Australian Bay Lobsters

ALGAE-FREE (QUATTRO®) ULTRASOUND TRIAL – REPORT 1
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 focusses upon an initial 21-day trial to evaluate the efficiency of an ALPHA 4-ways Ultrasound 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 mid-depth. 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.

 

LEFT: Initial Biofilm | RIGHT: Biofilm Levels After 21 Days of Treatment

COMMENTS AND 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 e.g. nylon, plastics, and/or composite products. We experienced developing crevice corrosion on two metallic components on the ALPHA 4-ways ultrasonic head. This corrosion became apparent after only 21 days in use. The electrical connection would likely fail and allow water to penetrate the electrical connections rendering the unit inoperable. ABLP has a preference for the ultrasonic heads to be supplied with a hard-wired 5m long electrical lead and sealed with an immersion rated IP68 gland fitting similar to plug connections should be avoided.

 

NOTE. The issue with corrosion has been corrected by DPI/Hydro BioScience® As of January 2020 with all units now shipping with hardwired cables.