Impact of fish feeds, fish oils, and amino acids on the performance of airlift pumps

The impact of the addition of a wide variety of commercial, experimental, and larval feeds as well as fish oils, specific lipid products, amino acids, and surfactants on airlift pumping rates were documented. At 250 min after addition, the airlift flow rate varied from 12% to 102% of baseflow for diffuser injection but only 77 to 85% of base flow for direct injection. As a group, the fish and algal-based oils had the greatest impact on airlift flow rate. It is hypothesized that the impact of feed addition is due to lipids and surface-active compounds leaching out of the feed and increasing bubble size. There was a significant correlation between gas holdup and airlift pumping rate. Higher gas holdup was positively correlated with higher water flows. There was also a wide range in speed and range of flow rate recovery; flow recovery may depend on adsorption of lipids on the tank walls or chemical reactions. There was a positive correlation between lipid content and flow reduction, but the physical characteristics of the feed and specific fatty acid profiles of the feed may be important. The use of performance information based on clean water tests may significantly over-estimate pumping rates of airlift pumps. For critical applications, on-site evaluation using actual airlift pumps and feeds may be needed. While feed addition had much more impact on the performance of airlift pumps using diffuser injection compared to direct injection, the significantly higher efficiency of diffuser injection makes this injector type a better choice for many applications.