How Far Can You Push Your Filters? Optimization Lessons

Transcription

1 How Far Can You Push Your Filters? Optimization Lessons Marvin Gnagy, P.E. President PMG Consulting, Inc. 51 st OTCO Water Workshop March 6, 2013

2 Agenda Two recent filter optimization projects Initial filter evaluations Floc retention profiles Backwash duration Solids mass balance Optimum filtration/backwash Filtration rate When is the media dirty When is the media clean Bed expansion and backwash duration 2

3 Agenda Filter performance criteria Gross water production (GWP) Filtration efficiency (FE) Washwater consumption FTW and ripening Head loss and run times Maximum head loss Maximizing run times 3

4 Agenda Optimization recommendations Performance criteria Run times Backwash cycles Washwater consumption and reduction Potential cost savings Optimizing backwash operations Optimizing run times 4

5 Filter Comparisons Filter A - Rebuilt 2009 Dual media - sand, anthracite 10 filters (1.25 gpm/ft 2 ) 740 ft 2 each Settled water 0.48 NTU average (0.067 NTU FE) Run times - 72 hrs. Head loss at backwash 2 feet GWP - 5,270 gal/ft 2 /run FE % L/D 10 ratio - 1,035 Filter B - Rebuilt 1987 Dual media sand, anthracite 18 filters (1.2 gpm/ft 2 ) 2,880 ft 2 each Settled water 0.49 NTU average (0.034 NTU FE) Run times hrs. Head loss at backwash < 2 feet GWP - 7,260 gal/ft 2 /run FE % L/D 10 ratio - 1,115 5

6 Bed Depth, inches How Far Can You Push Your Filters? - Optimization Lessons Filter A 0 NTU per 100 grams Floc Retention Before Backwash Less than 150 NTU per 100 grams at interface layer Indicates maximum run time Less than 3,500 NTU per 100 grams, excellent pretreatment Confirmed low solids loadings from settled water (0.5 NTU) Indicated longer run times possible No apparent potential for breakthrough No indication of breakthrough during filter run 6

7 Bed Depth, inches How Far Can You Push Your Filters? - Optimization Lessons Filter B 0 NTU per 100 grams Floc Retention Before Backwash Less than maximum 150 NTU per 100 grams at interface, potential for increased run times Less than 3,500 NTU per 100 grams, excellent pretreatment operations Indicates maximum filter run time Confirmed low solids loadings from settled water (0.48 NTU) Indicated longer run times possible No apparent potential for breakthrough No indication of breakthrough during filter run 7

8 Bed Depth, inches How Far Can You Push Your Filters? - Optimization Lessons Filter A 0 NTU/100 grams Floc Retention After Backwash Clean Range Media dirty above about 6-inches, possible sweep malfunction Potential issues with surface wash sweeps Much of top layers remained dirty after backwash Solids not accumulating in lower layers of media from previous runs, possible increase in run time can be accomplished Lower layers below clean range - likely due to low solids loading 8

9 Bed Depth, inches How Far Can You Push Your Filters? - Optimization Lessons Filter B NTU/100 grams Media primarily in clean range throughout filter bed, below clean range in the top 8-inches Clean Range Potential low bed expansion due to low washwater rate results in differential solids retention in different bed depth layers Floc Retention After Backwash Air scour time appeared too long Much of media fell within clean range Solids not accumulating in lower layers of media from previous runs, possible increase in run time could be accomplished Lower layers not accumulating solids - likely due to low solids loading 9

10 Washwater Turbidity, NTU How Far Can You Push Your Filters? - Optimization Lessons Filter A Backwash Duration minute wash period too long minutes needed this wash cycle Filter media clean when washwater turbidity fall below 10 NTU Appears that 11 minute wash period is excessively long. Much less than 10 NTU in washwater at end of wash period (1.1 NTU end of cycle) Backwash Duration, Minutes Bed expansion 25% at 22 o C 10

11 Washwater Turbidity, NTU How Far Can You Push Your Filters? - Optimization Lessons Filter B Filter media clean when washwater turbidity falls below 10 NTU Backwash Duration, minutes Typical filter wash 16 minutes per cell, signifiant washwater savings possible Backwash Duration 16 minute wash period too long - 4 minutes needed this wash cycle Much less than 10 NTU in washwater at end of wash period (1.1 NTU end of cycle) Bed expansion 17% at 7 o C 11

12 Loss of Head, feet How Far Can You Push Your Filters? - Optimization Lessons Filter A Head Loss Measurements Low head loss at backwash confirmed Extended run time hours increases head loss Head loss at 72 hours about 2 feet, longer run times possible Could achieve 200 hour run times at head loss goal Max head loss goal (5.5 feet) indicated longer run times were possible Filter Run Time, hours R² =

