FAT REMOVAL FROM PROCESS WATERS OF THE FISH-MEAL INDUSTRY - A STUDY OF 3 FLOTATION METHODS

Dissolved air flotation (DAF), column flotation and electroflotation w ere assayed as methods for fat removal from process waters (condensate s) produced during fish meal manufacture. DAF of the effluent was carr ied out in both batch and continuous modes at bench scale. The DAF met hod exhibited low efficiency in floating emulsified fat. Only a 34% of fat removal was attained. However, upon emulsion breakdown, the effic iency increased to 96%. Column notation was assayed in a batch and con tinuous mode at pilot scale. Maximum batch fat removal was attained wi th an air flow of of 357 x 10(-4) m(3) s(-1). Higher air flows induced turbulence that reduced the removal efficiency. The continuously oper ated 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)). Electroflot ation was assayed in the batch mode in a 0.011 m(3) cell. It was carri ed out at 4.7 Volts, 15 Amperes and at different current densities. At a current density of 130 A m(-2) the calculated maximal fat removal w as 76% with a residence time of 1584s. From an economic point of view, column notation 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 aver age for the last five years).