Toward a better identification of foulant species in MBR processes

This study aims to identify the nature of organic species (soluble or colloidal) governing membrane fouling within the context of a membrane bioreactor (MBR). A knowledge of their nature and origin (excreted during treatment or associated with the influent) can help to better adapt operational conditions and cleaning procedures. In this work, a fractionation step by ultracentrifugation and innovative organic matter characterisation were done in parallel with dead end microfiltration tests. The complementarities of classical parameters and innovative analyses can help depict foulant species physicochemical properties. Results show that the fouling layer is mostly governed by the deposition of soluble compounds whereas the impact of the colloidal fraction (poorly presents in supernatant) is less. HPLC–SEC and fluorescence analyses reveal the important role of proteins-like substances (polypeptides) in membrane bioreactor fouling.

This study aims to develop a method to identify the nature and configuration of organic components which govern MBR process efficiency. This approach, consisting of linking classical filtration parameters, a fractionation method, and specific analyses (HPLC–SEC, EDX and fluorescence analyses), appears relevant on the basis on these preliminary experiments. Thus, it appears that the soluble fraction play a more significant role in fouling mechanism than the colloidal fraction. Regarding molecular mass distribution, in our example larger proteins and some building block (as peptides) are rejected by the membrane, whereas most humic substances pass through the membrane. In addition, some EDX analyses show calcium and organic matter complexation. Nev- 4. Discussion Filtration tests and DOC analyses complementarities have shown that flux decline is mostly due to a membrane fouling comprised of components derived from the AS soluble fraction. More precisely, foulant species were demonstrated to be protein-like substances, by HPLC–SEC and fluorescence analyses. EDX analyses of a fouled membrane show a large quantity of calcium on/in the cake layer (Fig. 5). In some cases calcium and acidic functional groups (R–COOH) can form complexes and build a rigid organic matter network that may exacerbate flux decline [11].