uv disinfection for unfiltered surface water regulatory compliance

UV Disinfection for Unfiltered Surface Water Regulatory ComplianceKevin Castro, PE | GHD

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UV Disinfection for Unfiltered Surface Water Regulatory ComplianceKevin Castro, PE | GHD

2013 NYC Watershed/Tifft Science & Technical Symposium

Presentation outline

• Background• Regulatory Requirements• Water Quality• Basis of Design• Procurement/Construction• Benefits/Results• Lessons Learned• Questions

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Village of Skaneateles, New York

• Village demands– 0.6 mgd average daily demand– 1.2 mgd maximum daily demand– 2.0 mgd pump capacity

• Served off City of Syracuse Skaneateles Lake supply

• FAD since 1991• 3 log giardia inactivation through chlorination

(using City of Syracuse chlorination)• Population served ± 3,000


Skaneateles/Syracuse water supply system


Regulatory requirements

• SWTR– 1991 FAD– 3 log giardia inactivation through

chlorination– 4 log virus inactivation through

chlorination– Contact tank and contact

transmission main constructed 1995

• LT2ESWTR– 2 or 3 log cryptosporidium

inactivation– Two barriers: UV/Cl2


Water quality

• Turbidity– Average = 0.8 NTU– Range = 0.5 to 10 NTU– Syracuse intake shutdowns control turbidity

• UVT– Average = 97%– Minimum value = 92%– ICR = 96 to 98%– Limited historical data– Design Range = 90 to 98%

• Cryptosporidium– 1 oocyst detected since 1986

• 2 log cryptospordium inactivation required• Fouling Potential - Low

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Basis of design

• 2 log cryptospuridium inactivation = 5.8 mJ/cm2• 3 log giardia inactivation = 11 mJ/cm2• Designed for 3 log giardia inactivation• UVT – 90% minimum

- 95% average• Turbidity < 10 NTU• Lamp Technology – Medium Pressure or LPHO• Two 100% redundant UV reactors


Basis of design (cont’d)

• Max flow = 2 mgd• Ave flow = 1 mgd• Min flow = 0.5 mgd• Reduce giardia chlorine contact time requirements• Max headloss – 7 inches• Improved monitoring (UVT, Turbidity, Cl2)


Procurement

• Preselection vs. pre-purchase• Preselection approach chosen to give contractor ultimate responsibility for

system performance.• Life cycle cost bid

- Equipment costs- Lamp/ballast costs- Power costs


Procurement

• Procurement results• Trojan awarded selection

Equipment PV – Lamp Replacement

PV – Ballast Replacement

PV - Annual Power

Total Life Cycle Cost

Svern Trent $121,594 $5,173 $14,200 $9,884 $150,851

Trojan $117,000 $21,460 $5,976 $8,045 $152,481

Calgon $141,860 $9,079 $5,970 $9,986 $166,895


Construction

• Space available with BPS• Pump replacement *• VFDs provided *

- Reduce pump flow to 1 mgd (90% speed)- Reduce pump energy cost by $4,000/year- Reduce pump starts to < 4/day- Eliminate cavitation of pumps on low lake

level• SCADA for monitoring/control/reporting

*Provided through ARRA grant

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Construction

UV Disinfection UV Controls


Construction

Pumps

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SCADA


Construction

Turbidity/Chlorine/UVT Monitoring

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Chlorine Booster System & Monitoring


Results/benefits

• 2 log cryptosporidium inactivation – compliance• 3 log giardia inactivation through UV/Cl2• 4 log virus inactivation through Cl2• Use transmission main and contact tank for improved fire protection

(currently under development)• Reduced pump starts to < 4/day• Reduced energy/cost for pumping• Improved monitoring/reporting of CT, turbidity, Cl2 residual• < 0.1% off-spec water since March 2012


Lessons learned

• Validation layout ≠ Approved layout• Alarm management during maintenance

- Nuisance alarms during lamp and UVT transmitter maintenance

• Preselection was effective procurement approach

• Avoid pre-preselection design layouts ($$)• Define distances for power/instrumentation

cabling• LT2ESWTR allows off-spec water


Questions?

Please contact Kevin Castro at [email protected]


www.ghd.com

uv disinfection for unfiltered surface water regulatory compliance

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