Introduction To Uv Sterilizers

[jhnrb]

Written by: Logan,J

(PART-1 OF 2)

The UV sterilizer is a controversial piece of equipment, especially in reef tanks where diversity of life is considered an important factor. I haven't been able to find any conclusive evidence that reef organisms such as amphipods and copepods will suffer a significant decrease in population when UV sterilization is used. Of course, I didn't find any information claiming to prove they would not either. Notwithstanding this controversy, it is a useful tool for controlling micro-organisms and algae when properly implemented. “WHEN PROPERLY IMPLEMENTED†is the key phrase here. Often, the use of UV sterilization produces less than optimal, if any, results due to improper sizing and flow rates. Obviously, one does not need a 64 watt sterilizer for a 10 gallon tank while an 8 watt unit will not produce the desired results in a 180 gallon tank. But there is much more to it than just bulb wattage.

The function of the UV sterilizer is a combination of flow, diameter, and bulb wattage. These three factors combine to produce the “zap doseâ€. While I do not want to get into the mathematical equations here, let it suffice to say that the zap dose is the UV energy required to kill a given organism. The dose varies depending on the organism. For instance, Streptococcus bacteria needs a zap dose of approximately 9000, algae needs about 22,000, while some viruses need a whopping 440,000 to ensure total eradication. A small UV unit with a high flow rate will not effectively control most of the harmful organisms in the aquarium. In fact, to insure proper zap dosage with the recommended turnover of 2x tank size per day, sterilizers less than 25 watts are not practical for tanks above 20 gallons. On the other hand, a properly sized unit need not be run 24 hours per day to achieve the desired results, thus increasing bulb life. For example, running the sterilizer for two 11-hour cycles every 24 hours will result in a 10% increase in bulb life – a substantial savings when one considers the price of replacement bulbs.

Why is the diameter of the unit important? Contact time: a three-inch sterilizer at a given flow rate will produce a longer contact time than a ¾ inch sterilizer at the same flow rate. Again, without getting into the mathematics, three inches is the optimal diameter for maximum contact time without a reduction in intensity. The UV light is diffused in water and loses intensity as it travels further from the bulb. This is why a 6-inch diameter unit would not be effective – many of the organisms passing through the unit would be too far from the bulb to receive the required dosage. A three-inch, 25 watt unit is 55% more efficient than a two-inch model at the same flow rate. At 500 gallons per hour, the three-inch unit delivers a zap dose of 10,083 while the two-inch unit only delivers 6,512. This is due to the increased contact time allowed by the larger diameter. However, most of the sterilizers available are offered in either ¾ inch or two inches. So, one concludes that the two-inch model is the more desirable choice.

Another factor in choosing the proper unit is flow rate. As mentioned before, the target is two turns per 24 hours. Obviously, the higher the wattage of the bulb, the higher the flow rate for a given dosage. In many cases, a low wattage unit is combined with a high flow rate which produces unsatisfactory results. For example, at 500 gph, a two-inch, 25 watt unit delivers a zap dose of 6,512 while a two-inch, 64 watt unit at the same flow rate delivers 18,406. Staphylococcus would be eliminated by both units while salmonella would pass through the smaller unit with little damage. The larger unit would effectively eliminate the salmonella which has a zap dose of 10,000. Recommendations for flow ratings will be made at the end of this article.

The last factor is bulb wattage. Choosing a sterilizer that will deliver the proper dosage at the required flow rate involves using the proper wattage. As shown above, the higher the wattage of the bulb, the higher the flow rate can be for a given dosage. This is determined by the size of the aquarium. A flow rating of 50 gph might be sufficient to achieve 99.99% sterilization of the tank volume for two turns every 24 hours for smaller tanks. For larger tanks, a higher flow rating will be needed to meet the two turns per day requirement and this will require a higher wattage bulb. But – how to determine this?

Here is a fairly simple formula to determine what the flow rate needs to be for a tank of a given size. By changing the numbers in the equation, one can determine what size unit will be needed and how long it will need to run to achieve two turns per day. The formula is T = a(G/F) where:
T is the time required for 1 turnover of all the water in the tank.
a is the purity coefficient (insert 9.2 here – this is the coefficient for 99.99%)
G is the total volume of water in the tank
F is the flow rate through the sterilizer in gallons per hour.

