Maximizing Secondary Wet Weather Capacity at the Columbia Boulevard Wastewater Treatment Plant

Transcription

1 Maximizing Secondary Wet Weather Capacity at the Columbia Boulevard Wastewater Treatment Plant Adrienne Menniti1, Bruce Johnson1, Glen Daigger1, Samuel Jeyanayagam1, Lynne Chicoine1, Paul Suto2, Vu Han2, Chris Selker2, Mike Stebbins2, Mike Ciolli CH2M HILL City of Portland Bureau of Environmental Services

2 Portland Rain Fall Patterns We don t get more total rain than other cibes. Yearly Total Rainfall (in) New York, NY Miami, FL Boise, ID Seattle, WA Portland, OR Average from data from NOAA 2

3 Portland Rainfall Patterns 180 We get lower intensity rain more olen 150 Annual Days of Rain New York, NY Miami, FL Boise, ID Seattle, WA Portland, OR Average from , data from NOAA 3

4 Portland Rainfall Patterns Plant Influent Flow (mgd) Seasonal weather parerns translate to highly variable influent flows all winter long 0 12/25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010 Date 4

5 Columbia Boulevard WWTP Largest wastewater treatment plant in Oregon Average Winter Flow = 90 mgd Serves 614,000 people Discharges to the Columbia River Recent CSO storage improvements covey more wet weather flows to treatment plant, increasing peak flow from 300 mgd to 450 mgd 5

6 Columbia Boulevard WWTP Dry Weather Treatment Train 8 Square Secondary Clarifiers 8 Parallel Aera8on Basins Dry Weather Primary Clarifiers Permit Limits Monthly (mg/l) Weekly (mg/l) BOD TSS Includes sodium hypochlorite disinfec8on Headworks 6

7 Columbia Boulevard WWTP Wet Weather Treatment Train The wet weather primary clarifiers also provide storage for excess wet weather flow during small rain events Wet Weather Chemically Enhanced Primary Clarifiers Permit Limits BOD TSS Wet Weather Monthly (mg/l) Weekly (mg/l) Screening Facility Includes sodium hypochlorite disinfec8on Headworks 7

8 CBWTP Aims to Maximizes Flow Receiving Secondary Treatment 300 Influent Flow Secondary Flow 250 Plant is regularly pushing secondary treatment capacity to achieve this goal Flow (mgd) /25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010 Date 8

9 Challenges to Maximizing Secondary Treatment 1. High historical SVI values Design SVI = 200 ml/g SVI (ml/g) /25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010 Date 9

10 Challenges to Maximizing Secondary Treatment 2. Lack of Automation in Secondary Process (wasting, DO control) 600 SVI (ml/g) Extreme SVI excursion caused by manual wasting approach. Plant over wasted during a strong rain event, washing out selector /25/2008 4/28/2009 8/30/2009 1/1/2010 5/5/2010 9/6/2010 Date 10

11 Challenges to Maximizing Secondary Treatment 3. Lack of Wet Weather Operating Modes All the gates along the old complete mix distribution channel must be opened manually to step feed flow on current basins 11

12 Challenges to Maximizing Secondary Treatment 4. Poor clarifier design and performance Shallow (12.5 ft deep), square, peripheral-feed, peripheral-withdraw Effluent Feed 12

13 Project Goals 1. Maximize peak flow treated through secondary process Provide wet weather operating modes 2. Maintain stable operation during all flow conditions Maintain well settling sludge across all operating modes, provide tools to address settleability issues 3. Simple operation and intuitive control Decision to shift operating mode is intuitive, solutions are simple and robust to operate 4. Improve secondary clarifier performance Use CFD to evaluate potential clarifier improvements 13

14 Project Goals 1. Maximize peak flow treated through secondary process Provide wet weather operating modes 14

15 Two Types of Wet Weather Events 1. Several small to moderate rain events with dry weather in between 400 Influent Flow Plant Influent Flow (mgd) /12 5/17 5/22 5/27 6/1 6/6 6/11 6/16 Time (days) 15

16 Two Types of Wet Weather Events 2. Long rain events that fills the CSO storage tunnels 300 Influent Flow Plant Influent Flow (mgd) Completion of CSO storage tunnel project in Nov increased peak and duration 0 3/28 3/29 3/30 3/31 4/1 4/2 Time (days) 16

17 Two Wet Weather Operating Modes Step feed is the normal operating mode RAS % 35% To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic Wet weather maximum month treatment capacity = 98 mgd with 40% clarifier derating factor 17

