ABLP Ltd cultures Moreton Bay Bugs at its’ marine production facility located at Chinderah NSW. The facility uses the latest in membrane filtration technology and indoor recirculation aquaculture systems to ensure stringent standards in water quality and temperature are maintained through the production process.
The extent of biofilm development in a culture system is closely related to the systems’ feed input and management processes utilized to routinely remove the film. ABLP’s nursery systems are in continuous use which hinders routine disinfection (e.g. chlorination) and as such physical scrubbing is employed either by staff or by pool cleaning robots to control fouling. Additionally, system temperatures are maintained at 26 °C, these elevated levels contribute to rapid biofilm development.
This report focuses upon an initial 21-day trial to evaluate the efficiency of an ALPHA 4-ways Ultrasound (Quattro-DB unit manufactured by Hydro Bioscience, provided by Algaefree) in its ability to control biofilm development in a seawater storage reservoir, in one of ABLP’s nursery systems. The circular reservoir is 3.05m in diameter and constructed from HDPE. Water is continuously recirculated through the reservoir as part of the production process. The photo in Figure 1 was taken prior to the installation of the ALPHA 4-ways unit to give an indication of biofilm development at the onset of the trial.
Biofouling showed no initial response to the ultrasound installation during the first
week. By the beginning of the second week sections of biofilm began to ‘flake off’ and after approximately 16 days, the reservoir was almost completely clean. Figure 2 shows the ALPHA 4-ways installed centrally within the reservoir, positioned middepth. This picture was taken after 21 days of ultrasound treatment. Physical cleaning of the reservoir was not necessary during the trial period. Under normal circumstances the tank would have been cleaned twice weekly. On completion of the trial, the ALPHA 4-ways was removed and within 5 days biofilm began to re-establish, requiring the resumption of normal cleaning practices.
Comments & Observations
ABLP culture systems recirculate oceanic water containing 35–36 ppt dissolved salt. High chloride levels in combination with ambient 26 °C temperatures generate a highly corrosive environment. ABLP specifies that only Bumax 88 metallic fasteners and Duplex steels are to be used in wetted areas. Preferably, non-corrodible materials are selected, such as nylon, plastics, and composite products.
We experienced crevice corrosion developing on two metallic components of the ALPHA 4-way ultrasonic head. This corrosion became apparent after only 21 days of use. The electrical connection would likely fail and allow water to penetrate the electrical connections, rendering the unit inoperable. ABLP prefers that the ultrasonic heads be supplied with a hard-wired 5 m electrical lead and sealed with an immersion-rated IP68 gland fitting. Plug connections should be avoided. Note: The corrosion issue was corrected by DPI/Hydro BioScience® in September 2019, and all units now ship with hard-wired cables.
Following the first trial using the Algaefree ALPHA 4-ways Ultrasound (see Report 1) to control heterogeneous biofouling in one of ABLP’s nursery seawater storage reservoirs, the unit was transferred to a second nursery system with significant fouling dominated by calcareous sponges thought to be Sycon ciliatum. The floor and lower wall of the 3.05 m diameter HDPE reservoir are cleaned twice weekly using a robotic pool cleaner.
Biofouling is able to become established above the height (approximately 40 cm) that the robot cleaner can reach and must be routinely removed by vigorous scrubbing with scourers. On day zero of the trial, the upper walls of the reservoir had not been cleaned of biofouling for approximately six weeks.
There was no apparent change in the appearance of the biofouling during the first week of continuous ultrasound treatment. During the second week, the sponge began to fade in color and, within a few days, small pieces started to flake off. Routine robotic cleaning was continued to remove the settled material. By the third week, large bare patches were evident and the sponge appeared to be completely dead. Inspection of the dead sponge showed that it could be easily removed by hand without the need for scourers. After 28 days, the remaining sponge was completely removed.
ABLP Ltd was extremely pleased with the ultrasonic Algaefree results. When employed to control biofouling organisms in seawater reservoirs, the Algaefree ALPHA 4-ways system has proven to:
- Reduce labor requirements for system maintenance.
- Reduce biofouling organism loadings and the potential for disease vectors.
- Eliminates the risks and costs associated with chemical usage.
- Improves operator safety through the use of extra-low-voltage power to energize the ultrasound head.