On the effect of flocculation as pretreatment process and particle size distribution for membrane fouling reduction Original Research Article

This work deals with the feasibility of an olive vegetation wastewater purification process consisting of two consecutive steps: coagulation followed by membrane separation. The target of this work was to reach a purification grade of the wastewater compatible with the limits for the discharge into a municipal sewer that is a COD value less than 500 mg L−1. A feedstock with 55 g L−1 of COD was used for the experimental work. In a first step, the feedstock was pretreated by a flocculation process using as coagulant aluminium sulphate or aluminium hydroxide. Then, the pretreated wastewater stream was purified by four consecutive batch membrane processes consisting of microfiltration, ultrafiltration, nanofiltration and reverse osmosis, each with a recovery rate of 90%. For each membrane, at different recovery values, the critical flux values were measured. Finally, all the streams were analyzed by means of a nanosizer, capable to measure the suspended particle size distribution in the samples from 0.8 nm up to 6.5 μm.