8/8/2019 TECH9 Water Treatment Ozone

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OZONE AND OZONE-RELATED

ADVANCED OXIDATION PROCESSES

Ozone (O3) is one of the strongest disinfectants

and oxidants available in drinking watertreatment. Advanced oxidation processes (AOPs)in water treatment typically refers tocombinations of ozone and hydrogen peroxide(O

3 /H

2O

2), or of ultraviolet light and hydrogen

peroxide (UV/H2O

2). The O

3 /H

2O

2and UV/H

2O

2

processes enhance formation of the hydroxylradical (•OH) which is a more powerful broadspectrum oxidant than molecular ozone and thuscan oxidize a wider variety of organic andinorganic contaminants.

Ozone is widely used in drinking water treatment

for inactivation of Giardia and Cryptosporidium,and for its ability to oxidize many inorganic andorganic compounds (color, natural organicmatter, disinfection by-product precursors, tasteand odor, iron and manganese, etc.). AOPs havebeen demonstrated to be effective for theremoval/destruction of compounds not readilyoxidized by ozone, or which may require higherthan normal ozone doses for effective treatment(e.g., PCE, TCE, Atrazine, taste and odorcompounds such as MIB and geosmin). AOPsmay make oxidation of such contaminants more

economical.

Ozone can be applied at various points in thetreatment train, although it is usually appliedprior to coagulation (reduces coagulant demand)or filtration (causes micro-flocculation whichimproves filterability).Ozone is typically added to water via a diffusedbubble system in a special contactor consisting of multiple enclosed chambers.

The most efficient operational use of H2O

2 /O

3is

to add peroxide into the second chamber of anozone contactor. This configuration allows theutility to obtain disinfection credits for ozonationwhile achieving the benefit of AOP fordestruction of micro-pollutants. The mostcommon point of application for an UV/H

2O

2 

system is after filtration (lower turbidity, reducedobstruction/shielding of UV light, etc.).

Approximate capital and operations andmaintenance (O&M) costs for ozone are

provided in Table 1. Capital costs include theaddition of an ozone feed system, and contactor(12 minutes), ozone destruction equipment,associated piping and valves, and instrumentationand controls. O&M costs are based on an ozonedose of 7 mg/L and include chemicals, power,

replacement parts, and maintenance labor. Costsdo not include pH adjustment (which canenhance the oxidation process and can representa significant O&M expenditure).

Ozone and AOP reactions can produce a numberof unregulated disinfection by-products (DBPs),including aldehydes, ketones, carboxyl acids,epoxides, peroxides, quinine phenols, andbrominated organics. In some cases theseemerging DBPs can create new taste and odorsproblems. In many cases the health effects of 

these emerging DBPs are not well understood.Ozonation of water containing bromide can leadto the formation of bromate (BrO

3), which must

be maintained below the regulated 10 µg/L level.

Ozone oxidation will also break down manynatural organic compounds into smaller chainmolecules which can more easily serve as food formicroorganisms. This increase in assimilableorganic carbon (AOC) may cause problematicbiological regrowth in the distribution systemunless removed (typically by biologically-active

GAC filters).

Table 1. Approximate Costs of Ozone

Design Flow (mgd) 0.1 1.0 10 100

Average Flow (mgd) 0.03 0.35 4.4 50

Capital Cost ($/gal)1  $4.00 $1.00 $0.50 $0.25

Annual O&M Cost ($/kgal)2  $6.50 $0.50 $0.25 $0.20

1. Capital costs are based on $ per gallon of treatment plant capacity. For example, aof ozone at a treatment facility with a capacity of 100,000 gpd would be expected approximately $400,000 ($4.00/gal × 100,000 gal = $400,000).

2. Annual O&M costs are based on $ per thousand gallons treated. For example, annO&M costs for a system with an average daily flow of 30,000 gallons (5 kgal) wouapproximately $71,175 ($6.50/kgal × 30 kgal/day × 365 days/year = $71,175).