Developing the Design Basis for the World s Largest Full-Scale UV/HOCl AOP System

Transcription

1 Developing the Design Basis for the World s Largest Full-Scale UV/HOCl AOP System David Hokanson, Ph.D., P.E. 1, Yan Qu, Ph.D. 1, Aleks Pisarenko, Ph.D. 2, Shane Trussell, Ph.D., P.E. 2, Anthony Van 3 1 Trussell Technologies-Pasadena; 2 Trussell Technologies-Solana Beach; 3 City of San Diego February 28, 2018 Redondo Beach, California

2 Acknowledgments City of San Diego Public Utilities Department North City Water Reclamation Plant Trussell Tech Céline Trussell Rhodes Trussell Eileen Idica 2

3 Introduction to Pure Water Program 20 year program to supply 1/3 of San Diego s source water demand through potable reuse safe, sustainable, and economical Smart choice for San Diego: Reduces imported water (80-85% of its drinking water at present) Recycled Water (limits, scalping, ocean outfall) Environmental Buffer (reservoirs) Rising costs of imported water Reliable and cost effective

4 Phase 1 North City Pure Water Facility Ozone System Biological Activated Carbon Membrane Filtration Reverse Osmosis Ultraviolet Light Tertiary Effluent To Distribution System Conventional Water Treatment Plant Lake Miramar

5 Surface Water Augmentation San Diego s Pure Water Treatment Train provides beyond 12/10/10 protection against pathogenic organisms With additional treatment, a smaller surface reservoir can be used with the same or greater level of protection Pathogen WWTP O 3 /BAC MF/UF RO UV/AOP Total Virus Giardia Crypto

6 1 MGD Demonstration Pure Water Facility Commissioned in June 2011 testing San Vicente option Conceptual approval by the state (DDW) Sept Commissioned ozone and BAC in June 2014 testing Miramar option State Proposition 50 and 84 grants funds supported equipment and research to inform full-scale design Tours and reports information available at:

7 developing design criteria for San Diego Pure Water 7

8 Surface Water Augmentation UV AOP Regulatory Requirements 0.5-log 1-4 Dioxane Removal (SWRCB DDW, GRRW, 2014) NDMA does not exceed 10 ng/l (SWRCB DDW, GRRW, 2014) May require NDMA 0.69 ng/l (California Toxics Rule) 8

9 Test Conditions ~700 gpm (1 mgd) flowrate Conducted at ph of RO permeate (not adjusted) Collimated beam testing on-site Trojan (72AL75) demo reactor 72 lamps 250 W/lamp 18 kw 95% UVT (adjusted by adding chloramine) Spiking of NDMA and 1,4-dioxane 9

10 UV/HOCl Low ph environment required RO permeate has a typical ph of 5 to 6 Eliminates ammonia from chloramines through breakpoint reactions to help achieve strict Total N requirement = 1 mg/l

11 Fraction as HOCl is high at ph 6.5 (OCl - low) %HOCl ph 93% % % 5.5 and T=20 deg. C 11 Adapted from Crittenden et al. (2012)

12 UV/HOCl Allows free chlorine to be present in pipeline for additional virus credits (6-log with a CT of 8 mg/l-min with CA DDW) Cost effective compared to H 2 O 2 and reduces the number of chemical storage facilities needed Reduces the amount of dechlorination agent that must be used prior to discharge to water body

13 Lower Ammonia and Chemical Costs for Reservoir Projects Hydrogen Peroxide: Requires 7.5 mg/l of SBS to eliminate residuals prior to discharge and leaves ammonia behind Constituent Concentration, mg/l Ammonia 0.4 Chloramine 1.2 Hydrogen Peroxide 2 Sodium Hypochlorite: Requires 2 mg/l of SBS to eliminate residual prior to discharge with no ammonia Constituent Concentration, mg/l Ammonia 0.0 Chloramine 0.0 Free Chlorine 2

14 Methodology Bench and Demonstration Scale Testing Free chlorine as Oxidant RO permeate containing choramines (adjust to 95% UVT) Delivered UV dose Collimated Beam Photolysis Testing plus Demonstration Reactor Testing without oxidant Free chlorine dose determined from demo reactor tests Approach analogous to Reduction Equivalent Dose approach for UV disinfection Demo reactor UV dose adjusted by P changes 14

15 Determining the delivered UV dose Use Bench Test to Calibrate dose delivered in the field Sample C inf Field Measurement: Log[C inf /C eff ] Field UV Test Unit [specific flow, No. lamps] Develop field-lab test protocol for UV dose specifications that competing bidders must deliver Sample C eff Removal, log(c/c o ) (conducted with AOP influent from field) Bench Test UV Dose, mj/cm 2 Rated UV dose of field unit at flow & No. lamps tested

16 16 NDMA Collimated Beam Test Results

17 NDMA Demonstration-Scale Testing Results Pilot Reactor Power Level, % Demo Reactor Power, kw NDMA Feed, ng/l NDMA Treated Water, ng/l Log removal, NDMA a Testing conducted at 95% UVT 17

18 NDMA Demonstration-Scale Testing Results 18 a Testing conducted at 95% UVT

19 Determination of Delivered UV Dose (CB & Demo) 19 a Testing conducted at 95% UVT

20 Determine of Free Chlorine Dose with Demo Reactor Testing 20 a Testing conducted at 95% UVT

21 Demo Reactor Testing Results Free Chlorine with 1,4-dioxane Does not meet 0.5-log 1,4-dioxane Regulatory LRV FC=0.95ppm FC=1.79ppm FC=2.85ppm Meets 0.5-log 1,4-dioxane LRV 21

22 Design Criteria Parameter Design Criterion Minimum UVT 95.0% Minimum UV Dose 850 mj/cm 2 Minimum Free Chlorine Dose 2.0 mg/l as Cl 2 22

23 developing design criteria background factors 23

24 24 Change in ph with Free Chlorine Addition UV feed ph at HOCl 0 )

25 Change in ph with Treatment in the Demo Reactor ph=~1 25

26 26 Change in UVT with Treatment in the Demo Reactor UVT=~3%

27 27 NDMA CB Test with and without Oxidant

28 28 Questions