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Sizing of Ozone Equipment

This article provides Ozone equipment sizing guidelines to get your ozone systems sized correctly.

OZONE BASICS

DISSOLVED OZONE

CD, corona discharge, the method produces ozone by creating a constant, controlled spark (corona) across an air gap through which a feed gas is passed. Then, the feed gas can be dry air or oxygen enhanced air. Finally, the feed gas is dried to a dew point of -60 degrees F minimum. If moisture is present, nitric oxides produced by the corona will form nitric acid which will corrode the equipment.

The relative strength of ozone is expressed as a percentage of concentration by weight; 0.5 to 1.7% for dried air and 1.0 to 6.0% for oxygen air. In fact, this percentage relates to the amount of ozone in the discharged air as this air is not 100% ozone.

Ozone is a much more powerful oxidizer than chlorine, and efficiently oxidizes organics that cause taste, odor, and color problems without leaving a high residual. Ozone oxidizes and precipitates many metals and destroys some pesticides without leaving a trace. It also functions as a pre oxidizer of iron, manganese, and sulfide compounds, allowing for their removal by direct filtration. Contact times are 1 to 6 minutes for common contaminants – ozone has a half-life of 22 minutes in water.

EQUIPMENT TYPES

There are two types of systems that use different feed gas, either dry air or PSA oxygen. A higher ozone output and concentration can be attained using PSA oxygen.

Feed gas air is dried using either a replaceable or heat-regenerative desiccant. This can be either built into the unit or as a separate module.

Oxygen concentrators producing oxygen enhanced air dry up to -80 degrees F dew point and remove nitrogen to improve ozone output and concentration. Again, they can be either built into the unit or as a separate module.

MASS TRANSFER

Ozone is transferred into the water either by venturi (vacuum) or diffusion. Diffusers are used when long-term, passive contact is required e.g. water treatment. Venturi systems are used where smaller volumes of water are involved and precise dosages must be maintained e.g. bottle washing and bottled water.

OZONE EQUIPMENT SIZING 

As with UV WTU, there is a minimum amount of information required to ensure a system is effective.

There is two distinct type of application – single pass and recirculating.

Single-pass applications are bottling lines, discharge water, etc. where ozone is added once to the water.

Recirculating systems are fruit and veg. washing, cooling towers, etc. where extra ozone can be added to the ozone level remains constant.

Dissolved ozone monitors are used to analyze water inline and add ozone when required.

The basic information required is as follows:
– ozone demand (via water sample analysis) ozone dosage
– flowrate
– inline pressure
– the volume of water (for recirculating systems)

OZONE DEMAND

Iron                       0.14 to 0.50 mg/l
Maganese            0.88 mg/l
Sulfire                   2.2 mg/l
Colour                   1.0 mg/l per 10 color parts
Taste & odor       0.05 mg/l
Pheno                    2.0 mg/l
TOC                        4.0 mg/l
BOD                       2.0 mg/l
COD                       2.0 mg/l
Tannins                1.5 mg/l
Nitrite                   2.0 mg/l

The amount of ozone required is affected by ozone demand in the water. Hence, contaminants in the water will consume ozone and affect the dosage level in the water. The ozone dosage required per mg/liter of contaminant is as follows – this figure must be added to the target dosage to ensure there is enough ozone to be effective:

A water sample is required for analysis to ensure the correct dosage is provided.

DOSAGE

Dosage is expressed in mg/l ( milligrams per liter) or p.p.m. (parts per million).

Either value is the same. The ozone output of the equipment is expressed in grams per hour.

There is a large range of applications requiring different dosages.

Bottled water  0.05-0.3 ppm

Cooling towers 0.05 – 0.3 ppm

Reclaimed water 0.2 – 0.5 ppm

Bacteria & Virus 0.2 – 1.0 ppm

Calculate ozone demand (grams per hour) by multiplying the dosage required by contaminant level by flow rate.

For example, the dosage required is 2 p.p.m. – contaminant level is 8 mg/l. – flowrate is 4000 liters per hour

= 2mg / l x 8 x 4000

= 64000 mg per h + 25% safety factor

= 80000 mg per h

= 8 gr/h

Calculations are based on a water temperature of 16 degrees C. Add 25% for every extra 6 degrees.

CONTACT TIME – CT

Generally, 1 p.p.m. for 1 minute CT is sufficient to disinfect water. Furthermore, where inline CT is not available, a Contact Vessel is required to retain water and provide sufficient mixing of ozone and water to provide disinfection. This is most common in single-pass applications.

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