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ผู้เขียน หัวข้อ: Startup of a new System (recirculating aquaculture system)  (อ่าน 5922 ครั้ง)
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« เมื่อ: กรกฎาคม 15, 2007, 04:57:40 PM »

5542 Engineer Dr.
Huntington Beach, Ca 92649

by D. Weaver


Starting up a new recycle aquatic system can range from a complex operation to a relatively simple one, depending upon the specifics. This discussion is oriented towards more complex systems with high performance biofiltration systems and systems that require high levels of biosecurity.

The startup can be broken down into four stages:

Mechanical, hydraulic and instrumentation system performance verification.
Obtaining or producing a clean biological seed material, free of all fish pathogens.
Feeding the system and developing the biofilter before addition of aquatic stocks.
Adding the aquatic animals.

As the technology for recycle aquaculture and zebra fish research continues to improve, the complexity of the systems also increases with the addition of water quality monitoring systems, water chemistry control systems, alarm systems and automated feeding systems. Therefore, operator training and detailed operating protocols are required to prevent a malfunction that can result in the loss of stock. Starting up a modern facility resembles the start up phase of chemical processing plants and other continuous flow process plants, where startup must be a specified and budgeted part of the overall process. The startup can also involve specialists with experience in startup aquaculture systems and staff training.

More labs, research institutes and private corporations continue to make their systems more bio-secure in terms of limiting the introduction of pathogens. As a consequence of this increased biosecurity, beneficial microorganisms required for the functioning of the biofiltration systems may also be limited. There have been cases where biofilters could not start nitrification for 6 months without seed addition (one such case was a very high biosecurity shrimp hatchery). As the systems get better at preventing pathogen introduction, they are also better at preventing desirable organisms from entering.

Physical System startup:

Starting up a new system depends upon the size and design of the system. The typical stand- alone rack system or bench top system can be setup and plugged in as per the instructions. Larger systems with central filtration units require considerable effort and attention to detail to accomplish a successful startup. The balance of this discussion will be oriented towards these larger, more complex systems.

It is assuming that one is starting with a well designed system or a packaged system from design engineers, contractors or vendors with experience in live animal holding systems. It is further assumed that the basic design was reviewed by qualified outside engineers. The review engineers should also have extensive experience in the area of Aquaculture Engineering and preferably operational experience with the species in question. Eliminating future system and operation problems at the design stage is very desirable. As part of the design review, a failure mode analysis should be conducted and critical items delineated.

Once the installation is complete, but before water is added to the system, the system should be inspected looking for poor glue joints, fittings that were not installed correctly, and deviations from the specified process flow diagram. The electrical systems should also be checked out and all GFI outlets tested. If the pumps are on three phase power, the pumps should be "bumped" to check the rotation.

The system can now be filled with water and the circulating pumps started. When starting with a dry system, there may not be enough water in the sump to fill the entire system before the sump goes dry. This may require you to cycle the main flow pumps off and on until the system is full. Air visible in the water when flowing or in the pump baskets, is a red flag indicating to start checking for air leaks.

After leak inspection, the dynamic head of the system should be checked by shutting down the system for about 30 minutes and restarting. If correctly designed, you should be able to shut down all the pumps and excess water (dynamic head) will flow down the overflow drain, and when the system is restarted the sump level will decrease, but not enough to create a pump suction failure. If the pumps suck air, the water will be supersaturated with gas and can create a major mortality event.

With fluidized bed biofilters, shut down the clean water pumps or flows to the fish tanks and add the media to the filter. It is common to get a lot of fine solids in the form of silts and clays coming off the media and clouding the water. With the filter system on recycle add all the required media while checking the level, then let the system flush with fresh water until clear. The remaining silt that collected in the sumps should be suctioned out.

All instrumentation should be calibrated and tested. In particular, if the system has automatic pH control, both acids and alkali should be added to verify the response behavior of the system and make certain that no pulses of low or high pH water will go to the tanks. Small zebra tanks have no significant volume and have fast turnovers, therefore, the pH control system must not be allowed to overshoot or to oscillate. Adding pulses of acid or NaOH to the tank return water can be used for testing the system dynamics.

