Biofouling of hollow fiber ultrafiltration membranes: A novel multiphase CFD - Porous - CES model and experimental study

The present study focuses on developing a multiphase CFD - porous- CES model to investigate the effect of biofouling in a membrane reactor. An experimental setup with an ultrafiltration (UF) hollow fiber (HF) membrane was constructed to understand the deposition and development of the cake layer due to biofouling. The CFD - porous sub-models were used to study the effect of hydrodynamics on fouling. While the CES (combined extracellular polymeric substances (EPS) and soluble microbial product (SMP)) sub-model incorporated the effect of EPS and SMP on the cake layer formation. The EPS and SMP fractions constitute a significant portion of the microbial mass and are critical in analyzing the biofouling in UF and microfiltration (MF) membranes. The developed membrane fouling model was validated with both literature experimental results and experimental observations from the laboratory-scale UF-HF membrane setup. It was observed that the effect of cake deposition on transmembrane pressure (TMP) and permeate flux was 1.5% higher for experimental set 2 (synthetic wastewater with sludge seeding) as compared to experimental set 1 (synthetic wastewater with yeast sludge). Also, the maximum percentage error between the experimental and simulation values was +/- 6.2%, thus validating the model. The validated model was then used to investigate the sensitivity of the CES sub-model by comparing it with the sectional resistance model (a commonly used model in literature for predicting membrane fouling). It was observed that the sectional resistance model underpredicted the mass of cake deposited by 13% and overpredicted the limiting flux by 4%. The limiting flux has a significant effect while designing a membrane system, and its accurate prediction helps prevent premature fouling in UF membranes. Hence, the preceding results suggest the importance of accounting for the influence of EPS and SMP on the cake layer formation and biofouling and the relevance of the current study.