Fat removal from process waters of the fish meal industry. A study of three flotation methods

Abstract

Dissolved air flotation (DAF), column flotation and electroflotation were assayed as methods for fat removal from process waters (condensates) produced during fish meal manufacture. DAF of the effluent was carried out in both batch and continuous modes at bench scale. The DAF method exhibited low efficiency in floating emulsified fat. Only a 34% of fat removal was attained. However, upon emulsion breakdown, the efficiency increased to 96%. Column flotation was assayed in a batch and continuous mode at pilot scale. Maximum batch fat removal was attained with an air flow of of 357 × 10^‐4 m³ s^‐1. Higher air flows induced turbulence that reduced the removal efficiency. The continuously operated column had a hydraulic residence time of 1810 s for a fat removal efficiency of 64.3% (from 0.140 to 0.05 kg of fat m^‐3). Electroflotation was assayed in the batch mode in a 0.011 m³ cell. It was carried out at 4.7 Volts, 15 Amperes and at different current densities. At a current density of 130 A nr² the calculated maximal fat removal was 76% with a residence time of 1584s. From an economic point of view, column flotation is the most efficient method adding only US$ 0.023 to the cost of the processed metric ton of fish meal (US$ 477 as an average for the last five years).