13 Head Loss, feet How Far Can You Push Your Filters? - Optimization Lessons Filter B Head Loss Measurements Low head loss at backwash confirmed Extended run time hours increases head loss Head loss at 100 hours about 1.25 feet, longer run times possible Could achieve 410 hours at 5.5 feet head loss Max head loss goal (5.5 feet) indicated longer run times were possible Run Time, hours R 2 =

14 Solid Mass Balance Calculations Filter A 20.5 pounds solids deposited in filter media during run (0.50 NTU) 6.6 pounds solids in washwater 32.2% removal efficiency during backwash Limited backwash rate Low bed expansion Some mud ball formations observed Sweep malfunctions observed Filter B 85.4 pounds solids deposited in filter media during run (0.48 NTU) 80.1 pounds solids in washwater 93.8% removal efficiency during backwash Reduced backwash flow (70% of maximum) Low bed expansion Excessively long backwash Excessively long air scour 14

15 Optimum Filtration / Backwash Performance generally increases with filtration rate <1.4 gpm/ft 2 does not produce depth filtration, but surface filtration Filters operate well at 2 gpm/ft 2 or higher Solids accumulations Media retains solids until head loss indicates open spaces filled (5.5 feet maximum head loss from best practices) Dual media filters can accumulate up to 0.34 pounds suspended solids per cubic foot of filter media (site specific) Media backwashed when solids retention fills open spaces When maximum turbidity goals reached in filter effluent 15

16 Optimum Filtration / Backwash Filter-to-waste operations Generally operate lower than normal filtration rate Should produce ripening within 15 minutes or less Should be minimized to reduce wasted water volumes Bed expansion Backwash should expand media for most effective cleaning 30% minimum to allow grains to rub against each other 35% maximum to prevent excessive grain separation Use same range at all water temperatures Higher backwash rates in summer Lower backwash rates in winter 2% flow change for each 1 o C change in temperature 16

17 Water Temperature, o C How Far Can You Push Your Filters? - Optimization Lessons Optimum Filtration / Backwash y = x R² = Backwash flow needed for 30% bed expansion for XTZ treatment plant ,000 5,500 6,000 6,500 7,000 7,500 8,000 8,500 9,000 9,500 Backwash rate, gpm 17

18 Water Temperature, o C How Far Can You Push Your Filters? - Optimization Lessons Optimum Filtration / Backwash y = x R² = Backwash flow needed for 30% bed expansion for XTZ treatment plant ,400 gpm at 10 o C 0 5,000 5,500 6,000 6,500 7,000 7,500 8,000 8,500 9,000 9,500 Backwash rate, gpm 18

19 Optimum Filtration / Backwash Backwash duration Generally 6 minutes to 8 minutes provides effective cleaning Evaluate based on site specific operations and solids loadings Many filters backwashed too long Terminate backwash once washwater falls below 10 NTU Retain some solids in media to aid in ripening Filter ripening techniques Filter-to-waste (sometimes called rewash) Retain about 10% solids in filter media after backwash Allow media compaction after backwash by placing filters in standby 19

20 Filter Performance Criteria Gross Water Production (GWP) Measure of filter performance related to filter throughput 5,000 gal/ft 2 /run monomedia filters 10,000 gal/ft 2 /run dual media and multimedia filters Up to 20,000 gal/ft 2 /run in well optimized filtration and backwash operations Low applied water solids loadings Routine filter coring and floc retention analyses along with backwash evaluations Proper filter ripening operations Operator training and established performance target values 20

21 Filter Performance Criteria Filtration Efficiency (FE) Measure of filter performance as compared to washwater usage 95% or greater 99% or greater in well optimized filtration and backwash operations Routine filter evaluations Established performance target values 21

22 Filter Performance Criteria Filter Effluent Turbidity Regulatory levels must be achieved (0.3 NTU, 95% samples) Generally 0.1 NTU or less in first 15 minutes of operation Well optimized filtration and backwash operations Partnership for Safe Water goal Many plants meet 0.1 NTU or less (not always after 15 minutes) Monitored continuously in most cases Data can be used for trending Filter profiling observations Effluent target goals for initiation of backwash 22

23 Effluent Turbidity, NTU How Far Can You Push Your Filters? - Optimization Lessons Filter Performance Criteria Filter Effluent Turbidity Profile Initial turbidity from freshly washed and ripened filter Transitory turbidity from momentary increase in filtration rate Terminal turbidity indicating the need for backwash before breakthrough Filter Run Time, hours 23

