Approaches to Filter Condition Assessment and Optimization

Transcription

1 2014 NC AWWA-WEA Conference Winston Salem, NC Approaches to Filter Condition Assessment and Optimization Vinod Korategere, P.E. Principal Engineer, Brown and Caldwell Barry Parsons Water Supply Division Manager, City of Greensboro, NC Kelly Comstock, P.E. Vice President, Brown and Caldwell November

2 Acknowledgements Ali Khan, Supt., Operations & Treatment, Water Supply Division, City of Greensboro Danny Briggs, City of Greensboro Larry Nance, ORC, NL Mitchell WTP NL Mitchell WTP Staff Katie Dorety, Brown and Caldwell 2 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

3 Presentation Outline Filtration Basics Filter Assessment Tools and Techniques Backwash Optimization Case Study: Greensboro s NL Mitchell WTP 3 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

4 Filtration Basics Filtration is the fundamental treatment barrier in conventional water treatment Although it is a solids separation process, some other benefits can occur in filtration Adsorption (if GAC) TOC reduction (if operated biologically) Mn and Fe removal (when chlorine is added prior to the filters) 4 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

5 Filtration Particle Removal Mechanisms There are several Filtration Mechanisms that allow particles to be filtered out by granular media: 1. Sedimentation 2. Interception 3. Brownian Diffusion 4. Inertia Media Particle NOTE: Particle surface chemistry is also very important; Particles should be destabilized ; ~ zero charge 5 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

6 Filter Assessment Tools and Techniques Filter Surveillance - Should take place on a continuous basis when operating filters Filter Surveillance should be considered as Preventative Maintenance Conduct periodic in-depth reviews of Condition and Performance of the filters Establish a Filter Assessment Team for your Plant Get Mgmt approval for time and commitment Schedule assessments during low demand times Goal is to optimize filter performance and improve operational conditions Team Operations, Maintenance, Engineering 6 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

7 Filter Surveillance Techniques During Backwash: Look for uniform air distribution when air scour is on Watch for any boils during backwash Look for cracks, cavities, other abnormalities Observe media level 7 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

8 Filter Surveillance Techniques During Operation: Condition of Surface Sweeps Mudballs Excessive clean bed headloss Reduction in UFRV 8 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC (NOTE: Photos from AWWA Filter Surveillance Manual)

9 Filter Surveillance Techniques Unit Filter Run Volume (UFRV): Amount of water produced per square foot of filter area during a filter run UFRV goal of 5,000 10,000 gal/ft 2 UFRV (gal/ft ( 2 ) = Filtration Rate (gpm/ft 2 ) x Filter run (hr) x (60 min/hr) Recommend that Operators calculate and track UFRV - to be able to compare performance. Example: A filter running for 90 hours at 1 gpm/sf and a filter running for 45 hours at 2 gpm/sf have the same performance (UFRV of 5,400 gal/sf) 9 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

10 Filter Assessment Techniques Annual Filter Assessment: Take Filter out of service Look at filter media profile when drained Should be level across the surface of the media Look for abnormalities including cracks, issues at walls, craters, etc. Condition of troughs, influent and effluent valves, air blower, piping 10 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

11 Filter Surveillance Techniques Annual Filter Assessment: Conduct Filter Coring Evaluate Media Depth Conduct Sieve Analysis Look for Mudballs Evaluate Solids Retention (NOTE: Photos from AWWA Filter Surveillance Manual) 11 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

12 Filter Assessment Techniques Solids Retention Test: Evaluate Filter before and after backwash Sample media at 6 increments Wash in accordance with method Measure Turbidity Compare Results to see penetration of solids into filter and effectiveness of backwashing 12 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

13 Filter Assessment Techniques Solids Retention Example: 13 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

14 Filter Surveillance Techniques Tools available for efficient coring Allows for taking core without draining and entering filter Can be expensive, but very rapid payback on investment (NOTE: Photos from AWWA Filter Surveillance Manual) 14 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

15 Checking Bed Expansion Recommend checking bed expansion on a quarterly basis as temperature and water density changes occur. 15 Required flow to achieve desired expansion will be less in the colder water temperatures. NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

