Biologically Active Filtration - VA AWWA Operations/Biologically Active... · concentrations and/or...

Biologically Active Filtration

James DeWolfe, PE, BCEE, CWO

and

William Becker, PhD, PE

Erik Rosenfeldt, PhD, PE

Meric Selbes, PhD

VA Section AWWA Plant Operators ConferenceMay 5, 2016

Agenda

• Basics of biofiltration

• Experiences with biofiltration

• Design and operational aspects

• Conclusions and recommendations

3

Basics of Biofiltration

4

Drivers for Biofiltration

• Degrading water supplies

• Climate change and extreme weather events• Increased levels of natural organic matter

• Higher levels of DBP precursors

• More algal growth – toxic algal byproducts and tastes andodors

• More stringent future regulations

• Increased consumer sensitivity

• Use ozone?

Biofiltration is Filtration (with a twist)

ConventionalTreatment Process

Cl2

AerobicBiologicalTreatment

Cl2

6

O3

Hozalski and Bouwer, Water Research, Vol 35, Jan 2001

Benefits of Biofiltration

• DBP control

• Taste and odor control

• Trace organic contaminant removal

• Distribution system water quality control• Stability/regrowth control – BDOC/AOC removal

7

History of Water FiltrationFiltered Water Turbidity Standards

10.0

5.0

1.00.5 0.3 0.1

0.0

2.0

4.0

6.0

8.0

10.0

12.0

Turb

idit

y(N

TU)

Standards have lowered, butdesigns are basically the same

Biofiltration is still filtration…..

Must also consider

• Turbidity/particle removal

• Filter operations - headloss, filter run length

• Iron/manganese control

9

Biofiltration can be a Delicate Balanceof Priorities

Particle Removal

Filter Runtime /Hydraulics

ContaminantRemoval

AOC/BDOC

Taste andOdor

Free Chlorine /Chloramines

DistributionSystem Ops.

NutrientEnhancement

DBPs

10

A Holistic View of Biofiltrationconsiders:

• Raw water quality

• Pretreatment

• Post-treatment and distribution

• Benefits of biofiltration must be weighed againstpotential drawbacks

• FIRST QUESTION – is it really needed?

11

Holistic Biofiltration Example: Stability

• Stability in distribution is a function of biodegradable(BDOC/AOC)

r

Rapid Mix

UV

RawWater

Coagulant, PAC,KMnO4, Cl2? Floc / Sedimentation

Ozone

Filtration /Biofiltration

Cl2

Distribution

ChlorineContact

NH3?

Raw TOC =3.6 mg/L

NBDOC = 90%

AOC =10%

AOC =10%

NBDOC = 90%

Settled TOC= 2 mg/L

AOC =20%

NBDOC = 80%

Post-OzoneTOC = 2 mg/L

Conventional Filt. TOC = 2 mg/LAOC = 400 ug/L

TOC = 1.7 mg/LAOC = 100 ug/L

12

Experiences with Biofiltration

13

BAF Challenges

• Biological Regrowth• Colored water complaints, taste and odor, corrosion

• Headloss Concerns• Issue: Headloss on biological filters reducing plant capacity

• Manganese• Question: Can manganese be controlled adequately without

pre-filter chlorine?

• Limited removal of DBP precursors (NOM)

• Particle passage

14

Approaches for optimizing biofiltration

• Nutrient Enhancement – “Engineered Biofiltration”• Goal: DBP control (better TOC removal)

• Goal: Control EPS and improve biology through nutrientbalancing

• Operations• Pay attention to proper filter operations - BACKWASH

• Conduct filter media inspections regularly - annually

• Media – fines at the top with GAC (tarping effect)

• Oxidant addition before filters

• Filter Design• In many cases the filter media designs for biofiltration are

same as those for conventional filtration

15

Biofiltration Headloss Concerns

• The Issue: Significant Headloss Through Biofilters

16

0

20

40

60

80

100

Aug-10 Aug-11 Aug-12 Aug-13

Filt

erR

un

Tim

e(h

r)

Filter 1 (Conventional) Filter 6 (BAC)

• The results of these experiments suggest that water treatmentfacilities treating source waters with moderate organic matterconcentrations and/or employing biologically active filtrationhave a greater potential for oocyst breakthrough and propercoagulation is critical for effective removal of oocysts in the filters

• 28% reduction in bed porosity

Biofiltration Headloss Concerns

Nature of the Biofilm is important

• EPS – Extracellular Polymeric Substance• Organisms “excrete” EPS for adhesion, protection, energy

storage• Polymer type material, capable of binding and clogging

• EPS has been linked to head loss buildup and cloggingof filters

• Organisms are more likely to excrete EPS when“stressed”

• Food or nutrient limited• “Inhospitable” growth environment

• EPS makes up vast majority of filtration media biofilm

Theory: Control EPS and Control Filter Headloss Issues18

Biofiltration and headloss

• EPS makes up vastmajority of filtrationmedia biofilm

• EPS can reduceeffective porosity offilter bed

Sand GAC

Virgin

+ Growth

19

Take this into account when designing media

Nutrient Enhancement Findings…..

• Results of Testing• No improvement with chlorinated backwash

• Limited success with nutrient balancing and/or peroxideaddition

• Still an issue last summer

• Need to take this into account when designingfilters

20

Headloss in the Underdrains

• Pay attention to clean bedheadloss!!!