Biological Startup:

Once the physical system is operating properly, it is time to introduce the appropriate seed culture for the biofiltration. If the facility is operating with a low level of biosecurity or the system is in the same room as a working system, you may not need a seed culture. Just add some ammonia compound based NPK fertilizer or some animal urine to the system to get the nitrification bacteria to colonize the system.

However, if you are operating a truly bio-secure system that is starting sterile, there is no initial bacterial seed in the system. Systems such as these can go for 6 mo without any nitrification. This presents a significant problem, because there is an understandable resistance to transferring any bacteria from an existing system unless you can guarantee that the seed culture is free of all fish pathogens. To further complicate the problem, many more species than nitrification bacteria are required to make a biofilter work properly and recycle water suitable for fish culture. Some data indicate that 200 species of bacteria exist a fluidized bed biofilter (and these are only the species that can be cultured), each serving a different function in decomposing the fish waste. This means we can't just buy a few pure cultures.

One method that has been used for fish pathogen free startup is to load the system with about 5 ppm ammonia plus some NPK fertilizer and a small amount of FeSO4 (about .1 ppm). Obtain some soil from a dairy or cattle feed lot, which is well contaminated with cattle waste and urine and has been contaminated for a long time. This soil will contain a full range of decomposing bacteria required for the biofilter. Make a slurry of this soil and screen with a 500µ screen and put the material that went through the screen into the system sump. This material will not contain any of the more virulent fish pathogens. The risk of fish pathogens from this source is a lot less than from any existing fish facility. Over time, aquaculture facilities accumulate facultative pathogens in the system, which only become a major problem when there is some other stress problem or the fish has a weak immune system. This accumulation can make seed culture from any facility that has fish in the system suspect.

There are several manufactures that sell bacterial mixes for starting biofilters. However, we have found that unless the bacteria were originally grown on the biofilter media type used in the system and fed a complex diet beyond just ammonia, these materials do not work properly for starting up a sterile system. Even some of the newer and better brands don't work. I have had more than one client spend thousands of dollars on special bacterial cultures for startup and not succeed.

Once the system starts removing the ammonia, start daily additions. The amount added should be about 3% of the design feed rate (dry wt. of feed) per day as N (note: a 21-0-0 fertilizer -- ammonium sulfate is 21% N -- the numbers correspond to N, P, and K percentages). Once all the ammonia disappears and the system is also removing all the nitrite, the facility is ready for fish.

Fish Introductions:

Introducing fish into the system will depend upon how pathogen free you want to maintain the system. For very biosecure operation, the only animal introduced should be from stocks that are known to be free of any vertically transmitted disease (it is often not known whether a specific pathogen has true vertical transmission capability). Since the present state of knowledge of fish viral diseases is a developing field, we generally don't know what to look for and only have tests for a few viral diseases. This means that there is always a real risk from introducing any unknown animal.

Whenever possible, for maximum biosecurity, all introductions should be from bleached eggs from apparently disease free stocks. This is not always possible, which makes it desirable to have quarantine facilities for any incoming animals. It should be noted that with small fast reproducing animals like zebra fish and other ornamental fish, some producers have minimized their viral disease problems by selective breeding for resistance. This has resulted in animals on the market that are resistant carriers of some very lethal virus. These animals will pass normal quarantine, sometimes with sentinel animals in the quarantine. Know your supplier and discuss pathology issues and do not obtain animals from wholesalers or distributors unless the animals are traceable to quality sources of tank reared animals and biosecurity has been maintained (only true for a small percentage of laboratory supply companies.

Some of these aquatic virus appear to be very temperature sensitive (only active in a specific range), which means that unless you know what your are looking for and have a probe to detect it, it could flow through a quarantine without a problem. Limiting introductions to disinfected eggs could significantly reduce the probability of an unwanted pathogen introduction by eliminating all non-vertical pathogens.

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