USE OF FOAM FRACTIONATION IN COLLABORATION WITH A LOW-HEAD / LOW WATER LOSS POLYGEYSER BEAD FILTER TO ACHIEVE VISIBLY CLEAR WATER IN MARINE RECIRCULATING AQUACULTURE SYSTEMS

The yield and efficiency of raising aquaculture in marine systems are highly dependent on the suitability of their environment. In most instances, the source of low water quality is from the culture itself (Boyd & Tucker 1998). This analysis aims to focus on solids management, one element of water quality. The majority of solids produced in a marine system are from either uneaten feed or fish excretion. The presence of these solids provides a medium for bacteria growth, which subsequently results in increased Biological Oxygen Demand (BOD) and the proliferation of disease. To remove these solids, a PolyGeyser, floating bead filter, is the most efficient method. However, removal efficiencies decline from nearly 100% in the 30 - 50 micron size range, and becomes problematic in the 5 - 10 micron range (Malone & Gudipati, 2007).

To overcome this limitation, a foam fractionator can be utilized in addition to the PolyGeyser to remove these micro-particles to achieve visibly clear water. Turbidity, measured in Nephelometric Turbidity Units (NTU), is a measurement of the amount of light scattered when passing through a medium. The human eye can only detect turbid water at turbidity values greater than 5 NTU (Strausberg, 1983), values below that are considered completely clear. A particle size analysis was conducting on several lakes, measuring the amount and size distribution of micro-particles within. A strong correlation between measured turbidity and combined surface area of the particles measured was found. Using this correlation, the effect that a particular particle size has on turbidity can be derived, which can be seen in the figure above. Using measurements taken at various turbidity values, it can be seen that the particle size distribution, and its contribution to turbidity, is typically constant until your turbidity falls below 25 NTU. At this point, particles below 20 microns play a significant role in keeping the water turbid. The effectiveness of the combined use of a foam fractionator and a PolyGeyser bead filter has been proven in a recent 7-month study conducted by AST where shrimp systems went from turbid to clear within a month.