• Need to determine where thebottleneck is

Clean IMS Cap Clogged IMS Cap Catastrophic UnderdrainFailure

21

End of tube beveledInside scoredEnd of tube beveledInside scored

Core Sampling for Solids Retention

23

• BEFORE WHERE solids are stored in filter

• AFTER Determine backwash effectiveness

• Use core sampling tool and baggies to obtaindepth samples

• Take samples 0-2” and every 6” after

• Sample before and after backwash

• Wash 50 gms of each sample with 5successive 100 mL washes of lab water

• Measure turbidity of each sample

• Plot on graph as NTU/100 grams media

2”

6”

12”

24”

18”

30”

Solids Retention

0

20

40

60

80

100

120

140

160

0-2 in 2-6 in 6-12 in 12-18 in 18-24 in 24-30 in

NT

U/1

00

gra

ms

of

med

ia

Before

After

25

• Measuresbackwasheffectiveness

• Can show too littleor too muchbackwash

• Note changes inhistorical solidsretention results

• Graph results fordatabase

Pre-filter oxidant addition

26

Effect of Intermediate Chlorination onFiltered Water Turbidity Patuxent Plant

Filter 7

Elapsed time, hr

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Turb

idity

(ntu

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Chlo

rine

resid

ual(m

g/L

)

0

1

2

3

4

Backwash Backwash

turbidity

chlorine doseSource: WaterRF 2725

Effect of Intermediate Chlorination onFiltered Water Particle Counts

Elapsed time, hr

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Tota

lPart

icle

Counts

(#/m

L)

0

100

200

300

400

500

Chlo

rine

Resid

ual(m

g/L

)

0

1

2

3

4

particle counts

chlorine doseBackwash Backwash

Patuxent PlantFilter 7

Source: WaterRF 2725

Effect of Intermediate Ozonation onFiltered Water Turbidity

Filter 1: ozone

Filter 2: no ozone

Filter Run 24Patuxent Pilot Plant

Raw Water:Particle counts ~ 12,000/mLTurbidity: ~ 2.8 ntu

Filtration Rate: (6 gpm/sf)

Deep bed GAC/sand filters

29Ozone train: 1 – 1.5 mg/L O3

Elapsed Time (hr)

0 5 10 15 20 25

Filte

red

Wate

rT

urb

idit

y,n

tu

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Effect of Intermediate Ozonation onFiltered Water Particle Counts

Elapsed Time (hr)

0 5 10 15 20 25

To

talP

art

icle

Co

un

ts(#

/mL

)

0

20

40

60

80

100

120

140

160

180

200

Filter 1: ozone

Filter 2: no ozone


Raw Water:Particle counts ~ 12,000/mLTurbidity: ~ 2.8 ntu

Filtration Rate: (6 gpm/sf)


Ozone train: 1 – 1.5 mg/L O3

30


Effect of Intermediate Ozonation onHead Loss Development

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25

Lo

ss

ofH

ead

(feet)

Elapsed Time(hours)

GAC w/ozone

GAC no ozone


31


Effect of Ozone on Particle Removal

32

Elapsed Time (hr)

12 14 16 18 20 22 24

To

talP

art

icle

Co

un

ts(#

/mL

)

0

100

200

300

400

500

600

ozone airfeedturned off

ozone air feedturned back on

ozone generatorturned off ozone generator

turned back on

Filtration Rate: 4 gpm/ft2



Design and Operational Aspects

33

Backwash Effectiveness

Must remove accumulated solids

Filtration Model

Dr. Jin ShinDissertation – Johns Hopkins University

35October 2004

Model Inputs

Operational Parameters:

• Surface loading rate

• Run time

Influent Characteristics:

• Particle concentration

• Particle size

• Particle density

• Water temperature

Filter Characteristics:

• Collector efficiency

• Collection efficiency of retainedparticles

• Contribution of retained particlesto headloss

Media Properties:

• Depth

• Effective size

• Uniformity coefficient

• Porosity

• Media density

• Anthracite:• Depth = 18 inches particle size = 0.5 µm• L/d = 1118 4 gpm/ft2

• ES = 0.9 mm• Conventional mode (porosity 0.45)


• ES = 0.9 mm• Biological mode (porosity 0.40)









Media – Anthracite or GAC?

• Anthracite traditional• Larger ES• Lower UC• Make sure backwash system can handle expansion

• GAC• Lighter and supports biological community• Lower UC• Breaks down over time• Check abrasion number (> 60%)

• FILTER SURVEILLANCE

Conclusions and Recommendations

44

Biologically Active Filters -Conclusions

• Is it needed?

• Biofiltration is a viable process• Taste and odors

• Dirty water

• Biologically stable water

• DBP control

• Converting to biofiltration can result in filtration issuesincluding:

• Higher filtered water particle counts if preoxidant is not used

• Excessive head loss development and short filter runs

• Poor AOC/BDOC removal

• Poor manganese removal

45

Biologically Active Filters -Recommendations

• Consider pre-filter oxidant• Ozone or chlorine dioxide – maybe even chlorine

• Backwash system and controls

• Anthracite or GAC?

• Design filter media to account for biofilm• Larger effective size media

• Deeper beds

• Uniformity coefficient – as low as possible!!!

• Keep the layer of sand

• Validate with pilot testing

• Filter surveillance imperative

• Perform monitoring of process and trend analysis• New suite of parameters – DO, etc.

46

TurbidityRemoval

ContaminantRemoval

HydraulicPerformanceBiology

PhysicsChemistry

Biological GrowthNutrients Ratios, AOC, EPS, ATP

Designand

Operations

Holistic Approach to Optimizing Biofiltration

47

THANK [email protected]

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