Comprehensive Assessment of the Benefits and Challenges of Converting an Existing Ozone Facility to Biologically Active FiltrationJulius Patrick, Greenville Utilities CommissionDavid Briley, PE, Hazen and Sawyer

Co-Authors

Greenville UtilitiesJesse Chadwick, Laboratory Manager

Hazen and SawyerErik Rosenfeldt, PhD, PEThomas Worley-Morse, PhD, PE

Presentation Overview

• Brief Introduction to Biological Filtration

• Full-scale BAF demonstration

• Outline of a holistic approach to biofiltration

• Desktop Evaluation• Pilot Study

Greenville Utilities WTP

• Conventional WTP with intermediate ozone• Secondary disinfection with monochloramines• Conventional sedimentation basins• Shallow filter boxes with

sand and anthracite media, chlorinated

• No intermediate pumping added with ozone, so hydraulic head is a limitation

Biofiltration BasicsConventional

Treatment Process

Cl2

Cl2

Biologically Active Filtration

(BAF)

BAF Drivers and Concerns

• Drivers for Biofiltration• Biological Stability to improve distribution system quality• DBP reduction• Taste and Odor Control• Emerging Contaminants

• Concerns with Biofiltration• Manganese• Post-filter microbial quality• Filter Hydraulics• Chemical Addition• Capital and Operating Costs

Impact of Ozone on AOC

• Ozone breaks down NOM into more assimilable organic carbon (AOC)

• Higher levels of AOC can provide food source for regrowth

• In 2009-2010, GUC observed higher HPC counts in system, and more frequent nitrification

• GUC has since optimized ozone• BAF can reduce levels of AOC

UV

Advantages of Biologically Active Filters

• Destruction, rather than sequestration, of many contaminants

• Removal of inorganic contaminants: nitrate, ammonia, nitrite, perchlorate, iron, manganese, etc.

• Removal of organic contaminants: DOC, biodegradable organic carbon (BOC), assimiableorganic carbon (AOC)

• Removal of Trace Contaminants: algal metabolites, endocrine disruptors, pharmaceuticals, VOCs, pesticide, herbicide, DBPs, etc.

Challenges with Biologically Active Filters

• Hydraulics Concerns• Increased headloss development leads

to shorter runtimes and potential reduction in WTP capacity

• Manganese• Can manganese be controlled

adequately without pre-filter chlorine?

• Particle passage / Filter Effluent Microbial Quality

• Chemical Addition?• Capital and Operational Costs

Full-Scale BAF Demonstration

Full-Scale BAF Demonstration

• Full-scale BAF demonstration beginning in 2010• Filter 4 – with anthracite media• Filter 6 – with GAC media

• Stopped chlorination in filter influent of Filters 4 and 6• Other 5 filters operated with pre-filter chlorine feed

Observed Shorter Filter Runtimes with BAF

0

10

20

30

40

50

60

70

80

90

100

8/10/2010 2/26/2011 9/14/2011 4/1/2012 10/18/2012 5/6/2013 11/22/2013 6/10/2014

Filte

r Run

Tim

e (h

r)

Filter 1 (Conventional) Filter 6 (BAC)

Shorter Summer Run Times

Manganese Control in BAF

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Filte

red

Mn

(mg/

L)

Raw

Mn

(mg/

L)

GAC Biological Filter 6 Raw Mn Anthracite Biological Filter 4

Secondary MCL

• Observed Mn biodegradation in BAF. GAC more effective than anthracite

• BAF could not control Mn extremes (Hurricane Irene)

Holistic BiofiltrationEvaluation

A Holistic View of Biofiltration includes:

• The goals of biofiltration must consider the whole system

• Raw Water Quality

• Pretreatment

• Post-treatment and Distribution• Depending on the

contaminant, biofiltration can be one barrier in a multi-barrier approach

• Benefits of biofiltration must be weighed against potential challenges

Holistic Approach

1. Reviewed Regulatory Requirements (Current and Future) and Water Quality Goals

2. Analysis of distribution system water quality• Confirm nitrification occurrence and need for additional AOC control

3. Review Full-scale BAF Demonstration results4. Ozone-BAF pilot5. Evaluate impacts of BAF on facility

Assessing the Impacts of Benefits and Concerns

Finished Water Quality Assessment

• Nitrification indicators show that some level of periodic nitrification is likely occurring within the system, at sites with more than 24-hour water age.

