Operation and cleaning of ceramic membranes for the filtration of fish press liquor

This paper assesses the performance of three ceramic membranes of average pore size 50 nm, 200 nm and 1.4 μm in the treatment of the press liquor resulting from a compaction operation of sardine by-products. To this end, 2 L of pre-filtered press liquor with an average protein content of 44 g/L were filtered during 3 h through the three membranes assayed. Unexpectedly, the membrane of larger pore size, presented the lowest values for the flux of permeate at steady state at 20 L/(m2 h), while its average protein rejection (77%) was similar to that observed in the membrane of 200 nm. This fact was attributed to the difference in material of its active layer (α-alumina instead of zirconite). The cleaning efficiency of the membranes was assessed by the COD reduction in the permeate streams, related to that of the raw press liquor. The permeates obtained from the three membranes presented an average value of COD around 17,300 mg O2/L, which corresponds to a COD removal efficiency above 85%. Finally, a cleaning protocol comprising an alkali, acid and final disinfection stage was performed after the ultrafiltration. This sequence permitted to restore completely the initial permeability for the three membranes, although the acid step was found to be detrimental to the cleaning efficiency.