A Review of Membrane Fouling in MBRs: Characteristics and Role of Sludge Cake Formed on Membrane Surfaces

Abstract

Membrane bioreactor (MBR) has been deemed to be a promising technology for wastewater treatment and reclamation; however, the MBR filtration performance inevitably decreases with filtration time attributed to the deposition of soluble and particulate materials onto and into the membrane under the interactions between activated sludge components and the membrane. Cake layer formation on membrane surfaces has been a major challenge in the operation of MBRs under supra-critical flux operation, and/or caused by uneven distribution of aeration intensities, etc.; however, it was argued that a thin cake layer might improve filtration operation by some researchers. This paper provides a critical review on the formation mechanisms, properties, the role of sludge cake in membrane filtration, and the corresponding strategies of controlling cake fouling in MBRs. Drawbacks and benefits of the formation of sludge cake were also discussed in order to better understand the characteristics and role of sludge cake formation in MBRs.

Keywords:

• Cake layer
• membrane bioreactor (MBR)
• membrane fouling
• sludge cake characteristics

ACKNOWLEDGEMENT

Financial support of this work by the Independent Research Fund of Chinese State Key Laboratory of Pollution Control and Resource Reuse for Young Scholars (Grant No. PCRRY08005) and by Research Fund for Excellent Young Talents of Tongji University (Grant No. 2008KJ019) is gratefully acknowledged.

Notes

^a d _p, particle diameter (m); ρ_p, particle density (kg/m³); η, dynamic viscosity (Pa s); A, Hamaker constant; s, separation distance (m); ρ_l, liquid density (kg/m³); k, Debye-Hückel parameter; ε, fluid permittivity; δ, boundary layer thickness calculated by the Lévéque equation (m); ζ, zeta potential (mV); u ₀, average fluid velocity (m/s); h, half-channel height (m); T, Kelvin temperature (K).

^a SMBR, submerged MBR;

^b PE, Polyethylene; PTFE, Polytetrafluoroethylene; PCTE, Polycarbonate; PETE, Polyester;

^c TOC, total organic carbon; COD_c, colloidal COD; COD_s, soluble COD; DOC, dissolved organic carbon.

^a conjugated with tetramethyl rothamine isothiocyanate (TRITC).

^a resistance values calculated at 30 kPa.