing UV will provide a higher level of treatment for Denver Water:

– Multiple barrier disinfection (UV, free Cl2, chloramine)

– Cryptosporidium inactivation (not provided by free Cl2 or chloramine)

– Greater Giardia disinfection

– Reduced DBP formation (less free Cl2 contact time)

– Overall greater public health protection

• Implementing UV disinfection will provide a higher level of treatment at similar life-cycle cost

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PCMC 3Kings WTP

Park City, UT

• Historic silver mining town in mountains east of Salt Lake City

• Population 8,500 with tourism in winter and summer

• 8 water sources used in complex water system

• New 3Kings WTP – 6 mgd greenfield plant

• Will be constructed at location of existing Spiro WTP (to be demolished)

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3KWTP Treatment Process Schematic

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Clearwell Disinfection (Post-Filtration)

• 2 log virus and 0.5 log Giardia• New Clearwell

– Provide 0.5 log Giardia

– Provide 2 log virus

• Re-use existing Clearwell– Provide 0.5 log Giardia

– Provide 2 log virus (extra volume available for backwash supply)

• Initial design criteria– Minimum temperature = 0.5 degree C

– pH = 6.5-8.2

– Giardia = 0.5 log (CT = 34.5 to 60.3 mg-min/L)

– Virus = 2 log (CT = 6 mg-min/L, not pH dependent)

– Free chlorine residual = 1.75 mg/L

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Clearwell Costs

Treatment Step Size Facility Cost Notes

Existing Clearwell (0.5 log Giardia, pH 6.5)

184,600-198,000 gallons, depending on SWD (10.5-11 ft)

$0 Only able to achieve CT for pH of 6.5 (with 0% safety factor) at 1.75 mg/L of Cl2 and 0.5 deg C

Clearwell (0.5 log Giardia, pH = 8.2)

344,800 gallons N/A Not feasible in existing clearwell

Existing Clearwell (2 log virus) 28,500 gallons $42,000 Added baffle walls and weir

New Clearwell (0.5 log Giardia) 413,800 gallons86’ x 59’ x 14’ (12’ SWD)

$972,500 Size for pH of 8.2 and 20% safety factor

New Clearwell (2 log Virus) -tank

28,500 gallons, 19.5’ x 19.5’ x 10’

$101,300

New Clearwell (2 log Virus) -pipeline

14,100 gallons36” dia. x 267 linear ft

$199,650 Assume 4’ of burial

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UV Design Assumptions• Target disinfection = > 0.5 log Giardia (PCMC electing to be able to meet SWTR

requirements)• UVT (min) = 97.5%• Flow = 6.5 mgd• 1+1 or 2+1 reactor quantity• Pumped flow through filter pressure vessels

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UV Option Summary

Vendor Model/Lamp Type

Number of Lamps per

reactor

Headloss (ft)

Trojan 1 2L12 (MP) 2 0.8

Trojan 2 D12 (LPHO) 12 2.6

Trojan 3 D18 (LPHO) 18 1.2

Calgon Sentinel (MP) 3 2.2

Xylem 1 350e (LPHO) 6 2.9

Xylem 2 650e (LPHO) 8 1.0

• Build within existing building space (above disinfection contact basin for virus credit)• Pumped flow through filter pressure vessels• UV reactor cost: $105-190K for two reactors• UV piping cost: ~$100K• Compare to savings in reducing size of disinfection contact basin ($870K)

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Conclusions

− Providing robust, multiple disinfection barrier treatment

− Providing a higher level of disinfection

− Possibly reducing disinfection by products

• Greenfield WTPs offer different opportunities for UV disinfection compared to retrofits

• Two recent projects demonstrate that implementing UV disinfection for Giardia inactivation credit is less expensive than building a chlorine contact basin for Giardia inactivation credit

• Incorporating UV disinfection can save cost, while also:

Planning a New WTP? Use UV to Save Cost

Paul D. Swaim, P.E. – Jacobs/CH2M

Denver, Colorado

IUVA Americas Conference

February 27, 2018