O3 CONTACT TOWER
From: lider@aqualider.com.br
To: shrimp@egroups.com
Sent: July 27, 2000
QUESTION 1:
I would appreciate any help and ideas on sizing an ozone contact tower, to be installed on the seawater intake line just prior to entering the reservoirs at our L. vannamei hatchery. The seawater intake flow of said line is approximately 100 m3/h (26.420 GPH) at low tides and 20% above that at high tides. Average temperatures and salinities are 26-31°C and 20-35 ppm. Our O3 generator is rated at 1 lb/day or 2 lb/day, the latter if assisted with O2 intake. Once the seawater is in the reservoirs it is immediately put to use, which is to say the seawater coming out of the contact tower must be safe enough for larviculture, maturation, algae, etc.
Manoel Tavares.
Aqualider Maricultura Ltda.
R. dos Navegantes 2.277 sala D
Recife, PE - Brasil 51.020-011
Tel./Fax.: +55 81 465-8252
lider@aqualider.com.br
www.aqualider.com.br
***************
QUESTION 2:
I read that you are installing an ozone generator in your hatchery. I run a hatchery in Colombia, and I am looking for effective ways of getting rid of pesticides and pathogens that might be affecting my production. I have been searching for an activated carbon system for my problem, but it does not get rid of pathogens like bacteria. I would appreciate if you could provide me with some information about the benefits and disadvantages of using an ozone generator, and if you have information about the effectiveness of this equipment on pesticides. I have heard that its downside is that it can kill the shrimp if the ozone is not dosified the right way, and that this is really difficult to accomplish in a day to day basis.
Juan Martinez
Manager
PostLarmar
E-mail: postlarmar@geo.net.co
***************
COMMENTS 1:
The first thing would be to check the O3 demand of the water. You are
not adding very much ozone. If you have 100/m3/hr at 24 hrs = 2400 m3/day.
With 1000 gm of ozone/day = 2.4 m3/gm === 0.4 ppm of ozone (with O2 feed).
If there is any organic junk in the input water, that amount of ozone will
be gone long before you kill any virus.
If you think you have enough ozone to meet the demand and get some
residual, you can then think about sizing the contactors and the residence
time, storage times, etc. You can also start thinking about the bromate
problem. The contactors are the easy part. Just design at about 70% of the
flood point of the packing.
Dallas E. Weaver
E-mail: deweaver@gte.net
***************
COMMENTS 2:
If the water is going to be at rest in the reservoir for at least 30 minutes, you do not need any contact tower.
Just inject the ozone in a water line that has its suction from the same reservoir you are filling and send it back to it either directly into the supply line, or a small concrete tank were all the incoming water and the ozonated mater can mix just before the water enters the reservoir, or just pump it directly into the reservoir were the discharge is located.
The dosage will play the most important role on this since the contact time will most likely be larger that whatever the ozone will stay active. Ozone is very unstable in water and it will revert into O2 in salt water in less than 30 minutes for all practical purposes.
Jose Martinez
E-mail : farallon@pananet.com
***************
COMMENTS 3 :
Ozone can kill anything if there is a high enough dosage in the water for enough period, just like most disinfectant. They are meant to kill. If you don't want your larvae to be killed, all you have to do is let the ozone revert to O2 before you use the water. It is quite simple, wait a couple of hours. If you measure conductivity, you will be able to know that there is no residual ozone before you use it. Later on, you can smell it, and see the water colour and pretty much be sure that there is not a problem. Besides, in a tank with algae and a bunch of other microorganisms, ozone will not kill your larvae unless you buy a monster ozonator.
Jose Martinez
E-mail : farallon@pananet.com
***************
COMMENTS 4 :
O3 has a 2.08 oxidation potential (Volts) which is 1.5 times that of chlorine. This means faster disinfection. The molecular bond on O3 is very weak and one of the three oxygen atoms is crazy to divorce from this bond and attach itself to organics such as virus, bacteria, protozoa and fungi that may affect your production. You can find plenty of literature on the issue of O3 utilization in hatcheries. You can contact O3 generator manufacturers such as Osmonics at www.osmonics.com for specific questions and general information. And, best of all, you can get first hand info directly from hatcheries that either have or are currently using O3. We are not. I can't help you on the pesticide issue either because of lack of knowledge. But I can tell you my interest in O3 is for a cleaner and safer oxidizer. I find chlorine not only hazardous to store, handle, and use -- we have recorded various incidents with burns and inhalation -- but also it has oxidation by-products such as chloramines which we have to deal prior to stocking. Also, our shear volume of water demands huge amounts of desinfectants. O3 is no less hazardous as you can see from the oxidation potential. However it may be more practical since there is very little handling involved once the system is properly set up. We have an O3 generator sitting around for three years now because we found no one to do just that. From the little deployment of O3 generators on hatcheries, I conclude that our experience is not unique and that O3 generators are greatly underutilized.
Manoel Tavares.
Aqualider
E-mail: lider@aqualider.com.br
---------------------------------------------------------------------------------