For example, a 125 gallon tank with a flow rate of 110 gph would require 10.45 hours per turn: 9.2 x 125/110 = 10.45 hours

In summary, one can see that improper sizing or flow will reduce the effectiveness of a UV sterilizer to unacceptable parameters – the bacteria will come out the other side unharmed. Here, I will offer some general, and fairly conservative, guidelines for sizing and flow rates for a two-inch diameter unit. This assumes a zap dose of 30,000 which should be sufficient for algae and all but the toughest bacteria and viruses. Ich parasites have a zap dose of about 100,000. The following flow rates should be reduced by about 60% if UV is being used to control an ich outbreak.
25 watt unit = 80 gph
30 watt unit = 125 gph
64 watt unit = 275 gph

(CONT. PART-2)

 

[jhnrb]

Part-2

(CONT. FROM PART-1)

Written by: LoganJ

While the above is hardly enough to provide exact information, it is more than suitable to determine the wattage and flow rates needed to achieve sterilization for most harmful organisms in a tank of a given size. It is my belief that many manufacturers overrate their units and I would caution the reader about accepting advertised flow rates/tank size information when shopping for a sterilizer. I also recommend the following book for anyone who wishes to obtain a better understanding of UV sterilizers and other equipment associated with aquariums, including skimmers, reactors, pumps, heaters, ozone sterilization, and fluidized bed filters. “Aquatic Systems Engineering: Devices and How They Function†by P.R. Escobal. It is my opinion that UV sterilization would be beneficial for any freshwater tank or for a saltwater fish-only tank. I also would not hesitate to use it on a FOWLR tank. On a reef tank, and this is just my opinion, I would be hesitant to use UV on a regular basis. I believe it would be useful to control occasional disease or algae outbreaks, though.


An Explanation of the Purity Coefficient
Written by: LoganJ

As you know, sterilized water is pumped back into the tank where it mixes with unsterilized water. After the first second or so of operation, at any given time, a certain percentage of water that has already been sterilized will pass through the unit again. This has no effect at all on the ratio of sterilized to unsterilized water in the tank. Only "dirty" unsterilized water passing through the unit will change the ratio. Any percentage of water in the tank up to, but not including, 100% can be sterilized. This is proven by the following which is a differential equation and I'm not going to try to get into the methods for solving it...probably just confuse myself.

(1) T = (G/Fr)log(G/[G-Gs]) where:

T = time
G = total gallons in tank
Gs = sterilized gallons
Fr = rate of change of G to Gs
log = natural logarithm or log to base e (usually indicated by the "ln" key on your trusty Texas Instruments calculator)

When you plug in the numbers to the above equation, and as the value for Gs gets closer to the value of G, the logarithm becomes infinite. This indicates that T will also become infinite at 100% sterilization. If you add in the percentage of water that you wish to sterilize, represented by "w", you get the following equation.

(2) T = -(G/F)log(1-w/100) where:

T = time in hours
G = total gallons
F = flowrate in gph
w = percentage of water to be sterilized
log = base e as above

Although the above equation will provide the solution to "T", there is a much simpler format. The last part of the equation, log(1-w/100), will provide the purity coefficient "a" and goes as follows for 99% sterilization.

(3) a = log(1-w/100)
a = log(1-99/100)
a = log(.01) log to base e
a = -4.6

Since equation 2 begins with a negative, the negative value of the purity coefficient cancels out and it becomes a positive number anyway. We will use the positive value to solve for "T". And we have the following equation using "a".