24 Filter Performance Criteria Filter Run Times Generally 48 hours or greater for monomedia filters Generally 72 hours or greater for dual media and multimedia filters Well optimized filtration and backwash operations Maximize filter run times correlated to solids loadings and performance criteria 100 hours to 200 hours common Avoid run times greater than about 225 hours - excessive solids accumulations, backwash problems 24

25 Filter Performance Criteria Filter Head Loss Terminal head loss established 6 feet to 8 feet Generally 5.5 feet or less established maximum operating head loss Lower turbidity standards have reduced head loss operations Many filters backwashed at 2 feet loss of head or less Correlate head loss to run times Determine maximum run time at 5.5 feet head loss Establish maximum run time based on maximum head loss goal 25

26 Filter Run Time, hours How Far Can You Push Your Filters? - Optimization Lessons Filter Performance Criteria Filter Loss of Head Evaluations Graphical illustration of run times versus head loss measurements for a typical filter operation Loss of Head, feet R² =

27 Filter Performance Criteria Solids Mass Balance Calculations Calculate solids accumulations and solids remaining in the media Average applied water turbidity Average filtration rate Washwater turbidity measurements Washwater volumes used Calculate pounds of solids accumulated in media (total and pounds per cubic feet) Calculate solids in washwater Solids removal efficiency from backwash should be 85% or greater Maintains some solids in media for ripening 27

28 Filter Performance Criteria Filter Ripening Reduces turbidity spikes on freshly washed filters Filter-to-waste (FTW) is effective technique Removes initial slug of solids from filter media Should be 15 minutes or less Minimize FTW times to reduce waste flows Media compaction is effective technique Media compacts during idle operations to close open spaces Generally at least 4 hours stand-by operations following backwash Does not waste water like FTW Can easily be added to routine operations for filters 28

29 Filter Optimization Target Goals Filter A Washwater consumption 113 gal/ft 2 average 83,800 gallons per wash Backwash cycles 853 per year Washwater annual usage 71,481,000 gallons per year FTW gpm 86,400 gallons per filter Combined washwater and FTW 145,180,600 gallons per year Current Operations Filter B Washwater consumption 157 gal/ft 2 average 357,044 gallons per wash Backwash cycles 1,510 per year Washwater annual usage 539,136,349 gallons per year FTW 25 2,006 gpm 50,125 gallons per filter Combined washwater and FTW 614,825,100 gallons per year 29

30 Filter Optimization Target Goals Filter A Increase filtration rate to 2 gpm/ft 2 Operate 6 filters under normal conditions Review filter-to-waste needs GWP 17,000 gal/ft 2 /run Run times 140 hours minimum (up to 200 hrs. possible) Reduce backwash period to 6 minutes Reduce washwater usage at least 60% Filter B Maintain filtration rate at 1.2 gpm/ft 2 (for now) Operate all filters under normal conditions Review rewash needs GWP 13,000 gal/ft 2 /run Run times 175 hours (longer run times possible) Reduce backwash period to 5.5 minutes Reduce washwater at least 67% 30

31 Filter A Implementation (July 2011) Sweep bearings malfunctioning, replaced Washing wand used for agitation Increased filtration rate to 2 gpm/ft 2 Increased run times to 140 hours 6 filters in service, 4 on standby (12 mgd) GWP 17,000 gal/ft 2 /run Changed backwash to 6 minutes Tracked head loss data, run times, NTU Verified floc retention and backwash duration 31

32 Filter A Operations 2012 Maintained 2 gpm/ft 2 Normally 6 filters in service Run times at least 140 hours, up to 200 hours accomplished GWP >19,000 gal/ft 2 /run Surface wash 4 minutes Backwash 6 minutes (47,000 gallons per wash) Bed expansion still 25% (new BW pump under construction with new HS pump station) 32

33 Filter A Operations 2012 Head loss < 4 feet at backwash Filter-to-waste eliminated 74 MG annually Effluent turbidity averaged NTU Washwater usage reduced at least 63% Combined washwater and filter-to-waste reduced 82% 33

34 Bed Depth, inches Bed Depth, inches How Far Can You Push Your Filters? - Optimization Lessons Filter A Operations NTU per 100 grams NTU per 100 grams Less than 3,500 NTU per 100 grams Less than 150 NTU per 100 grams at interface layer No apparent potential for breakthrough 2012 Floc Retention 138 hours 2011 Floc Retention 88 hours Floc retention nearly the same at increased run times Longer run times possible 34

