Anti-fouling application of air sparging and backflushing for MBR

In membrane processes, fouling remains the main drawback and the toughest challenge at present and in the foreseeable future. The aim of this work was to combine anti-fouling strategies. In a membrane bioreactor (MBR) fed with synthetic wastewater with mixed liquor suspended solids concentrations between 3 and 10 g/L, the solid/liquid separation was achieved by a tubular membrane in side stream. For longer sustainable flux, air sparging was supplied to fight external fouling with the scouring effect of slug flow. Additional to that, backflushing was provided as a technique against internal fouling. The combination of both techniques showed very promising results and was superior to the operation of only one flux enhancement technique, yielding about three times higher fluxes compared to the NON-enhanced application after continuous filtration for 8 days. Backflushing accomplished significant flux increases with minimal product loss. The flux ratio of enhanced flux versus non-enhanced flux increased linearly with filtration time and air injection ratio. A simple model was developed to describe the development of the flux ratio over time for different air injection ratios. At high mixed liquor suspended solids concentrations (MLSS), where a high fouling potential exists, the combination of air sparging and back flushing was particularly effective in increasing the flux compared to non-enhanced filtration. Dimensionless fouling numbers increased with time, especially for lower air injection ratios.