16 Checking Bed Expansion Online Option Online bed expansion monitor Combined with turbidimeter Allows operator to quantify level of cleanliness of waste backwash water and confirm proper expansion 16 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

17 Backwash Optimization Surface Sweep Air-Scour Collapsed Pulse Improved Filter cleaning through combined air/low wash at subfluidized rates Extended Terminal Sub-fluidization Wash (ETSW) Sub-fluidized water flow at end of backwash cycle to remove backwash remnants in order to reduce filter ripening period 17 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

18 Collapse Pulse Methodology Backwashing filters with simultaneous air plus water at sub-fluidized rates provides the best cleaning of filter media during backwashing. Pulsation effect of low flow plus air scrubs media Typical Collapse Pulse BW Cycle Drain filter Air only Air + low wash to just below trough (Pause) Low wash; ramp to High wash Rewash cycle 18 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

19 ETSW Extended Terminal Sub-fluidization Wash Following a fluidized bed backwash, the backwash flow rate is dropped below the minimum fluidization velocity for an amount of time sufficient to pass one theoretical filter-volume of water through the filter Developed by Dr. James E. Amburgey, Associate Professor at UNC Charlotte Typical ETSW BW Cycle Drain filter Air only Air + low wash to just below trough (Pause) Low wash; ramp to High wash ETSW Low Wash Rewash cycle (if necessary) 19 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

20 Optimizing Filtration and Backwash Filter and Backwash Performance has many different variables It is imperative that the approach to filter operation and backwashing is consistent Without consistency it is nearly impossible to determine the effects of changing variables (water quality, temperature, filter condition, etc.) It is OK to make changes in procedure, the change must be done consistently Document the changes that you make and its impact on performance Consider having periodic meetings to discuss filter / backwash performance, review metrics, and strive for continuous improvements Consider seasonal impacts on operations 20 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

21 Effect of Temperature on Fluidization Velocity BW Flow Requirements During Cold Weather are Significantly Less > 20% Reduction 21 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

22 Case Study Greensboro NL Mitchell WTP 22 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

23 Overview Of Mitchell Filter Plant Filter Design Mitchell Filter Plant Utilizes Gravity Dual-Media Filtration Total of 12 Paired Filters 13 ft wide x 27 ft long Total Surface Area of 4212 ft 2 At 24 mgd, loading rate is 4.75 gpm/ft 2 (through 10 filters) 3.96 gpm/ft 2 with all 12 filters Utilized Leopold Low Profile SL underdrains with IMS Cap 8 of Sand: E.S. of 0.38 mm U.C. of of Anthracite: E.S. of 1.03 mm U.C. of NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

24 Filter Assessment Program Table 2. Average of Filter Media Core Samples Identified large amounts of anthracite in backwash basins. Diver in filtered water flume noticed anthracite was present. Decided to conduct a comprehensive evaluation of backwash procedures and perform a filter condition assessment. Included complete media removal and replacement from 2 of the filters (plant staff noticed media depressions). 24 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

25 Overview Of Mitchell WTP Backwash System Two Backwash Pumps: One Variable Speed Centrifugal Pump One Constant Speed Vertical Turbine Pump Air Scour - Positive Displacement Blowers 25 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

