The Navajo Tribal Utility Authority has agreed to bring six wastewater treatment facilities into compliance with the federal and Navajo laws in...
This column will discuss two important topics regarding the
use of ozone.
dosages. How much ozone is
"practical" for certain applications?
air treatment. How ozone can be used in
air treatment, what your liabilities are and precautions you should be taking.
Based on three criteria--application, gallons per minute
(gpm) flow rate and contaminate type and quantity--you will be able to
determine the amount of ozone that will need to be injected. (This dosage is a
product of more than 20 years of trial and error, not a theoretical
breaks the job down into two categories: Simple oxidation (SO) or complex
pertains to iron, sulfur and manganese, which oxidize quickly and easily. They
require very little ozone and no detectable ozone residual. (Residual is
undetectable with the inexpensive test kits on the market today.)
pertains to the oxidation of items such as volatile organic chemicals, organic
odors, microbes such as bacteria, protozoa, amoeba and viruses. CO also
pertains to the need to have ozone residual. When sizing an ozone unit for CO,
the gpm and the water analysis must be ascertained. (A rule of thumb is 0.3 ppm
of ozone residual for a three-minute contact.)
Ozone dose to applications. Certain applications require higher ozone residuals than others.
water--Low to mid-range residual (0.05-0.3 ppm).
towers--Low to mid-range residual (0.05-0.3 ppm).
reclamation--Mid to high-range (0.2-0.5+ ppm).
sulfur and manganese oxidation--Ultra-low range (below detectable levels).
reclamation for odor control only--Low range (less than 0.1 ppm).
kill--Mid to high range (0.2-0.5+ ppm).
The rule of thumb for sizing an ozonator is
sulfur, manganese oxidization = 0.5 grams/hr (500 ppm) per 5 gpm.
water to maintain purity = 1 g/hr/5 gpm.
bacteria (100 cfu) = 1 g/ 1 gpm.
Once the ozonator has been selected you then must decide the
type of ozone injector (ozone pump or venturi) and air dryer.
The other items to select are a contact tank, an automatic
ozone unit actuation switch and filtration.
Care must be taken when sizing ozonators.
producing more than 6 g/hr will require the piping to be Schedule 80 CPVC or
can be no brass or copper anywhere there is ozone residual.
must be certain O-rings and gaskets used; EPDM/Viton, Teflon or Silicone are
off gassing from the gas release device must be ventilated in such a way as to prevent
any ozone odor in the living or working area.
Ozone Air Treatment
Ozone air treatment is a viable method for eliminating such
Whether the treatment will be frequent or infrequent will
depend on the amount and frequency of contamination. Don't expect the air to
stay clean or smell good after one treatment if recontamination occurs.
This brings us to the most important point: contact with
ozone gas. Basically, there should be no contact on a regular basis. The rule
of thumb is "if you can smell it, don't be around it."
Ozone is detectable by the average human nose at 50 parts
per billion. OSHA's limit is 0.1 ppm in an eight-hour period. It is this
author's personal opinion that no one person or animal should be breathing
ozone for any period of time.
Indoor air quality standards are becoming stricter and are
being enforced more often. This could make what some companies are proclaiming
as safe and legal not so in the near future. Not only is there a
legal/liability issue, there also is an integrity issue. How many people would
sell or use chlorine in a dish with a fan blowing it into the air? Why would
someone do the same thing using ozone instead of chlorine? Ozone is a fantastic
oxidizer and disinfectant in the air and water. Ozone, as well as most
everything we use (chemical liquid, solid and gas) can be classified as a
pollutant and/or irritant.
Ozone used in water treatment has no chance of becoming an
irritant or pollutant if the system is designed and installed properly. Ozone
air treatment will not become an irritant and pollutant if designed and
installed correctly and the customer or end user is properly informed.