Effectiveness of pulse dosing of submicron super-fine powdered activated carbon in preventing transmembrane pressure rise in outside-in-type tubular and inside-out-type monolithic ceramic membrane microfiltrations

Abstract

Membrane fouling is still a major problem in water treatment that uses membrane separation. In this study, submicron-sized super-fine powdered activated carbon (SSPAC) was applied in a pulse/continuous dose to ceramic-membrane microfiltrations of two very different types: a submerged tubular membrane system that enabled vacuum-driven, outside-in filtration and a monolithic membrane system that enabled pressure-driven, inside-out filtration. Constant-flux filtration with repeated hydraulic backwashing was performed using diluted secondary-treated municipal wastewater and natural river water, and the effect and mechanism of membrane fouling mitigation were investigated. Pulse dosing with SSPAC alleviated a rise of transmembrane pressure (TMP) more than continuous dosing in the submerged tubular membrane system because of the effects, inter alia, associated with precoating the SSPAC layer as well as adsorption, by which soluble membrane foulants were effectively removed. Moreover, pulse-dosed SSPAC combined with a coagulant formed a precoat layer on the membrane that was easy to peel off with hydraulic backwashing. Continuous dosing of SSPAC was inferior to pulse dosing of SSPAC in terms of water quality, and some SSPAC was left on the membrane surface after hydraulic backwashing. In the monolithic membrane system, however, the superiority of pulse dosing of SSPAC was not observed: pulse and continuous dosing of SSPAC led to similar reductions of TMP rise. The SSPAC layer was unevenly distributed along the length of a channel and between channels in the monolithic membrane.