Study of OMWWs suspended solids destabilization to improve membrane processes performance

Olive Mill waste waters (OMWWs) are extremely polluting and need to be treated before being dis-charged or to provide opportunities for their reuse or recycling. Because of their high suspended solids content, a pre-treatment method able to abate the severe fouling occurring during the subsequent micro and ultrafiltration membrane processes is mandatory. In this paper, a new approach to the OMWWs pre-treatment based on suspension destabilization as a function of its zeta potential has been developed. The original feature of this method relies on the precise identification of the suspension destabilization conditions by zeta potential and light scattering measurements. The obtained results indicated that the ideal destabilization conditions occur at pH 1.8 (near to the isoelectric point), corresponding to the lowest zeta potential value and to the formation of large agglomerates with a mean particle size equal to 21 lm. The pre-treatment proved to be relevant for achieving the complete elimination of all the suspended solids making the OMWWs more suitable for the following microfiltration (MF) and ultrafil-tration (UF) processes. The performance of different membrane materials during MF and UF processes was evaluated in terms of total and dissolved solids, TOC reduction and phenols rejection. The highest permeate fluxes, 60 and 23 L/hm2 were obtained in the MF and UF processes, respectively, using ceramic membranes. Besides, results in terms of phenols quantification indicated that this pre-treatment preserves the polyphenols from oxidation. The suspension destabilization method here described provides a general approach to treat waste water with large suspended solids content, thus it can be easily extended to the pre-treatment of waste waters from different sources with the aim of reducing fouling during MF and UF membrane processes.