T = a(G/F) where:
T = time in hours for one turn
G = total gallons
a = purity coefficient from equation 3

99.99% sterilization is recommended by P.R. Escobal and resolves to a purity coefficient of 9.2. If you try to go any higher than this, your turn times get very long. Examples for a 180g tank with a flowrate of 125gph:

99% = 6.6 hours
99.99% = 13.2 hours
99.9999% = 19.8 hours

The formula, T = a(G/F), will also work for figuring filter turn times as filtered water mixes with unfiltered water the same as the sterilized water does. It will not factor in loss of flow due in increased resistance from the clogging filter element, but I don't think that's a factor for most of us when selecting a filter. I know that was not really simple and I can only plead my own ignorance of math as the reason I can't explain it better.


END

 

[jhnrb]

Another Opinion On Uv Sterilizers

UV Sterilizers and Their Use in Aquaria - written by Timbo2

Thinking about purchasing a UV Sterilizer? You may ask yourself, do I really need one? How will I know it is working or not? What size should I buy? Etc?

These are all valid questions and in the next few paragraphs, I will try to explain UV Sterilizers and how you can implement them into your system, to help maintain a virtually disease and parasite free habitat for your aquatic friends.

UV Sterilizers have been in use for many years and has provided the owners with a level of confidence that the chances of fish contracting a parasite or disease are lessened to a great degree. This of course is based upon implementation, strength, and contact time (flow). The way it works is, water from the tank flows through a chamber around an ultra violet light source, and then flows back into the tank. The return water is ?reduced? of the microorganisms that pass through it.

Are UV Sterilizers needed to keep a system free of disease and parasites?

This is a tricky question and a controversial one. Some say yes, and some say no. The UV light is an optional piece of equipment for preventative use, and should be used as that. Many make the mistake of purchasing one and then find out that parasites are still in the aquarium. I would suggest that the use of a UV Sterilizer should be thought through very seriously. If your tank is doing fine, and you don't have constant outbreaks of disease and parasites, as well as algal blooms, then the money you would spend on it could be used for a more immediate purchase. However, if you have problems with the fore mentioned, then a UV could help reduce the amounts of free radical microorganism?s that are causing problems. Keep in mind that this is a lengthy process and you will not see results for at least a week. If you need to get rid of an immediate illness, quarantine and treatment is still the best option.

What size UV Sterilizer Should I get?

UV Sterilizers are created in many different sizes from 8 watts to 240 watt for the aquarist, and even higher wattages for larger applications. What wattage to go with is decided by the size of the aquarium you plan to use it on. The unofficial rule of thumb in determining the wattage is 10 watts per 75 gallons water volume for saltwater application and 10 watts for every 150 gallons for freshwater closed systems. In pond application this is greatly increased to 10 watts per 1000 gallons, due to the suns natural capability of producing UV rays. It never hurts to get the next size up from the minimum to allow for bio-load, particles, and turbidity of the water. These factors affect the efficacy of the unit.

How fast should the flow be through the UV Sterilizer?

This is the most important part of the setup next to wattage that matters. Flow through the UV Sterilizer is what determines the kill ratio of the microorganisms. Too fast, and they slip right through. Too slow, and the water can heat up the aquarium more than intended and lessen the life of the bulb. When choosing the speed for flow, I have found it best to go with the manufacturers minimum flow rating and increase the flow 50gph. I have found this to be most effective. If you find that it is causing a heat problem, you can increase the flow 50 [acronym="Gallons per hour"]gph or so until the heat is not an issue. The key is to stay under the maximum effective flow rate by 50gph. This will present the best kill ratio.

Note: Some manufacturers make submersible pumps and power heads with variable flow selectors. I would recommend getting one of these to be able to adjust the flow. You will want to get the pump rated for just under the maximum flow suggested for the UV, i.e. if 500gph is the maximum flow rating from the manufacturer, you may want to get a 450gph pump. This will give you the ability to adjust the flow accordingly if heat becomes an issue.

How do I attach it to my system?

Most of the UV Sterilizers are inline units and require installation on the return line of your pump to the main tank and some are designed to hang on the aquarium like a hang on back power filter. However, with the many designs and customers setups, this question is ultimately between you and the manufacturers instructions based on the unit that is purchased. I would suggest reading the instructions to the best of your ability and if problems arise, see if the manufacturer offers a help line or check out the best online sources such as AquariumAdvice.com.
Note: It would be a good idea to use inline shutoff valves to aid in performing maintenance. This will allow you to take the UV out to clean it.

