Metabolites excreted by fish and other aquatic stock contribute to the carbonaceous biological oxygen demand (BOD) and the ammonia concentration of the circulating water. For prawns, for example, in order to ensure healthy stock the BOD should be less than 3.0mg/l and ammoniacal nitrogen below 1.0 mg/l – so treating the recirculating water to remove these contaminants is crucial.

Removal of BOD and ammonia can be achieved effectively using aerobic moving bed biofilm reactor (MBBR) technology, which combines the oxidation of carbonaceous BOD into carbon dioxide with nitrification to convert ammonia into nitrate. The process utilises bacteria grown on the surface of media, which use the contaminants in the water as a food source, forming a deposit on the media surface, called a biofilm, which removes the contaminants. Warden’s filter media offer large protected surface area, providing a range of micro-environments conducive to the growth of different bacteria to ensure high biomass attachment and efficient removal of both BOD and ammonia.

The high surface area increases the overall biomass concentration, therefore minimising the required aeration tank volume, and the large openings allow for the wastewater to freely pass through the media helping to maintain a healthy and thin biofilm.