Reversibility of fouling on ultrafiltration membrane by backwashing and chemical cleaning: differences in organic fractions behaviour

Abstract

Membrane fouling is an inherent phenomenon in UF membrane processes, making it necessary to periodically perform backwashes (BW) and chemical "cleanings in place" (CIP) to restore the initial permeability of the membrane. The objective of this study was 1) to explore systematically the effect of distinct BW-related variables (BW transmembrane pressure, duration, frequency, composition) on the reversibility of UF membrane fouling and on the permeate quality (in terms of total organic carbon, turbidity and UV absorbance) over successive filtration/BW cycles; and 2) to identify which organic fractions were most removed by the membrane and, of these, which were most detached after BW, alkaline and oxidant CIP and acid CIP episodes. For this purpose, a bench-scale outside-in hollow fibre module operated under dead-end filtration mode at constant transmembrane pressure and treating settled water from a drinking water treatment plant was employed. Dissolved organic carbon fractionation was performed by high performance size exclusion chromatography (HPSEC). Results showed that in general the more intensive a BW was (in terms of high transmembrane pressure, shortened frequency and prolonged duration) the more effective it was in removing fouling from the membrane. Concerning the composition of the water used for the BW, the addition of NaClO led to maximum fouling reversibility, closely followed by the combination of NaOH+NaClO, while citric acid and NaOH contributed little compared to water alone.However, results also showed that irreversible fouling was never completely avoided whatever the BW regime applied, leading to a gradual increase of the total resistance over time. Larger

The Performance and Fouling Control of Submerged Hollow Fiber (HF) Systems: A Review

“…The application of relaxation (intermittent cessation of permeation), backwashing (reversal of permeate flow through the pores), and air backwashing with or without air scouring are common physical approaches to remove fouling in submerged systems. It has been shown in many studies that relaxation and backwashing provide an effective removal of the fouling layer, thereby prolonging the filtration process in submerged membrane systems, especially at high imposed fluxes [88,90,131,286,287]. A significant challenge in the application of relaxation and backwashing is that only partial recovery of the permeability is achieved at the end of a filtration cycle, which implies a gradual loss of the effective filtration area due to fouling.…”

Composition and reversibility of fouling on low-pressure membranes in the filtration of coagulated water: insights into organic fractions behaviour

“…Additional CEBs based 20 on a combination of NaClO (7 mg/L) and NaOH (pH 10-11) were made every 3 BWs. The BW and CEB conditions were adopted after a previous study [31]. The total volume of feed water filtered was 4.0 L, of which approx.…”

Fouling Indices for Quantification of Natural Organic Matter Fouling and Cleaning in Ceramic and Polymeric Membrane Systems

“…This could be attributed to the high irreversible mass of alginate + Ca +2 compared to alginate -Ca +2 and humic acids (refer to Table 7.1). While NaOCl is known to cause swelling to hydrophobic polymeric membranes, and this assists in flushing out foulant material within the pores Zhang et al, 2017;Ferrer et al, 2016; the same cannot be said for ceramic membranes since they have solid structures and hydrophilic surfaces, thus, the swelling effect is not possible. Thus, in ceramic membrane the impact of NaOCl as a cleaning agent is reduced.…”