Mechanism Involved in the Evolution of Physically Irreversible Fouling in Microfiltration and Ultrafiltration Membranes Used for Drinking Water Treatment

Abstract

Control of membrane fouling is important for more efficient use of membranes in water treatment. Control of physically irreversible fouling, which is defined as fouling that requires chemical cleaning to be cancelled, is particularly important for reduction of operation cost in a membrane process. In this study, a long-term filtration experiment using three different types of MF and UF membranes was carried out at an existing water purification plant, and the evolution of physically irreversible fouling was investigated. The experimental results demonstrated that the extent of physically irreversible fouling differed significantly depending on the membrane type. Cleaning of the fouled membranes with various chemical reagents demonstrated that organic matter was mainly responsible for physically irreversible fouling. Organic matter that had caused physically irreversible fouling in the long-term operation was desorbed from the fouled membranes and was subjected to Fourier transform infrared and 13C nuclear magnetic resonance analyses. These analyses revealed that carbohydrates were dominant in the membrane foulant regardless of the type of membrane. Based on measurements of molecular weight distribution of organic matter in the feedwater and the permeates from the membranes, a two-step fouling mechanism is proposed to explain the dominance of carbohydrates in the foulant: hydrophobic (humic-like) components with small molecular weight are first adsorbed on the membrane and, consequently, narrow the size of micro-pores of membranes, and then hydrophilic (carbohydrate-like) compounds with larger molecular weight plug the narrowed pores or the hydrophilic compounds are adsorbed onto the membrane surface conditioned by the hydrophobic components.

Hydraulically irreversible fouling on ceramic MF/UF membranes: Comparison of fouling indices, foulant composition and irreversible pore narrowing

“…Internal fouling arises from the adsorption of organic matters that are smaller than the membrane pore size leading to the pore narrowing [16]. To determine internal fouling and its effect on hydraulically irreversible fouling, additional fouling experiments were carried out with the permeate water of the individual membranes.…”

“…Humic substances [10][11][12][13][14] and biopolymers [15][16][17][18][19][20][21] in natural surface water have been intensively acknowledged as the main organic foulants on UF/MF membranes in both hydraulically reversible and irreversible fouling. Zheng et al [22] identified organic matter larger than the UF pore size as the major foulants, which contribute to the cake layer formation, while only a small remaining portion (unquantified) remains as hydraulically irreversible fouling after backwash.…”

Investigation of organic foulants behavior on hollow-fiber UF membranes in a drinking water treatment plant

“…They reported that humic substances caused severe irreversible fouling due to adsorption, while alginate should have a most detrimental effect on membrane fouling, but mostly reversible. Through investigating the fouling behavior of natural water in three different types of MF and UF membranes, Yamamura et al [12] revealed that carbohydrates were dominant in the membrane foulants regardless of the types of membranes. Other researchers [13,14] considered that a high content of hydrophilic fraction or hydrophilic neutral fraction in the nature water caused serious flux decline, by using hydrophobic and hydrophilic MF and UF membranes on the NOM isolated from different surface water.…”

Enhanced fouling resistance of organosilane-grafted ceramic microfiltration membranes for water treatment

“…16) To achieve reliable membrane performance, the fouled membranes should be periodically recovered using hydraulic back-washing (for reversible fouling) or chemical cleaning (for irreversible fouling). 17) Even though other methods (such as pretreatment of the feed and optimization of the operating conditions) are available for membrane maintenance, they do not provide satisfactory results because of the increased operation cost and decreased membrane lifetime. 18) Thus, surface modification is becoming a critical technique for the development of novel ceramic membranes with excellent fouling resistance.…”