18 Two Wet Weather Operating Modes Wet Weather Step feed is provided for use during small to medium rain events Constant flow maintained to zone 1 Remaining flow pushed to zone 6 Avoids an operating mode shift for typical rain events RAS Adjustable set point Remaining Flow To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic Wet weather maximum month treatment capacity = 110 mgd with 40% clarifier derating factor 18

19 Two Wet Weather Operating Modes Step feed with RAS Storage is provided for use during large rain events Upstream feed point shifted to zone 2 Provides storage of RAS to protect inventory from washout Further reduces clarifier solids loading rate RAS % 35% To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic Wet weather maximum month treatment capacity = 116 mgd with 40% clarifier derating factor 19

20 Project Goals 1. Maximize peak flow treated through secondary process Provide wet weather operating modes 2. Maintain stable operation during all flow conditions Maintain well settling sludge across all operating modes, provide tools to address settleability issues 20

21 Maintain Well Settling Sludge Two types of selectors provided: Anaerobic selector at Zones 1 and 2 Aerobic selector at Zone 6 RAS % 35% To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Encourages PAO growth to remove soluble BOD anaerobically. Pipe Bridge Small, baffled zone creates high F:M, encouraging rapid uptake and storage of soluble BOD by heterotrophs Anaerobic Anaerobic/aerobic swing Aerobic 21

22 Maintain Well Settling Sludge Automated SRT control incorporated into design to avoid washing out anaerobic selector RAS TSS Probe RAS BOX WAS TSS Probe TSS Probe RAS % 35% To Secondary Clarifiers RAS To Secondary Clarifiers TSS Probe TSS Probe Aerobic RAS Storage Primary Effluent Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic 22

23 Provide Tools for Sludge Settleability Control Highly oxygenated wet weather flows can disrupt the anaerobic zone RAS % 35% To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Anaerobic/aerobic swing zone maintains sufficient anaerobic SRT under these conditions Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic 23

24 Provide Tools for Sludge Settleability Control Influent VFAs can decrease during wet weather making selector difficult to maintain RAS % 35% To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic RAS storage zone can be intermittently aerated to increase VFA production during long rain events Thanks to Dr. David Stensel for this idea! Aerobic 24

25 Project Goals 1. Maximize peak flow treated through secondary process Provide wet weather operating modes 2. Maintain stable operation during all flow conditions Maintain well settling sludge across all operating modes, provide tools to address settleability issues 3. Simple operation and intuitive control Decision to shift operating mode is intuitive, solutions are simple and robust to operate 25

26 Decision to Shift Operating Mode is Intuitive During wet weather events, plant staff set flow rate to secondary process Plant Influent Secondary Influent Flow (mgd) Time (days) 26

27 Decision to Shift Operating Mode is Intuitive The maximum flow rate to Zone 1 is also an operator set point. Excess flow is automatically directed to Zone 6 of each basin. So, operators don t need to initiate the change to wet weather step feed. Shift to Step Feed with RAS Storage is manually initiated but automatically executed RAS Adjustable set point Remaining Flow To Secondary Clarifiers RAS To Secondary Clarifiers Aerobic RAS Storage Primary Effluent Pipe Bridge Anaerobic Anaerobic/aerobic swing Aerobic 27

28 Additional Tools to Maximize Secondary Treatment Instrumentation provided for SRT and stepfeed control allows tracking of clarifier solids loading rate Channel Flow Meter RAS TSS Probe % 35% To Secondary Clarifiers RAS To Secondary Clarifiers Channel Flow Meter Primary Effluent Channel Flow Meter Pipe Bridge TSS Probe Aerobic RAS Storage Anaerobic Anaerobic/aerobic swing Aerobic Long term experience may allow an automated control strategy to adjust the secondary process flow based on clarifier solids loading rate 28

29 Project Goals 1. Maximize peak flow treated through secondary process Provide wet weather operating modes 2. Maintain stable operation during all flow conditions Maintain well settling sludge across all operating modes, provide tools to address settleability issues 3. Simple operation and intuitive control Decision to shift operating mode is intuitive, solutions are simple and robust to operate 4. Improve secondary clarifier performance Use CFD to evaluate potential clarifier improvements 29

30 Clarifier Assessment Approach 1. Use historical data to understand clarifier performance 2. Perform clarifier stress testing to calibrate CFD model 3. Use CFD to determine clarifier failure mechanism 4. Evaluate potential improvements using CFD 30

