Characterization of the biofouling and cleaning efficiency of nanofiltration membranes

Abstract

The nanofiltration (NF) drinking water production unit of the Mery-sur-Oise plant (Val d'Oise, France) consists of eight identical filtration trains composed of three stages positioned in steps for a production capacity of 140,000 m(3) day(-1). To gain a better understanding of the irreversible fouling of the NF membranes, spiral wound modules in operation for 8 years from each of the three stages of the plant were autopsied before and after chemical cleaning and analysis by Attenuated Total Reflection Fourier Transform Infrared spectroscopy, Inductive Coupled Plasma-Atomic Emission Spectrometry, contact angles, adenosine triphosphate (ATP) content measurements, and rheometry. The fouled membranes from the three stages had similar contact angles of approximately 60 degrees . Relative infrared signals typical of biofilms were classified in descending order from stage 1 to stage 3. The foulant matter of stages 1 and 2 contained similar but weaker ATP concentrations than stage 3. During rheometry experiments, rotation and oscillation analyses demonstrated that the biofilm of stage 3 was less viscous and less elastic than the biofilms of stages 1 and 2. After cleaning, all the parameters analyzed demonstrated a quantitative decrease in the fouling matter at the NF membrane surface, but a biofilm with intact viscoelastic properties (unchanged G' and G'' values) remained at the membrane surface for the three stages. The persistence of biofilm material with intact mechanical properties at the NF membrane surface after chemical cleaning may result in permanent permeability decreases.

The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes

“…This can be achieved by managing feedwater, operational conditions (flux, hydrodynamics) [13], cleaning strategies [131] and membrane selection. However, the costs associated with membrane cleaning and the costs associated with the increased energy expenditure in NF/RO operations under moderate biofouling necessitate further basic research into fundamental mechanisms governing biofilm development in NF/RO modules [112]. As part of this strategy is the need for a better understanding of bacterialmembrane interactions, an area of research that has not received priority but is nevertheless critical in order to fully understand several important aspects of NF/RO biofouling.…”

“…However, these studies were carried out at very low pressure conditions of less than 2.5 bar, when realistically the pressures used for NF and RO membranes in water treatment can go up to at least 17 bar [112]. Another study showed that under the same flux conditions the biofilm formed on the surface of three different RO membranes had similar characteristics.…”

“…Furthermore, in most cases, membrane fouling by natural organic matter, polysaccharides and inorganic material will occur, which can change substantially the membrane surface properties such as hydrophobicity [107], roughness [108] and surface charge [109]. Several membrane autopsies carried out on NF and RO membranes have showed the fouling layer to be composed of different materials [110][111][112][113], caused by the different water quality treated. The characteristics of the fouling layer can therefore be expected to influence the nature of subsequent bacterial adhesion and possibly biofilm formation.…”

Bacterial adhesion onto nanofiltration and reverse osmosis membranes: Effect of permeate flux

“…NF is principally used for the removal of hardness, trace contaminants, such as pesticides and organic matter (Cyna et al (2002)), while RO is used for desalination (Greenlee et al (2009)). NF and RO performance are however adversely affected by biofilm formation resulting in permeate flux and quality decline (Flemming (1997), Houari et al (2009), Ivnitsky et al (2007), Khan et al (2013), Vrouwenvelder et al (1998), Vrouwenvelder et al (2008)), generally caused by the initial adhesion and subsequent colonization of bacterial cells on the surface of the membrane, amalgamating in a biomass consisting of, and not limited to, polysaccharides, proteins, and extracellular DNA (Pamp et al (2007)). …”

Assessment of UV Pre-Treatment to Reduce Fouling of NF Membranes

“…Different types of NF fouling can be defined on the basis of fouling material: inorganic fouling due to deposition on membrane surface of inorganic scales; organic fouling due to humic acids, proteins and carbohydrates (natural organic material, NOM); biofouling due to biofilm formation at the membrane surface. Flux decline associated with NOM fouling and with biofouling can be partially restored by chemical cleaning (Al-Amoudi et al 2005, Houari et al 2010, Roudman et al 2000. Biofouling is distinct from NOM fouling caused by contaminated organic matter derived from biological systems (Flemming et al, 1997).…”