Management of Ulva lactuca as a biofilter of mariculture effluents in IMTA system

• Aeration of 15sec min-1 reduces Ulva yield by 50% but also reduces operation costs.
• Reduced aeration has no appreciable effect on the biochemical composition of Ulva.
• A reduction of 75% in aeration time reduces biofiltering efficiency by only 6%.

A strong aeration evens out light exposure, facilitates solute diffusion and increases yield in macroalgae cultivation. It is also responsible however, for up to 85% of the operating cost in the treatment of fish pond effluents. Optimizing and reducing excess aeration can therefore diminish the overall operation cost in monoculture and in Integrated Multi Trophic Aquaculture (IMTA). Biofiltration efficiency and crude biochemical composition of Ulva lactuca ponds were compared at two aeration regimes (continuous and 15 s min- 1 intermittent aeration) in algal culture ponds fed with effluent water from an intensive, semi-closed commercial fish farm. Protein content of the algal yields was similar in both treatments at about 35% in DW. Nitrogen uptake was only 6% lower with the intermittent aeration compared to the continuous aeration, even though the algal yield with continuous aeration was significantly higher. It is suggested that denitrification in the pond with intermittent aeration contributed to the nitrogen uptake efficiency. A significant reduction in aeration led to a shortage in algal yield, but it was coupled with only a relatively small drop in nitrogen uptake.