Treatment of seafood processing wastewaters by ultrafiltration–nanofiltration cellulose acetate membranes

The wastewaters generated by the cuttlefish processing contain a high organic (COD of 20,000–35,000 mg.L−1) and inorganic (TDS of 30–40 g.L−1) load. These seafood effluents were subjected to treatment with cellulose acetate (CA) membranes synthesised according to the phase inversion process. Two preparation parameters, i.e. polymer concentration in the dope solution and annealing temperature, were varied with the objective of tailoring the membrane performances from ultrafiltration to nanofiltration with respect to the separation needs. Membrane MWCO was determined by permeation of neutral solutes (sucrose, PEG, and BSA). Permeate solutions were characterised in terms of the COD, protein nitrogen (PN) using the Lowry’s method, turbidity and conductivity. The results showed that the COD was reduced up to 93% using NF membranes while the fouling index reached 80%. On the other hand, UF membranes exhibited lower fouling index and higher hydraulic permeability values (up to 45 L m−2.h−1.MPa−1) with a COD reduction of 50–65%.

CA membranes, prepared in our laboratory, were successfully used for experiments of seafood processing wastewater treatment. With regard to membrane MWCO, two kinds of membranes can be distinguished in relation to two filtration processes: ultrafiltration and nanofiltration. The obtained retention rates of COD and PN suggest that the NF process was more efficient in terms of retention of organic and biological matters, but UF results showed higher permeate fluxes. The distinction between the two phenomena has been basically determined by the concentration polarisation observed for UF membranes and by evidence of an osmotic pressure of about 0.35 MPa on NF membranes. To reduce the high values of reversible and irreversible fouling of membranes, a combination between the two membrane processes should be considered as well as the selection of membranes with the best properties. Pre- and post-treatment may also be envisaged in order to improve the whole treatment efficiency. Performance comparison with a trade membrane with 500 Da of MWCO and more important thickness showed a slightly higher retention rate for comparable filtration fluxes.