Influence of calcium-NOM complexes on fouling of nanofiltration membranes in drinking water production

Abstract

The application of nanofiltration is growing rapidly in drinking water and wastewater treatment. The main problem during the operation of nanofiltration membranes is membrane fouling, part of which is due to the presence of Natural Organic Matter (NOM) in sources for drinking water. In this work the effect of calcium was investigated on the nanofiltration fouling behavior in relation to NOM. From Li and Elimelech (2004) it is known that calcium enhanced membrane fouling significantly due to the formation of calcium-NOM complexes. Two techniques were used in our research to determine the part of calcium which is complexated by NOM and the free calcium ion in solution. Results showed that a minimum calcium concentration and a minimum NOM concentration were required for calcium-NOM complex formation. Furthermore, the influence of the calcium concentration on the flux decline during nanofiltration experiments was investigated for different types of feed water. The observed flux decline was proven to be only caused by NOM fouling rather than other membrane fouling types, such as biofouling, scaling or particulate fouling. Fouling of nanofiltration membranes was related to the calcium content in the feed water, and more specifically to the calcium-NOM complex concentration. Membrane cleaning with SDS was found to be very effective.

Analysis of UF membrane fouling mechanisms caused by organic interactions in seawater

“…When saline water feed was filtered, the rapid formation of brown deposit on the membrane surface could be observed visually, caused by the aggregation of humic substances due to its interactions with salt ions in seawater. The abundance of salt ions in the feed solution may have also contributed towards aggregation due to the formation of salt-NOM complexes (Cornelissen et al, 2006). Given the high salinity of the feed solution used in this study, the aggregation observed is likely to be more severe compared to other studies utilizing lower salt concentrations.…”

“…Both EPS and humic substances have the potential to cause significant irreversible organic fouling (Baghoth et al, 2008;Katsoufidou et al, 2008Katsoufidou et al, , 2010. Furthermore, a high concentration of divalent salts present in seawater significantly increases the fouling potential of organic matter (Cornelissen et al, 2006). Better understanding of the mechanisms involved may lead to more effective fouling mitigation methods.…”

Performances of dead-end ultrafiltration of seawater: From the filtration and backwash efficiencies to the membrane fouling mechanisms

“…Thus, divalent ions of seawater could significantly increase the fouling by the organic matter [36]. Therefore, several types of ions are added to the synthetic seawater.…”

A Hybrid Modelling Approach for Reverse Osmosis Processes Including Fouling

“…Including extra measurements such as total organic carbon and the concentration of individual ions in the feed water, can give more detailed data about these different types of fouling, and would thus further improve the predictive power of the data-driven model. For example, data on organic carbon (the quality of which was found to be insufficient here) is known to enhance fouling by forming complexes with calcium, and could have supplemented the calcium data (which was collected further in the distribution network) [53]. Nevertheless, lumping the different fouling dynamics in the online measured conductivity and the offline measured calcium concentration seems to be sufficient in practice here.…”