• Average total chlorine levels and other nitrification indicators are within acceptable levels.

• Free ammonia, HPC, and nitrite, do approach and exceed suggested action levels on occasion.

• Regulated DBPs (THMs and HAAs) are currently well in compliance.

Ozone/BAF Pilot

Overview of Pilot Testing Conditions

Column TreatmentGAC Media

SourceEffective

Size (mm)1 Control Henrico 1.35

2 0.2 mg/L as P Henrico 1.35

3 9 mg/L Caustic Henrico 1.35

4 0.2 mg/L as P + 9 mg/L Caustic Henrico 1.35

5 Upflow Benton 2.0

6 Peroxide (1.5 mg/L) Henrico 1.35

7 1.5 mg/L peroxide + 9 mg/L caustic Henrico 1.35

8 Control using Filter 6 media GUC No. 6 1.39

Ozone/BAF Pilot Results – Filter Runtime • UFRV for BAF filters was ~ 50% - 70% of UFRV for abiotic filters • Chemical addition increased UFRV by 10% to 15% (caustic and

peroxide). No further improvement with P

Results from Ozone/BAF Study

• Manganese was well removed with addition of caustic

0

10

20

30

40

50

60

70

80

SDS 1 SDS 2 SDS 3 SDS 4 SDS 5 SDS 6 SDS 7 SDS 8 SDS FS#6 SDSCombined

SDSFinshed

HAA

/TH

M u

g/L

Total HAA Total THM

Simulated Distribution System Testing15 min Free Chlorine Contact, 5 day SDS

TTHM MCL

HAA5 MCL

(Full Scale)

0

20

40

60

80

100

120

140

160

Cl2 Break Cl2 1 Cl2 2 Cl2 3 Cl2 6 Cl2 FS#6 Cl2 Combined

HAA

5/TT

HM

ug/

L

Total HAA Total THM

DBP Formation Potential with Free Chlorine5 day SDS with Free Chlorine

Stage 2 (TTHM)

Stage 2 (HAA5)

(Full Scale)

Results of ozone/BAF pilot study

• Filter Effluent Quality • Ozone-BAF provided up to 20% additional DOC removal• BAF enhanced DBP precursor removal

(30-45% reduction compared to abiotic filters)• Chemical additions did not enhance performance

• Biological Growth in Filters• ATP and EPS tests suggest that chemical addition did not impact

biological growth on media

Impacts on Operation

Net Water Production

• NWP calculations account for:• Potable water volume used

for:• Backwash: 102,000 gals per cycle• FTW: 30 mins

• Lost filter production if filter reaches terminal headloss/turbidity and filter already in backwash cycle

• 4 hr rest period for BAF following backwash

16

18

20

22

24

26

28

30

32

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

0 12 24 36 48 60 72 84 96 108 120

Net

Wat

er P

rodu

ctio

n (%

of C

apac

ity)

Filter Runtime (hrs)

Biotic Filter

Abiotic Filter

28.7 mgd

31.67 mgd

Net Water Production – 32 mgd WTP

Summary of BAF Performance

Enhanced DOC removal by 20%

Additional DBP precursor removal

Good Mn Control with caustic feed

Perceived improvement in biological stability

Perceived improvement in T&O, microconstiuents

Risk of Mn breakthrough at higher RW levels

Lower UFRV (50%)

Higher effluent coliform and HPCs

Key Takeaways: Critical Components of a “Holistic” Evaluation of Biofiltration

A holistic evaluation of biofiltration involves a look at how BAF fits in the entire system, answering the following questions• What are the water quality drivers and performance limitations

of concern?• What is the magnitude of the water quality driver impact?

• How does BAF improve the water quality?• How does BAF limit WTP performance?

• Can operational strategies be implemented to reduce performance limitations?

• Does capital need to be invested to improve filtration hydraulics?

• Piloting, full-scale optimization, and regular filter monitoring and maintenance are critical for successful BAF.

Questions?

Julius Patrick patricje@guc.com

David Briley, PEdbriley@hazenandsawyer.com