31 Clarifier Capacity Analysis Based on Historical Data March 2010 Rain Event Allowed Historical Stress Testing Secondary Flow Rate Blanket Depth Secondary Flow Rate (MGD) Peak flow event provided consistent secondary flow for 3 days 3/26/2010 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 4/2/2010 4/3/2010 Blanket Depth (ft) Clarifier blanket meters show a strong increase in blanket depth during storm 3/26/2010 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 4/2/2010 4/3/

32 Clarifier Capacity Analysis Based on Historical Data March 2010 Rain Event Allowed Historical Stress Testing /27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 3/27/2010 SVI = 205 ml/g 6.0 Blanket Depth (ft) Clarifier SLR (ppd/sf) 32

33 Clarifier Capacity Analysis Based on Historical Data March 2010 Rain Event Allowed Historical Stress Testing /27/2010 SVI = 205 ml/g 3/28/2010 SVI = 202 ml/g 15 3/27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 Blanket Depth (ft) Clarifier SLR (ppd/sf) 33

34 Clarifier Capacity Analysis Based on Historical Data March 2010 Rain Event Allowed Historical Stress Testing /27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 3/27/2010 SVI = 205 ml/g 3/28/2010 SVI = 202 ml/g Blanket Depth (ft) Clarifier SLR (ppd/sf) 34

35 Clarifier Capacity Analysis Based on Historical Data March 2010 Rain Event Allowed Historical Stress Testing /27/2010 3/28/2010 3/29/2010 3/30/2010 3/31/2010 4/1/2010 3/27/2010 SVI = 205 ml/g 3/28/2010 SVI = 202 ml/g 3/29/2010 SVI = 213 ml/g Blanket Depth (ft) Solids flux analysis - the clarifiers failed at a point 40% less than the theoretical capacity Clarifier SLR (ppd/sf) 35

36 Clarifier Failure Mechanism Failure exacerbated at high SVI because the sludge blanket is less dense At failure, dispersed layer extends throughout clarifier and outlet arrangement carries TSS over weir ` The turbulence creates a dispersed sludge layer above the thick blanket at high flows Influent flow jets into the sludge blanket 36

37 Clarifier Failure Mechanism Also used CFD to define clarifier capacity Effluent TSS (mg/l) Solids flux analysis with CFD results - the clarifiers failed at a point 20% less than the theoretical capacity The design is flexible enough to accommodate higher clarifier capacity Clarifier Solids Loading Rate (ppd/sf) 37

38 Clarifier Improvements Examined Modified Baffle Design Original baffle arrangement Modified baffle arrangement Effluent Effluent Avoids upflow created by inlet Feed Feed Protects sludge blanket from influent energy 38

39 Clarifier Improvements Failure mechanism the same with modified baffle Effluent TSS (mg/l) Original Baffle Modified Baffle Modified baffle doesn t increase capacity, it reduces the severity of clarifier failure No modifications to secondary clarifiers in this project 30 0 Pre-failure At failure 39

40 Conclusion 1. Project is currently under construction and will come online by June of CFD helped us understand clarifier failure mechanism but no cost effective improvements found 3. Wet weather flows receiving secondary treatment will be maximized by: Incorporating step feed for normal operation and two wet weather operating modes Addressing sludge settleability issues and providing tools to maintain well settling sludge Implementing a high degree of automation to accommodate the highly dynamic winter time flows and simplify treatment plant operation 40

41 Thank You! Questions? Contact InformaBon

42 State Point Analysis to Define Clarifier Capacity Solids Loading Rate = 25.9 ppd/l 2 Mass Flux Rate, lbs/day/ft Slope = overflow rate = 1,000 gpd/ L 2 Slope = - RAS rate = 40 MGD Depends on SVI SVI = 205 ml/g Ideal Clarifier Q inf = 125 MGD MLSS = 2,350 mg/l SVI = 205 ml/g RAS = 40 MGD SLR = 25.9 ppd/l ,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 Concentration, mg/l 30 Solids Loading Rate = 15.2 ppd/l 2 Mass Flux Rate, lbs/day/ft Solids flux analysis - the clarifiers failed at a point 40% less than the theoretical capacity 40% derabng Q inf = 125 MGD MLSS = 1,380 mg/l SVI = 205 ml/g RAS = 40 MGD SLR = 15.2 ppd/l ,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 Concentration, mg/l