Ozone and Biologically Active Filtration for Disinfection Byproduct Control

Tom Bell-Games, P.E.

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

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

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

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

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.

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

Ozone – Possible Points of Application

Pre-ozonation Intermediate ozonation Post treatment

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

Ozone – Production

Oxygen Source Air-fed

Ambient air Complex chemical reactions

Oxygen-fed LOX On-site generation (PSA)

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

Ozone – Production

Ozone generation

Ozone – Production

Ozone generationO3

O3

O2

O2

Corona Discharge Tube

Ozone – Production

Ozone generation

O3O2

O2O3

Discharge GapDischarge Gap

Discharge Gap

Glass Dielectric

Ground ElectrodeHigh Potential Electrode

Ozone - Production

Cooling Water Closed loop Open loop

Ozone - Production

Oxygen Ozone

Heat Exchanger

Closed Loop Cooling Water

Open Loop Cooling Water

Ozone Generator

Adding Ozone to Process Stream

Diffusion Sidestream Injection

Adding Ozone to Process Stream

Ceramic, Fine Bubble Diffusion Ozone Resistant Materials

316 Stainless Steel Viton PTFE (Teflon) PVDF (Kynar)

Adding Ozone to Process Stream

Diffusion

CAT

To Ozone Destruct

Adding Ozone to Process Stream

Sidestream Injection Eductors Flash Reactors

Ozone Gas

Adding Ozone to Process Stream

Typical Sidestream Injection System

SidestreamPump

VenturiInjector

Ozone Gas Feed

Ozone Gas Feed

Flash Reactor

Figure courtesy MWH Americas

Adding Ozone to Process Stream

Sidestream Injection Flash Reactors

Adding Ozone to Process Stream

Access to Ozone Contact Chamber

Ozone – Destruction

Prevent release of off-gas ozone into atmosphere

Prevent adverse impact on downstream equipment and processes from ozone residual in process flow

Ozone – Destruction

Off-gas destruction Thermal Catalyst (magnesium oxide)

Ozone – Destruction

Ozone residual quenching Calcium thiosulfate Sodium thiosulfate Sodium bisulfite Hydrogen peroxide

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

Ozone – Operational and Design Considerations

Ozonation Byproducts Bromate (MCL 10 µg/L) Br− + O3 → BrO−

Bromate mitigation strategies

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

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

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

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)

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

Biologically Active Filtration

Biofilm

TOC (AOC & DOC)

Assimilated organic carbon

Remaining TOC

Particulate contaminants

Retained Particles

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

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

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

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

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

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

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)

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

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

Applications in Ohio

Ozone Columbus – Hap Cremean, in design

Biologically Active Filtration GCWW – Richard Miller Others

Ozone and Biologically Active Filtration for Disinfection Byproduct Control

Tom Bell-Games, P.E.tom.bell-games@burgessniple.com