This document discusses ozone and biologically active filtration for controlling disinfection byproducts in drinking water treatment. It provides an overview of ozone production, application, safety considerations, and operational design. Biologically active filtration is described as using the same rapid sand filtration concepts while also removing assimilable organic carbon through the establishment of biofilm. The document outlines pilot demonstrations and applications of these technologies in Ohio drinking water facilities.

1. Ozone and Biologically Active Filtration
for Disinfection Byproduct Control
Tom Bell-Games, P.E.

2. Overview
 Ozone
 Use in Treatment
 Production
 System Components
 Operational and Design Considerations
 Safety
 Biologically Active Filtration
 Process Description
 Use in Treatment
 Operational and Design Considerations
 Demonstration Studies
 Applications in Ohio

3. Ozone
 O2 + energy O- + O-
 O- + O2 O3
 2O3 3O2
 Formed naturally during lightning storms
 Stratospheric (UV from sun + oxygen)
 Tropospheric (hydrocarbons, nitrogen oxide +
sunlight)
 Inherently unstable

4. Use of Ozone in Water Treatment
 Ozone discovered in mid- 1800’s
 First ozone generator manufactured by Von
Siemens in Berlin, 1857
 Disinfection of drinking water – Oudshoorn,
Netherlands, 1893; Nice, 1906
 49 installations by 1916
 Development of chlorine following WWI
 119 installations by 1940

5. Use of Ozone in Water Treatment, cont’d.
 > 2,000 by mid-1980’s
 Additional applications driven by recent
regulations within U.S.
 DBP precursors
 Organic micropollutants
 Cryptosporidium deactivation
 AOP
 Improvements in ozone generation systems,
methods of application, and analytical
instrumentation

6. Use of Ozone in Water Treatment
 Applications for ozone in water treatment:
 Reduction/removal of organics
 Reduction/removal of inorganics
 Enhanced flocculation/coagulation
 Reduction of disinfection byproduct precursors
 Enhanced disinfection
 Taste and odor control
 Ultrapure water systems, bottled water production,
etc.

7. Use of Ozone in Water Treatment
 DBP Reduction
 Some direct chemical oxidation of a fraction of NOM
 Partial oxidation: high molecular weight NOM
converted to low MW organics
 Increases biodegradable fraction of TOC (assimilable
organic carbon or AOC)
 Increase in AOC by 10 to 20 times
 Low MW compounds more easily transported across
cell membrane
 Low MW compounds more easily attacked by
metabolic enzymes

8. Ozone – Possible Points of Application
 Pre-ozonation
 Intermediate ozonation
 Post treatment

9. Ozone – System Components
 Oxygen source
 Supplemental air (nitrogen boost)
 Ozone generator
 Cooling water
 Contactor (basin or pipeline)
 Injection system (diffusion or sidestream
injection)
 Ozone destruct systems
 Ancillary instrumentation

10. Ozone – Production
Oxygen Source
 Air-fed
 Ambient air
 Complex chemical reactions
 Oxygen-fed
 LOX
 On-site generation (PSA)

11. Ozone Production – Preconditioning
 Preconditioning of inlet gas to avoid generation
of nitrogen oxides within the generator
 Air filters (dust)
 Air drying (humidity)
 Ambient air – 21% oxygen
 GOX – 95% oxygen
 Addition of small quantity of air (N) if using LOX

12. Ozone – Production
 Ozone generation

13. Ozone – Production
 Ozone generation
O3
O3
O2
O2
Corona Discharge Tube

14. Ozone – Production
 Ozone generation
O3O2
O2
O3
Discharge GapDischarge Gap
Discharge Gap
Glass Dielectric
Ground ElectrodeHigh Potential
Electrode

15. Ozone - Production
 Cooling Water
 Closed loop
 Open loop

16. Ozone - Production
Oxygen Ozone
Heat Exchanger
Closed Loop
Cooling Water
Open Loop
Cooling Water
Ozone Generator

17. Adding Ozone to Process Stream
 Diffusion
 Sidestream Injection

18. Adding Ozone to Process Stream
 Ceramic, Fine Bubble Diffusion
 Ozone Resistant Materials
 316 Stainless Steel
 Viton
 PTFE (Teflon)
 PVDF (Kynar)

19. Adding Ozone to Process Stream
 Diffusion
CAT
To Ozone Destruct

20. Adding Ozone to Process Stream
 Sidestream Injection
 Eductors
 Flash Reactors
Ozone Gas

21. Adding Ozone to Process Stream
Typical Sidestream Injection System
Sidestream
Pump
Venturi
Injector
Ozone Gas Feed
Ozone Gas Feed
Flash Reactor
Figure courtesy MWH Americas

22. Adding Ozone to Process Stream
 Sidestream Injection Flash Reactors

23. Adding Ozone to Process Stream
 Access to Ozone Contact Chamber

24. Ozone – Destruction
 Prevent release of off-gas ozone into
atmosphere
 Prevent adverse impact on downstream
equipment and processes from ozone residual
in process flow

25. Ozone – Destruction
 Off-gas destruction
 Thermal
 Catalyst (magnesium oxide)

26. Ozone – Destruction
 Ozone residual quenching
 Calcium thiosulfate
 Sodium thiosulfate
 Sodium bisulfite
 Hydrogen peroxide

