Critical flux in submerged membrane bioreactors for municipal wastewater treatment

In the field of the wastewater treatment, membrane bioreactor technology continues to gain more and more interest thanks to high purification performance, low environmental impact, high possibility of treated water reuse. The more crucial factor in membrane bioreactor application is fouling tendency. In this paper, three different submerged membranes were used for municipal wastewater treatment. The relationship between critical flux and mixed liquor suspended solid concentration was investigated. Information about the fouling tendency of the membranes was obtained by studying the flux vs. transmembrane pressure behavior.

The critical flux, as well as the fouling resistance of membrane, depend not only on the membrane porosity and pure water permeability, but also on the chemical nature of the membrane material. Strong interactions between hydrophobic PE membrane and the feed lead to cake formation and fouling phenomena, with a detrimental effect of the flux. The different behavior of the two PVDF membrane deserves further work aimed at obtaining deeper information on the chemical nature of the membrane and their more or less hydrophobic character. In any case, the critical flux value is influenced by both membrane pore size and morphology, and by the MLSS concentration in the system. Nomenclature BOD5 COD HRT Jc MLSS N–NO2– biological oxygen demand (mg L–1) chemical oxygen demand (mg L–1) hydraulic retention time (h) critical flux (L m–2 h–1) mixed liquor suspended solid (g L–1) nitrite form (mg L–1) N–NO3– N–NH4+ OD PE PVDF Rc Rf Rm Rtot SEM T TMP TSS Rc + Rf (1012 m–1) 1.36 1.51 2.39 1.43 2.02 0.74 nitrate form (mg L–1) ammonium form (mg L–1) oxygen demand (mg L–1) polyethylene polyvinylidenefluoride cake resistance (m–1) fouling resistance (m–1) membrane resistance (m–1) total resistance (m–1) scanning electron microscope temperature (°C) transmembrane pressure (mbar) total suspended solid (mg L–1)