Effect of solution chemistry on the fouling potential of dissolved organic matter in membrane bioreactor systems

Dissolved organic matter (DOM) as a potent foulant in membrane bioreactor (MBR) systems has attracted great attention in recent years. This paper attempts to elucidate the effect of solution chemistry (i.e. solution pH, ionic strength, and calcium concentration) on the fouling potential of DOM with different characteristics. Results of microfiltration experiments showed that the fouling potential of DOM having higher hydrophobic content increased more markedly at low pH due to the reduced ionization of carboxylic and phenolic functional groups of aquatic humic substances. In contrast, the fouling potential of hydrophilic DOM components and the molecular size of DOM appeared to be less affected by solution pH. The more compact molecular configuration of DOM at high ionic strength contributed to form a denser fouling layer, and limited the amount of foulants retained by the membranes on the other hand. DOM fouling potential greatly increased with increasing calcium concentration. The magnitude of the increase, however, was independent of the hydrophobicity of DOM, suggesting strong interactions exist between calcium ions and hydrophilic DOM components. Moreover, it was observed that the main mechanism governing the effect of calcium ions on the molecular size of DOM transited from charge shielding to complex formation as calcium concentration increased.