HSGAC: A Site Specific Granular Activated Carbon Model Design Tool

Transcription

1 HSGAC: A Site Specific Granular Activated Carbon Model Design Tool Mark Bishop, PE, Hazen and Sawyer Allison Reinert, EIT, Hazen and Sawyer Erik Rosenfeldt, PE, PhD, Hazen and Sawyer Ben Stanford, PhD, Hazen and Sawyer Viking Edeback, North Carolina State University Detlef Knappe, PhD, North Carolina State University Water JAM 2010

2 Motivation NC AWWA Water JAMWEA Stage 2 Disinfectant/Disinfection Byproduct (D/DBP) Rule More stringent THM and HAA levels Locational Running Annual Average (LRAA) monitoring Options for compliance Changing residual disinfectant Chloramines Remove more organic matter (OM) Coagulant / IX / PAC / Membranes Granular Activated Carbon (GAC)

3 Activated Carbon Base Materials Bituminous Coal Lignite Coconut Shell Wood Manufacture Pyrolysis Activation Heterogeneous Adsorbent Micropores and Mesopores Types Extruded Powdered (PAC) Granular (GAC)

4 Adsorption 1. Bulk Diffusion Adsorbate (Organic Matter) 2. Film Mass Transfer 3. Intraparticle diffusion 4. Adsorption Adsorbent (GAC)

5 Some GAC vs PAC Considerations PAC One Time Use Less expensive Capital Initial Treatment Process (Raw Water) Sludge Impacts GAC Can be Regenerated Passive Technology Final Treatment Process Ease of Operation/Reliable without Daily Dose Changes No Impact to Raw Water

6 Important Questions What is the appropriate Design Benchmark to achieve compliance goal of no LRAA MCL violations? Recognizing we only have historical data record Some level of risk is inherent in any design benchmark What level of risk is acceptable? Seasonality of DBPs Source WQ variability Possible Design Benchmarks All LRAA<MCL No Operational Evaluation (OEL) Violations All LRAA<80% MCL Maybe lower? Equivalent to chloramines

7 Important Quesions Will Full GAC Treatment be Successful? Under what conditions? What is the frequency of GAC changeouts? Will Partial Treatment Be Successful? If so, at what level? What levels of conservatism are appropriate? (ie, seasonality of DBP yields) What are the costs associated with each option? What tests are essential to understand how GAC will work with my water Rapid small scale column tests To estimate TOC breakthrough DBP yields DOC, mg/l EBCT = 10 minutes EBCT = 15 minutes EBCT = 20 minutes 0 10,000 20,000 30,000 40,000 Bed Volumes

8 Important Questions - Possible GAC Treatment Options and Costs? Water Source Water Treatment Plant Intermediate Pump Station Bypass GAC Chlorine Contact Distribution System DBP Compliance Points Options: Full Treatment Hybrid Blending Hybrid Seasonal Hybrid Trigger TOC

9 How do we answer these questions? Solution Build a model using Historical data and design parameters Historical TOC record Seasonal water production Future flows Inputs from RSSCT and Pilot Data TOC exhaustion rate DBP yields Operational Parameters GAC changeout schedule Design treatment capacity

10 GAC Performance Model Overview User Inputs Plant Specific Data Flow Historical TOC Data Desired Operations Full Treatment Hybrid Treatment Specific Pilot / Bench Data GAC Exhaustion THM / HAA Yields Calculations Module Treated / Bypassed Flow GAC Exhaustion / Changeout Predicted THMs / HAAs Carbon Consumption GAC Model Simulates capacity, operating conditions, and outcomes Summary Output MCL Violations OEL Violations THMs and HAAs Estimated Capital Costs Estimated Carbon Costs

11 How the Model Works Historical TOC Future Flows Number of contactors Input Partial Treatment How much future flow will be bypassed with a certain # of GAC contactors RSSCT equation (can be validated by pilot data, if available) RSSCT Number of GAC contactors Change out schedule Cost DBPs GAC Treated Blended TOC TOC effluent Bypassed TOC THM and HAA Yields TOC

