Pulsating CO2 nucleation radically improves the efficiency of membrane backwash

Abstract

Although membrane filtration became a dominant water treatment technology globally, it suffers from membrane fouling which aggravates with time and imposes severe adverse effects on process performance, permeate quality and, eventually, its related costs. In this work, we introduce pulsating CO2 solution backwash with intermittent pressure drops to maximize CO2 bubbles yield and radically enhance membrane cleaning. The novel backwash technique was probed during ultrafiltration (UF) of feed waters containing sodium alginate, a model polysaccharide foulants, sea salts enriched in Ca2+, and SiO2. Transmembrane pressures (TMP) observed during the experiments with pulsating CO2 backwash acquired an up/down profile indicating that a considerable portion of TMP was recovered after each backwash cycle, in contrast to insufficient fouling removal and subsequent TMP build-up observed with continuous CO2 and Milli-Q backwashes. Notably, pulsating CO2 backwash alleviated irreversible membrane fouling in highly saline conditions with 30 g/L of sea salts and when it is combined with 1 mg/L of SiO2 (i.e., when conventional membrane backwash was not effective). Furthermore, intense cleaning of the membrane surface and its pores was resembled by a lower fouling resistance in the subsequent UF cycles implying potentially longer operation time with less cleaning frequency and substantial energy savings.