Fouling control investigation by pH optimization during olive mill wastewater ultrafiltration

In recent years, the study of membrane processes for recovery of valuable phenolic compounds from olive mill wastewater (OMW) has been intensified. The selected OMW pH for ultrafiltration is one of the variables affecting membrane productivity, selectivity and fouling. An in-depth characterization of fouling was performed for the 150 kDa ceramic tubular membrane selected. At the three tested pH (2, 6 and 9), a high retention of suspended matter of 98% was associated to a low retention of phenolic compounds (1%). At pH 2, a volume reduction of only 15% was reached with a low permeate flux of 15 L.h(-1).m(-2). Adsorption phenomena due to the formation of a compact gel layer of pectin highly mineralized have caused severe membrane fouling. The productivity at pH 6 and 9 were quite similar with initial permeate flux of 160 L.h(-1).m(-2 )and a final reached volume reduction of 80%. As a fractionation of around 25% of carbohydrate content was measured at pH 6, this specific pH seems to be more relevant than pH 9 where only 7% were retained. Furthermore ultrafiltration of OMW at pH 6 was associated with a removable fouling mainly caused by a gel of pectin and suspended matter agglomerates.