BEAD FILTER APPLICATIONS IN MARINE AQUACULTURE AT THE UNIVERSITY OF SOUTHERN MISSISSIPPI  

Established in 2006, The Thad Cochran Marine Aquaculture Center (TCMAC) transformed the Gulf Coast Research Laboratory's aquaculture program into a modern state-of the-art 100,000 ft² marine hatchery. Because of the lack of a consistent supply of quality seawater and restrictions on effluent discharge, the hatchery was designed as a closed system, recirculating facility operating primarily on artificial salt water. As such, primary design criteria were to achieve minimal discharge and maximal retention of valuable artificial salt water. Other design criteria for our budget-conscious operation included low maintenance, small footprint, efficient filtration of fine particles, longevity and resistance to corrosion and low pressure operation which allows for the use of cheaper high flow/low head pumps. Bead filters are ideally suited to meet these criteria.

All TCMAC finfish filtration designs are variations on a single plan and include mechanical filtration, a moving bead bioreactor, foam fractionation, appropriate sanitization (ozone or UV), and oxygenation. Our designs have successfully employed Polygeyser Drop Bead filters, Bubble Bead filters, and Propeller-washed Bead filters for mechanical filtration in a variety of applications. Polygeysers accomplish the least water loss per backwash and, depending on which bead design is used, can provide some biofiltration, which we have found to be sufficient in some systems. In our experience they are most suited for broodstock applications with low biomass and a relatively low level of fine particles.  Bubble Bead filters lose more water per backwash than Polygeysers, but they allow control over backwash frequency, and they require no external inputs (i.e., air or electricity). Bubble bead filters are ideally suited for broodstock and larval rearing applications where a variety of particle sizes must be filtered. Propeller-washed Bead filters, although they can lose more water per backwash than either Polygeysers or Bubble Bead filters, provide maximum backwash flexibility and are ideally suited for high density, high biomass nursery and growout systems where feed rate and amount changes require frequent adjustment to backwash schedules.

Possible disadvantages include the potential for returning some fine particles to the system following backwashes, the low pressure thresholds of the units which require the use of a pressure bypass valve to avoid damage due to pressure increases, the time required for the bead bed to "mature" to achieve maximum filtration efficiency, and complexity of automation.

Overall, bead filters have made it possible for the TCMAC to use a common design to achieve substantial production capabilities while meeting our goals of salt water conservation, low discharge, and a budget-conscious operation.