26 Review / Modification of BW Procedure Collapse Pulse Procedure Table 6. Recommended Modification to Standard Backwash Procedure ( Variable Speed Pump ) Step Procedure 1 Record value for when filters are placed back in service 2 Close filter set influent valve/gate 3 Put flow controllers in manual mode. Allow water level in both filters to drop to 6 above the top of media and close the effluent valves. The chlorine pump stops the effluent valve closes 4 Open the waste valve 5 Open wash water valve for filter to be washed 6 Push FILTER AIR WASH button for filter to be washed. (This will start the air scour by opening the filter air valve and starting the blower.) 7 Wash filter troughs and walls down during air scour to wash away accumulated biofilms 8 Air Scour for 2 minutes of air scouring. 9 Push the ADJUSTIBLE SPEED BACKWASH CONTROL LOW RATE button. 10 When the water level gets to the bottom of the troughs, push The Stop Button New Pause for 60 seconds (to allow media to settle) 11 Push the ADJUSTIBLE SPEED BACKWASH CONTROL LOW RATE button. (Primer system will automatically run and then split case backwash pump will ramp up to low rate). 12 After 30 seconds, push ADJUSTIBLE SPEED BACKWASH PUMP CONTROL HIGH RATE button. 13 After water is cleared sufficiently, push ADJUSTIBLE SPEED BACKWASH PUMP CONTROL STOP button. (This will slowly ramp the pump speed down to 0%). 14 Close wash water valve for the filter that was just washed. 15 Repeat steps 4-10 for the second filter to be washed. 16 Close waste valve. 17 Open Influent valve. 18 When filters are full, open re-wash valves and monitor until turbidity is less than 0.1 NTU for each filter effluent. 19 Close rewash valves when turbidity is acceptable 20 With flow controllers still in manual mode, open effluent valves to obtain desired flow. 21 Put controllers in automatic mode 22 On SCADA set Filter Chlorine Pump back to recorded value: 23 Record backwash flow in database and complete paperwork. 26 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

27 Underdrain Assessment (Filters 11/12) Table 2. Average of Filter Media Core Samples Conducted complete assessment of underdrain of one filter pair Grout IMS Cap Fasteners Air piping Troughs Underdrain / grout / caps in good condition Some corrosion at trough supports 27 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

28 Filter Media Depth Assessment Table 2. Average of Filter Media Core Samples Average of Filter Media Core Samples Filter # Total Depth (in) Sand Depth (in) Anthracite Depth (in) DESIGN NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

29 Filter Media Sizing Table 2. Average of Filter Media Core Samples Media Sieve Analysis Results Filter # Sand Effective Size (mm) Sand Uniformity Coef. Anthracite Effective Size (mm) Anthracite Uniformity Coef Design Anthracite effective size can migrate over time if media loss is occurring Can eventually decrease filter performance 29 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

30 Filter Flume Media Investigation Table 2. Average of Filter Media Core Samples Installed 0.2mm mesh bags in flume at outlet of each filter to capture any sand / anthracite passing through underdrains. Installed for 1 month no sand / anthracite detected 30 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

31 Evaluation of ETSW Backwash Procedure Pilot Testing on 2 filters (Filters 7 & 8) Installed Entech unit and Particle Counters to monitor performance Very good performance essentially eliminated the need for rewash Significant reduction in water use and backwash time 31 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

32 Typical ETSW Performance Backwash Time Typical ETSW Filter Run: Air : 2.5 min Low + Air : 2 min Low : 2.5 min High : 5-6 min ETSW : 9 min Rewash : 0 min Total: min Typical Conventional Filter Run: Air : 2.5 min Low + Air : 2 min Low : 2.5 min High : 6-7 min Rewash: min Total: min 32 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

33 Typical ETSW Performance Water Usage ETSW Wash ETSW 11/23/ Filter 8 Duration (min) Flow (gpm) Total (gal) Low ,285 High ,345 ETSW ,180 Rewash to 0.1NTU Total 58,811 ETSW 1/31/ Filter 8 Duration (min) Flow (gpm) Total (gal) Low ,738 High ,862 Conventional Wash Conventional 11/23/ Filter 3 Duration (min) Flow (gpm) Total (gal) High 7 7,635 53,445 Rewash to 0.1NTU * Total 65,985 At least 15% Water Savings observed in cold weather conditions ETSW ,835 Rewash to 0.1NTU Total 56, NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

34 Additional Potential Water Savings During testing, average high backwash flow rate was 6,400 6,500 gpm Could see additional savings during cold spells by automating / adjusting rate based on temperature 6,400 gpm 5,950 gpm Potential additional savings of nearly 3,000 gal per backwash 34 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

35 Summary Filters are critical to proper water treatment Conduct continuous filter surveillance and periodic detailed assessment to make sure filter is performing properly Look for opportunities to optimize your backwash procedure Look at sizing / set points of backwash rates Evaluate ETSW Proactively plan out any changes and be consistent with implementation 35 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC

36 36 NC AWWA-WEA Annual Conference November 18, 2014 Winston Salem, NC Questions