27. Ozone – Operational and Design Considerations
 Ozone Demand
 Typical Types of Process Control
 Ozone gas concentration
 Ozone feed water flow (sidestream injection)
 Ozone residual at various points along contactor
 Mixing and contact time (HRT)
 UV254
 ORP

28. Ozone – Operational and Design Considerations
 Ozonation Byproducts
 Bromate (MCL 10 µg/L)
 Br− + O3 → BrO−
 Bromate mitigation strategies

29. Ozone – Operational and Design Considerations
 Hydraulics
 Seasonal variations in influent water quality
(temperature, pH, TOC)
 Dose and flow variations
 Method of application
 Oxygen vs. Air
 Materials of construction
 Gas phase
 Liquid Phase

30. Ozone – Safety
Oxygen
 LOX and Oxygen Gas
 Atmosphere
 78% Nitrogen
 21% Oxygen
 0.9% Argon
 0.03% Carbon Dioxide
 Oxygen >23% health issues
 Combustion in high-purity oxygen environment
 Oxygen heavier than air

31. Ozone – Safety
Ozone
 Concentrations detectible by scent
 0.01 – 0.05 ppm
 OSHA exposure limits
 8 hour continuous exposure @ 0.1 ppm
 15 minute continuous exposure @ 0.3 ppm
 Lethal limit
 1 minute exposure @ 10,000 ppm (1%)
 Health effects
 Acute: headache, dry and irritated mucous membranes
 Chronic: exacerbates asthma, emphysema, etc.
 Ozone heavier than air

32. Ozone – Safety
Equipment
 Ambient ozone and oxygen sensors
 Visual and audible alarm systems
 2-stage ventilation
 Proper Personal Protection Equipment (PPE)
 Training
 Maintenance (regular maintenance/monitoring
and prompt repair)

33. BAF – Process Description
 Same general filtration concepts as rapid sand
filtration
 Filters continue to be used for particle removal
while also removing AOC
 Biology establishes naturally – no need to
“seed” the filters
 Monitor development of biology through HPC

34. Biologically Active Filtration
Biofilm
TOC
(AOC & DOC)
Assimilated
organic carbon
Remaining TOC
Particulate
contaminants
Retained
Particles

35. BAF – Effect on Contaminants
 TOC removal affected by nature of NOM
 TOC removal by both physico-chemical and
biological processes
 Typically very high AOC removal
 Typically, 20-30% reduction in DBPFP with
Ozone + BAF

36. BAF – Operational and Design Considerations
 BAF filters can consistently meet particulate
removal standards
 BAF filters can be optimized for conventional
filter performance parameters
 Headloss
 Ripening time
 Low temperature – decreased organics removal
 Easily biodegradable compounds removed
within standard contact time of conv. filters

37. BAF – Operational and Design Considerations
 Backwashing with chlorinated backwash water
generally not an issue
 Backwashing with non-chlorinated water results
in slightly greater biomass
 Use of chlorinated backwash as a biomass
control strategy
 Performance typically fully recovered within the
filter cycle

38. BAF – Operational and Design Considerations
 Air scour as a supplement to hydraulic backwash
 Operating parameters typically unchanged
 Filter run time
 Rate of head loss
 Backwash frequency
 Potential for reduced filter run times if DOC
fraction is high (> 6 mg/L)
 Increase in filter media effective size may be
warranted
 Opportunity to optimize filtration

39. BAF – Operational and Design Considerations
 Ozonation by-products (e.g. aldehydes)
generally readily removed by BAF
 TOC removal generally independent of EBCT if
EBCT in range of 4 to 20 minutes
 BAF can be effective in reducing subsequent
regrowth in distribution system
 GAC generally more effective than anthracite or
sand
 Coal-based GAC generally better than wood-
based GAC

40. BAF – Operational and Design Considerations
 Control strategies similar to conventional
filtration
 HPC can be used to measure biological activity
 HPC affected by:
 Length of time since start-up
 Water temperature
 Media type
 Presence / absence of chlorine in backwash water

41. BAF – Operational and Design Considerations
 Implementation Considerations
 Most plants able to switch to BAF without change to
historical practices
 Most plants report improved particulate removal
and reduced turbidity
 Potential release of manganese in some systems
 Filters exposed to sunlight may exhibit growth of
algae
 Potential filter gas binding (not common)

42. Pilot-scale Demonstration
 Pilot-scale demonstration used to evaluate
water specific performance
 Dose-TOC reduction
 Various filter media configurations
 Sand / anthracite
 Sand / GAC
 Performance for other specific contaminants

43. Pilot-scale Demonstration
 Initial bench-scale evaluation of background
ozone demand
 4 to 6 weeks for establishment of biology
 6 weeks for official Ohio EPA approval
 Additional time for evaluation of other
conditions or optimization of operation

44. Applications in Ohio
 Ozone
 Columbus – Hap Cremean, in design
 Biologically Active Filtration
 GCWW – Richard Miller
 Others

45. Ozone and Biologically Active Filtration
for Disinfection Byproduct Control
Tom Bell-Games, P.E.
tom.bell-games@burgessniple.com