Experimental study on application of the boundary layer theory for estimating steady aeration intensity of precoated dynamic membrane bioreactors

This paper introduced an approach that used precoated dynamic membrane (PDM) formed from powder activated carbon (PAC) on common terylene filter cloth instead of the conventional MF/UF membrane to build a membrane bioreactor (MBR) for wastewater treatment. The influence of aeration intensity for the PDM stability and the performance of the precoated dynamic membrane bioreactor (PDMBR) for treating municipal wastewater were investigated. The results of the rheological behavior of activated sludge in MBR showed that this liquor was approximated to Newtonian fluid while MLSS was less than 8100 mg/L. From the view of the mechanism of PDM formation process, when the thickness of laminar flow boundary layer was equal to that of PDM, PDMBR would run steadily, and this aeration intensity was defined as steady aeration intensity (172 L/h), which was estimated through using the boundary layer theory in the Newtonian hydrodynamics. In order to confirm the validity of theoretical calculation according to the flat membrane boundary layer theory, transmembrane pressure and treatment performance were observed when aeration intensity by gradual regulation began with oxygen supply aeration intensity (3–5 mg/L), increased up to theoretical calculation results, then till PDM detached. During PDMBR steadily running (31 days), effluent COD was less than 12.5 mg/L and its average removal efficiency was 97.5%, NH4+–N was less than 5.3 mg/L and its average removal efficiency was 76.1%, while the transmembrane pressure just increased to 27 KPa. The results indicated that this operational mode could enhance the stability of PDMBR. During the late period, aeration intensity in practice in the range of 190–200 L/h was obtained. The experimental results concluded that application of the boundary layer theory in aeration intensity theoretical calculation was valid.