Protocol for Improved Ultraviolet Disinfection Design and System Optimization

Transcription

1 Protocol for Improved Ultraviolet Disinfection Design and System Optimization PNCWA 2010 Bend, OR 26 October 2010 Jeff Bandy, Ph.D. Carollo Engineers

2 Quick Outline 1. NWRI bioassay testing: requirements, nuances, and challenges 2. Case study: Trojan UV3000 at City of Escondido s Hale Avenue Resource Recovery Facility 3. A few take-home messages WRF06/2-019

3 NWRI Checkpoint Bioassay Requirements o Minimum of 8 biological tests, varying flow and UVT o MS2 bacteriophage o Demonstrate doses of o 100 mj/cm 2 (media filtered effluent) o 80 mj/cm 2 (MF effluent) o 50 mj/cm 2 (RO effluent) o Capacity is defined by the 75 th percentile confidence interval of UV dose o o o Non-infectious virus (+)ssrna 30 nm φ WRF06/3-019

4 System sizing must be based upon sound science 1. Characterize system performance based on the following variables: Head loss/water level UVT Flow Power Lamp aging Sleeve fouling 2. Testing is performed according to the 2003 NWRI/AWWARF Ultraviolet Disinfection Guidelines 3. Be sure to only use third partyvalidated reactors! WRF06/4-019

5 which results in complex dose algorithms/sizing formulas Dose = A B Q + C UVT Dose = ( EOLL FF ) ( A+ B logq+ C loguvt ) z 10 ( D+ E logq+ F loguvt ) 10 + n ( ) A+ B logq+ C loguvt 10 Dose = 10 A UVA B UVA S S Q o C+ D UVA+ E UVA 2 WRF06/5-019

6 which are based upon data with significant variability. WRF06/6-019

7 1) Examine the variability of the original data set Predicted UV Dose = UVT A Q B Banks C 10 D WRF06/7-019

8 2) Determine confidence interval around the average data set WRF06/8-019

9 3) Test system, demonstrate performance WRF06/9-019

10 Example WWTP in CA (~5 mgd) Wedeco Lancaster WRF06/10-019

11 William Duke System downrated by 5% and just barely makes capacity. WRF06/11-019

12 Quartz Sleeve Fouling and Lamp Aging Factors 1. UV system capacity is directly dependent on FF (fouling factor) and EOLL (end of lamp life factor) 2. Unless otherwise demonstrated, NWRI assumes Dose = EOLL extremely FF ( A + conservative B logq + C loguvt ) combined aging and fouling (CAF) factors o EOLL: 0.5 o FF: However, actual CAF factors are highly variable and site-specific WRF06/12-019

13 Site-Specific Sleeve Fouling Type of Wastewater Ballasted Flocculation / Filter Effluent Rate of Sleeve Fouling (% change in UVT per day) Secondary Effluent 7.1 Filtered Secondary Effluent 1.5 Filtered Secondary Effluent 2.5 Filtered Secondary Effluent 4 Filtered Secondary Effluent WRF06/ No fouling witnessed over 30 days

14 Assumed EOLL is Very Conservative Compare this to example assumed NWRI EOLL of 0.5 and a replacement period of 6,000 hours WRF06/14-019

15 Multiple Causes of Lamp Failure Excessive lamp hours Excessive lamp starts Ballast failure Dead spots in open-channel UV banks allow easy pathways for treatment targets and are opportunities for avoidable permit violations. WRF06/15-019

16 Regrowth Permit Violations WRF06/16-019

17 Where Should A UV System Be Sampled for Compliance? Rigorous channel maintenance and sampling after the last UV bank prevents effluent sample contamination. S S S S WRF06/ S

18 Benefits of Online UV Sensors o Real-time dose monitoring, facilitating maintenance o Full control of maintenance schedule o True measurement of dose o Similar to DW UV o Optimizes energy use o Not all systems use them, but they are strongly recommended WRF06/18-019

19 Case Study: City of Escondido Hale Avenue Resource Recovery Facility (HARRF) Trojan UV3000 Carollo was hired to benchmark Trojan UV3000 system, diagnose problems, and increase capacity for Title 22 reuse. WRF06/19-019

