Characteristics of oxygen flow through fine bubble diffusers used in the aquaculture hauling applications

The oxygen flow rate was studied for carbon stone and ceramic plate diffusers, two types of diffusers that are commonly used in hauling applications. New diffusers were used in all experiments. It was found that oxygen flow was largest for dry diffusers operated in air and reduced for diffusers started in air and then placed in water and further reduced for diffusers soaked in water prior to use. The coefficient of variation for the two types of diffusers ranged from 7 to 18% for new units. If individual flow adjustment is not provided for each diffuser in a manifold distribution system (one oxygen source, several diffusers), small differences in pressure losses between diffusers can result in significant differences in oxygen flows. The initial oxygen flow during the loading of fish may be depressed until accumulated water in the hose and diffuser is expelled. Under some conditions, the oxygen flow rate can increase by 2-4 times over a 6-8 h period. Decreases in oxygen flow due to prior history may make it difficult to achieve the needed operating flows in a timely manner without exceeding the diffuser's pressure rating. This problem is likely to become more important due to aging and clogging of the diffusers.