12 Example Evaluation for GAC Treatment All LRAAs < 80%; and Robustness Test of High Yields GAC Hybrid Decision Logic Scenario Not Considered NO Hybrid GAC Treatment Option NO No OELs? YES All LRAA <80% MCL? NO YES Robustness Analysis All LRAA<MCL YES Scenario Not Considered Scenario Not Considered Preferred and Possible Options

13 Example RSSCT and Pilot Data Breakthrough TOC Breakthrough (mg/l) RSSCT Breakthrough Pilot Data - 10 min Pilot Data - 15 min Pilot Data - 20 min Bed Volumes Treated Comparison of TOC breakthrough for RSSCT and pilot data

14 Total Organic Carbon Record Example TOC (mg/l) th percentile = 2.34 mg/l Historical record of post-filtered TOC

15 Example Plant Flows Daily Production 2020 Daily Production Monthly Averaged Production Record Daily production from 2011 adjusted to 2020 estimates

16 Example SDS DBP Yields Tests Option Viability (< 80% MCL); and Robustness (Hi Yield) Date of Sampling Treated Water DBP Yields (ug/mg) THM HAA SDS Testing Feb Mar May Jun Facility Average 71 60

17 Model Outputs NC AWWA Water JAMWEA Per a given scenario (number of contactors and change out schedule): TOC range THM range HAA range THM violations (LRAA and OEL) HAA violations (LRAA and OEL) 80% LRAA exceedences of THMs and HAAs Estimated cost of GAC per year Example for Utility in VA

18 Evaluated Scenarios Scenarios 100% Treatment WTP Plant 1 Plant 2 Number of Contactors Month Change Out 9 Month Change Out 6 Month Change Out Blending 12 Month Change Out 9 Month Change Out 6 Month Change Out Seasonal No Winter, 12 Month Change Out No Winter, 9 Month Change Out TOC Trigger 12 Month Change Out 9 Month Change Out

19 Goal = What can Meet the Objectives for DBPs? Scenarios 100% Treatment WTP Plant 1 Plant 2 Number of Contactors Month Change Out 9 Month Change Out 6 Month Change Out Blending 12 Month Change Out 9 Month Change Out 6 Month Change Out Seasonal No Winter, 12 Month Change Out No Winter, 9 Month Change Out TOC Trigger 12 Month Change Out 9 Month Change Out Options capable of achieving water quality criterion (yellow highlight is higher risk some LRAA vales over 80% MCL)

20 Cost Considerations Capital Costs Intermediate pumping Standby power Contactors in building or outside Number of Contactors (N+1) or lower EBCTs Site Issues for Truck Access, etc. Washwater handling O&M Costs Primary GAC changeout Virgin GAC 20% premium Custom regeneration (green) seems is current trend

21 Advantages of using HSGAC Capture potential benefits of GAC treatment Site specific Control DBPs and precursors Anticipate what large investments in activated carbon adsorption can achieve Compare treatment goals with economic constraints Allow for informed decisions about how much GAC treatment is needed Number of contactors Amount of treatment (seasonal versus year round) Budgetary information on capital and O&M costs

22 Water JAM

23 Water JAM 2010 BULLPEN

24 Model Parameters Site Specific: TOC Flow Number of contactors Partial Flow Treatment Based on # of contactors RSSCT Curve and RSSCT Equations (a, b, d equation) Effluent DBPs Uniform throughout analysis: GAC Change Out Schedule DBP yields Seasonality can play a role Estimated GAC Costs Based on # of contactors and change out schedule

25 Model Assumptions Historical TOC is representative of anticipated future trends Equal flow split to all reactors (equal blending) Constant 15 min EBCT Contactors are taken off line when flows are less than full GAC capacity