EVALUATION OF CRITICAL FLUX IN AN ULTRAFILTRATION SYSTEM WITH PRE-OXIDATION BY KMnO_4

摘要

The pre-oxidation before ultrafiltration (UF) system has been adopted to alleviate membrane fouling in drinking water treatment. The pre-oxidants mostly studied to date are chlorine and ozone, but there is less information available on potassium permanganate (KMnO_4). The concept of 'critical flux' has allowed for a relatively new operational optimization of UF in fouling control strategies. This paper presents experimental results of a pilot study designed to evaluate the critical flux in a KMnO_4/UF system filtrating sand filter effluent. The KMnO_4 pre-oxidation was implemented via direct and continuous dosing of KMnO_4 into the influent of the UF system. It showed that dosing with KMnO_4 before the UF system would enhance its critical flux. However, there was an optimal dosage of KMnO_4 for the maximum critical flux. In this experiment, when the dosage of KMnO_4 was greater than the optimal, the value of critical flux declined. Stable filtration under sub-critical flux operation was achieved successfully by effective membrane fouling control, whilst it failed for supercritical flux operation. Chemical cleaning of various fouled membranes was also investigated in this study, illustrating the effect mechanism of critical flux for the KMnO_4/UF system. It showed that the oxidation of KMnO_4 greatly alleviated membrane fouling, and an even better effect was attained by proper dosage. When dosing with excessive KMnO_4, the effect of relieving membrane fouling is limited due to increasing Mn in the UF effluent.