Fouling of low-pressure (MF and UF) membranes by wastewater effluent organic matter (EfOM): characterization of EfOM foulants in relation to membrane properties

Low-pressure (micro- and ultrafiltration) membranes are increasingly being used in water reclamation processes treating secondary or tertiary effluent from wastewater treatment plants. The main challenge remains the fouling of membrane surface/pores by organic matter which prevents efficient operation. The extent of this fouling strongly depends on feed water quality as well as membrane properties. The aim of this study is to characterize wastewater effluent organic matter (EfOM) and to describe its fouling behavior in relation to various membrane properties (pore size, charge, material, hydrophobicity) through evaluation with stirred cell experiments, elemental analysis, ¹³C-NMR spectroscopy, and atomic force spectroscopy. Four membranes are tested - one ultrafiltration (UF) membrane and three microfiltration (MF) membranes - with bulk EfOM, derived from the Boulder, Colorado, USA, wastewater treatment plant, as well as with EfOM isolates. The hydrophobic microfiltration membrane is most seriously fouled by bulk Boulder EfOM, while the two hydrophilic membranes (MF, UF) made of cellulose acetate are the least fouled. Differences between the flux decline curves of various membranes are less distinct with isolates than with bulk EfOM. The transphilic isolate (TPIA-Bld) exhibited a higher fouling potential than the hydrophobic isolate (HPOA-Bld). This behaviour is due to the different chemical characteristics of the isolates, namely the higher percentage of hetero-atoms (oxygen and nitrogen) of the transphilic isolate compared to the hydrophobic isolate. Finally, atomic force microscope (AFM) images present clear evidence of fouling. AFM is clearly able to detect the fouling layer, although it has not been possible to distinguish between pore blockage and surface fouling thus far.