20 Trojan UV3000 at HARRF N 2 Channels 5 Banks/Channel 320 Lamps/Bank 3,200 lamps Designed for 9 mgd Title 22 water WRF06/20-019

21 Trojan UV3000 at HARRF WRF06/21-019

22 2003 Comissioning report ID ed uneven flow split N Poor flow split: Eastern channel: 10-15% higher flow WRF06/22-019

23 Poor approach hydraulics crippled bank #1 dose delivery Bank # UV Dose (mj/cm 2 ) At NWRI/CDPH conditions: o 100 mj/cm 2 o UVT: 55% o EOLL: 0.5 o FF: 0.8 Capacity was limited to 4 mgd 5 MGD in lost capacity = $3~4M in lost revenue WRF06/23-019

24 Computational fluid dynamics suggested ¼ hp mixers o o o o o Simple solution Low cost Low energy No construction Homogenized flow could boost capacity Unfortunately, testing showed no significant benefit. WRF06/24-019

25 Restructure and repeat bioassay testing to isolate Bank 1 from Banks 2-5 WRF06/ Lower 75% Flow Rate UVT Banks Tested Test C.I. RED (mgd) (%) # (mj/cm 2 ) Isolate Bank , , , Test Additive , Banks , , , ,

26 Calculating the fouling factor Sleeve fouling after 59 days Relative Relative UV Sensor Read Intensity Fouled Clean Tested both sides (180 o rotation) of 4 sleeves after 60 days in operation. Average of 40% drop in intensity. WRF06/26-019

27 Calculating the fouling factor WRF06/27-019

28 Calculating the aging factor LSI UV6414 Low-Pressure UV Lamp Aging at HARRF Relative Output, EOLL 6000 hrs = Lamp Hours (hrs) At least 4 lamps per age, multiple sensor readings. Lamps should be tested far past 6,000 hrs to determine EOLL and replacement rate. WRF06/28-019

29 How we calculated UV dose RED calc = ( EOLL FF ) 10 + ( n ( A+ B logq+ C loguvt ) ( D+ E logq+ F loguvt ) 10 1) ( ) A+ B logq+ C loguvt 10 RED calc = Reduction Equivalent Dose (UV dose), calculated with the UV dose-monitoring equation above (mj/cm 2 ). EOLL = End of lamp life factor (0.927) FF = Fouling factor (0.746) UVT = UV transmittance (%). Q = Flow rate (million gallons per day [mgd]). n = Number of banks in operation WRF06/29-019

30 Capacity at 55% UVT, 4 banks RED75 RED (calc 75, calculated (mj/cm 2 ) Flow (mgd) EOLL = FF = Bank 1 Bank 2 Total Channel WRF06/30-019

31 Capacity at 65% UVT, 4 banks RED75 RED (calc 75, calculated (mj/cm 2 ) Flow (mgd) EOLL = FF = Bank 1 Bank 2 Total Channel WRF06/ o >8 mgd capacity through both channels o Recovered capacity at about $20k/mgd

32 A few take-home messages 1. Reuse UV designs require conservatism 2. Equipment sizing is no longer simple 3. When designing UV systems, especially in retrofitted chlorine contact basins, hydraulic concerns are paramount 4. Appropriate and flexible data analysis and dose monitoring equations may be a silver bullet 5. If possible, find out your site-specific EOLL and FF 6. A successful UV system needs a dedicated and proactive operations staff WRF06/32-019

33 WRF06/33-019

34 Separating Fact From Fiction Fact 1. UV is a robust disinfectant. 2. No DBPs or toxic residuals. 3. Costs less than hypo for many applications (but not all) 4. Regulatory review depends on truth in advertising : make sure that installation = approved design 5. Review delays poor scheduling compounded by lack of staff time 6. Review information lacking detail & completeness Fiction 1. Easy to design. 2. Low maintenance. 3. Simple to operate. 4. Simple field verification and regulatory approval. 5. Review not meant as impediment to project 6. Regulators have access to all necessary information, incl: 1. Design & installation procedures 2. Manufacturer information 3. Regulators = the experts WRF06/34-019