35 Bed Depth, inches Bed Depth, inches How Far Can You Push Your Filters? - Optimization Lessons Filter A Operations NTU per 100 grams NTU/100 grams Media dirty above about 6- inches, possible sweep malfunction Clean Range 15 Clean Range Solids not accumulating in lower layers of media from previous runs, possible increase in run time can be accomplished Floc Retention after 6 minute backwash 2011 Floc Retention after 11 minute backwash, surface wash bearings replaced Floc retention after backwash improved solids removal once the sweeps were functioning 35

36 Washwater Turbidity, NTU Washwater Turbidity, NTU How Far Can You Push Your Filters? - Optimization Lessons Filter A Operations Appears that 11 minute wash period is excessively long. Adjustment to SCADA programming is needed to reduce backwash time Backwash Duration, minutes Backwash Duration, Minutes 2012 backwash duration curve 138 hour run time 2011 backwash duration curve 88 hour run time Possible reduction to 5 minute backwash cycle 36

37 Filter A Operations 2012 Parameter Before Optimization Parameter After Optimization Filters used 10 Filters used 6 Filtration rate 1.25 gpm/ft 2 Filtration rate 2 gpm/ft 2 Run time 72 hours Run time 140 hrs to 200 hrs GWP 5,600 gal/ft 2 /run GWP 19,000 gal/ft 2 /run Filter efficiency 97.8% Filter efficiency 98.5% Average NTU Average NTU Max NTU 0.18 Max NTU

38 Filter A Operations 2012 Parameter Before Optimization Parameter After Optimization Washwater usage 83,500 gal Washwater usage 46,980 gal WW consumption 113 gal/ft 2 WW consumption 64 gal/ft 2 Backwash cycles 853 per yr. Backwash cycles 555 per yr. FTW usage 86,400 gal FTW usage 0 gal Annual water usage 145 MG Annual water usage 26 MG Annual water savings - Annual water savings 119 MG 38

39 Annual Costs How Far Can You Push Your Filters? - Optimization Lessons Filter A Operations 2012 $400,000 $350,000 $300,000 $250,000 $200,000 Initial $369, Annual Cost Savings $290,930 $150,000 $100,000 $50,000 Current $78,282 $0 Backwash / FTW Operations

40 Filter Run Time, Hours How Far Can You Push Your Filters? - Optimization Lessons Filter A Operations $150,000 $200,000 $250,000 $300,000 $350,000 $400,000 $450,000 Potential Annual Cost Savings R² =

41 Filter B Planned Operations 2013 Maintaining average 1.21 gpm/ft 2 (for now) Normally 17 filters in service May reduce filters in service with increased filtration rate later GWP 13,000 gal/ft 2 /run Run times at least 175 hours Air scour 3 minutes Backwash 6 minutes (115,500 gallons per wash) Bed expansion 16.7% at 11,600 gpm Washwater pump capacity 16,400 gpm (check expansion) Winter backwash rate 13,200 gpm, summer rate 16,400 gpm 41

42 Filter B Planned Operations Parameter Before Optimization Parameter After Optimization Filters used 17 Filters used 17 Filtration rate 1.21 gpm/ft 2 Filtration rate 1.21 gpm/ft 2 Run time 100 hours Run time (initial) 175 hours GWP 7,260 gal/ft 2 /run GWP 13,000 gal/ft 2 /run Filter efficiency 97.6% Filter efficiency 99.6% Average NTU Average NTU evaluating Max NTU 0.08 Max NTU evaluating 42

43 Filter B Planned Operations Parameter Before Optimization Parameter After Optimization Washwater usage 357,044 gal Washwater usage 115,500 gal WW consumption 157 gal/ft 2 WW consumption 51 gal/ft 2 Backwash cycles 1,510 per yr. Backwash cycles 863 per yr. FTW usage 50,125 gal FTW usage evaluating Annual water usage 615 MG Annual water usage 175 MG Annual water savings - Annual water savings 440 MG 43

44 Annual Costs How Far Can You Push Your Filters? - Optimization Lessons Filter B Planned Operations 2013 $350,000 $300,000 $250,000 $200,000 $150,000 Current, $317,961 Estimated Cost Savings, $258,537 $100,000 $50,000 $0 Proposed, 175 Hrs $59,425 1 Filter Backwash Operations 44

45 Filter Run Time Hours How Far Can You Push Your Filters? - Optimization Lessons Filter B Planned Operations $200,000 $210,000 $220,000 $230,000 $240,000 $250,000 $260,000 $270,000 Potential Annual Savings, Dollars R² =

46 Summary Filter optimization can improve performance and reduce operating costs Requires diligent filter evaluations and operational adjustments Operator training necessary for adjustments / goals Establishes scientific basis for performance goals Can reduce effluent turbidity Can change wasted water into increased revenue How far can you push your filters? 46

47 Marvin Gnagy