How do I know it is working or not?

For most aquarium owners, this is a question that is asked often. The only way to answer this, is, has there been an outbreak of illness or disease since the addition of the UV Sterilizer? If no, then possibly it is working fine. If the answer is yes, then there may be some things to check like bulb life, cleanliness, and flow rate of the UV Sterilizer. All of these things affect its efficientcy.

What does it look like inside? How much maintenance is involved?

The inside of the UV Sterilizer can differ greatly per manufacturer, but all work in the same way. Most of them have a canister type outside with a screw on end cap. In this end cap, there is a hole that accepts a quartz sleeve. This sleeve is made of a special quartz glass that aids the UV lamp in maintaining the correct heat and to protect the bulb from the water. This sleeve is mounted in the hole in the end cap with a compression ring. The inside of the canister is called the reaction chamber. There may or may not be a protective sleeve insert for the inside wall of the canister. This would be to protect the inside walls from becoming damaged due to the UV rays and becoming brittle. Again, there are many different manufacturers; therefore, you will have to follow their instructions for the type of unit you have.

Maintenance on a UV Sterilizer should be performed on a bi-weekly basis. Just as the inside of your return line gets lined with slime and becomes opaque, the inside of the UV will do the same. This will affect its ability to do its job. To clean a UV Sterilizer, you will have to be familiar with the inner workings of one. It is a simple design; however, there are a few parts that will need good cleaning. Make sure the unit is unplugged from the power source before attempting to do any maintenance. Most all UV Sterilizers for aquaria are designed with a hole or window that you can see the glow of the bulb while it is running.

When you remove the UV from the system, take it apart carefully and clean it inside and out with a mild bleach and water solution. After good and clean, rinse well and re-assemble. This would be a good time to inspect everything, and make note of anything that may need replaced due to deterioration. Many experts advise to replace the bulb after 6 months of use. Most manufacturers suggest at least replacing after 1 year, however, it has been noted that most UV lamps lose the ability to kill after about 9 months. Changing the bulb every 6 months will assure that it is going to work without flaw.

Ok, all of this talk about UV Sterilizers is ok, but what does it kill?

Since organisms are exposed to the UV light, the ultra violet rays cause a change in the chemical bonds of the DNA (deoxyribonucleic acid), preventing their multiplication, which will result in annihilation of the specie. Only microorganisms, like algae, parasites or viruses, floating in the water and exposed to the UV light are eliminated. Nitrifying bacteria contributing to the well-being of fish are not carried to the sterilizer, and therefore do not come in contact with the UV light and will not be destroyed. There have been some findings that the Amphipod populations are threatened by the use of UV Sterilizers. Although some of the larvae from the Amphipods and other benthic creatures could be waterborne, they usually lay their eggs in the substrata and in the rocks crevices and a very small amount would be released in the water column to be killed by the UV Sterilizer.

Note: In the case of using a refugium, I recommend placing the UV Sterilizer on a different return line altogether. Refugiums are usually designed to be pod farms and food sources for the main tank. Placing the UV after the refugium, would possibly kill the [acronym="copepods, amphipods, etc"]pods before making it back to the main tank.

I would like to close by saying that although UV Sterilizers have caught somewhat of a bad rap these days with other methods of eradication of parasites becoming easily added and less harmful to the fish and invertebrates as they used to be, I have a UV Sterilizer on my tank, and it runs 24 hours a day, 7 days a week. I have not had an outbreak of any parasite that I am visually aware of. My amphipod and benthic population is thriving, and most of all, my fish are happy. This makes me happy. So, if you want a UV Sterilizer, and are willing to maintain it, by all means get one. You won?t be sorry you did.

References:

Martin A. Moe Jr., The Marine Aquarium Reference "Systems and Invertebrates" Green Turtle Publications, 1989

Gregory Skomal, Setting Up a Saltwater Aquarium; Howell Book House Publications 1997

Vincent B. Hargraves, The Complete Book Of The Marine Aquarium; Salamander Books 2002