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
Source: WaterRF 2725
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
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
Ozone train: 1 – 1.5 mg/L O3
30
Source: WaterRF 2725
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
Filter Run 24Patuxent Pilot Plant
31
Source: WaterRF 2725
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
Deep bed GAC/sand filters
Source: WaterRF 2725
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)
• Anthracite:• Depth = 18 inches particle size = 0.5 µm• L/d = 1118 4 gpm/ft2
• ES = 0.9 mm• Biological mode (porosity 0.40)
• Anthracite:• Depth = 18 inches particle size = 0.5 µm• L/d = 1118 4 gpm/ft2
• ES = 0.9 mm• Biological mode (porosity 0.32)
• Anthracite:• Depth = 24 inches particle size = 0.5 µm• L/d = 1164 4 gpm/ft2
• ES = 1.1 mm• Biological mode (porosity 0.32)
• Anthracite:• Depth = 24 inches particle size = 0.5 µm• L/d = 1079 4 gpm/ft2
• ES = 1.3 mm• Biological mode (porosity 0.32)
• Anthracite:• Depth = 60 inches particle size = 0.5 µm• L/d = 1626 4 gpm/ft2
• ES = 1.5 mm• Biological mode (porosity 0.32)
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]